Part Two ( 16-30 )
What is the injection pressure of injection molding machine?
Injection pressure P（ kg / cm2 ） = [ л / 4 × ( D12-D22 ) × P × 2 ] / ( л / 4 × d2 )
What is the plasticizing capacity of injection molding machine?
Plasticizing capacity W ( g / sec ) = 2.5 × ( d / 2.54 ) 2 × ( h / 2.54 ) × N × S × 1000 / 3600 / 2h = screw front tooth depth (cm) S = raw material density
What is system pressure? What’s the difference with injection pressure?
System pressure ( kg / cm2 ) = the highest working pressure set in the hydraulic circuit. The injection pressure refers to the actual pressure of the injection molding machine. The two are not equal.
Requirements of hydraulic oil for injection molding machine:
(1) Appropriate viscosity and good viscosity performance
(2) Good lubricity and rust resistance
(3) Good chemical stability, not easy to gasify into colloid
(4) Good foaming
(5) Low corrosion to machine parts and sealing devices
(6) Low ignition point (flash point) and freezing point requirements
The influence of hydraulic oil viscosity on injection molding machine?
When the working environment temperature of the system is high, oil with higher viscosity should be used. Conversely, use oil with lower viscosity.
The oil with higher viscosity should be used. Because at high pressure under the high working pressure, sealing is difficult and leakage Is the main problem. Conversely, when the working pressure is low, oil with a lower viscosity should be used. When the working speed of the working parts of the hydraulic system is high, the flow rate of the oil is also high. At this time, the pressure loss will also increase, and the leakage will be relatively reduced. You should use oil with lower viscosity. Conversely, use oil with higher viscosity according to the low moving speed of working parts.
21. Release setting
Correct release position = moving position of the aprons + screw offside distance.
The importance of setting the release position
If the setting of the release position is too large, it will cause the return material to absorb oxygen, oxidize the rubber material and generate bubbles. If the position is set too small, the pressure in the barrel is high. The shear force is so high that the rubber will be decomposed and the nozzle will flood. So the position error cannot exceed 0.4 mm.
Setting of melt position
Melt position = product weight / ( maximum stroke / maximum melt amount )
The main advantages of gas-assisted injection ( GAM )
The core of thick material can be evacuated to make hollow pipe fittings, which can save materials and shorten the cycle time.
The use of gas in injection molding can evenly distribute the pressure. When the plastic cools and solidifies, the gas can compensate for the volume shrinkage of the plastic through expansion.
Reduce the internal stress of molded products, thereby improving the stability of the shape and eliminating deformation and warpage.
Why the outer diameter of the piston rod is small in the middle and large at both ends?
It’s caused by the overheated middle hole needle and the uneven shrinkage of product. The middle hole needle can be made of phosphor copper material with fast heat dissipation and the mold is exhausted in the middle of the product.
Cracking after spherical screen printing
Due to the stress on the surface of product, it causes cracking after screen printing. You can increase the mold temperature and reduce the stress. And annealing can be used to eliminate the stress.
The problem of fragility at the nozzle of the spectacle frame
The large injection pressure and holding pressure, and the residual internal stress at the nozzle make the product easily broken.
Solution: Try to reduce the injection pressure and holding pressure as much as possible, and increase the mold temperature appropriately.
The four pillars of the electrical enclosure are prone to bursting when screwing
Because of the weld line of column, the assembly column is prone to bursting. Solution: increase the exhaust of mold, appropriately increase the mold temperature and speed up the injection rate to reduce the weld line.
The deformation of product
It mainly results from the imbalance of heat shrinkage, or the internal stress of the product itself.
Bubbles appear in the transparent PC shell
Raw materials that are not dry enough, uneven thickness of the glue, poor exhaust of the mold, and easy decomposition of the raw materials may make the product bubbles.
Solution: Fully dry the raw materials, increase the mold exhaust, minimize the uneven thickness of the glue.