WIDE FLAP WHEEL
United States Patent 3645049
An abrasive flap-wheel comprising a plurality of abrasive packets secured about the periphery of a rotating hub wherein each packet comprises a plurality of abrasive sheets attached to a flexible securing root, the root being affixed to the rotating hub within a peripheral opening.
US Patent References:
Rotative surfacing tool and tufted packs therefor and method of making such packs
Cosmos - February 1959 - 2871632
Surface finishing drum
Block - October 1962 - 3058269
ABRASIVE DRUM CONSTRUCTION
Burns - October 1970 - 3533198
Rotative surfacing tool and tufted packs therefor and method of making such packs
Cosmos - February 1959 - 2871632
Surface finishing drum
Block - October 1962 - 3058269
ABRASIVE DRUM CONSTRUCTION
Burns - October 1970 - 3533198
Inventors:
Freerks, Conrad T. (St. Paul, MN)
Huppert, James C. (St. Paul, MN)
James, Ralph E. (St. Paul, MN)
Huppert, James C. (St. Paul, MN)
James, Ralph E. (St. Paul, MN)
Application Number:
04/769041
Publication Date:
02/29/1972
Filing Date:
10/21/1968
View Patent Images:
Export Citation:
Assignee:
Minnesota Mining and Manufacturing Company (St. Paul, MN)
Primary Class:
International Classes:
B24D13/06; B24D13/00; B24B9/02
Field of Search:
51/330-338 15/179-183
Primary Examiner:
Simpson, Othell M.
Claims:
We claim
1. A replaceable abrasive packet adapted to be inserted into a keyhole-shaped opening located adjacent to the periphery of a rotatable rigid core wherein said opening has a longitudinally extending chamber defined by a substantially cylindrical wall, and a radial-axial slot extending from the chamber to the periphery of the core, said packet comprising:
2. a plurality of abrasive sheets overlapped to form a tablet of said sheets;
3. a securing root which is relatively inextensible when subjected to centrifugal force caused by the rotation of the core, said root comprising a loop of flexible material formed into
4. a spacer located between said end portions and radially-axially extending from a position adjacent said bulbous portion to a position radially beyond said inner edge of said tablet to provide additional stiffness to said two juxtaposed end portions; and
5. means securing said tablet of abrasive sheets to said juxtaposed end portions of said securing root wherein the radially inner edge of said tablet is positioned adjacent to said bulbous portion to afford locating said tablet closely adjacent to the periphery of the core and wherein the radially outer edge of said tablet will abrasively engage the material to be abraded upon rotation of the rigid core.
6. A replaceable abrasive packet according to claim 1 further comprising rod means affixed to said root within said bulbous portion for affording engagement with a portion of said cylindrical wall to additionally secure said root to the rigid core.
7. A replaceable abrasive packet according to claim 1, further comprising a resin impregnating the radially inner ends of the tablet for
8. restricting the abrasive mineral from abrading said loop and
9. additionally securing the abrasive sheets to one another.
10. A replaceable abrasive packet according to claim 1, wherein said spacer comprises a sheet of abrasive interposed between said end portions and extending to the radially outer edge of said abrasive sheets.
11. A replaceable abrasive packet according to claim 1, wherein said securing root comprises a flexible synthetic polymeric material.
12. A replaceable abrasive packet according to claim 1, wherein said securing root comprises a flexible rubbery material that is reinforced with a high strength fabric.
13. A replaceable abrasive packet adapted to be inserted into a keyhole-shaped opening located adjacent to the periphery of a rotatable rigid core wherein said opening has a longitudinally extending chamber defined by a substantially cylindrical wall, and a radial-axial slot extending from the chamber to the periphery of the core, said pocket comprising:
14. a plurality of abrasive sheets wherein each abrasive sheet has a coated abrasive surface and an uncoated nonabrasive surface, said sheets oriented with said abrasive surfaces all facing the same way and overlapped to form a tablet of said sheets wherein said tablet has a coated abrasive surface and an uncoated nonabrasive surface;
15. a securing root which is relatively inextensible when subjected to centrifugal force caused by the rotation of the core, said root comprising a loop of flexible fiber-reinforced synthetic polymeric material formed into
16. means securing said tablet of abrasive sheets to said juxtaposed end portions of said securing root wherein the radially inner edge of said tablet is positioned adjacent to said bulbous portion to afford locating said tablet closely adjacent to the periphery of the core and wherein the radially outer edge of said tablet will abrasively engage the material to be abraded upon rotation of the rigid core.
