ABRASIVE JET STREAM POLISHING

Abstract: Abrasive jet stream polishing, wherein an abrasive is suspended in a flowable jet medium (24) and projected at high velocity and pressure at a workpiece (12), where the jet is projected at the surface to be polished at an oblique angle. The method is substantially improved by forming the medium of a polymer having reformable sacrificial chemical bonds which are preferentially broken under high shear conditions. Projecting the medium and suspended abrasive breaks the reformable sacrificial chemical bonds while polishing. The chemical bonds will reform permitting recycling (80, 82, 84) of the medium and abrasive for reuse in the method. The jet is effective at relatively low pressures of about 5 to about 80 MPa.

Description: ABRASIVE JET STREAM POLISHING BACKGROUND TECHNICAL FIELD The present invention relates to the field of j et stream polishing, coating removal and cleaning adherent materials from workpieces, and particularly to abrasive jet stream polishing, wherem a suspension of abrasive particles in a viscous medium is pumped under pressure and at high velocity against the surface of a workpiece to effect polishing and cleaning operations. Such operations are usefully employed in polishing the surfaces of metal sheet and plate, cast and forged metal articles, and related surfaces in the fabrication of useful articles. Typical applications are the polishing surfaces of materials which are difficult to machine, such as stainless steels, titanium, nickel alloys, tungsten carbide, tool steels and the like The technique may be employed in operations on non-metal surfaces as well, including reinforced polymer composites, ceramics, glass, rock and the like. The technique is also useful for cleaning and descaling metals, removal of paints and coatings, including ceramic coatings, from surfaces, and the like. PRIOR ART Polishing and related operations to smooth and finish surfaces are basic to the fabrication of metals to useful articles and have been practiced as long as the production and use of metals has been known. Indeed, in the fabrication of many metal articles, surface finishing operations represent a very substantial component of the total manufacturing operations required Such operations, in a variety of forms and techniques, are typically labor intensive and expensive All such techniques, of which there are large numbers, are based on the removal of elevated portions from the surface, to a level consistent with lower portions. The removal of such elevated portions requires the performance of work on the workpiece surface. Work on lower surface portions is avoided or rrαnimized. Viewed in such broad terms, the most commonly employed techniques are based on mechanical working of the surfaces, by such common techniques as sanding, grinding, lapping, and the like. Chemical and electrical techniques are also known. There is need in the art for more productive and economical polishing techniques which can be employed in less labor intensive operations, and to permit faster and more uniform producbon of finished workpieces with specified surface finish characteristics Work is often performed on metals and other materials by techniques involving propelling fluid or fltudized streams onto the surface. Among such techmques are sand blasting and related techniques, and jet stream cutting and machining, including abrasive jet stream cutting and macrαrung. Sand blasting is typically employed to roughen or peen surfaces or to remove rust and scale from metal surfaces and the like. Such techniques are not generally employed for polishing operabons, and are typically directed to operabons which produce surfaces which, in fact, do not require polishing in typical operahons. Sand blasting is often used, for example, to roughen surfaces to aid in the adherence of applied coatings or adhesive bonding to such surfaces. Abrasive water jets have grown to be widely employed in cutting and machining operahons, particularly with metal sheet and plates to effect rapid and economical cuttmg and related forming operahons. Typical applications have been the cutting of materials which are difficult to machine, such as stainless steels, titanium, nickel alloys, reinforced polymer composites, ceramics, glass, rock and the like. Such techniques are parbcularly advantageous to produce cutting acbon through very highly localized achon at low average applied force, to effect cuttmg of such materials with minimal thermal stress or deformahon, without the disruption of crystalline structure, and without delamination of composite materials. To effect abrasive water jet cutting, a specialized nozzle assembly is employed to direct a coherent collimated high pressure stream through a small diameter orifice to form a jet Typically, pressures of about 200 MPa (about 30,000 psi) and higher are applied to force the media through the nozzle oπfice. Typical nozzle assemblies are formed of abrasion resistant materials, such as tungsten carbide or boπde. The orifice itself may be formed of diamond or sapphire Abrasive particles are added to the high speed stream of water exiting the nozzle orifice by directing the water stream through a "mixing tube" and introducing abrasive particles into the tube in the region between the exit of the stream from the orifice and its entry mto the "mixing tube " The mixing tube, which is typically several inches in length, is a region of contained, extremely turbulent flow in which the relatively stationary or slow moving abrasive particles are accelerated and become entrained m the high speed water sbeam, which may have nozzle exit velocities as high as Mach 3 The enbamment process tends to disperse and decelerate the water stream while the abrasive parbcles collide with the tube wall and with each other. Relahvely wide kerfs result from the dispersed sbeam, energy is wasted, and the tube is rapidly worn, even when made from abrasion resistant materials, such as tungsten carbide or Boπde and the like. Some studies have shown that as much as 70% of the abrasive parbcles are fractured before they reach the workpiece to be cut. In recent developments, water jets without abrasives have been thickened with water soluble polymers, which aid in obtaining and maintaining coherent jet streams, in reducing the level of misbng, splashing and the like Somewhat narrower kerfs can be achieved Operating pressures and velocities remain quite high. It is also known to suspend particulate abrasives m water jets, ordinarily relymg on the thickening effect of the water soluble polymers to act as a suspending agent m the system. The abrasive cuts with greater efficiency than the water alone or the water with a thickenmg agent, but inboduces an entire new spectrum of difficulties. PROBLEMS IN THE ART Jet sbeam cuttmg and machining operabons have not been applied to polishing, and development of the technology has been focused m direchons which tend to be mcompahble with the requirements of polishing operabons Because of the high pressures and flow rates mvolved in jet sbeam cutting and machining, it is quite difficult to maintain coherent streams of t ie jet While the use of thickening agents provides important improvements, such operations tend to be expensive, as neither the water not the soluble polymer is reusable, because the high shear inherent in such operahons degrades the polymer, the degraded polymer remains dissolved in the water, providing waste disposal expense When abrasive is added to the system, for abrasive jet stream cuttmg and milling, the difficulties and expense are even greater. Nozzles employed for abrasive water jet cutting operabons are more complex and require ancillary equipment to add the abrasive to the sbeam, normally immediately adjacent the nozzle assembly or as a part of such a nozzle. The assembly includes a mixmg chamber where the abrasive is lnboduced into the medium, a focusing tube where the stream is accelerated, and a small orifice where the flow is collimated mto a coherent jet sbeam projected at the workpiece. The mixmg chamber and its associated hardware are complex, required by the necessity of injecting the abrasive particles mto the relahvely high speed stream The mixing chamber is required to m j ect the particles mto the intenor of the flowing stream as much as possible to minimize the extent to which the intenor surfaces of the mixmg chamber and orifice are abraded. Because the components have widely different densities, it has generally not been possible to premix the components pπor to the nozzle assembly because, even m thickened fluids, the abrasive particles tend to separate and settle at an appreciable rate Additional thickenmg is not cost effective in such systems Uniform dispersion of the abrasive mto the stream has proved elusive and mconsistent, largely attributable to the broad differences in density of the materials, the high velocity differences between the mjected particles and the fast flowing sbeam, and the resulting need for the stream to accelerate the abrasive particles. The mixmg of the particles mto the medium is often mcomplete and inconsistent, the accelerabon requirements of the abrasive slows the flow of the medium, and the incomplete mixmg mtroduces inconsistencies and inhomogeneities which cause divergent flows and differing trajectoπes of the stream or its components exit g the oπfice, producing mconsistent and/or increased kerf widths and imprecise and non-uniform cut edges on the workpiece The mixmg process causes the abrasive to produce high rates of wear in the mteπor of the nozzle elements, which have, as a result, a useful life measured m hours of operation