US2358861A - Grinding element - Google Patents

Description

Sept. 26, 1944. E.'A. Kol-:THER

GRINDING ELEMENT Filedmg. 2s, 19213 'LQ-QM.

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Gftorncgs Patented Sept. 26, 19.44

Y Emil A. Koether, Baltimore, Md.

Original applicationy January 24, 1940, Serial No. 315,438. Divided and this application August 23, 1943, Serial No. 499,687

1 Claim.

This invention relates to abradi'ng and particularly to means for improving the accuracyof grinding operations by cooling the grinding elements as uniformly and as effectively as practicable and by substantially preventing the transfer of heat from the grinding member to the supporting portions of the grinding machine, particularly the shaft bearings.

Arrest of the flow of heat from the grinding member to such supporting portions is a .sub-

stantial factor in the attainment of the desiredv result. Contrary to what might be expected, tests show that arrest of this heat flow (Without stimulation of air cooling, and even when the grinding surface of the disc and the air iiow over this surface of the disc are the same'as With conventional mounts) results in enhanced heat dissipation, as evidenced by marked reduction in the temperature of the discharging ground arti,-

cles. It is not here intimated that active cooling will not still further improve the operating conditions, particularly` with heavy cuts. The significant fact is that arrest of heat flow from Athe grinding disc toits support has a benecial effect which is always substantial and under some ing disc is unevenly heated, its form is affected and inaccuracies' result. Similarly, if the face plate on which the disc is mounted' is heated, and particularly if it is unevenly heated, similar distortions are caused. Finally, transmission of heat to the bearings increases the lubrication problem and requires the bearings to be more freely fitted when cold than would be required if it could be 'assured that the bearings would run cool at all times.

The present invention involves the mounting of the grinding disc on the face plate in such a Way that the grinding disc is spaced uniformly from the face plate, is cooled approximately uniformly on its back face and onits grinding face,

and, hence, is conditioned to operate with the utmost precision so far as any distortion of the grinding disc itself is concerned. At this point it may be; mentioned that a resin bonded Wheel is believed to transmit heat better than a ceramic wheel, so that the problem of uneven heating is lessy acute with the former than the latter. A

conditions appears to be as important as stimulated air cooling. Both effects are` present in the Vpreferred embodiments of the invention.

While the invention may be adapted to grind- Vers of various types, it nds itsgreatest utility in v connection with face grinders in which an `abrasive disc is mounted on a face plate and the kgrinding `is carried out on the plane surface of the grinding disc. Grinders of this type gener'- ate heat quite rapidly, and thisis particularly true of face grinders in Which two opposed discs Yafford a xe'd gap through which the articlesto be lground are fed in a substantially continuous stream. A typical example of such grinders is the type used for grinding the plane faces of piston tov this particular class of machine with marked success. l

In the prior art, cooling during grinding has been provided for but it hasbeen directed prias practicable' Athroughout the: grindingjdisc.'

The efects of heat are numerous andl diverse, a'ndaffectthe grinding'operation to anlvextent ,that was not appreciated until' atenuar@` cooling jvvas'ha'd.' Heating'affects'accurac'y; If the grind- A ring blanks and the invention has been applied A 45 marily to 4safeguarding the article being ground fafgainst, undue heating. 'Very' little consideration ,has been given in the past to cooling ofthe Y`grindingelements themselves, or to the ideaof maintaining uniformity of temperature as' nearly Bakelite resin bonded Wheel has a coefficient of expansionwhich approximates that of cast-iron,

-a point which is not Without signicance in view of the mode of mounting ,the discs. Further, the face plate is similarly cooled, and thus theheat `is dissipated at or near its source and is not transmitted to the face plate in any considerable degree. l y

As a consequencefonly a negligible portion of the heat developed by the grinding operation is transmitted through the shaft to the bearings, with the result that the bearings always run un- Vder normal temperature conditions and can be fitted Withthe utmost precision practicable in the bearing art, without risk that they will ever run hot.

'All' of these factors contribute to accuracy of grinding, but they have another and unexpected secondary result. The rate of development of heat increases rapidly as the abrasive becomes finer, and the heat effects impose a practicable limit on the iineness of the abrasive used in commercial grinding operations in which a substantial production rate is to be maintained. The

Yeffective and uniform cooling characteristic of Athe present invention permits the use of much ner abrasive at commercial rates and actually permits the production by grinding operations of Hfinishes notheretofcre commercially produced ex- 'cept bythe coarser lapping operations. Since the production rate of a'grinder is manytimesfthat of a lapping machine, lthe commercial importance `of this secondary result is marked.

The invention contemplates the support of the disc on the face plate in such a way that the closest practicable approach to a continuous air gap between the disc and the plate is afforded. It contemplates further, the iiow of air between the proximate faces of the grinding discs where two opposed discs are used and the iiow of air between each disc and its face plate.

In referring to air as the cooling medium, its ready availability is a controlling consideration and the possible use of other gases is appreciated.

As indicative of the importance of the invention, it may be said that precision is appreciably improved, the over-all life of a grinding disc is increased by about one-iifth of its normal life as heretofore used, and the periods when the machine is out of operation for the purpose of dressing the discs are reduced by about onethird of the number of such periods formerly required. Thus, productivity of the grinding machine is substantially increased. The figures given are conservative and ar-eexceeded in certain types of grinding operations.

The -possibility of using nner grits on the wheels has already been suggested. This possibility arises from a reduced tendency to glaze. There is also 'less tendency of the'grinding disc to assume what the operators call a smeary appearance. impairment of the grinding operation and while 4the exact cause is not known, it vhas been atsubject to variations to meet requirements of particular cases. is much more important, but it, too, is subject to some variation to conform to limits imposed v by the nature of the grinding machine or to meet special requirements incident to the form or material of the piece to be ground.