17. A replaceable abrasive packet according to claim 7, further comprising:
18. A replaceable abrasive packet according to claim 1, wherein said flexible material includes a strip of nylon cloth impregnated with chlorosulfonated polyethylene.
1. A replaceable abrasive packet adapted to be inserted into a keyhole-shaped opening located adjacent to the periphery of a rotatable rigid core wherein said opening has a longitudinally extending chamber defined by a substantially cylindrical wall, and a radial-axial slot extending from the chamber to the periphery of the core, said packet comprising:
2. a plurality of abrasive sheets overlapped to form a tablet of said sheets;
3. a securing root which is relatively inextensible when subjected to centrifugal force caused by the rotation of the core, said root comprising a loop of flexible material formed into
4. a spacer located between said end portions and radially-axially extending from a position adjacent said bulbous portion to a position radially beyond said inner edge of said tablet to provide additional stiffness to said two juxtaposed end portions; and
5. means securing said tablet of abrasive sheets to said juxtaposed end portions of said securing root wherein the radially inner edge of said tablet is positioned adjacent to said bulbous portion to afford locating said tablet closely adjacent to the periphery of the core and wherein the radially outer edge of said tablet will abrasively engage the material to be abraded upon rotation of the rigid core.
6. A replaceable abrasive packet according to claim 1 further comprising rod means affixed to said root within said bulbous portion for affording engagement with a portion of said cylindrical wall to additionally secure said root to the rigid core.
7. A replaceable abrasive packet according to claim 1, further comprising a resin impregnating the radially inner ends of the tablet for
8. restricting the abrasive mineral from abrading said loop and
9. additionally securing the abrasive sheets to one another.
10. A replaceable abrasive packet according to claim 1, wherein said spacer comprises a sheet of abrasive interposed between said end portions and extending to the radially outer edge of said abrasive sheets.
11. A replaceable abrasive packet according to claim 1, wherein said securing root comprises a flexible synthetic polymeric material.
12. A replaceable abrasive packet according to claim 1, wherein said securing root comprises a flexible rubbery material that is reinforced with a high strength fabric.
13. A replaceable abrasive packet adapted to be inserted into a keyhole-shaped opening located adjacent to the periphery of a rotatable rigid core wherein said opening has a longitudinally extending chamber defined by a substantially cylindrical wall, and a radial-axial slot extending from the chamber to the periphery of the core, said pocket comprising:
14. a plurality of abrasive sheets wherein each abrasive sheet has a coated abrasive surface and an uncoated nonabrasive surface, said sheets oriented with said abrasive surfaces all facing the same way and overlapped to form a tablet of said sheets wherein said tablet has a coated abrasive surface and an uncoated nonabrasive surface;
15. a securing root which is relatively inextensible when subjected to centrifugal force caused by the rotation of the core, said root comprising a loop of flexible fiber-reinforced synthetic polymeric material formed into
16. means securing said tablet of abrasive sheets to said juxtaposed end portions of said securing root wherein the radially inner edge of said tablet is positioned adjacent to said bulbous portion to afford locating said tablet closely adjacent to the periphery of the core and wherein the radially outer edge of said tablet will abrasively engage the material to be abraded upon rotation of the rigid core.
17. A replaceable abrasive packet according to claim 7, further comprising:
18. A replaceable abrasive packet according to claim 1, wherein said flexible material includes a strip of nylon cloth impregnated with chlorosulfonated polyethylene.
Description:
BACKGROUND OF THE INVENTION
This invention relates to heavy-duty coated abrasive flap wheels.
