Impregnated grinding wheel

Details Impregnated grinding wheel Impregnated grinding wheel

2002-02-19

2002-12-31

Rachuba, M. (Department: 3723)

Abrasive tool making process, material, or composition

With hydrocarbon

C451S534000, C451S540000, C451S544000, C451S548000, C051S295000, C051S296000, C051S297000, C051S300000, C051S309000

Reexamination Certificate

active

06500220

ABSTRACT:

I. FIELD OF INVENTION
This invention relates to vitreous bonded abrasive articles, particularly vitreous bonded grinding wheels. More particularly this invention relates to vitreous bonded abrasive articles having impregnated therein a grinding aid.
II. BACKGROUND OF THE INVENTION
Vitreous bonded abrasive articles have abrasive grains bonded by a vitreous matrix and are used to mechanically shape solids by material removal effected by an abrading action in which the abrasive grains cut material from the solid. It is known to abrasively shape solids of various materials, including, for example, metals, glasses and ceramics. Vitreous bonded abrasive articles are commonly formed into shapes suitable for machining wherein a rotating tool contacts a solid workpiece to be machined by the abrasive grains, most commonly such articles are formed into wheels and rims for wheels (machining is performed primarily by the circumference of the wheel), or disks and segments for disks (machining is performed primarily by the side of the disk), wheels and disks for bonded abrasives are herein referred to as “grinding wheels”. It is known to produce vitreous bonded abrasive articles having voids or “pores” in the matrix, interconnected voids being referred to as “open pores”. The pore structure of a vitreous bonded abrasive article affects a number of characteristics of the article including, for example, its physical strength, the rate of break down of the article into fresh cutting edges, and its effectiveness to eliminate swarf and to deliver metalworking fluid into the zone of material removal. In a vitreous bonded grinding wheel having open pore structure it is known to at times have a random distribution of pore sizes and shapes (some pores being relatively large and some pores being relatively small). Thus vitreous bonded grinding wheels may have a heterogeneous open pore structure with respect to pore size, shape and distribution.
As is well known, heat produced in abrasive shaping of solids, e.g. grinding of workpieces, can increase the rate of wheel wear and, in extreme cases, can adversely affect the quality of workpieces, producing out-of-tolerance dimensions, unacceptable surface finishes, as well as scorching workpiece material. The heat produced during grinding in large measure is the result of the sliding friction between the abrasive grain of the grinding wheel and the workpiece. The amount of heat produced can depend on many factors including, but not limited to, the composition and structure of the abrasive grain, the nature of the workpiece, the depth of cut taken during grinding, wheel speed and the vitreous bond used to bind together the abrasive grain. In the art it is known that different grinding operations (e.g. surface, internal, roll, plunge, snagging, creep feed, cut off) involve different forces, speeds, temperatures, infeed rates, metal removal rates and workpiece materials. Some grinding operations (e.g. finish or surface grinding) may employ relatively mild physical conditions involving low forces, infeed rates and metal removal rates. Other grinding operations (e.g. creep feed, plunge cut and cut off grinding) may employ relatively severe physical conditions such as high forces, infeed rates and high metal removal rates. It is therefore known in the art to produce vitreous bonded grinding wheels tailored to particular types of grinding operations and/or workpieces. Thus different vitreous bonded grinding wheels may be used for surface, plunge cut, internal, creep feed and roll grinding operations as well as for different workpiece materials such as various metals, glass and ceramic workpiece materials. Such grinding wheels may differ in the amount and kind of abrasive grain, vitreous bonding material and structure and degree of porosity.
To reduce or eliminate heat produced during grinding and thereby improve grinding performance and efficiency, it is known in the art to use metalworking fluids, more commonly called grinding fluids, in the grinding operation. These fluids are generally water or oil based fluids and are in many cases known to reduce friction and remove heat during grinding. The reduction of friction between the abrasive grain and the workpiece by the fluids can reduce the heat generated during grinding. The ability of these fluids to reduce friction between the grinding wheel and components thereof and the workpiece, and to remove heat during grinding may depend upon such factors as the composition of the fluid and the ability of the fluid to penetrate into the interface between the workpiece and grinding wheel, more particularly the interface between the workpiece and the abrasive grain during grinding. Penetration of the grinding fluid into the interface between the grinding wheel and workpiece, also known as the workzone, may in part be achieved by the rotating grinding wheel carrying grinding fluid into the grinding zone, at least partially by the open pore structure of the wheel at the grinding face of the wheel. Disadvantageously, interaction of the grinding wheel and the grinding fluid tends to displace fluid from the grinding zone and may produce mist that is susceptible of transport well beyond the grinding zone increasing the measures necessary for maintaining a clean working environment.
One way the art has sought to overcome disadvantages of use of grinding fluids and at the same time improve grinding performance of vitreous bonded grinding wheels is by impregnating grinding aids, such as lubricants into the pores of the wheel. The pores deliver the grinding aid to the grinding zone in this approach. To function as a grinding aid the impregnant or a component thereof must be available in the grinding zone in sufficient quantity to reduce friction or otherwise improve cutting efficiency so as to improve grinding performance. In the art sulfur, waxes, oils, graphite and halogen bearing polymers have been some of the materials impregnated into vitreous bonded grinding wheels in an effort to improve the grinding performance of the wheels in grinding operations which may or may not use grinding fluids (i.e. wet and dry grinding).
Because noxious sulfur vapors can be produced in the process of impregnation of bonded abrasives with sulfur and objectionable fumes can be given off during dry grinding with sulfur impregnated bonded abrasives, use of sulfur impregnated wheels has been limited in spite of the improved grinding performance obtained with such wheels.
Various oils have been used or proposed by the art to impregnate vitreous bonded grinding wheels. During grinding the rotating wheel creates centrifugal forces acting on the oil in the pores of the wheel. This centrifugal force tends to cause the premature expulsion of the oil from the wheel and/or can cause the oil to concentrate at the periphery of the wheel leaving the interior of the wheel devoid of oil or having a significantly reduced concentration of oil. The resulting wheel can adversely exhibit varying or decreasing grinding performance over the life of the wheel during a grinding operation. Lubricating oils, including low viscosity, non-polar, hydroscopic liquid oils, have been incorporated into waxes having melting points above room temperature as a means of impregnating vitreous bonded grinding wheels with the oil to improve their grinding performance. The wax serves as a carrier for the oil and aids in retaining the oil in the pores against the action of centrifugal forces generated by the rotating grinding wheel during grinding. At the grinding zone heat generated during grinding melts the wax carrier releasing the oil whereby the oil is available for reducing friction during grinding. In this approach, the impregnated wheel would have a lower concentration of oil for friction reduction than the direct impregnation of oil into the wheel, by an amount equal to the amount of carrier wax used.
Although improvements in grinding performance have to varying degrees been obtained with prior art impregnated vitreous bonded grinding wheels such wheels exhibit various shortcomings

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