To replace Vespel electrical insulators in plasma cutting torches, a manufacturer chose lower cost PEEK polymer that offered the same electrical insulating and high temperature properties.

When Esab Welding and Cutting Products of Florence, South Carolina, USA, wanted to replace the Vespel electrical insulators in their plasma cutting torches, they chose Victrex PEEK polymer. The polymer offers the same electrical insulating and high temperature properties as Vespel but is less expensive and easier to machine. Plasma cutting torches are used to cut and fabricate metal parts.

They utilize electricity to create an arc between the electrode (torch body) and the work piece.

'The arc is forced through a nozzle with a small hole in it along with a flow of gas, such as air, and this results in the air becoming very, very hot, up to tens of thousands of degrees,' explains Stan Severance, Staff Engineer at Esab.

'As a result, this high temperature effluent of gas along with the arc can cut through metal.' Located in the head of the torch, the PEEK polymer insulator electrically insulates two different potentials inside the torch from each other.

Explains Severance, 'A torch typically has two electrical potentials.

One is associated with the electrode and the other is associated with the nozzle.

In order to start the torch, an arc is struck between the electrode and the nozzle which is called a pilot arc.

Once the pilot arc makes contact with the work piece, the arc transfers to the work piece.

It is necessary to separate the electrode potential from the nozzle potential.

This means having one or more insulators inside the torch body to insulate the two potentials from one another.' Because the insulators are exposed to the high voltage electrical discharge used to start the torch, they must be able to withstand very high temperatures.

Explains Severance, 'To get the arc started, you can have very high voltages - up to 10,000V - at high frequency, plus temperatures can be very high especially in air-cooled torches.' Before switching to PEEK polymer, Severance said 'We looked at a variety of different materials.

Vespel is very expensive and it has a very complicated manufacturing process.

We wanted a material that would be substantially less expensive but still have all the properties needed to meet the requirements of the application.

In addition to good electrical insulative properties and good high temperature properties, we wanted machinability, heat aging and creep resistance.

PEEK polymer fulfills all these requirements.' With operations in a large number of countries, Esab is the world's largest producer of welding and cutting consumables and equipment.