Injection molding machine screw length and the injection stroke, suddenly see together are two different things, in fact there is a subtle 'quality and quantity', the relationship between the ratio is a qualitative measure.
The length of the screw, general need not absolute length, and measured by the length of the relative to the diameter.
In this way, the length of the different diameter screw can be compared.
The length of the length to diameter ratio, with L/D.
Screw length, of course, is only part of thread.
More accurate method is to calculate to the centerline of the hopper, called effective length or effective length to diameter ratio.
A usually has three injection molding machine
screw is optional, called A, B, C, screw, small diameter, respectively, in (
Their length to diameter ratio of 22, 20, 18 or so.
Uneven temperature had plasticizing plastic melt, store at the top of the screw, ready for the next injection.
The ideal melting temperature is uniform.
But in general, this is not the case.
Due to the heating tile is not surrounded by a 360 ° cylinder, but there is a gap, so the ring to the uneven temperature.
Heat of heating by gaiden, coupled with poor melting heat transfer, so the radial temperature is not uniform.
Plasticizing, screw as the back.
Effective length so gradually reduced.
Feeding schedule (
Effective length, the greater the change, the greater the axial temperature also is uneven.
Familiar with extruder's friends know it is not backward extrusion screw.
Therefore, melt extrusion is no axial temperature difference.
If the melting temperature difference between 15 ° C, the appearance of the finished product, mechanical properties, such as average.
Multi-cavity mould can produce more product difference between cavity and cavity, and even a cavity, a cavity, flash, and the situation without rules.
To improve this situation, the injection stroke should be designed to B 4 times the diameter of the screw.
Effective change of length to diameter ratio is also so for 4.
In this case, the injection stroke is A 4 the diameter of the screw.
4 times, also is the 3 C screw diameter.
The radial temperature difference with A screw, the largest C screw is minimal.
Increase the length to diameter ratio increases the length to diameter ratio can reduce the axial temperature difference, the reason is that the screw long, plastic turn more laps to run to the end of the screw.
Mixing, temperature is more even.
Under the condition of the injection schedule unchanged, the longer the screw, 'injection stroke length of present screw down, so the axial temperature difference also fell.
And B screw if can have 22 length to diameter ratio, length to diameter ratio better than 20, of course.
In general, the injection of large travel or short screw length to diameter ratio of design, the injection weight is big, but uneven axial temperature molten, only suitable for single cavity products with not high demand.
By limiting the injection stroke and screw of big length to diameter ratio design, guarantee the quality of the multi-cavity products.
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