The preferred embodiment of the invention will now be described in connection with the accompanying drawing, in which:

Figure 1 is a View of the'rear face of va grinding disc showing the connecting bushings arranged according to a pattern known in the face-grinding art, but indicating the use of special connections according to the presentinvention;

Fig. 2 is an enlarged fragmentary section showing the connection between the disc of Figure `1 and the face plate upon which it is mounted; and

Fig. 3 is an axial section through the grinding elements of a double disc grinder constructed according to the patent to Koether, No. 2,169,252, dated August 15, 1939, and indicating one mode of applying the invention which has Ydemonstrated marked utility. In this view the supporting bearings and driving motors are not indicated, the purpose being to simplify the view by limiting it to those features which are directly involved in the cooling function.

The path of flow of the air This appearance is attended 'with f lair is induced is a secondary consideration and -at its center and is provided at its rear face with a number of tapped inserts I3. These inserts are of a form better shown in Fig. 2 and receive bolts I4 which pass through the face plate I5 of ordinary form and connect the grinding disc to the face plate rigidly while maintaining between the proximate faces of the plate and disc, that is, between the forward face of the plate and the rear face of the disc, an air gap which is substantially continuous. The inserts I3, as indicated in Figure 2, are formed to include the spacing elements.

The arrangement described contemplates that the simple rotation of the grinding disc and its face plate will induce active flow of air through the interval between the face plate and the disc and usually this air will enter the central aperture l2 and ow outward. Practically all grinding wheels are shrouded or enclosed and the shroud is provided `with an air suction Aconnection which, in the old type of grinder was designed rchieiiy to carry away dust. According to the present invention, this offtake assumes al. new and secondary function of stimulating cooling air flow, and for best results it is considered desirable to increase the suction beyond that customarily used heretofore, thus circulating a greater quantity of air, to secure an adequate cooling eifect.

Face grinding machines using a single grinding disc are known, but a more desirable form involves the use of two grinding discs. One form using `two opposed discs, shown in the patent to Morton, No. 1,640,715, dated August '30, 1927, has the axes of the discs offset. The present invention can be used in such grinders. However, the offset disc type of grinder is being supplantedby the double disc type of grinder shown in the patent to Koether, above identified,

Ain which there are two pairs of coaxial discs opposed to each other.. The inner and outer discs of a given pair have their grinding faces in the same plane, and they are driven -at different speeds', and quite commonly in `opposite directions. These details depend on the type of nish desired.

The purpose of subdividing one vgrinding unit linto two concentric parts -driven at different angular velocities is to secure higher lineal speeds in the Acentral grinding area so that the disparitybetween grinding speeds near the center and at the outer limits will not be too great.

4same plane and their aXes are concentric, so

that the inner grinding unit 2B turns concentrically within'theouter unit 25. Each of the .grinding elements is connected to its face plate by rigid spacing connections generally indicated by the vreference numeral 2], and illustrated as conforming to the showing in Figure 2.

. A pair of trackways 28 and `29 extend between the discs and arenarrower than the interval 'between the grinding faces. 'These servev to guide aseries of'piston ring blanks, one of whichapand also through the slots which accommodate the guide tracks 28 and 29,

Grinding discs rotate at quite high speeds and there is a moderate centrifugal impelling effect so that air is drawn in through the central aperture of the inner grinding member and flows thence outward through the intervals between the various grinding members and their face plates. The

effect is to keep the grinding members cool and at uniform temperature, front and back. As indicating the effectiveness of such cooling, it may be said that a given grinder of the type illus- -trated in Figure 3 operating according to the invention, is so effectively cooled that'immediately after it is stopped, it is possible to place the hand on the grinding surface even of the inner disc which is the one where highest temperatures always exi-st.

Prior to the application of the invention, so much heat was developed and transmitted through the shafts to the bearings that after the machine had been running for two hours or more, the bearing housings were too hot to touch.

After the application of the invention, the bear-y ings were only slightly warm following many hours of running.

The inventive concept is not limited to any particular manner of circulating the air. It resides rather in the idea that the grinding discs are supported in such a way that a heat-insulating air gap is afforded between thev disc and. the

supporting face plate and some means is provided to cause or permit circulatory ow of air. The effect is to dissipate the heat and maintain the grinding discs at substantially uniform temperature throughout the grinding operation.

The present application. is a division of my allowed application Ser. No. 315,438 filed January 24, 1940Which has issued as patent 2,329,995, Sept. 21, 1943 and is directed to the structure of a grinding disc which has demonstrated peculiar utility in the performance of the invention.

What is claimed is: A grinding component for that type of grinding machine which has a power driven rotatable face plate on which is mounted coaxially a grinding disc with its grinding face parallel with the face of said face plate, said grinding element comprising a disc of substantial thicknes-s and composed of bonded abrasive material, said disc having its working face in a plane perpendicular to its axis of rotation and having inset permanently in its back and distributed over its back surface in substantially symmetrical relation to its axis and periphery a multiplicity of inserts, each insert having a shank which projects into the disc and is permanently xed therein, and a flat head seated on the back face of the disc, said inserts being provided with threaded sockets normal to the back face of the disc and adapted to receive threaded retaining means for rigidly attaching the disc toa face plate with the outer faces of the heads of said inserts engaging the face plate, all of said inserts having the outside faces of their said expanded heads in a common plane, parallel with the plane of the grinding face of the disc and spaced away from the rear face of such disc suiiiciently to afford an adequate interval between the back face of the disc and the plane of the outer face of the heads of the inser-ts to permit the circulation of air in quantity sufficient to'maintain the temperature of the disc when in operation. f

EMIL A. KOETI-IER.

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