US 3395417 A
Description (OCR text may contain errors)
Aug. 6, 1968 N. MATOUKA 3,395,417
BACKUP PAD ASSEMBLY Filed April 5, 1966 INVENTOR.
United States Patent 3,395,417 BACKUP PAD ASSEMBLY Nicholas Matouka, Royal Oak, Mich, assignor to Formax Manufacturing Corporation, Detroit, Mich., a corporation of Michigan Filed Apr. 5, 1966, Ser. No. 540,372 2 Claims. (Cl. -230) ABSTRACT OF THE DISCLOSURE A backup .pad construction with a soft flexible pad member secured to a flexible backup plate and with a rigid insert member connected to the backup plate. The inner face of the backup plate has spaced annularly extending grooves providing zones of flexibility.
The present invention relates to the construction of backup pad assemblies. Backup pad assemblies are used to finish workpieces and are made flexible to accommodate the different contours of the workpieces. Backup pad assemblies have been made of a backup plate of a relatively inflexible material and a pad member which is made of a soft rubber of plastic with the two bonded together by conventional means. With this type of construction, substantially all of the flexibility is provided by the pad and hence a relatively thick pad member must be provided. Normally, the juncture between the pad member and backup plate is in a single plane and hence the bond between the two is on this plane. It is important that this bond be secured in order to in sure that the pad member will not be torn loose from the backup plate. In present invention a backup plate having undulations is provided which lend both flexibility to the backup plate and also provide for better bonding between the pad member and the backup plate; also, in the present invention because a backup plate is provided which is flexible, the pad member need not be as thick and hence a lighter backup pad assembly can be provided. Therefore, it is an object to provide an improved backup pad assembly.
It is another object of the present invention to provide a backup pad assembly in which an improved bond is provided between the pad and the backup plate.
It is still another object of the present invention to provide a backup pad assembly in which the backup plate is flexible and enhances the total flexibility of the backup pad assembly.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which:
FIGURE 1 is a front elevational view of a backup pad assembly embodying features of the present invention; and
FIGURE 2 is a sectional view to increased scale of the backup pad assembly of FIGURE 1, taken substantially along the line 22.
Looking now to the drawings, a backup pad assembly generally indicated by the numeral 10 and includes a pad member 12 which can be made of a soft flexible material such as a soft urethane foam and which is provided with a tough face member 14 at its forward surface which is flat. The face member 14 is preferably made of canvas or some other porous material whereby the urethane of the pad member 12 will flow partially through the pores therein in molding and, hence, a secure bond is provided between the face member 14 and the forward surface of the pad member 12. The pad member 12 is secured at its opposite rearward surface to a backup plate 16 which can be made of a flexible material such as a flexible solid urethane. While the back- "ice up plate 16 is made of a flexible material it should be understood that it is substantially stiffer than the pad member 12. The backup plate 16 in turn is molded to a relatively stiff mounting insert 18 which is made of a strong and generally stiff material such as a polycarbonate. The insert 18 is less flexible than either the pad member 12 or the backup plate 16.
The insert 18 has a tubular portion 20 provided with a plurality of threads 22 whereby the backup pad assembly 10 can be mounted on one end of a threaded shaft for rotation thereby. Attached to the tubular portion 20 of the insert 18 is an annular web portion 24 which is generally of an irregular contour radially, The backup plate 16 has a hub portion 30 molded generally about the web portion 24 and the forward end of the tubular portion 20.
The insert 18 being made of polycarbonate is generally stiff; however, polycarbonate is a material which is easily moldable into a selected shape and has good strength characteristics whereby the tubular portion 20 and threads 22 are strong. However, because of its lack of flexibility, the polycarbonate does not lend itself to substantial flexing and can fail under repetitive, high loads. The backup plate 16 being made of a flexible solid urethane is more flexible and also has good fatigue characteristics and thus provides a good combination with the polycarbonate insert 18. The backup plate 16 has an annular contour and is provided with a radially outer tapering ring portion 26 which is connected to generally flat backed portion 28. The hub portion 30 of the backup plate 16 generally provides the connection between the portion 28 and the insert 18. The forward surface of the backup plate 16 is provided with an annular groove 32 which is just adjacent to and surrounds the hub portion 30. The groove 32 is contoured to project axially inwardly and provides at its root a reduced section portion 34. A second generally similarly constructed groove 36 is located adjacent to and surrounds the groove 32 and likewise projects axially inwardly to define a minimum or reduced section portion 38.
