BILATERAL ABRASIVE DISC PAD

Abstract

A bilateral abrasive disc pad is provided comprising a cylindrical mounting section, an inner annular section, and an outer annular section to which abrasive flaps are attached in an overlapping relationship. The cylindrical mounting section has a central screw-threaded mounting hole for threadedly connecting to a threaded driven shaft of a grinder. The outer annular section of one side is flat, while the outer annular section of the opposing side is convex. The cylindrical mounting section is substantially thicker than the outer annular section such that the ratio of the mass of the outer annular section to the mass of the combination of the cylindrical mounting section and the inner annular section is 2 to 1 or less. Such thickening of the central mounting section reduces runoff and vibration caused by uneven wear of the abrasive flaps and allows the pad to be securely attached to the shaft of the grinder without the need for a mounting nut.

Claims

1. A double-sided, rotatable abrasive pad, comprising: a cylindrical mounting section having a mounting hole concentrically arranged around an axis of rotation of the pad; an inner annular section connected around the circumference of the cylindrical mounting section, and an outer annular section connected around the circumference of the inner annular section and having opposing sides, each side being configured for the affixing of overlapping abrasive flaps, wherein the outer annular section of one side is parallel to a plane orthogonal to an axis of rotation of the disc, and the outer annular section of the opposing side is oriented at an angle to the orthogonal plane so as to form a convex frustro-conical surface.

2. The double-sided rotatable abrasive pad defined in claim 1, wherein the mass per unit radial length of the combination of the cylindrical mounting section and the inner annular section is greater than the mass per unit radial length of the outer annular section.

3. The double-sided rotatable abrasive pad defined in claim 2, wherein ratio of the mass of the outer annual section to the mass of the combination of the cylindrical mounting section and the inner annular section is 2 to 1 or less.

4. The double-sided rotatable abrasive pad defined in claim 3, wherein the radial length of the combination of the cylindrical mounting section and the inner annular section is about equal to the radial length of the outer annular section.

5. The double-sided rotatable abrasive pad defined in claim 1, wherein a thickness of the cylindrical mounting section along an axis of rotation is substantially greater than a thickness of the outer annular section along the axis of rotation, and wherein the mounting hole is screw-threaded for receiving a screw-threaded driven shaft.

6. The double-sided rotatable abrasive pad defined in claim 5, wherein the thickness of the cylindrical mounting section is about twice as much as the thickness of the outer annular section.

7. The double-sided rotatable abrasive pad defined in claim 1, wherein the opposing side of the outer annular section is oriented between about 10° to 20° relative to the plane orthogonal to an axis of rotation of the disc.

8. The double-sided rotatable abrasive pad defined in claim 1, further comprising a first plurality of abrasive overlapping flaps of uniform size and shape affixed to the outer annular section of one of the sides of the pad and a second plurality of abrasive overlapping flaps of uniform size and shape affixed to the outer annular section of the opposite side of the pad, wherein the extent of overlap of the abrasive flaps of both pluralities is no more than about half of a circumferential extent of the flaps.

9. The double-sided rotatable abrasive pad defined in claim 8, wherein the coarseness or fineness of the of the abrasive properties of the first and second pluralities of abrasive flaps are different.

10. A method of using the double-sided rotatable abrasive pad of claim 5, comprising the steps of: screwing the abrasive pad to a driven rotatable shaft having an exterior screw-thread engageable with the screw-thread of the mounting hole; rotating the rotatable shaft in a direction that tightens the screw thread engagement between the pad and the driven shaft; abrading a workpiece with a first of the opposing sides of the outer annular section; unscrewing the pad from the driven shaft, turning the abrasive disc 180°, and re-screwing the pad to the driven shaft; rotating the rotatable shaft in a direction that tightens the screw thread engagement between the pad and the driven shaft, and abrading a workpiece with a second of the opposing sides of the outer annular section.

Description

DESCRIPTION OF THE FIGURES

[0012] FIG. 1 is a perspective view of the rotatable disc-shaped pad of the abrasive disc of the invention with some of the abrasive flaps adhered thereon;

[0013] FIG. 2 is a front view of the disc-shaped pad of FIG. 1, showing one abrasive flap in phantom and the adhesive that bonds the flaps to the disc;

[0014] FIG. 3 is a side view of the double-sided abrasive disc of the invention, illustrating both the disc-shaped pad, and abrasive overlapping flaps bonded to the pad, and FIG. 4 is a cross-sectional side view of the double-sided abrasive disc of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] The invention will now be described with reference to the accompanying drawings. However, the invention is not limited to the particular illustrated embodiments. To the contrary, the invention is limited only by the accompanying claims and their equivalents.

