Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Using sonic – supersonic – or ultrasonic energy
Reexamination Certificate
1999-04-30
2002-07-09
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Using sonic, supersonic, or ultrasonic energy
C264S444000, C264S069000, C264S070000, C264S911000, C241S001000
Reexamination Certificate
active
06416705
ABSTRACT:
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of Application Serial No. 08/214,355, filed Mar. 16, 1994 now abn. The present invention relates generally to industrial processing, and more particularly, to improved apparatus and methods for devulcanizing elastomers or similar cross-linked polymers.
It is readily acknowledged that there is substantial motivation to develop practical methods and apparatus for devulcanizing rubbers, other elastomers, and in some cases, resinous products generally, i.e., polymer products that may be characterized as “cross-linked” or having a three dimensional molecular network.
In particular, rubber is used in million-ton quantities every year in the manufacture of tires, structural products, auto parts and in other applications too numerous to mention. The motivation for recycling rubber products is multi-fold. In one aspect, it is desirable to recycle rubber simply as the way of reducing the amount of waste and potential pollution that results from being unable to reuse the rubber incorporated into vehicle tires and other products.
Another aspect of the same problem is the economic benefit that could be gained by utilizing some or all the components of rubber or other elastomers again and again. In this connection, a great number of products are made from metal, particularly aluminum, that has been used one or more times. Such recycled material is capable of being used repeatedly, whether or not the material being recycled and reused meets the standards of virgin material.
At the present time, in the elastomer field, there are a number of products made from what may be termed “specialty rubbers”, and these products, while able to deliver outstanding performance in difficult applications, have historically been characterized by very high cost. Merely by way of example, there are many automotive products, such as seals, diaphragms, gaskets, O-rings, and the like that are called upon to provide service under severe conditions and survive difficult and hostile environments for greatly extended periods, all without failure in use.
However, in the process of resisting high and low temperatures, abrasive stress, chemically threatening solvents and the like, such products have increasingly come to made from exotic elastomers, including, by way of example, polymers that include fluorine or other halogens, nitrogens, and phosphorous. Because of the extreme expense of these materials, there is additional recycling motivation, namely, the potential for greatly decreasing the cost of raw materials used in replacement products. Again, while all materials reclaimed from such a process may not be suitable, at least without modification, for making products which are identical to their counterparts made with virgin stock, the potential for making useful products from reconstituted polymers is still very great. It has been demonstrated that such polymers, when devulcanized by a process such as that comprising the present invention, may be reconstituted by the use of cross-linking or vulcanizing agents and other suitable steps into regenerated or like elastomers having at least some properties that are substantially similar to those of the non-degraded, original elastomer. In particular, materials such as so-called “FKM”s or fluoroelastomers possess the potential ability to be recycled into useful products at significant cost savings.
The potential of recycling such products has eluded most workers for some time; however, one proposal process for devulcanizing existing elastomers has now been discovered, and has been described in general form and claimed in U.S. Pat. No. 5,258,413 issued Nov. 2, 1993. This process is one that basically involves confining particles of cured elastomer within a particular treatment zone, advancing them along a given axis through the zone under pressure, as by a feed auger, and then and there subjecting them to ultrasonic energy propagated along such axis. It is said that this can rupture the various bonds located where the reactive sites were on the monomer before vulcanization. Also, it is said that it is possible to rupture bonds in the linear or branched (but not cross-linked) polymers. These bonds include the carbon-carbon (C—C) bond, the carbon-sulfur (C—S) bond, and the carbon-oxygen (C—O) bonds known to exist in cured elastomers.
The methods described in the above '413 patent also call for positioning an ultrasonic horn as such that it substantially obstructs the outlet diameter of a die through which the material being processed passes under the force generated by an extruder. In the examples described, the horn end face has a diameter that is significantly larger, i. e., approximately twice the diameter, of the die. The axial spacing between the end face and the die is described as being less than 1 millimeter for a horn diameter of 12.7 millimeters. In this patent, the axial clearance is only about 4% of the horn diameter and less than 10% of the outlet die diameter.
A subsequent patent, U.S. Pat. No. 5,284,625 describes a similar apparatus, differing from that of the '413 patent in that it is said that the horn may be inside the area wherein the rubber is confined but still arranged coaxially with the die outlet. Another arrangement of the ultrasonic horns is described wherein two non-circular horn end faces are arranged in facing relationship to each other or with the faces parallel to the direction of elastomer movement. In such arrangement, however, there is no discussion of any particular type of cooperation between the horns, nor is there a discussion of energy confinement as opposed to attempts to input energy to the mass of material being treated.
The present invention is directed to confining and using energy that would otherwise be lost, and is also concerned with greatly increasing the rate of treatment or “throughput” able to be achieved.
Although it is now recognized that ultrasonic energy may be used in such devulcanization, it has also been determined that prior attempts, including those described in the above-referenced patents, have not been as effective as they might have been. Thus, in the past, the amount of energy actually used to rupture the bonds and devulcanize the elastomers in question has been very small in relation to the overall energy input required for the process. It is difficult to transmit the requisite energy in the ultrasonic wave frequency band unless conditions are ideal, because among other things, the rubber particles are non-uniform and they serve to absorb and/or dampen the incoming wave. In addition, the construction and arrangement of the apparatus used to transmit energy into the mass of rubber has not been fully effective to transmit the necessary energy to the rubber.
Accordingly, an effort has been made to increase the rate and level of energy transfer from the ultrasonic apparatus to what may generally be termed the treatment zone of an ultrasonic devulcanization apparatus. According to the invention, it has been discovered that if an ultrasonic horn is arranged in a particular way, or if two or more ultrasonic horns are arranged in one or more ganged, phased or otherwise cooperating arrays, greatly increased efficiency in the rate of energy transfer may be achieved, with the result that the total energy brought to bear on the devulcanizing process can be greatly increased relative to that available using prior methods. This can greatly speed up the devulcanizing process and make it more effective.
Another aspect of the invention is that, whether or not single or multiple horns are used, the remainder of the apparatus should be constructed so as to be reflective rather than absorptive of the energy transmitted to and through what may be termed the treatment zone.
According to the invention, one method of achieving this result in practice is to provide at least a pair or other phased array or gang of ultrasonic energy generators, and connect them by a triggering or energy source that includes a delay line providing a suitable time delay. Acc
Berdichevsky Alexander
Dinzburg Boris
Eashoo Mark
SKF USA Inc.
Vedder Price Kaufman & Kammholz
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