Expert advice aids selection of the right gasket material

There are a wide range of polytetrafluorethylene (PTFE) products to choose from in the industrial gasket market. The product has evolved dramatically since the late 1960s, from just virgin and commercial-grade PTFE to the present day offerings, including what is described as calendared or restructured filled PTFE sheet.

PTFE has many benefits. The two most notable are it has exceptional chemical resistance; there are only a few chemicals that will attack the polymer. Also, it can withstand temperatures up to 260°C (500°F).

However, the product has one significant weakness, as it exhibits creep and cold flow characteristics under compressive loads, thus affecting the gasket’s performance, since frequent retightening is required.

Most users of PTFE are unaware of the fact that several different materials can be used successfully for the same application. The question to ask is what product is right for your application.

There are varied processes in how PTFE sheet is manufactured, involving sintering the PTFE into a billet form and then skiving it into a sheet, or having sintered PTFE sheet manufactured from a moulding process. Fillers or fibres can be added in both processes to reduce the creep behaviour.

In another process of calendaring (where the sheet is made from a Teflon cake, as it were), the sheet is sintered, creating a sheet with a very even homogenous structure throughout the entire manufactured sheet, thus dramatically creep.

With any different processes, there are different costs associated with the various manufacturing techniques and these affect the cost to the end user. For example, prices in Canada can range anywhere from $750 for a 1/8x60x60-in. glass-filled, sintered PTFE product, up to $3,000 for the same size sheet manufactured from the calendared process – also known as the restructured process.

Pulp and paper mills in Canada use a wide range of PTFE gaskets in their facilities. As an example, for an application using sodium hydroxideor or sodium borohydride in the bleachery portion of the mill, the specifications call for a gasket manufactured from a restructured sheet process. This gasket is four times the price of a glass-filled, sintered process gasket.

In 85% of all applications, sintered PTFE products will work as well
as restructured Teflon. Researching and finding the correct gasketing product for each particular flange is the real challenge in increasing production and reducing costs.

The new PTFE has a wide range of fillers that can be incorporated into the sheet to meet many chemical service needs, including barite, synthetic and mineral silica, barium sulphate or hollow glass micro-spheres. Each filler has a specific service application for use with a particular chemical in a particular flange.

In the past few years, there have been PTFE resin shortages, resulting in large price increases being passed on to the manufacturers, resulting in an increased cost of finished sheet goods for the consumer. Those higher costs have not fallen all the way back from pre-shortage levels in Canada. Also, the Canadian market is now experiencing the introduction of restructured sheet from China at a significant cost savings to the industrial gasket consumer.

The choices are numerous and the cost savings to the consumer can be tremendous. But the work involves finding a reliable supplier/manufacturer to guide you in the correct direction for the most effective cost savings when purchasing PTFE gasketing products. The highest-price gasket product is not always the best selection. So just because it’s PTFE and it is white, it might not be right for your application.