US2586848A - Rotary disk platen - Google Patents

Description

Feb. 26, 1952 J MlLLER 2,586,848

ROTARY DISK PLATEN Filed July 19, 1945 2 SHEETSSFEET l AZ Zorn/e 5 Feb. 26, 1952 2,586,848

ROTARY DISK PLATEN Filed July 19, 1945 2 SX-IEETSSHEET 2 fvvenior Patented Feb. 26, 1952 ROTARY DISK PLATEN Theodore J. Miller, St. Paul, Minn., assignor to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application July 19, 1945, Serial No. 605,962

12 Claims.

This invention relates to supports or anvil members or platens for use in backing up or supporting sheet abrasives at the point where the workpiece being abraded contacts the abrasive coated side of the abrasive sheet during an abrading operation. V

It is particularly applicable to belt sanding or belt grinding, i. e., to abrading operations in which an abrasive belt or strip is employed, and the invention is accordingly illustrated in the present disclosure in connection with belt sanding apparatus.

A belt sanding apparatus usually comprises an endless abrasive belt mounted on two or more pulleys, and means for continuously driving the belt. Abrading operations with such apparatus may be divided roughly into two classifications, namely, unsupported operations and supported operations. An unsupported operation is where there is no support back of the belt at the point of contact with the work other than the tension of the belt that is applied between the adjacent pulleys or guides, whereas a supported operation is where there is.

The present invention relates to the latter type of operation, 1. e., to supported operations.

In the said supported type of operations there are at least two principal types or classes of supports. One is a wheel or pulley, usually one of the driving or idling pulleys aroundwhich the endless belt is mounted, the peripheral surface of the pulley being employed to bear against the work. This is sometimes referred to as a roll or line contact support, and is particularly suited for spot grinding and other precision work such as surfacegrinding. The second type of support is an anvil member or platen, usually substantially fiat, which is applied to a span of the belt between two of the pulleys, and it is to this second or platen type of support that the present invention relates.

' Heretofore the flat platen method of support has caused a decided drop in the efiiciency of the belt long before the mineral on the belt is .worn down or abraded off. This was due largely to a filling and glazing of the belt which developed rapidly early in the life of the belt so that only the tops of the highest particles'ever came into full use. Some attempts were made to improve thi situation, including the use of irregular surfaced platens but whatever improvement these may have produced in the way of lengthened belt life, was offset by an increased wearing or hollowing of the platen face.

Neverthelessgbecaus'eof its peculiar adaptability to certain types of grinding operations, fiat platen belt grinding must of necessity be used and it is therefore an objective of this invention to provide a platen or suitable supporting element for flat belt grinding which will provide inter alia (1) longer belt life, (2.) faster cutting and (3) retention by the platen of its fiat surface.

The present invention does indeed meet these and other objectives and solves these and other problems successfully, and, in its illustrated aspect comprises a belt-supporting platen having a generally planar working surface or face mounted adjacent the back of a span of the belt with the platen face substantially parallel thereto and means for moving the platen face during an abrading operation in a path substantially parallel to the belt span.

The motion of the platen may be effected in various ways, e. g., by oscillation, by providing a platen in the form of a disc and then rotating it; or by providing a platen in the form of an endless belt positioned to run in contact with the abrasive belt.

The platen face is discontinuous or broken. It may be broken in a variety of patterns, it being preferable to shape the irregularities or breaks so as to provide alternate areas of support and non-support for the belt and so as to produce what may be termed a line contact between the belt and the work.

The invention is exemplified by devices described hereinafter and illustrated in the accompanying drawings in which:

Figure 1 is a schematic view (front) of a belt sanding apparatus employing a rotary platen;

Figure 2 is a side view of the apparatus of Figure 1, showing a workpiece being abraded;

Figure 3 is a vertical fragmentary section (enlarged) on the line 3-3 in Figure 1 looking in the direction of the arrows, and showing a workpiece being abraded;

Figures 4, 5 and 6 are fragmentary front elevations of rotary platens.

Figure '7 is a side elevation of the platen fragment of Figure 6;

Figure 8 is a schematic view (front) of a belt sanding apparatus employing an oscillating platen;

Figure 9 is a side view of the apparatus of Figure 8; and

Figure 10 is a schematic view (side) of a belt sanding apparatus employing an endless belt platen.

