4286 4290.output

* GB784693 (A)

Description: GB784693 (A) ? 1957-10-16

Improvements in and relating to gyroscope apparatus

Description of GB784693 (A)

COMPLETE SPECIFICATION Improvements in amd reSatmg to Gyroscope Apparatus I, THE MINISTER GF SUPPLY9 of Shell Mex House, Strand, London, W. C. 2, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to gyroscope apparatus. Gyroscope apparatus is already known in which, with a view to reducing bearing or support friction and hence the rate of random wander, the rotor itself, or a mounting having an electrically driven rotor mounted on ball bearings thereof is supported by a flrn or layer ci air provided and maintained during operation by causing air to flow under pressure between support bearing surfaces. In one previous proposa a hollow spherical rotor formed with an internal circumferential rim, corresponding to an"equator", was supported within and driven relative to a closely fitting case by air introduced under pressure through a similarly disposed circumferential series of inclined passages or jets through the wall of the casing to impinge on the rotor and pass between the rotor and case to two exhaust ports through the walls of the casing at the"poles", respectively. Normally, the rotor position was such that the rotation axis coincided with the"polar"avis of the case. Also, the rotor speed was substantially constant and such that the driving torque balance the drag of the air in the small space between the rotor and the case. Because, however, the axis of the drag torque was coincident with the rotor spin or rotation axis and the axis of the driving torque was coincident with the case axis (i. e. the"polar"axis thereof) any relative deviation of the spin and case axes resulted in rapid precession of the spin axis towards the case

axis, and despite the provision of pneumatic type servo mechanism acting to cause the case, which was mounted on gimbals, to follow the rotor, the performance was poor. It has more recently been propose to drive the rotor electrically on ball bearings on a mounting which is supported on an air bearing of either spherical or cylindrical shape. Such electrically driven arrangements, however, have drawbacks consequent upon the heat generated during use and the presence of magnetic material. Whilst disturbances due to slow ambient temperature change may be avoided by the use of materials having the same temperature expansion co-efficient, local heating (e. g. at the stater) makes it difficult to maintain non-sprung bearings of a symmetrical gyroscope accurately adjusted and in the case of a rotor mounted symmetrically in a spherical or cylindrical casing makes ditortion of the latter almost unavoidable. Magnetic means are generally the most convenient for applying control torque to the gyroscope but local magnets, or even the earth's magnetic field, may produce disturbing torques by coacting with magnetic parts of the gyroscope. Further drawbacks of this more recent proposal are due to the ball bearings, any wear or any evaporation or movement of the lubricant of which can cause appreciable shifting of the centre of gravity of the air supported portion of the apparatus relative to the air bearing surface, and to the necessarily low ratio of rotor inertia to the total air supported weight. The cylinder or sphere of the air bearing must be extremely rigid in order to retain its shape with great accuracy and, unless light alloy is used with probable increased risk of distortion, the cylinder or sphere may well be heavier than the rotor necessitating a correspondingly high air pressure and so increasing in proporrion distuxbing torques due to impeifecdy symmetriail air (flow in the bearing. The present invention has for an object to provide improved low wander rate gyscope apparatus. In gyroscope apparatus according to the invention a rotor is supported upon a spherical air bearing within a concentric rotary casing to be driven by the drag of the air in said casing, which latter together with the ball or centre part of the bearing is fast upon ipon a tubular drive shaft affording a passage for air to the air bearing, and which shaft together with the casing is supported for rotation by conventional bearings. Preferably, means, such as a lost motion drive connection between the ball or centre part of the bearing and the rotor, are provided for limiting the totem to which the rotor is angularly displaceable

relative to the casing about the axis of the drive shaft. In operation a steady state is reached in which the rotor speed is substantially equal to that of the drive shaft, ball and casing, any slip being due to such small torques about the spin axis as may be exerted on the rotor by the air bearing. The tubular drive shaft may have provision for connecting it to a driving motor or it may be comprised by an extension of the armature shaft of an electric driving motor. In one apparatus according to the invention the rotor comprises a rim and thin vante-lite spokes, disposed each substantially at right angles to the general plane oi the rim, the casing is of circular section, and the drive shaft extends from one side of the casing to be journalled in ball race or other conventional bearings, the casing being formed with one or more ports for the exhaust of air from the bearing. In some cases pick ofr means responsive to deflections of the rotor relative to the casing may be of optical or photc-slectric type, the casing having a window and the rotor having a reflecting surface. For the application of control torques to the rotor the latter may have a small diameter, co-axial extension at that side remote from the tubular drive shaft and carrying a short bar magnet of which the polar axis is coincident with the spin axis, and this magnet may be influencez by a set of electro-magnets mounted on the outer wall of the casing, the electro-magnets being preferably such as to produce Selds which are steeply graded in intensity and the bar magnet being so short as to be but little affectez by nelds of relative uniform intensity. In order to reduce bearing load fluctuations in phase with the rotation the ball or inner part of the air bearing may be carried by a resilient cantilever shaft extending within the tubular drive shaft and secured to the latter at a point remote from the casing, there being clearance between the interior of the tubular drive shaft and the cantilever shaft and the latter itself being tubular for the passage of air to the air bearing at its free end. It is desirable, but not essential, that the casing should be disposed between the conventional bearings by which it is supported and also that a support member should extend from the casing to the ball or inner part of the air bearing at that side of the rotor remote from the tubular drive shaft. Prefcrably, the casing is internally at least of spherical configuration and the rotor is wheel shaped. Preferably, in an apparatus according to the invention the air drag forces which upon relarive deviation of the rotor spin axis and the axis of rotation of the casing act to tend to precess the spin arix

toward the casing rotation axis, are opposed by torques applied to the rotor by electro-magnetic means on the casing under the control of pick Oif means on the casing which are responsive to such defisction. In one arrangement two separate diametrically opposed pick off means serve to control the application of the opposing torques to the rotor by two separate diametrically opposite magnetic means, the diameter de6ned by said pick off mans being approximately at right angles to that defined by the opposing torque applying means. In all cases the rotor and/or the interior of the casing may be vaned and in sotte cases provision may be made for frictionally coupling the rotor temporarily to the positively driven parts, e. g. during running up. For use, the mounting of the conventional bearings supporting the casing for rotation, together with the driving motor, is mounted for defection and caused to follcw the rotor axis by follow-up servo mechanism controlled by pick off means on the casing which are responsive to relative deflection of the rotor spin axis and the rotation axis of the casing. Two forms of gyroscope apparatus according to the invention are illustrated by the accompanying diagrammatic drawings, of which Figure 1 is a sectional side view of an arrangement in which the casing is carried by horizontal bearings disposed to one side only thereof and Figure 2 is a sectional side view of an apparatus in which the casing is disposed between its supporting bearings. As shown in Figure 1, a gyroscope rotor indicated generally at 11 comprises a heavy rim 12 carried by a series of fat vante-live radical spokes of which two are indicated at 13,13 on a hub member 14 within which latter are held by a screw clamping ring 15 the two outer parts indicatrd at 16, 16 of a spherical air bearing. The bail or inner part 17 of this air bearing is fast on the free end of of tubular cantilever 18 which extends within and it fast at its other end to a tubular drive shaft 19 carried by two conventional ball races, 20,20. Fast on this drive shaft is a flat end wall 21 of a circular section casing indicated generally at 22 formed with openings of which t@ are indicated at 23, 23 for the exhaust of air from the bearings 16, 17. The ball 17 is formed as is usual with bearings of this kind with a plurality of radial air passages 24.... open at its curved surface where the latter is covered by the outer bearing pares 16,16. These passages comnunicate with the interior of the tubular cantilever 18 which thus serves as a passage for the supply of air to the bearing 16,17. The free end of the cantilever 18 and the adjacent end of the drive shaft 19 are made of complementary shape as shown and are so dimensioned as to limit the extent of permitted flexure of the cantilever 18.

