Patent Application
20060019579
The present disclosure relates generally to abrasive articles, and more particularly to back-up pad/abrasive disc combinations.
Back-up pads are used in the abrasives field to support an abrasive article, such as a disc or sheet during abrading. These abrasive articles can be in various forms, such as a disc, a sheet, or a polygon and, may optionally, contain holes or slits to aid in dust extraction. The back-up pad includes a generally planar major surface, to which the abrasive article, such as a disc or sheet, may be attached. Although back-up pads may be hand held, back-up pads are more commonly used in conjunction with a powered abrading apparatus such as electric or pneumatic sanders.
Abrasive discs and sheets (hereinafter collectively “discs”) may be attached to a back-up pad in various ways. One attachment method includes an abrasive disc having pressure sensitive adhesive (PSA) on one surface thereof, such that the abrasive disc may be adhered to the major surface of the back-up pad. The major surface of the back-up pad may have, for example, a smooth foam, vinyl, or cloth surface to facilitate attachment of the abrasive disc. An example of such a back-up pad is available from 3M Company of St. Paul, Minn., under the designation “STIKIT” brand back-up pad. An example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation “STIKIT” brand abrasive disc.
A second type of back-up pad includes a major surface having a plurality of hooks projecting therefrom. The hooks are adapted to engage certain structures provided on the back face of an abrasive disc to releasably attach the disc to the back-up pad. An example of such a back-up pad is available from the 3M Company of St. Paul, Minn., under the designation “HOOKIT” brand back-up pad, and an example of an abrasive disc for attachment to that back-up pad is available from the same company under the designation “HOOKIT” brand abrasive disc. Alternatively, the back-up pad major surface can include engaging structures to cooperate with hooks on an abrasive disc. An example of such an assembly is available from 3M Company under the designation “HOOKIT II” brand back-up pad and abrasive disc.
The present disclosure will be further explained with reference to the appended Figures, wherein like structures are referred to by like numerals throughout the several views, and wherein:
Generally, the invention of the present disclosure is directed to an abrasive article including a back-up pad removably attached to an abrasive disc. Within the context of this disclosure, removably attached means that the disc is secured to the back-up such that it will not detach during an abrading operation, but can be removed from the back-up pad via manual means, e.g., taken off by hand. The abrasive disc includes a plurality of perforations or holes therethrough for allowing passage of debris (swarf, dust, particles, metal, etc.) from a workpiece into the area or volume between the back-up pad and the abrasive disc.
Various perforation (interchangeably, also holes) configurations in the abrasive disc can be used with the particle impermeable back up pad.
While the above-described discs include circular holes (or perforations), other shapes can be used, either singly or in combination. Referring to
Other possible arrangements include the holes or perforations distributed over the entire disc, both uniformly and non-uniformly. The holes or perforations can also be distributed over annular sections of the disc. The perforations on a given disc can be of uniform size, or can be of various shapes and sizes.
To increases the amount of debris that can be accommodated between the disc and the back-up pad, means for accumulating the debris can be optionally included. For example, the back-up pad can have an undulating surface, wherein the low points in the surface will allow more debris to be trapped. The back-up pad can also include cavities, which allows debris to be trapped. An interface pad can also be included between the back-up pad and the disc, adding further debris holding capacity. An exemplary interface pad is available under the trade designation “SOFT INTERFACE PAD,” available from 3M Company, St. Paul, Minn.
The back-up pad of the invention can be used in any of a variety of desired abrading applications so long as it is properly designed to meet the requirements of the given abrading application. The foam material and mixing proportions of the components of the foam should be formulated to meet the needs of the desired abrading application.
It is within the capability of one of ordinary skill in the art to select the back-up pad to meet the requirements of the abrading for which the pad is used. It is to be understood that the term abrading, and its variants, as used herein are meant to include operations used to reduce or refine a workpiece surface through frictional contact between the workpiece surface and an abrasive article, such as grinding, sanding, finishing, cleaning or polishing operations. These abrading applications can vary widely from final polishing of ophthalmic lenses to heavy stock removal of metal parts. These abrading applications can also involve either abrading by hand or abrading with a machine as the mode of driving the abrasive article in motion. The abrading motions may include a linear motion, random motion, rotary motion, oscillation, random orbital motion, combinations thereof or the like.
