Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-06-16
2001-10-09
Knable, Geoffrey L. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S094000, C156S096000, C156S286000
Reexamination Certificate
active
06299717
ABSTRACT:
The invention relates to a method of renewing the worn tread portions of reinforced rubber tracks such as are used on certain industrial vehicles including mechanical diggers.
In recent years continuous reinforced rubber tracks have largely replaced segmented metal tracks on self-laying track vehicles which are nowadays used for a wide variety of applications, for example mobile cranes, mechanical diggers, personnel carriers and other vehicles of various types. These rubber tracks have several advantages, one of which is that vehicles using them can run on ordinary roads without destroying the surface of the roads.
Each such track usually comprises a pair of parallel endless treaded portions held apart by transverse sections which may be made of metal and having, on the side away from the treads, a row or rows of metal lugs or “teeth” which, in use, engage sprockets or “wheels” on the vehicle whereby the tracks are moved.
A major disadvantage of the rubber tracks is that their tread portions wear out relatively quickly. In practice, it is found that with a range of equipment the tracks generally have to be replaced after an average period of about two years. They are expensive items and the frequency of replacement is a significant disadvantage to the user.
Hitherto it has been impractical to prolong the lives of these tracks by renewing their tread portions, as it was expected that the labour and complexity of applying tread portions to old tracks, and the inadequate retentiveness of the new tread portions on the old tracks, would not make this worthwhile.
The present invention overcomes the disadvantages of the prior art and makes it possible to provide an effective, efficient and relatively inexpensive method of prolonging the lives of reinforced rubber tracks by renewing their tread portions.
The method of the invention involves placing a previously buffed track circumferentially around a correspondingly dimensioned holding ring so that the metal lugs of the track are supported by the holding ring; inserting two correspondingly shaped rings, one on each side of the row of lugs, so as to conform to the space between the track and the holding ring; applying pre-vulcanized tread to the track with a layer of unvulcanised rubber between the tread and the track; surrounding the thus-formed assembly with a generally airtight envelope; creating a vacuum within the envelope and vulcanizing the said unvulcanized rubber so as to bond the tread to the track.
In a preferred embodiment the holding ring is circular.
The said tread applied to the buffed track may, for example, consist of suitably shaped individual tread portions, or may consist of a continuous circular tread strip formed with appropriate protrusions.
The metal lugs on the rear side of the track, which are provided by the manufacturers so that the track can engage the metal sprockets or “wheels” of track laying vehicles, prevent a proper vacuum being formed unless the special above-mentioned rings are inserted so as to conform to the space between the underside of the track and the outer circumference of the holding ring or “mandrel”.
These rings are desirably formed of a flexible material, for example rubber, and are desirably profiled so as to conform precisely to the spaces which they are to fill.
By means of the invention, air or other gases can be completely excluded during the bonding of the vulcanizing process, which has been discovered to be essential in order to ensure correct and strong bonding.
The invention enables an effective vacuum to be maintained which can help the tread to be maintained under pressure against the track during the vulcanizing step.
By means of the invention the relatively simple and less expensive tread portion of a track can be renewed, while conserving the original complex and expensive reinforced portion of the track.
The tracks under consideration are often of considerable size and weight, and it is extremely difficult to “repair” them otherwise than by the method of the invention.
In one embodiment, the holding ring or “mandrel” is provided by the buffed surface of a lorry tire whose outer circumference is the same in length as the inner perimeter of the track.
In practice, the mandrel may be positioned horizontally, but it may be more practical to position it vertically.
In a preferred embodiment, the pre-vulcanized tread is applied to the track in the form of a pair of parallel spaced rings of rubber comprising appropriate tread protuberances, the treaded rings being joined by a flat strip.
Alternatively or additionally, a circumferential band of suitable material may be placed externally around the partially hollowed centre area of the buffed worn track, prior to insertion of the complete assembly into a suitable pressure chamber such as is used to bond new prevulcanized treads to prepared worn tires.
Again, the purpose is to ensure good airtight sealing and facilitate the formation of an effective vacuum and strong bonding of the renewed treads to the track.
REFERENCES:
patent: 2387802 (1945-10-01), Mayne
patent: 4600467 (1986-07-01), Perdue
patent: 2707536 (1995-01-01), None
International Search Report Apr. 16, 1998.
Fulbright & Jaworski LLP
Knable Geoffrey L.
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