Plastic and nonmetallic article shaping or treating: processes – Treating shaped or solid article – By a temperature change
Reexamination Certificate
2001-02-16
2004-02-10
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Treating shaped or solid article
By a temperature change
C264S326000, C425S445000, C425S446000, C425S028100, C425S036000
Reexamination Certificate
active
06689304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for improving the concentricity of an automobile tire in which its bead is subjected to post-treatment for improving its concentricity after vulcanization.
2. Discussion of Background Information
German Patent No. 458 554 discloses a process for balancing tube-like hollow shafts made of metal, in which, at the locations where an unevenness in mass distribution causes an excessively large centrifugal force to arise, small inward dents of the shaft wall, i.e., dells, are produced.
In 1972, the German utility model G 72 28 584.8 disclosed a device for monitoring the bead characteristics of motor vehicle tires. In this connection, the tire bead is moved onto a drum, which is apparently divided into segments, and the segments are moved radially apart. The reaction forces exerted on the segments in this process are measured.
In 1998, DE-OS 196 43 762 A1 disclosed a further development of the above-mentioned device in which the conicity of the segments that can be moved radially apart is adapted to the conicity of the rim seat surfaces for the purpose of evening out the compression. Here, it is discussed for the first time that bead rubber can flow plastically under extreme compression. By reducing the maximum compression, this source of errors should be stopped.
DE-PS 24 55 279 C2 discloses a process for balancing a pneumatic wheel by means of plastically deforming the rim.
It is known from DE-OS 27 15 111, in order to reduce tire unbalance, to expose completely vulcanized tires to such a post-treatment that additional rubber is applied or removed on the axially inner side of the bead.
It is known from EP 0 405 297 to locally shift the bead in an analogous manner as in the previously mentioned reference using a detachably mounted disk of adjusted thickness over the circumference in such a way that the bead creates a more even radial force in the tread zone at a given tire deflection.
DE-OS 43 09 513 A1 discloses various processes for improving tire concentricity of a pneumatic wheel, among those a plastic deformation of the rim.
It is known from DE 43 39 775 A1 to remove, preferably to grind down, some rubber from the radially inward pointing bead surface on those locations, i.e., phase positions, where the tire the tire creates too large a radial force or has too large a tread radius. This appears to us to be the nearest prior art.
U.S. Pat. Nos. 3,550,442; 3,719,813; 3,862,570; 4,016,020, and 4,414,843, as well as Japanese Application No. 61-195 809 also relate to the correction of tire unevenness.
The retroactive application of rubber, as known from the above mentioned DE-OS 27 15 111, causes difficulties in practice because the green tires are generally coated with a separation agent before vulcanization. At the locations where rubber is to be applied retroactively and be attached firmly by means of vulcanization, this separation agent must be removed thoroughly and the seam surfaces must be roughened; both processes are several times more expensive than removing rubber, regardless of where from.
A disadvantage of the method according to DE 43 39 775 A1 is that this type of fault compensation is practically irreversible because, as previously explained, the retroactive (re)application of rubber is very expensive; thus it follows that generally the first correction is also the last possibility. Therefore, there must be a very high degree of certainty as to how much must be removed at which location before the irreversible reduction is executed. According to prior experience, good results are achieved herewith only when each treated tire has previously been individually measured, even when the tires of the same batch contain a common systematic defect in addition to the random individual defects.
Another disadvantage of the above mentioned method is that the rubber abrasion causes soiling of the working areas.
Although EP 0 405 297, which has already been cited, avoids these two disadvantages, it is unfavorable for all tire-mounting enterprises, i.e., the automobile manufacturers and the tire dealers, because it requires the handling of two additional components per wheel.
SUMMARY OF THE INVENTION
The invention avoids the disadvantages mentioned herein.
By way of background, the inventors realized that the bead should remain the point of intervention because only by avoiding the tread as a point of intervention will the performance and the useful life of the tire remain unchanged by the correcting measure. They also realized that the problem they were facing could not be solved within the standard ways of thinking; after all, if no additional part is to be used, grinding is to be avoided due to its irreversibility, and its application is decidedly too expensive, no other options seem available at first.
The inventors broke into this seemingly hopeless situation of contradicting goals with their idea of attaining the object by plastically reshaping the bead during post-treatment, at least in certain areas. This is based on the surprising recognition that many rubber mixtures can be reshaped quasi-thermoplastically when a sufficiently high pressure, a sufficiently high temperature, and a sufficiently long period of influence are used. This is surprising insofar as vulcanized rubber mixtures are considered elastomers, see, e.g., DIN 7724. Here it is stated: “Elastomers, also called vulcanized materials or rubber, have a glass transition temperature T
g
of less than 0° C. and have no flow range above their operating temperature range up to their dissolution.” In the report on the conference “Elastomeric Sheets in Flat Roof Construction” on Mar. 24, 1981 in Frankfurt/Main, printed in the magazine “Kautschuk+Gummi·Kunststoffe, vol. 34, No. 11/81, pages 927 through 937 it is written on page 931, right column, from line 4 on:
“Elastomers are rubber elastic polymer materials which can no longer be molded thermoelastically, therefore, have no flow range. This is now accomplished by the vulcanization process in which the macro-molecules are interlinked via chemical cross-linking so that they can no longer shift in relation to one another, i.e., they cannot flow.”
The quasi-thermoplastic flow created according to the present invention proceeds considerably slower than in known thermoplasts and known thermoplastic elastomers. The quasi-thermoplastic flow seems to be not a pure physical gliding-by of chained molecules, but rather a dissolution of highly stressed sulfur bridges and a reconstruction of less stressed sulfur bridges, therefore a remodeling of sulfur bridges:
If the sulfur bridge that is stressed the most and thus contains the most energy is replaced by one of lower stress, then all the other sulfur bridges are stressed more by a small amount. The formerly second most stressed sulfur bridge surrenders also to the additional stress and replaces itself by a less stressed sulfur bridge while releasing energy, and so on. The suggested, but not completely proven, leap of the sulfur bridge connector from one anchor atom of the polymer atom and/or the filler atom to another anchor atom would therefore be in the end a mechanically induced chemical process.
Besides mechanical tension, the course and the result of this chemical process is also influenced by the process temperature and the time available for the process. An increase of the process temperature and/or of the process duration enables the achievement of the same lasting change of measurement by reshaping using a lesser mechanical stress; the reduction of the necessary mechanical stress at an increase of temperature and/or an increase in duration can only be depicted as a linear function in a very small temperature range, if at all.
Even when, with reduced mechanical stress and accordingly higher temperature and/or process duration, the same lasting change of measurement is achieved, the results are not identical because the hardness of the final product is also essential; an increase in process temperature and/or in process duration resu
Glinz Michael
Homt Günter
Sergel Horst
Continental Aktiengesellschaft
Greenblum & Bernstein P.L.C.
Vargot Mathieu D.
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