At that side remote from the drive shaft 19 and the supporting bearings 20,20 the casing 22 has a circular glass window 25 and the rotor has an annular reflector 26 whereby photoelectric means can be used to obtain electric signals corresponding to dlflecdon of the rotor 11 relative to the casing 22. This reflector 26 is carried by a cover 27 closing the hub member 14 and which is formed with a coaxial extension 28 which latter is drilled to afford passage for air from the bearing 16,17 and carries at its end a short bar magnet 29 disposed with its polar axis coincident with the rotor spin axis. This magnet 29 serves for the application of control torques to the rotor 11 by the energisation, by means (not shown) in a manner which will be apparent to those slulled in the art, of a group of four electroc magnets indicated generally at 30. It is desirable that the arrangement should be such that the fields of the electro-magnets 30 are steeply graded in intensity so that they will have a substantial effect on the magnet 29 and that the latter should be so short as to be but little influence by a relative uniform intensity field such as that of the earth. The ball 17 of the air bearing must run extremely truely if bearing load fluctuations in phase with the rotation are not severely to limit the accuracy of operation, but the need for extreme accuracy in the ball races 20,20 in this apparatus is avoided by the cantilever 18 which is sufficiently resilient largely to absorb any bearing load irregularities. If desired, means (not shown) may be provided for holding the cantilever 18 temporarily against flexure under anormal loading during running up or otherwise. If desired the conventional bearings on which the casing 22 is supported may be located at both sides instead of at one side only of the casing. For example, an additional bearing (not shown) corresponding to the supporting bearings 20,20 may be mounted on the shoulder of the casing 22 in which the window 25 is supported to annularly surround the window and this bearing may be alternative tothebearing 20 adjacent the end wall 21. Also if desired, the casing 22 may be of spherical internal configuration. Turning now to Figure 2 of the drawings, here a wheel-like rotor 31 of non-ferrous material is supported on an air bearing 32,33 (like the bearing 16,17 of Figure 1) concentrically within a spherical casing indicated generally at 34 built up from two substantially hemispherical shells 35,35 and an intermediate channel section, annular member 136. The shells 35, 35 have integral therewith short tubular stub shafts 36,36 carried by ball-races 37,37 which in turn are mounted in rigid plates 38,38 held in spaced parallel relationship by columns 39,39. The ball 33 is fast on the inner end of a tubular

drive shaft 51 which extends through the lower stub shaft 36 with which it is fast and constitutes therebelow the armature shaft for a built in electric driving motor indicated at 40 in a chamber 41 belon the lower plate 38 provided with an inlet connection 42 for the supply of air to the bearings 32,33. The upper shell 35 is formed with a number of openings 43 for the exhaust of air from the bearing 32,33. A support member 44 extends from the ball 33 and through and beyond the upper stub shaft 36 of the casing 34, with which it is fast, to brush gear indicated generally at 45. Means (not shown) are provided for pre- venting more than limited angular displacement of the rotor 31 about its axis relative to the casing 34, and, at diametrically opposed parts of its rim there are secured to the rotor 31 two iron armatures 46,47 opposite to which latter there are mounted within the channel section annular member 136, two pick off devices indicated at 48,49, respectively. These pick off devices are of the well-known alternating current excited type having an E-shaped iron circuit, opposed exciting windings on the outer limbs and an output winding on the centre limb of the iron, and are so arrange and connected that when the rotor spin axis is coincident with the casing rotation axis the armatures 46 and 47 lie symmetrically of the pick oSs 48 and 49 and there is no output from the latter and when the rotor spin axis is deflected the resulting outputs from the two pick offs 48 and 49 are added. The angular movements to which the pick offs are required to respond are extremely small and it will bs seen that with this arrangement any lateral or axial motion of the rotor bodily on the air bearing will not produce any output from the pick offs. The output from the pick offs 48,49 is taken via slip rings (not shown) of the brush gear 45 to appropriate amplifier apparatus (not shown) and thence via further slip rings (not shown) of the bush gear 45 to two torque motors (not shown) of known eddy current drag type mounted in the channel section annular member 136 diametrically opposite to one another and displaced at about 90 degrees from the pick offs 45,46. The design and adjustment is such that the torque so applied to the rotor under the control of the pick offs is of such magnitude and sense as substantially to balance out the precessing torque which naturally occurs upon relative deflection of the rotor spin axis from the axis of rotation of the casing. Such deflection results in periodic oscillation of the rotor rela tive to the casing and the damping of this oscillation by the air in the casing and in the air bearing causes the rotor to precess in such a way as to return the spin axis to coincidence with the casing rotation axis. The electrically provided opposing or compensating torque may be regarded

as"negative damping"and when such negative damping is equal to the positive damping by the air the rotor is free to remain without precession in any deflected position relative to the casing, and it is therefore possible to employ much less precise or accurate means for causing the casing to follow the rotor without causing precession of the rotor than would otherwise be necessary. The torque motors would be displaced by exactly 90 degrees from the pick offs if this air damping were the only disturbing influence. A small amount of restraint (normally causing conical motion ai the rotor spin axis) may be present and this effect can be compensated by an appropriate departure from exactly 90 degrees displacement of the torque motors from the pick offs. The supporting assembly, comprising the spaced plates 38, 38 is mounted on gimbals, of which the inner ring only is indicated at 50, and is provided with known type servo motors (not shown) controlled in known or convenient manner by the signals from the pick o, s 4S, 49 so as to cause the assembly to follow the rotor and maintain the casing rotation axis substantially coincident with the rotor spin axis. Outputs appropriate for this purpose are derived from the pick wEs 48, 49 via commutator segment and multiple brush connections of the brush gear 45 in a manner which will be apparent to those skilled in the art. For precessing the rotor 31 and with it the mounting assembly to a desired orientation as and when required, means (not shown) are provided for appropriately exciting by way of further commutator segment and multiple brush connections (not shown) of the brush gear 45 the above mentioned eddy current drag type torque motors (not shown) on the casing in a manner which will be apparent to those skilled in the art. The use of the pics off signals to control the application of torques to the rotor to give it a high degree of freedom as set forth abuse permits, for a given degree of overall accuracy a less accurate servo system to be employed to make the mounting assembly follow the rotor than would otherwise be required. It will be apparent that in the Figure 1 example the precessing torque which, due to the different drive torque and drag torque axes, acts on the rotor 11 when its spin axis is deflected from the casing rotation axis, may be counteracted or opposed by torque applied thereto via the electromagnets 30 and the bar magnet 29 under the control of the optical pick off means used in that example. What I claim is :- 1. Gyroscope apparatus in which a rotor is supported upon a spherical air bearing within a concentric rotary casing to be driven by the drag of the air in said casing, which latter together with the ball or

centre part of the bearing is fast upon a tubular drive shaft affording a passage for air to the air bearing, and which shaft together with the casing is supported for rotation by conventional bearings.

