Safety in injection techniques

The injection molding process enables batch, automatic and mass production of parts in thermoplastics, thermosets and elastomers, with high precision.

The resulting parts, ranging in size and weight from a few grams to 50 kg, have applications in all fields of activity. Examples include: small screws and bolts; items used in medicine and pharmacy; mechanical parts such as gears; housings or casings for computer, household appliance or electrical appliances and accessories; toys, sports and leisure equipment; and, for the very bulky, car bumpers, storage containers and furniture components.

The injection moulding machine allows :

• plasticize materials ;

• inject them under high pressure (around 500 to 1,500 bar) through a nozzle into the cavity of a two- or multi-part mold;

• hold the mold in the closed position during injection with high forces (from a few kilonewtons up to 50,000 kN (5,000 t for today's largest machines);

• open the molds after the parts have solidified;

• demould the resulting parts, by moving the ejection device.

To optimize the possibilities offered by the automatic mode of injection molding machines, auxiliary equipment such as : drying and automatic material feeding devices; automatic mold changing devices; mold heating and/or cooling devices; manipulators for introducing parts to be overmolded into the mold (inserts), for unloading molded parts and for removing solidified material waste in the cavity feed channels (sprues); shredders for fragmenting waste for immediate recycling; molded part handling and unloading facilities, are installed nearby. Their control system is linked to that of the machine.

Hazardous phenomena that occur during the operation of injection molding units are mechanical, electrical, thermal, related to the handling of machine equipment, molds and parts, or caused by noise and materials during processing. More specifically, the risks associated with the use of injection molding machines are currently under control during production periods. Technological developments (use of PLCs for control systems) and compliance with the essential safety requirements set out in regulations provide a good level of safety. However, during set-up and material changeover periods, mechanical and burn risks remain.

Statistical data for 1994, 1995 and 1996 relating to safety in the plastics injection molding industry, as well as for all activities governed by the General Social Security Scheme, are presented in Table A.

We note that, for activities involving...