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Bureau of Mines Information Circular/1986 
 
 Water-Jet-Assisted Roadheaders 
 
 By Robert J. Timko, Bradley V. Johnson, 
 and Edward D. Thimons 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
( J^JX^ JJ **» , (UjLW ^M ^J 
 
 Information Circular 9108 
 
 Water-Jet-Assisted Roadheaders 
 
 By Robert J. Timko. Bradley V. Johnson, 
 and Edward D. Thimons 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Hodel, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
Library of Congress Cataloging in Publication Data: 
 
 ■00' 
 
 Timko, Robert J 
 
 Water-jet-assisted roadheaders. 
 
 (Information circular ; 9108) 
 
 Bibliography: p. 11. 
 
 Supt. of Docs, no.: I 28.23: 9108. 
 
 1. Mining machinery. 2. Water-jet. 3. Jet cutting. I. Johnson, Bradley V. II. Thimons, Ed- 
 ward D. III. Title. IV. Title: Roadheaders. V. Series: Information circular (United States. 
 Bureau of Mines ; 9108) 
 
 TN295.U4 [TN345] 622 s [622'.24] 86-600153 
 
CONTENTS 
 
 Page 
 
 Bureau of Mines 
 Information Circular 9108 
 
 WATER- JET -ASSISTED ROADHEADERS 
 
 Abstract 1 
 
 2 
 2 
 2 
 2 
 6 
 6 
 6 
 
 By Robert J. Timko, Bradley V. Johnson, and Edward D. Thimons ° 
 
 8 
 8 
 8 
 8 
 9 
 .0 
 .1 
 
 ERRATA 
 Page 2, column 2, last line: Add "and" after "Bit wear was high," 
 Page 4, column 1, second line: Delete "and." 
 Page 9, column 2, line 2: Change to "an Mine in Sydney, NS (Canada)." 
 
 Page 10, column 1, lines 36-39 should read as follows: 
 
 3 
 
 the 200-psi conventional pressure. In cutting 235 ft of roadway, only o 
 
 5 bits had to be replaced at 3,000-psi water pressure, but 14 bits had / 
 
 to be replaced when cutting a similar length of roadway at 200-psi pressure. ^ 
 The use of 3,000-psi water did not reduce the machine specific ^ 
 
 4 
 Page 10, column 2: Delete last two lines, which are repeated on page 11. c 
 
 5 
 6 
 6 
 
 zies trom damage 7 
 
 12. Water-jet-assisted Anderson Strathclyde RH22 roadheader 7 
 
 13. Retrofitted water-jet-assisted Dosco Mk.IIA roadheader 9 
 

 UNIT OF MEASURE ABBREVIATIONS USED 
 
 IN THIS REPORT 
 
 ft 
 
 foot kW'h 
 
 kilowatt hour 
 
 gal/mln 
 
 gallon per minute ym 
 
 micrometer 
 
 h 
 
 hour pet 
 
 percent 
 
 hp 
 
 horsepower psi 
 
 pound per square inch 
 
 in 
 
 in st 
 
 short ton 
 
WATER-JET-ASSISTED ROADHEADERS 
 
 By Robert J. Timko, 1 Bradley V. Johnson, 2 and Edward D. Thimons 3 
 
 ABSTRACT 
 
 Water-jet-assisted cutting involves the use of a mechanical cutting 
 bit in combination with a high-pressure water jet directed just in front 
 of the bit tip. Such a jet can offer benefits in terms of improved cut- 
 ting, reduced dust and fines, and improved bit wear. The Bureau of 
 Mines, through a contract with the British National Coal Board, has re- 
 searched the use of water-jet-assisted cutting on roadheaders. After 
 several engineering design problems were overcome, this program led to 
 the successful underground testing of these roadheaders. Today, more 
 than 60 water-jet-assisted roadheaders are in operation around the 
 world, and numerous others are on order. This paper details the evolu- 
 tion of these machines and the benefits to be gained by their use. 
 