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* GB784694 (A)

Description: GB784694 (A) ? 1957-10-16

Gas-turbine-driven helicopter


PATEN SPECIFICATLON Inventors: ALBERT THOMAS and BRIAN HUDSON SLATTER Date of filing Complete Specification Oct 21, 1955. Application Date Nov 4, 1954. Complete Specification Published Oct 16, 1957. Index at Acceptance:-Class 110 ( 3), G 5 C( 3 A: 4). International Classification: -FO 2 c. COMPLETE SPECIFICATION Gas Turbine-Driven Helicopter We, ARMSTRONG SIDDELEY MOTORS LIMITED, a British company, of Park Side, Coventry Warwickshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a gas-turbinedriven helicopter power unit. The rotor of a helicopter is normally controlled to rotate at a substantially constant speed, i e, within a narrow speed range, for example, 230 to 260 r p m, during all flight operating conditions When using a gas turbine engine as the power unit it is desirable that this

should be ot the " free " turbine type, the compressor being driven by one turbine (this assembly being hereinafter termed the gas generator) and the free turbine being connected to drive the rotor through appropriate reduction gearing. With such an arrangement, the power developed depends mainly on gas generator speed and during descent of the helicopter it may be necessary to develop zero power which requires a low gas generator speed. This may result in a low gas generator rotational speed from which the gas generator is incapable of rapid acceleration to full power within say two seconds-such a rapid acceleration being a requirement in certain applications and it is an object of the invention to overcome this. According to the invention the power unit includes, in addition to the gas generator, an independent turbine, and a helicopter rotor, the independent turbine being arranged to drive the helicopter rotor, a one-way clutch (of the type commonly known as a " free wheel ") being interposed between the independent turbine and the gas generator, the driving member of the one-way clutch being connected to the independent turbine and the driven member of the one-way clutch being connected to the gas generator, so that whenever the gas generator speed lPce 3 s 6 d l is reduced sufficiently (and would otherwise normally fall below a speed corresponding to the predetermined minimum speed of the helicopter rotor) the one-way clutch will lock 50 to prevent the speed of the gas generator from falling below a selected value compatible with freedom from stalling and rapid acceleration to full power. In the accompanying diagrammatic draw 55 ings:Figure 1 is a sectional elevation of a gasturbine-driven helicopter power unit embodying the invention; and Figure 2 is a section on line 2-2 of 60 Figure 1. The gas-turbine-driven helicopter power unit shown in the drawings includes an air intake 10 leading to a compressor 11, a combustion chamber section 12 and a turbine 65 section 13. The rotor blades 15 of the compressor 11 are mounted on a shaft 16 journalled in bearings 17, 18, 19 Fast with the end of the shaft 16 remote from the compressor 11 are two tur 70 bine rotor stages 20 and 21 The portion of the turbine comprising the rotor stages 20 and 21, together with the shaft 16 and compressor 11, forms a gas generator unit. Two more turbine rotor stages 22 and 23 75 are fast with a shaft 24 journalled in a bearing 25, the two stages 22 and 23 forming the independent turbine A rotatable housing 26 through which the helicopter rotor 14 is driven is journalled in bearings 27 carried by a fixed 80 part of the casing 28 Fast with the shaft 24 is a gear 29 A

shaft 30 is journalled in bearings 31 and 32 in flanges 33 and 34 respectively integral with the housing 26 The shaft has integral with it a gear 35 which meshes 85 with the gear 29, and also has an integral gear 36 which meshes with a stationary annular gear 37 formed on the inner periphery of an internal flange of the casing 28. The helicopter rotor 14 is driven by the go independent turbine 22, 23 through the reduction gearing described, and is subject to con7849694 No 31878/54. stant speed control, within predetermined limits, by conventional means forming no part of the present invention. The independent turbine (comprising rotor stages 22 and 23), shaft 24, the abovedescribed gearing, and the helicopter rotor 14 together iorm an independent-turbine-helicopter unit The independent turbine is arranged to provide at least the power required for helicopter rotor operation, preferably having a small surplus power. Fast on the external periphery of the shaft 24 is the driving member 39 of a one-way clutch the driven member 40 of which is formed internally on the gas generator shaft 16 Movable clutch members 4 i are supported between the driving member 39 and driven member 40, the whole of the one-wvay clutch being in elect contained in the annular space between the shafts 16 and 24 The arrow 9 represents the direction of rotation of the members 39 and 40. With this construction, when descending, the gas generator can be throttled back to give minimum power, but during this period the compressor will always be prevented from falling below a selected speed compatible with freedom from stalling and with rapid acceleration to full powver because the one-way clutch will lock (to maintain the speed of the compressor) whenever the speed of the shaft 16 would otherwise normally fall below the speed of the shaft 24. Thus for a given predetermined minimum speed of rotation of the rotor 14 a ratio can be selected for the gearing 29, 35, 36, 37 such that the speed of the compressor will never be allowed to fall below the selected speed value (selected according to the characteristics of the gas generator) After the gas generator speed has fallen to this value, power can be reduced at a constant rotational speed. The one-way clutch provides the additional advantage that the independent turbine is prevented frcri overspeeding should it become isolated from the helicopter rotor, because as soon as the speed of the independent turbine tends to exceed that of the gas generator, the one-way clutch will lock and the gas generator V Jwill act as a brake on the independent turbine.

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* GB784695 (A)

Description: GB784695 (A) ? 1957-10-16

Improvements in or relating to electrolytic cells for the production ofaluminium


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CH299434 (A) DE1092215 (B) FR1061906 (A) CH301030 (A) FR1064743 (A) CH299434 (A) DE1092215 (B) FR1061906 (A) CH301030 (A) FR1064743 (A) less Translate this text into Tooltip

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PATENT SPECIFICATION Inventoar: CHARLES ERIC RANSLEY 784,695 Date of filing Complete Specification (under Section 3 ( 3) of the Patents Act, 1949) April 25,1952. Application Date May 4, 1951 No 10548/51. Application Date May 4, 1951 No 10549/51. Application Date April 15, 1952. complete Specification Published Oct 16, 1957.

