CALCULAT ING THE EFF IC IENCY OF CRUSHING

A. A. V ikh lyaev , V. V. Kamensk i i , and A. I. Fedu lov

PLANT

UDC 622.731 : 621.92 + 622.013

An engineering efficiency analysis of the operation of plants for crnsbing oversize rock fragments reveals that it is not altogether correct to assess their efficiency from results obtained only at the working site. In this article we will give a method of calculating the cost efficiency of such plant, based on the special features of their opera- tion, and yielding an estimate of the profitabiRties of their individual operations.

In association with the Mining Administration of the Kuznetsk Metallurgical Combine (GU KMK), a plant was put into experimental use by the Anterior quartzite mine. Like subsequent plants, this was based on a rubble ham- mer - a powerful pneumaKc percussion machine mounted on a manipulator of the gantry-crane type.

The various parts of the plant had the following working speeds: raising hammer, 4.55 m/rain; lowering hammer, 15.65 m/rain; traversing of crane on gantry, 11 m/rain; travel of gantry, 10 m/rain. For the average cycle duration of 15.6 sec, the time balance was as follows: operation of hammer, 11%; operation of mauipulator, 58%; standstills due to poor organization and technical causes not associated with operation of the plant, 31%.

The average throughput of the screen is 1250 t per shift; with 10-12% content (data from Aatonov mine) this constitutes about 150 t oversize fragments per shift, or 21 t/b. Remembering that the machine was hald up for 31% of the time by external causes, the throughput could, with appropriate organization of the work, be raised to 30 t/h.

To increase the throughput, we suggested increasing the speeds of raising and lowering the hammer to 18 m/rain, and those of traversing the crane and gantry to 30 m/rain. Calculations based on a machine time factor of 0.7 showed that in this case the plant could crush up to 60 t/h, i .e., with 150 oversize content, around 2800 t rock per shift, or, with two-shift working, about 1.5 mill ion tons per year. (We are excluding holidays (58) and days re- quired for maintenance (30).)

From the data acquired we can calculate the economic efficiency of the crushing plant. Usually one plant is manned by two workers - a grade Five machine operator with daily rate 3.30 rabies, and a compressor minder with rate 2.78 rubles. At the GU KMK additions to wages amount to 33%, so the yearly wages biU for two-shift plant operation amounts to 4732 rubles. Two mechanics are occupied in preventive maintenance and running repairs, and are paid 6.0 rubles per day. If they are employed for one month per year, we calculate that the yearly wage biU for maimenance work is 424.0 rubles; while the total wages bi l l for production and maintenance together amounts to 5156 rubles.

As a first estimate, we can calculate the cost per unit throughput (in this case, unit volume or weight of crushed rock) from the formula

C-- R. ~P._P_ (1) A

where R is the yearly running cost without allowance for wages, P is the yearly wage bil l with additions, and A is the yearly throughput of the crushing plant.

The yearly running costs of the plant can be found from the formula

R =,O+T+M+:B+ H (2)

where O is the cost of plant depreciation, T is the cost of running and intermediate repairs, M is the cost of repairs to equipment, B is the yearly cost of the air supply, and H is the cost of the tool-heads (hammers) required to secure normal working of the plant for a year.

Institute of Mining of the Siberian Branch of the Academy of Sciences of the USStL Novosihirsk. Translated from Fiziko-Tekhnicheskie Pmblemy Razrabotki Poleznykh Iskopaemykh, No. 6, pp. 69.-67, November-December, 196~. Original article submitted November 10, 1966.

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The cost of electrical power is 3-4~ and will be neglected.

Judging from experience, the life of a rubble hammer is two months, so to ensure normal operation during a year we need six of these. The cost of manufacture of each hammer (if mass produced) will be 500-550 rubles. Thus five additional machines will cost 2750 rubles. According to data from the Temir-Tau dolomite quarry of the GU KMK, the total cost of the plant with one hammer was 5505 rubles, or without the hammer at 550 rubles, the plant (manipulator) costs 4955 rubles. Suppose that the manipulator is amortized over five years; then the depre- ciatien costs are 20% or 991 rubles. For repairs to the equipment we subtract 25%0 of the cost of the plant with one hammer, divided by the service life in years - 275 rubles [1]. Deductions for running repairs (without labor costs) are taken as 6%0 of the initial cost - 330 rubles.

The cost of compressed air was reckoned from data on the continuous two-shift operation of a mobile com- pressor with output 9 mS/rnin, allowing for a machine t ime factor of 0. 9. The yearly consumption of air was taken as 1,900,000 m s. The actual consumption of air is due to the working time of the hammer (11%) and the auxiliary consumption (15 mS/rain) and during crushing is 4. 72 mS/t. According to data from mines of the GU KMK and other enterprises, the cost per cubic meter of air is 0.25 kopeks. Thus the yearly cost of compressed air consumed by the plant is 4750 rubles.

Starting from Eq. (2), the yearly costs of the plant will thus be 9008 rubles. Using Eq. (1) it is now possible to reckon the cost of production, which is 0.07 rubles per ton, or 0:19 rubles per cubic meter (for a ~lensity of 2.7 t/mS).

