Mixing Principle: Cold mastication & multi-surface milling
 

     Fig A.  HSM rotor                                     Fig. B   Flowpath between the
              and stator                                               HSM rotor and stator (section)

HSM is a novel type of internal batch mixer that applies very high levels of shear and extensional stress in visco-elastic materials such as rubber, doughs and certain pastes.  Typically, the HSM rotor is mounted below the stator and forms a chamber into which the material is loaded.  A non-rotating stator is then lowered towards the stator surface such that a small gap (0.5 to 5mm) is maintained between the rotor and stator surfaces.  When the rotor is moving, material is pulled through the rotor-stator gap and repeatedly cut and folded by the special geometries machined into both surfaces.  These geometries also interact to promote pumping and therefore excellent distributive blending.

With the large amount of energy applied to the fluid, a normal concern would be the rapid build-up of heat and resulting degradation of the material.  However, the large contact surface areas of the HSM rotor and stator are intensively cooled to ensure that all mixing can be conducted at low temperature.  Rubber compounding, for example, can be performed at 60-80°C so that single-step mixing can be performed, with temperature-sensitive additives included from the start.

Key to the performance of the HSM is close control over the rotor-stator gap.  Sophisticated closed-loop control systems operating high precision hydraulic rams ensure extremely tight control over this parameter, for consistent, high quality results.  Larger machines also have the ability to automatically empty (dump) material after processing to eliminate manual handling issues.

Benefits
Important benefits of HSM technology when compared to conventional internal mixers are:

• Very high energy input for good dispersion and short batch times
   

• Highly efficient cooling for low-temperature and single-step mixing
   

• No internal seals are required - this removes many maintenance issues and allows abrasive compounds to be mixed
   

• Competitive pricing - at or below that of internal mixers for equivalent throughputs

Note that HSM technology is also used by our associate company Watson Brown HSM Ltd. to mechanically de-vulcanise cured rubber.  Click here to visit the Watson Brown HSM website and find out more about this exciting new recycling technology.