Injection molding machine barrel principle and technical requirements

The injection molding machine barrel is a core component of the machine. The following is a detailed introduction to the barrel:

1. Structure and Materials
The injection molding machine barrel is typically a cylindrical metal tube with a specific length and diameter. Its material needs to be able to withstand high temperatures and the friction of plastic particles, so it is generally made of high-strength, wear-resistant, and corrosion-resistant alloys. The barrel interior undergoes special treatment to enhance its wear and corrosion resistance, thereby extending its service life.

2. Working Principle
The barrel's primary function is to contain and heat the plastic raw material, molten it, for injection into the mold cavity during the injection molding process to form the desired product. The barrel is typically equipped with a heating device, such as a resistance heating coil or electromagnetic induction heating, which uniformly raises the temperature of the plastic within the barrel, ensuring that it is fully melted and maintains good flowability. The barrel also needs to withstand a certain amount of pressure, so its structural strength and stability are crucial.

3. Functional Features
Heating and Plasticizing: The barrel heats the plastic raw material to a molten state through the heating device, and the rotation and pushing action of the screw plasticizes and uniformly mixes the plastic. Pressure Transmission: During the injection molding process, the barrel must withstand pressure from the screw and the plastic melt to ensure smooth injection into the mold cavity.
Wear and Corrosion Resistance: The barrel interior undergoes special treatment to enhance its wear and corrosion resistance, thereby extending its service life and reducing maintenance costs.
Technical Requirements for Injection Molding Machine Barrels:
1. Material Selection
Wear Resistance: The barrel must possess excellent wear resistance to withstand the friction of plastic particles during screw rotation. High-strength, wear-resistant materials such as nitrided steel (such as 38CrMoAlA steel) are typically used. The nitrided layer can reach a hardness of HV950-1200, effectively improving the barrel's ability to resist material friction and extending its service life.
Strength and Toughness: The barrel must possess sufficient strength and toughness to withstand the high pressures of the injection molding process. The material's yield strength generally needs to be greater than 600 MPa and its tensile strength greater than 850 MPa to ensure it resists deformation and cracking under operating pressures (typically 100-250 MPa). II. Structural Design
Inner Diameter Dimensional Accuracy: The barrel inner diameter requires high dimensional accuracy, with a tolerance typically controlled within ±0.05mm to ensure uniform clearance between the screw and barrel. The typical clearance is 0.1-0.3mm, ensuring stable material plasticization and conveying.
Aspect Ratio (L/D): The aspect ratio is generally between 18 and 25, with a common value around 20. An appropriate aspect ratio promotes adequate material plasticization. A too small aspect ratio may result in inadequate plasticization, while a too large ratio may cause material degradation.
Compression Ratio: The compression ratio is typically between 24 and 36. For crystalline plastics, a higher compression ratio, such as 34, can be used to facilitate the removal of air from the material and improve plasticization quality.
III. Temperature Control System
Temperature Control Accuracy: Temperature control accuracy is required to within ±2°C. Using a PID control algorithm combined with temperature sensors such as thermocouples, we can precisely control the temperature of each barrel section to meet the processing temperature requirements of different plastics (e.g., polyethylene processing temperature is 160-220°C, polypropylene 200-300°C). Heating Zones: The barrel is generally divided into 35 heating zones, each with independently adjustable temperature. The temperature gradually increases from the hopper end to the nozzle end, with a typical heating rate of 510°C/min.

IV. Surface Treatment
Inner Surface Treatment: After nitriding, the inner surface should achieve a surface roughness Ra of 0.4-0.8μm to reduce material flow resistance and improve plasticizing efficiency.
External Surface Treatment: The outer surface can be painted with a film thickness of 0.1-0.3mm for corrosion protection and aesthetics.