US2332133A - Apparatus for smoothing surfaces - Google Patents

Description

19, 4 R. w. DAYTON 2, ,1

APPARATUS FOR SM OOTHI NG SURFACES Filed Jan. 1, 1942 3 Sheets-Sheet l U Fi .3

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RUSSELLWDHYTQN Oct. 19, 1943. R. w. DAYTON APPARATUS FOR SMOOTHING SURFACES m MN M o E W PCLJSHiNG TIME. IN MINUTES 1943- R. w. DAYTON 2,332,133

APPARATUS FOR SIMOOTHING SURFACES Filed Jan. 1, 1942 3 She'ets-She'ei s Fin/3 'ffussL-L L WUH YTUN Patented Oct. 19, 1943 PATENT" oF lca 2,332,133 APPARATUS FOR SMObTHING SURFACES Russell Wendt Dayton,

Columbus, Ohio, assignor,

by mesne assignments, to Norton Company, Worcester, Mass, a corporation of Massachusetts Application January 1, 19 42, SerialNo. 425,312

- 3 Claims.

This invention relates to an apparatus for smoothing metal articles.

The standard apparatus used for grinding crankpins, sleeves andv various other bearing parts of gasolenemotors has required that the engine be broken-in slowly and under reduced power for a long initial period. That is, the comparatively rough surfaces with their scratches and sharp projections formed by a standard grinding, milling or turning operation should be worn down materially before the maximum load is applied, since any attempt at running the motor-initially at its full speed and under a normal or maximum load may result in pitting, galling, scoring or other detrimental wear on the bearing surfaces or cause them to seize. An aircraft motor may have to be broken-in for,ten or more hours before it can be used to develop its full horse power, and during this initial period the motor will consume a large amount of fuel and require the attention of experts and special apparatus for dissipating the power. in that wearing-in time would represent a large saving to the aircraft industry.

Various procedures and types of aparatus have been provided for creating a finer finish or smoother surface on such wear parts, such as the honing, lapping and superfinishing operations now in use. The standard apparatus involves the use of a solid rotatable abrasive wheel ora reciprocable abrasive stick or other type of movable tool in which the individual abrasive grains are bonded together as a rigid body by means of ceramic, resin, rubber or other bonds, or they are supported substantially rigidly during use, such 'as when carried by a metal or fibre surface charged or coated therewith. A standard procedure involves so moving the rigidly supported abrasive material relative to'the work piece that the abrasive grains travel in a series of crisscross or non-repeating paths and tend to develop a matte surface which may be ultimately reduced to a comparatively smooth finish. Such an operation may involve the useof expensive machinery and take a comparatively long period of time for finishing the surface. It has also been proposed to rub loose abrasive grains over a surface to be polished by means of comparatively rigid bodies which are rotated or reciprocated relative to the work. In that operation,- the abrasive grains are dragged or rolled around between the movable backing member and the work and thus still have a large opportunity for scratching the work surface. It is my belief that a rigidly supported abrasive grain necessarily A reduction scratches the surface over which it moves so that the finish is made up of closelyv spaced scratch marks; hence extremely fine abrasive grains and light pressures and a long-continued operation smooth surface.

In accordance with my experimentation, I have discovered that the ridges and projections left by a milling or lathe tool or by the application of rigidly supported abrasive grains in a standard grinding operation may be removed in a short period of time by means of loose abrasive material moved at high speed across the work surface by means of a soft and resilient applicator.

The primary objects of my'invention are to solve the above problems and to provide an apparatus which will serve for smoothing a metal surface rapidly, efflciently and economically,

Another object is to smooth a metal surface intended to contact slidably with another'surface and thereby to reduce the friction t2.:rebetween, or the tendency for seizure, or galling, or scoring, or scuffln'g, or the cutting wear or abrasion thereof.

A further object is to smooth a metal surface and thereby to reduce the tendency for such a surface to corrode or to crack under fatigue or otherwise to fail when operated in sliding contact with another surface in various types of 30mechanisms. a

A still further object is to provide a smoother bearing surface and to reduce the time of wearin for airplane and automobile parts or other mechanisms and to reduce th numberof failures as that occur in critical operating parts during such wear-in periods and the later operations of normal use. Other objects will be apparent in the following disclosure.

