A Roller Head offers two decisive advantages:
1) High uniformity of the material thickness over the entire sheet width, which ensures that there will be no air inclusions, even at higher thicknesses.
2) An outstanding homogenity of the material produced.
This is possible because the "Roller Head" unit can (in comparison to the classic calender line, which can only produce sheets of up to 3 mm thickness with a single path because of the risk of air inclusions) produce sheets of up to approx. 20 mm thickness.
The rubber compound is plasticized in the extruder and then fed into the preform head. It enters the calender directly in the roll gap, and is distributed over the entire working width of the calender. This direct feeding prevents the build-up in front of the nip, that would otherwise be expected as well as air inclusions, so that the sheet preformed in the head can have a thickness of 10 mm to 30 mm, which the calender then calibrates to the desired end thickness. The extruder has the same principle as a meat-grinder, with a screw that feeds the compound through a die. The compound is heated by friction and the extruder is cooled with water. |