Figures 1 and 2 show a belt sanding apparatus comprising an endless abrasive belt 3-! mounted on rotatable pulleys 2| and 22, means, such as an electric motor (not shown), for rotating the pulleys so as to drive the belt, and an anvil or supporting member or platen in the form of a disc P-l rotatably mounted, by means of a shaft 23 and bearings 24, adjacent the back of a span of the belt with the face 25 of the disc P-l substantially parallel to the span. The face 25 is substantially fiat or planar with its continuity broken at intervals by a plurality of depressions in the form of radially extending elongate aperportion of the belt that is opposite a slot2$ (and is thus unsupported) is-.thereby forced to yield slightly in a direction. inwardly: into the slot; whereas the portion of. the. belt thatcontacts the platen face (and is thus. supported). does not so yield, so that the belt isbent slightly. and. there is formed, in effect, a. temporary ridge or bumpru.

in. the. belt in conformity to. the contour of. the edges: (Figure *3). This causes what. may, for convenience, be termed a line contact between the belt and the workpiece, as contrasted with the-fiat 01' surface contact that results from continuous or. smooth. surfaced platens, the line being the impact ridge or bumpy whichcorn forms in length, direction, curvature, etc., ape proximately to the edge at. There is consequently produced an impact together with an increase in pressure per unit area between the belt and the work, which causes thebelt tocut: at each impactmuch more than when there-is simply a sliding frictional contact over-a broad area between the surface of the belt-and the surface of the work. The line contact-thus produces faster cut. It also produces longer belt life-because the bending of the belt at y opensitup, breaks up anyglaze that i has formed, exposes fresh unused portionof the mineral particles and results in keeping the belt at fullcutting efficiency until its entire coating of abrasive particles is substantially completely used up. There is'substantially no waste mineral.

The movement of the belt B4 in contact with the platen P-l causes the latter'to rotate; or, rotation may be effected by suitable driving means such as the electric motorM-l.

One very advantageous result of such movement or rotation of the platen is to distributethe pressure and the consequent-wear of the platen face throughout its workingarea, thereby preserving the desired overall planar profile of the Iorking portion of the platen face for a very substantial period of time, as contrasted with the rapid localized hollowing of the ordinary stationary platens. The latter commonly need replacement in a few hours, whereas rotary platens made in accordance with my invention have been known to run for several months without variation in the flatness of the working surface.

The depressions or slots 26 need not necessarily pierce the disc as long as the depression is of sufficient depth and with a wall 26a of suflicient steepness to form an effective impact edge :12. Also the depressions may take a wide variety of shapes, sizes, angles, frequency of occurrence, etc., as shown in Figures 4, 5, 6 and 7, it being understood that the designs as wellas the dimensions and angles there shown are illustrative and not limiting.

Figure 4 illustrates a preferred embodiment. To compensate for the difference in linear speed between portions of the disc face that are near to and far from its center, respectively, the depressions or slots 26' are here placed at an angle of 15- to the radial linewhich increases the space differential between their outer and inner ends; and each slot is narrowed toward its outer end, thereby decreasing the effective impact of the edge :2 against the work in proportion to the narrowing. The disc of Figure 4 thus provides evencutting acrossthe entire width of the workpiece. Also the angular position of the edges 3: in this disc provides something in the nature of a shearingeffect, a point by point contact between the belts impact ridge and the leading or upper'edge of the workpiece.

Figure 5 shows a still further variation, the depressions, here ,being circular apertures or-holes bored, through the disc, such a pattern being particularly suitable for fine precision grinding.

Figures 6 and 7 show what may. be termed a ridged type disc, carrying on its. surface a plurality of outwardly extending ridgesin spaced relation to.each other, theouter portions of the ridges together forming a composite surface of substantially planar contouruwhich constitutes the outer orworkingsurface 25" or. theplaten. It comprisesa disc base; 30 overlaid with ridges 3| which may be of any shape.in,cross-section. Here they are. circular,.being; rodsqthat are cut andwelded to. the base 30 to. form square depressions or spaces 26 between them, the .rods themselves forming atonce the impact edges :c and the platen face 25].. Such a disc isparticularly suitable for-very. fast .andvery, rough abrading or cutting. This. is due. partly to them.- creasein the size of .thebump or impact ridgeyf causedby the. relatively; wider, spacesor depresesions. 26 and partly to the. increasedpressure per square inch between. thebelt and the .workpiece caused by the smaller totaLcontactarea.

