Transfer moulding basics

Transfer moulding is one of the several methods used by engineers to create rubber components. The required amount of moulding material is measured, inserted, and placed into the moulding pot before the process begins. Then, as the material heats up, pressure drives it into the mould cavities.

The transfer moulding process

First, a piece of uncured rubber is placed into a pot that forms part of the mould. Then, the mould is closed, and hydraulic pressure is applied. This forces the rubber through a small hole into the mould’s cavity. While the rubber cures, the mould remains closed. Next, the plunger is raised, and the transfer pad material is removed. Finally, the mould is opened, and the part is removed. Any overflow material, also called flash, is trimmed away once the part is demoulded.

Transfer moulding applications

Transfer moulding is an excellent method for producing composite seals with insert moulding that float in the cavity. Because the cavities are not connected, they can move freely rather than being cut straight into the same plate. This absorbs tolerance changes, allowing the moulding to remain constant.

The composite seal may be made using a variety of inserts such as plastic and metal. These provide a multi-component sealing solution that helps minimise the total component count in assembly while also offering a stronger seal.

Natural gas industry: Metal-to-rubber face seals are used in the natural gas sector to establish an interface for gas valves.

Electrical industry: Wires are put into cavities to form connector seals around the wires. This is commonly used in spark plug wires.

Hydraulic industry: Transfer moulding provides sharper cut-offs during moulding, which significantly benefits lip or U-cup designs in the hydraulic sector.

The advantages of transfer moulding

  • A high number of cavities. Transfer moulded rubber goods, in many circumstances, require few and simple preforms. Hundreds of holes can be filled using a single preform. This is a benefit over compression moulding and can save substantial time throughout the moulding process. This is also advantageous over injection moulding since there is no runner to fill each cavity which would reduce the number of cavities.
  • Design adaptability. Sharper edges are possible using transfer moulding. Micro grind vents eliminate the requirement for overflows, allowing for near flashless components, a substantially reduced deflash procedure, or the ability to send parts with flash limitations. Simplified preforms are necessary for pot and plunger designs, allowing for improved uniformity and cost savings.
  • hort production cycle. Transfer moulding has faster cycle times than compression moulding and can also give better uniformity. Tighter tolerances and more complicated pieces are possible using this method.

The disadvantages of transfer moulding

  • Complicated moulds. Tooling can be costly because of the complex design and mould.
  • • Waste material. Transfer pots often generate more excess than regular compression tool overflows. Transfer moulding usually results in a big pad with sprues. Because the polymers are thermosetting, the scraps can’t be reused.
  • • Mould repair. Inserted transfer tools need more mould upkeep than compression tools. Inserts must typically be removed and reset to preserve movement over time. Cleaning the tool can be time-consuming, and special equipment like dry ice blasters are frequently needed to clean the complex transfer insert.

Contact Specialized Mouldings for details

Transfer moulding is just one of several moulding techniques used in the market. To discuss custom rubber moulding for your specific application, please get in touch with a representative from Specialized Mouldings South Africa today.