Thermoset materials were the first commercial plastic materials developed in the early 1900s to be processed into moulded form for many industrial and commercial applications.

The conversion of the raw Thermoset material into the moulded product requires heat and pressure to start the chemical chain reaction of the material from its original form into a hard moulded product. To do so requires the mould tools to operate at 150°C to 180°C, with minimum pressures of 23bar per square centimetre.

Usually, the tool size dictates the press size rather than the part size. The heat enables the resins to flow and then cure solid.

The pressure is to keep the mould closed and press out the volatiles/gas produced as the material flows to fill the tool cavity form.

Phenolic

Phenolic started life as a pure resin and was used for decorative objects of art, jewellery, and ornaments in the late 1800s and early 1900s. These objects have recently been prised for their value and appeal to collectors. Early examples were of an amber-coloured resin. This was before other colours became fashionable for jewellery and objects of art. As a resin, it was easy to create a design into a simple wooden mould and allow it to cure to become a solid part.

In the early 1900s in New York, a scientist turned the resin into what we now know as Phenol-Formaldehyde or its most common name Bakelite. It was not much later that the material became usable as a moulding material for many industrial and commercial products. At the same time, adding other compounds into the original resin further improved/enhanced the properties of Phenolic.

These ranged from wood powder, cotton fibres for improved impact resistance, minerals, such as silica, talc and mica, to increase the heat resistance, and glass fibres for impact and tensile strength, or a mixture of any of these as well.

Known for its Insulating properties, it became widely used in many electrical applications, such as Bobbins for windings/coils, Fuse Holders, Pan Handles and Ash Trays for their heat resistance, Telephones, Radio Cases, Bottle Caps for their smooth solid appearance, along with many applications in both WW1 and WW2, and many more since.

Over the years, the name Bakelite has remained a trade and company name, but the company name has become part of Sumitomo Bakelite. The original company and manufacturing facilities are now under the trade name Hexion. There are other manufacturers of Phenolic, mainly in the USA – Plenco, Norplex Micarta, but also in Europe such as Vyncolit, Hexion, and China.

Phenolic Material

Phenolic material is in a coarse granular form, which can be used as-is, or for more straightforward and speedier handling, can be pre-formed into (pellets/slugs). This requires the granular material to be pressed into a cold die in a pelleting machine/press. The ‘pellet/slug’ is ejected out and retains its shape. The shape, in most cases, is round but can be of the shape of the tool cavity form of the moulded part.

In most cases, the granules and ‘pellet/slug’ require preheating to soften the hard material before loading it into the mould tool. This heating process is usually by plate heating using high-frequency electrical energy and passing a current through the material to create heat.

In cases where just the granules are used, for small parts or complex mould tool cavities, the granules are poured into the cavity and allowed to sit for 5 to 10 seconds to warm through before the tool closes at slow speed. This allows for the material to soften before coming under the press pressure.

Granules and ‘pellets/slugs’ are sometimes used together. It is very much the choice of the best process and product design that dictates what is chosen by the setter and the quality.

The process of compression moulding phenolic resin is as follows: the material charge is placed into the tool cavity form, and the tool closes slowly to compact the material and start the chemical chain reaction.

The tool then opens partially for a few seconds to allow gas/volatiles and ‘flash’ (additional material to ensure the whole cavity is complete) to escape. The tool then re-closes and holds firm for a set period to allow the material to cure before finally opening fully.

At this point, the part is ejected by the tool and press movement and removed by the operator. The tool is then blown clean of debris before the cycle starts again.

Transfer Moulding of Phenolic

The phenolic moulding process is a versatile and cost-effective way to produce precision parts with a wide range of applications. The process begins with a chamber for the Phenolic to be placed in. The tool then closes, and a hydraulic ram is forced into the impression detail as part of the press function.

This is often supported with a vacuum arrangement to suck the air and gas out as the material is forced into the tool. After cooling, the part is removed from the mould, and trimming operations are performed as necessary. The phenolic moulding process offers many benefits, including high dimensional accuracy, smooth surface finish, and excellent resistance to wear and tear.

This method reduces the flash and presents a cleaner moulding but also enables the part design to be machined into both halves of the mould tool. The part split line can be suitable for the part gate feed and offers improved quality as the process eliminates porosity through gas trapping. Some of the compression presses at Merriott Plastics have this facility, 80t, 150t, 300t and 400t sizes.

DST (Direct Screw Transfer) Phenolic Injection Mould

Merriott Plastics also uses injection mould Phenolic in a process known as DST -Direct Screw Transfer.

The material comes into a rotating screw through a heated barrel, also used to soften the material. It is similar to the preheating described above.

The material is then forced into a closed tool, operating as a conventional injection machine. The tool is heated to the temperature of 150/170°C.

The benefit of this process is the increased yield for high quantity demands, improved cycle times, and in most cases, running fully automatically, thus reducing the labour cost.

Summary

Merriott Plastics produces many components using Phenolic material, despite many other thermoplastic materials being available. Still, they do not have the feel, strength, rigidity, insulation, heat resistance, or long-lasting as Phenolic.

We produce Fuse Carriers and Holders, used in electrical cabinets for industrial use. We also produce Insulators for many different electrical applications, where insulation and high heat are specified. Additionally, we produce mouldings for hazardous environmental areas due to the chemical and hardness of Phenolic.

Thermoset moulding may be the perfect solution if you are looking for a reliable and efficient way to produce plastic parts.

Contact us today to learn more about this process and how we can help you get started.