Tweet

---

April, 1961

---

The Gusto multiplough is another type of rapid plough developed in the Netherlands, designed particularly to suit relatively thin seams and rather difficult conditions.

In principle, small plough units, 3 ft. in length (Fig. 69), are spaced along the face 15 to 20 yds. apart, and are connected by steel ropes. At each end of the conveyor the free ends of the rope are coupled to smalldiameter drums driven from the conveyor motors. Plough units are pulled to and fro along guides which are integral with the conveyor.

There are three multiploughs installed in Britain. In an experimental face at Waterhouses Colliery, Co. Durham, the multiplough face has presented with a face O.M.S. of 3.8 tons in a seam of 21 in. thick.

A new British multiplough, maximum speed of which is 48 ft. per min., has been designed. Motive power for the plough units and the conveyor-pushing cylinders is obtained from an all-enclosed hydraulic unit driven by a 25 h.p. motor. Hydraulic cylinders, with a 6 ft. stroke, pull the ploughs to and fro, through the medium of round link chains. The power and cutting speed are adjustable as required. The application of hydraulic power to ploughs of this type is an innovation in Britain.

Activated ploughs

The ploughs described earlier can work in soft and medium hard coal. Attempts were made to design activated ploughs to deal with harder coal. In some designs the fixed shear blade of the plough was replaced by a series of heavy duty pneumatic picks, while in others a percussive action was induced by the oscillations produced by the rotation of two out of balance rotors. The most successful of these has been the Huwood slicer, designed in Britain, which is described in detail later.

Trials have been carried out on a percussive plough with activated blades in a similar manner to a pneumatic pick. The experimental work carried out by the Mining Research Establishment, Isleworth, resulted in making a production model of this machine. The plough is double ended, 6 ft. 9 in. long and 20 in. wide at the widest point. The baseplates, which are similar to those of Loebbe Hobel, extend underneath the conveyor. The percussive action in the blades is produced by compressed air.

The production model was installed at Warsop Colliery (East Midlands Division) in 1955. The haulage to the plough was provided by an Anbauhobel unit with the modification that the haulage characteristic was changed from constant speed to constant force. The plough was shortly taken out from the face and installed in another face more suitable for further investigation.

A considerable amount of experimental work is being done in the Mining Department of King’s College, Durham University under Prof. E. L. J. Potts to develop an auto-percussive plough. Experimental models are undergoing underground trials.

Huwood slicer loader

This is the most successful British plough and was first introduced in 1951 at Washington Colliery. It is an activated plough which is mounted on an armoured conveyor. It cuts and loads the coal as it is hauled backwards and forwards, along the face. It is a double ended machine. This slicer loader comprises three main units as follows (Fig. 70):

1. The main frame which travels on the face side of the conveyor and carries the slicing blades. It travels on rollers.

2. The adjustable goaf frame travels on the goaf side of the conveyor.

3. The power unit which joins the other two units and forms a bridge over the conveyor.

The main frame is positioned on the face side of the conveyor and consists of two static wedge heads which are coupled to a central gear box. The activated pick blades project in front of these two static wedges. The activated blades cut a vertical kerf of 1¾ in. width and as the slicer advances the wedge heads further break away the coal and load it onto the armoured conveyor on which the slicer is mounted. The thickness of the slice taken by the loader depends on the distance between the conveyor and the face and is limited to a maximum of 14 in. The width of the wedges at right angles to the face line is 15 in. and it slopes back (in plan) at an angle of 45 deg. In elevation these faces are vertical, with the exception of the lower 16 in. which are at angles of 75 deg. to the floor. This helps in deflecting the sliced coal on to the conveyor. A rotary action is given to the activated blades by a 60 h.p. motor driving through simple reduction gearing, two eccentrics which are keyed by a solid bearing bar to which the blades are bolted.

Different types of vertical moving blades and static bottom blade at floor level are available to suit different coal-face conditions. The normal slicer is 3 ft. 6 in. in height and where the coal does not readily part from the roof, separate extension blades of up to 6 ft 3 in.. can be bolted to the rotating bearing bar.