under favorable condihons, and less favorable conditaons can reduce nozzle and oπfice life to a matter of minutes. For example, precise alignment of the nozzle and focusing tube are quite critical The entrainment of the particles also tend to make the jet sbeam divergent rather than coherent, resulting m wide kerfs and extra time and effort m the cuttmg operation. When the jet sbeam mto which the abrasive is introduced is adequately thickened, shear degradation precludes reuse of the medium, and the cost is substantial. Considerable amounts of the polymer are required to achieve adequate thickenmg to effectively suspend the abrasives commonly employed. Water jet sbeam nozzle orifices are typically on the order of about 0.25mm (about 0.010 in.). When an abrasive is introduced, the minimum practical mixmg tube is about three tames the oπfice diameter, i.e., about 0.75 mm (about 0.030 m) or greater. Smaller nozzles have intolerably short service life from excessive erosion durmg operabons. The wider nozzle produces a wider sbeam and cuttmg kerf, and requires more medium and abrasive consumpbon per unit of cuttmg. Hollmger, et al., "Precision Cutting With a Low Pressure, Coherent Abrasive Suspension Jet," 5th Ameπcan Water Jet Conference, Toronto, Canada, August 29-31, 1989, have reported improved dispersions of abrasives in aqueous solutions of methyl cellulose and a propπetary thickening agent "Super Water" (trademark of Berkely Chemical Co.). Their work was based on attaining sufficient viscosibes, based on the use of 1.5 to 2 weight percent of the thickeners to permit pre ixing of the abrasive mto the polymer solutaons, eliminating the need for injechon of the abrasive at the nozzle. Hollmger, et al., reported that orifices as small as 0.254 mm (0.01 m.) could be effechvely employed. The work of Hollmger et al. has subsequently been embodied m U.S. Patent 5,184,434, issued February 9, 1993, on an application filed August 29, 1990. Crosshnking of the polymers employed is not contemplated. See also Howells, "Polymerblashng with Super-Water from 1974 to 1989: a Review", Int l. J. Water Jet Technol., Vol. 1, No. 1, March, 1990, 16 pp. Howells is particularly informative concerning the reasons why polymer jet stream media, with or without abrasives, has not been recycled and reused. See Pages 8 and 9. In many contexts, the water or aqueous based systems employed in the pπor art may not be used with some materials or particular workpieces where the presence of water or the corrosion it may produce cannot be tolerated. Jet sbeam cutting has not been applicable to such circumstances. In all the polymer based thickened systems of the pπor art, the degradation of the polymer chains by the high applied shear rates in the system has, to date, precluded effective techmques to recover and reuse the j et stream medium, resulting m substantial waste handling requirements and considerable expense for the polymer and abrasive consumed. We have now found that many of the attnbutes of j et stream cuttmg and particularly abrasive j et sbeam cuttmg can be adapted to the very different requirements of polishing operabons, to provide a polishing and finishing technique which is highly controlled, rapid, and efficient, and which affords high productivity and economies. OBJECTS AND SUMMARY OF THE INVENTION It is an ob j ect of the present invention to provide a jet stream polishing medium which is effective to polish workpiece surfaces. In particular, it is an object of the present mvenhon to provide reusable polymer thickened j et sbeam premixed media which effectively suspend abrasive parbcles, form stable jet streams, polish with high efficiency and conbolled mateπal removal from the surfaces of workpieces, and which are reusable, and thereby reduce waste handling requirements and raw mateπal costs. A further object of the present mvenhon is to provide techmques for jet sbeam polishing, particularly at low pressures and flow volumes. Another object is to permit abrasive jet sbeam polishing using a simplified nozzle, considerably less expensive and smaller and particularly shorter than those heretofore required for conventional abrasive water jet machining and cutting. Stall another object is the provision of a low cost jet stream pohshing system, based on the recirculahon and reuse of the thickened jet sbeam medium. In one embodiment of the present mvention, it is an object of the present venbon to provide non-aqueous jet sbeam media which permits the use of jet stream pohshing operations with materials and workpieces not previously usable with jet stream pohshing operabons. These and still other objects, which will become apparent from the following disclosure, are attained by forming a j et sbeam medium having a divergent flow which is impinged on the surface of a workpiece to expose raised surface areas to work by the fluid stream and remove such raised areas with minimal work is performed on other areas of the surface. Pohshing, and even the requirements of grinding operations, including deburπng, radiussing of edges and the like, can be effechvely realized In the present mvenhon, an abrasive jet stream, is formed and projected onto the surface of a workpiece m a fashion suitable to selectively effect work on the desired portions of the surface to effect polishing and gπnding to the required or desired extent In general, the workmg is at a lower rate than that employed for jet sbeam cuttmg, and employs operating conditions and techmques which are milder and less expensive to attain and employ than those ordmanly employed in jet sbeam techmques in the pnor art The milder conditions and the selechvity of the operation on desired segments of the workpiece surfaces are ordinarily attained by a combination of operating parameters, including the following- 1. The jet may formed with a divergent pattern, unlike cutting operahons where the maximum attainable coherence of the stream is ordmanly desired m order to focus the sbeam and maximize the work performed at the localized cuttmg area. Coherent j et streams may be of use, however, m polishmg corners and areas of detail where the acbon of the jet stream needs to be focused m a small area 2. The stream pressure and velocity are reduced below those typically employed for cuttmg operabons 3 The stream is desirably directed at the surface at an angle of greater than 45° from normal to the surface, and preferably greater than 60°, and as much as 80 to 89°, from normal, m conbast to cuttmg operabons where the sbeam is typically pro j ected at the surface at an angle of 5 to 30° from the normal to the surface. 4 The particle size of the abrasive should be the smallest size consistent with the required rate of polishmg, in light of the hardness and roughness of the surface to be worked and the surface finish to be attained, m conbast to the selechon cπteπa for cutting, which ordinarily employs the largest parbcle size consistent with the required kerf width to maximize the focused work applied to the cutting acbon 5. The hardness of the abrasive should be the highest value consustent with the cost of the materials and the limitations of the workpiece, m light of the hardness of the workpiece mateπal to be polished Cutting operabons also typically employ the hardest and fastest cuttmg abrasive available within cost-effectiveness limits The jet sbeam of the present invention is preferably formed of a polymer having referable, sacrificial chemical bonds, preferenbally disrupted and broken duπng processing and polishing under high shear conditions, and which then reform to reconstitute the medium m a form suitable for reαrculation m the process and reuse In one embodiment of the invenbon, the water jet sbeam is thickened with an ironically cross-linked water soluble polymer, wherein the ionic cross-links are formed by salts of metals of Groups III to VIII of the Peπodic Table. In a second embodiment, the aqueous jet is formed of a hydrogel of a water soluble polymer, preferably cross-linked with a gel-promobng water soluble salt of a metal of Groups II to VIII of the Penod c Table Cross-linking m such systems is based on intermolecular bonds, i e , hydrogen bonding, between polymer molecules In a third embodiment, a non-aqueous medium is formed of an intermolecular bond cross- linked polymer which itself forms the jet sbeam. In operation, the polymer suspends the abrasive particles. The polymer may be parhally broken down under the ^-ar forces of the operation by disrupbon of the intermolecular bonds which produce the cross-b f the polymer. After the jet performs its work on the workpiece, the polymer is collected, the L. >ss-lιnkιng bonds are allowed to reform, and the medium is recycled for reuse m the process The polymer may be plasbcized or thickened to conbol viscosity. Smaller orifice diameters, on the order of as little as about 0.1 mm (about 0.004 m.) can be effechvely employed if the particle diameter of the abrasive is sufficiently small BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of apparatus showing an embodiment of this mvenhon providing recirculated media for reuse; Figure 2 is a stylized schematic view of a workpiece surface and a polishmg jet stream showing the polishing action in accordance with the present mvention DETAILED DESCRIPTION In the present mvenbon, we employ a j et sbeam technique analogous to that employed jet sbeam cutting and machining to polish and smooth surfaces of workpieces. The mvenhon also serves to effectively perform many of the functions of grinding operations, including deburπng, radiussing edges, and the like, and within limits can be employed to "grind" surfaces to required