, Within certain'limits there; is adirect; inverse relationship between. contact. area and cutting.

speed.

From these-few illustrativeexamples it will.

Although movementpf-the platen, preferably in .a plane parallelwiththe belt, is. anessential element of. my invention, such; movement is not confined; to that. produced/by the :rotation. illus-v tratedand contemplated. in Figures 1 to.7, but may, for example; .be 'by; oscillation of the platen as shown in Figures ,8 and. 9, orby themovement of an. endlessbelt: platenras-shown in Figure. 10.

In Figures 8 and 9 the platen P-Z; (in' a belt sanding apparatus 1 which. is otherwise. the same asrthatuof Figures '1 and.-2), is, slidably held bya suitable support, I35 andoscillated-or reciprocatedup. and .downby a suitable: driving means,

such asanainengine reciprocator. (not shown) or. thecrank wheel [36 andpitmanlfl driven by=the; electric motor M-.-2. The face l25.-of the platen P-Z, like. that of P-|-, ,ispreferably substantially fiat or planar, with its-v continuitybroken at intervals by; a plurality; of depressions.

I2B.to form impact edges As. in, the; rotary platens of Figures 1 to '7, the -;depressionsof the oscillating platen P-Lof'Figuresj 8-,ands 9. may

have a. wide variety of depths,,sizes, shapea-angularity, frequency of occurrence, etc. as. lon as they provide impact edges suitable for operation on the. principles described above in connection with the impact edges :1: of Figures 1 and 3.

In Figure the endless belt or saddle belt platen P-3 (in a belt sanding apparatus which is otherwise the same as that of Figures 1, 2,8 and 9) is positioned so that one of its spans serves as the support back of a span of the abrasive belt B-3 opposite the point where the workpiece W-3 is pressed during an abrading operation. It is driven in the same direction as the abrasive belt 3-3 by reason of its frictional contact therewith, or itmay be driven by suitable power means, such as the electric motor M-3, through its supporting pulleys.

The face 225 of the belt platen P-3, like those of the platens P-l and P-2, 'is preferably generally planar with its continuity broken at intervals by a plurality of depressions 226 which may, for example, be such as to provide a plan and profile like that of the platen face in Figures 8 and 9. The said platen surface may be formed or constructed by molding; or by cutting the depressions in a smooth surfaced belt, in which case the original surface of the belt would become the platen face 225; or by fastening strips or patches of suitable material onto a belt, in which case the-original surface of the belt would become the bottom of the depressions and the tops of the ridges or patches would become the platen face 225. The belt may be of ordinary power belting material, such as rubberized fabric, leather rubber, etc., or itmay be synthetic rubber or resin, or any hard tough material of sufficient flexibility to serve as an endless belt. As in the rotary platens of Figures 1 to 7 and the oscillating platen of Figures 8 and 9, the depressions of the saddle belt platen P-3 of Figure 10 may have a wide variety of depths, sizes, shapes, angularity, frequency of occurrence, etc. as long as they provide impact edges suitable for operation on the principles described above in comiection with the impact edges :1: of Figures 1 and 3.

When a saddle belt platen is used, the opera: tion is not then, strictly speaking, a supported operation. In a sense it is supported, but the support is, in turn, simply the unsupported span of a second belt, so that the effect is to preserve the aspects of unsupported grinding in the way of yieldability and flexibility while adding the benefit of added support over and above that provided by the ordinary tension of the abrasive belt.

The cutting efficiency of the various types of broken-surfaced moving platens of my invention, increases as their linear speed approaches that of the belt, and substantially beyond that. Their movement may be in the same direction as that of the belt or it may be in the reverse direction.

It will be seen that sanding platens made in accordance with my invention possess numerous important and valuable advantages over those heretofore known, including (1) longer life of the platen and retention by the working portion of its exterior surface of the desired overall planar contour or flatness, due to the movement of the platen; (2) lower or cooler abrading temperatures due to numerous factors, including reduced friction, the faster cut and the movement of the platen; (3) longer life of the abrasive sheet due to numerous factors including the cooler abrading temperature and the fact that substantially all of the abrasive coating is rendered usable by the opening up effect of the platens impact edges; and (4) faster out, due to numerous factors including the broken-surface feature and the unique effect of a rotating disc platen.

