One of the trends in the technical refurbishment of mining departments at the cement works belonging to EUROCEMENT Group Holding is switching over to non-blast slicing mining technique using surface miners manufactured by Wirtgen.

Some positive experience was gained by mastering the new techniques at the Dzhegutinsk quarry worked by ZAO Kavkaztsement: starting since mid-2005 till now over 8 million t of limestones has been mined using non-blast slicing. Within this period the surface miners' operating factor in terms of time amounted to 0.75 in continuous running mode.

Within the program of technical upgrading a new technique is now introduced at some of the quarries involving the use of larger surface miners. Expansion of the production in the Dzhegutinsk quarry (ZAO Kavkaztsement) was realized by transition to more powerful surface miners of 2500 SM model (2 machines), one of them within the first two months of operation producing about 400 thousand t with shift productivity about 5,000 t (A more detailed description of the surface miners operations is presented in Gornaya Promyshlennost Journal 1/2008). The next target for this technique was the limestone quarry of Lipetsk cement works (Gornaya Promyshlennost Journal 1/2008).

The start of production in the limestone quarry of Pikelevo cement works is planned for the forth quarter of 2008. By the end of 2008 five surface miners of 2500 SM model will be working in the quarries the cement works belonging to EUROCEMENT Group.

Putting into operation of surface miners at the sites was accomplished by the representatives of Wirtgen together with Russian specialists refining the performance parameters of the surface miners operation in combination with the adjustment of the production to various lump sizes (fractions) of the raw material, refining of the loading scenarios, and training personnel in practical skills of operating surface miners and providing their maintenance.

Stopwatch studies were used to determine the time necessary for cutting, maneuvering, and turnover of dump trucks for loading. Idle time for various reasons< including shift servicing, was also registered. Shift servicing comprised refilling diesel fuel and water; examining surface miners blocks and aggregates; lubricating and cleaning the conveyor and cutter drum; checking the hydraulic system and actuating device.

The results of measurements and stopwatch studies were used for the calculation of the surface miner capacity using the following formulae:

Operation time (Top = Tc+ Tt + Tex) is the sum of cutting and loading time (Tc), time of turnaround at the end of each cutting pass (Tt) to start backward cutting (or idle return time), and the time of dump truck turnover for loading (Tex).

Operation capacity is the output rate during operation time (t/hr).

Technical capacity is the output rate during cutting and loading time, Tc (t/hr).

Table 1 shows data from surface miners pilot runs and operation at the mining sites of EUROCEMENT Group in 2005–208.

Table 1. Performance parameters of surface miners 2200 SM and 2500 SM in the quarries worked by ZAO EUROCEMENT Group

Parameters

ZAO Kavkaztsement

ZAO Lipetsktsement

ZAO Mikhailovsktsement

2200 SM

2500 SM;
no. 24

2200 SM

2500 SM; no. 27

2500 SM
no. 13

2200 SM

2500 SM
no. 13

2500 SM

no. 13

Mined material

Thinly laminated small-block limestones

Light gray with yellow hue limestones of medium strength, fractured, middle to large blocks, fine-grained.

Large-block limestones of various strength

Ultimate compression strength, MPa

35-70

40-80

80-120

Pick type

W47 K 17;
W47 K 19

W47 K 17; W47 K 19

W47 K 17

W47 K 19;

WSM17-42

W47 K 17

W47 K 19; W47 K 22;
W47 K 25

WSM19-42
WSM22-42

Drum type

НТ6

НТ6

НТ6

НТ6

НТ14

НТ6

НТ6

НТ14

Depth of cutting, cm

20-24

45-50

18-22

45-55

15

40-25

25

Picks wear, pcs/1000 t of mined product

1

1

2-3

0.25

0.30

3-4

13.8-19.8

8-11.5

Technical capacity, t/hr

400-600

590-715

320-370

480-540

145-300

305-420

180-300

Operational capacity, t/hr

270-530

515-580

250-300

360-400

140-280

200-320

145-300

Size distribution, %

< 50

61-77.5

65-75.7

84-92

66-78.5

83.4-64.8

66.5

+50-100

26.9-16.2

17.7-15.7

12.8-7

26.7-16.8

11.5-26.5

23.4

+100

12.1-6.3

17.3-8.6

3-1

7.3-4.7

5.1-8.7

10.1

Analysis of the results provided a means for adjustments of working scenarios in each of the quarries.

The general conclusion from the observations at all the sites was that there is a sufficient capacity reserve for increasing the production rate by reducing time taken up by maneuvers (as the skills in the miners control increase) and idle time due to waiting for dump trucks (18–40% of all idle time). Most of the lost time is the result of inefficient pattern of approach of a dump truck for loading or lack of drivers' skills in placing dump trucks for loading, which can be remedied by gaining some experience in the team work between the surface miners operators and truck drivers with time.

The general task to be solved in the transition from traditional techniques to the new one is the operation of a surface miner at the slope of the bench and in the zone near the side wall. This task is the result of the surface miner operations outside the caving wedge, the large-block structure of one of the target massifs which called for special organization of the process.