No 9474/52. Index at acceptance: Classes 1 ( 2), E 2 A 1; 41, Al F, B(IC'14); 82 ( 1), Y 1, Y 2 (A 1: H: W: Z 5: Z 9); and 87 ( 2), A 1 R( 39 F: 58). International Classification: B 23 n B 29 d C 01 g C 22 do COMIPLETE SPECIFICATION Improvements in or relating to Electrolytic Cells for the Product Eon of Aluminium We, THE BRITISH ALUMINIUM COMPANY LIMITED, a company registered under the laws of Great Britain, of Norfolk House, St. James's Square, London, S W 1, (formely of Salisbury House, London Wall, London, E.C 2, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is performed, to be particularly described in and by the following statement:- This invention relates to electrolytic reduction cells for the production of aluminium. Those cells which are at present in commercial use are employed to effect the electrolysis of an aluminium compound, generally aluminium oxide, while it is dissolved in a suitable flux which is mainly cryolite and has a fusion point usually in excess of 900 C. Since the cells therefore must be operated at a temperature in the neighbourhood of 1000 C., their construction has always presented considerable problems The flux, for example, is very reactive towards metals, with the exception of the noble metals, and towards normal refractory materials Thus difficulty is experienced in constructing a durable container for the molten flux and there is an even greater difficulty in finding suitable materials for the construction of the electrodes. Carbon is the only material that has hitherto been found to be capable of use for the purposes mentioned, this being employed both for lining the tank which is to contain the flux and for the construction of the electrodes. However, the use of this material entails a number of very considerable disadvantages, not the least of which is the fact that the electrodes must, in practice, be horizontally arranged so that the floor space occupied by a single cell is quite extensive and the cost of constructing such large cells is considerable. The necessity for this horizontal arrangement arises from the fact that molten aluminium does not wet a carbon cathode Hence the carbon lining of the floor of the cell is made the cathodic electrode so that the aluminium produced by the electrolysis may be deposited thereon as a pool of molten metal Unless this arrangement be adopted the current efficiency of the cell is very low. The use of carbon for the cathode and the horizontal arrangemcnt of the latter entail a number of disadvantages in operating the cell.

For example, the gradual penetration of molten flux into the carbon of the cathode causes this to disintegrate and shortens its useful life Deposits are formed on the surface of the cathode which increase the voltage drop across the cell and reduce the efficiency of the latter Satisfactory electrical contact between the cathode and the electrical current-supply conductors is difficult to achieve and there are appreciable losses also due to the electrical resistance of the carbon itself The horizontal construction necessary with a carbon cathode results in the cell having a large area with consequent high heat losses, which have to be compensated by a considerable dissipation ot electrical energy over and above that required for the electrolytic decomposition of the alumina. With a view to overcoming these disadvantages, we have been searching for a new cathode material We have concluded that the properties required in an ideal cathode may be summarised as follows:( 1) It should have a good electrical conductivity. ( 2) It must not react with nor be soluble in either molten aluminium or molten flux, at least to any appreciable extent. ( 3) It should be capable of being wetted by molten aluminium. ( 4) It must be cheap enough to be fabericated in the required form economically. The importance of "wettability" hadl not 784,695 previously been recognised clearly, but our research demonstrated that immediate advantage would follow if a material with this property could be developed. As the result of many experiments, it has become apparent that the materials which will exhibit all the properties listed above are very few in number but that titanium carbide and zirconium carbide are clearly included amrong them Titanium and zirconium are relatively abundant elements though the latter is somewhat rarer than the former, and their carbides can be manufactured with comparative ease The carbides have a relatively high eiectrical conductivity, are resistant to attack by molten flux and have a very low solubility -:molten aluminium at 1000 C They can be produced in a suitable form with good mechanical properties Furthermore, it is possible e'Lectively to wet the surface of a titanium carbide or zirconium carbide electrode withl molten aluminium, from which it results that, for the first time, a commercially practicable cell with vertical or inclined electrodes may be constructed Finally, these carbides can be connected without great dificulty to a metallic conductor to establish a good mechanical and electrical joint therewith. Broadly stated, therefore, our invention resides in an electrolytic reduction cell for the production of metallic aluminium embodying a cathode largely composed of at least one of the materials titanium

carbide and zirconium carbide The term "cathode" as here employed is intended to denote an electrode of plate, rod or other suitable shape at which aluminium metal is produced in a tangible form The cathode may, for example, consit of suitable pieces of titanium carbide or zirconium carbide, or a mixture of both, supported by a backing material such as carbon. It is preferred that the electrical connection to the cathods should also consist mainly of titanium carbide, zirconium carbide or a mixture of the two, this connection extending to a point where an external connection can be made to the electrical circuit. Although both the carbides referred to are satisfactory for the purposes in view, titanium carbide is preferred to zirconium carbide, not only because it is less expensive to produce but because it has a much higher resistance to oxidation than zirconium carbide When the latter is employed, in fact, precautions must be taken to ensure that it is never exposed to the action of air or oxygen or oxidising conditions while at a high temperature, e g the operating temperature of the cell, for which reason a cathode composed entirely or largely of zirconium carbide should be protected by rapid submersion in molten metal or flux, or by coating it with carbon, before its tempera ture is raised to any substantial degree In addition, zirconium carbide requires higher temperatures than does titanium carbide for the carrying out of the sintering operation which is necessary in order to produce a coherent mass of the carbide having the requisite mechanical strength For these reasons, the following description will be concerned 70 mainly with the use of titanium carbide but the several steps and procedures detailed in this connection will apply also in the case of zirconium carbide save where a note is given of the necessary modification or where the 75 necessity for protecting the zirconium carbide against oxidation will entail corresponding precautionary measures. It is preferred that the carbide in the cathode be substantially pure that is to say 80 substantialiy free from other elements or compounds which would lead to undesirable contamination of thie aluminium produced or to rapid disintegration of the cathode when in use In particular, it should be of low free 85 carbon content, "low" in this context meaning not greater than about 0 5,o Preferably the free carbon content should be less than 0.1 %. Nevertheless, the cathodes according to this 90 invention miy contain initially other compounds which are rapidly dissolved out when the cathode is first put into service, without thereby causing disintegration of the cathode, for example small proportions of titanium or 95 zirconium oxides. Another feature of the present invention is a cathode constructed

