Rubber Compounding

Rubber Compounding

This is one of the subjects to master in the field of rubber technology. Compounding is not really a science . It is part art, part science. In compounding one must cope with literally hundreds of variables in material and equipments. There is no infallible mathematical formulation to help the compounder, that is why compounding is so difficult a task

What is rubber compounding and Why are we doing it ?
How can we do it successfully?

Rubber compounding is the art & science of selecting and combining elastomers and additives to obtain an intimate mixture that will develop the necessary physical & chemical properties for a final finished products as per specification desired to achieve the required useable properties in all types of rubber products used in various applications.

Objectives of Rubber Compounding:

1. To secure certain properties in the finished product to satisfy service requirements

2. To attain processing characteristics necessary for efficiant utilisation of available equipments

3. To achieve the desirable properties & process ability at the lowest possible cost. In other words, the most important criteria in compounding is, to secure an acceptable balance among demands arising from the above criteria.

Equipment For Rubber Compounding

What is mixing?

Mixing is defined as a process of incorporating the compounding ingredients into the rubber, done on an open rubber mixing mill at the beginning of a mixing cycle the rubber is forced or drawn in to the working area between pair of rolls on open mixing mill . The process of incorporation, mastication, & dispersion are the most important functions of mixing which contributes to a very good product as regards a compound to meet all the desired properties as per specification of required compound.

What is a mixing mill?

Is defined as the machine with two differential speed rolls, running in opposite direction, forming a nip for mastication mixing , or warming before extrusion . The rotation of the rolls pulls the ingredients through the nip, which is the clearance between the rolls. The remaining surface of the roll is used as means of transportation for returning stock to the nip for further mixing

Internal Mixer is a machine with profiled rotors rotating in an enclosed chamber in opposite direction , it is used for rapid mixing and large throughput due to its versatility, it is tending to replace the open mixing mill, Specially as a batch mixer. The basic purpose of all internal mixers are the ability to exert high localized shear stress to the material being mixed. A lower shear rate stirring, a homogenous action, that is the effective ness of dispersive mixing results from the combination of high shear stress and large shear deformation. . An internal mixer design is a compromise based on experience to best accommodate the wide range of compounds typical of a manufacturing operation involving mixed products.

Banbury Machine:

Banbury mixer consists of a completely enclosed mixing chamber in which two sprial shaped rotors operate a hopper at the top to receive compounding ingredients for mixing and a door at the bottom for discharging the mixed batch of compound .the bulk of the shearing action takes place between the rotor and the chamber wall

A Compounder must have the following knowledge:

• An understanding of the plant, processing methods available to him in the organization,

• Moulding unit knowledge to develop compounds for compression moulding, transfer moulding and injection moulding
• In a tyre industry a compounder must have knowledge of tyre machinery, tyre moulds

• In extrusion industry he must have knowledge of the type of extrusion process in operation.

• Up to date and elaborate knowledge of both the chemical and the physical properties of elastomers is most essential

• Knowledge of vulcanizing system available, knowledge of in- process physical testing and also testing of finished products

• A good comppunder with experience must be able to convert science in to art. So that he has the capability of producing material that will be easy to process and he must be able to produce and formulate economical, practical compounds as competition in today’s world is quite severe.

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