System and method for continuously manufacturing cured membranes
A method of continuously manufacturing a cured membrane includes continuously compounding and mixing a vulcanizable rubber composition in a mixing extruder while continuously removing gasses from the vulcanizable rubber composition during mixing with a vacuum. The vulcanizable rubber composition may be continuously extruded to form an extrudate, which may be continuously calendered to form a green membrane. The green membrane may be continuously cured, such as by a hot air conveyor curing system, to form a cured membrane.
1. A method of continuously manufacturing a partially-cured extrudate, the method comprising:
(i) mixing EPDM rubber, filler, oil and curative within a mixing extruder to form a vulcanizable rubber composition;
(ii) subjecting the vulcanizable rubber composition to a reduced pressure by applying a vacuum to form a vulcanizable rubber composition with reduced levels of entrapped gases; and
(iii) extruding the vulcanizable rubber composition with reduced levels of entrapped gases to form a continuous partially-cured extrudate, where said step of extruding takes place at a temperature between 120 and 160° C.
2. The method of claim 1 , wherein the step of mixing includes conveying the vulcanizable rubber composition downstream toward an outlet end of the mixing extruder.
3. The method of claim 1 , wherein the step of mixing includes back-mixing the vulcanizable rubber composition in a portion of the mixing extruder.
4. The method of claim 1 , wherein the step of mixing includes maintaining a temperature of the vulcanizable rubber composition at any point along a length of the mixing extruder within +/−5° C. of a desired temperature.
5. The method of claim 1 , wherein the step of mixing includes maintaining a temperature of the vulcanizable rubber composition at all points on a section plane through the mixing extruder within a temperature variance of +/−5° C.
6. The method of claim 1 , where the rubber is added to the mixing extruder at a feed throat, and where the curative is added to the mixing extruder downstream of the feed throat.
7. A method of continuously manufacturing a cured membrane, the method comprising:
(i) providing a partially-cured extrudate;
(ii) calendaring the partially-cured extrudate to form a partially-cured membrane; and
(iii) curing the partially-cured membrane to form a substantially cured membrane, where said step of curing is devoid of elevated pressures.
8. The method of claim 7 , wherein the step of curing includes forcing hot air across the partially-cured membrane.
9. The method of claim 7 , wherein the step of curing includes applying heat and pressure to the partially-cured membrane.
10. The method of claim 7 , wherein the step of curing includes applying an electronic beam to the green partially-cured membrane.
11. A continuous method of manufacturing a partially-cured extrudate comprising:
(i) charging rubber, filler, oil, and a curative to a mixing extruder;
(ii) mixing the rubber, filler, oil and curative to form a vulcanizable rubber composition;
(iii) subjecting the vulcanizable rubber composition to a reduced pressure by applying a vacuum within the mixing extruder to form a vulcanizable rubber composition with reduced levels of entrapped gases; and
(iv) extruding the vulcanizable rubber composition with reduced levels of entrapped gases to form a continuous partially-cured extrudate, where said step of extruding takes place at a temperature between 120 and 160° C.
12. The method of claim 11 , where the total processing time from the step of charging the curative through the step of extruding the vulcanizable rubber composition is less than 7 minutes.
13. The method of claim 11 , where the total processing time from the step of charging the curative through the step of applying a compressive force to the extrudate is less than 7 minutes.
14. The method of claim 11 , wherein residence time of the curative within the mixing extruder is less than 6 minutes.
15. The method of claim 11 , where the vulcanizable rubber composition is between approximately 130 and 150° C. at the time of extruding.
16. The method of claim 11 , where the vulcanizable rubber composition is between approximately 135 and 145° C. at the time of extruding.