US3495960A - Parallel aligned abrasive filaments in a synthetic resin bond - Google Patents

Description

'Feb. 17, 1970 Y H. J. SCHLADITZ PARALLEL ALIGNED ABRASIVE FILAMENTS IN A SYNTHETIC RESIN BOND Filed Feb. 7, 1966 i O O F/QZ M w g F753 M F/Q5 Arm 0w"- rs I United States Patent 3,495,960 PARALLEL ALIGNED ABRASIVE FILAMENTS IN A SYNTHETIC RESIN BOND Hermann J. Sehladitz, 12-14 Rufiinistrasse, Munich, Germany Filed Feb. 7, 1966, Ser. No. 525,563 Claims priority, application Switzerland, Feb. 9, 1965, 1,719/65 Int. Cl. C08g 51/12 U.S. Cl. 51-298 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an improved finishing body for mechanically working the surface of precision articles. The invention also relates to the process for forming such a body.

In the past the surface treatment of precision workpieces has generally required several operations to achieve the desired surface finish. Therefore, the surface is first ground by abrasives of varying grades and then polished or else several grinding operations are carried out prior to the final mechanized and/or hand polishing.

Known prior art grinders frequently employ a wheel or a belt forming an abrasive support upon which particulate abrasives are rigidly bonded by means of a glue or the equivalent. Typical abrasives, in the particulate form, which are often used with such support structure are corundum, silicon carbide, diamonds, among others.

As may be apparent it is of extreme difficulty to employ particles, all of which have a relatively uniform size. Thus the abrasive support will carry particles of varying size, unless off sizes are painstakingly extracted during many screening operations. Due to the fact that these olf size particles often are not excluded from commercial grinders one of the major difficulties in wheel or belt grinding arises. This difficulty is exhibited by the formation of ruts in the surface of the precision article, caused by the larger particles breaking away from the support.

During the grinding operation the individual particles are worn by surface contact with the workpiece and this wearing creates increased friction. Since the heat transfer between each particle and the support is at best minimal, the larger particles undergo a rapid heat rise causing their bond to be broken, with a result that these particles tear loose from the support. Upon breaking away, the particles produce ruts in the workpiece due to the constant pressure between the abrasive support and the workpiece. These ruts, obviously, are only eliminated by a subsequent grinding operation whereby the surface adjacent the rut is ground to the depth of the rut.

This difficulty more often arises in fine grinding and therefore a high grade surface for precision workpieces, such as optical lenses, cannot be obtained through use of conventional belt or circular grinders and repeated grinding operations.

For this reason, fine grinding and polishing is carried out through the use of loose and loosely bonded movable abrasives which are generally pulverulent abrasives and suspended in a liquid medium or movably fastened on supporting bodies. But even with this operation particular difficulties arise, namely, that the worked surface takes on the appearance of frosted glass. The worked surface must thereafter be polished with a loosely bonded grain polishing agent having a grain size of below 1 micron for the surface to become transparent and shiny. This agent may be elastically embedded in a pliant material, such as pitch. Here too, unless the grains are all of a size under 1 micron, the larger grains tend to break loose from the pliant material, forming new ruts, all of which require a laborious final treatment by hand.

Faced with the aforenoted problem, i.e., the individual abrasive particles of conventional grinding and polishing bodies tending to break from its supporting base to mar or rut the workpiece to therefore required numerous grinding and polishing operations, either being mechanized or by hand, the present invention has for an object to provide a finishing body which is adapted to operate upon a workpiece and which body carries its working elements in a manner such that individual particles cannot tear loose from their support.

It is a further object to provide a finishing body with its abrasive or polishing elements embedded in a body so as to provide good heat transfer therebetwcen.

Other objects and advantages to be derived from the hereinafter described grinding and polishing member will be obvious to those skilled in the art.

In a broad sense the invention is directed to a process for forming an article of manufacture which is adapted for use in the surface treatment of precision workpieces and to the article which comprises a body of a plastic bonding compound having a smooth working surface and a multiplicity of elements embedded therein. The elements are aligned substantially in parallelism within said body with the longitudinal axis of each element positioned substantially transverse to the working surface formed by the body whereby coaction between elements and the workpiece is accomplished by providing that the end face of each element terminates on the working surface.