The annular ring portion 26 is blended into the groove 36 and defines a frusto conical section which tapers radially outwardly to a minimum section at its extremity.
By the provision of the grooves or undulations 32 and 36, points of reduced sections 34 and 38 are provided which provide areas of increased flexibility. With this construction, the flexibility of the pad assembly 10 is enhanced by the backup plate 16 because of the inherent flexibility both of the flexible urethane and also because of the provision of the areas of flexibility as at the reduced sections 34, 38. It should be noted that most of the work is done at the outer peripheral edges of the pad member 12 and hence most of the force will be applied thereto. The pad member 12 is of a larger diameter than the backup plate 16 and from a point extending radially outwardly from the groove 36 the pad member 12 gradually decreases in section. By locating a point of flexure or groove 36 near the outer end of the backup plate 16 the change in flexibility is gradual in a radial inward direct-ion providing for a well balanced construction. By the provision of the grooves 32 and 36 the flexing of the backup and assembly 10 is caused to occur at a point removed from the hub portion 30 and, hence, removed from the stilfer insert 18. Thus substantially little flexing is imposed upon the stiff insert member 18; since the backup plate 16 is flexible, the backup pad assembly 10 can readily conform to the contour of the part to be worked upon and because of the added flexibility provided by backup plate 16 the pad member 12 can be maintained at a minimum. The result is a generally lighter pad assembly 10. Note that the undulations or flexing grooves 32 and 36 provides -for a greater resultant area of contact between the backup plate 16 and the pad member 12; as a result, a better bond can be provided therebetween. Note also that the pad member 12 is molded to the tough front face 14 and the backup plate 16 with an impervious skin formed on the exposed areas; the result is that Water, etc. will not get into the interior of the pad member 12 and, hence, the backup pad assembly will maintain good operating characteristics under working conditions.
While it Will be apparent that the preferred embodiment of the invention disclosed is Well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.
What is claimed is:
1. A backup pad assembly comprising a pad member made of a generally flexible material and means for supporting said pad member comprising a backup plate secured to the backside of said pad member and hub means for engaging said backup pad assembly for rotation, said backup plate having flexing means comprising one area of reduced section betwen said hub means and the radially outer periphery of said backup plate whereby said backup plate is flexible about said one area, said reduced section defined by a first generally annularly extending groove, said hub means comprising an insert member of a rigid construction secured to said backup plate with said insert member including gripping means adapted to be gripped for rotation, said pad member being constructed of a soft, resilient material substantially more flexible than that of said backup plate, said backup plate being constructed of a hard, resilient material which is substantially more flexible than said insert member, said pad member having a generally uniform cross section from said hub means radially outwardly through said flexing means except for said reduced section, said flexing means comprising a second area of reduced section for providing flexing of said backup pad assembly at points removed from said hub means with said second area being defined by a second generally annularly extending groove, one of said first and second grooves being located near the radially outer end of said backup plate, said pad member having a portion extending radially outwardly beyond said backup plate withsaid portion tapering gradually radially outwardly of said one of said grooves to minimum thickness.
2. The assembly of claim 1 with said pad member composed of a flexible polyurethane foam, with said backup plate composed of flexible solid urethane and with said insert composed of a still, rigid plastic such as polycarbonate and with said gripping means comprising a threaded portion on said insert.
References Cited UNITED STATES PATENTS 2,217,791 10/1940 Burleigh 51-379 2,229,745 1/ 1941 Kneisley 51-379 XR 2,800,751 7/1957 Bruckcr 51-377 2,800,752 7/1957 Short 51-376 2,950,584- 8/1960 Welch 51-378 2,958,166 11/1960 Poland 51-358 3,082,582 3/1963 Jeske 51-358 3,315,420 4/ 1967 Moberg 51-378 FOREIGN PATENTS 321,223 6/ 1957 Switzerland.
DANIEL B-LUM, Primary Examiner.