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 system for continuously manufacturing cured membranes comprising:
(i) a planetary mixing extruder including a vacuum adapted to subject a vulcanizable rubber composition therein to a reduced pressure in a portion of the mixing extruder;
(ii) a roller head die for extruding and calendering the vulcanizable rubber composition to form a green membrane; and
(iii) a hot air conveyor for continuously curing the green membrane to produce a cured membrane.
2. The system of claim 1 , further comprising a pre-mixing extruder in communication with the planetary mixing extruder for premixing one or more components of the vulcanizable rubber composition.
3. The system of claim 1 , further comprising a pump in communication with the planetary mixing extruder and the roller head die to increase the pressure of the vulcanizable rubber composition.
4. The system of claim 1 , wherein the planetary mixing extruder includes a barrel, a main spindle, and a plurality of planetary spindles positioned radially between the barrel and the main spindle.
5. The system of claim 1 , wherein the planetary mixing extruder includes a feed section and at least one compounding section.
6. The system of claim 4 , wherein at least one of said plurality of planetary spindles is a back-cut spindle to provide for back mixing within a portion of the planetary mixing extruder.
7. The system of claim 1 , wherein said planetary mixing extruder includes at least 6 planetary spindles.
8. The system of claim 1 , wherein at least one of said barrel or said main spindle includes internal channels containing heating or cooling fluid.
9. The system of claim 1 , further comprising a flow impediment positioned immediately upstream of said vacuum to create an internal volume devoid of the vulcanizable rubber composition.
10. A method of continuously manufacturing a cured membrane, the method comprising:
(i) continuously extruding a partially-cured extrudate from an extruder, said partially-cured extrudate including partially cured EPDM rubber with filler and oil dispersed therein;
(ii) continuously calendaring the partially-cured extrudate to form a partially-cured membrane;
(iii) continuously curing the partially-cured membrane.
11. The method of claim 10 , where the temperature of said extrudate at said step of extruding is 120 to 160° C.
12. The method of claim 11 , where said step of continuously extruding includes continuously charging uncured EPDM, filler, oil and curative to an extruder, and continuously mixing the EPDM, filler, oil, and curative within the extruder.
13. The method of claim 12 , where said step of continuously charging includes charging uncured EPDM and then charging a curative downstream of the EPDM.