In the drawing which both illustrates and forms a part of this invention:

FIG. 1 is a plan view of the working surface of the finishing member;

FIG. 2 is a greatly enlarged view of a portion of FIG. 1;

FIG. 3 is a view taken along the line 3-3 in FIG. 2 showing a side elevational view which is partly in section; and

FIGS. 4 and 5 are views similar to FIG. 3 showing a second and third embodiment of the finishing member.

Referring now to FIGS. 1-3 of the drawing, a portion of the finishing member which embodies this invention is shown. The member, denoted by the numeral 10 in general, .is defined by a body 12 of a solidifiable bonding agent that supports, in fixed relation, a multiplicity of elements 14.

The elements may be in the form of rod-shaped filaments or flaky particles, but for the sake of clarity in the figures the elements are all shown to be of a uniform circular cross-section. Obviously this is not intended to be by way of limitation for in practice the elements could take any desirable cross-sectional appearance, such as polygonal, oval, etc., and are further of no single diameter or thickness other than that all elements have a diameter or thickness of less than 50 microns and a length to thickness ratio of at least 1021.

The elements are of a high strength material and, as will be more fully described when considering the process for forming the member, are embedded within the body 12. The body, as apparent, is a material of lower strength. Upon solidification of the body the elements are retained in the position as shown in the figures so that at least a portion of each element lies on the working surface 16, with the remaining portion being completely anchored by the enveloping bonding agent. Therefore, the elements are bonded to the body over practically their entire surface area such that gravity forces cannot break an individual element from the body. It should also be noted that even major fluctuations in the diameter or dimension of an individual element, pro= vided all are below 50 microns in cross-section and with a length to thickness ratio of at least 10:1, will have no effect on the possibility of breaking loose from the body. This is true, since in practice the elements have in excess of 95% of their surface area enveloped by the bonding material.

As noted above, one significant factor producing the breaking or tearing loose of the abrasive particle in the prior art grinding structures was the production of heat caused by friction between surfaces. A special advantage of the present structure is seen in the provision of the embedded elements. Whereas in the prior art structure, a temperature rise could be significant due to the wearing of an abrasive surface and the poor heat transfer to the abrasive support, it has been found in practice that the heat transfer capability in the present device is good and carried out over the entire surface area of the element. Practically though, the rise in heat in the present structure is not great due to the small cross-section of the elements (of the order of 10* sq. mm.). A heat rise in the prior art structure occurs when the particles become blunt on an edge to thereby increase in surface area. In the present structure the surface area of the elements remains relatively constant, the elements undergo no significant heat rise and therefore the hardness of the elements is not reduced.

The bonding agents which may be used to form the body may be any one of the well-known plastic materials, such as epoxy resin, unsaturated polyester resins or saturated polyester resins. The invention also contemplates that substances having corresponding physical characteristics and properties to the mentioned resins may be used to bond and support the elements in a fixed relation, both to one another and to the working surface 16. One such characteristic is that the agent provides a tensile strength of from approximately 100 to 450 kp./cm. and be inert to water.

With particular regard to the epoxy resin, practice has indicated that a preferred type which provides good results is one formed by the reaction of bisphenoi A and epichlorohydrin which is hardened by phthalic acid anhydride. Similar results are obtained through the use of an unsaturated polyester resin such as a maleic resin with ethyle-neglycol and a saturated polyester resin, such as polyethylene terephthalate.

FIGURES 4 and 5 show further embodiments of the member and differ from the showing in FIGURE 3 in that the working surfaces 16 and 16 respectively are smoothly convex and concave rather than flat as shown in the embodiment of FIG. 3.

Elements 14 may suitably be formed of iron, aluminum or ferric oxide, tungsten, molybdenum or titanium carbide as well as crystals having anisotropic strength and hardness properties, as for example, metallized flaky particles of graphite or molybdenum disulfide, provided these particles are so oriented that their slidable lattice planes extend substantially normal to the surface 16, 16' or 16" of the member 10. This can be achieved since the graphite or molybdenum disulfide particles are metallized and may be oriented by a magnetic field, as will be brought out below.

