The gas injection moulding technology (GIT) has been around for some time now for the production of hollow articles. It involves the use of gas pressure to form the cavity. More recently, the water injection moulding process (WIT) has also made its mark for such applications. Röchling Automotive (Mannheim / Germany; www.roechling-automotive.de) has now come up with a completely new method for the series production of hollow articles, namely the "projectile injection technology" (PIT).

With this technique, the cavity is produced by injecting a bullet-like projectile. It makes far lower demands on the material than the previous processes, say the developers. Although raw materials optimised for GIT and WIT also produced higher-quality results, it was possible for most applications to also use standard materials with differing levels of reinforcement.

Unlike the WIT process, no second component is needed. Consequently, says Röchling, branching can be achieved more economically and more reliably with PIT than with the two-component fluid injection techniques. Branches, fast-release couplings, clips and holders are moulded with the pipe in the same shot. This is the same as with the gas and one-component water injection technologies.

"The importance of PIT, however, lies not just in the purely application-specific selection of materials, but above all in the superior properties of the PIT parts," says Dr. Peter Barth, the member of the Röchling Board responsible for development and marketing. "Mention should be made in particular of the minimal wall thickness and ultra-low weight. This, in turn, results in significant material savings."

The projectile is able to produce a constant internal diameter over the entire length with minimal wall thickness, resulting in a weight saving in the order of 50 % compared with GIT parts. Because of the smaller external diameter, the build volume requirement is also smaller. Due to the nature of the process, the possibility of material accumulations can be excluded, and this leads to another significant advantage of the process, namely less warping and thus high dimensional stability. In addition, the low wall thickness results in shorter cycle times than with GIT. If water is used as the pressure fluid for the projectile, cycle times can be cut even further, claims Röchling.

Yet another advantage compared with WIT is that there are less voids and pores with PIT. Under the scanning electron microscope, the interior surface is said to look really good, with the matrix completely homogeneous and the glass fibres very well covered. There is no danger of the fibres being washed out.

The process is being used for the first time on a production scale for a cooling water duct for a member of the BMW 3 series, proving its ruggedness and suitability for tough practical applications. One advantage in application is that, because the inside pipe diameter remains absolutely constant, there is less pressure loss. It is basically now only governed by the length of the duct and its side exits.

For the Society of Plastic Engineers Central Europe (SPE, Hannover / Germany; www.spe-ce.org), the development was worthy of this year´s "Grand Innovation Award", which was presented at the 10th Automotive Awards ceremony – see Plasteurope.com Web of 07.08.2006. This is the highest distinction awarded by SPE Central Europe.