Aluminum Die Casting Demolding Solution

Process Issues

The aluminum die casting process involves heating aluminum alloy to a molten liquid state, injecting the aluminum liquid into the cavity under high pressure and cooling it. After the mold forms, the cavity is opened, and the aluminum alloy casting is ejected.

Before aluminum casting, the cavity is already in a high-temperature state, approximately 380°C. The robotic arm blows away dust and sprays water-based release agent. The release agent rapidly vaporizes upon heating, leaving only a trace amount of high-temperature resistant silicone oil evenly attached to the cavity surface as the demolding medium.

The retention time of aluminum die casting workpieces in the mold cavity is related to the workpiece size. Larger workpiece volumes require longer cooling times, thus higher temperature resistance requirements for the release agent. Therefore, the key to release agents lies in their high-temperature resistance. With advancements in aluminum die casting equipment technology, thousands-ton die casting machines have become widespread, mold holding times are continuously extended, and requirements for high-temperature resistant release agents are more stringent. Hence, demolding silicone oil must have excellent spreadability and not coke during high-temperature demolding. The demolded product surface is smooth and flawless, with good post-processing properties.

Common demolding issues: Difficult and unsmooth demolding, carbon buildup on molds polluting the mold, residual release agent on demolded products affecting post-processing (such as painting, labeling, etc.).

Solutions

The BD-257 high-temperature resistant silicone oil, developed and manufactured by our company, is a product specifically designed for aluminum die casting demolding in large-tonnage die casting machines. Ablation resistance tested up to 380°C. Even if degraded to trace amounts of silica powder above this temperature, it does not affect product appearance and is easily removed by blow nozzles.

Before use, BD-257 high-temperature resistant silicone oil must first be emulsified into an emulsion using a surfactant. Commercial release agents are generally emulsions containing 15% active ingredients. Dilute with water 100~150 times before use to prepare the working solution for robotic arm spraying.

For die casting machines of different tonnages and workpiece model complexities, the release agent dosage must be precisely controlled through experiments. Excessive dosage leads to redundant high-temperature performance, increasing costs and affecting demolding effects. Another approach to avoid redundant high-temperature performance is to blend appropriate amounts of low-end release agents such as synthetic esters and oxidized polyethylene wax after forming the emulsion, based on application experience. The addition of low-end release agents generally does not exceed 30%.

The comprehensive cost-performance ratio of release agents is crucial. Selecting the right high-temperature resistant silicone oil solves the problem (including mold cleaning) at a certain cost, regardless of the release agent price. Users must pay special attention to this point.

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Article Author: Hangzhou Baode New Materials Technology Co., Ltd. Application Technology Department — Ni Zonghao