Selection of thermoplastic materials for application in mixer cartridges based on the tribological properties between polymeric pairs

Abstract

The performance of the mixer cartridges that regulates the temperature and the water flow in most of the daily use faucets is based on the movement and geometry of two ceramic discs, whose relative position is set by moving the handle. During the transmission of the movement to the discs, we also submit relative movement to three thermoplastic pieces called ceramic holder, racord and housing, which are in permanent contact and compressed. The tribological behaviour of this system is crucial for the cartridge’s performance. Even if different greases are used as lubricants between the pieces, the raw material of these polymers is fundamental in terms of the generated friction and wear. In the present project, a selection process aimed at enhancing the thermoplastic combination currently used for the components has been done. A first selection phase, in where parameters such as dimensional stability associated to moisture absorption, thermal expansion, mechanical properties, availability or cost have been studied, has been done in order to choose potential substitutes. In a second selection phase, using a ball-on-disk device, tribological tests have been done to those combinations worthwhile to the project. In the final count, the results show that the current combination can be improved; being the use of polyoxymethylene (POM) in the ceramic holder, polyphthalamide (PPA) filled with 40% glass fibre in the racord and polybutylene terephthalate (PBT) filled with 15% glass fibre in the housing the best combination among those studied