 Physical scientist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA, 
 2 Staff engineer, Division of Mining Technology, Bureau of Mines, Washington, DC. 
 •^Supervisory physical scientist, Pittsburgh Research Center. 
 
INTRODUCTION 
 
 Mining through high-compressive- 
 strength rock is expensive and time con- 
 suming. Two basic methods are employed: 
 drilling and blasting and mechanical cut- 
 ting. In many countries, the mechanical 
 cutting is primarily accomplished by 
 roadheaders. 
 
 Roadheaders were first developed in 
 Hungary in the 1950's and are now used 
 worldwide for mining a variety of soft- 
 to medium-strength materials. The Bureau 
 
 of Mines, through a contract with the 
 British National Coal Board (NCB) 
 (4^), 4 has conducted research to improve 
 the performance of these machines by 
 equipping them with water-jet-assisted 
 cutting capabilities. Based upon previ- 
 ous laboratory studies, it was believed 
 that this addition would result in im- 
 proved cutting, reduced bit consumption, 
 decreased dust and fines, and possibly 
 even reduced frictional sparking. 
 
 PRELIMINARY WATER-JET-ASSISTED ROADHEADER STUDIES 
 
 PROTOTYPE ROADHEADER DESIGN 
 
 The first roadheader to be modified for 
 water-jet-assisted cutting was a Dosco 
 Mk.IIA, which is a 24-st crawler-track 
 machine capable of cutting both rectan- 
 gular and arch-shaped roadways (fig. 1). 
 Its cutting capacity is normally limited 
 to rock with compressive strengths under 
 12,000 psi. This prototype was fitted 
 with a water-jet-assisted system consist- 
 ing of a high-pressure pumping system, a 
 rotary seal, and water-jet nozzles (fig. 
 2). 
 
 The pumping system was a hydraulically 
 powered intensifier (fig. 3). It con- 
 sisted of a swashplate hydraulic pump 
 driven by an electric motor that de- 
 livered pump-pressurized oil to the in- 
 tensifier. Flexible hoses carried 2,000- 
 psi oil from the pump to the intensifier. 
 The pump was mounted on a sled behind the 
 roadheader, and the intensifier was 
 mounted on the cutting boom. High-pres- 
 sure water, at a maximum flow of 12 gal/ 
 min at 10,000 psi, was carried from the 
 intensifier to the cutting head via 
 rigid steel pipe. 
 
 The cutting head, located at the end of 
 the boom, was driven by a 65-hp electric 
 motor. The boom was a turret, powered by 
 hydraulic cylinders. The large, 5.5- 
 in-diam cutting-head shaft required that 
 the rotary seal handling the high- 
 pressure water to the cutting head be 
 
 ^Underlined numbers in parentheses re- 
 fer to references at the end of this 
 report. 
 
 large. The seal (fig. 4) was a BAL U- 
 ring type seal, energized by an ellipti- 
 cal coil spring (fig. 5). The sealing 
 faces were ridged to give three sealing 
 points around the circumference 
 of the opening. The seals were made of 
 a graphite-filled Teflon fluorocarbon 
 polymer. 
 
 The standard Dosco cutting head (fig. 
 6) has bits arranged in a three-start 
 helix, with seven bits on each helix. 
 Two sumping bits are located at the very 
 front of the cutting head. The standard 
 bits and bit blocks were replaced with 
 circular-shank, forward-attack bits and 
 blocks to allow the water jet to be 
 produced parallel to the bit tip without 
 adjacent bit-block interference. Fifteen 
 synthetic sapphire, high-pressure nozzles 
 were installed, five on each helix. 
 Since there were 21 bits on the cutting 
 head, not every bit had a nozzle. The 
 nozzles were countersunk into the cutting 
 head to protect them from damage. They 
 could be selectively capped to increase 
 the water flow to the remaining nozzles. 
 The nozzle-to-bit-tip standoff distance 
 was 5 in (fig. 7). 
 