The shape of the foam back-up pad may be a square, triangle, rectangle, oval, circle, pentagon, hexagon, octagon, polygon, or any other suitable shape. The diameter for a circular back-up pad ranges from about 0.5 to 50 inches (1.25 cm to 127.0 cm), typically 1 to 30 inches (2.5 cm to 76.2 cm). The length and/or width of the back-up pad can range from about 0.05 to 50 inches (0.13 cm to 127.0 cm), typically 1 to 30 inches (2.5 cm to 76.2 cm). In some instances, a coated abrasive article will overhang the back-up pad by a very slight amount, i.e., typically less than 0.1 inches (0.25 cm), preferably less than 0.05 inches (0.13 cm). The thickness of the foam body member generally will range from between about 0.2 cm to 7.0 cm typically 0.5 cm to 5.0 cm, and preferably between 1.0 cm. to 3.0 cm.
The foam back-up layer, as used in most abrading applications, will be molded to present a pair of substantially parallel spaced major surfaces or faces. Referring to
If the foam back-up pad is intended to be used in machine driven applications, it will typically have some type of mechanical attachment system opposite the side of the loop fabric to secure the back-up pad to the machine. One such system comprises rigid backing plate 122 fixed to the rear surface 119 of the foam back-up pad 110 with threaded stud 123 fixed to the plate 122 (e.g., by welding) for attachment of the foam pad 110 to a drive motor, such as described in U.S. Pat. No. 4,844,967 (Goralski), incorporated herein by reference. Backing plate 122 is affixed (e.g., by rivets) to a larger diameter fiberglass plate (not shown) or an equivalent member, and the foam surface 119 is bonded directly to the fiberglass to thereby affix the mounting system to the back-up pad 110. Any of a variety of systems or means can be provided for detachable coupling of the foam pad 110 to different types of drive motor assemblies. Such means are known in the art and may include, for example, central concentric openings extending through the foam and the backing plate and accommodating the threaded end of a headed bolt, with the bolt head abutting the surface of the backing plate affixed to the foam with the head of the bolt positioned in the central opening of the foam and the threaded end of the bolt engaging the drive member of a drive motor assembly. For random orbital applications, the support member may contain a threaded studded or other attachment system for mounting onto the machine. Other means that can be provided to adapt the back-up pad for operation with drive mechanisms include those disclosed in U.S. Pat. No. 4,631,220 (Clifton), incorporated herein by reference. It will be understood that the invention is not limited by the specific mounting system employed, and those skilled in the art will appreciate that the specific mounting system employed for use with a specific back-up pad will depend on the type of tool to be used with the pad.
For manual abrasive operations held in the hand, various shapes or configurations of foam back-up pads may be utilized. Two such types include hand pads and foamed back-up pads used on long planing boards. The strength and other physical properties required for these manual abrasive operations is less than those for random orbital applications where the strength and physical property requirements of the foam become much more significant. The physical properties of the foam depend on the end use application. As the back-up pad is used in abrading applications, there can be a manual grip handle associated with it.
In some instances, it is preferred to incorporate a pressure sensitive adhesive onto the backside of the abrasive article so that the backing of the abrasive article can be secured to the facing layer of the foam back-up pad. Representative examples of pressure sensitive adhesives suitable for this invention include latex crepe, rosin, acrylic polymers and copolymers e.g., polybutylacrylate, polyacrylate ester, polyvinyl ethers, e.g. polyvinyl n-butyl ether, alkyd adhesives, rubber adhesives, e.g., natural rubber, synthetic rubber, chlorinated rubber, and mixtures thereof. The preferred pressure sensitive adhesive is an isooctylacrylate: acrylic acid copolymer.
Alternatively, a hook and loop type attachment system may be employed to secure the abrasive article to the facing of the foam back-up pad. The hook fabric may be on the backside of the abrasive article with hooks on the front side of the back-up pad. Otherwise, the hooks may be on the backside of the abrasive article with the loops on the front side of the back-up pad. This hook and loop type attachment system is further described in U.S. Pat. No. 4,609,581 (Ott); U.S. Pat. No. 5,254,194 (Ott et al.); U.S. Pat. No. 6,579,162 (Chesley et al.); U.S. Pat. No. 5,505,747 (Chesley et al.); U.S. Pat. No. 5,607,345 (Barry et al.); and U.S. patent publication No. 03-0159363-A1 (Chesley et al.); each of which is incorporated herein by reference. The opposite exposed front side of the abrasive article has an abrasive coating that is responsible for the abrading action.
The following materials were obtained from 3M Company, Saint Paul, Minn. As noted, some materials were subsequently modified for evaluation purposes.
