Blow molding

Blow molding, also known as hollow molding, is a manufacturing process for forming hollow plastic parts: it was initially used to form glass bottles. Generally speaking, there are three main ways of blow molding: extrusion blow molding, injection blow molding and injection stretch blow molding. The blow molding process begins with melting the plastic and forming a parison, or in the case of injection and injection stretch blow molding (ISB) preforms). The parison is a tubular plastic part with a hole at one end through which compressed air can pass. The utility model relates to a molding method for blowing and expanding the closed thermoplastic in a mold into hollow products by using gas pressure, which is used for manufacturing hollow products.

The blank is then clamped into the mold and air is blown into it. The air pressure is then pushed out of the plastic to match the mold. Once the plastic cools and hardens, the mold opens and the part is ejected.

Blow molding, also known as hollow molding, defines the manufacturing process of forming hollow plastic parts

catalogue

1 Abstract

2 Application

3. Typology

▪   Extrusion blow molding

▪   Injection blow molding

▪   Blow out molding of injection mould

4 advantages and disadvantages of blow molding

5 see

abstract

The principle of blow molding is the same as blow glass. The plastic particles are heated and melted to form a mold embryo, which is placed in a split die to make the mold embryo cling to the inner wall of the die, thus forming[ 1]

In addition to injection molding, extrusion molding, the third plastic processing method.

application

Widely used in toy industry, daily necessities industry, chemical industry, cosmetics industry, food industry and so on. The common blow molding products are: toy car, teapot, toolbox, wheel, mineral water bottle, lampshade, flowerpot, bucket, can, pipeline building materials, car conduit, hose, container, oil depot equipment, stadium seats, etc.

Typology

Extrusion blow molding

The screw rotates to make the plastic material fill the waiting room to full load. Through the screw and the use of external heater 6, the softened and melted plastic is extruded into a hollow tube while it is hot. The tube is clamped in a pre designed hollow mold, and the softened plastic is inflated to the inner wall of the mold by high-pressure air, Finally, the excess part of the bottle mouth is removed from the outside of the mold.

Injection blow molding

This part is very similar to the general injection molding, the hot hair embryo (uncooled) is made first, and then the primary embryo is blown into the shape of the inner wall of the mold through high-pressure hot air. The advantage of using preforms is that these can be injected and stored to produce different colors and sizes, which may be different in place where there will be blowing. The preform is stable and can be blown at high speed according to the demand.

Blow out molding of injection mould

This method is very similar to injection blow molding, the difference is that it will go through a process of pulling the embryo before blow molding. This process can get up to 10 containers fair, but not too close to tolerances.

Advantages and disadvantages of blow molding

Advantages: compared with injection molding, extrusion blow molding has the following advantages:

(1) The cost of blow molding machinery (especially blow molding mold) is low (when molding similar products, the cost of blow molding machinery is about 1 / 3-1 / 2 of that of injection machinery), and the production cost of products is also low.

(2) In blow molding, the parison is formed through the die under low pressure and inflated under low pressure (mostly 0.2-1.0mn). Therefore, the residual stress of the product is small, the resistance to various strains such as tension, impact, bending and environment is high, and the product has good service performance. In injection molding, the melt must pass through the mold runner and gate under high pressure (15-140ypa), which will lead to uneven stress distribution.

(3) The relative molecular weight of blow molding grade plastics (such as PE) is much higher than that of injection grade plastics. Therefore, blow molded products have high impact toughness and high resistance to environmental stress cracking, which are suitable for the production of containers or barrels for packaging or transporting detergents and chemical reagents.

(4) Because the blow mold is only composed of female mold, the wall thickness of the product can be changed by simply adjusting the die gap of the die head or extrusion conditions, which is very beneficial to the products that cannot accurately calculate the required wall thickness in advance. For injection molding, the cost of changing the wall thickness is much higher.

(5) Blow molding can produce products with small wall thickness, which cannot be produced by injection molding.

(6) Blow molding can produce complex, irregular and integral products. When injection molding is adopted, two or more products should be produced and then combined together by means of snap fit, solvent bonding or ultrasonic welding.

Disadvantages: the precision of blow molding products is generally not as high as that of injection molding products.