 PROTOTYPE CUTTING TRIALS 
 
 Initial cutting trials were held in 
 a limestone mine in Middleton, Derby- 
 shire (5). The compressive strength of 
 the limestone was 17,000 psi, well 
 above the normal cutting capability 
 of the Dosco Mk.IIA (fig. 8). Cutting 
 without the high-pressure water was 
 very difficult. Bit wear was high, 
 
zL~t 
 
 A 
 
 
 ^, _ 
 
 FIGURE 1.— Standard Dosco Mk.MA roadheader. 
 
 Intensifier- 
 
 r— Hydraulic 
 \ pump 
 
 Water -jet 
 nozzles- 
 
 Rotary \ 
 seal — i 
 
 ,jmi 
 
 FIGURE 2.— Prototype NCB-modified Dosco Mk.MA roadheader showing pump and intensifies 
 
High-pressure 
 water out 
 
 Intensifier piston 
 
 Nonreturn 
 valve 
 
 Water in 
 
 High-pressure oil 
 
 Oil reservoir 
 
 -Hydraulic pump 
 FIGURE 3.— Pumping sytem showing location of intensifier. 
 
 -Pressure cylinder 
 SeaK \ ^Seal 
 
 FIGURE 4.— Cutting-head shaft showing location of rotary 
 seals. 
 
 Graphite-carbon-glass- fiber - 
 filled Teflon body 
 
 Polyamide 
 
 anti-extrusion' 
 
 ring 
 
 FIGURE 5.— Rotary seal schematic showing coil spring. 
 
 boom instability and bounce were prob- 
 lems. The addition of and 8,000- to 
 10,000 psi water-jet assist resulted in 
 significant improvements. Bit wear, 
 while still heavy, was greatly improved, 
 and ma-chine vibration was visibly re- 
 duced. The overall cutting rate was 
 
 FIGURE 6.— Standard Dosco cutting head. 
 
 approximately doubled, probably owing to 
 proved bit wear. 
 
 For further testing, an artificial 
 sandstone heading was constructed from 
 eight 3-ft sandstone cubes laid two-high 
 and cemented together with shotcrete 
 (fig. 9). The compressive strength of 
 
the sandstone was 6,500 psi. The sand- 
 stone was cut with and without water-jet 
 assistance. Water-jet pressures between 
 
 FIGURE 7.— Prototype NCB-modified water-jet-assisted 
 Dosco cutting head. 
 
 6,000 and 10,000 psi were used. Flow 
 rates were varied from 0.9 to 3.6 
 gal/min. No reductions in machine spec- 
 ific energy^ resulted due to the water- 
 jet assist, probably because of the soft- 
 ness of the rock. However, the 
 high-pressure water did visibly eliminate 
 frictional sparking and reduce dust. 
 
 Throughout this testing, the inten- 
 sifier system worked without problems, as 
 did the high-pressure jet nozzles, 
 although occasional unplugging of jet 
 nozzles was needed. No water leakage oc- 
 curred at either the nozzle-cutting head 
 interface and or the cutting head-drive 
 shaft interface. The only major mechan- 
 ical problem involved the life of the 
 rotary seal, which varied during the 
 testing from a minimum of 3 h to a max- 
 imum of 19 h. Because the seal is located 
 in the cutting boom, each seal change 
 caused considerable downtime. To deal 
 with this problem, the NCB rede- 
 signed the seal to reduce its size. A 
 cartridge assembly was developed that 
 incorporated a small-diameter, readily 
 accessible, easy-to-change BAL seal with 
 a graphite-carbon-glass fiber-filled Tef- 
 lon body. To install the seal in the 
 boom, a layshaft gearbox was placed into 
 
 -"Machine specific energy is the energy 
 consumed by the machine without consider- 
 ing the energy required to supply the 
 high-pressure water. 
 
 FIGURE 8.— Dosco Mk.HA roadheader preparing to cut Middleton limestone using water-jet assist. 
 
3-ff-cube 
 sandstone blocks (8) 
 
 Rock 
 pillar 
 
 Gap between blocks 
 
 and rock face 
 filled with shotcrete 
 
 FIGURE 9.— Schematic diagram of artificial sandstone 
 heading. 
 
