Views: 74 Author: Site Editor Publish Time: 2022-07-20 Origin: Site
The size of the screw diameter directly affects the size of the plasticizing capacity and the size of the theoretical injection volume.
L is the effective length of the threaded portion of the screw. Under the premise of a certain screw diameter, the larger the L/D, the longer the thread length, which directly affects the thermal history of the material in the screw and the ability to absorb energy; if the L/D is too small, it directly affects the melting of the material effect and melt quality; if L/D is too large, the transmission torque will increase and the energy consumption will increase.
Screw Barrel for Injection Moulding Machine
The length of L1 should ensure that the material has enough space for conveying, because too short L1 will lead to premature melting of the material, so it is difficult to ensure the conveying conditions of stable pressure, and it is difficult to ensure the plasticizing quality and plasticizing capacity of each section after the screw.
If h1 is deep, it can accommodate more materials, which improves the feeding amount and plasticizing capacity, but it will affect the plasticizing effect of materials and the shear strength of the screw root. Generally, h1≈(0.12~0.16)D.
The length of L3 contributes to the fluctuation of the melt in the screw groove, and has the effect of stabilizing the pressure, so that the material can be discharged from the head of the screw in a uniform amount. Generally, L3=(4~5)D.
The small h3 and the shallow screw groove improve the plasticizing effect of the plastic melt, which is conducive to the homogenization of the melt, but if the h3 is too small, the shear rate will be too high, and the shear heat will be too large, which will cause the degradation of the molecular chain, affect the melt quality; if h3 is too large, due to the enhanced backflow effect of screw back pressure during pre-plasticizing, the plasticizing ability will be reduced.
Its size affects the helix angle, thereby affecting the conveying efficiency of the screw groove, generally S≈D.
ε=h1/h3, that is, the ratio of the depth h1 of the screw groove in the feeding section to the depth h3 of the screw groove in the melting section. When ε is large, the shearing effect will be enhanced, but the plasticizing ability will be weakened.
A screw must first be able to produce products that meet the quality requirements. The so-called quality requirements mean that the products produced should meet the following requirements:
(1) It has various properties that meet the requirements. Have the required physical, chemical, mechanical and electrical properties.
(2) It has the required apparent quality. If it can meet the user's requirements for bubbles, crystal points, dyeing dispersion uniformity, etc.
(3) The plasticizing quality of the screw that meets the requirements.
Injection Moulding Screw Barrel Manufacturer
The so-called output refers to the output or extrusion volume through a given head under the premise of ensuring the quality of plasticization. As mentioned earlier, production is generally expressed in kilograms per hour or kilograms per revolution. A good screw should have high plasticizing capacity (production capacity).
The so-called unit consumption refers to the energy consumed per kilogram of plastic (rubber) extruded, generally expressed by N.
(1) The larger this value is, the more energy is required to plasticize the same weight of plastic, which means that the more heating power is consumed, and the more the mechanical work done by the motor enters the material in the form of shearing and frictional heat more. Vice versa.
(2) For a good screw, the unit consumption should be as low as possible on the premise of ensuring the plasticizing quality.
(1) The adaptability of the screw refers to the adaptability of the screw to process different plastics, match different heads and different products. Generally speaking, the stronger the adaptability, the lower the plasticizing efficiency is.
(2) Therefore, we always hope that a good screw should have both adaptability and high plasticizing efficiency.
A good screw must also be easy to manufacture and low cost.
In the pre-molding stage of the screw, when the screw rotates in the barrel to transport the material along the screw direction and back up to accumulate the material for the next injection, the screw will also slip. If the screw starts to slip during the pre-moulding stage, the axial movement of the screw stops while the screw continues to rotate. The main reasons for the slippage of the screw of the injection molding machine are: the feeding port has difficulty in pressing the material and the length of the barrel cannot form enough adhesion, then the screw slips.
There are two solutions to the screw slip of the injection molding machine:
The first method: add a small amount of material to start cleaning the end of the barrel, and check the melting temperature at the same time. Short residence time will cause the melting temperature to be lower than the set value of the barrel temperature.
The second method: pay attention to observe the molded products, if there are black spots, light streaks, or marble patterns, it means that the materials are not well mixed in the barrel.
During injection molding production, it is often encountered that the screw rotates but does not discharge the material, and normal production cannot be completed. Common reasons and solutions for the screw of the injection molding machine not to discharge:
(1) The feeding port of the barrel is blocked, and check whether there is a molten plastic block bonding there.
(2) The temperature control is inaccurate, and the rear end temperature of the barrel is too high. Adjust the temperature setting and check whether the cooling water circuit is blocked.
(3) The screw is covered with glue - the plastic wraps the screw and rotates together.
(4) Too much oil is added to the plastic, causing the screw to slip.
(5) Too much recycled material is added to the plastic.
(6) The wear of the screw and the barrel and the wear of the rubber ring may cause the screw of the injection molding machine not to discharge, causing the plastic leakage to not be conveyed to the front end of the barrel.
(7) If the plastic particles are too large, bridging phenomenon will occur, just crush the plastic again.
(8) If the newly replaced screw does not discharge, it may be that the design of the barrel and the screw feeding port is not appropriate. For the screw, the screw groove of the feeding section of the screw is too shallow, so that the screw cannot drive the plastic forward when it rotates, it is also possible that the amount of material conveyed is very small and the barrel is the design of the feeding port.
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