Coated abrasive flap wheels, comprising an annulus formed from coated abrasive packets extending radially from a central core, have been known for several decades. In recent years there has been a growing appetite for wider and wider flap wheels, e.g., for use in the scale removal and grind-finishing of steel sheets, strips, and the like. Such strips may range up to, say, 10 feet wide, and it is desirable to achieve a uniform finish all across their width; accordingly, it is desirable to have a single-abrasive wheel which is at least as wide as the strip to be finished rather than a plurality of narrower wheels which are ganged or staggered.
The most successful prior art flap wheel for grind-finishing wide steel strips has employed a central hub having a peripheral axially aligned keyhole-shaped openings, a metal anchor plate with an enlarged end fitting within each slot and being attached, at its radially outer end, to two tablets of coated abrasive sheets. Considerable pressure is exerted in the grind-finishing operation, typically resulting in failure of the wheel by breakage of one or more anchor plates long before the useful abrading life of the attached coated abrasive sheets has been exhausted. Such breakage consumes valuable production time in packet replacement; endangers nearby personnel and often damages the strip being finished.
A representative example of the prior art flap wheels just described is disclosed in U.S. Pat. No. 3,058,269. The patentee discloses metal anchor plates, suggesting that high-tensile strength steel be employed for longer life of the anchor.
SUMMARY OF THE INVENTION
The present invention provides a coated abrasive flap-wheel structure which can be made up to 10 feet or more in width and which permits nearly complete utilization of the available abrading life of the coated abrasive. The flap wheel is not subject to the failure which typified the wide flap wheels of the prior art. This novel wheel is also less expensive to fabricate.
The wheel of this invention employs a simple, but completely contraindicated, modification of the wide flap wheels of the prior art. Like such earlier wheels, the wheel of this invention employs a central hub with peripherally extending axially aligned keyhole-shaped slots, a tablet of coated abrasive sheets being connected to a securing root which is held within a corresponding opening. Unlike the earlier wheels, however, the root attaching the tablet to the core is of far lower tensile strength than even cold-rolled steel, let alone spring steel. This root is also far more flexible than the anchor plates of the prior art wheels, readily yielding even when subjected to modest pressures.
Other uses and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like numerals designate like parts throughout the figures and wherein:
FIG. 1 is a perspective view of a rotatable abrasive flap wheel in a typical grinding operation;
FIG. 2 is a partially exploded perspective view of the flap wheel;
FIG. 3 is an enlarged cross-sectional view of a portion of the flap-wheel assembly; and
FIG. 4 is an enlarged cross-sectional view of another embodiment for securing an abrasive packet to a rotating hub.
Referring now to the embodiment, illustrated in FIGS. 1-3, there is shown in FIG. 1 a typical grinding operation comprising an abrasive flap-wheel assembly 10, ranging up to 10 feet in width and 2 feet in diameter but not limited to these dimensions, for descaling or grind-finishing sheets and ribbons of steel material 11. A drive assembly (not shown) advances the conveyor belt 12 and the material thereon in the direction of the arrow 14 and a motor assembly (not shown) rotates the abrasive wheel 10 in the direction of the arrow 16 about the longitudinal axis 18. A frame 20 supports the entire assembly and a roller-bar 22 keeps the material in engagement with the conveyor belt 12.
The abrasive flap-wheel assembly 10 comprises a hub 24 and a plurality of abrasive packets 28 secured to, and about, the periphery of the hub 24 by a flexible securing root 30.
The hub 24, which is best shown in the cross-sectional view of FIG. 3, includes a supporting drive arbor 26 and a core 27 having an outer cylindrical surface 29. The core 27, which may be constructed of a single piece of extruded aluminum, cast from relatively hard plastic material, machined from steel or constructed of other similarly rigid material, includes a plurality of longitudinally extending keyhole shaped openings 32. These openings may be skewed from, or coaxially aligned with, the longitudinal axis 18. Each opening 32 has a cylindrical inner chamber 34 defined by a substantially cylindrical wall 35 and a relatively narrow flat slot 36 extending radially from the chamber 34 to the peripheral surface 29.
Each abrasive packet 28 comprises a plurality of overlapped radially-axially extending abrasive sheets 38 and a relatively flexible securing root 30. The abrasive sheets 38, in both embodiments, are positioned with the abrasive mineral 40 on the leading side of the rotating packet 28 and the radially inner edge of these sheets 38 is positioned closely adjacent to the cylindrical surface 29. The abrasive sheets 38 are secured to the root 30 by piano wire stitching 42, stapling or other suitable mechanical means.