If our cost calculations are based on the level of production already achieved in practice (21 t /h or 82,000 tons per year), this index will be 0.1~/rub/ton or 0.4"/rub/m s.

These results can be compared with data from, for example, the Zalatin gypsum mine of the "Vosrsibugol' " group. Here we find up to 120 tom of oversize rock per shift, or, with two-shift operation, about 74,000 tons per year; this is reduced by drilling with an ~RP-5 mine electric drill, followed by blasting. According to the data from this mine the cost is 0.89 rubles per ton of oversize rock. For the output of the Zalarin mine (74,000 tons per year) the cost of mechanical crushing would come to 0.19 rubles per ton. Thus the use of a crushing plant at this mine would achieve an economy of 0.40 rubles per ton.

The yearly gain from the use of a crushing plant can be calculated [2] from the expression

Ry = (C I -- C~) A - E D- Q, (3)

where C I is the cost of production before introduction of the plant, C z is the estimated cost of production achieved by the crushing plant, E is the capital return efficiency for the given region, D is the additional capital cost, A is the yearly volume of production, and Q is the pre-production cost.

The pre-productton costs of research (wages, mateziais, preparation of pilot plant~ travelling expenses, etc.) total 10,500 rubles.

Before the introduction of the plant, the cost C I of unit production (crushing of oversize rock) depends on the method used. In some pits and quarries, in particular in Gomaya Shoriya, oversize rock is crushed by hand and by blasting. When the screens are manually operated, oversize pieces obtained in the course of breaking down the rock are first broken up by blasting, but even this does not fully eliminate the use of hammers at the screens. According to data from the Antonov mine, the wages of one screen operative are 2.78 rubles per shift, and the expenses per ton of oversize rock broken up come to 3.7 kopeks per man. Thus the norm for manual crushing of oversize rock is 7.fi tons per shift. If the ore contains 12% oversize, this mine will incur additional crushing of up to 150 tons of rock. The screen operators (four men per shift)' process 30 tons, and the rest must be blasted separately in the quarry (80%). On this basis the yearly amount of manual processing with two-shift working for the Antonov mine is 18,500 tons, while 73,500 tons is crushed by blasting. The expense of manual crushing is mainly due to the cost of labor (neglecting the cost of tools), and in this case is 8650 rubles per annum.

The cost of crushing by blasting is made up of the cost of drilling and that of blasting. According to 1Rerature data [3], of the total cost of drilling the labor costs amount to 40-60%, the cost of drining tools is 20-30%, and the cost of compressed air is %12%. In Table 22 of reference [3], data from Soyuzvzryvprom (union Blasting Industry) are given on the consumption of air per meter of hole; for rock with hardness of 14-16 it is 53.5 mS/m.

According to numerous observations made in the Laboratory of Ore Deposit Working of the Iustitute of Mining of the Siberian Branch of the Academy of Sciences of the USSR in the field of crushing of oversize rock by blasting

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[4], the relative depth of hole drilled for explosive charges is 1.3 m/m s, which for the conditions at the Antonov mine comes to 0.48 m/t (density 2.7 t/mS).

From these data we can calculate the expense of additional crushing by blasting. Thus, if half the volume of the rock is crushed by drilling and blasting, if the relative length of the blast holes is 0.48 m/t and the consumption of air is 53.5 mS/m, the amount of air used is 950,000 mS/year, which costs 2375 rubles. From the data in [3] we infer that these costs constitute 10% of the total cost of drilling blast holes. Thus the cost associated with drilling is 23,750 rubles per year.

The cost of high-velocity, and other explosives, can be calculated from the relative costs found by the Lab- orabory of Ore Deposit Working for the total usage of borehole and surface charges. According to their data, the consumption of high explosives (HE) is 6.4 kg/m s, that of detonating fuses (DF) is 4.8 m/m s, that of time fuses (TF) is 2.2 m/m s, and that of detonator caps (DC) is 1.5 per ms. For the rock volume found above (73,500 tons of blasted rock) the yearly consumption is as follows: HE, 179,000 kg; DF, 134,000 m; TF, 59,600 m; DC, 44,700. Accord- ing to data from mines of the GU KMK, the cost of loese ammonite is 0.15 rub/kg, that of DF is 0.09 rub/m, that of TF is 0.023 rub/m, and that of DC is 0.017 rubles each. Hence the total cost of high and other explnsives is 40,900 rubles per year.

According to [5], for underground workin.g with 10% oversize content, for passage through manually operated screens at a rate of 38 m s per 6-hour shift, 0.5 shifts of blasting operatives are required for crushing the debris by high explosives. In open-cut working at the Antonov mine, where up to 115 m s rock is put through per man per %hour shift, we can also allow 0.5 blasting shifts for this volume. Then if there are four screen operatives the quarry must employ two blasters at a cost of 6.0 rubles, and two assistants at 3.3 rubles per shift. Thus the wages bill for blasting to crush the rock, allowing for additions, is 14,460 rubles per year. In this case the cost of crush- ing oversize at the Antonov mine is 0.95 rub/t. If we were to use a plato which takes a yearly volume of 92,000 tons of rock for crushing, the cost would be 0,16 rubies/t, or 0.43 rub/m s .

