Incorrect installation is still the main cause for the failure of radial shaft seals. The second generation PTFE Simmerrings, supplied by CORTECO in many different dimensions, have a different design which helps to prevent assembly faults.

Polytetrafluorethylene (PTFE), also commonly known under the name of Teflon, has become a powerful material for industry and is suitable for a multitude of applications – also in sealing technology. In addition to a wide temperature range of -200 °C to +260 °C, the material has very low friction values, prevents the ,stick-slip‘ effect and is self lubricating. PTFE is also highly resistant to chemicals, which is why it is increasingly being used as a sealing material for cars. Seal developers compensate material related disadvantages in the form of poor cold flow characteristics and low abrasion resistance by using fillers such as graphite, glass-fibre or bronze. This increases creep resistance, heat conductivity and wear resistance. Freudenberg, CORTECO’s parent company and original equipment supplier to the automotive industry, has been using PTFE for twenty years in their Simmerrings. By now, the second generation of PTFE radial shaft seals has reached the market, characterised mainly by their more compact design. They can be recognised by their moulded sealing lip towards the dry side. Due to the fact that the PTFE shaft seals can be obtained with the same dimensions as the previous elastomer seals, the aftermarket can also benefit from the advantages of the better material. The new shaft seals are able to replace the old ones, providing the mechanic observes a few important points when replacing them.

Significant Advantages

The new shape means that there is more oil under the sealing lip during operation. The engineers compensated the resulting higher chance of leakage with a spin, integrated into the sealing lip, which is to ensure a continuous re-flow of oil. However, the larger amount of oil under the sealing lip also has advantages: the temperature in the sealing gap is reduced by approximately 10 °C, which noticeably reduces the creation of oil coke deposits there. Naturally, the additional lubrication and the excellent self-lubrication mean that friction values are reduced – by up to 40 percent. Both effects increase the life span of the new crankshaft seals, resulting in lower warranty costs for the automotive manufacturer.

Sealing Only if Assembled Correctly

According to research carried out by CORTECO, incorrect assembly is with 34 percent the most common cause for the failure of a radial shaft seal.This indicates that among workshops there is obviously still need for further information. Both the traditional elastomer Simmerrings as well as the first generation of PTFE rings required great care during assembly: their moulded sealing lip on the oil side usually required the use of a suitable fitting sleeve to ensure safe assembly. This opened the sealing lip, allowing the safe positioning of the seal on the shaft which is to be sealed. Sealing lips of the second generation of PTFE-Simmerrings cannot fold over during assembly and therefore do not require a fitting sleeve, making the installation less risky. A fitting sleeve is only required with shafts which have sharp toothed edges, in order to protect the sealing lip from being damaged. One general rule applies: in order to ensure good sealing, the engine should not run for at least eight hours following the installation, to allow the sealing lip to return to its original position. Modern PTFE Simmerrings from CORTECO are clearly less sensitive than their predecessors – providing the mechanic adheres to the assembly instructions. Only a correctly installed seal can reach its full life span and fulfil its sealing function for as long and as well as possible.

Greasing During Installation – Yes or No?

Many mechanics are hard to convince that not all shaft seals have to be greased before installation. However, CORTECO’s sealing experts know better: a few drops of oil or some grease are only useful in connection with elastomer-based shaft seals. PTFE seals can even be damaged through this. Greasing agents, additionally applied during installation, can lead to coke deposits under the PTFE sealing lip, which could prevent the re-flow effect and thereby have a destructive effect on the seal. The superior material characteristics make greasing superfluous, as the material has a high temperature resistance and is self-lubricating.