Calendering is one of the oldest rubber processing technologies. The Rubber machinery that helps you do calendering is known as a Calender (…obviously!!).
The word ‘calender’ itself is a derivation of the word κύλινδρος kylindros – the Greek word that is also the source of the word ‘cylinder’.
In 1836 Edwin M. Chaffee, of the Roxbury India Rubber Company, patented a four-roll calender to make rubber sheet. He worked with Charles Goodyear with the intention to “produce a sheet of rubber laminated to a fabric base”. Despite this development, calendering as a process became popular only after the 1930’s.
And, so the Calender was never ‘popular’ when it was first invented over 2 centuries back. Here’s why.
Calendering is a mechanical process by which rubber is pressed into textiles (cloth, fabric, tire cord) forming composite sheets.
In this process, you pass pre-selected fabric and rubber through a series of rolls to flatten, smoothen and sandwich the materials.
Depending on your end-use, the calendered sheets could have multiple layers “sandwiched” together.
A Rubber Calender can help you get either ‘supported’ or ‘unsupported’ calendered sheets.
- ‘Unsupported’ sheets contain only layers of rubber that has been joined together.
- On the other hand, a ‘supported’ sheet has textile fabric or steel cord coated with a film of rubber (aka “skim stock rubber”) on both sides and into the material. Supported rubber sheets give you higher strength or tear resistance.
Coating of fabrics has been done for almost 200 years. Steel cord and fabric cord topping is a process in your tire manufacturing. Specifications and tolerances for calendered cords are very tough. So you will find it difficult to fulfill the thickness variation across the calendered ply and the cord density.
The calender never did become very popular when it was first invented mainly because it was difficult to adjust the desired gap between rolls. Consequently, it was difficult to get an accurate rubber sheet thickness.
Hence, the process did not become popular till the calender machines became easier to adjust (i.e until the 1930’s).
Since then, features have evolved. Modern calenders’ can achieve tolerances around ±0.005mm and their lines are adaptive for most sophisticated precision requirements of your product.
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