Preparations before forming

CHECKING AND STORAGE OF RAW MATERIALS
After receiving the raw materials, random samples are taken for comparison with certificates from the supplier. It can happen that, for example, viscosity or moisture has changed due to incorrect transportation. It is important that correct storage conditions are adhered to, in order to avoid later problems in the process. Most of the raw materials can be stored at normal temperatures but a few need a cold storage area.

Preparations before mixing
Natural rubber may need to be decristallized before it is used in the mixing operation. In this case, it is heated up in a “heating chamber,” normally at a temperature of 95-104 F. For special raw materials, a check will be made to ensure that no changes have occurred during storage, and then the mixing can be started.

MIXING OF THE COMPOUND
The mixing operation can be compared with other mixing processes, as for example in a bakery. All ingredients are weighed according to an established formula and are then mixed together with unspecified parameters in the mixer.

Weighing
Each product has a compound made from a special formula, and therefore the number of raw materials used is fairly high. From storage bins or direct from bags, the ingredients are weighed according to the formula, with high accuracy. If a mistake is made here, it is too late to correct it later on in the process. Each bag of raw material is properly marked to identify ingredients and weight.

Mixing
Mixing is carried out either in open mills or in an enclosed chamber containing rotors. In both cases, the basic idea is to distribute and disperse all the ingredients in the rubber through heavy mechanical processing.

Storing the compound
Every batch is controlled against a specification, and a maximum storage time is also specified.

The first trace of rubber used in Europe shows up in coal deposits in Germany
The raw material was not from the rubber tree, and the material, believed to be 55, 000 to 60, 000 years old, still had some elasticity.

- The guide to polymer processing technology, materials, additives & equipment - Life insurance