The adjustable goaf frame is made up of two parts. One part is bolted to the motor while the second part is coupled to the first part and is fitted with two screw jacks and guide wheels. These two parts can slide in the vertical plane with respect to each other.

This allows the slicer loader to be tilted towards or away from the face by adjusting the screw jacks.

The 60 h.p. motor bridges the conveyor and is a connecting link between the main frame and the goaf side frame of the loader. The motor is mounted at such a height as to allow the flow of coal underneath it. The controls are situated on the goaf side of the power unit. The control unit consists of a start and stop button for the slicer, a start and stop button for the haulage motor, and a lever for controlling the direction of rotation of cutting blades.

An endless chain hauls the slicer to and fro along the face. The hauling unit, consisting of the power unit, the gear box and the automatic chain tensioner, forms an integral part of the conveyor tail end assembly. The haulage motor can be manoeuvred from the control panel on the slicer loader—control being established through the main slicer trailing cable—but reversal of the motor can only be effected by a switch located on the haulage unit itself.

The armoured conveyor is powered by two 60 h.p. 1470 r.p.m. or 40 h.p. 960 r.p.m. motors. The conveyor consists of 5 ft. sections. Each section has special welded channels to provide tracks on which the slicer travels.

A simple double-ended plough is towed about 3 yds. behind the machine to clean the track which facilitates the snaking of the conveyor. This plough is 4 ft. 6½ in. long, 2 ft. 6½. in. high and 19 in. wide.

Technical specification of the machine:

Height	3 ft. 6 in.
Width	4 ft. 7 in.
Length	9 ft. 6 in.
Weight	5¼ tons.
Haulage chain	in. dia.

Clearance between slicer power unit 171 in. high and and conveyor for passage of coal 20 5/8 in. wide.

Underground operation

The slicer can work satisfactorily in seams of 4 ft. 6 in. thickness and over. Although the overall height of the machine is only 3 ft. 6 in. a clearance at roof level is necessary for the roof bars. The slicer can also work in thicker seams. In one case it is working in a 7 ft. 3 in. thick seam. The slicer can work on any type of floor except where the floor is so soft as to allow floor penetration. Weak roof conditions can be overcome by leaving some coal in the roof in thicker seams. Being a double ended machine, it will work best on strike faces but gradients of 1 in 4 along the face and gradients of up to 1 in 10 to the dip or rise have been successfully negotiated. Precutting of the seam is necessitated in very hard coals. The cut can he made either through a dirt band, near the roof or floor or in the middle. Usually the horizon of the cut is governed by the nature of the seam. In one case the slicer cut through a hard sandstone intrusion. A middle cut should be preferred to avoid large lumps. The depth of the precut is governed by the number of slices to be taken by the machine. In certain cases precutting to a depth of only two slices may help to prevent roof deterioration.

The length of the face depends on several factors but in this case it is limited to a maximum of 300 yds. imposed by the pulling power of the haulage. Other factors affecting the length of the face are the gradient and the conveying power of the conveyor. A face length of 200 yds. is considered to be satisfactory. A minimum length of 10 yds. is required for stable holes in the tail gate while in the mother gate about 12 yds. are required.

Difficulties are experienced when large lumps of coal have to pass underneath the power unit. In such cases considerable spillage may occur. Such conditions arise when the slicer is travelling in the opposite direction to that of the conveyor and the direction of the cleat is such as to favour the production of large lumps.

A large spillage may not be completely cleared by the cleaning plough and this will limit the foreward movement of the conveyor, which in turn will affect the thickness of the slice to be taken by the slicer loader in the next web.

Fig. 71 shows a Huwood slicer with an overcutting disc. This machine is undergoing trials.

Scraper box plough

This is a development of scraper box loading first used in Britain in 1929. The modern scraper box plough was designed and developed by German and Dutch engineers. The type of plough consists mainly of scraper boxes fitted with cutting blades on the face side of the box. A number of boxes are spaced along the face and are joined by ropes. The boxes are pulled to and fro along the face scraping the coal from the solid and carry them to the loading gate. No conveyor is used on the face. The boxes are maintained against the face by guide rails which extend the length of the face and are under constant pressure from pushing cylinders. The endless rope haulage unit is usually situated in the gate road and uses large winches.

