Granular Thermosets pose a challenge in processing but are an ideal fit for the components which must remain dimensionally stable under demanding conditions in the long term. KraussMaffei has come up with APC plus machine function for thermosets which does away with the issues of high fiber content and batch fluctuations. Thereby, ruling out complications in shot weight consistency.
Brake pistons and components for oil pumps cannot escape the high stress. It is imperative that temperatures up to 400 degrees Celsius and corrosive media have no impact on their proper functioning.
Fiber-reinforced thermosets are suitable material for highly complex technical parts. However, they impose specific pre-requisites for processing. For example: processing must take place devoid of a check valve because of partial curing takes place in the screw. Moreover, Batch fluctuations are clearly visible as compared to thermoplastics while shot weight consistency is another challenge.
Seeing all this, KraussMaffei has further improved the proven APC (Adaptive Process Control) plus machine function and now offers it for thermosets as well. APC plus uniformly measures the viscosity of the melt, taking material properties such as the respective compression curve into account, and adjusts the change-over point and the holding pressure level in the current shot based on a predicted injection volume.
This is extremely essential for high filler content of up to 80 percent. Due to these facts as well as the low processing temperatures, the molding compounds are barely compressible compared to thermoplastics. Minimal deviations of the start of filling, which are not visible to the machine operators in the process, or of the residual melt cushion have an immediate impact on injected volumes. Without an automated correction option, one is powerless against this.
In contrast, APC plus keeps the volumetric filling of the cavity uniform and does so equally for free-flowing thermosets, BMC (Bulk Molding Compound) and liquid and solid silicones (LSR and HTV). For example, if the barrel temperature rises by two degrees Celsius in BMC processing, which can quickly happen with a drifting tempering unit or in the summer heat, and if the plastic becomes less viscous due to that, APC plus switches from to injecting to holding pressure at an earlier point in time. Furthermore, the holding pressure level is lowered. Both are done to prevent component overflow.