dimensions with accurate and precise tolerances. In the present mvenhon, a jet sbeam, preferably an abrasive jet sbeam, is formed and projected onto the surface of a workpiece m a fashion suitable to selectively effect work on the desired portions of the surface to effect polishing and grinding to the required or desired extent. While the details of the mvenbon will vary with the nature of the polishing operation to be performed, the cenbal thesis of pobshmg and grinding m the present mvention is the adaptation of jet stream technology to operate with suitable selectivity on the surfaces of the workpieces to be polished, rather than focusing the sbeam at a smgle pomt to be cut As a consequence of these distinctions m the nature of the process, there are significant differences m the methodology and equipment employed and m the formulation of the pobshmg media suitable for use m formmg the jet stream. In general, the workmg is at a lower rate than that employed for jet stream cuttmg, and employs operating condibons and techmques which are milder and less expensive to attain and employ than those ordinarily employed m jet sbeam cuttmg techniques in the pπor art. In pobshmg operahons, the removal of mateπal is mtended to be limited to the "high spots" on the surface of the workpiece, so that stock removal is limited to magnitudes consistent with the pohshing or gπnding functions mtended. The milder conditions and the selectivity of the operation on desired segments of the workpiece surfaces are ordinaπly attained by a combmation of operating parameters, including the following: 1 The jet is preferably formed with a divergent pattern, unlike cuttmg operabons where the maximum attainable coherence of the stream is ordmaπly desired in order to focus the stream and maximize the work performed at the localized cuttmg area For work in limited areas, a more focused pattern may be required, but is generally not preferred. In the present mvenhon, the jet sbeam is relied upon to work surface areas of the workpiece rather than to focus the work at a cut to be made. In addition, the work to be performed is generally reduced, m that the amount of material to be removed from the workpiece surface is generally very small. In context, the usual colhmabon of the stream to focus the forces are accordingly not wanted m the operahons of the present mvenhon. 2. The stream pressure and velocity are reduced below those typically employed for cuttmg operahons. The high force requirements of jet stream cuttmg are not involved m the present mvention, and the operational conditions are far milder than those employed in the pnor art As a result, less expensive equipment and mateπals can be employed, and the conditions and techmques of use may be less demanding of operator expertise. 3. The stream is desirably directed at the surface at an angle of greater than 45° from normal to the surface, and preferably greater than 60°, and as much as 80 to 89°, from normal, m conbast to cutting operabons where the stream is typically projected at the surface at an angle of 5 to 30° from the normal to the surface. By directing the jet at an oblique angle to the surface, the work performed is concentrated primarily on the portions of the workpiece surface which are raised above the design surface and which are to be removed m the operabon, while impingement of the jet stream on the design surface is minimized. The operation is accordingly easy to conbol and operate When grinding operabons are performed, to remove modest amounts of material from the entire surface to achieve dimensional changes, the obliquity of the jet tends to facilitate material removal m a fashion which is uniform, preventmg the development of gouges, holes, or other surface defects and artifacts which might otherwise occur It is preferred to employ a jet stream containing an entrained abrasive. When an abrasive is employed, there are desirable additional parameters m the present mvenhon: 4. The parbcle size of the abrasive should be the smallest size consistent with the required rate of pobshmg, m bght of the hardness and roughness of the surface to be worked and the surface finish to be attained, in conbast to the selection criteria for cuttmg, which ordinarily employs the largest particle size consistent with the required kerf width to maximize the focused work applied to the cutting acbon. Smce the removal of mateπal is mtended to be limited in the present mvenbon, the selechon of the abrasive is different from that to be employed in cuttmg. In general terms, the smaller the parbcle or "gπt" size of the abrasive, the smoother the surface attained. 5. The hardness of the abrasive should be the highest value consistent with the cost effectiveness limits of the procedure and the hardness of the workpiece mateπal to be polished. As a general rule, the harder the abrasive, the faster and more efficient the pohshing operation. Limiting the hardness of the abrasive may cost-effective m some cases, since, typically, the harder the matenal, the more expensive it is. In addihon, the employment of softer abrasives limits the matenal removal rate, which may be desirable m limited circumstances to facilitate control. Limiting the pohshing rate is often important to provide control of the operation, as noted above. By limiting the jet sbeam pressure and flow rate, the surface pobshmg rate can be estabhshed at any value, up to a maximum, consistent with the requirements of the workpiece surface. It is also preferred to employ a polymer based or thickened viscous medium to form the pohshing jet. The preferred embodiments of the present mvenbon are grounded on the observation that the shear stresses imposed in the formation and use of polymer containing jet sbeams employed for jet sbeam pohshing operabons are necessarily high. While a number of steps can be taken to minimize the appbed shear sbesses m the nozzle assembly, the impact forces of the jet sbeam on the surface of the workpiece are also high and also break down the polymer structure. Smce high shear is an inherent feature of the pobshmg operation, techmques for reducing polymer breakdown are, at a certain po t, incompatible with the requirements of the polishing operabon itself, and are thus limited. The inclusion of one and one-half or two weight percent of thickener or polymer matenal m the jet sbeam medium typically employed m the pnor art is thus a very substanhal proportion of the cost of the operabon. The tune and energy requirements for dissolving the polymer mto the aqueous medium is also a substanhal factor m operating costs and can, if not adequately planned, impose substantial delays in operahons because of the significant tame required to dissolve such polymers. If not consistently controlled, vaπahons m the soluhon may inboduce a lack of uniformity m pobshmg and machining operations and impair the quality of the result After use, the degraded polymer soluhon is a substantial collechon and handling burden on the operabon, and there are no known uses for the resulting waste material. Handling and disposal costs are typically a significant cost of operahons. In that context, the employment of more complex and more expensive polymers to afford certain specific benefits to the operabon are generally offset by the added costs. The degradation of the polymers m jet sbeam pobshmg systems is produced by the breaking of the chemical bonds which make up the polymer, and particularly the chemical bonds which form the polymer chain backbone. The result of such effects is to reduce the molecular weight of the polymer, and a consequent reduction of the viscosity and loss of the capacity of the medium to effechvely suspend the abrasive parbcles, to form an effective jet stream, and to limit abrasive erosion of the equipment. In the present mvenbon, these difficulties are overcome by the employment of polymer materials which have the capacity to reform chemical bonds broken dunng the jet sbeam pobshmg operabon, and can thus be reconshtuted m a fully effective form to permit recycling and reuse. Thus, while the chemical bonds will be broken duπng the pobshmg operahons, under the influence of high shear m the nozzle and by the impact on the workpiece, such effects are no longer destructive to the usefulness of the jet sbeam medium In practice, the polymers employed m the present mvenhon may be recycled through the operahon for many operating cycles. In time, there will be a more severe degradation of the chains of the polymer backbone (normally covalent bonds) which will limit the number of cycles Generally, the preferred polymers of the present mvenbon may be cycled through the system for twenty to one hundred cycles or more before replacement is required The reformabon of the broken bonds to reform the polymer thickener in useful form requires that the polymer contain bonds which are sacrif ced under the high shear and high impact conditions of the pobshmg operabon, and which will reform to reconshtute the onginal polymer structure. This requires that the polymer contain an adequate population of chemical bonds other than covalent bonds. When covalent bonds are broken, the fragments are so highly reachve that the broken chains are normally terminated by very nearly instantaneous chain terminating reachons, and the onginal bonds cannot be reformed. There are three types of chemical bonds which have thus far been evaluated m the present mvenhon, and which have proven effechve. These are lomc bonds and intermolecular B:0 bonds. lo c bonds are frequently employed in ionic cross-linking of a vaπety of polymers. Such polymers are often water soluble types well suited to use m the present