Drying of inorganic powders with vacuum and refrigeration technology

For the manufacture of tools with additive manufacturing (3D printing), very dry metal powder is required. To achieve the required degree of dryness, the powder is dried with a combined vacuum and refrigeration process. The process facilitates effective, even drying at low temperatures. With the aid of a protective atmosphere comprising inert gas, the metal powder can be shielded against the introduction of moisture or reaction with the ambient air.

Vacuum drying process improves fluctuating metal powder qualities of powder manufacturers

By means of the vacuum process, all inorganic powder materials, including metal powders such as aluminium, titanium, and tool steel alloys can be dried. The process involves the evaporation (sublimation) of the water adhering to the metal powder at low temperatures and pressures. During the vacuum drying process, a vacuum and uniformly low temperature must be produced in all of the metal powder to be dried. This is the only way to achieve workpieces of constantly high quality.

Metal powder drying in hermetically sealed system

In vacuum drying, a vacuum pump sucks the moist air out of the drying tank.

With the aid of a cooling unit, the metal powder in the drying tank is cooled to a temperature that is low enough for drying. It is continuously stirred and dried until the required level of moisture has been achieved. For the drying process to be effective, both the air pressure and temperature in the system must be continuously regulated. Modern vacuum driers are equipped with extensive sensors and programs for fully automated process step regulation.

From the powder drier to the storage tank, the metal powder passes through a system that is hermetically sealed from the ambient atmosphere. This is done to prevent it from absorbing moisture from the ambient air. High-performance metal powder driers dry the powder to a residual moisture level of only a few ppm (parts per million). Despite its high level of effectiveness, the vacuum drying process saves a significant amount of time.

Argon generates a protective atmosphere for safe storage

When the dried metal powder is filled for storage, argon can be used to produce a protective atmosphere. Argon is heavier than air and lies directly on the dried powder, preventing it from reacting with the ambient air or absorbing moisture. Argon is also an inert gas and does not react with the metal powder. To prevent metal oxidation, argon is also used in additive manufacturing processes.

With high-performance vacuum driers, metal powder can be dried without any negative effects on its material properties. The vacuum driers improve powder flowability. They also reduce the number of air inclusions in finished workpieces, which enables higher material densities. Vacuum drying also saves time and requires shorter cycle times.

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