mainly from titanium carbide or zirconium carbide which has been pre-;vetted, after its formation with molten o 100 aluminium. While a cathode according to this invention may be employed with advantage in a cell of orthodox construction, its use greatly reducing the cathode voltage drop which would other 105 wise be experienced, its greatest value is to f roun d in the fact that it can be used satisfactorily in a vertical or inclined position. there are considerable advantages to be gained by constructing a cell with a cathode 110 or cathodes so disposed. Accordingly, a further feature of this invention consists in an electrolytic reduction cell for the production of aluminium embodying a cathode largely composed of titanium carbide 115 or zirconium carbide, as set forth above, wherein the cathode is so disposed that at least one operative face thereof is at such an angle to the horizontal that liquid metal deposited thereon may drain ow therefrom under the 120 action of gravity The cathode may be so arranged in the cell that its operative face or faces is or are disposed at a relatively large angle to the horizontal, the deposited aluniinum continuously draining down the face 125 or faces concerned, preferably to collect in a pcol in contact wvith the lower part of the cathode from which pool it may be withdrawn from time to time in the usual manner If desired the pool of molten aluminium thus 130 784,695 formed may be utilised as part of the currentsupply means for the cathode The operative face or faces of the anode or anodes in a cell embodying inclined cathodes according to this 1 invention is or are also disposed at a substan i tial angle to the horizontal. Due to the inclined or substantially vertical arrangements of the electrodes, the floor space occupied by the cell is very considerably reduced in relation to that which is at present required Moreover, the electrodes may be arranged to operate within a relatively confined body of molten flux and this may, in turn, be surrounded by solidified flux which may be retained in its desired external shape by a simple wall of steel or other suitable material, the construction of the cell being thereby considerably cheapened A further great advantage of the cell construction embodying inclined cathodes according to this invention is -that the disposal of the noxious or unpleasant fumes generated during the operation of the cell is considerably simplified, due to the much smaller area over which they are evolved It will also be appreciated that the cell may be designed in such a way that wasteful loss of heat is reduced to a minimum. Yet a further advantage which flows from the inclined positioning of the cathode is that surging oi the molten aluminium is very much less likely to occur so that the spacing of the electrodes may be substantially reduced compared with that adopted in cells as

heretofore known and the dissipation of electrical energy in the flux correspondingly reduced One further point of importance may be noted and this is that owing to the relatively high electrical conductivity of the cathode, as compared with that of a carbon cathode, the voltage drop usually experienced due to the passage of the very high operating current through the cathode material is reduced to a corresponding degree Sludge formation at the bottom of the cell, which can cause an undesirable voltage drop at the cathode in the existing horizontal cells, cannot affect the operation of the new type of cell according to this invention. We have, for example, constructed an electrolytic reduction cell using a conventional flux with a titanium carbide cathode and a carbon anode, both dispersed substantially vertically The cathode loss was found to be less than 0 2 volts, compared with the customary cathode loss of 0 5 to 0 7 volts encountered in orthodox cells of comparable size, and the current efficiency was also found to be considerably higher than that obtainable in such orthodox cells. As an example, a cathode according to this invention may be prepared by compacting powdered titanium carbide, e g a powder having a mean particle diameter of about 1 to 2 microns, with which has been mixed a small proportion of a binder say 1 % of paraffin wax dissolved in benzene The benzene is evaporated off on a water bath or at a temperature sufficiently high to melt the wax prior lo the compacting operation, the pressure employed in the latter being in the range 0 5 70 to 5 tons per square inch, e g 3 tons per square inch The compacting step may be efiected by simple pressure between male and female dies, either at ordinary temperature or at an elevated temperature Alternatively, 75 the powdered mixture may be extruded into the desired shape If the initial titanium carbide powder had a sufficiently low content of iree carbon, it may be directly compacted as above and then pre-fired in vacuum to a tem 80 perature of 11000 C (about 16 U 00 C for zirconium carbide) It may then be worked by sawing, filing or like shaping operations to produce a cathode of appropriate form, although it will be understood that the electrode will 85 usually be finally shaped in the compacting operation The electrode is then fired in vacuum at a temperature 16000 C (about 2200 ' C for zirconium carbide), although this may be varied according to the density desired 90 in the final product, to produce a robust, sintered element having a porosity which may be of the order of 20 % by volume. Generally, the titanium carbide powder of commerce contains about 90 % of Ti C and 1 95 to 2 % of free carbon, the balance being titanium oxide If a powder of this character be treated as above set forth the cathode obtained is not always suitable for the purposes in view

because the content of tree car 100 bon is not necessarily reduced to a safe level during a sintering operation carried out at a temperature of 16000 C ( 2200 ' C for zirconium carbide) in vacuum The use of a higher temperature either in vacuum or in a 105 furnace in which an atmosphere of a neutral gas, such as hydrogen, is maintained, results in improved products but some of these may still have a content of free carbon amounting to 0 6 % It is found that a sintered titanium 110 carbide compact which contains more than about 0 5 % free carbon shatters or disintegrates when wetted by molten aluminium, probably due to the formation of aluminium carbide Obviously, such a compact would 115 not be suitable for use as a cathode in an electrolytic reduction cell for the production of aluminium However, the difficulty can be overcome by incorporating into the titanium carbide powder to be used in the pro 120 duction of the compact a proportion of powdered calcined alumina Preferably, the alumina is added to the commercial Ti C powder and the mixture then ball-milled for a relatively long period in the dry state until 125 it is reduced to a mean particle diameter of about 1-2 microns The amount of alu. mina added depends to some extent upon the content of free carbon in the commercial Ti C powder but is usually equivalent to about 2 130 784,695 to 3 ', of the weight of tlhe Ti C employed. The finely powdered mixture of Ti C and ALO, is then moistened with a suitable binder e g parafflin wax dissolved in benzene, and the solvent driven off prior to compacting the mass under pressure as set forth above. The firing of the compact obtained is effected in a furnace through which a stream of a neutral gas, e g hydrogen, is passed, the tempera. ture preferably being higher than 1600 C, for example about 2200 C (about 2700 C for zirconium carbide) The finished product contains substantially no free carbon and the residual aluminium therein, whether present as A 120 a or A 11,C 3, is very small As an example, a titanium carbide powder initially containing between 1 % and 2 %g of free carbon, when mixed with 2 5 % of calcined alumina and treated as above set forth, yielded a cathode compact containing only 0 2 % of free carbon Increasing kth amount of Al IO, added to 3 /o resulted in a product containing O 05 % of free carbon. It is preferred that the content of free carbon in the finished cathode shall be below 0.1 % but somewhat higher percentages of free carbon can be tolerated provided that the figure of O 5 % be not reached Cathodes thus prepared from substantially carbon-free Ti C will be wetted freely by molten aluminium without any tendency to shatter or break up and without any sign of cracks developing The density of dthe product before wetting, is about 4 5 gins per c c corresponding to a porosity of about 10 %, by volumne.