 Layshaft gearbo 
 Cutting-head shaft 
 -Cutting-head 
 
 Epicyclic gearbox 
 
 Water passage 
 
 Smail-diameter rotary seal 
 
 FIGURE 10.— Section through layshaft gearbox showing 
 location of U-ring seal. 
 
 the boom in front of the cutting-head 
 shaft (fig. 10). Laboratory tests with 
 
 this new seal showed that a seal 
 over 900 h could be expected. 
 
 life of 
 
 PREPRODUCTION WATER-JET-ASSISTED ROADHEADER RESEARCH 
 
 Following the prototype research de- 
 scribed above, roadheaders were retro- 
 fitted with water-jet-assist capabilities 
 by NCB and by two machine manufacturers, 
 Dosco and Anderson Strathclyde. Each 
 machine was evaluated separately in 
 underground trials. 
 
 NATIONAL COAL BOARD MODIFIED DOSCO 
 ROADHEADER 
 
 Description 
 
 The NCB made several modifications to 
 its prototype Dosco Mk.IIA roadheader. 
 The oil-water intensifier, which provided 
 a maximum flow rate of 12 gal/min at 
 10,000 psi, was powered by a swashplate 
 hydraulic pump mounted on the rear of the 
 machine. A valve assembly allowed the 
 operator to select 10,000-psi water for 
 harder strata or 2,000-psi water in soft- 
 er rock for dust suppression only. The 
 layshaft gearbox was installed in the 
 boom. Water was plumbed from the 
 intensifier, through the rotary seal, to 
 the cutting head. 
 
 Tungsten carbide water-jet nozzles 
 were installed on the cutting head; but 
 unlike those on the prototype roadheader, 
 these nozzles were raised above the 
 cutting-head body to reduce the standoff 
 
 distance from nozzle to bit tip to 3.5 
 in, creating a more concentrated water 
 jet. To protect the nozzles from damage, 
 they were surrounded by steel shrouds 
 (fig. 11). Supply water was filtered to 
 40 ym. 
 
 The water-jet system was interlocked 
 with the roadheader's electric and hy- 
 draulic systems. In this way, the high- 
 pressure water could only be turned on 
 when the cutting head was running. 
 
 Cutting Trials 
 
 In the underground test, this machine 
 cut a 240-ft-long entry in sandstone hav- 
 ing a compressive strength of 13,000 psi. 
 At 10,000-psi water pressure, bit life 
 was doubled compared with that achieved 
 using conventional cutting at lower water 
 pressure. Significant dust reductions 
 were seen up to about 3,000-psi water 
 pressure with no additional improvement 
 above that pressure. No frictional 
 sparking was observed when the high- 
 pressure water was on, but did occur when 
 it was off. Unfortunately, no machine 
 specific energy measurements were made 
 
 O). 
 
 Because the boom-mounted intensifier 
 obstructed the operator's vision, it was 
 remounted on the roadheader mainframe 
 
with a shrouded flexible hose carrying 
 water to the boom. The intensifier 
 worked flawlessly. Contamination pro- 
 blems did occur in the hydraulic power 
 pack that drove the intensifier, but 
 
 regular flushing and filter changes rec- 
 tified them. Debris in the water supply, 
 even with the 40 ym filtration, caused 
 repeated nozzle plugging, but the nozzles 
 could be quickly cleaned with a twist 
 drill bit. 
 
 FIGURE 11.— NCB-modified Dosco cutting head showing 
 steel shrouds used to protect nozzles from damage. 
 
 MODIFIED ANDERSON STRATHCLYDE ROADHEADER 
 
 Description 
 
 The Anderson Strathclyde RH22 is a 
 medium-weight crawler-track machine that 
 weighs 37 st and is usually limited to 
 cutting rock with compressive strengths 
 less than 14,000 psi (fig. 12). This 
 machine was modified for water-jet assist 
 by installing a triplex pump and header 
 tank on the rear of the machine, behind 
 the operator seat. Maximum water- 
 pressure capability was 14,500 psi, but 
 the pressure was limited by a relief 
 valve to a maximum of 10,000 psi for safe 
 operation. Water flow and output pres- 
 sure could be varied from 4.7 5 gal/min at 
 580 psi to 19.8 gal/min at 10,000 psi by 
 
 Triplex 
 pump 
 
 Header 
 tank-. 
 
