July 14, 2022

How bakelite is manufactured?

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Bakelite is an old trade name for Phenolic thermoset plastic which was developed by Leo Bakeland about 100 years ago. Phenolic resins are the result of a condensation reaction of phenol and formaldehyde. There are two basic phenolic resins, Resole (single-stage) and Novolac (two-stage), novolac being the more common. Resole is truly thermosetting with heat, while novolac requires a catalyst to supply the additional formaldehyde needed for crosslinking. The catalyst is typically hexamethylenetetramine. Molding materials are typically filled with cellulose or mineral and are compounded either on rolls or twin screw extruder.

If you intend to purchase the base phenolic resin and what you are interested in is the compounding. If that is correct, you will want to buy the Novolac (two-stage) resin. The step by step process to compound phenolic isn’t that complicated, but a through explanation would take more time and space than can be presented here. The very simple explanation is that all the necessary raw materials are premixed in a ribbon blender at room temperature and then sent to either heated calender rolls or a twin screw extruder. If sent to rolls, the sheets are cooled and sent to a grinder and the granulated material is then screen classified to remove overs and fines. If an extruder is used, there is some process to make pellets, either a die and strands or die and fly knife cutter. Putting in a compounding operation is a bigger deal than you might think. Back when I was in the industry I had customers with similar usage and they bought material from a compounder (the company I worked for). They could not justify the cost of all the equipment needed for compounding.

Injection molding
of phenolic has been around most of the 40 years I’ve been in the industry. Although it’s not conventional (same as thermoplastic) equipment it is quite similar. It does take a special screw and a jacketed barrel, the basic concept is the same as thermoplastic injection molding and the same basic machine can be used with the proper modifications to the screw and barrel. In my opinion, this is the easy part and the part that is already being done by REHA, the complicated part is compounding the resin into a molding compound. Compounding is not really something that I would suggest a molder take on.

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