Abstract
Abstract Regardless of colouration for functional or aesthetic purposes, technical polymer parts, like gears, require consistent properties. However, there is a lack of research into the effect of colourants on the tribomechanical properties of gears. Therefore, the effects of two pigments, titanium dioxide (white) and chrome antimony titanium oxide (yellow), and three delivery methods, masterbatch, liquid colour and direct compounding, on part morphology, dimensions, tribological and mechanical performance of injection-moulded polyoxymethylene (POM) spur gears are investigated in this paper. The white pigment accelerates the crystallisation of POM, causing fine and highly-crystalline morphological structures and smaller dimensions. However, the yellow pigment decelerates crystallisation, resulting in a coarser morphology with highly crystalline core material and bigger parts. Furthermore, the delivery method affects only the tribomechanical properties. Using a masterbatch decreases loads at break and increases deflection at break, since the carrier material acts as an impact modifier and a weak spot. The liquid colour decreases wear due to lubricating properties, whereas the pure pigments increases abrasion, especially in combination with a coarse microstructure. However, the effects of carrier systems and changes in morphology are always superimposed. Considering the performance and tolerance of technical components, colourants have to be carefully selected to ensure beneficial properties.
Highlights
Due to their high freedom of design, low weight, good dry running capability, beneficial wear behaviour and cost-efficient production, injection-moulded polyoxymethylene (POM) gears have a wide array of applications, from household appliances to actuating drives in the automotive sector
The effects of two pigments, titanium dioxide and chrome antimony titanium oxide, and three delivery methods, masterbatch, liquid colour and direct compounding, on part morphology, dimensions, tribological and mechanical performance of injection-moulded polyoxymethylene (POM) spur gears are investigated in this paper
Compared to the base material, there was little to no significant difference in the crystallisation speed between the delivery methods masterbatch, liquid colouring and direct compounding for the TiO2 pigments
Summary
Due to their high freedom of design, low weight, good dry running capability, beneficial wear behaviour and cost-efficient production, injection-moulded polyoxymethylene (POM) gears have a wide array of applications, from household appliances to actuating drives in the automotive sector. Pigments can be added to the base material to produce pre-coloured granulate. This is suitable for large batches of material and frequently used colours such as black and white [4]. Liquid colours can be used instead of masterbatches, allowing for a more flexible mixing of pigments and a wider range of colours without keeping too much stock [3]. Masterbatches and liquid colours are more expensive than pre-died material, but they are more flexible [4]. Liquid colours require additional dosing equipment, which is not necessary for masterbatches, since those can be mixed into the base material [3]. A commercially often applied variety of titanium mixed phase pigments is chrome antimony titanium oxide rutile pigment, known
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