Over the last few years Joy has revamped its approach to drum design lead by the company’s Drum Center of Excellence in Franklin, Pennsylvania.

“We went through a thorough self-examination,” said lean manufacturing specialist Chris Wright, “during which we examined, tested and refined our processes. We determined the best practices and set up standard procedures in which the entire drum design and manufacture team has been trained and cross-trained. This enables us to provide consistently superior products and service while dramatically reducing lead-times from weeks to, in some instances, less than a week.”

A feature only Joy offers on its drums is induction hardening whereby the bit holder is hardened to a medium hardness for toughness and weldability. The bore then is selectively induction hardened to a higher hardness for wearability. This leaves the hard but brittle induction hardened area surrounded by somewhat softer but tougher steel to support it.

Among the variables affecting the final design are the physical characteristics of the material being mined. The single most influential factor is the friability, or the hardness, of the material being mined, which most typically is coal, accounting for about 95% of continuous miners and longwalls currently in operation

The presence of rock in the seam is also significant and the more rock present in the seam, the closer the spacing between the bits. This acts to reduce the cores that build up between the bit groups during the cutting process.

“With a significant presence of rock in the seam, the machine is cutting rock-coal, rock-coal, rock-coal, and the resulting hard cores cause the continuous mining machine to bounce and steer sideways. Tightening the spacing, and thus reducing the size of the cores, minimizes these effects. In addition to accommodating the amount of rock present in the seam, narrowing the bit spacing can extend the life of the bits as well,” said Mike O’Neill, Joy Mining Machinery’s senior engineer.

Where conditions allow, wider spacing offers advantages in product size, dust control, and production rate and Joy reports using spacing of up to six inches with excellent results.

According to O’Neill, bit holders probably are the single most determinant factor in the operating life of a cutting drum. “Drum life can vary from six months mining on some longwalls up to two years on continuous miners operating in pretty nice conditions,” he said.

“Because of the effort put forth in the manufacture and hardening of the sleeves and bit holders, as well as the improved drum shells on which they are mounted, Joy believes their drums are the longest-lasting drums available today. This is an important advantage for the mine operator and, we are told, they mine the seam more efficiently as well.”

Continuous miners are typically supplied with OEM drums and have a certain commonality of design.

“However, when conditions and circumstances dictate, we have and will design a single cutting head for a single machine in a single application. We do whatever it takes to maximize the cutting ability of our machines,” O’Neill said.

Once a design has been established for certain parameters, most of the changes made in a continuous miner drum are of the fine-tuning variety.

On Friday Joy outlines some of the challenges related to shearer drum design.