The scraper box consists of two side plates which are rigidly connected together at the top edge. The box is open on the bottom front and at the top. The back of the box is formed by a flat which is hinged at the top and opens towards the inside of the box only.

The length of the travel usually adopted is the spacing between boxes plus 5 yards. The capacity of the boxes varies from 19 to 35 cu. ft.

In Britain there are 10 scraper plough installations. The seams in which these ploughs are operating varies between 12 in. and 3 ft. 6 in. In 1954, the total output from scraper ploughs was about 150,000 tons at a face O.M.S. of a little over 4 tons.

General considerations in ploughing

Ploughs are suited to seams of thicknesses greater than 1 ft. It is difficult to put an upper limit to the thickness of coal seams suitable for ploughing because it largely depends on the ease with which the coal parts from the roof. The upper limit may be taken to be about 5 ft., but may be exceeded in certain cases.

Generally, the coal should not be hard. Hard coals require high haulage power and also difficulties arise in keeping the conveyor rigid along the face. Hard seams may require pulsed infusion or precutting before ploughing. If the coal sticks to the roof then overcutting will be necessary which will obviously raise the cost of production. If the coal is hard and sticks to the floor then the plough tends to rise and leave its level. For successful ploughing the floor should be hard although it is claimed that the distribution of cutting edges can keep the plough out of a soft floor.

Other factors affecting the operation of the ploughs are the pressure on the coal face, the direction of cleavage and the method of roof support at the face and in the waste. The blade angle and the blade design also affect the plough operation.

MACHINES FOR BORD AND PILLAR WORKING

Short wall coal cutters

Short wall coal cutters are specially adapted for heading work or pillar extraction. They may also be used where faces are too long. In these machines the jib is permanently fixed in line with the machine. The machine is designed to sump straight in the coal and cut across a short face and then be withdrawn.

There are two types of machine:

1. Rear discharge type (Fig. 72): The A-B rear discharge type machine is of 60 h.p. and is made in two units—the motor, and the haulage gear case. The latter provides the drive to the cutting chain carried on a jib, which is rigidly mounted below the body of the machine so that the cuttings are discharged at the control end. Ample clearance is provided for a free discharge of these cuttings. A gummer can also be fitted at this end of the machine to improve the discharge. The flitting speed of the machine is 30 ft. per min. and the cutting speed can be varied within a range from 9 in. to 36 in. per min. The use of a double-drum haulage is particularly advantageous where the heading is advancing to the rise. The machine is 1 ft. 11½ in. high, 3 ft. 11 in. wide and 5 ft. 6 in. long.

2. Low seam type: This is particularly suitable for thin seams (Fig. 73). The reduction in height is achieved by making the machine in three sections—the motor unit, the haulage gear case unit and the gear head unit. In this case the cuttings are discharged at the neck of the gear head. The machine is fitted with a fixed jib bracket, but provision can be made to fit, if required, a swinging jib bracket, so that slabbing or arcing cuts may be made. This machine is 1 ft. 4 in. high, 3 ft. 7 in. wide and 7 ft. 10 in. long.

Arcwall coalcutters and shearers

The arcwall machine is similar to the shortwall machine and is used for driving narrow headings. It is mounted on crawler tractors (Fig. 74), or on wheels (Fig. 75). These machines can be supplied as an undercutter or overcutter and have electric or compressed air drive. The dimensions are as follows: (i) tractor type—height=3 ft. width= 4 ft., length= 10 ft.; (ii) rail mounted— height 2 ft. 6 in., width=3 ft., length= 10 ft. The machines are arranged to cut at nearly 1 ft. above the floor level. Machines to cut at different heights are also available. The machine cuts the heading in the form of a semi-circular arc from one central position.

