Our readers who read 5 Answers to the Most Frequently Asked Questions about Rubber Calendering, would recall my apprehensions, I had on the topic.
However, to my surprise, I admit that my industry friend was right when he said that for many rubber good manufacturers, a Rubber Calender continues to be amongst the “mysterious” rubber machinery.
And I am glad that I was wrong. Because, if not, I would have not written the post that many readers found useful. Thank you Henry!
Rubber Calendering is classified based on what you are calendering
- Fabric calendering and
- Steel cord calendering.
Well, that’s the basics. Let’s explore a bit further.
What I Wish I Knew a Year Ago About The Different Types Of Rubber Calendering
The materials that go into your fabric calendering are your softened rubber compound (from mills) and Nylon or Polyester from the Dip Unit.
In this process, the tension, temperature and humidity are critical parameters of your fabric cords before they are calendared with the rubber compound. And hence is the reason you will observe that the fabric cord is kept in a room (where temperature and humidity are controlled well) once this raw material arrives in your shop floor.
This textile is arranged in a flat and parallel manner. Under proper tension they are continually pressed through two rolls. Simultaneously, you add the rubber compound to the opening area or nip between the rolls. As a result, a thin layer of rubber is applied into top of and the bottom layers of the fabric.
Then you make this continuous sheet of fabric and rubber go through many additional rolls to ensure that rubber is penetrated properly between the cords achieving the desired adhesion between rubber and the fabric.
The sheets are cut at required angles so that the cords are set at predetermined angles across the sheet.
Even inner liners for tyre manufacturing are calendered the same way into sheets of required thickness and then cut into appropriate widths for use in tire construction.
Finally, your calendered fabric sheets are wound into rolls with layers of woven fabric liner to prevent the surfaces of sheets from sticking together.
Steel Cord Calendering:
In the tire industry, steel cord calendering is for the radial tires.
Here, the body plies and reinforcing strips incorporate polyester cord that is coated in an adhesive liquid. This cord is passed between large, heated rolls of a rubber calender machine. Woven fabric is similarly prepared and calendered for the anti-chafing strips.
Since your rubber compound will not adhere to bare steel, the steel cord wires for the steel belts are coated with a very thin layer of brass. These high-tensile brass-coated rubber-encased steel cords (multi-strand cables) become the steel belts.
You may note that the steel cords come in various arrangements like cross-section of pairs, triplets and so on.
The brass-coated steel wires used in the manufacture of tire components are also extremely moisture sensitive. Hence, they must be protected in a temperature and humidity controlled environment – right from procurement, to during shipment and at the tire plant location. More importantly, any exposure to moisture can result in corrosion and a breakdown in rubber adhesion when calendered.
At your plant, these wires are stored in an environmentally controlled “Creel Room” until it is processed in your rubber calender. You pass a preset number of steel cords under proper tension from the creel room on rolls through aligning combs into the calender where the wires are coated with a thin sheet of skim stock rubber. For maximum adhesion, the rubber should also penetrate these steel cords. Maximum adhesion also means least rusting.
These steel cords are cut at specified angles and widths for use in tire building process.
In ground reality, the distance between the creel room and your rubber calender (varying between 20 – 60 feet depending on your layout) is usually not environmentally controlled and, hence the wire may be exposed to moisture prior to its being encapsulated in rubber.
This problem is worsened by slowdowns, temporary shutdowns, humidity spikes and failure to adequately control temperature and humidity within the creel room. Once the belt wire becomes contaminated with moisture, it becomes more difficult to obtain proper adhesion of the rubber to the brass-coated wire.
The strongest possible bond between the rubber and the belt wire is critical in the construction of your steel belted radial tires.
Next, how do you judge the quality of a calendered sheet?
Well, you could quantify the quality of your fabric calendered sheet in terms of your pre-desired
- Thickness of the sheet
- Spacing between cords
- Number of cords and
- Penetration of rubber into the space in between cords.
Summarizing, Rubber Calendering is classified into Fabric Cord Calendering and Steel Cord Calendering based on what you are calendering. Each of these is different yet similar in operations and sensitive to environment influence for your high quality product.
Let me know your views.
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