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The production of packaging containers do not worry about a text, read hollow blow molding technology

Number of visits: Date:Jul 30,2017

Hollow blow tube is placed in the extrusion or injection molding mold will be obtained, in the tube pass into the compressed air blowing, so close to the cavity wall, the cooling mould to obtain the forming method of hollow products. This molding method can produce bottles, pots, buckets and other packaging containers, daily necessities and children's toys and so on.
I. blow molding material
The plastics used for blow molding are polyethylene, polyvinyl chloride, polypropylene, polystyrene, linear polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin. The consumption of HDPE occupies the first place, and is widely used in food, chemical industry and packaging of liquid. High molecular weight polyethylene is suitable for manufacturing large fuel tanks and barrels and other white spirit. PVC is widely used in cosmetics and detergent packaging because of its better transparency and tightness. With the development of non-toxic PVC resin and additives, as well as the development of stretch blow molding technology, the amount of PVC containers in food packaging is increasing rapidly, and has been used for beer and other drinks containing carbon dioxide gas packaging. Linear polyester material is a new type of material in the field of hollow blow molding in recent years. Due to the mechanical strength and the container products have a glossy appearance, excellent transparency, high goods in good preservation, the advantages of waste incineration without polluting the environment, so in the packaging bottle has developed rapidly, especially in the use of pressure plastic food container is the most widely. Because of the modification of resin and processing technology, the use of polypropylene is increasing year by year.
Two. Classification and characteristics of process
Blow molding technology
1, according to the parison forming method different classification: extrusion blow molding: the production method is simple, high yield, low precision, more applications. Injection blow molding: high precision, good quality, high price, suitable for large quantities of products.
2, according to the molding process different classification:
Ordinary blow molding
Stretch blow molding: products are tensile, high strength, good tightness. Extrusion stretch blow molding (for short, extrusion, pull, blow). Injection stretch blow molding (referred to as injection pull blow).
3, according to the number of pipe blank classification:
Single blow molding
Multi layer blow molding: comprehensive performance, complex production, suitable for packing high demand product packaging.
Three, influencing factors
1 blowing pressure: blow molding, compressed air has two functions, one is to expand the tube and die cavity wall, forming the shape required; two is cooling.  According to the plastic varieties and parison temperature difference, the air pressure is not the same, generally controlled at 0.2-0.7 MPa, the most appropriate is to make the product in shape, pattern and display clear pressure. For low viscosity and easy deformation, lower values should be taken; higher viscosity and higher modulus plastic; larger volume and thin-walled products should use higher pressure; small volume and thick wall products use lower pressure.
2, the inflation rate: in order to shorten the blowing time, in order to obtain a product of uniform thickness and good surface, the inflation rate (the volume of air through the unit of time) to be as large as possible, but should not be too large, otherwise it will bring bad effects to the products: one is the cause of vacuum in the air inlet. The parison within this part of the depression, and when the parison completely blown, invagination can form a diaphragm plate; followed by the parison die part may be fast air break, resulting in waste. Therefore, it is necessary to increase the caliber of the blowpipe or to reduce the charging speed properly.
3, blow ratio: usually the product size and parison size ratio is called blow up ratio.  When the size and weight of the parison are fixed, the larger the size of the product, the greater the expansion ratio of the parison. Depending on the variety and nature of plastics, the shape and size of the product and the size of the parison, the ratio of swell to swell should be determined. The blowing ratio is usually controlled at 2 or 4 times.
4, mold moderate cooling time: in order to ensure product quality, mold temperature should be uniform distribution, mold temperature is generally maintained at 20-50 degrees. Mold temperature is too low, will make the extension of the plastic at the mouth of the mouth to reduce, not easy to blow up, and make the product in this part of thickening, while making the molding difficult, the product contour and pattern are not clear. Mould temperature is too high, cooling time is prolonged, production cycle is longer. The product is deformed and enlarged. The mold temperature depends on the variety of the plastic. When the glass temperature of the plastic is higher, higher mould temperature can be adopted; on the contrary, the die temperature can be reduced as much as possible. Generally, as the wall thickness increases, the cooling time is prolonged. Sometimes, in addition to cooling the mold, the product can be internally cooled, that is, through the product into a variety of cooling media (such as liquid nitrogen, carbon dioxide, etc.) for direct cooling.
5, molding cycle: blow molding cycle includes extrusion parison, interception billet, mold, blowing, cooling, bleeding, opening, take out the product (subsequent dressing, matching, packaging, other plans) and other processes.
Four, product features and Applications
Blow molding technology
LDPE: food packaging containers
HDPE: Commodity containers
Ultra high molecular weight PE: large container, melting pot
PVC: mineral water, detergent bottle
PP: thin walled bottles
PET: beverage bottle
Polycarbonate bottles can be used under high temperature filling and packaging of goods, but if the polycarbonate bottles used for containing carbonated beverage with good barrier properties need (the need to prevent escape of carbon dioxide in the drink) or edible oil (to prevent oxygen entering the bottle, so as to avoid the oxidation of edible oil rancidity)

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