Crumb rubber is made by a combination or application of several size reduction technologies. These technologies may be divided into two major processing categories, mechanical grinding and cryogenic reduction.

Mechanical Grinding: Mechanical grinding is the most commonly used  process. The method consists of mechanically breaking down the rubber into small particles using a variety of grinding techniques, such as cracker mills, granulators, etc. The steel components are removed by a magnetic separator (sieve shakers and conventional separators, such as centrifugal, air classification, density, etc. are also used). The fiber components are separated by air classifiers or other separation equipment. These systems are well established and can produce crumb rubber (varying particle size, grades, quality, etc. ) at relatively low cost. The system is easy to maintain and requires few people to operate and service. Replacement parts are generally easy to obtain and install.
The other important advantage of mechanical grinding relates to the shape and physical properties of the crumb rubber particles. The shape and surface texture of the crumb rubber particles are relatively round and smooth, and are able to form molecular cross-links with virigin rubber material. The rubber particles are broken down under high shear stress. Since the tire compound consists of a carbon-sulfur cross-linked matrix (see Anatomy of a Tire), the grinding process causes 'de-linking' of the material. The resulting 'de-linked' material is more viscous compared to virgin rubber and is a unique characteristic of mechanically ground crumb rubber. For applications involving compounding with virgin rubber or plastic, crumb rubber provides some advantageous attributes to the viscoelastic compound. The crumb rubber particles do not cause a deterioration of tensile strength at low to moderate loading levels.
The main disadvantage relates to cost.
Cryogenics: The cryogenic process consists of freezing the shredded rubber at an extremely low temperature ( far below the glass transition temperature of the compound). The frozen rubber compound is then easily shattered into small particles. The fiber and steel are removed in the same fashion as in mechanical grinding.
The advantages of the system are cleaner and faster operation resulting in the production of fine mesh size.
The most significant disadvantage is the slightly higher cost due to the added cost of cooling (liquid nitrogen, etc.).

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