Abrasive Disks

Abstract

The present invention relates to a grinding disk or wheel, flap disk or cut-off disk which will increase the effectiveness of each battery charge during tool use.

Claims

1. An abrasive grinding wheel for use on a cordless battery-operated grinder comprising abrasive grains and a bonding agent wherein the abrasive grains comprise friable white alumina grain and wherein the bonding agent is a soft bonding agent and further comprises an active filler.

2. The grinding wheel of claim 1 wherein the abrasive grains additionally comprise black silicon carbide grain.

3. The abrasive grinding wheel for use on a cordless battery-operated grinder of claim 1 wherein the active filler comprises a wax-based lubricant.

4. An abrasive flap disk for use on a cordless battery-operated tool comprises a plurality of radially arranged flaps wherein each flap is coated with an abrasive grain further the flaps are arranged in a hybrid stack pattern containing at least two flaps per hybrid stack wherein the abrasive grain of a top flap of each hybrid stack contains a friction reducing coating.

5. The abrasive flap disk for use on a cordless battery-operated tool of claim 4 wherein the abrasive grain is ceramic abrasive grain.

6. The abrasive flap disk for use on a cordless battery-operated tool of claim 5 wherein the friction reducing coating is stearate.

7. An abrasive cut-off disk for use in a battery-operated tool comprising abrasive grains and a bonding agent wherein the abrasive grains comprise Alumina oxide grains and the bonding agent is porous.

8. The abrasive cut-off disk for use in a battery-operated tool of claim 7 wherein the abrasive grains further comprise 10% to 100% Zirconia alumina (40Zk).

9. The abrasive cut-off disk for use in a battery-operated tool of claim 7 wherein the cut-off disk has a thickness less than 1.7 mm.

10. The abrasive cut-off disk for use in a battery-operated tool of claim 7 wherein said bonding agent is a hard material.

11. The abrasive cut-off disk for use in a battery-operated tool of claim 7 further comprising two sides pressed with rubber molds.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0039] FIG. 1 shows the battery life of a standard product versus protype designs of the present invention.

[0040] FIG. 2 shows number of cuts made per battery charge for the present invention cut-off disks.

[0041] FIG. 3 shows the material removal rates per battery charge for the present invention cut-off disks.

[0042] FIG. 4 shows the relationship between the thickness of the disk versus the number of cuts the disk will make per battery charge for the present invention cut-off disks.

[0043] FIG. 5 shows the effect of greater bond stiffness in increasing the number of cuts for the present invention cut-off disks.

[0044] FIG. 6 shows various grain types and ratios when tested against a control of 100% brown fused alumina for the present invention cut-off disks.

[0045] FIG. 7 shows the effect of bond hardness for discs greater than 1.7 mm for the present invention cut-off disks.

[0046] FIG. 8 shows the battery life compared to the number of flaps for the present invention flap discs.

[0047] FIG. 9 shows the amount of material removed per battery charge for different abrasive materials for the present invention flap disks.

[0048] FIG. 10 Shows battery life and metal removal per battery charge as function of white alumina content for the present invention grinding wheels.

[0049] FIG. 11 shows the material removed per battery charge versus the total time the total run time from one battery charge.

[0050] FIG. 12 is a perspective cutaway view of a cut-off disk of the present invention.

[0051] FIG. 13 is a bottom view of a flap disk of the present invention.

[0052] FIG. 14 is a cutaway view of a grinding wheel of the present invention.

DESCRIPTION OF THE INVENTION

Experimental

[0053] Test disks were made for the following types: depressed center grinding wheel (DCW), razor thin cut-off and flap disc.

[0054] For thin cut-off, disk life was based on number of cuts per battery charge. Ten cuts were made prior to removing the disk from the grinder for measurement. The disk was then placed on the grinder, repeating the ten-cut test until the battery or the wheel was spent. If the disk was spent prior to battery, another was used until the battery was spent, the idea being that it is faster to change a wheel than wait for a battery to charge. A 1-inch1-inch angle profile was used for cutting tests.

[0055] For depressed center and flap disc, disk life was measured in minutes grinding. One minute of grinding was done in between measurements. The test continued until the life of the battery was spent. For material removal rates a new battery was placed on the grinder and used until the disc was used for 15 minutes. A 2-inch-inch steel bar was used for grinding.

[0056] All wheels were used on the Hilti Grinder described in the background of the invention.

Cut-Off Disk

[0057] FIG. 12 shows a cutaway perspective view of a preferred embodiment of a cut-off disk of the present invention.