mvenbon. When such polymers are ironically cross-linked, they typically form water swollen gels, having effechve viscosity levels to effect highly durable suspensions of the high density abrasive parbcles to be added in the procedure of the present mvenhon. In ironically cross-linked hydrogels, the lomc bonds are weaker than the covalent bonds of the polymer backbone, and it is the ionic bonds which are preferentially disrupted and broken upon exposure to high shear sbesses. The ionic species produced when the bonds are broken are relatively stable, and in the context of the polymer systems employed herem will react only to reestablish the broken cross-links, and thus reestabbsh the high viscosity hydrogel structure once the high shear stress is removed. In an alternate embodiment, gel-forming water soluble polymers are formed into hydrogels, with or without gelation promoters such as water soluble salts of metals of Groups III to VIII of the Penodic Table. Hydrogels are based on the formahon of intermolecular bonds, between the polymer molecules. Such bonds are weaker than ionic bonds and, in the context of the present mvention, facibtate thinning of the medium under the high shear stresses imposed m the formahon of the polishing jet and providing the sacrificial bonds which protect the covalent bonds of the polymer and πurumize cham sαssion. These hydrogels also serve to promote high viscosity at rest, whether the intermolecular bonds are formed in makeup of the gel or reformed after use, which is highly desirable m preventing settling out of the abrasive particles. While a number of water soluble polymers have been employed m formulating jet sbeam pohshing formulations, including some gel-forming polymers, they have been employed without gelation promoters and at concenbations at which spontaneous gelation does not occur. The addition of such polymers in the pπor art has focused mainly on mcreasmg coherence of the jet. Without the formation of a substantial population of sacrificial bonds, the polymer is significantly degraded m a smgle use and is not reusable. The j et formulations of the pπor art are normally discarded as waste. Non-aqueous polymer formulabons are also possible where the polymer is cross-linked by other types of sacnfiαal intermolecular bonds. Such formulations are particularly significant to polishing and machining mateπals which are vulnerable to water, such as ferrous metals and the like. A preferred non-aqueous polymer, cross-linked and/or chain extended by intermolecular bonds, is the family of polyborosiloxanes. These polymers are cross-linked by electron pair sharing between tertiary B atoms m the polymer chain with O atoms in the chain of adjacent polymer molecules. The specific properhes of significance to the present mvenbon may be very directly and finely conbolled, including molecular weight of the polyborosiloxane and the like. The formulabon of pobshmg media based on the use of polyborosdoxanes, as described m greater detail below, is particularly preferred m the present mvenhon because of the non-aqueous nature of the media, the close degree of conbol of viscosity, and the ability to balance rest viscosity and high shear reduced viscosity to suit the requirements of the polishmg and machining operahons to be performed. Intermolecular bonds, including B:0 bonds, are also weaker than covalent bonds, and polymers are employed which readily form intermolecular bonds, particularly m non-aqueous jet stream processing m the present mvenhon. Under the high shear operabons mvolved in the producbon of the jet sbeam and under the forces of impact on workpiece surfaces, the intermolecular bonds will be broken preferentially, absorbing a portion of the energy imposed on the polymer, and preserving the covalent bonds which make up the polymer backbone. Hydrogen bonding alone is not adequate to afford sufficient absorption of the high shear operabons and preferably should be rebed upon only in combinabon with other non-covalent sacrificial bonds. Hydrogen intermolecular bonds are very weak bonds. These intermolecular bonds will readily reform over time once the high shear sbess is removed, restoring the cross-linked structure and the gel-like high viscosity required of the system. In the context of the present mvenhon, the cross-linking bonds, i.e., ionic or intermolecular bonds, are those first broken under the high shear and high impact conditions of the operabon, and thus sacrifice themselves to absorb the energy applied They are, in that sense, sacnfiαal bonds which serve to protect the covalent bonds from the degradation that would otherwise disrupt the polymer chains m permanent, irreversible fashion characteπsbc of the polymer degradation of the pnor art matenals and procedures. The disrupted bonds will reform spontaneously when the shear stresses are removed, e.g., when the medium is allowed to stand Breaking of the bonds converts the energy to heat, and cooling may assist m reforming the medium. The basis for the ionic bonds remains intact, as it is the ionic speαes characteristic of the formahon of such bonds in the onginal polymer medium which is produced by the breaking of the bonds duπng operation of the jet sbeam pobshmg process. Such bonds are reversibly formed in the first mstance, and exist m an equibbπum state in aqueous media m any case. The rate of reformation of the bonds is predominantly dictated by the mobility of the polymer chains m the used and degraded medium. At the reduced viscosity of the medium under such conditions, mobility is relatively substanhal, and the gel will typically reform within a few minutes of collechon It is accordingly desirable to provide for mixmg of the collected polymer soluhon and abrasive to assure the substantially homogeneous dispersion of the abrasive parbcles m the hydrogel, although it is also possible to re-disperse the abrasive mto the reformed gel after the ionic bonds are fully restored. The thinning of the polymer component m response to high appbed shear is itself of benefit to the abrasive jet sbeam formation, as the formulation will show reduced viscosity in the j et sbeam so that the appbed energy is imparted m higher proportion to the abrasive particles, enhancing their pohshing effechveness. The polymer acts to produce a highly uniform and controllable jet sbeam and serves to minimize abrasion within the equipment. It is the specific viscosity parameters and changes which permit simphficabon of the equipment requirements, relative to pnor art abrasive water jet stream techmques Because the entrainment of the abrasive m the medium occurs at make-up in the usual mixmg equipment employed, there is no need to provide a separate supply of the abrasive to the nozzle, to feed the abrasive parbcles into the sbeam, or to provide a mixmg tube, all of which are normally required m the pnor art. Disrupted intermolecular bonds will spontaneously and rapidly reform, and re-dispersion of the abrasive is rather simple to effect, if required at all. As the polymer systems are recycled through the jet sbeam pobshmg process and the reformation of the disrupted chemical bonds, there will be some disruption of covalent bonds on each cycle Although the proportion of irreversibly disrupted bonds in each individual cycle will be modest, the effect is cumulative, and after a substantial number of cycles, the permanent degradation of the polymer will become significant. As the polymer is cumulatively and irreversibly degraded, the viscosity of the reformed polymer will gradually decline, and the medium will eventually begin to exhibit an undesirable degree of tackiness In the efforts to date, the polymer thickeners employed m the water jet stream pobshmg operahons of the present mvenhon may be successfully recycled for up to as many as one hundred use cycles before replacement is required. The non-aqueous media of the present mvenbon are at least as durable, and often far more durable than the aqueous systems The number of cycles will vary, of course, with the particular polymer, the process conditions, and the like, but it is readily apparent that the medium of the present mvenhon has contπbuted a significant degree of recyclmg compared to the pπor art which does not admit of reuse of the medium after a smgle pass through the oπfice It is generally desirable to peπodically or even continuously add small quantities of "fresh" abrasive-polymer mix to maintain the consistency and uniformity of the mateπal duπng use Equivalent mcrements of mateπal are desirably removed to mamtam a relatively constant volume of the medium in the equipment Ironically cross-linkable polymers suitable for use m the present mvention include any of the water soluble polymers which form ironically cross-linked gels with metal salts, metal oxides or metal organic gelation agents of Group II to Group VIII metals Preferred species are those water -12- SUBSTrπjTE SHEET (RULE 26) soluble polymers having substantial proporhons of hydroxyl groups. The polymers may also contain active lonizable reachve groups, such as carboxyl groups, sulfonic acid groups, amine groups and the like. The ionic cross-linking polymers and cross-linking systems are similar to the hydrogels formed by intermolecular hydrogen bonding, except that the ionic bonds are only formed under conditions which promote the ionization of the cross-hnkmg species. Such conditions may require control of pH, the presence of reachon catalysts or promoters, such as Lewis aαds or Lewis bases, and the like. The formahon of such ironically cross-linked polymers is generally well known and characterized m the chemical literature, as those of ordinary skill m