The following test methods were used.
Off-Hand Abrasion Test.
An abrasive disc was secured to the appropriate size backup pad according to the respective attachment system. The disc pad was then attached to a dual action sander, commercially available as model number “57015”, from the Dynabrade Company, Clarence, N.Y. Abrasion tests were run for up to 138 seconds, in various intervals, over three adjacent sections of the test panel, at an air pressure of up to 620.5 kPa (90 Psi) and a disc-to-panel angle of 0-2.5 degrees.
Surface Finish
Surface finish (Rz) is the average individual roughness depths of a measuring length, where an individual roughness depth is the vertical distance between the highest point and the lowest point. The surface finish of abraded test panels were measured using a profilometer under the trade designation “PERTHOMETER MODEL M4P-127527” from Mahr Corporation, Cincinnati, Ohio. Surface finish values were measured at five points within each of the three abraded sections of the test panel at the end of the third sanding interval.
Cut Rate
Cut-rate refers to the ability of the abrasive article to remove stock material or surface particles from the workpiece. The cut rate is the amount of weight loss of the test panel during the sanding operation. The test panel was weighed with an accurate electronic balance before the sanding test began. Using the sample test fixture the painted panel was sanded as described above. After each sanding cycle the test panel was cleaned of accumulated swarf by blowing with compressed air. The test panel was re-weighed to establish the weight loss (cut) during each sanding interval. The cumulative weight loss for each sanding interval was then recorded. The tests were run in triplicate.
Stiction
Sanding a smooth abrasive coating may create what is known in the industry as “stiction”, whereby the abrasive coating may stick to the workpiece surface, with unwanted results. It is preferred to minimize stiction in fine finishing applications.
Samples of test panel TP1 were sanded according to the method described above at a pressure of 620.5 kPa (90 Psi). Results are listed in Table 1.
Samples of test panel TP2 were sanded according to the method described above at a pressure of 620.5 kPa (90 Psi). Results are listed in Table 2.
Samples of test panel TP1 were sanded according to the method described above at a pressure of 620.5 kPa (90 Psi). Results are listed in Table 3.
Samples of test panel TP1 were sanded according to the method described above at a pressure of 620.5 kPa (90 Psi). Results are listed in Table 4.
Samples of test panel TP3 were sanding according to the method described above at a pressure of 248.2 kPa (36 Psi). An interface pad, commercially available under the trade designation “HOOKIT II SOFT INTERFACE PAD” from 3M Company, was applied between the abrasive disc and the back-up pad. Results are listed in Table 5. Three different lots of “260L P1000 HOOKIT II DISC” and “260L P1000 HOOKIT II DUST-FREE DISC” were evaluated.
Samples of test panel TP2 were sanded according to the method described above at a pressure of 275.8 kPa (40 Psi) using a STIKIT disc pad. Results are listed in Table 6.
Samples of test panel TP4, moistened with a thin film of water, were hand sanded using HOOKIT II discs attached to hand HOOKIT II center water feed back up pad. Results are listed in Table 7.
Samples of test panel TP5, were dry hand sanded using HOOKIT II sheets attached to hard hand sanding block BP6, in a series of 4 intervals of 5 strokes (backward-forward) each. Cut performance and stiction ratings, as an average of triplicate samples, are listed in Table 8.
Samples of test panel TP3 were sanded according to the method described above at a pressure of 248.2 kPa (36 Psi). With respect to Example 20 and Comparative R, an interface pad, commercially available under the trade designation “HOOKIT SOFT INTERFACE PAD” from 3M Company, was applied between the abrasive disc and the back-up pad. With respect to Example 21 and Comparative S, an interface pad, commercially available under the trade designation “HOOKIT II SOFT INTERFACE PAD” from 3M Company, was applied between the abrasive disc and the back-up pad. Results are listed in Table 9.
Samples of test panel TP2 were sanded according to the method described above at a pressure of 275.8 kPa (40 Psi). With respect to Examples 23-24 and Comparatives U-V, interface pads, as described previously, were applied between the abrasive disc and the back up pad. Results are listed in Table 10.
The abrasive disc, the means for the attachment of the article to the back-up pad, the foam facing layer, the rigid backing plate and threaded stud, as mentioned above in connection with the discussion above, while useful and necessary from a practical standpoint to the present invention, can be supplied by known means and constructions in the field and thus should require no further details than that provided herein to be understood by one of ordinary skill in the art.
