Rubber compression moulding and transfer moulding presses use compressed air for press opening, part ejection and mould cleaning in a cyclic pattern. Each press cycle involves a burst of air demand during press operation, followed by low demand during the rubber cure dwell time (typically 3–20 minutes depending on the compound and part thickness). A rubber moulding shop with 10–20 presses operating simultaneously creates synchronised demand spikes as multiple presses cycle at the same time. If the compressed air pressure drops during the press opening and part ejection cycle, the part may not demould cleanly — rubber flash remains stuck in the mould cavity, the part tears during ejection, or the mould release agent deposits in an uneven pattern that causes the next moulded part to have a surface defect. For rubber seals and O-rings supplied to pharmaceutical, chemical or food processing customers with specified surface quality requirements, a demoulding pressure drop can cause an entire batch of parts to fail surface inspection. A CP VFD screw compressor sized for the peak simultaneous demand of all presses, with a correctly sized receiver tank, prevents these pressure drop demoulding failures.

Rubber vulcanisation (the chemical cross-linking that converts raw rubber compound into the final elastic product) requires specific time and temperature conditions. If moisture from the compressed air contacts the rubber compound surface during moulding, the moisture disrupts the vulcanisation chemistry at the surface layer. This causes three types of defects: (1) Surface pockmarks or pinholes from steam formation at the rubber surface as moisture flashes to steam in the hot mould at 150–180°C — visible surface defects that cause part rejection; (2) Inhibited surface vulcanisation where moisture at the surface retards the cross-linking reaction, producing an under-vulcanised skin with lower hardness and tensile strength than the interior — affecting seal performance in service; (3) Flow lines or voids in the rubber part from steam formation in the mould parting line. For rubber gaskets, O-rings and seals used in pharmaceutical equipment (where extractables from under-vulcanised rubber are a regulatory concern) or chemical service (where incorrect hardness causes premature seal failure), surface defects from moisture are cause for rejection. A refrigeration air dryer on the compressed air supply to rubber moulding operations prevents all three moisture-related defects.

In rubber hose extrusion, the extrudate exits the extruder die and enters a calibration section where compressed air blown into the bore of the hose maintains the internal bore diameter as the rubber cools in a cold water bath. The calibration air pressure directly controls the internal bore diameter of the finished hose. If the calibration air pressure fluctuates during extrusion, the bore diameter varies along the length of the hose. For rubber hoses with specified bore tolerances — pharmaceutical tubing (USP Class VI silicone or EPDM hoses), food-grade hoses (FDA-compliant), hydraulic hose inner tubes, or chemical transfer hoses — bore diameter variation outside the specified tolerance makes the length of hose non-conforming to the buyer’s specification. For rubber profile extrusion (door seals, window seals, industrial gasket profiles), calibration air pressure maintains the cross-sectional shape. Variation in calibration air pressure = variation in profile cross-section = dimensional non-conformance that can only be detected by cross-sectional measurement after cutting. A CP VFD screw compressor maintaining consistent calibration air pressure prevents bore diameter variation in rubber hose extrusion and cross-section variation in profile extrusion.