Details of Injection Molding for Office Chairs
The details of injection molding for office chairs are mainly reflected in core structure and process, temperature control, pressure control, speed control, other parameters, and mold-related aspects.
Core Structure and Process: The seating system of office negotiation chairs adopts injection molding technology, using high-quality PP (polypropylene) plastic to form an integrated structure of the chair back and seat in one piece. This process enables the design of complex curved surfaces, ensures uniform wall thickness, and avoids local stress concentration.
Temperature Control: For PP material, the front section of the barrel is set at 180 - 220โ, the middle section at 190 - 230โ, and the rear section at 170 - 200โ. In actual production of ordinary household PP seats, the front section is set at 200โ, the middle section at 210โ, and the rear section at 185โ. The nozzle temperature is 5 - 10โ lower than that of the front section of the barrel, typically set at 190 - 195โ. The mold temperature is generally controlled between 30 - 60โ. Maintaining it between 30 - 50โ can reduce internal stress and improve crystallinity, with appropriate increases for thicker walls or complex reinforcing ribs.
Pressure Control: For small PP plastic seats (1 - 3kg), the injection pressure is 60 - 100MPa; for medium-sized seats (3 - 8kg), it is 80 - 130MPa; and for large seats (over 8kg), it is 100 - 160MPa. The holding pressure is usually 30% - 60% of the injection pressure, with small seats at 20 - 50MPa, medium-sized seats at 30 - 70MPa, and large seats at 40 - 90MPa.
Speed Control: For PP plastic seats with simple structures and uniform wall thickness, the injection speed is 30 - 60cmยณ/s; for seats with complex structures, thin walls, or fine parts, it is 15 - 30cmยณ/s.
Other Parameters: When processing backrest accessories for desk and chair sets, the back pressure is set at 0.5 - 2MPa, and the screw speed is controlled between 30 - 60rpm.
Mold-Related: The mold structure is designed based on the product's 3D drawings, and optimized using CAE mold flow analysis software. Ordinary desk and chair molds often use pre-hardened steels such as P20 and 718H, while high-demand or long-life molds use heat-treated steels like H13 and S136, or stainless steel. Sufficient draft angles should be designed for the side walls and reinforcing ribs of desk and chair sets. For large thin-walled seat molds, considerations should be given to the gate location and cooling sequence. Molds should be stored closed and sprayed with anti-rust oil, with residual material in the cavity cleaned before mold closing, and relevant information clearly marked on the mold frame exterior.
