Wear mechanisms in polyoxymethylene (POM) spur gears (original) (raw)

The wear of PEEK in rolling-sliding contact - simulation of polymer gear applications [Open Access]

Wear, 2013

The wear and friction in the pitch region of the centre of polymer gear teeth are not well understood. The transition around this point of the tooth between rolling and sliding has an important effect on the durability of polymer gear drives and can be simulated using a twin-disc configuration. This paper investigates the rolling–sliding wear behaviour of two poly-ether-ether-ketone (PEEK) discs running against each other with a simplified method of analysing and understanding the dynamic response of high performance polymeric gear teeth. Tests were conducted without external lubrication over a range of loads and slip ratios, using a twin-disc test rig. The wear and friction mechanisms were closely related to surface morphology, with changes in crystallinity correlating with the severity of operating conditions. Observed failure mechanisms were also related to the structure of the contact surfaces, and included surface melting and contact fatigue. Overall the PEEK discs were capable of running at low slip ratios for both low and high loads. Their performance reduced with an increase of the slip ratio. The results presented can be used in conjunction with the design process to allow the PEEK to be engineered for a specific high performance gear contact conditions.

The effect of the teeth profile shape on polymer gear pair properties

Tehnicki vjesnik - Technical Gazette, 2016

Original scientific paper The paper presents an extensive research on two different tooth-flank geometries, i.e. involute and S-gears. A significant difference between the two analyzed geometries was observed during the lifetime testing. The tests were conducted on special test equipment with an axis distance of 20 mm. The material used for the tested gears was POM for the driver gear and PA6 for the driven gear. The same sizes of driver and driven gears were used (m = 1 mm, z = 20). Gears of this size are particularly suitable for micro-gear transmissions. The tests were carried out using different rotational speeds and torques, between 0,8 N•m and 1,5 N•m. During testing the thermal state of the gears was measured with a thermal camera. The stress and deformation analyses of the tested gears were undertaken using numerical simulations employing the finite-element method.

Assessing Wear Coefficient and Predicting Surface Wear of Polymer Gears: A Practical Approach

2024

With the ever-increasing number of polymer materials and the current number of commercially available materials, the polymer gear design process, regarding the wear lifetime predictions, is a difficult task given that there are very limited data on wear coefficients that can be deployed to evaluate the wear behavior of polymer gears. This study focuses on the classic steel/polymer engagements that result in a wear-induced failure of polymer gears and proposes a simple methodology based on the employment of optical methods that can be used to assess the necessary wear coefficient. Polymer gear testing, performed on an open-loop test rig, along with VDI 2736 guidelines for polymer gear design, serves as a starting point for the detailed analysis of the wear process putting into service a digital microscope that leads to the evaluation of the wear coefficient. The same wear coefficient, as presented within the scope of this study, can be implemented in a rather simple wear prediction model, based on Archard’s wear formulation. The developed model is established on the iterative numerical procedure that accounts for the changes in tooth flank geometry due to wear and investigates the surface wear impact on the contact pressure distribution to completely describe the behavior of polymer gears in different stages of their lifetime. Although a simple one, the developed wear prediction model is sufficient for most engineering applications, as the model prediction and experimental data agree well with each other, and can be utilized to reduce the need to perform time-consuming testing.

Different teeth profile shapes of polymer gears and comparison of their performance

Journal of Advanced Mechanical Design, Systems, and Manufacturing

This article presents a lifespan testing analysis of polymer gears manufactured by cutting. Compared to injection molding, machine cutting provides higher accuracy of gear geometry. Two different tooth flank geometries were tested; i.e. involute and S-gears. In theory, S-gears have several advantages over involute gears due to the convex/concave contact between the matching flanks. The theoretical tooth flank geometry of S-gears provides more rolling and less sliding between the matching flanks, compared to involute gears. The convex/concave contact leads to lower contact stress, which in combination with less sliding means lower losses due to sliding friction and consequently less heat generated. The goal of our research was to prove that tooth flank geometry affects the lifetime of polymer gears, and to find the mechanisms and quantitative differences in the performance of both analyzed geometries. The gears were tested on specially designed testing equipment, which allows exact adjustment of the central axis distance. Two different material pairs (POM/POM and POM/PA66) of the drive and driven gears were tested. Each test was done at a constant moment load and a constant rotational speed. Several tests were conducted using the same conditions due to repeatability analysis. All the tests were performed till the failure of the gear pair and without lubrication. In lifespan testing, the polymer S-gears showed better performance and longer lifespan than involute polymer gears. means higher heat generation as a result of losses due to friction in contact. A more significant difference between the load capacities of both gear geometries was detected when testing the POM/PA66 material combination. Because the POM/POM material combination is tribologically incompatible, gears wear too quickly, tooth profile shape is no longer right and all of the advantages of the S-gear profile shape are lost. This time, tests were conducted under high loads in order to obtain results in a reasonable time. Overloading triggers the overheating failure mechanism. Practical applications often require material data after 10 or even 100 million load cycles. A different failure mechanism is expectedfatigue. For this reason, future tests will be carried out under lower load levels. Priority will be given to material pairs that are tribologically compatible and interesting for real applications (such as POM/PA).