the art will understand. A substantial number of hydrogelable polymers and gelling agents are known, and substantially any of those available may be successfully employed m the present mvenbon. Examples of the preferred hydroxyl group containing water soluble polymers include, but are not limited to, guar gum, xanthan gum, hydroxypropyl and hydroxyethyl denvahves of guar gum and/or xanthan gum, and related hydroxyl group containing or substituted gums, hydroxymethyl cellulose, hydroxyethyl cellulose, and related water soluble cellulose denvahves, hydroxyl-group containing synthehc polymers, such as hydroxyethyl methacrylate, hydroxypropyl methacrylate, and other water soluble polymers, such as polyacrylamide, and the like. Also of interest are hydroxyl group terminated, water soluble species of low molecular weigh polymers and oligomers, such as polyethylene oxide, polyoxymethylene, and the like. Among the preferred gelling promoters of Group II to Group VIII metals that may be employed are bone acid, sodium borate, and metal organic compounds of titanium, aluminum, chromium, zinc, zirconium, and the like. A particularly preferred species for the modest cost requirements is a sodium borate gelled soluhon of about 2 to 2.5 weight percent guar gum m water. This particularly inexpensive hydrogel has demonstrated a capacity to survive up to twelve cycles of jet stream pobshmg operahons at 14 MPa followed by gel reformation with no detectable permanent degradation of the polymer gel A preferred non-aqueous intermolecular bond cross-bnked polymer is afforded by a composition of polyborosiloxane polymer, a hydrocarbon grease or oil extender or diluent, and plash zer such as steanc acid or the like, having an effechve jet sbeam viscosity. The polyborosiloxane polymers as a class are strong intermolecular bonding species and, when suitably plasticized to viscosibes suitable for jet formation, are an excellent j et stream medium for water sensibve appbeabons. In addition, the polyborosiloxane formulations are generally non-tacky, non- adherent matenals which are readily removed from the surface of workpieces after the pohshing operation is completed. The borosiloxane polymers for use m the present mvenhon will generally have molecular weights from about 200,000 up to about 750,000, preferably about 350,000 to about 500,000. The atomic rabo B:Sι will preferably be m the range of from about 1:3 up to about 1:100, preferably from about 1:10 up to about 1:50. The borosiloxanes are highly compabble with a wide vaπety of fillers, softeners and plashαzers. It is common to employ ert fillers as diluents to reduce materials costs, and to employ suitable plasbcizers and softeners to further dilute the polymer and to control viscosity In the present mvenhon, the abrasive parbcles will ordmanly be the sole mert filler, although other fillers may be employed if the amount of abrasive is correspondingly reduced As noted above, the abrasive (and other filler, if employed) may range from about 5 to about 60 weight percent of the formulation, while about 25 to 40 weight percent is generally preferred. Plashαzers and softening diluents are employed to regulate the viscosity of the abrasive j et medium. Suitable plasbcizers for use m silicone polymers are quite numerous and well known m the art and the selection of suitable viscosity controls is not narrowly significant to the present mvenhon. Suitable matenals mclude, by way of example and not by limitation, fatty aαds of from about 8 to 30 carbon atoms, parhcularly about 12 to 20 carbon atoms, such as palmitic acid, steanc aad and oleic acid; hydrocarbon paraffin oils, particularly bght oils such as "top oil" and other peboleum distillates and by-products; vegetable oils and partially or fully hydrogenated vegetable oils such as rapeseed oil, saf flower oil, soybean oil and the like, hydrocarbon-based greases such as automotive lubncahng greases and the like; mono-, di-, and tπ-esters of polyfuncbonal carboxylbc aαds such as dioctyl phthalate (DOP), dnsononyl phthalate (DINP) and the like. Liquid or semisohd sibcone oils may also be employed, and may confer considerable benefits, despite their cost, when the medium will be subjected to high temperatures and/or oxidizing conditions which may degrade hydrocarbon based plasbcizers and diluents. As mentioned, the plasbcizers and softening diluents are added to conbol viscosity of the formulabon A standing or rest viscosity of typically about 300,000 cps at ambient conditions, as measured by a Brookfield viscosimeter is suitable and convenient. As is well known, borosiloxane polymers exhibit a substanhal apparent increase m viscosity m response to appbed shear, and even exhibit plug flow through configured flow paths at high shear While there is no available technique for direct measurement of viscosity m the nozzle of the present mvenhon, we have found that formulations with standing viscosities of from about 200,000 cps to about 500,000 cps are generally suitable and a viscosity of about 300,000 is quite rebable. We have calculated effecbve viscosity as a function of the appbed pressure and resulting jet sbeam volumes and bebeve the effecbve specific viscosity at the nozzle is on the order of about 5,000 poise to about 20,000 poise. When the jet sbeam matenal is collected and allowed to stand, the viscosity rapidly returns to substantially the onginal standing viscosity, typically within five minutes or less, often within one minute. We bebeve that the return to the onginal viscosity demonstrates the reformation of the lnhamolecular B:Sι bonds and the relatively insignificant level of chain sαssion While there will be some degradation over a number of use cycles, the level does not become significant until, typically, 20 or more cycles, and may not be notable until 100 cycles or more of use have occurred. The long-term degradation LS readily offset by the peπodic or contmuous addition of fresh, unused media and withdrawal of an equivalent amount of spent media Such a procedure also serves to replace worn abrasive parbcles with new, sharp particles, and to limit the accumulation of pohshing or machining debris in the medium. In the present invention, injection of the abrasive at the nozzle is not preferred, and is generally not desired. It is prefened that the abrasive particles be mixed into the gelled polymer in a separate, prior operation, and pumped by a suitable high pressure pump to the nozzle. In the aqueous hydrogel systems, the polymer and its gelling agent will typically be on the order of from about 1 to about 20 weight percent of the medium, most often about 2 to 5 percent, and typically, for most polymers, about 2 to 3 percent. The exact proportions can be optimized for any particular gel in relahon to the parbcular abrasive, its particle size and density, and the proportion to be added. The abrasive will most often have a particle size of from as low as about 2 micrometers up to about 1400-1600 micrometers (about 16 mesh). More commonly, the abrasive grain size will be in the range of from about 20 to about 200 micrometers, preferably from about 20 to about 80 micrometers. The jet stream medium may contain from about 1 to about 75 weight percent abrasive. More often, about 5 to about 50 weight percent, and preferably about 15 to about 30 weight percent is preferred. In operabon, the formulations are employed in a fashion which differs in a number of respects from jet sbeam pohshing as practiced in the prior art and as familiar to those of ordinary skill in the art. In the context of the present invention, the polymer formulation is sensitive to viscosity in two distinct regimes. First and foremost, the polymer must afford sufficient viscosity to effechvely suspend the abrasive particles in the formulation, under low shear conditions, a parameter most closely defined by static viscosity. In addihon, the formation of the jet stream, under high shear conditions, can substantially affect the coherence of the jet and the homogeneity of the abrasive particle dispersion in the jet. These parameters are defined by dynamic viscosity. Although polymer solutions are non-Newtonian, they exhibit fluid behavior which approximates Newtonian fluids under stabc conditions. In addition, Newtonian fluid flow characteristics again predominate at high shear conditions. The time for a spherical particle to settle through a given height under the force of gravity in a static fluid requires a particular time. Thus, from fluid mechanics, 18 h H t = a 2 [D P - D L ] g where: t = Time h = Viscosity of the Fluid H = Settling Height -15- SUBSTΪTUTE SHEET (RULE 26) a = Particle Diameter Dp - Density of the Parbcle DL = Density of the Flmd g = Accelerabon of Gravity We have observed that the following assumptions, on which the foregomg formula is dependent, are sufficiently vabd for the purposes of the present invention Laminar Flow: At very low velocibes, characteπsbc of the settling of abrasive particles, flow characteristics are laminar or very nearly so Newtoman Fluid: Under nearly static conditions mvolved m parhcle settling, the polymer formulations are sufficiently flmd in character that substantially Newtoman flow characteπshcs are exhibited. Spheπcal Parbcle Shape: The irregular shape of abrasive parhcles introduces some error, but because the average parhcles do not vary widely m their major and minor dimensions, and because over a substanhal number of particles these variations tend to average out, the vaπation can be safely ignored m the present context. Formulations suitable for use m the present mvenhon will have low shear rate viscosity (Brookfield) on the order of about 75,000 to 