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.

Description

FIELD OF THE INVENTION

The invention relates to a bilateral abrasive disc pad for grinding, polishing, and lustering a workpiece.

BACKGROUND OF THE INVENTION

Abrasives are used for polishing, cleaning, finalizing, and giving an aesthetic appearance to a workpiece. The smoother surfaces created by abrasives can also promote corrosion resistance and fracture resistance. Therefore, continuous improvements and innovations are made on abrasives.

One type of abrasive disc pad known in the art as a flap-type disc comprises a disc-shaped pad onto which a plurality of overlapping abrasive flaps are glued or otherwise attached. In use, the flap-type disc is detachably mounted to the shaft of a hand grinder and the surface of a workpiece is abraded by the rotating abrasive flaps with the help of electrical power. While such flap-type abrasive discs have a more complex structure than simple abrasive discs that utilize only a single circular sheet of abrasive material, they have the advantage of being substantially more flexible than simple abrasive discs and hence are easier to use on workpieces with contoured or complex surfaces.

SUMMARY OF THE INVENTION

In some cases, abrasive flaps having different grit sizes must be used on the work piece. Grit size determines the coarseness or fineness of the grinding properties of the abrasive flaps. Oftentimes, a grinder operator will initially grind a work piece with abrasive flaps having a relatively coarse or large grit size that quickly removes material from the work piece surface, and then subsequently re-grind the workpiece with abrasive flaps having a smaller, finer grit size as the sizing or surface polishing of the workpiece approaches its desired end point. Most prior art abrasive disc pads are capable of supporting only a single type of abrasive flap on a single side. Consequently, the operator must remove one disc pad from the machine and mount a different disc pad to the machine in order to change the grit size of the abrasive applied to the workpiece. The continuous exchanging of different abrasive discs slows the grinding operation and impairs productivity.

To overcome these limitations of single-side abrasive disc pads, double-sided disc pads have been developed. Such disc pads are shaped either as a cylindrical disc having a uniform thickness throughout its radius, or sometimes as a bilateral lenticular disc having a slightly increasing thickness toward its center portion along its radius. The coarseness or fineness of the abrasive flaps secured to the opposing sides may be different, advantageously allowing two different grinding or polishing stages to be efficiently and quickly performed by merely detaching, flipping, and re-attaching the double-sided disc pad to driven shaft of the grinder.

However, while such double-sided disc pads have increased operational efficiency, the applicant has observed several shortcomings which compromise the performance of such disc pads. For example, such prior art disc pads, whether single or double-sided, are mounted onto the driven shaft of the grinder by means of a nut. Consequently, when either switching from one single-sided disc pad to another, or flipping the side of a double-sided disc pad, the nut must be unscrewed from and re-screwed to the driven shaft of the grinder typically with the help of a wrench. Such unscrewing and re-screwing of the mounting nut protracts the time necessary for a multi-stage grinding or polishing operation. Another shortcoming associated with such prior art disc pads is their tendency to develop runout or vibration as a result of uneven wear of the overlapping abrasive flaps. The resulting vibration compromises the quality of the griding or polishing operation and accelerates the fatigue of the operator. While both uneven flap wear and the resulting vibration may be ameliorated by grinding or polishing as a lower rotational speed, such a lower speed slows down the grinding or polishing operation. Finally, the applicant has observed that there are some grinding operations that require the subsequent use of a flat disc pad side and a convex, lenticular disc pad side. In such a case, a disc pad having two convex sides or two flat sides must be replaced rather simply flipped in order to proceed to the next stage of grinding or polishing.

Accordingly, there is a need for an improved flap-type abrasive disc pad that expedites the detachment and re-attachment of the disc pad to the grinder shaft. Ideally, such an improved flap-type abrasive disc could be used at high rotational speeds with substantially less runout and vibration over the lifetime of the abrasive flaps. Finally, it would be desirable if such an improved flap-type abrasive disc could accommodate grinding and polishing operations requiring the subsequent use of a flat arrangement of overlapping abrasive flaps and a convex, lenticular arrangement of overlapping abrasive flaps.

To these ends, the invention is a bilateral, rotatable abrasive disc pad, comprising a cylindrical mounting section having a screw-threaded 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. The outer annular section of one side is flat, i.e. parallel to a plane orthogonal to an axis of rotation of the disc, while 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. 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 such that the 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. Such a ratio is accomplished by increasing the thickness of the cylindrical mounting section so that it is approximately twice as thick as the average thickness of the inner and outer annular sections. Additionally, 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.

The relatively greater thickness of the centrally-located mounting section and the provision of screw threads around the mounting hole obviates the need for a separate mounting nut to secure the inventive disc pad to the threaded driven shaft of the grinder. The disc pad may easily be unscrewed from and re-screwed to the threaded grinder shaft by pushing the shaft lock button on the grinder and manually applying torque to the edge of the disc pad. The relatively thicker mounting section and longer mounting hole also effectively distributes torque from the grinder shaft through a great enough area of the disc pad to avoid thread strippage despite the fact that the material used to form the disc pad is softer than the steel used to form the grinder shaft. Moreover, the higher concentration of mass of the disc pad toward its center (such that the 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) substantially reduces runout and unwanted vibration during the lifetime of the abrasive trips. By way of comparison, in a disc-shaped pad wherein the outer annular section began at the midpoint of the radius, the amount of mass of the outer annular section would be four times that of the remainder of the disc. By contrast, due to the increased relative thickness of the central mounting section of the inventive disc pad, the amount of mass of the outer annular section is less than two times that of the remainder of the disc. Such a mass distribution along the radius of the disc substantially reduces the amount of runout and vibration generated during the lifetime of the overlapping abrasive flaps.

The outer annular section of the convex side of the disc pad is oriented between about 10° to 20° relative to the plane orthogonal to an axis of rotation of the disc. A first set 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 set of abrasive overlapping flaps of uniform size and shape affixed to the outer annular section of the opposite side of the pad. Preferably, the extent of overlap of the abrasive flaps of both pluralities is no more than about half of a circumferential extent of the flaps. Such an arrangement more efficiently distributes the wear over each set of abrasive flaps, and further keeps the overall thickness the inventive disc pad across the outer annular sections to that of a conventional abrasive pad so that the inventive disc pad can be used in any grinder without scraping against the disc guard.

The invention further encompasses a method of using the previously-described bilateral disc pad that comprises 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 while abrading a workpiece with a first of the opposing sides of the outer annular section; unscrewing the pad from the driven shaft by locking the shaft and manually turning the pad, flipping 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 while abrading a workpiece with a second of the opposing sides of the outer annular section.

DESCRIPTION OF THE FIGURES

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;

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;

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

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.

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.

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.

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.

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.

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.

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.

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 t₁ of the inner annular section 27, and selecting the taper angle θ so that the average thickness t_2ave of the outer annular section 29 is about 82% of the thickness t₁ of the inner annular section 27. In this example, this relative thickness criteria between t_2ave and t₁ is accomplished when the taper angle θ is about 15°. Additionally, the radius R_m of the cylindrical mounting section 15 should be between about 21% and 25% of the overall radius R_d of the disc, and the radius R_ia of the inner annular section 27 should be about 50% of the overall radius R_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.

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.

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, andan 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, andabrading a workpiece with a second of the opposing sides of the outer annular section.