A kinematic analysis of meshing polymer gear teeth

Proceedings of The Institution of Mechanical Engineers Part L-journal of Materials-design and Applications, 2010

This article describes an investigation into the contact behaviour of polymeric gear transmissions using numerical finite element (FE) and analytical techniques. A polymer gear pair was modelled and analysed using the ABAQUS software suite and the analytical results were calculated using the BS ISO 6336 rating standard. Before describing the results, the principles of the strategies and methods employed in the building of the FE model have been discussed. The FE model dynamically simulated a range of operating conditions. The simulations showed that the kinematic behaviour of polymeric gears is substantially different from those predicted by the classical metal gear theory. Extensions to the path of contact occur at the beginning and end of the meshing cycle. These are caused by large tooth deflections experienced by polymer gear teeth, as a result of much lower values of stiffness compared to metallic gears. The premature contact (occurring at the beginning of the meshing cycle) is hypothesized to be a factor in pitch line tooth fractures, whereas the extended contact is thought to be a factor in the extreme wear as seen in experiments. Furthermore, the increase in the path of contact also affects the induced bending and contact stresses. Simulated values are compared against those predicted by the international gear standard BS ISO 6336 and are shown to be substantially different. This is particularly for the case for bending stresses, where analytically derived values are independent of contact stiffness. The extreme tooth bending and the differences between analytical and numerical stresses observed in all the simulations suggest that any future polymeric gear-rating standard must account for the effects of load sharing (as a result of tooth deflection) and friction (particularly in dry-running applications).

IJERT-Modeling and Prediction of Wear for Gears in Plastic Materials and Their Composites

International Journal of Engineering Research and Technology (IJERT), 2020

https://www.ijert.org/modeling-and-prediction-of-wear-for-gears-in-plastic-materials-and-their-composites https://www.ijert.org/research/modeling-and-prediction-of-wear-for-gears-in-plastic-materials-and-their-composites-IJERTV9IS070048.pdf This work deals with the modeling and prediction of the wear of plastic gears and their composites. The literature shows that the worn shape of gear teeth for gears in plastic materials and their composites differs from that of their metal gear counterparts. This makes existing models of wear prediction in metallic gears unsuitable for gears made of plastic materials and their composites. Two models based on Archard's law, namely the adapted Flodin model and a new model with an exponential coefficient of wear, are developed in this study. Simulations on acetal gears were implemented using models developed with Matlab code and the numerical results obtained are presented and discussed. The results of the two wear models effectively give the worn shape of the profiles in accordance with t h a t o b t a i n e d b y t h e e x p e r i m e n t a l t e s t s o f D ü z c ü k o ğ l u [ 1 1 ]. The new wear model compared to the Flodin model presents a simplicity in determining its exponential wear coefficient λ. The exponential wear coefficient λ is more stable face the variations of the operating p a r a m e t e r s t h a n t h e w e a r c o e f f i c i e n t k o f t h e F l o d i n m o d e l. Using the results of experimental tests carried out on acetal gears by K. Mao [9], a validation method is proposed and shows a good agreement between the experimental results and those of our new model.

Modeling and Prediction of Wear for Gears in Plastic Materials and Their Composites

International Journal of Engineering Research and, 2020

This work deals with the modeling and prediction of the wear of plastic gears and their composites. The literature shows that the worn shape of gear teeth for gears in plastic materials and their composites differs from that of their metal gear counterparts. This makes existing models of wear prediction in metallic gears unsuitable for gears made of plastic materials and their composites. Two models based on Archard's law, namely the adapted Flodin model and a new model with an exponential coefficient of wear, are developed in this study. Simulations on acetal gears were implemented using models developed with Matlab code and the numerical results obtained are presented and discussed. The results of the two wear models effectively give the worn shape of the profiles in accordance with t h a t o b t a i n e d b y t h e e x p e r i m e n t a l t e s t s o f D ü z c ü k o ğ l u [ 1 1 ]. The new wear model compared to the Flodin model presents a simplicity in determining its exponential wear coefficient λ. The exponential wear coefficient λ is more stable face the variations of the operating p a r a m e t e r s t h a n t h e w e a r c o e f f i c i e n t k o f t h e F l o d i n m o d e l. Using the results of experimental tests carried out on acetal gears by K. Mao [9], a validation method is proposed and shows a good agreement between the experimental results and those of our new model.

On tribological design in gear tooth contacts

The correct tribological design will have a considerable effect on a gear's service life and efficiency. The purpose of this thesis is to clarify the impact of variation in the gear tooth flank tribological system on the gear contact load capacity -to increase the understanding of how surface topography and lubricant interact.