ROLLED PRODUCTS

THE R E L I A B I L I T Y AND S E R V I C E L I F E OF

(UDC 621.771.2.019.3)

G. L. K h i m i c h a n d N . N . B e l y k h

Uralmashzavod (Urals Machine-Building Plant) Translated from Metal lurg, No. 3, pp. 24-26, March, 1966

R O L L I N G M I L L S

Improving the re l i ab i l i ty and service l ife of rolling equipment is a basic condit ion for making production more eff icient . At one of the country's me ta l lu rg ica l plants the cost of one hour of idleness is a follows: 1150 blooming mi11-420 rub., 950/800 ra i l -s t ructural mi11-575 rub., and 650 rolling m i l l - 4 4 5 rub. The mean period

of idleness per year for the same mil ls , determined by the re l iab i l i ty and service life of the whole set of machinery, over the last three years, referred to calendar t ime , is as follows: for the blooming mi l l 14.03~ or 1230 h, for the ra i l -s t ructural mi l l 11.07% or 970 h, and for the rol l ing mi l l 650 12.03% or 1055 h.

Thus the cost of idle periods per year on the part of the mills is 510,558 and 470 thousand rubles, respect ively. This does not take into account loss of the economic profits that could be gained by the nat ional economy if products were being turned out during the idle periods.

The development of ro l l ed -meta l production at the present t ime is marked by a great increase in the operat ional rate of the equipment due to an increase in the roll ing rate, reduction rate, weight of the rolled ingots, and extensive introduction of continuous and endless types of roll ing, which, natural ly, result in greater wear and tear in parts and to greater losses over the same period of idleness. The complex mechanizat ion and automat ion of the production operations introduced into rol led me ta l production also demands greater re l iab i l i ty and longer service life of the equipment , which should take the form of:

a) constant perfecting of equipment design:

b) manufacture of parts from mater ia ls possessing the opera t ional ly stable necessary phys ica l - chemica l properties;

c) high-grade manufacture, assembly and adjustment of machinery and correct operation of i t .

At present machine-bui lders are in a position to improve the re l i ab i l i ty and service life of the machinery they make: they have a wide select ion of mater ia ls ,proven technological procedures; data from exper imenta l analyses, and so on.

But the possibilities cannot a l l be u t i l ized fully since we have sti l l not accumula ted sys temat ized and pract ica l data on the parts of the machines requiring improvement in this respect . It is only object ive information on the operation of current equipment plus research based on these data for rolling mills that enable us to make worthwhile recommendations for improving machine design and re l iab i l i ty and service l i fe .

The chief designer's department for rolling equipment of the Uralmashzavod has organized the col lec t ion and

analysis of s tat is t ical information in the following manner .

First, in view of the great variety of machinery used in rolling milts , the designers themselves are invited to take part in the work to make the s ta t is t ical analysis and col lec t ion of information more effect ive . The work is incorporated in the design office schedules which are based on the year 's equipment study program. This makes it possible to pick out the weak points in the equipment , chiefly through accumulat ion of data on the service l ife of parts and information obtained from servicing personnel on the degree to which equipment can be repaired.

Second, weak points in the roil ing mi l l equipment and the repai rabi l i ty of it can be ascer tained by analyzing idle periods, repair costs and losses due to idleness for each part of the machine and the machine as a whole.

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Furthermore, this side of the operation makes it possible to bring to light general operational indices of the rolling rnills that greatly reduce their efficiency (for example, idling necessitated through changing the rollers, adjustment, and so on) and draw the designer's attention to them.

The second phase of the work is carried out by designers and economists specially trained for this purpose. The two phases complement one another and can be used to check one another.

The collection of information, however, is complicated by the fact that calculation of the repairability of machinery and its performance characteristics at metallurgical plants does not make allowance for demands of further improving the machine's design. Often the only source of information on service life of parts and completed repairs, in the rolling shops is the memory of the servicing personnel. It is quite natural that this source cannot always be reliable and objective.

Logbooks and i temized lists of expendable parts, which the rolling mill mechanical services have to keep under the "Regulations on Scheduled Preventive Repairs (SPR) to Equipment and Transportation at Enterprises of the Metallurgical Industry" dated 1964, cannot be used in practice for gathering information on operation of the ma- chinery since the logs are not kept regularly and the lists are still not being compiled at most plants.

Nor does assessment of the technical-economic operational data from the rolling mills meet the requirements of further improving machinery design. The data are not sufficiently broken down and not tied in with individual parts of machines and machines (by this is meant periods when the machinery is idle, repair costs, using-up of spare parts, and so on).

The tying in of this data with the individual parts and machines in the relevant documentation of the roiling shops is also of interest to the mechanical services of the metallurgical enterprises. Strict observance of requirements as regards this documentation, with allowance for figures relating to idle periods, repair costs, and so on for individual parts and machines, will enable us to obtain complete and authentic information on the work of the rolling equipment.

The new documentation being developed at present by VNIIOChERMET for assessing the work of equipment in metallurgical plants, including rolling shops, does not take into account, in our opinion, the aforesaid require- ments. It is advisable, when compiling the documents, to give consideration to the wishes of machine-building plants, who are the suppliers of meta lh rg ica l equipment. For example, very important in further improving rolling mills is analysis of technical-economic figures for the operation of them: the complex operational reliability factor, specific metal consumption on repairs, specific repair costs, etc. , These figures can be taken from now on as the basis for planning the reliability and service life of newly designed rolling mills.

An important problem in improving the reliability and tile of rolling machinery is keeping the efficiency of it at the same level as when originally delivered by the manufacturer. This refers to organization of the production of spare parts, the grade and life of which should not be inferior to those originally supplied. Otherwise the problem cannot be solved.

At present many metallurgical plants use a system of part-by-part and unit-by-unit replacement of worn-out elements. This technique necessitates further capital expenditure on spare units and machines and additional space in the shops, but, on the other hand, is of definite advantage in that it cuts down the amount of time spent on repairs and improves the quality of the repairs. We need a thorough economic analysis of these methods to deter- mine their real efficacy. Naturally, an economic analysis of the efficacy of part-by-part and unit-by-unit repairs should be carried out by one of the metallurgical indnstry's research institutes,

Of great importance is joint study of the state of repair of rolling equipment by roller metallurgists and engineers. It is a useful thing to discuss these questions in All-Union schools for gaining experience in servicing and repairing rolling equipment, enlisting the aid of rolling mill designers for the purpose.

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