The foregoing process for reducing the fee-


* GB784696 (A)

Description: GB784696 (A) ? 1957-10-16

Improvements in or relating to electrolytic cells for the production ofaluminium


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CH299434 (A) DE1092215 (B) FR1061906 (A) CH301030 (A) FR1064743 (A) CH299434 (A) DE1092215 (B) FR1061906 (A) CH301030 (A) FR1064743 (A) less Translate this text into Tooltip



PATENT l SP 1 CIFICATION Inventor: CHARLES ERIC RANSLEY 784696 Date of filing Complete Specification (under Section 3 ( 3) of the Patents

Act, 1949) April 25, 1952. Application Date Aug 3, 1951 No 18490/SI. Application Date April 15, 1952 No 10552/52. (Application No 10552/52 divided out of Application No 9474/52 l 784,695 l). Complete Specification Published Oct 16, 1957. Inde MRATUM< SPECIFICATION 10 784,69 C 6 Page 5, L Ine 45, for "it Wt" read "It Is". THE PAT Et;T OFFICE, 17th January, 1958 uy ueciare me invention tor which we pray that a patent may be granted to us and the method by which it is performed, to be particularly described in and by the following statement: - This invention relates to electrolytic cells for the production of aluminium. Such cells are of two characters, namely, the reduction cell in which aluminium is produced from an aluminium compound, generally aluminium oxide, while it is dissolved in a suitable flux, and the three-layer cell in which impure aluminium is purified electrolytically As operated commercially, these cells have certain features in common including the necessity for establishing an electrical connection from an external source of supply of electrolysing current to a body of molten metal, whether it be the pool of molten aluminium which accumulates on the floor of a reduction cell, the pool of aluminium alloy forming the bottom layer in a three-layer cell, or the layer of highly purified aluminium forming the top layer in such a cell The arrangements at present made for leading the current into the respective bodies of molten metal are not entirely satisfactory and this is particularly true of the reduction cell where relatively substantial losses in efficiency and increase in construct tional and maintenance costs are directly traceable to the nature of the current leads which have to be employed. It is the object of the present invention to provide improved current leads for electrolytic cells of the characters indicated which shall not be subject to the disadvantages of the existing arrangements. lPrice DB 01944/1 ( 2) /3632 150 1158 R titanium carbide and zirconium carbide at least where it is in contact with the metal. Titanium and zirconium are relatively 50 abundant elements, though the latter is somewhat rarer than the former, and their carbides can be manufactured with comparative ease. The carbides have a relatively high electrical conductivity, are not appreciably attacked by 55 the molten fluxes used in the electrolytic cells and have a very low solubility in molten aluminium at 1000 C They can be produced in a suitable form with good mechanical properties Furthermore, it is possible effectively to 60 wet the

surface of a titanium carbide or zirconium carbide current lead with molten aluminimum, with obvious advantages Finally, these carbides can be connected without great difficulty to a metallic conductor to establish 65 a good mechanical and electrical joint therewith Aluminium, for example, may be fused against them to produce an excellent electrical connection which leads to the substantial elimination of any appreciable voltage drop 70 between the busbar and the surface of the body of molten metal into which the current lead extends. Although both the carbides referred to are satisfactory for the purposes in view, titanium 75 carbide is preferred to zirconium carbide, not only because it is less expensive to produce but because it has a much higher resistance to oxidation than zirconium carbide When the latter is employed, in fact, precautions must 80 be taken to ensure that it is never exposed to the action of air or oxygen or oxidising conditions while at a high temperature, e g the operating temperature of the cell, for which Intel PATENT SPECIFICATION Inventor: CHARLES ERIC RANSLEY 784696 Date of filing Complete Specification (under Section 3 ( 3) of the Patents Act, 1949) April 25, 1952. Application Date Aug3,1951 No 18490/51. Application Date April 15, 1952 No 10552/52. a W (Application No 10552/52 divided out of Application No9474/52 Complete Specification Published Oct 16, 1957. Index at acceptance: -Classes 1 ( 2), E 2 A 1; 41, Al F, B( 1 C: 14); 82 ( 1), Y 1, Y 2 (A 1: H: W: Z 5: Z 9); and 87 ( 2), AMR( 39 X: 58). International Classification: -B 23 n B 29 d C Oig C 22 d. COMPLETE SPECIFICATION Improvements in or relating to Electrolytic Cells for the Production of Aluminium We, THE BRITISH ALUMINIUM COMPANY LIMITED, a company registered under the laws of Great Britain, of Norfolk House, St James's Square, London, S W 1, (formerly Salisbury House, London Wall, London, E C 2, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is performed, to be particularly described in and by the following statement: - This invention relates to electrolytic cells for the production of aluminium. Such cells are of two characters, namely, the reduction cell in which aluminium is produced from an aluminium compound, generally aluminium oxide, while it is dissolved in a suitable flux, and the three-layer cell in which impure aluminium is purified electrolytically As operated commercially, these cells have certain features in common including the necessity for establishing an electrical connection from an external source of supply of electrolysing current to a body of

molten metal, whether it be the pool of molten aluminium which accumulates on the floor of a reduction cell, the pool of aluminium alloy forming the bottom layer in a three-layer cell, or the layer of highly purified aluminium forming the top layer in such a cell The arrangements at present made for leading the current into the respective bodies of molten metal are not entirely satisfactory and this is particularly true of the reduction cell where relatively substantial losses in efficiency and increase in construct tional and maintenance costs are directly traceable to the nature of the current leads which have to be employed. It is the object of the present invention to provide improved current leads for electrolytic cells of the characters indicated which shall not be subject to the disadvantages of the existing arrangements. According to the invention, in an electrolytic cell for the production or refining of aluminium, electrolysing current is supplied to a body of molten metal by way of a lead largely composed of at least one of the materials, titanium carbide and zirconium carbide at least where it is in contact with the metal. Titanium and zirconium are relatively abundant elements, though the latter is somewhat rarer than the former, and their carbides can be manufactured with comparative ease. The carbides have a relatively high electrical conductivity, are not appreciably attacked by the molten fluxes used in the electrolytic cells and have a very low solubility in molten aluminium at 10000 C They can be produced in a suitable form with good mechanical properties Furthermore, it is possible effectively to wet the surface of a titanium carbide or zirconium carbide current lead with molten aluminimum, with obvious advantages Finally, these carbides can be connected without great difficulty to a metallic conductor to establish a good mechanical and electrical joint therewith Aluminium, for example, may be fused against them to produce an excellent electrical connection which leads to the substantial elimination of any appreciable voltage drop between the busbar and the surface of the body of molten metal into which the current lead extends. Although both the carbides referred to are satisfactory for the purposes in view, titanium carbide is preferred to zirconium carbide, not only because it is less expensive to produce but because it has a much higher resistance to oxidation than zirconium carbide When the latter is employed, in fact, precautions must be taken to ensure that it is never exposed to the action of air or oxygen or oxidising conditions while at a high temperature, e g the operating temperature of the cell, for which. Pnrice 784,696 reason a current lead composed entirely or largely of zirconium carbide should be protected by rapid submersion in molten