In accordance with my invention, loose abra- 40 sive material is momentarily supported by a rapidly moving, soft and resilient backing member and passed at highspeed across and in yielding contact with the work surface under conditions which cause the abrasive to remove the fuzz or fine roughness and round off the contours of the ridges and projections of the work surface caused by grinding or other preliminary shaping opera-.

tions. To that end, the work piece may be held stationary or mounted for rotation or a cyclic reciprocation, and preferably at a slow rate, while a slurry of abrasive grains suspended in a suitable fiuid medium, such as oil or water, is pro-' pelled rapidly across that surface by a soft and yielding member, such as a rubber, felt or other type of body, which is rotated or otherwise moved may be required to produce a satisfactorily at a comparatively high rate of speed. The abrasive propelling body is preferably a rotatable wheel having a .body or surface layer of what may be termed live rubber adapted for temporarily supporting and moving the abrasive grains rapidly in a yielding and sliding contact with the work but without itself being worn away at a material rate.

Various types of soft resilient bodies will serve my purpose, provided they will carry the abrasive slurry through the zone and support it so lightly that it will not scratch the work materially; but I prefer to employ -a sponge rubber or similar type of soft, yielding and resilient material which contains a substantially uniform dispersion of separate cells of substantially equal sizes separated by flexible webs of rubber. Such a wheel presents at its surface a large number of small pockets or open cells capable of supporting the abrasive slurry and carrying it through the smoothing zone.

Referring to the drawings:

Fig. 1 illustrates diagrammatically the princi ples of the method;

Fig. 2 is a diagrammatic view of one form of apparatus adapted for carrying out the method;

Fig.8 is a curve showin gthe rate of removal of stock by this method; and

Figs. 4 to 15 inclusive are reproductions of photographs and curves showing the results obtained by the method and apparatus.

Many types of apparatus may be employed, such as a modified form of a standard cylindrical grinding machine, in which the grinding wheel is replaced by sponge rubber or other suitable type of abrasive impelling body, and wherein the cooling water or aqueous compound, that is customarily used for removing heat from the work, is replaced by an abrasive slurry. This operation may also be performed in a modified centerless grinding machine in which the grinding wheel is replaced by a sponge rubber wheel and the slurry is fed thereto. The work regulating wheel in such a machine may be of a standard or suitable construction and preferably one with a surface which will serve to rotate the work without scratching it. A wheel made of rubber or one containing bonded abrasive grains of fine size may be employed for rotating the work. Similarly, for polishing plane surfaces, it is desirable to employ a cylindrical grinding wheel making only a substantially linear or narrow band contact with the work, as distinguished from a type of wheel which makes an extensive surface contact as is found in a lapping or plane surfacing machine. The work may be moved or held substantially stationary depending on the work shape and the requirements of a particular operation.

Referring to Figs. 1 and 2 of the drawings, a preferred type of machine for polishing cylindrical work pieces comprises a rotatable sponge rubber wheel l suitably cemented to or. clamped between collars on an arbor II which is rotated rapidly by an electric motor l2 belted thereto or by other suitable mechanism. The work piece l5, shown as a cylindrical piece, may be suitably mounted between clamping rings on an arbor and arranged for slow rotation by a motor IE or other suitable source of power. The wheel and work may be rotated in various directions but preferably downwardly in the smoothing zone or in the direction of slurry feed, as indicated by the arrows in Fig. 1. The abrasive slurry i1 is fed to that zone from a nozzle l8, preferably shaped to provide a narrow and elongated outlet arranged to supply a thin stream across the entire width of the rubber wheel, which is preferably as wide as the work except where a long piece of work is to be smoothed. A sump 20 may be arranged beneath the smoothing zone to catch the slurry 2|, and a suitable pump 22, such as a centrifugal blade type of pump, is arranged to withdraw the slurry through the pipe 23 and feed in through the pipe line 24 to the nozzle I8. A by-pass pipe 26 may be used to force some of the slurry back into the sump and keep it agitated and hold the abrasive in suspension. Valves 2! and 28 may serve to control the slurry feed. Various types of machine constructions may be employed for controlling the operation. If the work is long and it is desired to provide for a relative traversing between the wheel and the work the construction of Fig. 2 may be employed.- The wheel may be rotatably mounted in suitable bearings carried on a wheel slide 29, the position of which is adjusted manually by a screw 30 and cooperating half nut 3| to locate the wheel properly and provide the required pressure between the wheel and the work. The wheel may be fed forward periodically to make adjustment for the unavoidable surface wear of the wheel. The work piece may be suitably mounted on a reciprocable slide 32 mounted on V- and flat ways 33 and traversed manually or automatically by means of standard constructional features. Many types of grinding machine ha ing a rotatable grinding wheel may be readily adapted for this operation.