After a passage along the upper edge of the bench, removing a layer 40–50 cm deep, there remained a block in the form of a step, later on removed by a ripper-dozer unit to the lower horizon (Fig. 1).

The route of the passage closest to the bench edge was about 1 m away from the break along this edge.

The fragments of limestone thrown down will be crushed by a hydraulic hammer or, as the working site of the surface miner moved down, will be worked by the surface miner itself after the appropriate leveling.

Fig. 1. The block remaining after the surface miner worked the passage closest to the slope is pushed down, to the base of the bench.

In some cases the mined limestone was transported by the miner conveyor to the lower bench in order to increase the stability of the slope of the mined bench (Fig. 2) and at the same time to create a backup store of raw material. The crush-rock pad at the lower part of the slope makes it possible for the surface miner to move closer to the slope as it mines the upper bench, without leaving a step )block) at the edge.


Fig.2. Spilling the mined limestone along the lower edge of the slope, creating the backup store and increasing the stability of the slope.

Another task to be solved while converting to the new techniques is to ensure the optimum size distribution (fractional makeup) in the produced limestone to meet the requirements of the cement works.

In the process of pilot runs of surface miners of various standard sizes on all the sites, various performance parameters (cutting depth and operating rate while cutting — usually three variants each) were studied in the context of the produced fractions (lump sizes). For this purpose sample screening was carried out: during the working passages of the surface miner limestone material was stacked in piles from where samples were taken.

Cutting depth was 15–25–45 cm, operating rate 2 to 6 m/min. Samples were taken from the middle of the pile along its cross-section (traversing all the layers of the triangle section of the pile).

The limestone samples were passed through the screen with mesh 100–150 by 150 and 50 by 50 mm producing three fractions: > 100-150; – 100-150+ 50; < 50 мм. Each fraction was weighed and the data was put into the chart. Screening and weighing of fractions less than 50 mm in size were accomplished in the laboratory of the cement works.

Data obtained during the start of operations of 2 surface miners at the Sokolsko-Sitovsk quarry of the Lipetsk cement works are presented in Table 2.

Таблица 2. Fractional yield of limestone produced by surface miner no. 13 from the large-block massif (cutting depth 40–45 cm, operating rate 5–6 m/min, picks with 22 mm inserts, drum of HT14 type).

Fractions (lump size), mm

Fractional yield

Mass, kg

Part, %

Progressive total, %

< 5

50.9

13.9

13.9

5-10

38.0

10.4

24.3

10-20

55.0

15.0

39.3

20-30

42.3

11.6

50.9

30-40

40.5

11.1

62.0

40- 50

60.3

16.5

78.5

50 – 150

61.4

16.8

95.3

>150

17.1

4.7

100.0

365.9

100.0

The first screening was made from the surface layer of the working site. Similar screenings using the above procedure were made in the layer 1–1.2 m below the initial surface.

The second screening was made after the replacement of the picks with hard-face inserts of miner no. 13 by picks of WSM-17-42E type with 17 mm insert (Fig. 3).

The results of screening are presented in Table 3.

Table 3. Fractional yield as surface miner no. 13 mined the large-block massif (cutting depth 40–45 cm, operating rate 3.6 m/min, picks with 17 mm inserts, drum of HT14 type)

Fractions (lump size), mm

Fractional yield

Mass, kg

Part, %

Progressive total, %

< 5

40.5

8.7

8.7

5-10

39.1

8.4

17.1

10-20

62.8

13.5

30.6

20-30

46.0

9.9

40.5

30-40

43.2

9.3

49.8

40- 50

75.3

16.2

66.0

50 – 150

124.2

26.7

92.7

>150

33.9

7.3

100

465.0

It should be noted that replacement of picks with more sharp ones resulted in the increase of limestone fraction +50 mm from 21.5 to 34%.

Similar procedure was used for screening of limestone produced by surface miner no. 27 with HT6 drum and picks with 19 mm inserts (Table 4).

Table 4. Fractional yield of limestones produced by surface miner no. 27 from the large-block massif (cutting depth 40–45 cm, operating rate 5–6 m/min).

Fractions (lump size), mm

Fractional yield

Mass, kg

Part, %

Progressive total, %

< 5

42.5

20.6

20.6

5-10

27.4

13.3

33.9

10-20

33.0

16.0

49.9

20-30

19.1

9.2

59.1

30-40

20.4

9.9

69.0

40- 50

29.1

14.1

83.1

50 – 150

26.8

13.0

96.1

>150

8.0

3.9

100.0

206.3

The data on the fractional composition of limestone provided by the pilot runs of various surface miners (see Table 1) lead us to an important conclusion: yield of fractions less than 50 mm in size may be 75 to 85% irrespective of geological and mining conditions. Thus the new surface miners make away with the process of coarse primary crushing and radically reduce the load at the medium crushing stage.

Use of these surface miners also significantly alleviates the environmental impact of mining in the affected areas, increases safety in mining.

M. Pihler, President of Wirtgen International GmbH

V.A. Guskov, Head of the Department of Mining, ZAO EUROCEMENT Group

Yu. B. Pankevich, Cand. of Sci. (Technical), Sales Manager of Wirtgen International Service

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