The injection moulding / manufacturing process is a well tried and proven process. However we are often asked by modellers how the product is made. Whilst details of our carbon fibre production process will never be released, we are however more than happy to tell all (well almost) re injection moulding, read on ....
The part is formed inside a 2 part (top and bottom) steel die. The die is clamped into an injection moulding machine. These machines are normally quoted in clamping force tonnage. Our biggest product is moulded in a machine of 850 tons clamping pressure. Such a machine is huge - you need a ladder to climb to the top. Most of our props are made in 30 - 80 ton machines. That's a lot of force holding the two halves of the mould together - and it's needed. Not a play thing in any way.
Getting an injection moulding machine up and running can be a tedious process. It takes time to get everything just right. Before being used, the base raw material has to be dried to remove any traces of moisture. Once dry, it's loaded into the machine's material hopper. From there it heads into the core of the machine be heated to over 250 degrees C (480F) before it can be used. At that temperature the polymer is in a liquefied state. At those temperatures one needs to be very careful.
Once everything is ready, the injection moulding machine (which on the factory floor is more often called a press), clamps the mould halves together. The liquefied raw material is then injected into the mould cavity under great pressure. It takes just seconds to fill the mould - the slowest part of the moulding process is then waiting for the newly formed propeller to cool down. More often than not the moulds have water cooling (or heating) to maintain consistent temperatures.
Once the product inside the mould has cooled to a solid state, the press is opened, pulling the two mould halves apart and triggering a mechanism that ejects the part from the mould and into a waiting container. The machine closes and the cycle begins all over again. Such machines can run the same die for weeks on end without a break - i.e. mobile phone cases.
We normally throw away the first 50 parts as it can take that long to purge old material and get the operating temperature to stabilise sufficiently to be making consistently good quality parts.
Not only do we throw away the first 50, we also hold the press closed 5 or 10 seconds longer than the ideal fastest cycle time. Waiting those for extra seconds ensures a much more stable part with minimal chance of distortion.
That's not the end of it however - in fact the moulding cycle is the fastest part of the whole process. The ejected part will normally have a "sprue" that needs trimming and the central hole needs drilling. Well it does if the propeller is made with central injection. Some of the cheaper propellers on the market are injected from the side - and its little wonder the strength and balance of such props is generally very poor.
ProGlass propellers are then printed with our logos and allowed to sit around for a few weeks before being packaged. The reason for not packing the propellers immediately is to enable them to absorb moisture from the atmosphere - which believe it or not improves the strength of the propeller. For this reason it is best to NOT store your propellers in a hot, dry sunny place. Many years ago it was the fashion to boil nylon propellers to improve their strength - and indeed we would also need to do that if the propeller was to be used a few hours after moulding.
A few props from every batch are checked for balance and a note made to adjust the tooling next time around if we find any problem. It is rare - but we have been known to rejected a whole batch.
So there you have it - the whole process from cradle to your model. It's expensive and exacting but fast to make a consistent product in the thousands at a time. If only we could make carbon fibre - epoxy propellers that fast ......