Balinit coating protects injection moulds against aggressors

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The tool and mould maker Siebenwurst and Mercedes-Benz rely on the Balinit Croma Plus coating from Oerlikon Balzers Coating for the processing of glass fibre reinforced plastics.

Injection moulding tools from Siebenwurst in Dietfurt, Bavaria, are used to injection mould the so-called load compartment recesses for the electric car EQS from Mercedes-Benz. Lightweight construction also plays a major role here, they say. Fibre-reinforced composites are among the preferred materials for making electric vehicles as light as possible, in order to ensure a satisfactory driving range later on. So-called organosheets, for example, in which a stable matrix of thermoplastic wraps glass, carbon or aramid fibres, play a role. They are stable enough to replace metal components and save weight at the same time. For the load compartment recess of the current Mercedes-Benz electric model EQS, it is a mix of polypropylene (PP) with 50 percent glass fibre that Siebenwurst had to deal with in terms of processing technology, as it goes on to say. The challenge was to protect the surface of the injection mould from the very abrasive glass fibres.

For the Stuttgart-based premium car manufacturer, however, the aforementioned loading space recess was not the first project with Siebenwurst. The Stuttgart OEM approached the Dietfurt-based company back in 2008. At that time, the project manager recommended a coating from Oerlikon Balzers to protect injection moulding tools from such heavily wearing types of plastic.

The positive experiences led to the fact that a product from Oerlikon Balzers also found its way into the specifications for the current project - Balinit Croma Plus. The protective coating, which shimmers like a rainbow, is applied via the PVD process (Physical Vapour Deposition). It is considered a top candidate when it comes to making injection moulds as wear-resistant as possible. The moulds for the polypropylene cargo troughs are now equipped with it and are in service at the Hamburg plant. There, the particularly resistant layer ensures very high shot numbers and correspondingly long maintenance intervals.

Balinit Croma Plus also causes the plastic melt to slide easily on the moulding surface of the injection mould. As a result, the plastic flows more freely into the mould, which makes it possible to reduce both the injection pressure and the holding pressure on the injection moulding machine in order to fill the cavity.

This reduces the stresses on the mould and the machine, as well as wear and energy requirements. In addition, the friction-minimising layer prevents deposits from accumulating on the mould surface over time. As a result, the areas of the injection mould that carry the melt are easier to clean, which also reduces the use of release agents.

According to Siebenwurst's experience, coatings are indispensable today for getting to grips with the many challenges posed by modern plastics. But it is not only the advantages of such coatings that are increasingly appreciated in this field of application. For the next project with Oerlikon Balzers, Siebenwurst will not only receive the performance-enhancing coating for an injection mould but also a hot runner system from the company's sister company Oerlikon Hrsflow.

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