The finishing member may be formed in accordance with the following exemplary process. Rod-shaped filaments of iron, ferric oxide, tungsten oxide, manganese or titanium, or metallized filaments of aluminum oxide or metallized particles of graphite or molybdenum disulfide, all of which have a thickness of less than 50 microns and a length to thickness ratio of at least 10:1, are disposed in a chamber having a supporting surface. This surface defines the final working surface 16. A magnetic field of from approximately 1000 to 20,000 gauss, determined by the viscosity of the resin to be used and the desired lateral spacing of the elements in final relation, is applied across the chamber with the result that the individual elements are oriented by the magnetic field. The orientation of each element will be substantially parallel to adjacent elements and substantially normal to the future working surface 16. After alignment, a charge of bonding agent, either in liquid or vapor form, is injected into the chamber. Injection is preferably carried out under atmospheric pressure conditions and the elements are maintained in their orientation by the magnetic field. Depending upon the resin used, hardening will commence within 15 to 30 minutes. Thereafter, the field may be withdrawn with the elements being fixed upon solidification.

This result may also be achieved by charging the multiplicity of elements into the still liquid bonding agent and similarly aligning the elements with the field.

It may be desirable to obtain a higher concentration of oriented elements throughout a cross-section of the member and this may be accomplished, before solidification of the bonding agent, by a uniformly applied compressive force on the agent in a direction substantially normal to the orientation of the elements. In practice, the side watts of the chamber may be displaceable. Therefore, due to the field strength and the magnetism inherent in the elements, the latter will arrange themselves at substantially equal lateral distances from one another. Thus, the percent of resin per cross-sectional area may be varied from below 20% to a maximum of 92%.

Therefore it is seen that the invention provides a mechanical working member for the surface treatment of precision workpieces which provides, among others, the advantages noted and overcomes the deficiences in the prior art.

Although several preferred embodiments have been disclosed in detail herein, it should be understood that this invention is in no sense limited thereby and its scope is to be determined by the appended claims.

Having described the invention what is claimed s:

1. An article of manufacture for mechanically surface finishing a precision workpiece consisting of a bondable and solidified support member formed of a plastic bonding compound having a relatively smooth working surface and being of a material selected from the group consisting of epoxy resins, saturated polyester resins, and unsaturated polyester resins, a multiplicity of metallic magnetizable rod-shaped abrasive filaments of high strength having a thickness no greater in dimension than 50 microns and a length-to-thickness ratio of at least equal to 10:1, said bodies being fixedly embedded within the support member substantiaiiy parallel to each other and substantiaily perpendicular to the working surface so that one end of body defines a part of said working surface with rod having a cutting edge exposed across said working surface.

2. An article of manufacture for mechanically surface finishing a precision workpiece consisting of a bondable and solidified support member formed of a plastic bonding compound having a relatively smooth working surface and being of a material selected from the group consisting of epoxy resins, saturated polyester resins, and unsaturated polyester resins, a multiplicity of metallized flaky particles having their slidable lattice planes extending substantially perpendicular to said working surface, having a thickness no greater in dimension than 50 microns and a length-to-thickness ratio of at least equal to 10:1, said bodies being fixedly embedded within the support member substantially parallel to each other and substantially perpendicular to the Working surface so that one end of body defines a part of said working surface with rod having a cutting edge exposed across said working surface.

3. The article as, defined in claim 1 wherein said rodshaped abrasive filaments have a cross-section of substantially 10- sq. mm.

4. The article as defined in claim 2 wherein said flaky particles are graphite.

5. The article as defined in claim 2 wherein said flaky particles are molybdenum disulfide.

References Cited UNITED STATES PATENTS Crane 264108 Eisenhardt 264108 Donal 26424 Jurkat 51299 Baermann 26410'8 Blume 264108 Salyer et al. 26424 US. Cl. X.R.

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