During the operation of the wide flap-wheel 10, each radially-axially extending packet 28 is subjected to stresses caused by nonengaging forces (e.g., centrifugal force) and a variety of stresses caused by the packet assembly 28 engaging the material 11 (e.g., impact forces). These stresses, particularly the engaging stresses, caused fatigue failures within the metal roots of the prior art before the coated abrasive had been completely consumed.
These fatigue failures are caused by repeated loadings of the anchors to stresses that are greater than the endurance limit, or fatigue limit, (both meaning the same), for the specific root material utilized (such as metal).
The fatigue limit of any material, such as the root material used in securing the packets 28, to the hub 24, varies with the material selected. For example, the fatigue limit in reversed flexure for a plastic material may be approximately 4,000 p.s.i.; the fatigue limit for aluminum is approximately 13,000 p.s.i.; for hot rolled steel of 0.18 percent carbon, the fatigue limit is approximately 30,900 p.s.i.; quenched steel of 1.02 percent carbon has a fatigue limit of approximately 105,000 p.s.i. Thus, if the material fails in fatigue at a specific stress, the apparent solution would be to substitute a material having a higher fatigue limit, e.g., low carbon steel for a plastic material, and similarly, to substitute high carbon steel for low carbon steel. However, even high carbon steel roots, which have a relatively high fatigue limit and thus are able to withstand greater cyclic stresses, have also failed, apparently because of greater engaging stresses generated within these more rigid roots. A flexible root such as root 30 used in this invention, having a lower tensile strength and a much lower fatigue limit, has outlasted these relatively rigid roots in actual grinding operations. It is thought that the engaging stresses generated within the relatively flexible root are lower than the corresponding endurance limit for the flexible material and that this low stress permits a long operating life of the wheel and complete utilization of the abrasive.
The flexible securing root 30, used in both embodiments, comprises a bulbous portion 44 and a flexible member 46 radially-axially extending from the bulbous portion 44 to a position radially beyond the inner edge of sheets 38.
The root 30 includes a loop of relatively flexible material formed into a bight portion 44 and two juxtaposed end portions which form the flexible member 46 to which the abrasive sheets 38 are secured by the stitching 42. Through the bight portion 44 is a retaining rod 48 to secure the root 30 to the core 27. The bight portion 44 may be first inserted in the chamber 34, as shown in FIG. 2, and subsequently the rod 48 may be inserted through the bight portion 44. Alternatively, the rod 48 may be inserted through the bight portion 44 and adhesively affixed thereto, to form a bulbous portion 45 of the root 30, wherein the bulbous portion 45 is longitudinally inserted into the chamber 34.
Between the ends 46 of the root 30 is a spacer member 50. The spacer 50 radially-axially extends from a position within the slot 36 to a position radially beyond the stitching 42 to provide additional securing stiffness to the packet 28 relative to the hub 24. The spacer shown in FIG. 3 is constructed of an abrasive sheet 38, although a plastic or rubbery material could be used, and radially extends from within the slot 36 to the periphery of the abrasive sheets to minimize the gap between the abrasive sections.
DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Although this invention is subject to considerable variation without departure from spirit thereof, it is believed that a specific example, taken from actual field experience, will facilitate understanding.
An abrasive spacer was formed by superposing a pair of 4 3/8×39 inches Grade 80 drills cloth-backed coated abrasive sheets, immersing one long edge to a depth of three-fourth inch in a polyamide-epoxy adhesive 52, and curing the adhesive-coated flaps between release-coated platens at 190° F. for 45 minutes.
A flexible securing root was formed by medially folding a 3 1/4 inch strip of synthetic polymeric sheet material about the resin-impregnated end of the abrasive spacer so as to leave a five-sixteenths extending approximately five-sixteenth inch beyond the end. The sheet material was made of an extremely flexible nylon cloth impregnated with chlorosulfonated polyethylene, weighing 17 ounces per square yard and having a tensile strength on the order of 400 lbs. per inch of width.
