In an earlier post on Calender staying unpopular for 100 years since its invention, I had introduced you to this oldest rubber processing technology.
Recently, an industry friend confided that for many rubber good manufacturers, a Rubber Calender continues to be amongst the “mysterious” rubber machinery.
This statement, I found interesting. Is it true?
I let you to be the judge and let me know. However, even if a small share of rubber goods producers aspires to know more on Rubber Calendering, this post should help. Here it is:
5 Answers to the Most Frequently Asked Questions about Rubber Calendering
1. What is Rubber Calendering?
Calendering is a mechanical process by which rubber is pressed into textiles (cloth, fabric, tire cord) forming composite sheets.
2. What are the different types of Rubber Calenders?
A calendar is heavy-duty rubber machinery consisting of two or more rolls that revolve in opposite directions. The Classification of Rubber Calenders is based on
- The Number of rolls
- The Position or Orientation of the rolls
Hence you will see various rubber calender manufacturers offering you,
- 2-Roll Horizontal Type Calender
- 2-Roll Vertical Type Calender
- 2-Roll Inclined or Tilted Type Calender
- 3-Roll Vertical Type Calender
- 3-Roll Offset Stack Calender
- 4-Roll Vertical Type Calender
- 4-Roll Offset Stack Calender (Inverted ‘L’ Type)
- 4-Roll Offset Stack Calender (‘S’ Type)
- 4-Roll Offset Stack Calender (‘Z’ Type)
(You will hear more on Calender construction and their various types in my next few posts.)
3. What are the different types of Rubber Calendering?
Calendaring is classified based on what you are calendaring – Fabric calendaring and Steel cord calendaring. The adhesion of rubber to the fabric or steel cord is critical to final performance. And the rubber compound that you coat the fabric is different from the one used to make the tread or that which coats the cords.
4. Where is Rubber Calendering adopted?
For example, you use calendared textiles for casing and cap plies and chafers in tyre industry. And you use calendered steel cord for belts. The sheets you produce by this calendering process falls into two categories: either fabric inserted, or unsupported (do refer my earlier post). Calendering is also well adopted in plastic industry (say, PVC sheeting).
5. What are the functions of Rubber Calendering? And which Rubber Calenders to use?
Calendering can help you perform
- Skim Coating or Topping
Here, rubber is coated on both sides of the substrate (i.e your fabric or steel cords). This operation strengthens the adhesion between rubber and the substrate.
Your process decides whether you use a 3-Roll Calender or a 4-Roll Calender. (Let’s cover more on this in future post lest we digress).
Here, you use calendering process to force rubber into the fabric weave. Frictioning imparts good adhesiveness. You deploy 3-Roll Calender, where the top and bottom rolls have a lower speed than the middle roll. 4-Roll Calenders cannot be used for Frictioning, because obtaining a speed difference between fabric and compound is difficult.
Here, you just allow hot rubber compound to pass through a 2-Roll Calender and get a continuous sheet of rubber of thickness 3 – 4 mm.
- Embossing & Profile Calendering
If you produce tread sections of cycle tires or involved in hand building of foot wear, you may choose a Calender with “patterns” on the rolls to produce profiled treads or patterned sheets.
A step forward of Rolling, here you press a heavy engraved roll against hot rubber compound. You would consider this if your sheet needs a”design” look. The engraved design of the rolls is transferred to your rubber sheets.
Summarizing, Rubber Calendering, one of the oldest rubber processing technologies, is a mechanical process by which rubber is pressed into textiles (cloth, fabric, tire cord) forming composite sheets.And Calendering operations need critical checks to ensure you get high quality products.
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