Filling Problems in Rubber Moulds?
In SIGMASOFT, the calculation of the scorch index is a common tool to professionally analyze the filling of the part.
For more than 10 years, our customers have been relying on the coupled calculation of polymer flow and heat flow not only in the rubber material, but also in the mould and between rubber material and mould. Using the exact predictions regarding the scorch index
--> See animation, our customers are able to virtually optimize not only the mould but also the corresponding process parameters.
The injection moulding process is not really straightforward. Why?
In the filling phase, high-temperature rubber material is injected into a hot mould.
Depending on the chosen process conditions (temperature and time), there may occur the first filling problems:
- Scorching of the rubber material
- Weld lines in the part
- Air entrapments that can burn the rubber material
- Filling defects that prevent the filling of the cavity
- Too high air pressure
- "Burner" in the part (Diesel-phenomenon)
- Not enough machine performance --> viscosity vs. required pressure!
In other words, a compromise between injection velocity, mould temperature, and mass temperature has always to be found. If the injection happens to quickly, too many air entrapments will develop facilitating the formation of burners. If the injection happens too slowly, the rubber will vulcanize and stick to the mould wall. If the rubber material is moved further into the cavity, e.g. by increasing the injection pressure, surface defects and/or mechanical failures may occur. As shown in the animation, the areas influenced by jetting are to be considered as critical. Here, the scorch index significantly rises and may lead to optical and mechanical defects. SIGMASOFT allows you to detect all those problems and effects beforehand giving you the opportunity to take appropriate actions.
SIGMAdata is another tool that provides early information on cross linking and incubation time.
Without any additional cost, the user can easily manipulate this database. You are able to enter the data yourself, allowing you to more precisely predict the consequences when changing one parameter.
That saves you real money! Using simulation not only reduces development costs but also any type of mould costs. That makes you by far more efficient and you can successfully stand your ground on the competitive market.
What is scorch?
"The premature scorching is described by the "scorch index" and is hence a direct measure for the processing security. If the scorch index exceeds a certain value, the filling is to be considered as critical or erroneous".
When starts the filling of a part?
"This phase starts directly after the mould closure. At this point in time, metal or polymer inserts are already inside the mould and are subject to thermal strain (heat up).
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