The rubber sponge wheel l0 may be made by any standard method, such as is involved by incorporating with the plastic rubber and sulfur and other vulcanization agents a suitable powdered medium, such as ammonium carbonate, which is distributed throughout the mass. When subjected to heat this forms a gas and blows the rubber into a cellular structure. The rubber may then be cured or vulcanized to a suitable degree, but it is preferably left in a very soft condition, such as is obtained by the use of only a small amount of sulfur, such as 3% or less by weight. The sponge rubber may also be made by incorporating sulfur in rubber latex and forming a foam therefrom. The foam is shaped and the latex then coagulated, heat being applied to cause suitable vulcanization of the rubber. The sizes and spacings of the cells may be suitably varied and various types of structure made as desired. The standard types of sponge rubber sold on the market for domestic use as scrubbing sponges and flexible pads may be readily used. Suitable steps may be taken to mount the shaped cylindrical body as a wheel, such as by vulcanizing the sponge rubber to outside plates of rubber or metal arranged for mounting on the wheel spindle.

Although various types of abrasive materials.

may be used for the polishing compound, including silicon carbide, boron carbide, metallographic rouge and emery, I find that crystalline alumina and levigated alumina give the best results, and probably because they are not so sharp cornered and quick cutting as are the carbides, but have smoother surfaces and are tougher and more durable and are thus able to remove the very fine projections on the surface of the work without forming new deep scratches therein. The polishing compound should be very finely divided in size. For example, it is preferred that the crystalline alumina be as small as 600 grit size or finer, such as is obtained by water classification, and it is also desirable that the powder be free from elongated splinters or over size particles which could form deep scratch marks. Levigated alumina is preferred for polishing certain metals because of its non-scratching nature, and its extreme fineness, and because of the greater ease of maintaining a suspension. Levigated alumina is an impalpable powder of loosely bonded ag regates of alumina crystals but which has not been crystallized from a fused bath.-

The selected polishing compound may be suspended in any suitable material, such as water or kerosene or other oil. If water is used, it is preferable to have a rust preventive incorporated therein, such as soda or soap compounds, etc. A satisfactory slurry has the following composition:

Parts by weight Levigated alumina 91.4 Tri-sodium phosphate 7.1 Sodium chrom 0.4 Water 71.1

While various work and wheel speeds may be' 'close to the point of contact between the wheel andthe work, and in order to maintain proper working conditions it is preferred to force the rubber wheel into the work under a low pressure, such as 1 to pounds per linear inch, depending on the porosity and flexibility of the wheel. For

example, the wheel may be moved into contact w .1 he work and then forced forward about 0.075 inch. I

The rubber webs yield or bend as they touch the work and so form a wide band or zone of contact, which insures that the abrasive carried in the cells in the .face of the rubber wheel will maintain contact with the work for a material length of time and long enough to rub across some of the ridges or projections in the slowly rotating or-stationary work surface. The work and the wheel may rotatein opposite directions but preferably downwardly in the same direction at the point of contact, when the slurry is introduced from above. Hence, each projecting ridge of the workpiece is subjected to the rubbing action of the abrasive carried by an appreciable width of wheel surface in the operating zone.

Although this invention is not to be construed as limited to any particular theory of operation, I believe that the open pockets," (Fig. 1 of-the sponge rubber, which move "at a high speed through the operating zone, serve to'carry the abrasive grains in a predetermined path in smoothing contact with the work surface, and that this high speed wheel provides each individual abrasive particle of the slurry with sufficient kinetic energy'to insure that it will have enough rubbing contact with the work to accom plish the desired purpose. That is, it is the kinetic energy of the abrasive particles: that causes thesmoothingoperation, and the rubber that it will not be permitted to scratch deeply into the work, as is the case when the grain is confined in a rigid mounting or beneath the extensive surface of a plane faced rigid or flexible wheel. Also, the high speed wheel cells serve to move the slurry in a plane or a slightly arcuate band shaped path and so cause a large proportion of the grains to touch the narrow contact" face of the work rather than permit them to ass through the outer space without abrading contact, as would be the case if one directed a high speed stream of slurry against the workwithout the presence of the yielding wheel body to position the grains. Hence the wheel not only pro- *vides the kinetic energy sufficient to cause the which an abrasive grain is forced to travel through an arc of contact with the work so that wheel serves chiefly to-provide that energy rather than to accomplish any abrasion directly. At the same time, the very soft and yielding rubber it cuts a groove of an increasing and then decreasing depth. That is, a rigid wheel removes metal by the successive applications of rigidly supported abrasive grains which are obliged to cut a series of arcuate shaped channels through the work and thus generate a surface. In my process the wheel and the abrasive do not generate a surface but merely smooth that surface. The wheel is so flexible and deformable that it cannot reduce the size of the work much beyond that of smoothing'down the surface ridges.