500,000, preferably about 150,000 centipoise (cp). A 320 mesh SiC parbcle with a specific gravity of 3 will give a settling rate of 6.8 x 10" seconds per inch (approximately eleven weeks, and suitable for the present mvention) At higher shear rates, the behavior of polymer formulations becomes non-Newtonian, where viscosity is dependent on shear rate, m a Power Law relationship. This dependence holds until at a high shear rate, when viscosity agam becomes substantially independent of appbed shear, and substantially Newtoman flow characteπshcs agam apply One of the particular virtues of the jet stream formulations of the present mvenhon is the reduction m pressure required m the formation of the jet to produce effechve pobshmg effects. Typically, the pressures required will be on the order of about 5 to about 80 MPa (about 750 to about 12,000 psi), compared to pressures of typically at least 200 MPa (30,000 psi) and higher m the pnor art jet sbeam cuttmg operabons. As a convention, the pressure employed is measured as the pressure drop across the jet forming nozzle. As those of ordinary skill m the art will readily recognize, pressures of up to 80 MPa do not require the complex, expensive, and attention demanding equipment employed at pressures of 200 MPa and higher typically required m the pπor art. Thus practice of the present mvenhon require the employment of equipment equivalent m function to pressure compensated hydraubc pumps, high pressure intensifiers, and accumulators but the highly demanding engmeeπng specifications required for jet stream cutting operabons can be greatly simplified. The present mvenbon can be practiced with readily available and mexpensive convenbonal posihve displacement pumps, such as piston pumps, which may be hydraulically dπven or the like at the pressures required. At the nozzle orifice diameters effective in the present mvenbon, nozzle velocities will range from about 75 to about 610 meters per second (about 250 to about 2,000 ft per second), preferably from about 150 to about 460 meters per second (about 500 to about 1,500 ft per second), which has proven to be fully effecbve m the practice of the present mvention. Selection of the abrasive matenal is not cntical in the present mvenbon, and any of the commonly employed mateπals w l be effecbve Examples of suitable matenals mclude, for illustration, alumina, sibca, garnet, silicon carbide, diamond, and the like At higher viscosibes it may be possible to use tungsten carbide, although it's density may pose problems m maintaining effecbve dispersion m the medium. The reuse of the pobshmg medium permits economic use of harder, but more expensive abrasives, with resulting enhancements m the efficiency of pobshmg and machining operahons to increase the polishing rate when required. For example, silicon carbide may be substituted in pobshmg operations where garnet has been used In general, the abrasive will desirably be employed at concentrations m the formulation at levels of from about 3 to about 60 weight percent, preferably about 10 to about 30 weight percent. We have found that operabon at the preferred range, and lower m some cases, is quite effechve As noted above, the abrasive particles can range from 2 to 2,000 micrometers in their major dimension (diameter), preferably from about 20 to 200 micrometers. For surfaces where a fine surface finish is desired, particle sizes of from about 20 to about 100 micrometers are particularly advantageous. It will generally be appropnate to employ the smallest particle size consistent with the required pobshmg rate It is preferred that the parbcle diameter or major dimension not exceed about 20% and preferably not exceed about 10% of the orifice diameter If the parbcle size is larger, there is a nsk that "bπdgmg" across the orifice will occur, plugging the flow through the nozzle, which is self-evidently undesirable. At particle sizes of less than 20%, bπdgmg seldom occurs, and at less than 10% such effects are very rare. The nozzle shape and size is generally determined by other parameters. In particular, the design of the nozzle orifice is determined by the divergent jet stream pattern desired. A number of nozzle designs for producing a vanety of patterns of flow are known in the art, and those of ordinary skill m the art will be able to choose among them with no difficulty. The orifice may be formed from hard metal alloys, hard facmg matenals such as tungsten or sihcon carbide, cerarmc formulations, or crystalbne matenals such as sapphire or diamond. The selechon of suitable matenals will ordinarily be determined by the hardness and particle size of the selected abrasive and the cost of the nozzle matenal. Diamond is preferred Natural, compacted or synthetic diamond or "near diamond" film coatings may be employed. The standoff distance, i.e., the distance between the nozzle and the workpiece surface, has proven to be an important factor m the quahty of the surface finish attamed, but is not nearly so important as m abrasive water jet cuttmg. The present mvention is capable of pobshmg at standoff distances of up to about 25 to about 30 cm (about 10 to about 12 mches). Jet stream pohshing m accordance with the present mvention can be employed to pobsh any of the mateπals for which such techmques have heretofore been employed. Notably, particularly matenals which are difficult to machine, including many metals and alloys, such as stainless steels, nickel alloys, titanium, ceramics and glasses, rock mateπals, such as marble, granite and the like, are all effechvely pobshed with considerable precision by the present techniques. Among the benefits of the present invention, achieved usmg gel-thickened polymer media with abrasive mateπal in suspension is die ability of the present mvenbon to provide premixed suspensions of fine abrasive parbcle sizes not previously used Abrasive parbcle sizes finer than about 200 micrometers, and particularly less than about 100 micrometers, for example, were not previously preferred. Use of such fine abrasive particles m convenbonal abrasive hydrodynamic j et sbeam pobshmg and machining tended to result m abrasive mateπal ogging at angles, loops and sags m abrasive matenal feed lines, and such fine abrasive matenals are also more difficult to introduce mto jet streams m a conventional mixmg chamber or mixmg tube Because of these difficulbes, such small particle sizes have largely been avoided m the practice of abrasive jet sbeam pohshing and machining. Utilization of a premixed abrasive matenal suspension m the present mvention eliminates the need for additional feed lines and equipment in the nozzle assembly Fme abrasive particles improve pobshmg and machining quahty and precision, and reduce abrasive particle damage to the workpiece surfaces adjacent the pobshmg area. Therefore, fine abrasive parbcles may be particularly useful m appbcations where additional finishing steps can be eliminated. Having an essentially uniform suspension of abrasive matenals and having abrasive parhcles movmg at speeds comparable to those of the earner medium, which is a consequence of usmg premixed abrasive matenal suspensions, significantly reduces the tendency for abrasive matenals to bndge or pack at the nozzle orifice. Therefore, nozzle oπfice diameters can be reduced. Depending on abrasive parhcle size, nozzle oπfice diameters can be as small as about 0 1 mm (about 0.004 in.). Such smaller orifices provide comparably smaller diameter jet streams enhancing polishing and machining precision by producing more finely selective pobshmg and decreasing media consumption rates. Dispersions of the abrasive mto the medium is achieved by simple mixmg techmques, and is not narrowly significant to the practice of the mvenhon. As noted previously, the design and structure of the nozzle elements for use m the system of the present mvenhon are greatly simplified by the elimination of the mixmg tube, the abrasive feed mechanism, and the abrasive bansport conduit, typically a hose The features and their bulk, complexity, expense, weight and dependence on operator j udgment and skill are all eliminated to the considerable benefit of abrasive jet stream pobshmg and machining operahons It is also desirable that the specific design of the nozzle to be employed be configured to minimize the appbcation of shear to the polymer constituent of the jet stream medium. It is accordingly prefened that the rate of change of the cross-sectional area of the nozzle from the -18- SUBST1TUTE SHEET (RULE 26) relahvely large inlet to the outlet of the nozzle orifice be developed m smooth, fair contmuous curves, avoiding as much as possible the presence of edges or other discontinuities. Acceleration of the flow is achieved by reducing the cross sechonal area through which the medium is pumped, and high shear stresses are necessarily appbed to the polymer. It is bebeved, however, that chain scission and polymer degradataon are minimized by avoiding stress concentrations at edges and the like, where the rate of change m the sbess is very high, and proportional to abrupt changes m the rate of change of the cross sechonal area Such features in the nozzle also serve to avoid producmg turbulent flow in the medium. Coherence of the jet sbeam is favored by laminar flow through the nozzle orifice, so that the indicated nozzle configurabon serves to limit and control divergence of the stream. Minimizing induced shear sbesses is helpful m the context of all aspects of the present mvenhon. In particular, shear sbess magnitudes sufficient to generate turbulent flow m passing media are to be avoided. Shear stresses of this magnitude for high velocity flow are