[0016] With reference to FIGS. 1-3, the double-sided abrasive pad 1 of the invention includes a flat side 3, a convex side 5, and two sets 7a, 7b of overlapping, fan-shaped adhesive flaps 9 mounted on the sides 3, 5 of the pad 1. Each of the flaps 9 has a bound side 11a affixed to the pad 1, and a free or loose side 11b that overlaps the bound side 11a of an adjacent flap 9. A cylindrically-shaped mounting section 15 forms the center section of the pad 1. The mounting section 15 has a mounting hole 17 concentrically positioned around the axis of rotation of the disc 1. The inner surface of the mounting hole 17 includes a screw thread 19 that is engageable with a complementary screw 21 thread of a driven shaft 23 of a grinder (not shown), which may be either stationary or portable.

[0017] The pad 1 further includes an inner annular section 27 and an outer annular section 29. The inner annular section 27 is integrally formed between the outer circular edge 25 of the mounting section 15 and the inner annular edge 31 of the outer annular section 29. The outer annular section 29 supports the two sets 7a, 7b of the adhesive flaps 9. To this end, the two opposing faces of the outer annular section 29 each include a plurality of narrow, radially-oriented recesses 33 that are divided along the radius of the outer annular section 29 by a circumferential rib 35. These recesses 33 are filled with a layer of adhesive 37 that binds the bound side 11a of the abrasive flaps 9 to the pad 1, while the other side 11b remains free to overlap the bonded side 11a of the adjacent flap 9.

[0018] The circumferential rib 35 divides each of the radially-oriented recesses 33 into two shorter recesses 39a, 39b. This dividing up of each of the recesses 33 into two shorter recesses 39a, 39b ensures that the level of the adhesive 37 will always be high enough in each of the recesses 33 to firmly bond the side 11a of the adhesive flaps 9 to the pad 1. As is indicated in FIG. 2, the free, unbound side 11b of each of the adhesive flaps 9 overlaps the bound side edge 11a of the adjacent flap 9. The resulting sets 7a, 7b of overlapping adhesive flaps 9 on either side 3, 5 of the pad 1 advantageously provides flexibility to each of the opposing grinding surfaces of the resulting double-sided abrasive pad 1, allowing it to better grind or polish rounded or non-planar surfaces. Preferably, the extent of overlap of the abrasive flaps 9 of both sets 7a, 7b is no more than about half of a circumferential extent of the flaps 9. Such an arrangement more efficiently distributes the wear over each set 7a, 7b of abrasive flaps 9, and further keeps the overall thickness the inventive disc pad 1 across the outer annular section 29 to that of a conventional abrasive pad so that the inventive disc pad 1 can be used in any grinder without scraping against the disc guard.

[0019] In the preferred embodiment, the pad 1 is formed from a fiber-reinforced, moldable polymer. Examples of such materials include polyurethane or nylon reinforced with glass fibers or aramid fibers. The abrasive flaps 9 may be formed from a sheet material onto which an abrasive grit has been adhered. Examples of suitable sheet materials include paper and plastic sheet material, either with or without reinforcing fibers. The abrasive grit may be sand, carborundum, or diamond. The abrasive flaps 9 may also be formed from a buffing cloth or sheet material devoid of abrasive grit, such as felt, wool, or sponge-like sheet materials used for polishing.

[0020] With reference now to FIGS. 3 and 4, one side 5 of the pad 1 has a convex, lenticular shape due to the tapered section 41 formed in the outer annual rection 29. Specifically, because of the linear tapering of the section 41, the convex side 5 of the pad 1 has a frustro-conical shape. In the preferred embodiment, the angle 0 of the taper is between 10° and 20°, and is more preferably 15°. A larger angle may compromise the strength of the outer edge of the pad 1, while a smaller angle may not provide enough convexity to substantially facilitate the grinding or polishing of curved or irregular surfaces. Such a shape, in combination with the flexibility afforded by the sets 7a, 7b of overlapping abrasive flaps 9, facilitates the grinding or polishing of rounded, curved, and irregular surfaces particularly in the case where the double-sided abrasive pad 1 is used in conjunction with a portable grinder, where the grinder operator can easily tilt and otherwise manipulate the pad 1 into engagement with such non-planar surfaces. One side 3 of the pad 1 may be a Type 29 115 mm sanding surface while the other side 5 may be a Type 27 115 mm sanding surface and the pad 1 may produced according to this size standard. In addition, in an alternative configuration, both surfaces 3, 5 can be sized in the type 29 115 mm standard and both surfaces 3, 5 can be sized in the type 27 115 mm standard. Finally, the production diameter of the pad 1 is 125 mm.

