The present invention relates to mining and construction cutting bits and holders, the holders being attached to a rotating cutting drum. The holder includes a replaceable wear sleeve that receives the cutting bit tool.
Cutting tools are subjected to large torques and loads. The cutting bits generally need to be replaced daily. Since the cutting tools require routine maintenance there is a preference and need in the industry to construct a cutting tool assembly that is easily and quickly replaceable in the field.
The holders are often designed to permit the cutting tool to rotate to avoid uneven wear of the bit tool holder and cutting bit. This rotation of the bit causes the holding surface of the bit holder to wear at an accelerated rate. The bit holders become unusable after they wear causing the cutting bit to stop rotating or to fall out of the bit holder. The bit holders take a significant amount of time to replace, typically either by blow torching off the old bit holder and welding a new bit holder onto a rotatable drum, or by mechanically removing the old bit holder mechanically fixing on a new bit holder.
To extend the life of bit holders in the prior art a replaceable wear sleeve is inserted into the bit holder. The sleeve limits the internal wear to which the bit holder is subjected by the cutting bit tool. Eventually these wear sleeves fail and must also be replaced. Prior art wear sleeves are provided with an upstream shoulder that surrounds the aperture of the bit holder to resist the axial forces and loads that would otherwise be directly absorbed by the exposed top face of the bit holder during operation of the cutting tool to prevent wear of the bit holder. Nonrotating wear sleeves tend to wear unevenly on upstream shoulder of the protective sleeve.
In U.S. Pat. No. 5,088,797 to O'Neill, a replaceable wear sleeve for bit holders is disclosed. The wear sleeve is fixed to the tool holder by interference fit. The interference fit is designed so as to permit the sleeve to be removable in the field. Such interference fit designs require precise manufacturing tools for cutting out the outside diameter of the wear sleeve and precision honing equipment for constructing the sleeve holder bore in the bit holder. The holding and cutting equipment for such precision is costly and the manufacturing steps time consuming. Slight deviations in the outside diameter of the sleeve and diameter of the bit holder bore affects the amount of interference and results in large variations in the amount of manual force necessary to remove the wear sleeve from the bit holder.
In the prior art designs such as in U.S. Pat. No. 4,542,943 wear occurs between a replaceable bit holder and a support block that is welded onto a drum. The contacting joint surfaces between the bit holder and support block in this prior art wears during the lifetime of the assembly on account of a yaw movement imposed upon the pick tool assembly during cutting operations. In some less friendly environments silica accumulates between the bit holder and support block and the wear rate between the bit holder and support block significantly increases. This continual wear between the holder and support block also requires that operators constantly tighten the fastening bolt to adequately secure the bit holder to the support block, preventing undesirable catastrophic failure caused by rocking and fretting as the bolt becomes loosened. In some severe environments the wear between the blocks and bit holders becomes so great that the support block and bit holder have to be serviced as frequently as on a monthly basis.
In Montgomery U.S. Pat. No. 4,542,943 the T-shaped shank that fits into the support block groove includes a preferential failing groove situated along the peripheral surface of the shank. Cutting tools are employed in constructing this peripheral groove about the shank. This groove is costly and time consuming to manufacture.
Applicant has invented a non-rotatable wear sleeve that will significantly reduce wear of the bit holder but can still be removed manually while the mining equipment is at its field location.