[0058] For battery life, it was found that the cut-off disk should be as stiff and as hard as possible. These characteristics reduce disk wobble or distortion and the related frictional losses. The disk wobble causes contact with the walls of the cut in addition to the friction in the bottom of the cut where material removal is desired.

[0059] Traditionally disk thickness was increased to create a stiffer disk. This provides more support while permitting use of softer lower temperature active and inactive bonding materials. The softer bonding material allows friability of the abrasive material more easily exposing sharper abrasive material. While lower temperature active fillers decreases heat and friction. However, this was not shown to work in the present case.

[0060] The disk construction consisted of two sides pressed with rubber molds to provide reduced frictional losses while cutting. Different grain type systems were investigated and it was found that a 20%-100% zirconia abrasive mixture was optimal with a 100% zirconia grain abrasive to be ideal. Data in Utilizing 100% zirconia and rubber molds on each side showed 80% more cuts can be made, and 74% better metal removal rates than a standard product offering per battery charge. FIG. 2 shows number of cuts made per battery charge. The number of wheels used to deplete the battery is listed next to the product ID. The standard product chosen for this wheel type is T003-17. The standard wheel is zirconia alumina and ceramic coated (Fe2O3) aluminum oxide. The present invention disk showed zirconia is beneficial over 10% by weight. FIG. 3 shows the material removal rates per battery charge. The number of wheels used is listed next to the product ID. The standard product chosen for this wheel type is T003-17. Time for disk changeover is not included in metal removal rate.

[0061] FIG. 4 shows the simple inverse relation model for the thickness of the disk versus the number of cuts the disk will make per battery charge. However, the thicker disk removes more material creating greater frictional losses and a related reduction in cuts per battery life.

[0062] FIG. 5 shows the effect of increasing bond stiffness increases the number of cuts. Bond type 1 shows how increasing bond content while keeping the bond the same plays a role in determining battery life. Differences in the three bond types show that selection of bond type also plays a role in determining wheel hardness and battery life. This is counter intuitive as harder bonds reduces friability of the abrasive material thereby reducing new fibers in the abrasive material causing increased friction with duller abrasive material exposed for longer periods before being released by the bonding material.

[0063] FIG. 6 shows various grain types and ratios when tested against a control of 100% brown fused alumina. In general, larger harder grains were able to make more cuts, except for the 50% semi-friable grain mixture. This is because the larger harder grains were more friable and allowed pores to form in the disk. Pores are voids or air pockets in the disk. Mixes containing Zirconia alumina (40Zk) performed the best in terms of number of cuts, and the number of cuts increases with increasing zirconia content. Due to the size of the Zirconia alumina (40Zk) larger pores form in the disk permitting easier removal of debris from the work area.

[0064] FIG. 7 shows the effect of disk hardness for discs greater than 1.7 mm. Here the trend showed that softer wheels made more cuts.

[0065] Therefore, in the preferred embodiment of FIG. 12, a cut-off disk 1 for use in a battery-operated tool should be constructed having two sides 2, 3 pressed with rubber molds to provide more room for chips to form and reduce frictional losses while cutting. The rubber mold permits the wheel to preferably have a thickness less than 1.7 mm and having a bonding material 4 that is as hard as possible while having the coarsest grain 5 the spreading system will allow. The coarse grain increases the number and size of pores. The Pores provide space for debris to be removed from the working area. Further, an abrasive Alumina Oxide mix utilizing 10-100% Zirconia alumina (40Zk) preferably 100% Zirconia alumina (40Zk) should be used.

Flap Disc

[0066] The FIG. 13 shows a bottom view of a preferred embodiment of the flap disk of the present invention.

[0067] It is shown that both reducing the number of flaps and increasing the number of flaps as compared to a standard product can increase battery life for a cordless tool. Reducing the number of flaps reduces disk weight thereby increasing battery life while increasing the number of flaps increases the angle of the flap therefore reducing the overall work contact area and thereby reducing drag and increasing battery life. FIG. 8 shows the battery life compared to the number of flaps for flap discs. The wheels lasted the entire test. Flap discs with less surface area (more flaps or staggered flap pattern) or less weight performed longer than discs that were heavier or had more contact area per flap.

[0068] FIG. 9 shows the amount of material removed per battery charge for different abrasive materials. The flap wheels lasted the entire test. Due to the difference in amount removed per charge, the stearate coated ceramic+ceramic flap disc was selected.

