Introduction to rubber processing and safety issues - HSE

When assessing the risks and precautions needed, consideration should be given to:
the closing speed;
the number of moulds and amount of daylight;
whether up-stroking or down-stroking;
type of moulds (loose or fixed);
mode of operation, in particular, if worked at one or both sides and the number of operators;
the amount of body access between the moulds.
Many incidents happen during maintenance and tool changing and adequate controls against preventing falls due to
gravity are important for down-stroking presses. These could include scotching or having a pilot operated check
valve and counterbalance valve assembly in the hydraulic circuit.
For further information on guarding requirements see:
BS EN 289 Plastics and rubber machines — Presses — Safety requirements
BS EN 201 Plastics and rubber machines - Injection Moulding Machines
Autoclaves
Introduction
Autoclaves, known as 'curing pans' or 'vulcanisers', are pressure vessels filled with steam that are used to
cure rubber articles not contained in moulds (hose, extruded section, coated cloth, retread tyres, and small
cable batches). Most are horizontal with vertical autoclaves now rare. They can have either quick opening
doors or multi-bolted doors.
Autoclaves have been involved in three fatalities since 2008. HSE have produced guidance on Safety
requirement for autoclaves. This provides information on the safe operation and maintenance of these
devices. It specifically addresses the risks associated with safeguarding, training and maintenance.
Continuous vulcanisation
Introduction
Products produced on a continuous process such as rubber covered cable and strip are continuously cured, rather
than on a batch basis. There are various methods but each one is sited just after the exit die of the extruder or
calender.
Liquid salt baths
These are usually gas-fired troughs of molten sodium and potassium nitrate mixtures. This method is particularly
suited for peroxide cured compounds, which must be cured in the absence of oxygen. The main hazard is fire and
explosion associated with the use of molten salt at high temperature. Totally enclose salt baths as water in the
molten salts could result in an explosive generation of steam. To prevent localised hot spots and overheating use
effective temperature control. There is a potential danger of splashing with hot salt when leading the extrudate
through the salt bath and during maintenance and cleaning so suitable protective clothing, including full-face
protection, should be worn.
Pressurised liquid salt continuous vulcanising (PLCV)
Cable making often uses this process. It consists of a long gently slopping pressure chamber or tube fixed to the
extruder die. Vulcanising occurs by passing the cable through a molten mixture of salts in the pressurised chamber.
The cured cable then passes through an enclosed water-cooled chamber to emerge cold at the end of the line. The
main hazards associated with this process arise from the high temperatures and pressures involved. They include:
burns from accidental contact with the molten salt;
fires from accidental mixing of salts with combustible materials;