SURFACE MODIFICATION | SCRATCH AND WEAR
Right: Witcom is working to produce PTFE-free versions of all of its lubricated compounds
ever, lower shrinkage and a reduced crystallisation rate compared to PA66 make for a glossy, smooth- er, more uniform, and easier-to-clean surface. In addition, the smooth surface minimises friction noise and wear. G7V also benefits from reduced moisture absorption and comparable stiffness and strength in a dry and conditioned state.
Surface replication The company says the delayed freezing behaviour of Grivory G7V means it reproduces the mould surface very well without extending the cycle time. Another advantage of the aliphatic polyamide is its minimal shrinkage. This allows for the precise production of components, while the risk of ending up with a wavy surface (‘orange peel’) is significant- ly reduced. Even the basic grade, Grivory G7V-5H (GF 50), can produce low-distortion parts with a high-quality surface and an average roughness depth (Rz) of less than 1 micron. Special X-types reduce distortion even further. Grivory G7V was developed for high-gloss component design and straightforward processing by injection moulding methods. The material is said to be easy to process due to its high flow and wide processing window. A good surface finish is achieved at melt temperatures of 270°C and above in combination with normal mould temperatures between 100°C and 120°C. Due to the low melt and mould temperatures, injection moulders can save energy and reduce costs. The company says that Grivory G7V can be used in a wide variety of applications. The material is particularly well-suited for structural components in automotive interiors, such as air vents, indicator and gearstick levers, and handles, for example. Grivory G7V is just as suitable for functional components in mechanical engineering. Potential end products can also be found in the food and medical industries, where a crack and pore-free surface is particularly important to minimise the risk of pollution and, at worst, cross-contamination. Witcom Engineering Plastics is a major supplier of speciality engineering compounds, including products with solid internal lubrication. “The main market driver for these materials remains weight reduction and the characteristics that can be achieved in mechanical, chemical and electrical properties resulting from the use of additives,” says Ronald Pet, Global Business Development Man- ager. “There is still a focus on traditional materials and additives but due to environmental issues we are also seeing an increasing demand to move towards the use of more ‘eco-friendly’ additives. For our materials, growth is based on industrial
26 COMPOUNDING WORLD | February 2022
applications in different industries, for example, industrial robotics, e-mobility, medical and domes- tic appliances, and agricultural and industrial machinery.” Pet says new developments in surface modifica-
tion are still being driven by the well-known advantages for the use of plastics in technical applications, however, the importance of recycled materials and additives, and sustainability in general, is increasing. For example, the forthcom- ing EU (and UK) approach on reducing PFOA/PFAS in plastics is likely to have a big impact on the way lubricated materials will be formulated in the future. This could result in a ban on use of PTFE as an additive in the most extreme cases. There could also be temporary issues regarding availability of certain materials and additives.
Targeting alternatives
Witcom develops compounds to customer specifications, but its main focus for lubricated materials is to develop non-PTFE filled materials for current and future applications. “Applications for these materials are in different industries,” says Pet. “These include bushings and guiding strips for mechanical applications, parts and bushings in e-automotive, bushings and housings in water treatment systems, and parts and bushings for food industry machinery. All of these applications are driven by the need to reduce weight and the removal of external lubrication. We are currently involved in studies to replace PTFE in lubricated wear compounds, while maintaining a low coeffi- cient of friction and good wear characteristics. One of the applications is a housing in a dosing system, revolving at a medium velocity.” Witcom says it aims to be able to offer PTFE-free solutions for all its compounds. “We are also focusing on helping customers to operate as sustainably as possible,” adds Pet. “For example,
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IMAGE: WITCOM
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