Technicals

Which type of molding process is right for your application?

There are a number of factors to consider when determining the type of molding process required. Some of these include:

• The size and geometry of your part
• The weight of your part
• The Material required
• The volume of parts required

Whether your parts require commercial or precision tolerances we offer our customers cost effective molded rubber solutions.

Rubber Moulding

Rubber Moulding is a process by which rubber components, commercial rubber products and specialist custom rubber products are created. The rubber moulding process can be done in three ways:

• Compression Rubber Moulding
• Injection Rubber Moulding
• Transfer Rubber Moulding.

Rubber Compression Molding

Compression Moulding is a method of moulding in which the preheated moulding material is first placed in an open, heated mould cavity. It is ideal for low to medium production volumes and is a particularly useful molding process for molding gaskets, seals, O-rings, and large, bulky parts.

Processes

• Molding compound is placed in an open, heated mold cavity.
• The mold is closed and pressure is then applied to force the material to fill up the entire mold cavity.
• When the cavity is filled, excess material spills out into overflow grooves. Then the rubber is demolded, & the final molded rubber product is produced.

Advantages

• Ideal process for low production volumes.
• Maximized cavity count.
• Economical process for medium precision.

Disadvantages

• Greater Waste
• Higher labour Cost
• Not suitable for complex moulds
• Difficult to control flash

Rubber Transfer Molding

Transfer Moulding combines the advantages of injection molding with the ease of compression molding. Rubber transfer molding is an ideal process for molding parts that require multiple cavities, intricate parts that require a closed mold, bonding rubber to metal parts and if the geometry of the part might cause mold cavities to trap air.

Processes

• The pre-heated, uncured molding compound is placed in the transfer pot.
• A hydraulically powered plunger pushes the molding compound through the sprue(s) into the pre-heated mold cavity. The mold remains closed until the material inside is cured or cooled.
• The mold is split to free the product, with the help of the ejector pins.
• The flash and sprue material is trimmed off.

Advantages

• Product consistency better than compression molding, allowing tighter tolerance and more intricate parts
• Production speed higher than compression molding
• Fast setup time and lower setup costs than injection molding
• Lower maintenance costs than injection molding
• Ideal for Rubber to metal bounding parts
• Ideal for moulding article with complex geometry that it eliminate trapped air

Disadvantages

• Wastes more material than compression molding cause increase weight due to flash pad which remains in the pot after transfer moulding & has to be discarded.
• Production speed lower than injection molding
• Expensive tool cost than compression moulding

Rubber Injection Molding

Injection molding is considered to be the most important process for rubber moulded products. It is preferred over transfer moulding & compression moulding especially if the large volume production is required. This process was originally developed for the manufacture of thermoplastic materials. Processing with this equipment for rubber parts has been possible by adjusting plastification units, especially to the temperature controls of screw & plunger cylinder. It is an ideal process for large shot weights, high volumes of small to medium size parts, incorporating bonded inserts, achieving close dimensional tolerances, and making components that require uniformity or consistency of colour.

Processes

• Uncured rubber is extracted into the machine using a screw feeder system. The screw feeder takes in the exact amount (or shot size) of material needed to create the desired number of parts.
• Rubber is fed from a hopper into a heated barrel, and the material is slowly pushed by a screw-type plunger into a heated chamber. Material is then preheated to a state that will allow material to flow through a gate and runner system to fill the desired cavities evenly.
• The mold remains at a set temperature so it can solidify once it is filled.
• When material has reached a cured state, the mold will open and parts can be removed manually or using a brush system to strip them off of the mold.

Advantages

• Reduced cycle time
• Flash less tooling
• Economical process for high volumes of medium to high precision components
• Capable of producing over molded components
• Minimal material Waste

Disadvantages

• Higher set-up costs
• More expensive machinery & tooling
• Small runs of parts can be costly