Long Wall mining is an underground mining process where a coal shearer is mounted to a series of hydraulic ceiling supports that cuts coal from the wall face in a single slice or panel. With long wall miners being around 250-400 meters wide, a fully operational long wall installation can extract up to 5000 tonnes of coal per hour and consists of hundreds of roof shields which are connected to each other with hydraulic assemblies.

These self-advancing roof shields are operating at working pressures of 350 bar, putting 81 kNm of force against the fitting of the hydraulic connection. Additionally with hoses and fittings subjected to pressure spikes from pumping equipment, impulses from the self-advancing shields and corrosion created by coal dust, moisture and highly emulsified hydraulic fluids, the component conditions are extremely tough!

Across the globe and over the last decades numerous incidents have taken place with hydraulic hose and staplelock fittings causing injuries, even with fatal consequences. Some regrettable widely known examples are Sanborn Creek Mine – US (04.12.2000) 1 person killed, 1 person injured when staple fitting broke and hydraulic hose under pressure hit people in the walkway on the long wall. At Angus Place Colliery –Australia (26.07.2006) 1 person died when being injured by hydraulic injection from open high-pressure staple connection.

All these incidents have triggered both governmental organizations and private companies to take specifications and alerting for extreme caution when being in contact with these types of connection. The US Mine Safety and Health Administration (MSHA) published a safety bulletin back in 2007 to prevent accidents when using staple-lock couplings.

A year before the NSW Department of Primary Industries issued a similar safety alert in Australia. In 2011 the same NSW Government undertook a review of “Escape of fluid” incidents (reportable since their 2006 regulation), they noted 1186 incidents from 2007 to 2010, of which more than half occurring at the long wall face resulting from hydraulic hose or fitting failures, with 13 percent resulting in an injury or suspected injury.

Staple Lock

Mining conditions require a strong coupling, easy to understand, quick to connect and disconnect. The clip fastener fitting as described in the SAE J1467 standard – commonly known staple lock – has fulfilled these requirements for decades. The staple lock connection includes a male fitting with cylindrical seal that is pushed into a female end, a U-shaped retaining clip or staple is then inserted into the female, passing the groove in the male end to lock both ends together.

The advantages of staple lock over classical threaded connections were clear:  

• Simple and easy to understand design
• No special torque equipment is required 
• Proof of proper connection is provided by the fully inserted staple

Mines across the globe have taken staple lock on board as standard.

The first patented staple lock design goes back to 1946. As time and machinery moved on, improved staple designs became more and more needed.

With longwall equipment becoming more sophisticated and powerful and a continuous push for increase in performance, in output, and even more in safety, the mining industry is faced daily with the inherent limits of the staple lock design.

There are two major limitations:

• Even a fully inserted staple only makes contact with ¼ to 1/3 of the flange area. Increasing operating pressures on today’s longwall hydraulic systems, put more and more pressure on a limited contact, increasing the chance for staple deformation and breaking.
• Staple-lock fittings remain for months in a corrosive underground atmosphere.

The staples become corroded and deformed. They have become fused in the grooves of the fitting and are extremely difficult to remove. This can take up a lot of time and leads workers to abuse the hose and couplings, creating dangerous situations in the attempt to disconnect them.

How can we retain all the advantages of the staple-lock coupling and lock out its disadvantages?

Safe Productivity

Gates has tackled this challenge with the development of his patent pending iLok coupling. The iLok™ coupling is a threaded design. The flat, wide spaced threads resist seizing due to damage or corrosion. To connect the fitting, the nut on the male end is hand-tightened to pull the male sealing surface under the seal in the female.

As the seal pack is in the inside surface of the female fitting where it is less subject to accidental damage, while the sealing surface of the male is also protected by the swivel.

The iLok™ is quite simple to understand and to use as people are familiar with tightening a nut to make a hydraulic connection. However, unlike nuts on threaded fittings, it does not require torque to create preload and assure a good, consistent seal.

To secure the connection, a cable or other locking device is inserted into the holes in the nut trough grooves in the female and locked. The cable will not pass through the groove unless the nut is completely tightened. The cable also provides positive proof of a secure connection and keeps the nut from backing off during operation.

For disconnecting the coupling, the cable is cut and removed so the nut can be loosened by hand. The back of the swivel nut is provided with slots so a spanner wrench can be used in case an extra tool is needed to loosen the coupling.

The ease to connect and disconnect is a key element to improve both safety and productivity. iLok™ can save hundreds of man-hours on every longwall move since the average disconnect time per coupling can be reduced up to 90 percent compared to staple lock.

Should the cable lock be removed while the line is still under pressure, the nut continues to hold the fitting together, dissipating the pressure to the side of the coupling, away from the worker’s face. In contrary a staple-lock fitting can blow apart when the staple is removed from a pressurized line.

Rather than using a staple which contacts only about one fourth or one third of the flange area, the iLok™ uses a nut which contacts the entire flange surface, distributing the forces evenly, eliminating pressure points and preventing the flange from deformation. No tools are needed to engage or disengage the coupling, so workers will not be tempted to use hammers or chisels as they often do to remove staple-lock fittings.

The iLok™ coupling is also compact, roughly the diameter of a standard staple-lock coupling without the staple and significantly more compact once the staple is in place. Not having the sharp ends of the protruding staple will additionally avoid damage and abrasion of neighbouring assemblies and parts.

To further improve the lifetime of iLok™ assemblies in the highly corrosive mining environment, the couplings are plated with Gates TuffCoat™ Extreme® coating. It offers 840 hours of red rust protection under ISO 9227 salt spray conditions, which means more than 10 times better than the 72-hours requirement in given standard.

The coupling has not only been tested at 420 bar pressure for 300.000 impulse cycles as applicable in mining ratings for static applications, it is additionally also tested to 1 million impulse cycles at 133 percent of 350 bar working pressure for hydraulic application standards. The connectors can be used on original equipment as well as in replacement projects using the appropriate adapter to connect to staple lock or flange.

Real Life

Gates iLok™ is meanwhile proving its capabilities in underground mines. Some of the most important mining corporations in the US, among which, Bridger Coal (Wyoming) and Bowie Resources (Colorado), have discovered the value that this new coupling brings to their operations. After several months of on-the-job testing all connections were easily disconnected by hand and these companies have since replaced staple lock in major hydraulic hose and couplings applications on the long wall such as shield to shield connections, pan lines and monorails.

Other companies like PeabodyTwentymile Coal (Colorado) and Walter Energy (Alabama) have committed and are now preparing the conversion, and a bunch more are now in the test phase. The key drivers for these companies to change to iLok™ are the simplicity, ease of use, improved safety and time and labour savings in disconnecting and reconnecting.

Johan De Moor,

Technical Support Engineer,

Gates BVBA