A few special resin require high temperature injection and widely use for medical plastic parts, such as PEI, PSU and PEEK etc.
Characteristics and applications of PEI materials
PEI is an amorphous high-performance polymer with excellent heat resistance, good chemical resistance, inherent flame retardancy and excellent dimensional stability.
Based on the characteristics of PEI, the material is often used in the medical, aircraft, automobile, tableware/public catering industry, telecommunications, molded interconnect device (MID), electrical and lighting industries. The following focuses on the application process and mold analysis of PEI materials in the propulsion rack parts of the stapler.
Since the material is a high-temperature material, all corresponding mold features must also be processed according to the manufacturing method of high-temperature molds. The corresponding manufacturing methods of high-temperature molds have the following precautions:
It takes time to consider the insulation design when designing the mold;
The mold needs to consider the thermal expansion coefficient of the mold base, mold core and other sliding parts;
The selection of mold steel and the selection of materials for various parts need to be of high temperature resistant type;
When designing the mold, each sliding movable part shall be marked with reasonable tolerance and matching clearance;
Pay attention to the design of runners and entry points;
The waterway layout should be reasonable to maintain the consistency of the mold temperature.
High temperature mold injection process characteristics
This material is a high temperature material, and some of it contains glass fiber, and its viscosity is high, and the fluidity is slightly poor. The corresponding molding process characteristics need to pay attention to the following matters:
A special high-temperature mold special machine equipped with a special screw is required;
Mold temperature controllers, water pipes, machine heat insulation boards, etc. need to use special types;
The moisture content of the material has a great influence on the appearance, so it is necessary to ensure the adequacy of drying;
Control the heat in the hot runner and control the crystallinity of the molding material;
Combine mold flow analysis and scientific mold testing to determine a reasonable injection speed (speed affects viscosity and shear heat.
A case of PEI material mold opening on stapler propulsion rack parts
The push rack part is a part in the ultrasonic knife of the medical stapler. The part has certain requirements on the strength of the product, and the product is long and not easy to fill. The deformation and straightness of the product are required.
SEASKY TOOLING adopts the production method of high temperature mold, adding heat preservation measures during mold design, combining mold flow analysis and the physical property of the material, using two plate mold and gate on the end of medical plastic part.
Guide column guide sleeve, middle toss, counter and other parts, all adopt high-temperature mold special models. When designing the mold, reasonable tolerances and matching gaps are set for the sliding parts based on the consideration of thermal expansion coefficient to ensure the high volume production of the mold. The mold production adopts special double alloy screw injection molding machine, and the best production process is obtained through the combination of scientific mold test method and mold flow analysis.
Problems that are easy to occur when PEI advances rack production
Material viscosity is high, the screw of injection molding machine should be cleaned reasonably before each production, otherwise the product is easy to produce black spots.
After production, synchronization needs a timely and reasonable way to clean the screw;
The product is prone to discoloration in the production process, so it is necessary to control the mold temperature, material temperature and injection speed in the process;
During production, the thickness of meat is easy to produce shrinkage marks. It is necessary to confirm the stable molding process through scientific mold trial method in the early stage, and monitor the molding process for each batch.