AU736898B2 - Tyre rasp blade and assembly - Google Patents

Description

P00011 Regulation 3.2 Revised 2/98

AUSTRALIA

Patents Act, 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT TO BE COMPLETED BY THE APPLICANT NAME OF APPLICANT: ACTUAL INVENTOR: ADDRESS FOR SERVICE: INVENTION TITLE: DETAILS OF ASSOCIATED

APPLICATION(S):

SPENCER INDUSTRIES PTY LIMITED (ACN 000 441 001) ANTHONY COLLINS Peter Maxwell Associates Level 6 Pitt Street SYDNEY NSW 2000 TYRE RASP BLADE AND ASSEMBLY Divisional of Australian Petty Patent No.

719,185 (58,291/99) filed on 4 November 1999 The following statement is a full description of this invention including the best method of performing it known to me:- 2 The present invention is in the field of tyre retreading and relates to improvements in both the process and apparatus used for the retreading of tyres. In particular, the invention relates to rasp blades, and in an improved assembly of such blades on tyre rasp hubs for buffing away the tread on worn tyres.

It is becoming increasingly accepted that the retreading of worn tyres, also known as casings, contributes positively to both the economic and environmental well being of the community by providing reduced manufacturing *i and purchase costs and by preventing large numbers of worn tyres from polluting and destroying the environment, whether as land fill or discarded otherwise. Also, as tyres are petrochemically derived products, large reserves of oil and other energy forms are used in their manufacture, and the resultant polluting emittents are an undesirable by-product. It is generally not well known that most of a worn tyre remains useful as the tyre body or walls, comprising a significant major portion of the tyre, are normally in excellent condition and have about the same strength as a comparable new tyre.

The conventional process by which suitable worn tyres, or casings, are 9 retreaded is-to buff away the worn tread, selectively repair any damage that may remain in the casing after buffing, bond the new tread to the casing by a selected vulcanizing process, cure the rubber so as to harden and shape it into the desired tread design, before final inspection for suitability for use.

In order to buff and cut away the worn tread, the casing is mounted on a buffing machine (or lathe type machine) and inflated. A tyre buffing rasp hub, comprising a hub core having a large number of toothed rasp blades mounted thereon, is then rapidly rotated, say, on a motor driven shaft, and the peripheral surface of the casing is moved against the rotating rasp hub so as to loosen, tear and grind off the excess rubber and roughen it sufficiently so that the I. i 3 buffed surface of the casing can bond the new rubber tread in the vulcanizing process. Each tyre has a predetermined crown width, profile and radius and the casing must be buffed to the particular shape, size and texture to receive a new tread that ensures optimal tread to road contact. Buffing of the worn tread is therefore a critically important stage of the retreading process.

Rasp blades of the prior art comprise numerous configurations and shapes, a particularly preferred type having teeth of essentially dove tail shape projecting from the outer working edge of an arcuately shaped rasp blade, 9 each of the teeth having a notch cut out from the most distant surface from the body of the blade to form a series of substantially shaped teeth separated by recesses of partly incomplete circular shape. The notch formed in each tooth divides it into halves, and each half is offset to opposite sides of the general plane in which the blade lies, thus creating a second edge immediately behind the cutting edge of each tooth. As the rasp hub is rotated, the first or 15 leading edge buffs or cuts the surface of the casing to a texture which markedly improves the bonding of new rubber thereto.

A typical tyre buffing rasp hub which includes such rasp blades as aforementioned has the form of a hub core defined by interconnected front and back cylindrical end plates having mounted therebetween arcuate or quadrant shaped rasp blades stacked in four (or more) separate parallel arrays with a partly spiral inclination around the circumferential perimeter of the rasp core.

Each rasp blade of any one stack is separated from its adjacent other blade of the stack by spacers, the stack being secured in position between the end plates by support pins. Removable fastening means hold the end plates together, sandwiching the rasp blades, thus allowing for dismantling of the rasp hub for purposes of maintenance and repair, such as when the teeth become worn or are broken.

I VP Ir..

4 Prior to the present invention, all blades of whatever configuration and shape used on tyre rasp hubs were of identical shape, size and distribution of teeth for that particular tyre rasp hub. For instance, any two adjacent blades in a stack had identical secondary and tertiary configuration and any one tooth of one blade was aligned substantially horizontally (or vertically depending on the set up of the buffing machine) with a tooth of the adjacent blade. This was usually facilitated by fixing each blade of a stack in a "name down" direction, whereby the manufacturer's name which appeared on only one of the two opposed faces of the blade indicated the direction to which the name side of all blades of that stack were to face. Where this technique was not employed, some other means of facilitating the stacking of the blades in a commonly aligned direction was used. Furthermore, all of the teeth on each blade were "symmetrically disposed across the working edge of the blade. For instance, the tooth closest to one end,was located the same distance from that end as 15 the tooth closest to the other end was located from that other end.