The major portion of the finishing operation is accomplished in the first few seconds of application of the abrasive slurry and thereafter the reduction in work size is hardly measurable, as is shown by the curve in Fig. 3 which represents the decrease of weight per minute of time of a ground work piece when smoothed by an abrasive slurry and a sponge rubber wheel. This curve shows that the major portion of the fuzz or the higher projections on the work surface is removed in about the first ten or fifteen seconds of operation. The diameter of the work piece is not decreased appreciably; but it is found that for a rough ground work piece the diameter may be decreased by about 2 to 5 micro-inches in depth, as calculated from weight loss figures. After the surface fuzz has been removed in that first short, period of time, the metal removal is much slower and may practically cease, and the diameter is not thereafter decreased measurably although the operation continues to smooth the surface. A harder rubber wheel works much slower'and less efilciently. It is an important feature of this invention that the work surface is brought to substantially a final and satisfactory finish within a short time, such as within a few minutes, so that the time consumed in polishing work pieces is extremely small as compared withthe slow moving time-wasting operation of lapping wheels and reciprocating honing sticks which are required to size the work as well as to finish its surface. It, of cdurse, is-to be understood that this operation of my invention does not serve to size the work except incidentally and that its primary purpose is to form a smoother surface.

This method is. useful for finishing all types' of surfaces and particularlythose which have been ground, lapped or, otherwise finished by rigidly supported abrasive grains and which have been ground to the desired dimensions and require only that a wear surface be made smoother. A roughly ground surface may have the general appearance shown in Fig. 4 which shows a taper section, enlarged in the vertical dimension, of a piece of steel that has been subjected to a standard type of grinding operation. It will be observed that the surface has high projections and deep crevices therein. As the result of subjecting such a surface to a smoothing operation by means of a sponge rubber wheel and abrasive slurry as above described that surface has the appearance shown in Fig. 5. This shows that the operation is one of removing the high projecting ridges and smoothing over the resultant surface although the crevices or deep scratch lines between the smoothed parts are not materially affected. A surface originally ground to a fine finish may not have the deeper scratch lines, and my smoothing operation may not give as marked an effect, although the actual smoothing of the surface is very substantial. Surfaces having fuzz are addicted to galling; hence the removal of the fuzz by this smoothing operation makes galling unlikely, so that a shaft and its bearing may wear in properly.

Figs. 6 to 8 inclusive show the effect of, this smoothing operation on a piece of steel used in an aeronautical motor which has a hardness of 59 on the Rockwell C scale and made of carburized S. A. E. 3312 steel. The steel was subjected to a normalgrinding operation in which the work was rotated at 100 R. P. M. and the grinding wheel at 6200 S. F. M., the wheel being a standard wheel that .was considered best adapted for sizing the work piece. The grinding wheel produced a standard type of surface having a roughness measured as 8 micro-inches on a profilometer. The same piece of steel was also subjected to a superfinishing operation which gave a profilometer measurement of only 0.8 micro-inch. These specimens were polished by means of a sponge rubber wheel of four inches diameter and rotating at 1750 R. P. M., the slurry being levigated alumina suspended in water. These particular specimens were. held against the smoothing wheel by hand and thus were stationary. They were smoothed with the direction of rotation at right angles to the initial scratch direction and this smoothing was performed only in spots for a comparison of the surfaces.

Fig. 6 shows a photomicrograph of 100 magnification, vertical illumination, of the original piece after it had been rough ground. The vertical lines in this illustration represent the scratch marks or the ridges on the work surface. Fig. 7 shows the surface appearance of that rough ground piece after a 2.5 minute smoothing operation. Fig. 8 shows the appearance of both the ground and the smoothed parts of the same work piece, the photograph being one of four magnification, axial illumination. The central dark spot represents the smooth portion after a one minute treatment by my process and the outer lighter part represents the rough ground and unsmoothed portion. Fig. 9 shows the surface appearance of a work piece after a superfinishing operation, when in a fine grained abrasive block had been passed repeatedly across the surface ofthe work with a criss-cross or break up motion. The criss-cross scratch marks, which show clearly in the two outer portions of .the photograph, measured about 0.8 micro-inch on the profllometer. Although that piece had a very .smooth surface, yet it was made much smoother by my process, as shown by the central dark portion representatlng the part that had been subjected to a one minute smoothing operation by my sponge rubber wheel and abrasive slurry. Fig. 10 shows a photomicrograph, magnification, of a similar superfinished steel piece prior to the smoothing operation and wherein the criss-cross lines are clearly evident, these lines having a profilometer measurement of 0.8. Fig. 11 shows the final appearance of the super-finished steel piece of Fig. 10 after it had been smoothed for 2.5 minutes by my process. It will be evident that the criss-cross marks have been eliminated.