 FIGURE 12.— Water-jet-assisted Anderson Strathclyde RH22 roadheader. 
 
maneuvering a single joystick located at 
 the operator position. 
 
 The RH22 boom contained an axial water 
 passage with a small-diameter rotary seal 
 at the motor end. Because the boom tele- 
 scopes, a sliding seal was built into the 
 water passage on the cutting-head end. 
 High-pressure water was fed to the cut- 
 ting head through a flexible hose, which 
 was shrouded for safety by a second, 
 larger diameter flexible hose. The cut- 
 ting head was a standard RH22 cutting 
 head with tungsten carbide high-pressure 
 nozzles installed in front of each of the 
 24 bits. 
 
 Cutting Trials 
 
 This RH22 water-jet-assisted roadheader 
 was tested in the Sutton Manor Colliery, 
 where it was used to drive a 1,150-ft 
 entry in rock of compressive strength up 
 to 24,000 psi. Operating at 10,000 psi, 
 water-jet assist resulted in a 50-pct in- 
 crease in advance rate over normal oper- 
 ation at 100 psi (_]_)• There was a de- 
 crease in machine specific energy of 
 about 30 pet, although the total specific 
 energy^ actually increased when the pump- 
 ing energy was considered. A respirable 
 dust reduction of 70 pet occurred as the 
 water pressure was raised from 100 psi to 
 3,000 psi. Additional increases in water 
 pressure had no effect on dust levels. 
 Machine vibration was visually reduced, 
 and no frictional sparking was evident 
 when the high-pressure water was used. 
 Significant reductions in bit wear oc- 
 cured. At 10,000 psi, bit wear was as 
 low as 0.20 bit/ft of advance as compared 
 to normal bit wear of 0.83 bit/ft of ad- 
 vance. The greatly improved bit wear may 
 have been responsible for much of the in- 
 crease in advance rate. 
 
 A bit longevity experiment was per- 
 formed by plugging one of the front jet 
 nozzles. In cutting an advance of ap- 
 proximately 3 ft, the bit that received 
 no water owing to the closed nozzle had 
 to be replaced three times, while only 
 one other bit on the entire cutting head 
 had to be replaced. 
 
 "Total specific energy is energy re- 
 quired to supply high-pressure water plus 
 the machine specific energy. 
 
 Overall, this machine performed well 
 during the cutting trials. A few prob- 
 lems did occur. The sliding seal on the 
 telescoping boom failed and had to be re- 
 designed in order to improve its durabil- 
 ity. Additionally, nozzles frequently 
 became plugged owing to impurities in the 
 water supply, but these orifices were 
 easily cleaned with twist drills having 
 the same diameter. 
 
 RETROFITTED DOSCO ROADHEADER 
 
 Description 
 
 Dosco retrofitted an Mk.IIA roadheader 
 with a water-jet-assist system similar to 
 that used on the NCB prototype, except 
 that the water pump was installed on the 
 roadheader frame (fig. 13). Dosco used 
 the NCB-developed layshaft gearbox with 
 its small-diameter seal. The high- 
 pressure water was delivered to the cut- 
 ting head via rigid steel pipe with hori- 
 zontal and vertical articulating joints 
 to accommodate movement of the boom. 
 Synthetic sapphire, water-jet nozzles 
 were supplied in front of the bits on the 
 standard Mk.IIA hardrock cutting head 
 (2). 
 
 Cutting Trials 
 
 This machine was tested in the Bentinck 
 Colliery where the strata ranged from 
 soft mudstones to hard laminated sand- 
 stones, having compressive strengths ap- 
 proaching 20,000 psi. It was used to en- 
 large an existing roadway. Floor water 
 problems resulted in the high-pressure 
 water being used only intermittently, and 
 conclusive data on its performance were 
 not obtained. 
 
