Annealing treatment of plastic products

Time：2023-03-11 11:51:53 / Popularity： / Source：

Annealing treatment of plastic products

Due to uneven plasticization of plastic in barrel or inconsistent cooling rate in cavity, uneven crystallization, orientation and shrinkage often occur, resulting in internal stress in product, especially when producing thick-walled products and products with inserts. Existence of internal stress will reduce mechanical properties of product during storage and use, silver streaks will appear on the surface of product, even deformation and cracking will occur. In actual production, the most effective way to solve this problem is to anneal product.

Annealing method is to place product in a constant temperature heating liquid medium (such as hot water, mineral oil, glycerin, ethylene glycol, liquid paraffin, etc.) or a hot air circulation box for a period of time, and then slowly cool to room temperature. Use heat during annealing to accelerate relaxation of macromolecules in plastics, thereby eliminating or reducing residual stress after product molding.
Annealing temperature is generally controlled at 10-20℃ above temperature of product, or 10-20℃ below thermal deformation temperature of plastic. If temperature is too high, product will warp and deform, and if temperature is too low, annealing effect will not be achieved.
Annealing time depends on factors such as type of plastic, temperature of heating medium, shape and thickness of product, and precision requirements of product, so as to eliminate internal stress of product. Products after annealing treatment should be cooled slowly to room temperature, if cooling is too fast, internal stress may be regenerated. For thin-walled products, cooling rate is 50~60℃/h; for thick-walled products, cooling rate is about 10℃/h or less.
Annealing conditions of different plastic products are shown in Table 1.
Table 1 Annealing treatment conditions of different plastic products

Plastic name	Handling media	Product thickness/mm	Processing temperature/℃	Processing time/min
ABS	water or air	—	60~75	16~20
P.S.	water or air	≤6	60~70	30~60
P.S.	water or air	>6	70~77	120~360
PMMA	Air	—	75	16~20
POM	Air	2.5	160	60
POM	Oil	2.5	160	30
PP	Air	≤3	150	30~60
PP	Air	4~6		60
HDPE	water	≤6	100	15~30
HDPE	water	>6		60
PC	oil or air	1	120~130	30~40
		3	120~130	180~360
		>6	130~140	620~960
PET	Nitrogen furnace	3	130~150	30~60
PBT	Nitrogen furnace	3	130~150	30~60
PA6	water	>6	100	25
PA66	Oil	3~6	130	20~30
PA66	Water: potassium acetate (1:1.25)	3~6	100	120~360
PA1010	water	6	100	120~360
PPO	oil or air	3~6	120~140	60~240

Not all plastic products need to be annealed. Generally, plastics used have relatively rigid molecular chains, thick product walls, metal inserts, wide operating temperature ranges, high dimensional accuracy requirements, large internal stress and are not easy to self-eliminate products that need to be annealed. For products with relatively flexible molecular chains and low glass transition temperatures (such as polyoxymethylene and chlorinated polyether plastics), although there is internal stress, internal stress can slowly disappear by itself. If temperature requirement for product is not high, heat treatment may not be required.

What should I do if hydraulic vane pump of injection molding machine encounters a failure?

Fault	Reason	Troubleshooting
A. No oil discharged	1. Rotation direction is wrong (forward and anticlockwise)	Immediately stop and correct rotation direction of motor.
	2. Pump does not rotate	Check whether motor power supply is powered on, and check whether coupling or key is damaged.
	3. Pump shaft is broken and rotor does not rotate	Repair pump, confirm whether motor rotation speed is too high and whether axis is aligned with center
	4. Suction pipe is blocked	Check suction line
	5. Suction filter is blocked	Clean suction filter
	6. Insufficient flow rate of fuel tank filter	Replace larger suction oil filter, at least 2.2 times flow rate of pump per minute
	7. Temperature of oil is too high	Replace specified oil viscosity (according to sample)
	8. Number of revolutions is not enough	Select motor rotation speed according to minimum rotation speed specified by pump (according to sample)
	9. Airtightness of suction pipe is not enough	Check suction line
	10. Tank filter above oil level	Add oil to reference point above oil level gauge
	11. Blades cannot slide out of rotor pockets	Repair pump
B. High noise	1. Suction pipe is too small	Suction vacuum at least 200 mmHg or less
	2. Suction filter is clogged	Clean suction filter
	3. Insufficient flow rate of fuel tank filter	Replace with a larger suction oil filter, at least 2.2 times flow rate of pump per minute
	4. Temperature of oil is too high	Replace specified oil viscosity (according to sample)
	5. Wrong suction pipe when using double pump	Correct piping
	6. Suction pipe sucks in air	Lock suction flange of pump, and check whether other suction pipes are locked
	7. Air is sucked into oil seal of pump shaft	Check if axis is concentric
	8. There are air bubbles in fuel tank	Is oil return pipeline configuration and length normal?
	9. Tank filter above oil level	Add oil to reference point above oil level gauge
	10. Blades cannot slide out of rotor pockets	Repair pump
	11. Coupling noise	Replace coupling and check whether shaft is concentric
	12. Fuel tank air filter is clogged or specification is too small	Clean air filter or replace filter with appropriate specifications
	13. Rotation speed is too high	Select motor rotation speed according to maximum rotation speed specified by pump (according to sample)
	14. Set pressure is too high	Check whether pressure gauge is set properly
	15. Pump bearing damage	Replace pump and check if shaft is concentric
	16. Cam ring wear	Abnormal wear is caused by cleanliness of oil being too dirty.
	17. Pump cover is not tightly tightened	Reassemble pump with a torque wrench
	18. Pump is severely worn (cam rings, rotors, diverter plates, vanes)	Oil cleanliness is too dirty, replace pump and hydraulic oil
C. Insufficient flow	1. No oil discharge	Refer to method A
	2. Suction vacuum is too large, causing cavitation due to suction of air	Check suction filter screen, try to use hose or straight pipe
	3. Rotor and manifold wear	Repair pump
	4. Pump cover is not tightly tightened	Reassemble pump with a torque wrench
	5. Oil temperature is too low	Change oil and install cooler
D sealing ring oil leakage	Oil leakage at sealing ring	Replace sealing ring

Gud Mould Industry Co., Ltd