The original shearers, or cutter-loaders as they were known, were rope hauled with the haulage being mounted at the end of the longwall face. As haulage powers increased to match the higher production requirements, the haulage drive was moved on-board the shearer and the rope replaced with a chain.
With further increases in haulage power the chain size grew to 22mm, however, the presence of a highly tensioned chain along the length of the face created a serious safety issue. Chain breakages and violent movements of the chain caused many serious and even fatal accidents. It had to go!
During the 1970s the development of chainless haulage systems was started. Two famous systems were patented, Dynatrac by Halbach & Braun and Eicotrack by Eickhoff. However, there were many more systems that failed the test of time, with fanciful names such as Pinwheel, Rackatrack, Multirack, Supertrac, Rollrack, Miikitrac, Peratrak and Startrack. All the systems eventually evolved into two generic types: rack systems and captivated chain systems based on the original concepts of the original Eicotrack and Dynatrac systems. As the power of the shearers continued to increase the haulage systems were upgraded to improve their strength, life and reliability.
Manufacturing materials were improved to give better yield strength and wear resistant properties; the tooth profile was changed from a simple round pin or chain to an involute form and the construction was changed from simple fabrications to more robust methods of construction.
Suppliers of shearers and AFC equipment all offer rack or captivated chain systems to work with the current range of shearers. In most of the commonly used rack systems the racks are nominally half the linepan length, with one rack mounted in the middle of the panline and a second straddling each pan joint. A horizontal slot in the rackholder allows movement of the rack relative to the pan minimising the variation in pitch between each rackbar as the panline articulates.
The original Eicotrack welded round pin arrangement has developed into a fully cast steel rack with “near involute” shaped teeth at 126mm pitch with crowned bearing faces. The system is used widely around the world; Australian installations include Tahmoor, Ulan and Capcoal Central.
The Longwall Associates Super GearRack is offered in 126mm and 147mm pitch versions and comprises a fabricated rack with 450HB sideplates, and forged and hardened (52/56Rc) involute profile pins. The rack is retained with a headed pin and gravity plate for simple installation and removal. There have been five systems supplied into the USA market over the past three years and a system supplied to Capcoal Southern in late 1999.
Joy Mining Machinery’s Ultratrac 1500/2000 rack is a single-piece forged-steel unit incorporating involute profile teeth made from 42CrMo4 steel. The teeth are induction hardened and tempered to 55/60Rc. There have been more than 20 sets supplied to USA and China and installations are in operation at Moranbah North and Cumnock in Australia
Deutsche Bergbau Technik’s Jumbotrac is very similar to SuperGeartrac, a fabricated rack with Hardox 400 side plates and forged involute pins. There are two systems operating in USA at Consol Blacksville and Consol Mine 84.
The Long-Airdox Ultrahaul is a fabricated rack system employing XAR400 sideplates and 42CrMo4 forged pins.
A captivated chain system features a continuous chain that runs the full length of the face and is captivated within a casting that also acts as the captivation for the shearer shoe. The vertical link of the chain, which is usually forged, is profiled to act as a flexible rack.
DBT’s Rhinoride is the leading chain-based shearer haulage system on the market. It employs 38/42mm chain with forged involute shaped vertical links. This heavy duty system has given good service at top performing mines such as Twentymile and South Bulga.
Both H&B in Germany and Britain’s RMI supply a Dynatrac style system. The (Joy) Mecolink captivated chain-based system with an unusual forged link arrangement is operating at Springvale and Angus Place. It is no longer offered by Joy.
Both the rack and chain system types work well in normal conditions, however, in extreme conditions the strengths and weaknesses of each type become more evident. Following is a summary of the advantages and disadvantages of each type of system:
* Rack advantages — Broken or worn racks are easily replaced. The haulage system provides solid traction for the shearer in hard cutting conditions and wrap-around trapping gives a positive captivation for the shearer shoe. Each rack only sees half the total shearer traction force.
* Chain advantages — The chain system accepts greater panline articulation and maintains constant pitch in all conditions. It is “elastic”: it absorbs shock loads, protecting shearer traction and cutting elements. The chain can be turned through 180 degrees, which doubles its life.
* Rack disadvantages — It offers no cushion to shearer traction and during face transfer a pin has to be removed and replaced on each pan. The pitch varies when the panline is articulated.
* Chain disadvantages — Breakages are difficult to repair and repair links are a point of weakness. Special handling is needed for a single length of chain on face transfers. With high-powered shearers a dynamic chain tensioning system is necessary, and the hook captivation is liable to wear in downhill applications.
When selecting a new shearer haulage system consider the following points:
* Hardness of cutting (tractive effort required) — A chain will be kinder to the shearer in tough cutting conditions, but a breakage will be more likely and more difficult to fix. A rack system will provide a more solid reaction for the shearer, eliminating surging.
* Undulations along the face — Chain systems can have advantages in undulating conditions, since perfect pitch is maintained at all times. (Some rack systems have been proven to work successfully at up to 6 degrees pan articulation).
* Dip of the face — Wrap-around captivation is better in steep downhill applications.
* Direct or indirect traction — Direct drive systems, where the final drive sprocket is itself driven by the primary drive gear, has a lower life than an indirect drive system where the final drive sprocket is a compound gear arrangement. However, indirect drives are wider and will increase the roof support tip-to-face distance.
* The total cost of ownership should be investigated — This includes analysis of the life, cost and availability of sprockets and shoes in addition to the haulage elements. Ensure the haulage system supplier clearly specifies the operating parameters of the system and that the shearer manufacturer agrees to accept them.
Learn from other operators experienced in similar mining conditions. Select the best shearer haulage system for you by carefully considering both the application and the shearer to be employed. Getting it wrong and having to change systems can be very expensive. If in doubt ask a longwall consultant for some independent advice.
* Mark Kingshott is director of KIT Longwall Consulting.
Originally published in the March 2001 edition of Australia's Longwalls.