Introduction to rubber processing and safety issues - HSE

Cleaning and maintenance
The greatest hazard at internal mixers is during maintenance and cleaning, including, clearing of blockages. Operators
may need access to the mixing chamber/rotors, normally via the discharge opening. There is an incentive to do this
quickly as the compound hardens as it cools and a possible temptation to take shortcuts.
Maintenance staff are more likely to use the rear inspection door.
A trapped key interlocking system is required at both the rear inspection and discharge openings.
Because of the size of internal mixers, operators can be working at three levels: the rear inspection door on the feed
platform; the discharge door at the motor platform; and the dump chute access at floor level. Communication is
therefore difficult with the potential to increase risks.
In addition, stored electrical, hydraulic and pneumatic energy as well as the potential energy from gravity fall of the
floating weight and inertia from run down of the rotors, may be released if the correct run down procedures are not
followed.
A trapped key interlocking system on all access doors, including a time delay and scotching of the floating weight is
one means of preventing access to widely separated danger areas and is the accepted industry standard.
The principle employed is that all sources of power are isolated and all stored energy is dissipated, before
access is possible.