Thus the yearly economic effect from the introduction of the new crushing method amounts to 62,706 rubies per annum; since according to data from the GU KMK the cost efficiency is 0.15, the yearly total advantage is 62,706 rubles, or. for a yearly output of 760,000 t, 0.083 rubles per ton of rock.

The above calculations are based on the assumption that the introduction of the plant completely eliminated secondary blasting to crush oversize rock. In mi~ng practice conditions may arise in which specially large frag~ ments are formed needing blasting to disintegrate them. For this reason, for greater reliability of the calculations, we allow the possibility of blasting oversize rock even when the plant is in use, and assume that the volume of rubble needing additional blasting is 9200 t (10~ of the yearly volume). If we allow for these additional costs, the net cost of crushing by the plant is 0.27 rub/t, and the yearly economic advantage is 92,566 rubies, or 0.069 rubles per ton of rock. Assuming that this requires 0. 5 of a blasting operative per day, we can find the saving in labor costs. For two-shift operations, the plant frees 4 screen operatives and 7 blasting operatives, which amounts to 23,639 man-hours per year.

Similar calculations can be performed for the dolomite quarry of the Temir-Tan mine. Here three screen operatives per shift give a yearly throughput of 120,000 t rock of density 2.85 t /m s and 12-15~ oversize. Assum- ing that 20% of the rock is crushed by blasting (with a 50% ratio of borehole to surface charges), we will need one blasting operative with daily pay of 6 rubles. Using the same method as for the Antonov mine we find that the crushing costs are 13,560 rubies per year. Hence the net costs are 0.9 rub/t.

After the crushing plant is adopted, we are left with two rubble hammer operatives per shift. With three- shift operations, their yearly wages are 6530 rubies, allowing for additions. If the plant is fed from the mine air maim, the air used per ton of rock crushed is 4. 72 ms. If the loss factor is 1. 3, the amount of air used by the plant is about 100,000 mS/year, costing 250 rub/year. Hence, allowing for maintenance and running costs, the yearly ex- penditure on the plant is 11,230 rubies, corresponding to a net cost of 0.74 rub/t.

However, this net cost does not allow for pessible expenditure on additional blasting of specially large frag- ments (by analogy with the foregoing), and is based on the premise that the wages of the rubble hammer operative and rabblers are 2. 78 rubies per man-shift. In this case the yearly economic advantage (not allowing for preproduc- tioa costs) is 1500 rubles.

However, in its official records, the mine shows a planned reduction in the cost per ton of rock by 0.037984 rubles, and a yearly economy of 2893 rubles, when the plant is introduced. The discrepancy with our calculations is easy to explain away if we analyze the method used by these enterprises to calculate economic efficiency. In

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the official records issued by the mine, the yearly economic efficiency is found from the economy of the wages bilL The yearly economy for the Antonov mine is 4465 rubles. Undoubtedly such a method of calculation does not take account of all the costs associated with the crushing of oversize rock, and therefore fails to present a tree balance.

Our method of calculating the economic efficiency gives a more faithful picture of the tree position, and is a rational approach to the problem of the introduction of new methods and the organization of the work. This is con- firmed by the exampie of the Temir-Tau dolomite quarry. We caicniated that the introduction of the plant would give a smail economic gain, because it is underloaded (total load 18%). Thus one way of increasing ire efficiency is to increase the volume of rock to be crashed. This can be done by increasing the yield of ovezsize rock, which may save money on the main blasting operations.

We must draw attention to the high propertional cost of wages (88%) and consider how to reduce it. This could be achieved by cutting down on supervisory staff, reducing the number of shifts, and increasing the load per shift.

Our engineering efficiency analysis of the operation of a crashing plato has shown that if it is efficiently utilized and if a11 the work is appropriately organized, the yearly saving may reach 40-50 thousand rubles. Our method of calculating the cost efficiency permits us to analyze the utilization of the plant and shows how to achieve max imum efficiency.

L ITERATURE C ITED

1. S. E, Kantorer, Bases of Efficiency in the Use of Machines .in Constructional Work [in Russian], Gosstmiizdat, Moscow (1961).

2. Methodological Basis for Determining the Economic Efficiency of Scientific Research [in Russian], ~konomika, Moscow (1964).

3. K. L Ivanov, V. N. G1azunov, and IvL F. Nadion, Modern Methods of Drilling Hard Rock [in Russian], Gnsgor- tekhizdat, Moscow (1964).

4. E.P. Ryabchenko and Yu. L Karapetyan, "Crushing Large Ore Fragments by Blasting," In: Advances in the Theory and Technique of Mining [in Russian], Nedra, Moscow (1964).

5. E P. Ryabchenko, "Determining the Opt imum Diameter for Boreholes in Underground Ore Mining," In: Im- provement of the Technology of Underground Ore Mining [in Rnssian], Nedra, Moscow (1965).

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