Problem solving

Machining PTFE

A new way of extracting chips, shavings and machining waste

PTFE is a high-quality sealing material used throughout industry. It has excellent anti-friction properties and a high thermal and chemical resistance.

However, manufacturing PTFE seals is not exactly simple because the standard processes for machining plastics cannot be used. A PTFE seal starts out as a round, sintered blank which is then machined to the required shape and size on a metal cutting machine tool. In order to produce a smooth, uniform surface, the cutting tool must remain in constant contact with the workpiece during machining.

This presents the machine operator with a problem. What do we do with the shavings? You should note that shavings in this case are long and continuous and can reach lengths of 10 or 20 metres. The shaving cannot be left inside the machine and at the same time it cannot be removed because the machine tool safety door must remain closed during the cycle.

IDT GmbH in Annaberg-Buchholz, manufacturer of PTFE seals and profile gaskets of all types, has solved the problem in collaboration with Ruwac Industrie-Sauger GmbH.

Using standard components, Ruwac developed an extraction unit tailor-made for this particular application to the customer's specifications. The blank is clamped in the chuck of a CNC turning centre. An extractor pipe takes the continuous shaving strip directly from the blank as it is shaved off during machining. The vacuum of 280 mbar is produced by a side-channel blower designed for continuous operation.

The shaving is fed into a pre-separator container and then vacuum compressed together with the other extracted material. This solution ensures a long service time to the next emptying cycle. Emptying the container is quick and easy. The container holds a re-usable fleece sack which is simply returned to the container after emptying.

The pre-separator is connected to its own vacuum unit which in turn has another filter. The exhaust air is passed through a silencer and then out through a diffusor. This has another advantage: the suction air remaining in the working area improves the energy balance.

Ruwac also developed another special feature to deal with the shaving produced when the inside diameter of the blank block is being machined. In this case the unit extracts the shaving through the hollow shaft of the clamping block. An automatic switch controls this particular extraction connection and is triggered by the machine tool PLC.
This solution is now fully operational and is giving reliable service. The continuous shaving strip is extracted without any problems and without influencing in any way the safety level and productivity of the CNC turning machine. Despite being highly customised, there is nothing experimental about this solution. Ruwac used tried-and-tested components from its modular system range to produce this application.

The customer is so satisfied with this extraction unit that it has ordered another continuous shaving extractor from Ruwac.