Round-shank bit for a coal cutting machine

Details Round-shank bit for a coal cutting machine Round-shank bit for a coal cutting machine

1999-01-27

2001-03-13

Lillis, Eileen D. (Department: 3673)

Mining or in situ disintegration of hard material

Cutter tooth or tooth head

Rolling or rotatable bit

C299S079100, C299S113000

Reexamination Certificate

active

06199956

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a round-shank bit for a coal cutting machine or the like, having a bit head and a bit shank, wherein the bit head has a bit tip, maintained by a base element in a receptacle of the bit head, and starting at the base element, the bit tip tapers in a direction toward a free end of the bit tip, wherein the base element forms a maximum diameter of the bit tip, and the bit tip has recesses on an outer contour.
2. Description of Prior Art
A conventional round-shank bit is known from German Patent Publication DE 34 42 546 A1.
Such round-shank bits are installed in bit holders, which are fastened to a rotating body. When using the tool, the bit tips engage and penetrate the material to be removed, for example, rocks, coal, road covering and the like. The bit tip wears during this engagement. In order to obtain even wear over the entire circumference of the bit tip, the bit shank of the round-shank bit is rotatably held in a bit holder. For improving the rotational behavior of the round-shank bit known from German Patent Publication DE 34 42 546 A1, the bit tip has recesses on an outer circumference, which extend in a longitudinal direction of the round-shank bit. In this case the recesses extend from the bit tip as far as the bit head, where the recesses end continuously. Because of the cross-sectional weakening as a result of the recesses, rapid wear of the bit tip results when these conventional round-shank bits are used. The round-shank bit furthermore has a tendency for blockage when the lands formed between the recesses are worn out, but when the wear limit is not quite reached.
SUMMARY OF THE INVENTION
It is one object of this invention to create a round-shank bit of the type mentioned above, wherein a good rotational behavior over an entire length of wear is assured.
This object is attained with a base element having recesses on its outer circumference, which constitutes the maximum diameter.
With the arrangement of the recesses in accordance with this invention, the outer contour of the bit tip on a side facing the bit head has alternatingly recesses and intermediate elements located between the recesses. This results, for example, in a star-shaped or a tooth-shaped outer contour of the base element. When using the tool, the removed material is taken away in a definite manner via the recesses toward the bit head. Thus, an intentional wear of the bit head is caused, which carries the recesses on in the form of wash-outs in the bit head.
In connection with the feed movement of the tool, the removed material introduces a force component in a circumferential direction into the round-shank bit via the recesses and wash-outs. Thus, the rotating property of the round-shank bit is assured up to the wear limit. The design of the bit tip in accordance with this invention also utilizes knowledge that in a not yet worn out state the bit tip must have sufficient support on the bit head in order to be able to dependably deflect occurring transverse forces. During increasing wear, however, lesser bending stresses are transmitted via the transition between the bit tip and the bit head because of the wear-induced shortening of the bit tip. At the beginning of use, the intermediate elements between the recesses assure sufficient support of the bit tip. With increasing wear the intermediate elements are also ground down, so that the contact surface of the bit tip on the bit head is reduced. Thus, with increasing shortening of the bit tip, the diameter of the base element and of the bit head are also reduced, so that the round-shank bit retains a cutting-friendly slim geometry up to the time it fails.
In accordance with a preferred embodiment of this invention, the recesses are uniformly cut into the base element up to an interior graduated circle extended around the center longitudinal axis of the bit tip. In a plan view the bit tip is designed star-shaped on its outer contour defined by the base element. A uniform rotational behavior can also be assured because of the uniform erosion of the recesses.
If the recesses terminate continuously and directly in the tapered area of the bit tip adjoining the base element, a precise flow of the removed material becomes possible. In order not to cause an unnecessary weakening of the bit tip and rapid wear, the recesses should terminate directly adjoining the base element.
A preferred embodiment is distinguished because the receptacle in the bit head is enclosed by a collar around the circumference, and the recesses extend in the axial direction of the bit tip past the collar into the contact surface of the bit tip on the bit head. With a round-shank bit of this type the recesses do not contact or only partially contact the removed material at initial use of the tool. In this state the round-shank bit is capable of sufficient rotation because of its geometry alone. When used, the collar is ground off and the recesses are increasingly exposed. Thus, the support of the rotation in accordance with the invention then becomes effective.
In another preferred embodiment of this invention, the area of a free end of the bit tip has a conical first area, which makes a transition into a second cylindrical transition area, and following the cylindrical transition area, the bit tip extends in a direction toward the base element over a truncated cone-shaped or concavely tapered area. A round-shank bit of this type has very good cutting properties and a long service life.
Long service life can also be achieved if in the region of the free end the bit tip has a conical or approximately conical area, and if a second area in the shape of a truncated cone or nearly truncated cone adjoins the first area, having a cone opening angle less than the cone opening angle of the first area. The second area transitions into the base element via a further, third area in the shape of a truncated cone or nearly truncated cone, wherein the cone opening angle of the third area is greater than the cone opening angle of the second area.


REFERENCES:
patent: 5161859 (1992-11-01), Larsson et al.
patent: 5219209 (1993-06-01), Prizzi et al.
patent: 5324098 (1994-06-01), Massa et al.
patent: 5484191 (1996-01-01), Sollami
patent: 5551760 (1996-09-01), Sollami
patent: 5873423 (1999-02-01), Breise
patent: 5931542 (1999-08-01), Britzke et al.
patent: 34 42 546 A1 (1986-05-01), None
patent: 3712427 (1988-10-01), None

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