(For this week's Die Casting News, we'll republish the highlights of this technical paper by Dr. Giovanni Rampi Jodovit s.r.l. - Lonate Pozzolo - Italy. View the entire document here http://www.jodovit.com/doc/HTDC%20English%20.pdf)
The job in formulating release agent is mostly empirical and requires a lot of experience.
Die casting release agents are called in foundry world also lubricants because they must have also a very good lubricating power. Are commonly water based and applied at high dilution rates to use the great water evaporation heat to cool the moulds.
Everyone today knows that die casting release agents are water based. The active ingredients are emulsified (emulsified itself means emulsified in water). The practice of using water based products comes from a long time ago. Using solvent based products is very dangerous considering the temperature levels common in our field. Solvent based products are dangerous for the health, for the environment, and because of the risk of explosions. But another consideration led to the use of water based release agents: the very high evaporation heat of water is greatly helpful in cooling down the mould. The cooling effect was in the past the only way to control and reduce the mould temperature and is still important today when moulds temperature is commonly thermostatically controlled.
Products Commonly Used:
We can divide the products normally used by Release agents Formulators in five big families: Mineral oils, Ester oils, Siliconic oils, Waxes, and Surfactants. A release agent technician has only four tools. A generic knowledge of materials properties, his fantasy, intuition and experience. He can only extrapolate a behavior of a certain material at supposed working conditions. Our job is based on practical tests in production where we compare situations and performances and try to understand which are the focal points that make difference. We suppose a certain behavior and if it happens we believe to have been right, if not we exclude it, with the complication that results are often apparently contradictory.
Release Agent Application:
Die casting release agents are not used as supplied but are diluted with water, of course, at a ratio ranging from 1% up to 4%, mostly from 1% to 3%, of product as received and applied with automatic dispensers. Only few customers still apply it manually. Automatic dispensers are of three types. Based on vertical sliding with multiple nozzles that wash the mould; with vertical sliding again but with oriented nozzles to spray better where necessary to apply more lubricant; with multiple axes robots. First two are the most popular because they are less expensive than anthropomorphic robots. But dispensers with oriented nozzles or robot assisted are used on well thermoset moulds because they apply less release agent than the first one and do reduce less the mould over temperature.
Lubricant based on heavy mineral oils are of little interest now. Only few traditional commercial products survive but are less used day by day. Heavy oils with a very high thermal resistance were necessary long time ago when pieces were thick and their exotermicity high but today the moulding technology has reached a good level and we produce pieces with very narrow thickness with low exotermicity and with complicated shapes.
We said above that the job of release agent technician is empirical. The hope for the future is to know with sufficient precision the liquid metal flow so that we can see point by point what is the local temperature and heat exchange ratio to see the thermal stability required. It is also necessary to know the local pressure on mould walls to establish the resistance to the washing necessary for a specified geometry. Of course thermal resistance and flow resistance are not independent but must be considered as two faces of the same problem. We must know what happens in the very short time during the injection.
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