One of the methods of varying the height of the horizontal cut is shown in Fig. 76 which shows a M. & C. arcwall machine mounted on jacks and crawler undercarriage. This model can he raised to make a horizontal cut at a height of 4 ft. 10 in. These power operated jacks can lift the machine by a maximum of 12 in.

Another method of varying the height is shown in Fig. 77 where the height can be varied up to 14 in. by means of jacks and 18 in. by the turret head. This machine can provide an overcutting height of 6 ft. 1 in.

A universal Arc Shearer differs from the arcwall coal cutter in that it can cut at floor level or any height up to a certain maximum height depending uponthe design of the machine. It can cut or shear at any desired angle. One type of this machine (A-B ‘Dreadnought’ arc shearer) is shown in Fig. 78. Fig. 79 shows the machine making a shearing cut underground. The gear head in this machine consists of two sections, the main head and the jib head which carries the jib and the cutting chain. The main head is mounted on the machine, whilst the jib head is installed eccentrically on the main head, and each section is capable of complete rotational movement about a parallel axis.

The main advantage of this machine is that it can deal with variable conditions underground.

The performance of a "Universal" arc shearer in the high main seam in a Northumberland Colliery is worth mentioning. The seam was 5 ft. thick and the coal was of a tough nature. The machine with a 6 ft. jib was cutting about 5 yds. wide. The average cutting in this seam was 10 places per shift undercut and sheared, with about 600 yds. of flitting, In the places which were not sheared, three shots at least were required, resulting in a 50 per cent saving in explosives.

In each of the places with shearing there was a saving of half an hour, which was the average time required to bore and blast the centre shot.

Victor coal saw

The prototype of the coal saw was first made in April 1955. The Victor coal saw is used to make a horizontal or shear cut in coal. This unit is very simple, cheap and light. It is shown in Fig. 80 and consists of

(a) Traversing tube

(b) Mounting carriage

(c) Reciprocator unit

(d) Cutter Bar

(e) Traversing gear unit

(f) 4 in dia. pilot and reamer bit with drill rod

(g) Double clamp

The traversing tube consists of a 3 in. diameter tube with rock teeth. It is supplied in variable lengths to suit different conditions. One end of the tube is usually fitted with an extension rock assembly.

The mounting carriage accommodates the reciprocator unit and a standard rotary drilling machine. The web drive chuck of the coal drilling machine is situated on the drive pin of the driving sleeve which in turn rotates the main driving socket at a speed of 410 r.p.m. To the main driving socket is incorporated a swash plate cam and on each side of the cam face there is a roller mounted on a pin and bush. The end of the main driving shaft is spined. so on rotating the cam housing the main shaft has a reciprocating action. This rotation is obtained by a spur gear lay shaft which rotates the cam housing at a speed of 236 r.p.m. The cam throw is 125 in. and for every 2.3 revs of the main shaft, the cutter bar traverses one complete axial reciprocation.

The cutter bar has a helical scroll wrapped along its entire length. The scroll contains milled slots into which are fitted 60 tungsten tipped picks with the square heads situated in the scroll. On the extreme end of the cutter bar the tungsten star cutter is screwed on to a Whitworth thread. The cutter bar rotates in a clockwise direction when observed from the machine end and care should be taken to make sure that the picks have their tungsten tips facing the direction of rotation.

The traversing gear unit is supplied with two different speeds to suit either hard or soft coal. These are so arranged as to obtain a rate of feed of 3-5 in. per minute or 5-6 in. per minute on rotating the crank handle at 50 r.p.m.

Installation

When a horizontal cut is required there are two methods of erecting the traversing tube, depending on the underground conditions.

Method No. 1

In headings up to 12 ft. wide an extension rack assembly can be fitted to the traversing tube (as shown in Fig. 80) and the tube then tightened across the heading.

Method No. 2

In places above 12 ft. wide it is advisable to do without the extension rack and mount the traversing tube between two vertical props.

Two double clamps hold the traversing tube in position on the vertical props and cutting takes place between these vertical props, which can be moved along when a cut longer than the traversing tube is required.