 Several mechanical problems with the 
 rotary seal did develop. Owing to metal- 
 lic contamination of the water supply, 
 the rotary seal eroded and failed after 
 very short periods of use. This problem 
 was overcome by using impoved hydraulic 
 components. Additionally, the high 
 cyclic loading generated by the eight- 
 cylinder pump and the rigid steel pipe 
 caused another failure of the rotary 
 seal. This problem was solved by re- 
 placing the eight cylinder pump with 
 
Water-jet -assiste 
 cutting head- 
 
 Hydraulic 
 pump 
 
 FIGURE 13.— Retrofitted water-jet-assisted Dosco Mk.llA roadheader 
 
 a four-cylinder version and substituting 
 flexible hose for the steel pipe (6). 
 With these modifications, the rotary seal 
 
 was able to operate for approximately 
 900 h before breakdown. 
 
 CURRENT WATER-JET-ASSISTED ROADHEADER STATUS 
 
 Both Anderson Strathclyde and Dosco now 
 commercially market water-jet-assisted 
 roadheaders. More than 60 of these ma- 
 chines are operating around the world, 
 and many more are on order. They are 
 available in a variety of machine weights 
 and have water-jet-assist capabilities 
 ranging from 2,000 to 10,000 psi. In ad- 
 dition, Dosco offers a water-jet-assist 
 retrofit system for roadheaders that al- 
 ready have a water lance through the 
 boom. The average price of the retrofit 
 system is about $75,000. 
 
 Currently, three Dosco Mk.IIB and two 
 Anderson Strathclyde RH22 water-jet-as- 
 sisted roadheaders are in operation at 
 
 the Cape Breton Development Corp. 's Phel- 
 an Sydney, NS (Canada). These roadhead- 
 ers are cutting five parallel develop- 
 ment drifts on a 16° slope. Some mech- 
 anical problems, such as leaking seals 
 and plugged water-jet sprays, have occur- 
 red but overall performance has been 
 good and the mine has ordered two more 
 water-jet-assisted machines. These will 
 be low-profile Dosco L-1300 roadheaders 
 with 3,000-psi water-jet capability. 
 Dust measurements made by the Canada 
 Centre for Mineral and Energy Technology 
 (CANMET) on the roadheaders at this mine 
 showed dust reductions as much as 80 pet 
 greater than conventional spray systems 
 
10 
 
 with 3,000-psi water pressure; no further 
 reductions occurred as the pressure was 
 increased above this level. At 10,000 
 psi, there was no increase in cutting ad- 
 vance rate when cutting rock or coal. 
 
 Both Dosco and Anderson Strathclyde now 
 feel that for many mining operations, es- 
 pecially in softer materials, water pres- 
 sures well below 10,000 psi will be 
 sufficient to gain the benefits of 
 water-jet-assisted cutting in terms of 
 dust reductions, bit wear improvements, 
 f rictional-sparking reductions, and de- 
 creased fines. Lower pressure machines 
 will also entail fewer engineering design 
 problems, cost less, and be safer and 
 more economical to operate. 
 
 Dosco recntly supplied a medium- 
 pressure water-jet-assisted Mk.IIB road- 
 header to the Beringen Mine in Belgium. 
 This machine was specially designed to 
 deliver a maximum water-jet-assist pres- 
 sure of 3,000 psi. In place of the large 
 electric motor and pump required for 
 10,000-psi operation, this machine em- 
 ploys a compact three-cylinder positive- 
 displacement hydraulic pump capable of 
 supplying 10.5 gal/min at 3,000 psi. The 
 water is delivered to 20 of the 24 cut- 
 ting bits. For approximately 6 months, 
 this roadheader has been cutting coal 
 having banded rock intrusions with com- 
 pressive strengths of 14,000 psi. At 
 3,000-psi water pressure, respirable dust 
 was reduced by 75 pet from its level at 
 the 200-psi conventinal pressure. In 
 cutting 235 ft of roadway, only 5 bits 
 had to be replaced at 3,000-psi water 
 did not reduce the machine specific 
 
 energy, indicating that no cutting-force 
 reductions occurred. In fact, there was 
 a slight increase in total specific en- 
 ergy due to the energy required to supply 
 the 3,000-psi water. 
 