[0021] The abrasive flaps 9 used in the two sets 7a, 7b of overlapping flaps preferably have different grinding or polishing properties. For example, one set 7a of flaps 9 on one side 3 of the pad 1 may employ a coarse grit in order to rapidly remove a rough surface on a workpiece or to rapidly size a workpiece while the other set 7b of flaps on the opposite side 5 of the pad 1 may employ a finer grit to polish or to precisely size a workpiece. It is also possible that one set 7a of flaps 9 may have an abrasive grit while the other set 7b of flaps 9 may be formed from buffing cloth or sheet material devoid of abrasive grit, such as felt, or sponge-like sheet materials used for polishing. Finally, it is possible for both sets 7a, 7b of abrasive flaps 9 to have identical grinding or polishing properties. Such a configuration would be useful in operations requiring only a single, simple grinding operation (as opposed to a staged grinding operation utilizing multiple abrasives), and would be useful in rapidly replacing a set of worn-out abrasive flaps 9 with a set of new abrasive flaps 9 by merely detaching, flipping, and re-attaching the pad 1 to the driven shaft 23.

[0022] With reference again to FIGS. 3 and 4, the relative axial thicknesses and radial extents of the cylindrical mounting section 15, the inner annual section 27 and the outer annular section 29 are an important aspect of the inventive disc 1. Generally, these relative axial thicknesses and radial extents are selected so that the mass per unit radial length of the combination of the cylindrical mounting section 15 and the inner annular section 27 is greater than the mass per unit radial length of the outer annular section 29. In particular, these relative axial thicknesses and radial extents are selected such that the ratio of the mass of the outer annual section 29 to the mass of the combination of the cylindrical mounting section 15 and the inner annular section 27 is 2 to 1 or less when the inner annular edge 31 of the outer annular section 29 starts at about the midpoint of the radius R of the disc 1. In this example of the inventive disc 1, such a mass ratio is accomplished by increasing the thickness T of the cylindrical mounting section 15 so that it is approximately 2.4 times the thickness t.sub.1 of the inner annular section 27, and selecting the taper angle θ so that the average thickness t.sub.2ave of the outer annular section 29 is about 82% of the thickness t.sub.1 of the inner annular section 27. In this example, this relative thickness criteria between t.sub.2ave and t.sub.1 is accomplished when the taper angle θ is about 15°. Additionally, the radius R.sub.m of the cylindrical mounting section 15 should be between about 21% and 25% of the overall radius R.sub.d of the disc, and the radius R.sub.ia of the inner annular section 27 should be about 50% of the overall radius R.sub.d of the disc. As previously mentioned, such proportioning of the axial thicknesses and radial extents of the components of the pad 1 results in a ratio of about 2 to 1 or less of the mass of the outer annual section 29 to the mass of the combination of the cylindrical mounting section 15 and the inner annular section 27. By contrast, in a disc-shaped pad where the outer annular section starts at the midpoint of the overall radius of the disc, the ration of the mass in the outer annular section to the mass of the rest of the disc is 4 to 1. The 50% reduction in the relative amount of mass provided in the outer annular section of the pad substantially reduces runout and vibration caused by uneven wear in the sets 7a, 7b of the flaps 9 on either side of the disc 1 of the invention. Additionally, the relatively greater thickness T of the cylindrical mounting section 15 increases the amount of surface-to-surface engagement between the driven shaft 23 and the pad 1 in the vicinity of the mounting hole is large, thereby advantageously dissipating the torque applied to the mounting section 15 in the vicinity of the mounting hole 17 and suppressing the stripping of the threads 19 circumscribing the mounting hole 17 during start-up and operation of the grinder.

[0023] In the method of the invention, the double-sided abrasive disc 1 is first detachably mounted onto the driven shaft 23 of a grinder such that the first set 7a of abrasive flaps 9 on the flat side 3 may be used to conduct a first grinding or polishing operation. This is accomplished by manually screwing the threaded mounting hole 17 over the screw thread 21 of the driven shaft 23. Advantageously, no wrenches, tools or fastening nut is needed to complete this operation. After the pad 1 is attached to the driven shaft 23, the grinder is actuated such that the driven shaft is rotated in a direction that maintains if not tightens the screw joint between the driven shaft 23 and the cylindrical mounting section 15. After the first grinding operation is completed, the grinder is turned off, and the double-sided abrasive disc 1 is detached from the driven shaft 23. This is accomplished by locking the shaft 23 from rotation (many grinders have a spring-loaded, push-in shaft lock for this purpose) and manually unscrewing the disc 1 from the shaft 23. The disc 1 is then flipped 180°, and is then detachably re-connected to the shaft 23 by screwing together the threaded mounting hole 17 and driven shaft 23. such that the second set 7b of abrasive flaps 9 may be used to conduct a second grinding or polishing operation.