Nov.2023 30
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What you need to know about blow molding machines
Introduction
Blow molding machines have revolutionized plastic production, from extrusion to injection and stretch blow molding, with each method offering unique properties. Blow molding machines are essential for the manufacture of containers, packaging and industrial parts, highlighting technological advances in plastics processing and contributing to various industries around the world.
Details
What is a blow molding machine?
Blow molding machine, also known as hollow blow molding machine, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in a separate mold while it is hot (or heated to a softened state), and immediately after the mold is closed, compressed air is introduced into the parison so that The plastic parison is blown up and tightly attached to the inner wall of the mold, and various hollow products are obtained after cooling and demoulding. The manufacturing process of blown film is in principle very similar to the blow molding of hollow products, but does not use a mold. From the perspective of plastic processing technology classification, the molding process of blown film is usually included in the extrusion process. During World War II, the blow molding process was used to produce low-density polyethylene vials. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology was widely used. The volume of hollow containers can reach several thousand liters, and some production is already computer controlled. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The resulting hollow container is widely used as an industrial packaging container. According to the manufacturing method of the parison, blow molding can be divided into extrusion blow molding and injection blow molding, among which multi-layer blow molding and stretch blow molding are newly developed.


What is hollow blow molding machine? What types are there?

(1) Hollow blow molding Hollow blow molding is an important method of thermoplastic plastic molding. It is a plastic molding method that uses gas pressure to inflate the hot mold closed in the mold into a hollow product. Hollow blow molding is mainly used to produce plastic hollow packaging containers and industrial hollow parts.


(2) Hollow blow molding type
There are many types of hollow blow molding processes. According to the different molding processes of the parison, it can generally be divided into two categories: extrusion hollow blow molding and injection hollow blow molding. According to the different blow molding and stretching conditions, it can be divided into ordinary Blow molding, stretch blow molding and three-dimensional (3D) extrusion blow molding of hollow plastics; according to the product structure, it can be divided into two categories: single-layer blow molding and multi-layer blow molding.

(3) Characteristics of various types of hollow blow molding
① Extrusion hollow blow molding Extrusion hollow blow molding is to melt and plasticize thermoplastics, extrude the parison through the extruder head, and then place the parison in the blow mold and pass in compressed air (or Other media), blow the parison, and after cooling and shaping, the product can be obtained. Extrusion blow molding can be divided into continuous extrusion blow molding and intermittent extrusion blow molding according to its discharging method. The continuous extrusion hollow molding method refers to the extruder directly and continuously extruding parisons through the machine head. It is mainly used to produce hollow products with large output and small volume (no more than 8L capacity). The intermittent extrusion hollow molding method means that the extruder intermittently extrudes the parison directly or squeezes the molten material into a storage tank. When the molten material in the storage tank meets the needs, it is extruded through the die of the die The parison can be used to obtain large-capacity hollow products after blow molding, cooling and shaping.

②Injection hollow blow molding Injection hollow blow molding uses an injection machine to inject molten material into the mold to prepare a parison, and then puts the parison into the blow mold while it is hot, and introduces air to inflate the parison. Forming method. Injection blow molded products generally do not need to be trimmed, have less leftover materials, good parison wall thickness uniformity, and good dimensional accuracy of the product, especially bottle containers, with high bottle mouth accuracy and good surface finish of the product. However, when producing in small batches, the product cost is high, and it is not suitable to form products with too complex shapes and structures.

③ Stretch blow molding Stretch blow molding is to heat the prefabricated parison to an appropriate temperature below the melting point, place it in the blow mold, use a stretch rod to stretch it axially, and then blow it to stretch it transversely. Stretch forming method. Stretch blow molding can be divided into two process types: extrusion-stretch-blow molding and injection-stretch-blow molding according to the preparation method of the parison. Extrusion-stretch-blow molding is to first melt and plasticize the material through an extruder, and then extrude the parison, then heat the parison to the stretching temperature, and then perform axial stretch blow molding. Injection-stretch-blow molding uses an injection method to shape the parison, then heats the parison to the stretching temperature, and then performs axial stretch blow molding. The transparency, impact strength, surface hardness, rigidity, permeability barrier and solvent resistance of stretch blow molded products.


