From opening the sunroof in your car, pumping insulin in a medical device, aligning solar panels in a satellite to moving toy cars, plastic gears are widely used in small gearboxes. In many cases, plastic materials can provide a good alternative to steel because of its low weight, good damping properties and lower cost for serial production.
Many applications using plastic gears have a relatively small continuous torque, but must, at the same time, also be able to transfer a high static torque – for example, when the seat adjustment mechanism in a car runs against the block. Such gears can be designed according to their static strength. In gear applications for medicine or food industry, plastic gears are often not allowed to operate in lubricated conditions. In such cases, the wear of the tooth flank is the main criterion for failure.
The strength of plastic gears greatly depends on their temperature. Determining required material properties for the design of the gears takes a lot more time and effort than for steel gears, as the properties have to be measured at different temperatures.
In KISSsoft, ninety-seven plastics are available for calculation of cylindrical and crossed axis helical gears. The materials range from unreinforced POMs and PAs to high performance reinforced and internally lubricated materials. This range of plastics covers properties from VDI 2545 and VDI 2736 which are essential for the analysis of strength, wear and vibrations. KISSsoft enables the calculations according to VDI methods, as well as using contact analysis, “Pech” wear calculation and tooth root form optimization through FEM.
A progressive wear method is used in KISSsoft to calculate the flank wear if the wear coefficient kw of the corresponding material is known. The method is based on the contact analysis and uses an iterative process to simulate the actual wear. Wear is displayed either in 2D or in 3D and can provide a clear evaluation of the various modifications involved such as the effect of tip relief on wear behavior.
KISSsoft performs a service life calculation by comparing cumulated wear removal over service life with permissible wear. These wear properties are very helpful for designing dry running gears and, when combined with the KISSsoft calculation software, produce results
and service life values that are close to reality.
For more information: www.kisssoft.com