Plastic barrel hollow blow can be divided into two categories: Extrusion blow molding and injection blow molding. The main difference between the two lies in the preparation of the blank, and then the blow molding process is the same. On the basis of these two methods to carry out: Extrusion stretch blow molding (abbreviated as extrusion blow), injection stretch blow molding (short note – pull – blow) and multilayer reflection. Injection blow molding (note – blowing) plastic bottle adopts the injection molding the plastic bottom slab, the parison while hot moved to blow mold, blow molding hollow products. Note – blowing hollow container with no flash, good dimensional stability, excellent quality of the bottle mouth and the thread, the parison thickness can be pre conditioning, good luster of products, save raw materials. However, injection blow molding is not suitable for large and complex consumption of the container, but also because of the use of injection and blow molding two deputy mold, so the equipment investment is relatively large. Note – blowing hollow container outside shaped cylinder single small bottle body mainly, it can use a variety of polyvinyl chloride, polyethylene, polypropylene and polyethylene, polyester, polyamide resin consumption. Mainly used in medicine, food, cosmetics packaging for blow molding hollow plastic are polyethylene, polyvinyl chloride, polypropylene, polystyrene, linear polyester, polycarbonate, polyamide, cellulose acetate and poly acetal resin etc.. High density polyethylene in the first place. It is widely used in food, chemical industry and the disposal of liquid packaging. High molecular weight polyethylene is suitable for manufacturing large fuel tanks and barrels and other white spirit. PVC because of its good transparency and tightness, so in terms of packaging of cosmetics and washing agent get widely used. With the development of non-toxic PVC resin and additives, and stretch blow molding technology development, PVC container in the food packaging quantity rapid increase, and have begun to beer and the other containing carbon dioxide gas beverage packaging. Linear polyester material is a new type of information in the field of hollow blow molding in recent years. Advantages due to its products with a shiny appearance and excellent transparency, high mechanical strength and container goods keep good, burning of waste disposal, polluting the environment, so in terms of packaging bottle carry out very quickly, especially in the aspect of pressure resistant plastic food containers is the most widely used. Due to the modification of the resin and the improvement of the processing technology, the application of PP has increased year by year.
Main raw materials and typical formula
- Polyethylene resin with L ~ 6 melt index.
- Polypropylene, polypropylene, 4, 2.
- Polystyrene resin with general purpose or anti punching type for polystyrene.
- Rigid PVC transparent bottle formula.
Main equipment and characteristics of plastic bucket
- The extruder and the die are basically the same as the common extrusion blowing method.
- Installation of parison disposal by extruding a tubular billet, after the installation of the stop cut, at the bottom of the fusion and neck processing, made of tube shaped bottom of the parison.
- The heating installation of the heating installation of the heating and heating installation of the heating installation is provided with an oven, a heating sleeve, a heating channel, etc., and the heating mode can be heated by electric heating or infrared heating.
- nstallation of the mandrel and the tensile tensile tensile fixture two.
- Drawing mandrel Drawing mandrel is inserted from the upper part of the type blank, in under the action of hydraulic withstand parison bottom, stop the longitudinal tensile, and the mandrel air vent into the compressed air blown, stop the radial tensile. Most stretch forming is used in this kind of tension installation.
- Tension clamp The tension clamp is clamped from the outside to the two ends of the tubular shaped blank, and the longitudinal tension is stopped under the action of hydraulic pressure, and then the radial tension is stopped. At the neck and at the bottom, there is a need to trim the fly edge.
- Squeeze – pull – blow molding machine Abroad there are a variety of types and specifications of the squeeze – pull – blow molding machine, there is no domestic special equipment
Plastic barrel production process
Injection blow molding is made up of two processes of injection molding and blow molding products, and the injection molding process is the key to the whole process of consumption.
Process control of injection molding
Injection temperature Injection temperature and the types and characteristics of raw materials, the type of injection molding machine and the thickness of the products, etc.. For crystalline resin, such as polyethylene, polypropylene, injection temperature should be higher than its melting point. For amorphous polymers, such as polystyrene and polyvinyl chloride, the injection temperature is higher than the viscosity of the polymer. The resin with a low number of melt batches is higher than that of the melt index. The use of plunger type injection molding machine than the screw type injection molding machine processing temperature is higher. The high injection temperature of the thin wall blank is higher than that of the thick wall slab. The injection temperature of the ordinary polystyrene is 140 degrees Celsius to 240 degrees Celsius, the polyethylene is 150 to 280 degrees Celsius, the polypropylene is 205 to 285 degrees Celsius, and the polyvinyl chloride is 160 to 190 degrees Celsius. Injection mold temperature is 40 C to 80 C.
Injection pressure The melt index of the common resin is low, the shape of the blank wall is thin, the pressure of the injection is higher, and the lower the pressure is relatively low. Plunger type injection molding machine than the screw type injection molding machine high pressure. Under the condition of ensuring the quality of production, as far as possible, the use of lower injection pressure. The injection pressure of ordinary polystyrene is 58.8 ~ 107.9MPa, the PE is 58.8 ~ 98.06MPa, the polypropylene is 54.9 ~ 98.06MPa, and the polyvinyl chloride is 78.4 ~ 127.5MPa.
