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Forming process debugging of square stacking bucket
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2021-05-26

Introduction to square barrel extrusion and blowing process

The machines that produce 20~30L packaging barrels are divided into storage type and continuous extrusion type according to the extrusion method. The blowing process is divided into up-blowing and down-blowing. Generally, the storage type machine chooses the down blow moulding method, and the continuous extrusion type machine is suitable for both blowing techniques.

Here we focus on the down-blowing device with storage material.

1.Sequence of action program
The sequence of actions of the blowing machine under the storage material is: Sub-mold closing → pre-clamping → supporting rod closing, downward blowing → injection → supporting material opening → fast mould clamping → slow mould clamping, low pressure blowing → mould connecting in place, high-pressure clamping, high pressure blowing → down Blow the upper punch cut → cycle blowing and venting → → secondary micro-opening → lower blowing needle micro-extraction → secondary micro-opening → sub-mould opening → rapid mould opening → slow mould opening, end of mould opening → lower blowdown, Product removal (Note: The program terminology is by the standard program language specifications of the relevant equipment manufacturers)
2.Parison wall thickness control
To ensure the uniform wall thickness of the product, the machine that produces 20L~30L packaging drums is usually equipped with a parison wall thickness control system. In the processing of such packaging barrels, the axial parison wall thickness control system is generally used. The radial wall thickness control system currently produces hollow blow moulding of such packaging barrels due to the complicated hardware structure, great technical difficulty, and high price. There are fewer matching on the forming machine, Therefore, the application is relatively small, but with the advancement of technology, the application will gradually increase. There are professional companies in China that provide supportive services for the radial wall thickness control system. Currently, commonly used machines are mainly equipped with axial wall thickness control systems.
3.Die, blowing needle, mould
The structure of the die is divided into expansion type and contraction type. Generally, the design and size of the dice are determined according to the geometric size of the product. For the 20~30L packaging barrel, the expansion type is better. According to the shape of the packaging barrel, the die and core can be processed into a heterogeneous structure, which can improve the uniformity of the product's wall thickness.
The primary considerations for the design of the blowing needle (blowing rod) are: the blowing diameter should be large enough to ensure the speed of blowing and deflation, which is beneficial to improve the surface quality of the product and shorten the moulding cycle; the cooling water flow is sufficient, and the blowing The needle is thoroughly cooled as a whole, which is conducive to the cooling and shaping of the barrel; the position of the blowing hand is easy to wear and become blunt. As far as possible, the incision position is designed into a replaceable incision ring form for easy replacement.

Packaging barrel moulds usually adopt a three-stage combined design. The mould is divided into barrel bottom, barrel body and barrel top and then assembled into a whole. The base or top of the bucket can be made into a sub-mould (driven by a hydraulic cylinder) that can be moved up and down according to needs to facilitate product demolding. Movable sub-moulds usually require good guidance and synchronization mechanisms to ensure reliable movement. The barrel thread inserts and cut-out rings are typically designed to be detachable and replaceable, which is convenient for adjustment and maintenance. The design of the die edge and the remaining material trough is essential for the strength of the product parting line and needs to be carefully considered. The exhaust design of the mould affects the surface quality of the product; the design and manufacture of the cooling system think the cooling needs of the geometric shape of the product and the thickness difference of different parts.

4.Debugging of moulding process parameters

The moulding process parameters of blow-moulded barrel-shaped products mainly include processing temperature, extrusion screw speed, hydraulic system pressure, blowing pressure, moulding period, etc.
1). Processing temperature. The processing temperature of bottle-shaped blow moulding products is mainly related to the characteristics of the plastic raw materials and equipment used. Under normal circumstances, medium and small barrel-shaped initial velocity products generally use HDPE or a blend of HDPE and LDPE with good fluidity. The processing temperature is between 130 and 180 ℃, and the processing temperature of a few materials may be higher than 180 ℃. The temperature setting is set from low to high from the feed port of the extruder to facilitate standard processing and moulding.
2).Rotation speed of extrusion screw. The screw diameter of the hydraulic system of the medium hollow moulding machine is smaller, and the screw speed can be relatively higher. The speed can be adjusted according to the characteristics of the product and the necessary screw. The screw speed is controlled by 10~70r/min.
3). Hydraulic system pressure. The pressure adjustment of the hydraulic system of the small and medium-sized hollow moulding machine is between 8 and 14 MPa. It is mainly adjusted according to the moulding characteristics of the blow-moulded product. When the moulded blow moulded product requirements are met, the pressure of the hydraulic system can be adjusted to a lower level. Working under pressure is conducive to energy saving and prolonging the service life of the hollow moulding machine.