It has now been found by the present inventor that by off-setting or indexing all of the teeth to one side of their position in prior art symmetrically S.disposed blades by a quarter of the pitch that separates each tooth in the blade, and by fixing each blade of a stack in a repeating "name up", "name down" direction, a superior and longer lasting buffing performance and buffed texture is achieved. The assembly of blades so formed presents one form of a staggered teeth array across each stack of the rasp hub.

It is therefore an object of the present invention to provide a rasp blade of the aforementioned indexed teeth type developed by the present inventor that can be used in the assembly of a tyre rasp hub having an alternating staggered teeth array across each stack of the rasp hub.

It is another object of the present invention to provide an arrangement of blades on a tyre rasp hub in which the aforementioned alternating staggered teeth array is adapted to buff away worn tread from a casing at a rapid rate while developing a minimum amount of heat that might otherwise adversely affect the texture of the buffed surface needed for suitable retreading.

According to the present invention there is provided an arrangement of rasp blades on a tyre rasp hub, wherein at least one stack of spaced apart rasp blades is fitted to the rasp hub as a parallel array extending .0 circumferentially around the tyre rasp hub, said arrangement comprising, in 10 any two adjacent rasp blades in the or each stack of spaced apart rasp blades: a first blade including a first set of teeth uniformly distributed along a working edge of the first blade, said first set of teeth having a predetermined pitch, and 15 a second blade including a second set of teeth uniformly distributed along a working edge of the second blade, said second set of teeth having the same pitch as the first set of teeth but located in a staggered *relationship to the first set of teeth.

Preferably, the first blade has a first tooth of its set of teeth at a first predetermined location relative to a reference end of its working edge, and the second blade has a first tooth of its set of teeth at a second predetermined location relative to the end of its working edge closest to the reference end, the said first and second predetermined locations being offset by a half of the said predetermined pitch of the teeth to produce the said staggered relationship of the said set of teeth.

In a preferred form, the first and second blades are of identical shape and configuration, each of the said blades having a first tooth of its set of teeth 6 at a first predetermined location relative to a reference end of its working edges, and having a second tooth of its set of teeth at a third predetermined location relative to the end of its working edge furthest from the reference end, the said first predetermined location being offset from the reference end by a quarter of the said pitch and the said third predetermined location being offset from the end furthest from the reference end by a quarter of the said pitch, the first and third blades being disposed in oppositely facing directions whereby, in any two adjacent rasp blades in a stack, the said first and second :o o o o predetermined locations are offset by a half of the said pitch.

10 In order that the invention may be readily understood and put into o*eo practical effect, reference will now be made to the accompanying drawings, in which:- Fig 1 is a side elevational view of a prior art rasp blade having teeth of essentially dove tail shape, Fig 2 is a plan view of the prior art rasp blade of Fig 1, Fig 3 is a side elevational view of a rasp blade, having teeth of essentially dove tail shape, said rasp blade being in accordance with a preferred embodiment of the present invention, the teeth having been offset or indexed from one end of the blade by a quarter of the pitch of the teeth, Fig 4 is a schematic view of a portion of a stack of rasp blades mounted to a rasp hub according to the prior art, Fig 5 is a schematic view of a portion of a stack of the rasp blades of Fig 3 mounted to a rasp hub according to a preferred staggered arrangement of rasp blades on a tyre rasp hub of the present invention, and Fig 6 is a graph of buffing performance versus number of tyres being buffed with both a rasp blade arrangement of the present invention and a rasp blade arrangement of the prior art.

The rasp blade 10 of the prior art shown in Figs 1 and 2 is quadrant shaped or arcuate. The manner of manufacturing and form of the rasp blade having a set of teeth 12 of essentially dove tail shape is well known, as exemplified in US Patent No. 3,082,506, the contents of which are incorporated herein by reference.

10 The set of teeth 12 are uniformly distributed along a working edge 14 of ooo° the blade 10 and have a predetermined pitch or distance by which each tooth 12 is repeated. A first tooth 12a closest to a first end 18 of the working edge 14, and a second tooth 12b closest to the end 20 of the working edge 14 furthest from the first end 18, are located an equal distance away from each respective end 18, 20 so that the set of teeth 12 are symmetrically disposed across the working edge 14 of the blade In a rasp hub upon which a plurality of the rasp blades 10 are mounted in stacks of four separate parallel arrays with partly spiral inclination around the circumferential perimeter of the rasp hub, each of the spaced apart blades of the stack have their respective sets of teeth 12 lined up substantially horizontally or vertically in use, as is also well known in the prior art, and as shown in Fig 4.

