The challenge of developing roadways in steep seams is evident in Germany, Poland, Russia and China where mining of horizontal roadways in dipping seams with a sloping top is either being carried out by hand or using boom type road headers, with attendant low rates of production.

Australia, too, has its fair share of steeply dipping seams, with 16% of the country’s coal dips at or over 30 degrees and 49% dips at five or more degrees, according to a University of NSW survey.

To date, many of the world’s steeply dipping resources have not been mined because the currently available continuous miners, which are capable of high rates of production, are designed to work in flat seams where the roof can be cut parallel to the floor.

“Whilst working in Wyoming in the USA in 1980, I observed the difficulty of developing longwall gate roads on virtual strike with a cross grade of 1-in-4,” Caldon said.

“More recently, I have seen the limitations of current continuous miners in Indonesia in working underground steep seams, where it is necessary to form a roof parallel to the bedding plans of the seam whilst having a level cross grade floor. In these applications, a boom type road header was being used, which whilst it could cut the required profile, was inherently low in productivity.

“It occurred to me that if the cutting boom of the continuous miner could be swivelled transversely to the tracks and chassis of the machine to cut the desired inclination of the roof and then lowered and levelled, it could then cut down to the floor, thus cutting an inclined roof and a level floor, but with the high capacity of a drum type machine.”

To prove the concept, Caldon has developed a powered working model of a continuous miner where the head is rotated transversely by hydraulics. He said the model has demonstrated that the swivel mechanism can be installed without fouling other components and that there are adequate clearances for the machine to operate.

Whilst Caldon owns the patent for the swivel head continuous miner, a complete design and test of a full-scale prototype machine that conforms to the appropriate regulatory regimes still needs to be carried out.

“I have had preliminary discussions with some of the major mining machinery manufacturers. Whilst there has been some interest expressed, there has not been a great enthusiasm, as most of these companies currently have full order books and cannot keep up with the demand for their present marketed models,” Caldon said.

“I believe, however, that should an operator have a specific need that may be satisfied using this concept, then if this is put to various manufacturers, there will be an earnest interest as full order books occur and evaporate according to the prosperity of the industry, and when times are a little tougher the companies with innovation succeed and market share moves.”

When mining inclined seams, it is desirable for the roof to be cut parallel to the bedding plains of the strata. Caldon’s swivel head allows the inherent high rate of production of the cutting drum of a continuous miner to be achieved and the drum to be tilted transversely thus:

• Allowing the roof to be cut at the required inclination with the continuous miner standing on a floor with no cross grade.
• Enabling the horizon transitions to be cut in the floor from roadways driven on full dip to horizontally floored roadways driven on strike, and all directions in between.
• Enabling adjustments to be made to the inclination of the floor without the need to resort to packing under the continuous miner’s tracks.
• Can be fitted to new equipment or retrofitted to many existing drum type continuous miners.

The currently available drum type continuous miners have cutting heads that vary in the range of approximately 3-5m (10-18 feet). The heads can be raised and lowered but are parallel to the chassis of the continuous miner. This limits the drum type continuous miner to cutting essentially rectangular roadways, Caldon said.

The relatively large width and simple up and down motion allows large power ratings to be employed, high shearing forces to be applied and consequent high rates of production.

“The swivel head invention is designed to enable the high rates of production of the drum type continuous miner to be employed in situations where an inclined roof is required by providing a mechanism to transversely tilt the drum to cut an inclined roof with the added benefit of cutting transverse transitions in the floor grade,” he said.

The cutting drum is supported by and powered from a gear case with electric drive motors mounted on the rear of the gear case. The gear case is mounted on a substantial shaft, which is supported in bearings on a sub-frame. The supporting sub-frame is raised or lowered by hydraulic shear jacks powered from the continuous miner’s hydraulic system.

The shaft, which supports the gear case, is rotated clockwise and anti-clockwise by hydraulic rams powered by the hydraulic system of the continuous miner. This causes...click here to read on.