Two tablets were formed by superposing seven 4 ×39 inch Grade 80 drills cloth-backed coated abrasive sheets and immersing them to a depth of three-fourths inch in polyamide-epoxy adhesive. While the adhesive was still wet, one such tablet was placed on each side of the abrasive spacer, overlying the ends of the flexible securing member, with the abrasive surfaces all facing the same way and the uncoated ends of the tablets and abrasive spacer aligned. The resultant layup, with the impregnated end of the spacer extending three-eighths inch beyond the impregnated ends of the tablets, was unified to form a packet by stitching with piano wire staples through the resin-impregnated portions of the superposed abrasive sheets.
A 6 inch diameter cylindrical aluminum core, having 30 equally spaced circumferential openings was then loaded with the packets just described. Each such opening was axially aligned, with a narrow radially outer slot and an enlarged inner chamber, thus defining a keyhole-shaped cross section. In each case, the flap packet was so mounted that the abrasive spacer and the immediately adjacent flexible securing root were inserted within the slot, with the bight of the loop extending into the chamber. A 39 inch retaining rod having a diameter of thirteen sixty-fourths inch was then inserted through the bight of the loop, thereby filling the chamber and anchoring the packet firmly in position. The radially inner end of the packet was thereby positioned approximately one-sixteenth inch from the periphery of the core.
The loaded wheel was then mounted on a stainless steel production line to remove slivers, rough spots, etc., from the surface of a coil of 0.150 inch stainless steel strip following shot blasting, pickling, washing and drying. The wheel was rotated at 1,850 r.p.m., against the direction in which the steel was being fed, and simultaneously axially oscillated over a short distance at 180 cycles per minute. Steel strip, supported by a conveyor, was passed beneath the wheel at 15 feet per minute, while the wheel was subjected to a force such that the current drawn by the driving motor was approximately 15-18 amperes. In this operation, the wheel functioned effectively for 188 hours, during which time it cleaned over 540,000 square feet of steel. At this point the coated abrasive packets were so worn that they were unusable, only 1 1/4 inch of flap remaining. In contrast, the prior art wheel employing a steel anchor plate instead of the flexible root of the present wheel, often fails before 100 hours have elapsed and does not last long enough to permit full utilization of the coated abrasive packets. Even if only one such anchor plate fails, it is necessary to stop the operation, remove the defective packet, trim a new packet to the appropriate length, and replace it; even when this is done, there is no assurance that some other pack will not fail soon.
Depending upon the specific industrial application, the construction of the flexible securing root is subject to considerable variation. By and large, it has been found that synthetic polymeric materials of the type described are particularly effective, but other synthetic polymers such as 35-mil strip of high impact grade polypropylene, 40-mil Eastman "Tenite" polyallomer 5,320, etc., have also performed satisfactorily. For many operations saturated drills cloth is quite satisfactory.
If desired, the flaps making up each packet can all be the same length, with a spacer formed of 30-mil fiber, 40-mil polyethylene, 60-mil polystyrene, 35-mil polypropylene, three additional strips of impregnated nylon cloth, 40-mil "Tenite" polyallomer, etc., inserted in the middle of the resin-impregnated end of the packet, extending perhaps three-eighths inch beyond the end. Although a spacer offers the advantage of completely filling the peripheral slot it is not absolutely essential. Where the flexible securing root comprises a loop of sheet material, it is generally preferred to have its radially outer portions somewhat separated, but even this is not always required.
To simplify assembly, it is also contemplated that the steel rod may be permanently incorporated within and adhered to the bight of the loop. The flexible securing root can alternatively, be affixed to the nonabrasive surface of the packet, further simplifying construction. At least in some instances it may be possible to attach the flexible member to the abrasive surface of the packet provided that the adjacent flap packs are not too close together. In still another variation, a loop of flexible material may straddle the entire packet, a spacer extending from the middle of the packet radially inwardly beyond the impregnated ends to minimize play.
While these embodiments of the invention have been shown and described, it will be appreciated that this is for the purpose of illustration and that modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.
This invention relates to heavy-duty coated abrasive flap wheels.