associated with passage over discontinuities and edges A consequence of such flow is generation of stress stresses in the media of sufficient magnitude to break polymer bonds Breaking polymer covalent bonds with the attendant irreversible molecular weight reduction are all manifestations of polymer degradation, and are best avoided or minimized when possible As illustrated in Figure 1, the operation of the pohshing procedure of the present mvenhon is represented quite simply m schemahc form Specific apparatus to perform the mdicated operahons and to practice the mvenhon are individually known to those of ordinary skill m the art. In combmation, a workpiece (10), having a surface (12) to be worked, having roughness (14) to be removed by polishing, is mounted m position so that the medium used to work on the workpiece is collected m a catchment, shown m Figure 1 as an open top tank (30). The collected medium m tank (30) is pumped via conduit (32) through an optional but prefeπed filter (84), which removes large parhcles from the medium, and then through conduit (36) to pump (80) Pump (80) fills high pressure pump (66) by passing the medium mto chamber (64), bounded by displacement piston (74), with its associated dnve mechamsm (70). When chamber (64) is full, displacement of piston (74) forces the medium at operating pressure to nozzle (20) via condmt (22), to form j et (24). In Figure 2, a more detailed schemahc view of the pobshmg operation is shown, where a workpiece (10), is exemplified in the Figure as a flat plate with pobshmg bemg performed on the upper surface (12) to remove roughness (14). In operabon, a divergent flow nozzle (20) is supphed with the fluid jet sbeam medium via a suitable conduit (22) The medium is propelled through nozzle (20) to form a jet stream (24), which is projected agamst the rough surface (14) of the workpiece (10) at an angle of about 75° from a line normal to surface (12), to remove roughness (14) The other portions of the upper surface (12) are shown as smooth, as previously produced by the pobshmg acbon of the jet sbeam (24) While the mvenbon is illustrated m the drawings with regard to flat plate workpieces, the mvenbon may be employed to pobsh and grind workpieces of any shape As those of ordinary skill m the art will readily recognize, care must be taken when pobshmg at or near corners. As the operabon is performed m the immediate vicinity of mside corners, it needs be recognized that deflection and overspray is likely to perform at least some work on the areas of the workpiece other than the specific area at which the jet sbeam is directed When workmg at outside corners, it is important to recognize that points, edges and the like are more rapidly worked than flat areas and care must be taken to avoid excessive workmg of the surface at such locations. Those of ordinary skill m the art will recognize, given the guidance of the present disclosure that the mvenbon is not limited to the specific apparatus illustrated m the drawmgs, and that the components of the system employed may be selected from among a diverse and substantial number of parts which are famibar to the art. The specific embodiments shown m the drawmgs are selected for the claπty of illustration and for their simpbcity, ready availability and low cost. Performance of the present mvenhon m pobshmg and grinding of surfaces of a number of matenals has been demonsbated to be at least equal and often supeπor to the performance of pπor art techniques. The greatest advantage of the system of the present invention stems from the capaαty to collect, recycle and reuse the medium, typically for 20 to 100 cycles for many of the formulations Another considerable advantage is the simplification of the equipment required for abrasive jet stream pobshmg and machining operahons, operating at lower pressure. These features provide considerable cost savings, and reduce dependence on the skills and expeπence of operators of the equipment. For a given abrasive particle size, we have also observed that the surface finish of the workpiece is rapidly brought to the same levels attainable with hand polishing techniques, but with far less labor and time. When coupled with the abibty to use smaller particle sizes, it is possible to produce surface finishes which require no hand surface finishing procedures, reducing the number of operabons and the amount of labor and equipment required in production. When used to break sharp edges and remove burrs, the technique is rapid, effective and readily controlled. The polishing rates attamed m the present invention vary with the conditaons employed Generally for a give matenal to be worked and a particular parhcle size EXAMPLES Examples 1 to 3. An aqueous solution of guar gum, at 40% by weight, is formed by mixmg the gum and water at slightly elevated temperature, of about 35° C, for a penod of about thirty mmutes, until the gum is fully dissolved. To the soluhon thus formed, 0.60 weight percent of a high molecular weigh alkali deacetylated polysacchande of mannose, glucose and potassium gluconurate acetyl-ester is added and dissolved. To that soluhon, an equal volume of an aqueous soluhon of 35 weight % bone acid and 2.0 weight % sodium borate is added and mixed until homogeneously blended, accompanied by the initiation of hydrogel formation To the forming hydrogel, 50 parts of SiC, having a particle size of 45 micrometers (325 mesh) is added, and the combined materials are thoroughly mixed until a homogeneous dispersion of the abrasive is achieved. The result is a friable powder hereafter referred to as a precursor concentrate. The above precursor composition is generally utilized in a dry powder form and mixed with various percentages of water, depending upon the size of the nozzle orifice through which the medium must pass during jet sbeam pohshing and machining, together with appropriate percentages of finely divided abrasive for polishing and machining. Preferably, but not necessarily, a minor amount of paraffin oil or hydrocarbon grease is added to the composition as a humectant to inhibit formation of crust upon the medium if it is not used immediately. The characteristics of suitable formulations by volume for different nozzle orifice sizes are bsted below in Table I. TABLE I Nozzle Orifice Vol. % Vol. % Static Example Size (mm) Water Oil Abrasive Viscosity 1 0.129 20-50 1-10 0-20 72,00C 2 0.254 10-20 0-5 0-20 368,00C 3 0.635 7-12 0-3 0-20 4,520,00C The oil component in the above-defined compositions not only delays or prevents crusting. It also controls tackiness. With httle or no oil, the medium may be adherent to metal as well as the hands of the operator. A suitable humectant oil is, therefore, a preferred additive. Sometimes, shelf life of the above media is limited to attack by bacterial or fungal growth. The addition of a very small amount of a biocide, such as methyl- or parahydroxy-benzoate, typically in proportions of less than about 1%, and often less than about 0.5%, is often helpful to control such attack. Examples 4 to 26. The following components were combined in a planetary mixer: Component Parts By Weight Polyborosiloxane 35.0 Stearic Acid 21.5 Light Turkey Red Oil 8.5 Hydrocarbon Based Grease 35.0 The polyborosiloxane had a molecular weight of 125,000 and a ratio of Boron to Sihcon of 1:25. The grease was an automotive chassis lubricating grease obtained from Exxon. The components were mixed under ambient conditions until a smooth homogeneous blend was achieved, and was then divided into portions. Each portion was then combined and mixed with abrasive particles, as indicated in Table II, to form a plurabty of abrasive jet stream media. Each formulation was adjusted by the addition of steaπc acid to produce a standmg viscosity of 300,000 cp. Each of the media formulations was employed to pobsh aluminum plate under the condibons indicated in Table II, and the surfaces were evaluated. TABLE π Δ B C β £ i G H I 4 SiC 40 220 0.020 1 6 3000 80 946 5 SiC 25 220 0.020 025 4000 80 9.46 6 Garnet 50 220 0020 025 4000 80 946 7 BC 58 320 0.015 0075 7200 80 946 8 SiC 58 320 0015 0.075 7400 80 946 9 SIC 58 320 0015 0075 7200 80 946 10 SiC 58 320 0.020 0.75 7400 50 46 11 SiC 58 320 0020 075 7400 60 946 12 SiC 58 320 0020 075 7400 70 946 13 SiC 58 500 0015 0075 7100 87 946 14 SIC 58 500 0020 0075 7100 85 946 15 SiC 58 320 0.020 0075 7100 80 946 16 SiC 58 320 0.020 0075 7000 70 946 17 SiC 58 320 0020 0 50 7200 70 9.46 18 SiC 58 320 0020 1 00 7200 70 946 19 SiC 58 320 0.020 1 50 7200 70 946 20 SiC 58 320 0.020 0075 7000 88 946 21 SiC 58 320 0.020 0075 7000 80 946 22 SiC 25 320 0.012 0.50 9700 88 946 23 SiC 25 320 0.012 050 9700 85 946 24 SiC 25 320 0012 0.50 9700 80 946 25 SiC 25 320 0.010 0.50 9700 75 946 26 SiC 25 320 0008 0.50 9700 70 946 Legend A - Example No D ' * Mesh G " Pressure (psi) B = Abrasive h = = Nozzle Dia , ιn |dn] H = Angle of Incidence, (deg ) C = Conc (wt %) F = ■ Stand Off, in [SOD] Ratio 1 - Initial Roughness Ra (μm) As shown by Table II, a wide vanety of conditions may be employed m the present invention. High quahty pobshed surfaces were obtamed, which vaπed with the abrasive mesh size and, to a lesser degree with the angle of mcidence. All angles were measured relahve to the normal to the surface of the plate. Examples 27 - 62 The base formulation used m Examples 4 - 26 was agam employed, and mixed with the abrasives set out m Table III; the viscosity was agam adjusted with steanc acid to a restmg viscosity of 300,000 cp, and the formulation was employed to pobsh alummum plate. The pohshing conditions are set out m Table III. The characteπshcs of the pobshed surfaces of the plate were measured for surface roughness. The measured values are set out m columns G and H of Table III. [Table III appears on the next page.] As those of ordmary skill in the art will readily recognize, the surface finishes measured and reported in Table III are of exceptional quahty The foregoing examples are intended to be illustrative of the present invention, and not limiting on the scope thereof The mvention is defined and limited by the followmg claims, which set out in particular fashion the scope of the mvention -25- SUBSTrrUTE SHEET (RULE 26)

