BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to an article for improving the efficiency of operation of carbide-tipped cutting bits utilized in rotary machines adapted for pulverizing concrete and asphalt roadways and similar surfaces. More particularly, the invention relates to articles for improving the cutting action of rotatable carbide bits, and for protecting the support blocks in which the bits are mounted.
In the prior art, cutting bits are mounted to be rotatable about the central axis of the cutting bit mounted in a support block. The rotation of the cutting bit provides for uniform wear of the cutting bit improving the effective life of the cutting tool. The rotatable cutting bits have a flange bottom face that bears against the top face of the support block.
During the operation of prior art cutting bits, the support block experienced wear due to the contact between the cutting bit and the support block, as well as the impingement of the debris from the cutting operation. While the cutting bit was replaced on a periodic basis after the expiration of the useful life thereof, the support block was typically intended to be functional much longer than the cutting bit. As the bore and front face of the support block became worn, the support block lost its effectiveness due to deformation and wear of the bore and the front face thereof. In the case of the bore, it lost its initial cylindrical shape by becoming out-of-round, oversized or bell-mouthed at its opening. In the case of the front face of the support block, it lost its flatness. Each one of these conditions impeded the satisfactory rotation of the cutting bit in the support block.
Although providing the capability for free rotation of the cutting-bit results in more uniform wear and extended life of the bit, wear of the bit support block continues to be a problem. The flat, upper transverse face of the bit support block is continuously impacted with abrasive materials during the operation of the rotary drum pulverizers or wheel machines. Also, if a bit wears down to the extent that it extends only a short distance out from the face of its support block, more rapid and destructive wear of the support block occurs. Excessively worn bit-support blocks must be removed from the pulverizer drum or wheel with a cutting torch, and a new support block welded onto the drum or wheel. This replacement process is time consuming, and therefore, costly. Furthermore, it frequently happens that replacement of support blocks under field conditions results in a misalignment of the bore axis of the holding support block from its optimum orientation, decreasing the effectiveness of machine operation.
Efforts have been made in the industry to alleviate the wear problems discussed above. In the prior art, bearing washers, such as U.S. Pat. No. 4,818,027, are comprised essentially of a flat, hardened steel annular ring or washer which is adapted to fitting between the enlarged base of a cylindrical cutting bit, and the transverse outer face of the holding block which rotatably supports the bit. In addition to absorbing wear, which would otherwise be experienced by the bit holding block, this bearing washer provided other advantages. One advantage is the reduction of cutting bit friction; the bearing washer was free to rotate allowing the cutting bit to rotate more freely. This results in cooler operation and more even wear of the cutting bit, substantially extending its life.
Although providing the capability for free rotation of the cutting bit results in more uniform wear and extended life of the bit, wear of the bit holding block in prior art continued to be a problem. The flat, upper face of the bit holding block is continuously impacted with abrasive materials during the operation of the rotary pulverizers. Wear in such prior art designs also occurred on account of relative rotation between the bearing washer and face of the holding block. It should be noted that the rate of wear to the holding block due to the bearing washer was much less than the rate of wear caused by a rotating cutting bit without a bearing washer. Wear of the bit holding block requires that the worn blocks be removed from the pulverizer drum with a cutting torch, and a new block welded onto the drum. This is a time consuming, and therefore, costly operation. Furthermore, it frequently happens that replacement of holding blocks under field conditions results in a misalignment of the bore axis of the mounting block from its optimum orientation.
Other efforts have been made to reduce the undesirable wear that occurred on the top face of the support block. U.S. Pat. No. 5,931,542, to Britzke et al., discloses a method of protecting the front face of a cutter bit holder block. Britzke '542 illustrates a thrust-bearing washer at 50. The washer is keyed with sleeve 42 so as to be fixed in position. Accordingly no wear occurs between the washer and top face of the bit holder block. The cutting bit on this prior art design did not rotate as freely as cutting bits having bearing washers that were also free to rotate as discussed above.
The Ojanen U.S. Pat. No. 5,251,964 discloses an attempt in the prior art to protect the face of a block wherein a plurality of carbide inserts are brazed to the face of the block to limit the rate of wear to the front face of the block. This design was ineffective because the cutter bits are made from hardened steel in order to limit wear to the tool during use. The bottom face of the cutter bit shoulder in contact with the top face of the support block is made from such hardened steel. The contact of prior art cutter bit hardened steel against the top face of the support block shaved and fractured the plurality of carbide inserts.
It would, therefore, be very advantageous to provide a cutting bit, which, during operation, protects the bore of the bit holder, as well as the front face of the support block, from deformation. By providing this protection, a cutting bit would help prolong the useful life of the support block, as well as, help the rotation of the cutting bit.
OBJECTS OF THE INVENTION
An object of the present invention is to provide an efficient means for protecting holding support blocks, of the type used to hold rotating cutting bits used in a pulverizer and rotary drum or wheel machines, from excessive abrasion and impact damage.
Another object of the invention is to provide a cutter block assembly which has both great hardness for providing high abrasion resistance and high impact strength to limit damage to a support mounting block.
Another object of the invention is to provide a combination of elements for cutter bit holding block assemblies which is free to rotate with respect to the shank of the cutting bit providing uniform wear of the cutting bits.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
In one embodiment the hardfacing material is a composition of nickel metal, iron-nickel and has a Rockwell Hardness “C” value of between 57-63. A suitable powder for hardfacing the support block of the present invention has a particle size of 32 microns and a percent weight composition as follows: Silicon: 0.75%-5.0%, Chromium: 8.0%-15%, Iron: 2.0%-5.0%, Nickel: 68%-78%, Carbon: 0.0%-1.5%, and Boron: 1.00%-5.00% %. In one embodiment the hardfacing composition is about 75.7% Nickel, about 3.8% Iron, about 3.6 % Silicon, about 2.35% Boron, about 10.8% Chromium, and the remainder a variety of impurities. Another contemplated powder composition is 78% Nickel, 11.7 % Chromium, 4.1% Iron, 0.9% silicon and 0.5% tungsten.