System and method for continuously manufacturing cured membranes
View Patent ↗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 cured membrane, the method comprising:
mixing EPDM rubber, filler, oil and curative within a mixing extruder to form a vulcanizable rubber composition;
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;
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.;
calendaring the partially-cured extrudate to form a partially-cured membrane; and
curing the partially-cured membrane to form a substantially cured membrane, where said step of curing is devoid of elevated pressures.
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. The method of claim 1 , wherein the step of curing includes forcing hot air across the partially-cured membrane.
8. The method of claim 1 , wherein the step of curing includes applying heat and pressure to the partially-cured membrane.
9. The method of claim 1 , wherein the step of curing includes applying an electronic beam to the partially-cured membrane.
10. A continuous method of manufacturing a cured membrane comprising:
charging rubber, filler, oil, and a curative to a mixing extruder; mixing the rubber, filler, oil and curative to form a vulcanizable rubber composition;
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;
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.;
applying a compressive force to the partially-cured extrudate to form a partially-cured membrane; and
applying energy to the partially-cured membrane to form a substantially cured membrane, where a total processing time of the method after charging, including the steps of mixing, subjecting the composition to a reduced pressure, extruding, applying a compressive force, and applying energy to the partially-cured membrane is less than 2.0 hours, and where the time from said step of charging rubber, filler, oil, and curative to a mixing extruder to said step of applying compressive force to the partially-cured extrudate is less than 8 minutes.
11. The method of claim 10 , 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.
12. The method of claim 10 , 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.
13. The method of claim 10 , where a total elapsed time between the steps of extruding the vulcanizable rubber composition and applying a compressive force to the extrudate is less than 20 seconds.
14. The method of claim 10 , wherein residence time of the curative within the mixing extruder is less than 6 minutes.
15. The method of claim 10 , where the vulcanizable rubber composition is between approximately 120 and 160° C. at the time of extruding.
16. The method of claim 10 , where the vulcanizable rubber composition is between approximately 130 and 150° C. at the time of extruding.
17. The method of claim 10 , where the vulcanizable rubber composition is between approximately 135 and 145° C. at the time of extruding.