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Debugging of PC barrel molding process
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2021-07-06

-----------------Temperature setting-----------------

 

1) The temperature setting of plasticizing system is determined by the characteristics of raw materials and machines, and is also affected by the ambient temperature. The general rule of temperature setting is that the screw section temperature is slightly higher, the joint neck and die temperature is slightly lower, and the die temperature is slightly higher. The principle of this setting is: high screw temperature, good plasticization, high transparency of products, fast extrusion speed under the load of hydraulic motor, however, the billet temperature is high and soft, and the material from the screw enters the joint neck and die head for cooling to improve the hardness and drapability of the billet; Slightly higher die temperature is beneficial to the surface quality and transparency of products.

 

2) The temperature of die affects the flanging of tube blank. The temperature of the die is high, and the parison is easy to turn inward; The die temperature is low, and the parison is easy to turn out.

 

3)PC material is sensitive to temperature, and the change and fluctuation of temperature have great influence on the molding process. The plasticizing system requires high temperature control accuracy, and the surrounding environment temperature needs to be relatively stable. Fans in the working environment should avoid blowing to the die or near the die, so as not to affect the temperature stability of the die.

 

4) New materials. The temperature of the first 1~7 stages of screw is generally 250~260℃, the temperature of the fourth stage is 5~15℃ lower than that of other regions of screw, the temperature of the eighth ~ eleventh stage (die) is slightly lower than that of screw, and the temperature of the twelfth stage (die) is similar to that of screw.

 

5) New and old mixture. The temperature of screw section is generally 240~250℃

 

6) Fully recovered materials. The temperature of screw section is generally 230~240℃

 

-----------------Pressure setting-----------------

 

1) the maximum pressure of the main hydraulic system is 13.5MPa (corresponding to the set graduation: 999)

 

2) The twisting pressure is generally 10~13MPa. Keeping the screw at a high speed is beneficial to keep the oil temperature of the main hydraulic system constant and not overtemperature. If the screw speed is too slow, the screw temperature can be appropriately increased to reduce the load of screw rotation. Generally speaking, the extrusion pressure should be able to ensure that the extrusion action stops before the end of the expected time for mold opening.This is conducive to the stability of the working temperature and molding cycle of the extruder system.

 

3) The back pressure of stranded materials should be kept at an appropriate value, generally between 1 and 2 MPa. Back pressure is related to screw speed. When the position of back pressure valve remains fixed, the higher the screw speed (stranding pressure), the higher the back pressure. The back pressure is low, the screw load is small, and the twisting speed is fast, but the product may produce unstable bubbles; When the back pressure is high, the screw load is large and the extrusion speed is relatively slow.

 

4) The automatic injection pressure is generally 6~7MPa, and the automatic injection time is generally 5~8 seconds, which is executed in sequence from 1: 00 to 10: 00. The shooting speed is too fast, the transparency of the product is reduced, and the wall thickness is not good; The shooting speed is too slow, which affects the molding cycle, and the parison may sag seriously.

 

-----------------Wall thickness adjustment-----------------

 

SHOT ZIZE refers to the shot quantity, that is, the total mass shot at one time. Generally speaking, the mass of PC barrel is 750g, and the mass of head and tail flash is about 150~200g, so the total mass needed to make a barrel is about 900~950g. Therefore, when the running state of the machine is stable, the value of SHOT SIZE should be determined and kept relatively stable. After the total mass is fixed, the quality and thickness of bottles are related to the shape of wall thickness curve and graph thickness. If the total mass is constant and the wall thickness is reduced, the tube blank will be lengthened and the bottle quality will be reduced; Thickening the wall thickness will shorten the tube blank and increase the bottle quality. The wall thickness of bottle is a result of the comprehensive action of graph curve thickness, sagging stretch, length and inflation ratio of pipe blank, which is a comprehensive corresponding relationship.

 

The wall thickness of the first and second points of the graph will affect the flanging of the tube blank, and the thickness is large and there is a tendency to flanging outward; The thickness is small, and it tends to turn inward.

 

The thickness of the 27th ~ 30th point will affect the thickness of the bottle bottom, so it is necessary to maintain an appropriate thickness to offset the influence of the fluctuation of tube blank length.

 

The pressure of small hydraulic source in wall thickness control system is generally 6MPa

 

The GAIN TIMES is generally set to 6, which keeps the system sensitivity relatively high.

 

Adjustment of screw position: when setting the EMPTY position, attention should be paid to not shooting the hydraulic cylinder to the bottom, and a buffer of about 10mm should be reserved, and the proximity switch of the empty limit should be adjusted to ON. When the storage is FULL, the maximum stroke of the shooting hydraulic cylinder is 300mm, and generally speaking, the storage stroke of 250mm is enough.The position of the sensing block of the storage limit proximity switch should be adjusted to be slightly larger than the position required for production. The purpose of this is to prevent the inductive block from touching the storage limit proximity switch when the electronic ruler circuit fails, so that the storage limit becomes ON and the twisting can stop, thus effectively protecting the screw. Please refer to relevant specifications for setting of wall thickness controller.