Fig. 12 shows a curve made by a brush analyzer which indicates the profile of the surface of, a ground work piece. The vertical magnification is 40,000 and the horizontal magnification 85. The work piece had been ground by a grinding wheel of resin bonded abrasive grains of extremely fine size, smaller than 500 grit size. Fig. 13 shows 'the brush analyzer curve for the same piece of of honing or superfinishing abrasive blocks.

Ordinarily. one minute is sufficient time for removing the original scratches from a superfinished body and produce an entirely different type of surface. Since this method does not change the dimensions of the work piece materially, it can be used after the proper size has been obtained by standard procedure. It will be evident that the smoothing operation serves not only to remove the minor scratch marks but to round over the projections and the side surfaces of the deeper scratch marks and thus remove all but the major imperfections. Because of the smoother surface thus provided, a metal bearing is less likely to corrode or to crack under fatigue, and the tendencies toward seizure, galling, pitting, scoring and scufiing are minimized. Hence, a bearing surface as thus smoothed has many of the characteristics of one which has been carefully run in by slow movement for a long period of time.

It will now be appreciated that many modifications may be made in this apparatus and that various types of abrasive materials may be used. Numerous shapes and structures of abrasive propelling wheel are also usable, depending upon the desired results; but I have found that the spongy and softer types of rubber wheel are more efllcient and economical in use than are those wheels having a harder although flexible rubber surface. The speeds of rotating the work and the wheel may be widely varied, provided the operation is so carried on as to propel the abrasive slurry across the work surface at a comparatively rapid rate as distinguished from a slow moving scouring action involved in the standard polishing operations, such as those heretofore conducted with abrasive powder embedded in the soft face of a wheel or loosely rolled and rubbed around between a polishing body and the work. Hence, it will be understood that the above disclosure is intended to set forth the principal features of my invention and the preferred methods and embodiments thereof and not as limitations on the claims appended hereto.

I claim:

1. An apparatus for smoothing the surface of a metal work piece comprising means for supporting and rotating the work piece slowly, a soft elastic yielding sponge rubber wheel having open surface pockets on its periphery, means for rotating the wheel rapidly in the direction of work rotation at the point of contact, wheel and holding its periphery in. a wide band rubbing contact with the work, means providing a supply of a slurry of finely divided abrasive suspended in a liquid medium, and means including a pump for feeding said slurry to the surface pockets of the wheel in substantially the direction of its rotation, said rotating wheel serving to propel the slurry rapidly in an extensive wide band contact with the work surface and cause it to smooth the work by a'succession of momentary applications of loose abrasive grains moved at high speed and pressed lightly and yieldingly against the work.

2. An apparatus for smoothing the surface of a metal work piece comprising means for supporting and moving the work surface slowly, a wheel whose peripheral surface portion is made of a freely yielding resilient material having open face gportion against the pockets, means for holding said peripheral surwork in a' contact zone of variable width, means rapidly relative to the surface speed of the work, and means associated therewith for supplying continuously to said pockets as they approach the work a slurry of fine abrasive powder carried in a body of liquid, so that the slurry is propelled freely in one direction across said contact zone and the work is smoothed by a succession of momentary applications thereto of loosely supported rapidly moving grains.

3. An apparatus'for smoothing the surface'of a metal work piece comprising means for supporting and rotating the work piece, a wheel whose peripheral surface portion is formed of rubber sponge having open cells separated by resilient webs, means for rotating the wheel at a rapid surface rate, regulatable means for holding a variable area of said peripheral wheel surface yieldingly against a narrow moving contact zone on the work, and means including a nozzle for feeding to said cells on that part of the peripheral wheel,

surface which is approaching the work a slurry of finely divided abrasive material suspended in a liquid, said parts being so constructed that the wheel propels the slurry rapidly in one direction acrossthe contact zone of the work.

RUSSELL WENDT' DAYTON.

for rotating the wheel

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