(i) theoretical part:
1. Definition of blow molding: a plastic forming method that allows the hot blank in the mold to blow and swell into the hollow product by means of the gas pressure.
2. Blow molding machine structure: hydraulic system, composed of electromagnetic flow proportional valve, oil pump, seat, oil pipe and oil cylinder.
3. Electrical control system: it consists of programmable controller, time relay, ac contactor, electromagnetic proportional amplifier, power amplifier, power supply and frequency converter.
4. Thermostat system: it consists of cooling fan, heating coil, heat resistant hot-line, thermocouple and temperature control module.
5. Transmission system: consists of decelerator, belt, pulley and motor.
6. Air pressure system: it consists of air needle, air valve, air pipe and oil and water separator.
7. Cooling system: consists of water nozzle, water pump, water pipe, water distributor and cooling water tower.
8. Extrusion plasticizing system: it consists of gun barrel, screw rod, die head and material storage cylinder.
9. Properties of high-density polyethylene materials: oil resistance, lipid resistance, acid resistance, alkali resistance.High rigidity, strength, hardness, gloss and moisture resistance, poor transparency, thermal and oxygen aging, poor photoaging performance.
Relative density: 0.92-0.97
Water absorption: less than 0.01%
Molding shrinkage: 2.0-5.0%
Tensile strength: 221-237mpa
Rockwell hardness: 70
Thermal deformation temperature: 78
Embrittlement temperature: less than -140~-120 degrees Celsius
Blow molding temperature: 170-190 degrees Celsius
(ii) general parameter Settings:
Temperature: 170-200 degrees
Principle: the screw torsion distance should not be too large, the raw materials should be well plasticized, the mold blank has certain viscoelastic and strength, no obvious sagging phenomenon.
Pressure: 4-6 kg
Principle: the lower the pressure, the better, while ensuring that the equipment can work properly and produce qualified products.
Time: blowing air for 60-100s
Pressure protection: 0.1 second to 0.3 seconds
Exhaust: 10-20 seconds
(iii) actual operation:
1. Preparation before starting:
A. Is the mold in good condition and the fastening bolt locked?
B. Whether the cooling water is unimpeded and leaking.
C. Whether the pneumatic needle demoulding mechanism is smooth.
D. Whether the safety grating is intact and effective.
E. Whether labor protection products are worn, tools, electronic scale, positioning tooling is ready.
F. Check whether the color of the raw material is correct and whether there are any impurities before feeding.
2. Starting procedure: A. After the check temperature reaches the set value, keep the temperature constant for 1.5-2 hours to protect the screw.
B. Start the main oil pump, servo oil pump and idle for 2 minutes.
C. Start the glue melting motor at low speed (about 10) for 2 minutes, and start feeding after the screw is normal.
D. Gradually add a small amount of material. After the manual extrusion blank is normal, gradually increase the speed to the required speed of the process.(note: no one should be near or in front of the die before plastic extrusion)
E. After normal extrusion, start automatic production and enter normal production.Safety code: non-shift operator shall not press any switch without permission of anyone. If any abnormality is found, the operator shall immediately stop the machine and report it to the foreman or supervisor.
3. Stop procedure: A. Turn off the glue melting motor, main oil pump and servo oil pump within 1 hour in case of equipment failure or suspension of production.
B. Empty the feeding tube, storage tank, and turn off the motor within 8 hours after the shutdown, and reduce the temperature of each section by 20 degrees.
C. Stop for more than 8 hours, empty the feeding tube, storage tank, turn off the motor, temperature and cooling water.
D. Stop production for a long time, repeat step C, clean and rust proof all parts of the machine, cover the hopper, and turn off the power, water and gas sources.
E, encountered in the production of all of a sudden power failure, shall be immediately shut down the main oil pump, oil pump, plastic motor, the speed switch back to zero, to restore power, low speed start melt motor, to the normal extrusion.
4. Daily maintenance and maintenance of blow molding machine:
A. Check the oil temperature every day, and timely troubleshoot the cold water channel.
B. Add lubricating oil to all moving parts.
C. Check the travel switches and check whether the screws are loose.
D. Whether there is oil leakage in the tubing joint.
E. Clean all parts of the fuselage.