[0069] The double stacking of the strip in hybrid formation consistently shows higher removal rates at no cost to battery life. This is believed to be due to reduced contact area of the abrasive, reducing drag forces on the motor. The top flap has more material exposed, and does most of the work, while the rear flap supports the top flap, however, the two flap materials should wear at similar rates to be effective. This is typically achieved using differing bonding agents or different abrasive materials.

[0070] By adding a lubricating coating on the top flap layer further increases battery life. Adding this layer increased battery life 20% over a non-lubricated ceramic product of similar construction, and a 33% increase in battery life over the standard zirconia product construction.

[0071] Therefore, in a preferred embodiment the flap-disk 6 for use in a battery powered tool has a layer of 60-80 flaps in a hybrid stack 7 pattern. Each hybrid stack 7 consists of a top flap 8 and a bottom flap 9. The top flap 8 and bottom flap 9 are arraigned such that as the flap disk 6 rotates in direction 10 the top flap 8 of each hybrid stack contacts the work surface before bottom flap 9. Further top flap 8 is substantially exposed compared to bottom flap 9. The rotation direction 10 can be reversed however, the overlapping of the hybrid pattern would also be reversed. The top flap 8 of each hybrid stack is preferably a stearate coated ceramic abrasive material while the bottom flap 9 contains a ceramic abrasive material.

Grinding Wheel

[0072] FIG. 14 is a cutaway view of a preferred embodiment of the grinding wheel of the present invention.

[0073] Typical grinding operations required a user to exert considerable force on the grinding tool to create the necessary frictional forces to effectively remove material from a work piece. This requires very rigid grinding disks with very fine grains that are not very friable. For AC powered grinding tools this is not a problem as more powerful motors are utilized which can overcome the frictional grinding forces and can maintain sufficient RPM to effectively remove material from the work piece.

[0074] The grinding wheel consumption was quite low as was the metal removal rates in our testing of standard products on battery operated grinding tools when compared to an electric grinder. This makes standard grinding wheels when used in a battery powered grinding tool more susceptible to loading, glazing and burning. This is further evidenced by low material removal rates per battery charge. This is primarily due to present technology grinding wheels utilizing a finer less friable grain abrasive. This abrasive is typically set in a hard bonding agent to prevent grinding wheel flex during typical grinding operations.

[0075] It would therefore be assumed that by decreasing thickness and consequently grinding wheel weight a corresponding increase in battery life would occur. However, it was found that decreasing wheel thickness had little effect on battery life.

[0076] FIG. 10 shows the battery life and metal removal per battery charge as function of the coarseness of the abrasive. Use of coarse, friable grains show an increase in material removal and battery life. Use of friable white alumina increases battery life. While black Silicon addition increased battery life significantly, it correspondingly decreased the material removal rate per charge.

[0077] The use of softer bonds showed an increase in battery life as it permitted the abrasive material to be refreshed with newer sharper grains. Further it provided significantly larger pores allowing more effective removal or waste material for the work area. Coupling a soft bond with a wax lubricant in the wheel showed the greatest increase in battery life. Additionally, using wax based lubricants significantly increases the material removal per battery charge.

[0078] FIG. 11 shows the material removed per battery charge versus the total time the total run time from one battery charge. Lightest wheels gave better life. Wheels containing wax show an improvement in grinding wheels. Products in the upper right corner are more desirable. Interestingly enough, the wax also increases the cutting efficiency dramatically when compared to similar wheel formulations that do not contain wax. The soft bond in conjunction with the more friable grains allow the grain to wear down faster than our standard product line, thus exposing fresh grains for rapid and cooler-cutting metal removal. The battery life with present invention is 33% longer and removes 16% more material per battery charge.

[0079] In a preferred embodiment, to make a grinding wheel such as grinding wheel 11 that performs better on a cordless grinder, we design a wheel containing a soft bond 12 and a friable white alumina grain 13. Black silicon carbide was also found to dramatically increase battery life, but removal rates on steel were significantly reduced. Additionally, the selected bond 12 contains a wax lubricant. This bond formulation reduces frictional forces between the wheel and workpiece, which eases demand on the battery.

[0080] A secondary aspect of design is the reduced weight and thickness of the wheel reducing the contact area. With this feature, pressure is more effectively distributed to the work area, increasing the amount of work done per battery charge. The reduced weight keeps in mind the portability needs of a cordless grinder and makes it easier to maneuver in tight spaces.