Coated abrasive flap wheels, comprising an annulus formed from coated abrasive packets extending radially from a central core, have been known for several decades. In recent years there has been a growing appetite for wider and wider flap wheels, e.g., for use in the scale removal and grind-finishing of steel sheets, strips, and the like. Such strips may range up to, say, 10 feet wide, and it is desirable to achieve a uniform finish all across their width; accordingly, it is desirable to have a single-abrasive wheel which is at least as wide as the strip to be finished rather than a plurality of narrower wheels which are ganged or staggered.
The most successful prior art flap wheel for grind-finishing wide steel strips has employed a central hub having a peripheral axially aligned keyhole-shaped openings, a metal anchor plate with an enlarged end fitting within each slot and being attached, at its radially outer end, to two tablets of coated abrasive sheets. Considerable pressure is exerted in the grind-finishing operation, typically resulting in failure of the wheel by breakage of one or more anchor plates long before the useful abrading life of the attached coated abrasive sheets has been exhausted. Such breakage consumes valuable production time in packet replacement; endangers nearby personnel and often damages the strip being finished.
A representative example of the prior art flap wheels just described is disclosed in U.S. Pat. No. 3,058,269. The patentee discloses metal anchor plates, suggesting that high-tensile strength steel be employed for longer life of the anchor.
SUMMARY OF THE INVENTION
The present invention provides a coated abrasive flap-wheel structure which can be made up to 10 feet or more in width and which permits nearly complete utilization of the available abrading life of the coated abrasive. The flap wheel is not subject to the failure which typified the wide flap wheels of the prior art. This novel wheel is also less expensive to fabricate.
The wheel of this invention employs a simple, but completely contraindicated, modification of the wide flap wheels of the prior art. Like such earlier wheels, the wheel of this invention employs a central hub with peripherally extending axially aligned keyhole-shaped slots, a tablet of coated abrasive sheets being connected to a securing root which is held within a corresponding opening. Unlike the earlier wheels, however, the root attaching the tablet to the core is of far lower tensile strength than even cold-rolled steel, let alone spring steel. This root is also far more flexible than the anchor plates of the prior art wheels, readily yielding even when subjected to modest pressures.
Other uses and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like numerals designate like parts throughout the figures and wherein:
FIG. 1 is a perspective view of a rotatable abrasive flap wheel in a typical grinding operation;
FIG. 2 is a partially exploded perspective view of the flap wheel;
FIG. 3 is an enlarged cross-sectional view of a portion of the flap-wheel assembly; and
FIG. 4 is an enlarged cross-sectional view of another embodiment for securing an abrasive packet to a rotating hub.
Referring now to the embodiment, illustrated in FIGS. 1-3, there is shown in FIG. 1 a typical grinding operation comprising an abrasive flap-wheel assembly 10, ranging up to 10 feet in width and 2 feet in diameter but not limited to these dimensions, for descaling or grind-finishing sheets and ribbons of steel material 11. A drive assembly (not shown) advances the conveyor belt 12 and the material thereon in the direction of the arrow 14 and a motor assembly (not shown) rotates the abrasive wheel 10 in the direction of the arrow 16 about the longitudinal axis 18. A frame 20 supports the entire assembly and a roller-bar 22 keeps the material in engagement with the conveyor belt 12.
The abrasive flap-wheel assembly 10 comprises a hub 24 and a plurality of abrasive packets 28 secured to, and about, the periphery of the hub 24 by a flexible securing root 30.
The hub 24, which is best shown in the cross-sectional view of FIG. 3, includes a supporting drive arbor 26 and a core 27 having an outer cylindrical surface 29. The core 27, which may be constructed of a single piece of extruded aluminum, cast from relatively hard plastic material, machined from steel or constructed of other similarly rigid material, includes a plurality of longitudinally extending keyhole shaped openings 32. These openings may be skewed from, or coaxially aligned with, the longitudinal axis 18. Each opening 32 has a cylindrical inner chamber 34 defined by a substantially cylindrical wall 35 and a relatively narrow flat slot 36 extending radially from the chamber 34 to the peripheral surface 29.