Advantages of hydraulic drive system of hollow blow molding machine
The hydraulic device used in the hollow blow molding machine is generally small in size, light in weight, and occupies a small area. However, compared with other transmission methods, the hydraulic device is more powerful under the same production conditions;

The operation is smooth, which is also due to the advantage of the hydraulic device's light weight. It has light weight, small inertia generated by operation, fast response, and can make timely action responses;

The hollow blow molding machine adopts a hydraulic drive system, which can improve the automation level of the equipment. Especially since the process of the hollow blow molding machine is relatively complex, the hydraulic drive system can also realize the processing actions in an orderly manner;

Compared with other transmission methods, the hydraulic drive system can better help the hollow blow molding machine achieve remote control and overload protection;

The hydraulic drive system is relatively simple to use and easy to operate. This is because the components of the hydraulic system are relatively standardized, systematic and universal, making it easier to operate;

Since the hydraulically driven medium usually has certain rust resistance and lubricity, generally speaking, the service life of the hydraulic drive system is relatively long;

The device of the hydraulic system is relatively flexible, and the components and accessories can be randomly arranged according to the actual production situation;

The special point that distinguishes it from other driving devices is that the heat generated by the hydraulic system is discharged along with the hydraulic oil, so there will be no system overheating caused by long-term operation.


Several important precautions for hollow blow molding machines

1. Blowing pressure of blow molding machine
In blow molding, compressed air has two functions. One is to expand the tube blank and close to the wall of the mold cavity to form the required shape; the other is to play a cooling role. Depending on the type of plastic and the temperature of the parison, the air pressure is also different. It is generally controlled between 0.2-0.7 MPa. The most suitable pressure is the pressure that can make the shape, pattern, etc. of the product clear after molding. For plastics with lower viscosity and easy deformation, use a lower value; for plastics with higher viscosity and modulus, use a higher value; for large-volume and thin-walled products, use higher pressure; for small-volume and thick-walled products, use lower pressure. 

2. Inflation speed of blow molding machine
In order to shorten the blowing time and help the product obtain a more uniform thickness and better surface, the inflation speed (volume of air flowing per unit time) should be as large as possible, but it should not be too large, otherwise it will cause problems to the product. Adverse effects: First, a vacuum will be created at the air inlet, causing this part of the parison to be indented. When the parison is completely inflated, the indented part will form a diaphragm; secondly, the parison in the die part may be The extremely fast air flow breaks off and causes waste products.
To this end, it is necessary to increase the diameter of the blow pipe or appropriately reduce the inflation speed.

3. Blowing ratio of blow molding machine
Usually the ratio of the size of the product to the size of the parison is called the blow-up ratio. When the size and weight of the parison are constant, the larger the size of the product, the greater the inflation ratio of the parison. The blowing ratio is determined according to the type and nature of the plastic, the shape and size of the product, and the size of the parison. Usually the inflation ratio is controlled at 2 or 4 times.

4. Blow molding machine mold temperature and cooling time
In order to ensure product quality, the temperature of the mold should be evenly distributed, and the mold temperature is generally maintained at 20-50°C. If the mold temperature is too low, the extensibility of the plastic at the clamp will be reduced, making it difficult to blow up, and the product will become thicker in this part. At the same time, it will be difficult to mold, and the outline and pattern of the product will not be clear. The mold temperature is too high, the cooling time is extended, and the production cycle is lengthened. The product will be deformed when released from the mold and shrinkage will increase.
The mold temperature depends on the type of plastic. When the glass transition temperature of the plastic is higher, a higher mold temperature can be used; otherwise, the mold temperature should be lowered as much as possible.
Usually as the wall thickness of the product increases, the cooling time increases. Sometimes in addition to cooling the mold, the molded product can also be internally cooled, that is, various cooling media (such as liquid nitrogen, carbon dioxide, etc.) are introduced into the product for direct cooling.

5. Blow molding machine molding cycle
The cycle of blow molding includes processes such as extruding the parison, cutting the parison, clamping the mold, blowing, cooling, deflating, cutting, and taking out the product (the subsequent trimming, matching, and packaging are additional).


How big is the bottle blowing machine?
Type 55/65/75/80/90/110/120


What size products can each model of the blow molding machine produce?
Model 55 can produce less than 1 liter, 65 can produce less than 5 liters, 75 can produce less than 10 liters, 80 can produce less than 12 liters, and 90 can produce less than 25 liters.

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