Patent
Since the beginning of reclaiming technology, chemicals have been used to aid the reclaim process. Almost all processes start with grinding the material, usually through a cracker mill or a mechanical grinder. There were 7 different reclaiming processes, but they all had one thing in common; they all relied upon some type of chemical additive to achieve "devulcanization".
In "The Applied Science of Rubber" published in 1961, chapter IV, PART TWO, by W. E. Stafford and R. A. Wright, the authors refer to the seven types of modern reclaiming.
1. Digester (Neutral or Alkali).
2. Pan or Heater
3. Acid
4. Reclamator or Dip
5. Thermal
6. Thermodynamic of Hot Banbury
7. Palmer or High Pressure Steam
All of the processes discuss the combined use of steam heat (except the thermodynamic process) and chemicals. The chemicals range from acid to caustic soda to reclaim oils and sulfur based peptizers. The temperature ranges go from 100 PSI (327.81 F) to 200 PSI to 300 PSI (381.79 F to 417.33 F) and the Palmer method used 1000 PSI (544.61 F) for 10 minutes, then treated it as other reclaim (used chemicals)
The Anderson patent #4,544,675, assigned to Goodyear, employs essentially the same process as the Pan or Heater process except the aryl disulfide peptizer is distilled prior to treating the rubber to get rid of the noxious sulfur odor (rotten egg odor) prior to reacting in a steam autoclave at the traditional pressures and temperatures. (230 - 260 PSI or approximately 400 F)
POINTS OF CLARIFICATION:
1. Boiler - A boiler is simply a pressure cooker with a maximum operating pressure/temperature. The boiler is constructed to hold a certain amount of water at a maximum pressure, i.e. 250# per sq. in. One type of boiler is a fire tube boiler where a gas flame is fired through the tubes to create heat. A thermometer connected to a control switch measures the temperature of the water and shuts off the flame after the water has reached a certain temperature; or a pressure switch shuts off the flame after a certain pressure is reached.
2. Autoclave - A steel container rated for certain pressures and temperatures. The steam autoclave is only a holding vessel for the steam generated by the boiler.
3. When the boiler reaches the set temperature and pressure, a valve is opened in a high-pressure pipe that conveys the high-pressure steam to the autoclave. When the pressure in both the autoclave and the boiler have equalized, the boiler shuts down. The temperature in the autoclave is always controlled by the boiler in this type of operation.
NOTE: Although the old literature refers to any temperature over 212 F, or atmospheric pressure more than one, as superheated, this is not the definition used in the TRC patent application. Every pound of pressure raises the temperature of the steam as indicated in Chart #1. During the development of the atomic submarine, the U.S. Navy took the steam generated by high-pressure boilers to drive the turbines, but discovered the fine particles of water in the steam were destroying the blades on the turbines. They came up with the concept of "superheating" the steam to rid it of the water particles. This "superheater" was installed between the boiler and the turbines and this is part of the basis of TRC's patent application. Instead of a super saturated steam, we are now dealing with a super dry steam at temperatures well above the temperature indicated in Chart #1 for the corresponding pressure.
In the article TECHNOLOGY OF RECLAIMED RUBBER, there are several references to the adverse effects of heat on the rubber. On page 270 it states, "Of late there has been a trend towards reducing heating to a minimum necessary for fibre destruction, with a view to minimising the serious heat hardening of the SBR components of tire waste." On page 272 it further states, " While opinions vary, it is thought that thermal reclaims are inferior to those prepared by more conventional processes and, moreover, the process is not readily adaptable to SBR and certain other synthetic scraps."
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