Process control of blow molding and extrusion blow molding process is the same
Main equipment and characteristics
Injection molding machine With ordinary injection molding machine structure are basically the same, but lower injection pressure, screw length diameter ratio of the smaller, tightening than also shoulds not be too big.
mould Including injection mold and blow mold. The information of the injection mould and the common injection mold is the same as the processing request, but the core must be hollow so that the air can be compressed into the air. Blow mould and extrusion blow molding die is the same.
Stripping installation And extrusion blow molding is different, blow molding process is completed, open blow mold, will be with molded products to the core die to be sent to the installation, from the template will be separated from the mold and core modules.
Injection blow plastic bottles there is no national standards and ministerial standards, product specifications can refer to polyethylene blow moulding barrel specification and make necessary corrections. But in the same kind of raw material, the performance of the injection blowing hollow container is better than that of the extrusion blow hollow container.
A large hollow container generally refers to the volume of various plastic barrels in more than 50L of body, tank, storage tank, tank and other large hollow products. The main material of the raw material is polyethylene resin, and the molding process is extrusion blow molding method and rotary molding method.
Extrusion blow molding of large containers is the same as the plastic bucket, only a slight difference in raw materials and equipment.
Main raw material request Consumption of plastic barrels of ordinary low density polyethylene resin or high, low density polyethylene resin mixture mainly, and the consumption of large containers, high density polyethylene and high molecular weight polyethylene resin.
Main equipment and characteristics The consumption of large container extrusion blow molding machine and installation and equipment of the consumption of plastic barrels of the same, but should be in the extrusion machine barrel and the head is additionally arranged between the stocker. Because the large size of the product is also very large, if the extruder is slow to extrusion, the shape of the slab will be a serious cause of the weight of the vertical extension phenomenon, the formation of the vertical wall thickness of the product is not uniform. At the same time, because of long extrusion time, so that the type of billet due to cooling and warm crossing is too low, it will affect the quality of blow molding. Added stocker after installation, extruding machine, the molten material continuous to squeeze into the reservoir feeder, when storage material reaches a certain amount, namely pressure feeding installation fast material extrusion, average thickness, temperature appropriate parison. Thus additional stocker can not only reduce the parison vertical extension, adhere to the parison temperature, can use smaller extruder products of large consumption.
Plastic barrel product standard
Extrusion blow molding large hollow containers at present there is no country, the Department of standards, can refer to GB 13508 a 92 polyethylene blow molding barrels standard for the necessary amendments. PETP soft drink bottles to perform QB1868 a 93 standard.
Extrusion stretch blow molding (abbreviated as extrusion blow) Plastic bottle is first by extrusion method tubular preforms made of resin, and the bottom of the parison formation of the bottom of the fusion, and the parison processing to the ideal tensile temperature of plastic. The mechanical force of the internal (drawing mandrel) or external (tensile fixture) of the longitudinal tensile and at the same time or later by compressed air blown radial stretching of the hollow products. After biaxial stretching, the plastic is re oriented, so the impact toughness, low temperature strength, transparency, surface gloss, rigidity and barrier properties are obviously improved and improved. In addition, the thickness of the wall of the product after stretching can be reduced, which can save the material and reduce the cost. Currently used for production push pull blowing plastic hollow container is mainly PVC and PP, products mainly to small, thin-walled bottle for packaging of food, beverages, cosmetics, daily chemical products and so on.
Squeeze – blowing is divided into one – step and two – step two. One step process of making, drawing, blow molding in one device for continuous, also known as hot billet method. Two – step process in the production of the time, location and equipment, and heating, stretching, blow molding separately, also known as cold billet method.
Main raw materials and typical formula The requirements for polypropylene resin and the formulation of the PVC container are all the same as that of the extrusion blow molded containers.
Consumption technology Squeeze – pull – blow method in the extrusion and blow molding process control, and extrusion blow method is the same. The following focus on the process of drawing control.
Stretching temperature The control of suitable stretching temperature is the key to stop the biaxial tension, otherwise it will not be the purpose of the re orientation of plastic molecules. For the non crystalline polyvinyl chloride, such as the use of one step, the billet can be extruded from 190 to 200 degrees Celsius to 90 degrees Celsius to be cooled to 100 degrees Celsius to degrees Celsius, stop stretching and blow. At this time than the glass temperature of 10 degrees Celsius to 20 degrees Celsius, is the most ideal drawing temperature. For the crystallization of polypropylene, such as the use of one step, the shape of the billet to the aid of effective cooling.
From extrusion of 210 DEG C to 230 DEG C, cooled quickly to 90 DEG C ~ 105 DEG C between the crystallization temperature, restrain the spherulites, and then heated to between the glass transition temperature and the melting temperature of 150 DEG C to 160 DEG C to stop the biaxial tensile. Whether polyvinyl chloride or polypropylene, if the use of the two step, the need for pre made to re heating of the preform to the respective tensile temperature, and then stop stretching and blow.
draft ratio In addition to the conditions of tensile temperature, the molecular orientation state of the biaxial tension product is determined by the stretching ratio, and the drawing rate is determined to improve the performance of the product. The drawing ratio is the product of the ratio of the tension to the blowing ratio, the ratio of the length to the length of the billet, and the ratio of the length to the length of the billet. Blowing ratio is the ratio of the maximum diameter of the product and the diameter of the blank, which is the radial tensile rate. Low drawing ratio is too low to play the role of molecular reorientation and improve the performance of products. The drawing ratio is too high, it will cause the material damage and make the processing condition is not easy to control. The drawing ratio of ordinary polyvinyl chloride was 4 ~ 6, and the polypropylene was 6 ~ 10.