The Wear Mechanism and Friction of PEEK Simulation Gear applications

Z. M. Shukur^1,2, *K. D. Dearn¹, S.N. Kukureka³

¹School of Engineering, Department of Mechanical Engineering, University of Birmingham, UK.

²School of Metallurgy and Materials, University of Birmingham, UK.

³Department of Mechanical Engineering, University of Kufa, Iraq.

*K.D.Dearn@bham.ac.uk

INTRODUCTION:

Polymer gears are widely used in many industrial applications due to its advantages in noise reduction, self-lubricating features, dramatic weight reduction and cost savings. One of the unique polymers used recently is poly-ether-ether-ketone (PEEK) as it is used to make high temperature gears and gears where exceptional strength¹. To design a polymer machine element effectively requires a detailed understanding of the material properties, the kinematics of machine element motion and the application the machine elements is to be used in, and this can be challenging to simulate.  For example, the physical process of a gear’s action is difficult to model without suitable gear test facilities. The main difficulty in analysing gear contact loads are due to the continuously changing values of sliding velocities, contact loads and radius of curvature along the line of action². The majority of polymers are injection moulded. However, recent developments in additive manufacturing methods have meant that geometry, that was previously very complicated to manufacture, can now be produced automatically through layer deposition techniques. High temperature selective laser sintering (HT-SLS) is a method of additive layer manufacturing (ALM) used mainly in the aerospace and medical industries³. ALM refers broadly to a process by which digital 3D design data is used to build up a component in layers by depositing material. This paper will investigate the rolling–sliding wear behaviour of unreinforced laser sintered polymers material poly-ether-ether-ketone (PEEK), printed with an EOS PEEK HP3 printer disc against steel AISI 52100 disc and compered the result with polymers material poly-ether-ether-ketone (PEEK450G) discs running against steel AISI 52100 disc. It was used this as a simplified method of analyzing the dynamic response of high performance polymeric gear teeth.

MATERIALS AND METHODS:  The test discs were machined laser sintered polymers material poly-ether-ether-ketone (PEEK), printed with an EOS PEEK HP3 printer and PEEK against steel AISI 52100.

Fig. 1 shows the twin-disc test rig that was used for unlubricated, rolling– sliding tests. Two cylindrical discs were mounted on spindles contained in a friction block and a pivoted loading block.

Figure 1 Schematic view of the twin-disc test rig.

discs were driven at a controlled speed with the relative slip ratio between the contacting discs adjusted by altering the gear ratios. The system is capable of simulating then on conformal contact found in common machine components such as gears and cams. Loads were applied to the system by a weight (5) attached to the upper pivoted loading block (4) to provide a normal force between the two discs. The lower block was mounted on vertical leaf springs and strain gauges were used to determine the sliding frictional force by noting the tangential force on the lower disc. Wear of the samples was approximated by detecting the displacement of the upper block using a linear variable displacement transducer (LVDT) to record the displacement of the disc centers.

Interfacial temperature: The predicted temperature generated at the interface between two contacting discs can be modelled as the sum of the prevailing temperatures at that point (Eq. (1))

Where Tflash is the instantaneous temperature due to frictional heating, and Tbulk is the measured bulk temperature of the two bodies, combining ambient temperature and physical heating effects⁴.

RESULTS: 

Wear mechanisms: when operating under severe loading conditions and slip ratios EOS PEEK HP3 shows significantly a smaller amount wear than other reported PEEK materials². Although the wear rates in some of the more severe tests are high, at lower temperatures there was very little visible wear.

Measured temperature and friction: wear rate was, increased at the end of testing where much surface material was removed as debris.

DISCUSSION: The wear mechanisms of EOS PEEK HP3 running against itself in non-conformal, unlubricated rolling- sliding contact have been investigated over a range of loads and slip-ratios. Overall, the possibility of using EOS PEEK HP3 in low slip ratio conditions, for both low and high loads, has been demonstrated with high temperature operation being possible despite an increase of wear. It has been shown that wear, friction and temperature increase as the slip ratio and the load are increased. However, the wear rates are significantly lower than for other polymers tested using the twin-disc configuration. The results presented in this work can be employed in conjunction with the design process to permit the EOS PEEK HP3 to be engineered for a specific high-performance gear contact conditions.

REFERENCES: