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España1. Injection speed
01. What is the injection speed
Usually, the injection speed we set refers to the speed at which the screw advances. But what really matters is the speed of the melt advancing in the cavity, which is related to the size of the cross-sectional area in the flow direction.
02. How to determine the injection speed
As a principle, the injection speed should be as fast as possible.
It is determined by the cooling rate of the melt and the viscosity of the melt: a melt with a fast cooling rate or a high viscosity uses a high injection rate.
Note: The speed of cooling depends on the properties of the material itself, the thickness of the wall, and the temperature of the mold.
03. The injection speed is too fast/too slow
Too fast injection speed: prone to focal spots, flash, internal air bubbles, or melt injection
Injection speed is too slow: prone to flow marks, weld lines, and causes a rough, dull surface
2. Turning pressure point
01. How to determine the transfer point
Generally speaking, the pressure transfer point refers to the switching point from injection to holding pressure when the product is pumped to 95% full under the condition of zero holding pressure. For thin-walled products (such as cable ties): generally hit 98% of the product
For unbalanced flow channels: generally, 70%-80%, depending on the specific situation. And it is recommended to use slow-fast-slow multistage injection.
02. The transfer pressure point is too high / too low
The transfer pressure point is too high: the product is insufficiently filled, the weld line, the depression, the size is too small
The turning pressure point is too low: flash, difficult demoulding, large size, etc.
3. Holding pressure
01. How to determine the holding pressure
The optimal packing pressure is generally the middle value of the minimum packing pressure and the maximum packing pressure.
Minimum holding pressure: On the basis of the accurate pressure transfer point, a certain holding pressure is given, and the holding pressure when the product just has insufficient mold filling
Maximum holding pressure: On the basis of the accurate pressure transfer point, a certain holding pressure is given, which is the holding pressure when the product has just appeared burrs.
(From the minimum and maximum packing pressure we can see the safe range of product process fluctuations)
02. Generally speaking:
PA holding pressure=50% injection pressure
POM holding pressure = 80% injection pressure;
100% injection pressure for products with high size requirements
PP/PE holding pressure=30-50% injection pressure
4. Holding time
01. How to determine the holding time
The dwell time is determined on the basis of gate condensation. Determined by weighing the product.
02. The pressure holding time is too long / too short
Holding time too long: Affects the cycle
The holding time is too short: insufficient weight, hollow inside the product, small size
Note: The holding pressure will affect the length of the holding time. The higher the holding pressure, the longer the holding time.
5. Screw speed
The goal of pre-plasticizing is to obtain a uniform and stable melt (that is, uniform plasticization, no cold material, no degradation, and no excess gas).
01. How to determine the screw speed
As a principle, the determination of the screw speed must make the pre-molding time of the screw, the sum of the suction time and the return time of the injection table slightly shorter than the cooling time.
02. The screw speed is too fast/too slow
The screw speed is too fast: uneven plasticization (causing cold product, insufficient mold filling and fracture, etc.), material decomposition (causing focal spot, chromatic aberration, fracture, etc.)
The screw speed is too slow: affecting the cycle
6. Cooling time
As a principle, the setting of the cooling time should be as short as possible, and the basic requirements are that the product does not deform, does not stick to the mold, and does not have too deep ejection marks.
And: screw speed:
PA<1.0m/s;
POM < 0.7 m/s;
PP/PE/PS < 1.3m/s;
ABS/PC/PMMA < 0.6m/s