metal or flux, or by coating it with carbon before its temperature is raised to any substantial degree. In addition, zirconium carbide requires higher temperatures than does titanium carbide for the carrying out of the sintering operation which is necessary in order to produce a coherent mass of the carbide having the requisite mechanical strength For these reasons, the following description will be concerned mainly with the use of titanium carbide but the several steps and procedure detailed in this connection will apply also in the case of zirconium carbide save where a note is given of the necessary modification or where the necessity for protecting the zirconium carbide against oxidation will entail corresponding precautionary measures. It is preferred that the carbide in the current lead be substantially pure, that is to say, substantially free from other elements or compounds which would lead to undesirable contamination of the aluminium produced or to rapid disintegration of the lead when in use. In particular it should be of low free carbon content, "low " in this context meaning not greater than about 0 5 % Preferably, the free carbon content should be less than 0 1 %. Nevertheless, the current leads according to this invention may contain initially other compounds which are rapidly dissolved out when the current lead is first put into service, without thereby causing disintegration of the current lead, for example, small proportions of titanium or zirconium oxides. It is a further feature of this invention to employ a current lead constructed mainly from titanium carbide or zirconium carbide which, after its formation, has been pre-wetted with molten aluminium. As an example of the way in which a current lead according to the invention may be prepared, a body is first produced by compacting powdered titanium carbide, e g a powder having a mean particle diameter of about 1 to 2 microns, with which has been mixed a small proportion of a binder, say 1 Co of paraffin wax dissolved in benzene Benzene is evaporated off on a water bath, or at a temperature sufficiently high to melt the wax, prior to the compacting operation, the pressure employed in the latter being in the range 0 5 to 5 tons per sq in, e g 3 tons per sq in The compacting step may be effected by simple pressure between male and female dies either at ordinary temperature or at an elevated temperature Alternatively the powder mixture may be extruded into the desired shape If the titanium carbide powder has a sufficiently low content of free carbon it may be directly compacted and the compacted product is then prefired in a vacuum to a temperature of 1100 C (about 1600 C for zirconium carbide) It may then be worked by sawing, filing or like shaping operations to produce a current lead of appropriate form although it will be

understood that the current lead will usually be finally shaped in the compacting operation The current lead is then 70 fired in vacuo at a temperature of 1600 C. (about 2200 ' C for zirconium carbide), although this may be varied according to the density required in the final product, to produce a robust sintered element having a poro 75 sity which may be of the order of 20 % by volume. Generally the titanium carbide powder of commerce contains about 90, of Ti C and 12 %so of free carbon, the balance being titanium 80 oxide When a powder of this character is treated as above set forth, the current lead obtained is not always suitable for the purpose in view because the content of free carbon is not necessarily reduced to a safe level during 85 a Eintering operation carried out at a temperature of 1600 C ( 2200 C for zirconium carbide), in vacuum The use of a higher temperature either in vacuum or in a furnace in -w-hllich an atmosphere of a neutural gas, 90 such as hydrogen, is maintained, results in improved products but some of these may still have a content of free carbon amounting to 0.6 %' It is found that a sintered titanium carbide compact which contains more than about 95 0.5, of free carbon shatters or disintegrates when wetted by molten aluminium, probably due to the formation of aluminium carbide. Obviously, such a compact would not be suitable for use as a current lead in an electrolytic 100 cell for the production of aluminium However, the difficulty can be overcome by incorporating into the titanium carbide powder to be used in the production of the compact a proportion of powdered calcined alumina Pre 105 ferably, the alumina is added to the commercial Ti C powder and the mixture then ball-milled for a relatively long period in the dry state until it is reduced to a mean particle diameter of about 1 to 2 microns The amount of the 110 alumina added depends to some extent upon the content of free carbon in the commercial Ti C powder, but is usually equivalent to about 2-3 % of the weight of the Ti C employed. The finely powdered mixture of Ti C and 115 Al OQ is then moistened with a suitable binder, e.g paraffin wax dissolved in benzene, and the solvent driven off prior to compacting the mixture by one of the methods set forth above. The firing of the compact obtained is effected 120 in a furnace through which a stream of a neutral gas, e g hydrogen, is passed, the temperature preferably being higher than 16000 C for example about 2200 C (about 27000 C for zirconium carbide) The final product 125 contains substantially no free carbon and the residual aluminium therein, whether present as ALO, or A 11 C, is very small. As an example, a titanium carbide powder initially containing between 1,% and 2 %o of 130 784,696 free carbon, when mixed with 2 5 % of

calcined alumina and treated as above set forth, yielded a current lead containing only 0 2 % of free carbon Increasing the amount of alumina added to 3 % resulted in a product containing 0.05 %,' of free carbon. It is preferred that the content of free carbon in the finished current lead shall be below 0.1 % but somewhat higher percentages of free carbon can be tolerated provided that the figure of 0 5 % be not reached Current leads thus prepared from substantially carbon-free Ti C will be wetted freely by molten aluminium without any tendency to shatter or break up and without any sign of cracks developing. The density of the product, before wetting, is about 4 5 gms per c c, corresponding to a porosity of about 10 % by volume The foregoing process for reducing the free-carbon


* GB784697 (A)

Description: GB784697 (A) ? 1957-10-16

An improved process for the reduction of the free carbon content in titaniumcarbide

Description of GB784697 (A) Translate this text into Tooltip



PATENT SPECIFICATION Inventor: CHARLES ERIC RANSLEY Date of filing Complete Specification May 6, 1953. Application Date April 15, 1952. 784,697 No 12675153. (Divided out of Application No 9474/52 l 784,695 l). Complete Specification Published Oct 16, 1957. Index at Acceptance:-Classes 1 ( 2), E 2 A 1; 22, J(Q: 2: 9: 10: 33); and 82 ( 1), Y 1, Y 2 (A 1: W: Z 5). International Classification: -B 23 n C 01 g C 04 b. COMPLETE SPECIFICATION An improved Process for the Reduction of the Free Carbon Content in Titanium Carbide We, THE BRITISH ALUMINIUM COMPANY LIMITED, a company registered under the laws of Great Britain, of Norfolk House, St James's Square, London, S W 1, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the reduction of the free carbon content in titanium carbide. Titanium carbide is manufactured by heating a mixture of titanium oxide and carbon to a temperature of 18000 C or higher, the constituents being employed in approximately stoichiometric proportions Nevertheless, for various reasons, including that of the occurrence of an appreciable back reaction, the commercial product contains a relatively high proportion, for example, from 1 to 3 % of free carbon which is usually present in the form of graphite Titanium carbide finds many uses in industry in view of its great hardness, for example, in high speed cutting tools, and it has been found in such applications that the presence of an excessive amount of free carbon is a considerable disadvantage. We have recently proposed the use of sintered titanium carbide in the production of current-carrying elements for use in electrolytic cells for the production of aluminium. In particular, in the single complete specification filed on the 25th April, 1952, in respect of Application Nos 10548 J 51, 10549/51 and 9474/52, (Serial No 784,695) we have described and claimed an electrolytic reduction cell for the production of metallic aluminium embodying a cathode largely composed of at least one of the materials titanium carbide and zirconium carbide Further in the single complete specification filed on the 25th April, 1952, in respect of Application Nos 18490/51 and 10552/52 (Serial No 784,696) we have described and claimed an electrolytic cell for the production or refining of aluminium wherein electrolysing current is supplied to a body of molten metal by way of a lead largely composed

