High Performance MIM Vacuum Sintering Furnace

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In order to meet the needs of the industry for the continuous development of technical requirements and related specifications, we must explore the growth space of MIM process equipment in terms of accuracy and efficiency.

Currently, limitations such as the mechanical and chemical properties and optical appearance of parts are mainly caused by the following aspects: 1) non-uniform shrinkage (geometric deformation) powder and raw material mixed unevenly; density fluctuations caused by injection or first debinding stage; Uneven temperature in the sintering furnace. 2) Chemical decomposition and discoloration: imprecise process gas management; redeposition of binders in the second debinding step; residual sintering furnace contamination.

In addition to these technical constraints, a highly competitive market environment shifts cost pressures to component manufacturers. Because of this, in order to push the MIM industry forward, higher-yielding, sophisticated production equipment and materials are crucial. In addition to high raw material procurement costs (such as: fine-grained metal powders, polymer binders, and ready-made injection materials), high-temperature sintering is one of the main cost drivers in the MIM process. The investment and operating costs of the debinding sintering furnace are the key to the competitiveness of MIM parts manufacturers.

1.MIM vacuum sintering furnace hot zone design and gas management system

The degassing process of the residual polymer binder occurred when the heating and average heat treatment temperature reached 600 °C. In order to effectively transport gaseous substances outside the hot zone, there needs to be a continuous and homogeneous purge flow at all points in the cabinet. The design of the airtight furnace (or muffle) can reduce the size of the vacuum sintering furnace and realize external heating. The main advantage of this design is that the furnace provides a high purity atmosphere and ensures a uniform flow of hot air across the part. However, it is not an easy task to install a cooling fan inside the furnace, which will result in a longer production cycle, and the furnace will also generate more investment, maintenance and energy costs.

2.MIM vacuum sintering furnace degreasing system

After careful removal of polymeric binder residues in the hot zone, continuous and effective treatment and filtration of the binder-laden process gas is required in order to avoid binder deposits on pipes, valves or pumps.

Protecting critical structural components through an effective binder collection system must be considered if uninterrupted production and low maintenance costs are to be maintained. Separation of gas flow and binder can be achieved in modern vacuum sintering furnaces. Efficient evacuation of the hot zone is achieved by a vacuum pump, which consists of a Roots pump supported by a mechanical pump. The high-temperature and high-velocity process gas carries the saturated evaporated polymer material and is drawn out through the exhaust pipe at the bottom of the vacuum furnace shell. When the air flow is turned by the influence of the cold pipe wall, it suddenly slows down and cools down, causing part of the gaseous binder to condense again instantly; in this way, up to 20% to 25% of the binder material has been deposited in the pipe, which will eventually lead to The pipe is clogged. To avoid manual maintenance, the necessary cleaning procedures are automated by means of electric extruders (pistons) that extrude the deposits out of the pipes. By different cooling and heating sequences, binder condensation and subsequent removal can be improved. The water-cooled support of the double-walled tubing improves condensation of the binder material, but also causes the condensate to freeze more quickly. Therefore, heating coils wrapped around the pipe must help re-soften the adhesive layer before the electric extruder operates.

After passing through the horizontal duct, about 75% of the binder contamination was still contained in the air stream. In order to protect the most important and valuable structural components from damage and to ensure smooth further cleaning procedures, a dedicated filter system is connected upstream (before the pump). Depending on the binder used and individual program parameters, it may be most effective to deviate from conventional filtration concepts. An easy-to-clean cartridge-style filtration system works that drastically reduces maintenance time. It features a four-stage dirt retention system: the first stage utilizes a large surface area to capture heavy particles, condensed volatile solids and liquids; the second and third stages filter progressively through wire mesh screens installed at specific locations Binder; the last stage is used to trap gaseous particulates that may have been missed in the previous stages. The modular system includes heating, which dissolves the trapped binder and collects it in a bucket that can be easily removed and cleaned.

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