Thermoset compression and transfer molding

Wishing to know more about thermosetting materials compression and transfer molding processes?

Well, you’re in the right place.

At Setvis, we have gained lots of experience in thermoset molding of technical products over the years, or better, since the ‘50s, when it was the core business of our company.

Still today the use of compression moulding machines is the solution adopted for many of our plastic molding projects.

Why?

Let’s get into some aspects of this technology and find it out:

Characteristics and main types of thermosetting materials

Thermosetting polymers allow plastic molding of very thick items with remarkable mechanical resistance.

They’re suitable for electro-mechanical applications thanks to dielectric strength, heat resistance, arc resistance, high chemical resistance, bending modulus of elasticity and antistatic properties.

Moreover, minimal withdrawal rates make thermoset polymers ideal for moulding items requiring decimal tolerances.

Pressure values in compression molding and cross-linking reactions of thermosetting polymers chemical structure are the two main phenomena of plastic transformation.

Due to their crosslinked structure, phase transitions in thermosetting polymers are irreversible. For this reason, unlike thermoplastics, thermosets cannot go back from solid to fluid-elastic material once they’ve been molded.

Although making thermosets non-recyclable, this is what gives them all the properties mentioned.

Using thermosetting materials is recommended when the mechanical properties we described are essential, as well as when variable thicknesses are needed in the product section.

No contractions and alterations in the inner cavity, dimensional stability over time and elevated resistance to high temperatures are even more other excellent features of thermosetting materials.

From compounds to traditional and reinforced resins, the main thermoset can be divided in the following types:

Bulk Moulding Compounds – BMC

BMC are compound materials ordinarily used in compression and injection moulding. They can be reinforced with fiberglass, carbon fiber, mineral, aramid, natural or mixed fibers, with 65% maximum charge. Main applications include components for the electric market (electrical household appliances too) and the transport industry.

Sheet Moulding Compounds – SMC

SMC are very similar to BMC.The key difference is that they are shaped in rolls or sheets approximately 1m wide. This enables to reinforce polymers using long fibers with extremely low withdrawal rates (close to 0 %).

Melamine Resins – MF

Condensation polymers of aldehyde with melamine used when products require excellent aesthetics results besides a good mechanical resistance.

Phenolic Resins – PF

These are condensation polymers of phenol with formaldehyde. They can be distinguished in novolacs and resols based on the concentration of the reagents. Phenolic resines also include Bakelite, the first synthetic plastic ever.

Types of thermoset molding

Irreversible plastification process is something common in thermosetting polymers molding. Since compression molded objects cannot be remolded, you should use this method for manufacturing plastic products with no particular aesthetics and uniformity requirements.

Direct compression moulding

Direct compression molding with vertical molding machines is frequently used because of its remarkable versatility and mould production lower costs.

How does it work?

Punch and die arranged in open position are filled with material in the form of powder, fabric or paste. After the mold is closed and heated, the punch compression (hence the name of this molding technique) eases the flow of the material so that under the compression pressure it acquires the expected mold shape and the molecular crosslinking process gets started.

When heating cycle time is up, the mold is opened and the molded product removed.

Transfer moulding

This method makes use of both compression and injection molding techniques. In this case, the filling material can be forced into the mould cavity even when this is closed, and this is suitable for manufacturing complex-shape products, for which the open mould filling is not recommended.

After being placed in a pre-chamber, the material is injected into the mould cavity by a plunger to conform to the mold shape. Here starts the molecular crosslinking process. Once this stage is completed, the mould can be opened to remove the product.

Examples of thermoset molding

To get an idea of the objects you can make through compression molding, see below some examples from our protfolio of works.

Machine component for use at 350,000 Volts

Piece moulded in thermoset resin, reinforced, low shrinkage, used at 350,000 Volts.

Pieces in thermo hardening resins, low shrinkage, thickness up to 60 mm

Co-moulded pieces for textile machinery in thermo hardening, reinforced resin, low shrinkage, thickness up to approximately 60 mm, tropicalized iron inserts and CNC brass bushings.

Ultralight airplane rim

Five inch rim moulded in thermo hardening polymer with elastic module of 20,000 Mpa and glass fibers up to 50 mm. The product passed all the tests it was subjected to, improving the performance reached previously by the aluminum wheel that was being used by the customer.

Transfer molded design parts

Glossy and aesthetic items, transfer moulded in phenolic resin, resistant to detergents, for household items with bi-directional threading and closure cams obtained through moulding.

Getting to know the characteristics of thermosetting polymers, the compression molding technology and its applications is essential, don’t you think?

With this guide, now you have everything you need to move your first steps in plastic manufacturing.