The rasp blade 22, as shown in Fig 3, whilst having identically shaped and configured teeth 24, differs from the rasp blade 10 in that all of its teeth 24 are indexed or offset from the first end 26 of the working edge 28 by a quarter of the pitch by which each tooth is repeated. It will, of course, be readily appreciated by persons skilled in the art that the extent of indexing or offsetting 8 of the teeth in the blades used in the arrangement of the present invention may vary, on the proviso that a staggered relationship of the set of teeth of any two adjacent blades in a stack of a rasp hub is produced. When offset by a quarter of the pitch in, say, an anticlockwise direction across the blade 22, the tooth 24a closest to the first end 26 will comprise a half complete tooth structure whereby it is split symmetrically therethrough, and the tooth 24b furthest from the first end 26 will comprise one complete tooth structure. It should be noted that in the prior art blade 10, the equivalent teeth 12a and 12b each comprise a three quarters complete tooth structure.

10 The rasp blades 22 are arranged in a stack of a rasp hub whereby, in any two adjacent rasp blades (22a, 22b), a first blade 22a is disposed in an oppositely facing direction to a second blade 22b. In this way, the set of teeth 2' 24a of the first blade 22a will be offset by a half of the pitch of the teeth from the set of teeth 24b of the second blade 22b, to produce a staggered relationship of the two sets of teeth-(24a, 24b), as shown in Fig A staggered relationship of the respective sets of teeth of any two adjacent rasp blades in a stack of a rasp hub, may also be produced by utilizing the rasp blades of the prior art, namely those having their set of teeth symmetrically disposed across the working edge of the blade .(such as in Fig but locating these blades in an unaligned stack of blades where every second blade of the stack is shifted sideways in its position relative to its immediately adjacent blades (on either side thereof) by a distance of, say, half the pitch of the teeth, so as to create the arrangement shown in Fig A rasp hub fitted with a series of stacked rasp blades 22 arranged whereby the teeth are staggered in the manner shown in Fig 5 provides superior buffing performance over rasp hubs fitted with prior art blades in the conventional manner. Not only is texture of the buffed surface improved, but the overall number of tyres which can be buffed to an acceptable standard is greatly increased with the arrangement of the present invention, as shown in Fig 6, which graphs buffing performance against number of tyres. The R.M.A.

scale from 1 to 6 of texture is based on accepted industry standards of smooth (value of 1) to rough (value of 6) textures. A value of 3 or 4 is acceptable (3 is preferable), and significantly more tyres can be buffed to an acceptable texture having the R.M.A. value of 3 or 4 with the present invention than with the prior art.

Various modifications may be made in details of design and construction 10 without departing from the scope and ambit of the invention.

oo a g oo* *o

Claims (3)

1. An arrangement of rasp blades on a tyre rasp hub, wherein at least one stack of spaced apart rasp blades is fitted to the rasp hub as a parallel array extending circumferentially around the tyre rasp hub, said arrangement comprising, in any two adjacent rasp blades in the or each stack of spaced apart rasp blades: a first blade including a first set of teeth uniformly distributed along a working edge of the first blade, said first set of teeth having a predetermined pitch, and a second blade including a second set of teeth uniformly distributed :oo:.along a working edge of the second blade, said second set of teeth having the same pitch as the first set of teeth but located in a staggered relationship to the first set of teeth.

2. The arrangement of rasp blades of claim 1 wherein the first blade has a first tooth of its set of teeth at afirst predetermined location relative to a reference end of its working edge, and the second blade has a first .sea tooth of its set of teeth at a second predetermined location relative to the end of its working edge closest to the reference end, the said first and second predetermined locations being offset by a half of the said predetermined pitch of the teeth to produce the said staggered relationship of the said set of teeth.

3. The arrangement of rasp blades of claim 1 or claim 2 wherein the first and second blades are of identical shape and configuration, each of the said blades having a first tooth of its set of teeth at a first predetermined location relative to a reference end of its working edges, and having a 11 second tooth of its set of teeth at a third predetermined location relative to the end of its working edge furthest from the reference end, the said first predetermined location being offset from the reference end by a quarter of the said pitch and the said third predetermined location being offset from the end furthest from the reference end by a quarter of the said pitch, the first and second blades being disposed in oppositely facing directions whereby, in any two adjacent rasp blades in a stack, the said first and third predetermined locations are offset by a half of the said pitch. Dated this 31st day of July, 2000 Patent Attorneys for the Applicant S. See. PETER MAXWELL ASSOCIATES *•il °oO