Erection and use of the equipment for cutting

The mounting carriage is first slid on to the traversing tube which is mounted in at a distance back from the coalface of 15 in.

A 4 in. diameter hole is then drilled to a depth of 4 ft. 6 in. with the hole centre 4 in. above the traversing tube.

The mounting carriage is then moved along the tube to a place immediately in front of the drilled hole. The cutter bar, with its 60 picks and star cutter is pushed in the hole and the reciprocator unit situated on the mounting carriage and secured in position by means of the single wing bolt fixing.

The drilling machine is next mounted on the carriage, positioned on the driving shaft of the reciprocator, and secured by the two clamps around the machine handles and tightened down by the two wing nuts. The traversing gear unit is next fitted and secured by means of the tee-bolt fixing.

Cutting can then commence by operating the drill and applying pressure to the crank handle of the traversing gear unit. An alternative method to horizontal cutting is to shear, or vertically cut, the coal by fixing the traversing tube between the roof and floor. It is advisable in this case to cut from the floor upwards to allow the cuttings to fall away from the cutter-bar during the operation.

The Victor coal saw is most popular on longwall faces in "Licensed Mines". About 40 of these machines are now in use on longwall faces to make horizontal cuts. The length of face does not exceed 40 yds., with an approximate output of 60-70 tons per shift. There is no reason, however, why longer faces should not be cut with this equipment, provided that the coal to be cut is not "woody".

The price of the machine is low compared with that of ordinary coal cutters. The approximate price of the whole unit, suitable for use in a working space of more than 12 ft. in width, is only £350.

The Siskol coal cutter

Siskol machines are manufactured for use with pneumatic and electric power. The former was introduced into the British coal mines about 1901. The machine was then known as the “Champion “. It was also, as now, mounted on a toothed segment, which can be adjusted on a column, set between roof and floor, making a horizontal or vertical cut. About this time, longwall coal cutters of the disc type were in use in these mines, and there was a need to develop new faces quickly, and to keep the stables at each end of the face in advance. The machine was ideal for these jobs, because it was cheap to buy and could be easily moved out of the stable when the longwall machine moved in.

Where seams of coal remained thick or where roof conditions were bad, the bord and pillar system developed on a large scale.

In 1924 the Siskol electric heading machine was introduced into mines in Northumberland. This machine was constantly improved until finally it became the 5 h.p. machine of today. Well balanced, easy to operate, this machine is a great favourite with small units, which need good quality coal with a minimum of capital outlay. Vertical cutting is no longer popular in British mines, so development has been directed mainly to the horizontal cutting machine. Vertical cutting machines are manufactured when required by the consumers.

The electric machine is column mounted and is flitted from place to place on a carriage bolted to the base of the column and running on the mine track. It can cut anywhere between floor and roof, the usual cut being 3¼ in. wide. In cases where it is absolutely necessary to keep the cut at floor or roof level and strictly parallel to the floor or roof, a wider cut is made with a larger diameter cutting bit so that the cut covers the width of the machine itself. Similarly wider cuts can be made at any horizon to cut out a dirt band etc. Cutting speed with the hand operated machine (type E) is approximately 1 sq. ft. per minute. This speed is increased, however, by 50 per cent or more by the addition of a hydraulically powered traverse in the newly designed (type H) electro hydraulic coal cutter (Fig. 81). Type E machines can be converted to type H without difficulty. Both types can be fitted with a flexible shaft drilling attachment for drilling shotholes.

In very thick seams the machine can work independently of the roof, being bolted by a special attachment to the floor. Maintenance of the machine is cheap and simple, the 5 h.p. motor AC. or D.C. is well above its required power for the duty.

In the compressed air machine 300-350 blows per minute are given to the cutting bit which rotates at 80-90 r.p.m. The whole machine weighs 5-6 cwts. and two men can handle it easily.

In the electric machines the cutting bit rotates at 400 r.p.m., the main action being rotary instead of percussive as in the compressed air machine.

(To be continued)

Drawings and Photographs accompanying the article