 An Anderson Strathclyde RH22 roadheader 
 with 5,000-psi water-jet assist has been 
 successfully operating at the Kellingly 
 Colliery in North Yorkshire. Cutting 
 dry, an average of 60 bits per day had to 
 be replaced, but at 5,000 psi, the aver- 
 age was only 24. Although no dust mea- 
 surements have been made, there was 
 a significant visual reduction in dust 
 when the 3,000-psi water was used. 
 
 Currently, research is being done by 
 NCB and by Bergbau Forschung of the 
 Federal Republic of Germany to determine 
 the effect of higher water-jet-assisted 
 cutting pressures (20,000 psi and above) 
 on roadheaders. While major reductions 
 in dust and bit wear can be achieved at 
 lower pressures, it is believed that much 
 higher pressures are needed to have a 
 significant impact on cutting forces. 
 The West Germans have demonstrated that, 
 as the water pressure on a roadheader was 
 raised from to 21,000 psi, the machine 
 energy consumption fell from 130 to 85 
 kW*h. However, the total energy consumed 
 increased from 130 to 310 kW*h. Thus, 
 the cost of operating at these higher 
 pressures is significant. The West 
 Germans are willing to accept this if 
 it makes it possible for them to effec- 
 tively cut the high-compressive-strength 
 rock they encounter in their mining 
 operations. 
 
 SUMMARY 
 
 Testing of water-jet-assisted road- 
 headers has shown that significant respi- 
 rable dust reductions occur at pressures 
 approaching 3,000 psi. Raising the water 
 pressure above that level has no effect 
 on dust reduction. Improved bit wear and 
 reduced frictional sparking also result, 
 but the optimum water pressures to ob- 
 tain these benefits are not as clearly 
 defined. 
 
 A reduction in machine specific energy 
 (improved cutting) was also seen in the 
 cutting of harder materials, but was not 
 
 evident in the cutting of lower- 
 compressive-strength materials such as 
 coal and soft rocks. However, the total 
 specific energy always increased owing to 
 the energy required to supply the high- 
 pressure water to the nozzles. 
 
 More than 60 water-jet-assisted road- 
 headers are in operation worldwide, and 
 several others are on order. These have 
 water-jet pressure capabilities ranging 
 from 2,000 to 10,000 psi. Currently, 
 European researchers are concentrating 
 their efforts on studying the effects of 
 
11 
 
 European researchers are concentrating 
 their efforts on studying the effects 
 of water-jet assist on high-compressive- 
 
 strength materials by using 
 pressures of 20,000 psi and abave. 
 
 water 
 
 REFERENCES 
 
 1. Clark, R. A. Success for Anderson 
 Strathclyde High-Pressure-Water Road- 
 header. Colliery Guardian, July/Aug. 
 1984, pp. 255-256. 
 
 2. Colliery Guardian. Dosco "Experi- 
 ence of High Pressure Water Assisted Cut- 
 ting Trials at Bentinck Colliery." July/ 
 Aug. 1984, pp. 258-259. 
 
 3. Erhart, P. P. Water-Jet-Assisted 
 Cutting Nears Commercialization. Coal 
 Min. , v. 21, No. 12, 1984, pp. 55-59. 
 
 4. Mining Research and Development Es- 
 tablishment, National Coal Board, Tun- 
 nelling and Transport Branch. Water Jet 
 Assisted Roadheader. Ongoing BuMines 
 contract J0133929; for inf., contact R. 
 
 J. Timko, TPO, Pittsburgh Research 
 Center, BuMines, Pittsburgh, PA. 
 
 5. Plumpton, N. A., and M. G. Tomlin. 
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 Roadheader. Paper in 6th International 
 Symposium on Jet Cutting Technology 
 (Univ. Surrey, United Kingdom, Apr. 6-8, 
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 6. Straughan, J. High Pressure Water 
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