07-04-2009, 10:30 PM
Calendering consiss of a number of rolls held in a frame work. It is an expensive piecce of equipment containing usually three rolls and products sheet with smooth surface and accurately controlled uniform thickness. The rolls are therefore carefully ground and top and bottom ones are adjustable. Vertically related to the center fixed roll. So that the thickness if the sheet can be varied. Calendering machine used in rubber industries are 3 ot 4 roll calender.
In the case of three roll calender usually the center roll is driven and upper and lower rolls are driven with the help of the center roll using gears. The three rolls are usually vertical but the modern three roll calender may have an offset top roll which assist the feeding from the feed strip. In vertical calenders pigs or dollies are used. A part from 3 roll calenders , 4 roll calender of vetical ('L'inverted 'L', 'Z' etc are also used. The later ones are the most modern. The vertical calenders are more easily fed manually but alternation in the secind nip affect the secind nip also. Inverted 'L' and 'Z' configuration calenders are used mainly for coating fabrics in both sides in one operation.
The roll used in calender machine are mode of chilled irons abnd are quite heavy and are made hollow to that stream, hot water or cold water may be circulated to maintain the correct roll temperature. Proper control of roll temperature is very important to get a good quality product to decide thickness and finish.