Stone working – Tools
Reexamination Certificate
2002-12-27
2004-05-25
Hail, III, Joseph J. (Department: 3723)
Stone working
Tools
C125S036000, C125S040000, C299S079100, C299S105000, C299S110000, C299S111000, C299S113000
Reexamination Certificate
active
06739327
ABSTRACT:
The present application relates to cutting tools having hardened tungsten carbide tips and, in particular, to a new tip having a tapered base, that is a base having a large forward diameter complementary to the diameter of the mouth of the seat of the tool and a smaller rearward diameter recessed in the seat.
BACKGROUND OF THE INVENTION
Machines used to cut hard surfaces such as asphalt and concrete have a plurality of tools mounted on a wheel or drum which is forced against the surface to be broken. Each tool has an elongate steel body at the forward end of which is a tungsten carbine insert for breaking up the hard surface to be cut. The tools are mounted in tool holders on the wheel or drum such that the tools move through a circular orbit as the wheel rotates with each tip penetrating the hard surface and removing a small amount of material to thereby advance the cut.
As the machine cuts away hard material, the tools become worn. The hardened cutting tip at the forward end of the tool body is gradually eroded away as the tip is repeatedly forced into the hardened material, and behind the cutting tip, the metal tool body is worn away by the movement of particles of hard material around the steel body causing a phenomenon commonly known as “wash away.”
In the summer months, especially in the southern states, the steel of tools on machines used to remove the upper surfaces of an asphalt highway can become so eroded by wash away that the forward end of a tool takes on an hourglass contour. An hourglass contour is one which the tool body is narrower at its midsection than it is at either the end mounted in the tool holder or the end holding the cutting insert, such that further use of the tool will soon result in failure.
After the cutting tools of the machine become worn, the machine must be taken out of service and the tools replaced, a process which consumes a considerable amount of time, and it is not uncommon in warmer states to replace the tools of a machine two or three times during the course of a single working day. It is, therefore, desirable to design tools and the inserts of tools so as to maximize their useful life.
A common cause of tool failure is the braze which binds the tungsten carbide insert into the seat at the forward end of the tool body. Although braze material bonds readily to the steel of the tool body, brazing material binds only to the cobalt or nickel which makes up only a small percentage of the tungsten carbide insert. A certain percentage of all tool failures are the result of defects in the braze causing the tungsten carbide insert to fall out of the tool body before either the tool body or the insert has become sufficiently worn to be taken out of service. As a result, the provision of a consistent high quality braze between the tool body and the insert is a necessary element for extending the useful life of a tool.
SUMMARY OF THE INVENTION
Briefly, the present invention is embodied in a tool having an improved cutting tip resulting in the reduction of damage to the tool body by virtue of wash away and a reduction of tool failure as a result of defects in the braze joining the tungsten carbide tip to the tool body. The tool includes a tool body having a longitudinal axis, a tapered cutting portion symmetric abound the axis, a radial flange behind the cutting portion, and a cylindrical shank behind the radial flange. The shank of the cutting tool is sized to be received within a cylindrical tool holder mounted on the machine. The tapered cutting portion of the tool body has a seat at the forward end thereof and brazed into the seat is an insert in accordance with the present invention.
The insert is made of tungsten carbide and has a forward cutting end for cutting a hard surface. Rearward of the forward cutting end is a base portion having an outer surface which is complementary to the inner surface of the seat at the forward end of the tool body. The forward end of the seat is defined by a generally circular mouth rearward of which is a frustoconical inner wall, and rearward of the inner wall is a transverse bottom surface, which may be conical, semi-circular, or any other configuration to define the distal rearward end of the seat. The base of the insert has an outer wall complementarily in shape to the frustoconical inner wall and a rear surface complementary in shape to the transverse bottom surface of the seat. In accordance with the invention, the outer surface of the base of the insert tapers from a relatively large diameter at the forward end thereof to a somewhat smaller diameter at the rearward end.
In one preferred embodiment, an insert in accordance with the present invention has a forward cutting end defining a maximum outer diameter. Rearward of the forward cutting end is an elongate tapered central body which narrows from the maximum outer diameter of the forward cutting end to a smaller diameter defining the rear of a base, and behind the rear diameter is a transverse rear surface. The insert is received in a tapered seat which is symmetrical about a longitudinal axis and is complementary in shape to the rear portion of the tapered outer surface of the insert and to the transverse rear surface.
In another preferred embodiment the tool body has a seat in the forward end and an insert in the seat, the insert and seat being configured as described above with respect to the first embodiment. Surrounding the seat is an annular groove coaxial with the axis of the seat, and brazed into the annular groove is an annular tungsten carbide collar. The annular collar which extends around the base of the cutting insert serves as a shield that protects the tool body from the ravages of wash away and therefor extends the life of the tool. The collar can be of a different hardness than the insert and the braze material used to retain the insert in the seat can have different properties from the braze material used to retain the collar in the annular groove.
There are many benefits to the configuration of an insert having a base in accordance with the present invention. The taper of the outer wall of the base from a large diameter at the mouth of the seat to a smaller diameter rearward of the mouth provides for self centering within the complementary shaped inner wall of the seat. The most expensive portion of such a tool is the insert because tungsten carbide is a very expensive material, and an insert with a body which tapers inwardly toward the rear is less expensive to manufacture than a cylindrical body or one that tapers outwardly toward the rear. The taper also permits the provision of a plurality of protrusions aligned to define a circle around the base of the insert, the circle defined by a plane perpendicular to the axis, for spacing the outer surface of the base from the complementary shaped inner surface of the seat for allowing braze material to flow therebetween. By providing two pluralities of protrusions, each plurality defining a plane perpendicular to the axis of the insert, where the planes are spaced from one another and engage the inner wall of the seat, the insert becomes self centering and self aligning. It should be appreciated that an insert with a cylindrical seat, as is the case with the prior art, cannot be self-aligning and is always somewhat misaligned.
The tapered configuration also permits the burping out of steam and other gases. Small amounts of water permeate the flux needed to properly braze the parts. As the parts are heated to melt the braze, the moisture turns to steam and unless the steam can be released, it forms a pocket between the surfaces of the base and the seat, ejecting the carbide insert from the seat. Where the outer surface of the base is tapered, the steam can push the insert outward of the seat and escape between the outer surface of the base and the inner surface of the seat as a burp. In similar fashion the tapered configuration allows flux and excess braze to escape during the brazing process. The tapered configuration of the base and the seat also allows the tungsten carbide insert to forg
Hail III Joseph J.
Marsh Robert L.
McDonald Shantese
The Sollami Company
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