Lecture 08: Compression, Transfer & Blow Moulding

Vocabulary flashcards for Compression, Transfer & Blow Moulding

Compression Moulding

A composite manufacturing process normally used to produce composite components in high production volume such as automotive components. It is usually done at 5–10°C above the glass transition temperature of the polymer.

Typical Compression Moulding Process

Performed at a mould temperature of 180°C and mould pressure of 700 kPa with curing time of 3 min.

Compression Moulding Applications

Electric plugs, sockets, housings, pot handles, and dinner plates

Cycle of Compression Moulding

Mould Preheating or Preparation, Charge Preparation, Charge Loading, Compression, Curing, Cooling, Ejection

Mould Preheating/Preparation

Cleaning the mould, applying release agent, Heating to increase the viscosity of the charge when it is eventually loaded

Charge Preparation Includes

Unpacking, Cleaning, Cutting, Sizing and weighing, Heating

Charge Loading

Placing the charge on the lower part of the mould to ensures the best compression result.

Compression Aims

Force the charge to fill the entirety of the intended volume in the cavity left by the mould. Ensure the desired density of the product. Facilitate curing

Three Important Parameters During Compression

Temperature, Pressure, Time

Curing (Polymerisation)

The hardening/setting of the compressed charge into the final product. Types: Condensation type (uses a tin catalyst), Addition type (uses a platinum catalyst).

Curing with Temperature

The mould is heated, and temperature is increased which consequently lead to an increase in pressure. During the adapting time the temperature is maintained for curing to complete. The pressure is reduced due to solidification of the part.

Cooling Purposes

Ensuring the mould has the ideal temperature for subsequent moulding cycles. Ensuring the component develops the desired mechanical (and thermal) properties for the subsequent removal and storage/shipment/usage.

Ejection

The release of the product after curing; can be manual or automated.

Transfer Moulding

TS charge is loaded into a chamber immediately ahead of mould cavity, where it is heated. Pressure is then applied to force soft polymer into heated mould where it cures.

Types of Transfer Moulding

Pot transfer moulding - charge is injected from a 'pot' through a vertical sprue channel into cavity. Plunger transfer moulding – plunger injects charge from a heated well through channels into cavity.

Transfer Moulding vs. Compression Moulding

Transfer moulding is capable of moulding more intricate part shapes and is suited for moulding with inserts (overmoulding on metallic parts).

Blow Moulding

The forming of a hollow object by inflating or blowing a thermoplastic molten tube called a 'parison' in the shape of a mould cavity.

Blow Moulding Process Steps

1. Fabrication of a starting tube, called a parison, by either extrusion or injection molding. 2. Inflation of the tube to desired final shape.

Three Main Thermoplastic Blow Moulding Processes

Extrusion blow moulding, Stretch blow moulding, and Injection blow moulding.

Stretch Blow Moulding

Has mechanical assistance that stretches the part in the longitudinal direction at the same time blowing the part causing a stretch in the part along the hoop or radial direction, this results in biaxial orientation and increased properties.

Blow Molding Materials

high density polyethylene (HDPE), polypropylene (PP), polyvinylchloride (PVC), and polyethylene terephthalate (PET).

Products of Blow Molding

disposable containers for beverages and other liquid consumer goods, large shipping drums (55 gallon) for liquids and powders, large storage tanks (2000 gallon), gasoline tanks, toys, and hulls for sail boards and small boats