Innovations MECHANICAL TUNNELLING

The Northern Miner Magazine interviewed representatives of each of these companies at the recent International Congress on Progress and Innovation in Tunnelling, held in Toronto in September. That meeting was sponsored by the Tunnelling Association of Canada, the National Research Council of Canada and the International Tunnelling Association. It was attended by more than 550 delegates and featured more than 60 display booths. CUB Joint Venture

Two Canadian mining companies, Falconbridge Ltd. and Placer Dome, are working jointly, along with mining contractor J.S. Redpath of North Bay, Ont. and U.S.-based Boretec of Solon, Ohio, to design and manufacture a short, powerful (405 KW) TBM. It will be built to drive small-diameter (2.4-m) exploration drifts in underground hardrock mines at rates of about 12 m per day. The idea is to drive access drifts for underground diamond drilling in exploration areas at depth (where diamond drilling from surface would be prohibitively expensive).

The project, which has been dubbed cub (Compact Underground Borer), has received substantial financial support from the federal government ($987,000). Falconbridge is acting as project manager. Thomas Pugsley, director of mining engineering research for Falconbridge, says the machine will be put to the test driving a 1.5-km-long exploration drift through hard norites (with a uniaxial compressive strength of up to 360 MPA) at the Fraser mine in Sudbury this month (November). J.S. Redpath will be the operator of the machine under contract to Falconbridge. Once the design concept is proven for hard rock applications, 50 CUB machines are to be built.

The components of the machine were to be assembled under a sub- contract agreement in the shops of Howden Canada in Scarborough, Ont., in October. The project is about eight months behind schedule. Boretec, which is run by former Robbins employees, has engineered the machine and is supplying the disc-cutters. Most of the other machine components are being manufactured in Canada. Boretec redesigned its disc- cutters by reducing their width. This was necessary to fit more of the 46-cm-diameter cutters on the small- diameter cutter head, Project Engineer Dennis Ofiara of Boretec explained. Twenty disc-cutters are needed to give an average spacing of about 6.8 cm between kerfs (the circular cuts on the face of the excavation made by each cutter as the cutting head rotates). This minimum spacing prevents large blocks of broken ground from getting jammed in the muck buckets. Boretec is co nsidering looking at manufacturing disc cutters in Canada.

The largest operating cost items for a TBM in hardrock conditions are usually power (600 KVA electrical power) and replacement disc-cutters. Typically, disc-cutters fail through excessive wear (due to skidding and overloading) and loss of a seal which can then lead to oil loss and bearing failure. Cutters will be supplied to the job on a contract basis. That contract will be based on how many cubic metres the cutters excavate, given a certain set of ground conditions. Should the ground conditions change unexpectedly, the contract will likely be restructured.

The cutter head, manufactured in Vancouver, will be equipped with three scraper blades situated on the outer circumference of the head. These lift the broken rock into three muck buckets. As the head rotates, the muck falls into a hopper which funnels the muck on to a conveyor belt inside the CUB.

To maintain machine orientation along the drift centreline, two small stabilizer pads have been installed immediately behind the cutter head. Just enough hydraulic pressure is applied to these pads to present the machine from wandering off course. The machine is anchored in the drift by a much larger gripper pad behind the stabilizer pads. This gripper pad is equipped with hydraulic cylinders, which can exert a pressure of 1.8 MPa on the drift walls to provide enough clamping force for the cutter head to advance under pressure a distance of 0.6 m. Once the head has reached the end of the stroke length of these so-called propel cylinders, the front of the machine is locked in place by the stabilizers and the grippers are advanced 0.6 m and reset. The pressure is then reduced on the stabilizers and the head is advanced another 0.6 m. The main motors are kept running during resetting, but the cutter head is disengaged.