Each abrasive packet 28 comprises a plurality of overlapped radially-axially extending abrasive sheets 38 and a relatively flexible securing root 30. The abrasive sheets 38, in both embodiments, are positioned with the abrasive mineral 40 on the leading side of the rotating packet 28 and the radially inner edge of these sheets 38 is positioned closely adjacent to the cylindrical surface 29. The abrasive sheets 38 are secured to the root 30 by piano wire stitching 42, stapling or other suitable mechanical means.
During the operation of the wide flap-wheel 10, each radially-axially extending packet 28 is subjected to stresses caused by nonengaging forces (e.g., centrifugal force) and a variety of stresses caused by the packet assembly 28 engaging the material 11 (e.g., impact forces). These stresses, particularly the engaging stresses, caused fatigue failures within the metal roots of the prior art before the coated abrasive had been completely consumed.
These fatigue failures are caused by repeated loadings of the anchors to stresses that are greater than the endurance limit, or fatigue limit, (both meaning the same), for the specific root material utilized (such as metal).
The fatigue limit of any material, such as the root material used in securing the packets 28, to the hub 24, varies with the material selected. For example, the fatigue limit in reversed flexure for a plastic material may be approximately 4,000 p.s.i.; the fatigue limit for aluminum is approximately 13,000 p.s.i.; for hot rolled steel of 0.18 percent carbon, the fatigue limit is approximately 30,900 p.s.i.; quenched steel of 1.02 percent carbon has a fatigue limit of approximately 105,000 p.s.i. Thus, if the material fails in fatigue at a specific stress, the apparent solution would be to substitute a material having a higher fatigue limit, e.g., low carbon steel for a plastic material, and similarly, to substitute high carbon steel for low carbon steel. However, even high carbon steel roots, which have a relatively high fatigue limit and thus are able to withstand greater cyclic stresses, have also failed, apparently because of greater engaging stresses generated within these more rigid roots. A flexible root such as root 30 used in this invention, having a lower tensile strength and a much lower fatigue limit, has outlasted these relatively rigid roots in actual grinding operations. It is thought that the engaging stresses generated within the relatively flexible root are lower than the corresponding endurance limit for the flexible material and that this low stress permits a long operating life of the wheel and complete utilization of the abrasive.
The flexible securing root 30, used in both embodiments, comprises a bulbous portion 44 and a flexible member 46 radially-axially extending from the bulbous portion 44 to a position radially beyond the inner edge of sheets 38.
The root 30 includes a loop of relatively flexible material formed into a bight portion 44 and two juxtaposed end portions which form the flexible member 46 to which the abrasive sheets 38 are secured by the stitching 42. Through the bight portion 44 is a retaining rod 48 to secure the root 30 to the core 27. The bight portion 44 may be first inserted in the chamber 34, as shown in FIG. 2, and subsequently the rod 48 may be inserted through the bight portion 44. Alternatively, the rod 48 may be inserted through the bight portion 44 and adhesively affixed thereto, to form a bulbous portion 45 of the root 30, wherein the bulbous portion 45 is longitudinally inserted into the chamber 34.
Between the ends 46 of the root 30 is a spacer member 50. The spacer 50 radially-axially extends from a position within the slot 36 to a position radially beyond the stitching 42 to provide additional securing stiffness to the packet 28 relative to the hub 24. The spacer shown in FIG. 3 is constructed of an abrasive sheet 38, although a plastic or rubbery material could be used, and radially extends from within the slot 36 to the periphery of the abrasive sheets to minimize the gap between the abrasive sections.
DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS
Although this invention is subject to considerable variation without departure from spirit thereof, it is believed that a specific example, taken from actual field experience, will facilitate understanding.
An abrasive spacer was formed by superposing a pair of 4 3/8×39 inches Grade 80 drills cloth-backed coated abrasive sheets, immersing one long edge to a depth of three-fourth inch in a polyamide-epoxy adhesive 52, and curing the adhesive-coated flaps between release-coated platens at 190° F. for 45 minutes.
A flexible securing root was formed by medially folding a 3 1/4 inch strip of synthetic polymeric sheet material about the resin-impregnated end of the abrasive spacer so as to leave a five-sixteenths extending approximately five-sixteenth inch beyond the end. The sheet material was made of an extremely flexible nylon cloth impregnated with chlorosulfonated polyethylene, weighing 17 ounces per square yard and having a tensile strength on the order of 400 lbs. per inch of width.