The principle of a broken, irregular or variate surfaced moving platen, as taught by my invention, may be employed in ways other than those described herein and in connection with abrasive materials and structures other than belts. For example the invention may be adapted for use with abrasive discs by using a broken surfaced back-up pad adapted to move or to rotate in relation to the disc.

The invention is not to be understood as restricted to the details set forth since these may be modified within the scope of the appended claims without departing from the spirit and scope of the invention.

The construction of platen disclosed in Figures 6 and 7 is claimed in my divisional application, Ser. No. 212,223, filed Feb. 23, 1951. The construction of platen disclosed in Figures 8 and 9 is claimed in my divisional application, Ser. No. 225,397, filed May 9, 1951.

I claim:

1. In a belt sanding apparatus which comprises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc positioned with a portion of a surface thereof adjacent the back of a span of the belt and substantially parallel thereto, the said portion of the surface being substantially planar with its continuity interrupted by a plurality of depressions, a wall of a depression and a planar surface of the disc meeting to form an edge.

2. In a belt sanding apparatus which comprises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc positioned with a portion of a surface thereof adjacent the back of a span of the belt and substantially parallel thereto, the said portion of the surface being substantially planar with its continuity interrupted by a plurality of depressions, a Wall of a depression and the planar surface of the disc meeting at an approximate right angle to form an edge.

3. In a belt sanding apparatus which comprises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc positioned with a portion of a surface thereof adjacent the back of a span'of the belt and substantially parallel thereto, the said portion of the surface being substantially planar with its continuity interrupted by a plurality of elongate depressions extending outwardly from the central portion of the disc towards its periphery.

4. In a belt sanding apparatus which comprises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc positioned with a portion of a surface thereof adjacent the back of a span of the belt and substantially parallel thereto, the said portion of the surface being substantially planar with its continuity interrupted by a plurality of elongate approximately radially disposed depressions.

5. In a belt sanding apparatus which com prises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc posi- 7 tioned with a portion of a surface-thereof adj acent the-back of a span of the. belt and. sub stantially parallel thereto, the said portion of the-surface being substantially planar with its continuity broken by a plurality of approximately radially disposed depressions, a wall of a depression and the planar surfacecof the. disc meeting to form an edge.

6. The device-of c1aim5 in whichthedepressio'ns are at an acute; angle to the radii; that intersect, them".

'7. The device; of claim 5. in which the-depressions are narrowed towardtheir'outer ends and are at an acute: angle; to theradii that. intersect them.

8. In a belt sanding apparatus which comprises an endless, abrasivebelt and means/for continuous propulsion. thereof, a. belt-supporting platen comprising a rotatably mounteddisczpositioned with a portion of a surface? thereof adjacent the back of a span of thebelt and substantially parallel thereto, the said portion of the surface being substantially planar with' its continuity interrupted-by a plurality of, circular depressions.

9. In a belt sanding apparatus which comprises an endless abrasive belt and means for continuous propulsion thereof, a belt-supporting platen comprising a rotatably mounted disc positioned with a portion of a surface thereof adjacent the back of a span of the belt and substantially parallel thereto, the said portion of the surface being substantially planar with its continuity interrupted by a plurality of apertures that pierce the disc.

8 10;"The deviceof claim 9 in which the aper tures are elongate;

11'. The device of claimv 9 inwhich the apertures aretcircular."

12. In an abrading operation which comprises propelling.- arr. endless abrasive belt with a span of: the belt in contact with the workpiece, the stepstcomprising pressing the span against the workpiece with an interrupted surface. disc platen: and causing the platen face to rotate in relation. to. the, span in a. plane. substantially parallel to: the movement of the span and ate different linear speed.

THEODORE J. MILLER.

REFERENCES CITED The following references are of record in the file-of this patent:

v UNITED STATES PATENTS Number Name Date 685,328 Gale Oct. 29, 1901 891,251 Harbers June 23, 1908 910,634 Allen Jan. 26, 1909 1,036,783 Bein Aug. 2'7, 1912 1,043,194" Blevney Nov. 5, 1912 1,064,572 Trogdon June 10, 1913 2,195,340 Potash Mar. 26, 1940 2,232,149 Tautz Feb. 18, 19 41 FOREIGN PATENTS Number Country Date 29,731 Sweden June 18, 1909 32,310 Sweden Nov. 8, 1910 695,453 Germany Aug. 26, 1940

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