of at least one of the materials, titanium carbide and zirconium car 50 bide, at least where it is in contact with the metal Here again the presence of an excessive amount of free carbon in the titanium carbide employed in such cathodes or current leads has proved to be a disadvantage because 55 such cathodes or current leads have a tendency to shatter or disintegrate when wetted with molten aluminium In this case the permissible upper limit for the content of free carbon in the titanium carbide appears to be 60 in the region of 0 5 % In the case of the production of cutting tools or similar products from titanium carbide, the permissible upper limit for the content of free carbon may be even lower, for example, in the region of 65 0.2 %. It is an object of the present invention to provide an improved process for reducing the free carbon content in titanium carbide and in particular a method for the production of 70 improved sintered compacts from titanium carbide, such compacts being characterised by having lower final free carbon contents than is normally obtained. According to this invention, a process for 75 the manufacture of titanium carbide, having a free carbon content less than that normally present in titanium carbide produced by heating a mixture of titanium oxide and carbon, comprises intimately mixing alumina with 80 free-carbon containing titanium carbide or with the raw materials employed in the production thereof and subjecting the mixture obtained, in vacuo or in a protective atmosphere, to a temperature which, in the case of 85 the titanium carbide mixture, is high enough to cause the carbon to react with the alumina or, in the case of the raw materials mixture, is high enough to produce the formation of titanium carbide 90 When the alumina, which is preferably employed in the calcined state, is incorporated in the mixture of raw materials, i e titanium oxide and carbon, the raising oi the temperature of the mixture to the level normally used in the manufacture of titanium carbide is also sufficient to cause the excess iree carbon to be removed However, in some circumstances it is preferred to carry out the process according to this invention by adding the alumina, preferably calcined, to the titanium carbide after this has been produced by the usual methods. In both cases, the mixture obtained may, with advantage, be subjected to a grinding operation betore being heated whlich wiil result in the alumina being uniformly distributed throughout the mixture in finely divided form. In general, the titanium carbide powder of commerce contains about 90 % of Ti C and 1 to 2 % of free carbon Withi such a commercial product the proportion of calcined alumina which is required for the purpose of this invention is in the region of 2 0 to 3 %. The invention will be clearly understood from the following examples

of the manner in which it may be carried into practical effect. The first example illustrates the production of a sintered compact of titanium carbide with a low final free carbon content from a com0 mercial titanium carbide powder having a relatively high content of free carbon. A commercial titanium carbide po yder containing about 90 % of Ti C and 1 to 2 % of free carbon has admixed therewith a proportion of powdered calcined alumina and the mixture is then ball-milled for a relatively long period in the dry state until it is reduced to a mean particle diameter of about 1-2 microns The amount of alumina added depends to some extent upon the content of free carbon in the commercial Ti C powder but is usually equivalent to about 2 to 3 % of the weight of the Ti C employed. The finely powdered mixture of Ti C and Al O, is then moistened with a small proportion of a suitable binder, e g 1 % of para Tein wax dissolved in benzene The benzene is evaporated off on a water bath, or at a temperature sufficiently high to melt the wax, and the mass subjected to a compacting operation, the pressure employed being in the range 0 5 to 5 tons per square inch, e g 3 tons per square inch The compacting step may be effected by simple pressure between male and female dies, either at ordinary temperature or at an elev-ated temperature. Alternatively, the powdered mnixture may be extruded into the desired shape, but in this case a binder other than wax may be desirable, e g a small percentage of woodtar. The firing of the compact obtained is preferably effected in a furnace through which a stream of a protective gas, e g hydrogen, is passed, the temperature preferably being higher than 1600 C, for example, about 2200 ' C Alternatively, tile sintering may be carried out in a vacuum furnace, again in the same temperature range The finished product ccn-Lamins substantialiy no free carbon and the residual aluminium therein, whether pro 70 sent as A Lo or Al C 3 is very small As an example, a titanium carbide powder initially containing between 1 % and 2, of free carbon, when mi Nxed with 2 5, of caicined alumina and treated as above set forithl, yielded 75 a coinpact containing onyif O 2 of free carbon Increasing the amount of AI,Q added to 3 resulted in a product containing O 05 ' of free carbon. When tile sintered compact obtained is 80 intended for use as a cathode or current lead in an electrolytic cell for the production of aluminium, it is preferred that the content of free carbon in the finished compact shall be below 0 1 c% but somewhat higher percentage 85 of free carbon can be tolerated provided that the figure of 0 5 % be not reached Cathodes thus prepared from substantially carbon-free Ti C will be wetted freely by molten aluminium with-out any tendency

to shatter or break up 90 and without any sian of crac ks developing. The S cond example is ccncernad with the prodiucu-n of a rlauely cirbion-free titanium carbide podaer suitable for use in ithe production of shaped articles composed of titanium 95 carbide by hot-pr ssing, sntoring and like operations For tins purpose, the product obtained by neating commercial Ti C with alumina must be suafficiently friable to make it ccmarai'vely easy to grind to the di-ree of 100 fineness required. In this example, relatively coarsely-ground commiercia titalium carbide (pass 200 mesh B.S S), containing 1 5 to 2 of free carbon, is mixed with 2 5 to 3 caiellned alumina and 105 charged into a graphite boat in as loosely packzed a manner as pssible The boat is then heated for example, in a carbon resistance furnace, to 2200 C in a stremn of hydrogen being held at this maximum temperature for 110 fromi 5 to 10 minutes The product obtained has a free carbon content of 0 1 to 0 2 %D and may be ground comparatively easily to a particle size suitable for powder metallurgy purposes 115 It may be mentioned that te elriminaiicn of the free carbon by the alu nina may be effected at a rather lower temperature (about 1609 O G.) if the treatment be carried out in vacuum instead of in a current of hydrogen 120 The third example is concerned with the production of a relatively free carbon-free titanium carbide from the raw materials rutile and coke. 3620 grms of rutile were mixed with 1390 125 grins of coke and ground together for 17 hours in a ball mill The resulting powder was then divided into two halves each of 2505 grms. These two halves will be referred to as charges A and B respectively 785 grins of molasses 130 784,697 784,697 were added to charge A as binder and the charge was extruded in the form of pills, dried and then calcined for a period of about 7 hours, raising the temperature of the charge to about 8000 C The charge A was allowed to cool and was then fed to a high temperature furnace and subjected to a temperature of about 22000 C in a protective atmosphere of carbon monoxide produced in the reaction The resultant product was found to have a free carbon content of 0 86 % by weight and a total carbon content of 20 27 % by weight from which it was calculated that the product contained 96.8 % by weight of titanium carbide. Charge B was treated in exactly the same way as charge A except that 30 grms of alumina were added to the charge prior to the addition of the molasses thereto The product was found to have a free carbon content of 021 % by weight and a total carbon content of 19 58 % by weight from which it was calculated that the product contained 96 7 % by weight of titanium carbide The residual alumina in the charge was found to be about 0 03 %. It will be seen that the product of the charge treated with alumina

contained 0 65 % free carbon less than the product of the charge not so treated. It may be calculated that each charge should produce about 1350 grms of titanium carbide and it will be seen that 30 grms of alumina added to charge B constitute approximately 2.2 % of the estimated weight of titanium carbide capable of being produced from the charge.


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