Claims: CLAIMS What is claimed is: I. A method of jet stream polishmg and grinding the surfaces of a workpiece, omprising the steps of: A. forming a fluid jet stream medium, wherem said fluid jet stream medium comprises a particulate abrasive suspended in a viscous earner medium; B. projecting said fluid jet stream medium at a surface of a workpiece at an angle of incidence at least about 45° from a line normal to said surface for a time and at a pressure sufficient to reduce roughness of said surface. 3. In the method of abrasive jet stream pohshing and grinding of claim 1, wherein a plurality of abrasive parhcles is suspended in a flowable jet medium and projected at high velocity and pressure at a workpiece, the improvement comprising: A. forming said medium of a polymer having referable sacrificial chemical bonds which are preferentially broken under high shear conditions; B. projecting said medium and suspended abrasive at said workpiece to effect said polishmg and grinding under shear conditions which break said referable sacrificial chemical bonds; C. reforming said chemical bonds; and D. recycling said medium and abrasive for reuse in the method. 4. The method of claim 3 wherem said medium is pro j ected through an oπfice to form a jet stream at a pressure of from about 5 to about 80 MPa. 5. The method of claim 4 wherein said j et stream is projected at a velocity of from about 200 to about 1,000 ft per second. 6. The method of claim 3 wherem said abrasive particles have a particle size of from about 2 to about 1,600 micrometers in their major dimension. 7. The method of claim 3 wherem said medium is an aqueous gel of a water soluble polymer ironically cross-linked with a compound of a Group II to Group VIII metal. 8. The method of claim 3 wherem said medium is a non-aqueous plasticized polymer which forms mtermolecular bonds to form a gel. 9. The method of claim 3 wherein said gel has a static viscosity of from about 200,000 to 600,000 centipoise. 10. The method of claim 3 wherem said medium is an aqueous hydrogel of from about 1 to about 20 volume percent of a hydroxyl group containmg water soluble polymer gelled by formation of mtermolecular hydrogen bonds promoted by the action of a gellmg promoter containmg a metal from Group II to Group VIII. II. The method of claim 3 wherem said jet stream is formed by forcing said thickened aqueous medium through a nozzle means hav g an mtenor entry port surface and mtenor exit orifice surface with an interconnecting transition zone surface; all of said entry port surface, said transition zone surface and said exit orifice surface bemg in contact with said thickened aqueous medium passing through said nozzle means and said transition zone surface and said exit onfice surface defining a continuous function without discontinuities. 12. The method of claim 4 wherem up to 50 weight percent of said abrasive particles are added to said medium. 13. The method of claim 5 wherem said water soluble polymer is a member selected from the group consistmg of guar gum and its hydroxypropyl denvatives, cellulose denvahves including carboxymethylethyl cellulose, or synthetic hydroxyl functional polymers including polyacrylamide and polyoxymethylene. 14. The method of claim 8 wherem said medium compnses from about 1 to about 20 volume percent of said water soluble polymer. 15. The method of claim 5 wherem said aqueous medium compnses from about 50 to about 75 weight percent of guar gum, from about 30 to about 40 weight percent of bone acid, and from about 1.0 to about 2.5 weight percent sodium borate. 16. The method for jet stream pohshing and grinding wherem collecting said jet stream a catchmg means after said jet stream has worked a workpiece, wherem said catching means compnses a containment vessel and a decelerating medium for decelerating said jet stream. 17. The method of claim 34 wherem said decelerating medium compnses the same medium as used to form said jet stream. 18. The method of claim 35 wherem said deceleratmg medium and said decelerated medium are recycled for reuse as jet stream medium. 19. The method of claim 3 wherem adding up to 10 weight percent of a humectant od to said thickened aqueous medium. 20. The method of claim 3 wherem a biocide is added to said thickened aqueous medium. 21. The method of claim 8 wherem providing a soluble thixotrope for improved rheological behavior. 22. The method of claim 31 wherem addmg about 0.25 to 0.60 weight percent of a high molecular weight polysacchande to said gelation agent. 23. The method of claim 32 wherem said polysacchande compnses the alkali deacetylated denvahve acetyl ester of a polymer selected from the group consisting of mannose, glucose, potassium glucuronate, and mixtures thereof. 24. A polymer containmg abrasive jet stream pohshing medium compnsing a particulate abrasive dispersed m a polymer composition, said polymer havmg referable sacrificial chemical bonds which are preferentially broken under high shear conditions and which reform under low stress conditions, said polymer composition havmg a rest viscosity or from about 100,000 to about 500,000 cen poise, and a dynamic viscosity of from about 3,000 to about 30,000 poise under shear conditions represented by flowing said medium through an onfice havmg a diameter of from about 0.1 to about 1 mm at a pressure of from about 5 to about 80 MPa 25. The abrasive jet stream polishing medium of claim 24 wherem said referable sacrificial chemical bonds are gel forming cross-link bonds, selected from the group consisting of ionic bonds and mtermolecular bonds 26. The abrasive jet stream polishmg medium of claim 24 wherem said medium compnses an aqueous hydrogel of a water soluble polymer and a gel promoter 27. The abrasive jet stream pobshmg medium of claim 24 wherein said water soluble polymer compnses guar gum and its hydroxypropyl denvahves, cellulose denvahves including carboxymethylethyl cellulose, or hydroxyl terminated synthetic polymers including polyacrylamide and polyoxymethylene and said gel promoter compnses a metal oxide or metal organic compound for promotmg hydrogel formahon compnsmg a member selected from the group consistmg of bone acid, sodium borate, organometalhc compounds of at least one Group II through Group VIII metal, and mixtures thereof. 28. The abrasive jet stream polishing medium of claim 27 wherem said gel promoter is an organometalhc compound of a metal selected from the group consistmg of titanium, aluminum, chromium, zinc, zirconium and mixtures thereof. 29. The abrasive jet stream pobshmg medium of claim 26 wherem said hydrogel compnses from about 1 to about 20 volume percent of said water soluble polymer and about 99 to about 80 weight percent water. 30. The abrasive jet stream polishmg medium of claim 26 wherem said medium further compnses a water soluble thrxotrope 31. The abrasive jet stream polishmg medium of claim 26 wherein said hydrogel polymer compnses from about 50 to about 75 weight percent of guar gum reacted with from about 30 to about 40 weight percent of bone acid and from about 1.0 to about 2.5 weight percent borax. 32. The abrasive jet stream polishing medium of claim 26 wherem said medium further compnses about 0.25 to 0.60 weight percent of high molecular weight water soluble polysacchande 33. The abrasive jet stream polishing medium of claim 32 wherem said polysacchande compnses the alkali deacetylated acetyl ester of potassium glucuronate 34 The abrasive jet stream polishmg medium of claim 26 wherem said medium further compnses about 0.5 to 100 weight percent of a humectant od 35. The abrasive jet stream polishing medium of claim 24 wherem said abrasive parhcles compnse alumina, silica, garnet, tungsten carbide, sihcon carbide, and mixtures thereof. 36. The j et stream polishing medium compnsmg of claim 24 a non-aqueous plasticized cross-linked polymer gel, cross-linked by mtermolecular bonds, said medium havmg a stahc viscosity of from about 200,000 to about 600,000 cenhpoise. 37 The j et stream pobshmg medium compnsmg of claim 36 wherem said polymer is a polyborosiloxane havmg boron - oxygen mtermolecular cross-linking bonds. -28- SUBSTTTUTE SHEET (RULE 26) 38. The jet stream polishing medium compnsmg of claim 36 wherein said polyborosiloxane has a molecular weight of from about 200,000 to about 750,000, and a boron - silicon atomic ratio of from about 10 to about 100. 39. The jet stream pohshing medium compnsmg of claim 24 wherem said abrasive parhcles have a maximum dimension of from about 2 to about 1,400 micrometers 40. The jet stream pohshing medium compnsmg of claim 24 wherein said abrasive particles have a maximum dimension of from about 10 to 200 micrometers. 41 The jet stream polishmg medium compnsmg of claim 24 wherem said abrasive particles have a maximum dimension of from about 20 to about 100 micrometers. 42. The jet stream polishing medium compnsmg of claim 24 wherem said medium has a viscosity at rest of about 300,000 cp.

Inventors: RHOADES LAWRENCE J, RHOADES, LAWRENCE, J.
Applicants: EXTRUDE HONE CORP, EXTRUDE HONE CORPORATION
Application year: 1997
Main classification: B24B1
IPC codes: B24C1, B24C11