First of all, metal powder injection molding is to uniformly mix solid powder and organic binder. After granulation, it is injected into the mold cavity by an injection molding machine to solidify and form, and then the formed blank is chemically or thermally decomposed. The binder is removed in the final product by sintering and densification.

The methods of degreasing in metal powder injection molding include thermal decomposition, solvent degreasing, catalytic degreasing, etc. Among them, the products produced after catalytic degreasing have high dimensional accuracy, and catalytic degreasing is used.

Taking polyoxymethylene (POM) binder as an example, the degreasing process is divided into three stages: pre-rinsing, degreasing and post-rinsing.

Pre-rinsing stage: Since the degreasing product of the metal powder injection molding green embryo will react with oxygen, the air in the furnace cavity needs to be diluted before degreasing, so that the internal oxygen content reaches a safe value. In the pre-flushing stage, the furnace cavity, flue and nitrogen pipes will be heated, and the fan in the furnace will be started at the same time to deliver nitrogen into the furnace.

Degreasing stage: refers to the process in which the binder (polyoxymethylene) in the raw embryo in the degreasing furnace is decomposed into formaldehyde at a set temperature. The furnace is in a heat preservation state, the nitric acid pump is started, and nitric acid is injected into the furnace. Under the acidic atmosphere, the decomposition reaction rate of polyoxymethylene is accelerated.

Post-rinsing stage: After the degreasing stage is over, nitrogen begins to fill the furnace cavity, and the formaldehyde and nitric acid produced in the furnace through the degreasing stage are discharged through the heating tube. Formaldehyde and nitric acid will be heated and burned in the tube, and only carbon dioxide, water vapor and nitrogen dioxide will be finally discharged to the outside world. These are gases that make up air and meet environmental protection requirements.

The degreasing rate of the metal powder injection molding green embryo after catalytic degreasing is as high as 90%, and it becomes a gray blank. The next stage is to enter the sintering furnace for sintering.