Vulcanisation (including presses, autoclaves and continuous
vulcanisation)
Moulding
Introduction
All vulcanising methods can cause burns. Insulate hot machine surfaces to prevent accidental contact where
possible. Otherwise, warning signs and protective clothing (for lower arms as well as hands) are likely to be
required.
Compression moulding
Compression moulding is the most common moulding technique used in the rubber industry. It involves
pressing uncured rubber between heated moulds so that the rubber compound first fills the mould cavity
before curing to produce the finished article. The presses are usually hydraulically or pneumatically powered
and the moulds can be heated electrically, by steam, or by oil.
Compression moulding presses are generally vertical (the moving platen is raised or lowered in the vertical
plane). The bottom platen can be up stroking or the top platen down stroking. Moulds may be fixed to both the
platens, part fixed to a platen, or totally free to be drawn out of the press and loaded and unloaded on a press
table. These loose moulds are usually charged (loaded) and stripped (unloaded) by hand. On fixed mould
presses, mechanical devices, such as ejector pins or strippers will speed up the operation. This can reduce
the need for close approach by the operator but can introduce additional trapping hazards.
When thin sheets such as car mats and gaskets, are being moulded it is possible to mould several items per
press cycle by using several sets of moulds. Each mould is placed between platens in a multi-daylight press -
the number of daylights is the number of spaces between the platens.
Transfer moulding
This is a variation on compression moulding and involves loading a pre-formed blank of rubber in a cavity
connected to the mould cavity by a runner. The blank is compressed when the mould closes and is forced
under pressure into the mould cavity. The safety considerations are the same as for compression moulding.
Injection moulding
This produces precision mouldings. The rubber is pre-heated and a rotating screw forces it into the mould
cavity under pressure. Vertical injection moulding machines are more common than the horizontal type
generally used in plastics processing.
Injection moulding machines can have a manual mode where the operator removes the moulded item at the
end of each cycle. More common are semi-automatic or fully automatic machines where conveyor or pick and
place robots remove the moulded product. Injection moulding machines tend to operate at faster speeds and
on shorter cycle times than compression/transfer moulding, which effectively increases the potential risk to
the operator from mechanical hazards.
Tyre curing presses
These are usually down-stroking machines, most often electrically or pneumatically powered. They have a
rubber bladder, which is inflated into the tyre once it is in the mould and then filled with steam or highpressure
hot water to aid curing inside the tyre. Bursting or leaking bladders can cause serious scalds,
particularly during press opening. Pressure sensitive switches should prevent opening when internal pressure
is present.
For cross-ply tyres the moulds with the tread pattern are usually in two pieces (top and bottom).
Tyre curing press mould
Radial tyres have a segmented matrix which close together to enclose the tyre once in the press. These have
additional traps between the segments.
Tyre loading devices can have additional trapping and impact hazards. There should be mechanical
stops/scotches to prevent gravity fall of the loading chuck. Fit arrestor gear (to activate on loss of tension) in
the chains supporting the chuck.
Mechanical hazards
These vary considerably with the press type and the operating procedure used. At most presses there are
trapping hazards between:
the moving moulds/platens, either under power and by gravity fall;
the moving platens and the press frame/press tables;
mould loading and stripping devices.
The following diagrams shows the main danger areas on a frame construction down-stroking compression
press and how fixed and interlock guards can be used to minimise the risk.