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Introduction to blow moulding machines and their characteristics

Views: 8     Author: Site Editor     Publish Time: 2022-01-20      Origin: Site

Blow moulding, also known as hollow blow moulding, is a rapidly developing method of plastics processing. The thermoplastic resin is extruded or injected into a tubular plastic blank, which is placed in a counter-mould while hot (or heated to a soft state), and immediately after the mould is closed, compressed air is introduced into the blank, causing the plastic blank to expand and cling to the inner wall of the mould, which is then cooled and demoulded, resulting in a variety of hollow products. The manufacturing process of blown film is very similar in principle to hollow products blow moulding, but it does not use moulds, from the perspective of the classification of plastics processing technology, the molding process of blown film is usually included in extrusion. The blow moulding process began to be used during the Second World War for the production of low density polyethylene vials. the late 1950s saw the birth of high density polyethylene and the development of blow moulding machines, which led to the widespread use of blow moulding technology. Hollow containers are available in volumes of up to several thousand litres and some production has been computer controlled. Suitable for blow moulding plastics are polyethylene, polyvinyl chloride, polypropylene, polyester, etc., the resulting hollow containers are widely used as industrial packaging containers.

Blow moulding machines can be divided into three categories: extrusion blow moulding machines, injection blow moulding machines and special structure blow moulding machines. Stretch blow moulding machines can fall into each of these categories. The extrusion blow moulding machine is a combination of extruder, blow moulding machine and mould closing mechanism, consisting of extruder and blank die head, blowing device, mould closing mechanism, blank thickness control system and transmission mechanism. The die head is one of the most important parts in determining the quality of blow moulded products, and usually has a side feed die head and a central feed die head. For blow moulding of large products, the cylinder type blank die head is mostly used. The minimum volume of the accumulator is 1kg and the maximum volume is 240kg, the thickness control device is used to control the wall thickness of the blanks, the control points are up to 128 points, generally 20-30 points. Extrusion blow moulding machines can produce hollow products with a volume range of 2.5ml to 104l.

The injection blow moulding machine is a combination of injection moulding machine and blow moulding mechanism, including plasticising mechanism, hydraulic system, control electrical and other mechanical parts. Common types are three-station injection blow moulding machines and four-station injection blow moulding machines. Three-station machines have three stations for preforming, blowing and demoulding, each station being 120° apart. The four-station machine has one more preforming station, each 90° apart. In addition, there are duplex injection blow moulding machines with stations 180° apart. The injection blow moulding machine produces precise plastic containers without secondary processing, but the moulds are more expensive.

Special construction blow moulding machines are blow moulding machines that use sheets, molten material and cold blanks as blanks to blow hollow bodies with special shapes and uses. Due to the different shapes and requirements of the products produced, the structure of the blow moulding machine also varies.

Features of blow moulding machines.

1. The screw centre shaft and cylinder are made of 38CrMoAlA chromium, molybdenum and aluminium alloy treated with nitrogen, which has the advantages of high thickness, corrosion resistance and wear resistance.

2. The die head is chrome plated and the screw mandrel structure makes the discharge more even and smooth for a better finish of blown film. The complex structure of the film blowing machine makes the output gas more uniform. The lifting unit adopts a square frame platform structure and the height of the lifting frame can be adjusted automatically according to different technical requirements.

3. The unloading equipment adopts tare rotating equipment and centre rotating equipment and adopts torque motor to adjust the film smoothness, which is easy to operate.

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