Two tablets were formed by superposing seven 4 ×39 inch Grade 80 drills cloth-backed coated abrasive sheets and immersing them to a depth of three-fourths inch in polyamide-epoxy adhesive. While the adhesive was still wet, one such tablet was placed on each side of the abrasive spacer, overlying the ends of the flexible securing member, with the abrasive surfaces all facing the same way and the uncoated ends of the tablets and abrasive spacer aligned. The resultant layup, with the impregnated end of the spacer extending three-eighths inch beyond the impregnated ends of the tablets, was unified to form a packet by stitching with piano wire staples through the resin-impregnated portions of the superposed abrasive sheets.
A 6 inch diameter cylindrical aluminum core, having 30 equally spaced circumferential openings was then loaded with the packets just described. Each such opening was axially aligned, with a narrow radially outer slot and an enlarged inner chamber, thus defining a keyhole-shaped cross section. In each case, the flap packet was so mounted that the abrasive spacer and the immediately adjacent flexible securing root were inserted within the slot, with the bight of the loop extending into the chamber. A 39 inch retaining rod having a diameter of thirteen sixty-fourths inch was then inserted through the bight of the loop, thereby filling the chamber and anchoring the packet firmly in position. The radially inner end of the packet was thereby positioned approximately one-sixteenth inch from the periphery of the core.
The loaded wheel was then mounted on a stainless steel production line to remove slivers, rough spots, etc., from the surface of a coil of 0.150 inch stainless steel strip following shot blasting, pickling, washing and drying. The wheel was rotated at 1,850 r.p.m., against the direction in which the steel was being fed, and simultaneously axially oscillated over a short distance at 180 cycles per minute. Steel strip, supported by a conveyor, was passed beneath the wheel at 15 feet per minute, while the wheel was subjected to a force such that the current drawn by the driving motor was approximately 15-18 amperes. In this operation, the wheel functioned effectively for 188 hours, during which time it cleaned over 540,000 square feet of steel. At this point the coated abrasive packets were so worn that they were unusable, only 1 1/4 inch of flap remaining. In contrast, the prior art wheel employing a steel anchor plate instead of the flexible root of the present wheel, often fails before 100 hours have elapsed and does not last long enough to permit full utilization of the coated abrasive packets. Even if only one such anchor plate fails, it is necessary to stop the operation, remove the defective packet, trim a new packet to the appropriate length, and replace it; even when this is done, there is no assurance that some other pack will not fail soon.
Depending upon the specific industrial application, the construction of the flexible securing root is subject to considerable variation. By and large, it has been found that synthetic polymeric materials of the type described are particularly effective, but other synthetic polymers such as 35-mil strip of high impact grade polypropylene, 40-mil Eastman "Tenite" polyallomer 5,320, etc., have also performed satisfactorily. For many operations saturated drills cloth is quite satisfactory.
If desired, the flaps making up each packet can all be the same length, with a spacer formed of 30-mil fiber, 40-mil polyethylene, 60-mil polystyrene, 35-mil polypropylene, three additional strips of impregnated nylon cloth, 40-mil "Tenite" polyallomer, etc., inserted in the middle of the resin-impregnated end of the packet, extending perhaps three-eighths inch beyond the end. Although a spacer offers the advantage of completely filling the peripheral slot it is not absolutely essential. Where the flexible securing root comprises a loop of sheet material, it is generally preferred to have its radially outer portions somewhat separated, but even this is not always required.
To simplify assembly, it is also contemplated that the steel rod may be permanently incorporated within and adhered to the bight of the loop. The flexible securing root can alternatively, be affixed to the nonabrasive surface of the packet, further simplifying construction. At least in some instances it may be possible to attach the flexible member to the abrasive surface of the packet provided that the adjacent flap packs are not too close together. In still another variation, a loop of flexible material may straddle the entire packet, a spacer extending from the middle of the packet radially inwardly beyond the impregnated ends to minimize play.
While these embodiments of the invention have been shown and described, it will be appreciated that this is for the purpose of illustration and that modifications may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.