Behind the cutter head module are four sleds which advance with the cutter head. (The only stationary component during operation is the gripper pad.) The operator control centre and lube system is situated on the first sled (closest to the face), hydraulics on the second, transformers and control cabinet on the third and ventilation fans and storage space for spare parts on the fourth. The overhead conveyor extends behind the last sled to a stationary support roller anchored to the back, allowing four mine cars to be loaded with muck. To allow the entire unit to negotiate curves, the conveyor is equipped with side guide idlers. The joint-venture partners are considering mounting a hydraulic drill boom on the trailing sled for roof bolting as the drift advances.

One operator can control the machine, which probably will be driving on two shifts, with the third shift reserved for routine maintenance. Besides replacing disc-cutters, maintenance includes hardfacing of the scraper blades.

The CUB is being designed so that, depending on the type of roof support used in a mine, the machine may be moved, intact, from job to job within the same mine. The machine can be broken down into smaller components measuring 1.7 m by 1.7 m, an ideal size for old mines with narrow shaft access.

The biggest problem with a TBM in an operating mine is removing the muck it produces. At an advance rate of 12 m per day, that entails an awful lot of hoisting. Disc-cutter skidding at the center of the face center will likely be another problem. Because of the close cutter configuration, the face- centre cutters typically do not turn a true circle. Instead, they skid, increasing wear rates on the disc-cutters. The machine operator can only detect cutter failure by either the feel of the machine or through periodic head inspection. Another serious challenge is the main bearing of the machines. Should this fail in mid-project, it can take up to nine weeks to replace.

The 1.5-km maiden run through Sudbury norite will be interesting to watch.Ci rcle Reply Card No. b Roger Machines

Another Canadian company, Roger Machines of Val d’Or, Que., is also developing a new TBM based on the successful design of a raise-boring machine it developed two years ago. The new machine will use the rock- breaking action of a number of hydraulic in-the-hole hammers to advance the face (rather than conventional disc-cutters). This project is also being supported financially by the federal government to the tune of $985,600.

These two Canadian projects will have a tough row to hoe, however, competing on their ow
n home turf. Already, significant mining TBM technology exists in Europe and that technology is coming to North America. Several coal mines in Germany currently use small-diameter, small- turning-radius machines. Although these TBMs are used in soft-rock applications, machine specifications are similar to those of the TBMs being developed by Boretec and Roger Machines. Circle Reply Card No. b American Tunnelling

One of the leading European TBM manufacturers, Voest-Alpine of Zeltweg, Austria, which has built a total of 50 TBMs to date, has entered the North American race through a marketing and manufacturing agreement with American Augers of Wooster, Ohio. American Augers has been reconditioning TBMs for about 16 years now, says Michael Vinson, director of marketing but they have never built a machine from the ground up.

A separate division of American Augers, called American Tunneling Equipment, will build Voest-Alpine TBMs for the North American mining industry. All the machine’s components will be manufactured in the U.S., except the disc-cutters supplied by Demag, a part of Voest-Alpine.) Circle Reply Card No. b Howden Canada

The other European TBM manufacturer which has entered the North American market is Wirth of West Germany. That company was bought in November, 1988, by the Howden Group of companies based in Scotland. Howden Canada, of Scarborough, Ont., one of the Howden Group of companies, has become the manufacturing plant for Wirth TBMs in North America. Howden Canada was previously contracted by the CUB Joint Venture to assemble the CUB at its plant in Scarborough. “We’ve satisfied Boretec that we will honor our agreement with them and that there is no conflict of interest with respect to our purchase of Wirth,” says Robert Hawker of Howden Canada and project manager of the CUB. Circle Reply Card No. b Robbins Equipment

Robbins Equipment Co. of Kent, Wash., in the U.S. also manufactures TBMs suitable for use in the mining industry. This company has built a total of 158 TBMs and has considerable experience in hard rock projects worldwide. Two machines are currently operating in Norway using Robbins’ new 48-cm-diameter disc- cutters, the largest in the industry. Circle Reply Card No. b

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