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What is a blow molding machine?

Blow molding machines are also called blow molding machines or blow molding machines. It is a manufacturing process automation machine for forming hollow plastic parts, most widely used in the manufacture of PET bottles.

How does a blow molding machine work?

From the working principle and mechanical process of the blow molding machine to explain:

The working principle of the blow molding machine

Generally speaking, there are three main blow molding manufacturing methods for blow molding machines: extrusion blow molding, injection blow molding and injection stretch blow molding.

The manufacturing method is to melt the plastic into a flowing state at the beginning, and then make the plastic into a small plastic preform with an empty middle basket and put it in the mold. After molding, the finished product can be obtained after cooling. The earliest hollow injection was used to make glass bottles.

The operation process of the blow molding machine

Blow molding machine is usually used to make plastic bottles, and it is also the most common injection method for hollow plastic workpieces.

The original parison was a tubular plastic piece with a hole at one end through which compressed air could pass. A molding method in which a thermoplastic plastic closed in a mold is blown into a hollow product by gas pressure, which is used to manufacture a hollow product. The parison is then clamped into a 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.

What machine is used for blow molding?

Blow molding machines can be used in the manufacture of various containers, etc. It uses a mold to blow out the required container shape, and the size of the container mouth will be smaller than the bottle body. Most of them are used in plastic containers, fresh milk containers, juice containers, food containers, medicine containers, cleaning supplies containers, industrial oil containers and tool boxes.

What are the types of blow molding machines?

Blow molding machine can be divided into hydraulic type, oil-electric hybrid type, all-electric type blow molding machine according to the power source; there are also special blow molding machines for certain materials, including: PE, PP, ABS, PETG, PCTG, EVOH, PA, PC, PU, PET, PVC, TPEE, NYLON…etc.

(All-electric type blow molding machine)

Generally speaking, it is distinguished by the forming method. Blow molding machines can be divided into two types, “Injection Blow Molding Machine” and “Pressure Blow Molding Machine”:

Injection stretch blow molding machine

Also known as “one-step/single stage bottle blowing machine“, it adopts the direct blow molding method. In this method, the molten preform is first shot out on the same machine, and then the blow molding is extended in the hollow mold. 

Since the molding of the preform and the stretch blow molding are carried out in the same machine, that’s why it’s called “one step”. Moreover, this method uses the heat retained by the preform to perform extended blowing when the preform has not yet cooled, so there is another way of calling it “hot preform method”.

Its processing flow is as follows:

  1. Dehumidification and drying of PET raw materials.
  2. The raw material is melted and injected into the preform mold through the injection screw.
  3. PET molten raw material and preform mold cooled to 120 degrees Celsius
  4. Put the hot embryo into the bottle mold for dual axis stretch blow molding

Scope of application

One step method: Because the one-stage molding method shoots the embryo and blows the bottle on the same machine, the tooth mouth of the embryo is covered in the tooth plate to adjust the temperature and blow the bottle, and the conveying of the embryo will not have contact and collision with other objects. The appearance of the bottle can be kept bright and complete without scratches. It is suitable for the production of blown containers with high texture and high unit price, such as various shapes of tooth-mouth bottles, cosmetic bottles, perfume bottles, etc. For example, if the screw is replaced, bottles of different materials such as PET, PP, HDPE, PC, and PEN can be produced.

limitation factor

One step method: Since the preform is not easy to be inspected before blowing, the operator must have both injection knowledge and blowing technology to effectively judge whether the defective bottle is caused by injection or blowing. There are many peripheral equipment required, including the injection peripheral and the blowing peripheral; the finished product is easily affected by the season, and a large storage space is required.

Extrusion blow molding machine

Also known as “two-step/stage blow molding machine“, it adopts the ‘extension blow molding method. In this method, the preform is first shot by an injection molding machine, and then the cooled preform is heated by a stretch blow molding machine, and then stretch blow molded in a hollow mold.

This method is called the “two-step method” because it goes through the secondary processing of the injection molding machine and the stretch blower. This method is to heat and extend the air after the preform is cooled, so it is also called “cold preform method”.

Its processing flow is as follows:

  1. Dehumidification and drying of PET raw materials.
  2. The molten raw material is injected into the preform mold by the injection machine.
  3. Wait for the PET molding preform to cool down to room temperature.
  4. After the preforms are sorted by the aligner, they are sent to the stretch blow molding machine for reheating and biaxial extension stretch blow molding.
    Note: “biaxial extension” means that the extension rod is used for longitudinal extension and the high-pressure air is used for transverse extension.

Scope of application

Two step method: During the reheating process, the heating position, heating range and heating power can be adjusted according to different PET preforms and different bottle shapes, so that the preforms can be stretched evenly and produce bottles with uniform thickness. Therefore, it is suitable for the production of high-capacity and lightweight bottle shapes, such as: low-cost products suitable for packaging drinking water bottles and carbonated beverage bottles. Preforms can be purchased or produced in-house. It can be connected to the filling machine for filling. The separation of injection and blowing is not affected by off-season and peak season, and embryos can be shot continuously in off-season to prepare for peak season demand.

limitation factor

Two step method: Injection and blowing are separated, and the preforms need to be stored, transported, and lined up before they can be blown on the blow molding machine. There will be scratches on the surface of the preforms, which are still faintly visible after blowing. When the preform is reheated, the temperature difference between the inside and outside is large, which limits the blowing range. Flat bottles, square bottles, handle bottles and other special shapes are not easy to blow; the tooth shape is limited by the alignment and blowing, and a complete bearing The bottle can only be blown by a flat surface, which is not suitable for blowing the bottle type that has a positioning relationship between the bottle cap and the bottle body.

What are the types of blow molding machines?

Differences in molding products

The difference between the two depends on the finished product of plastic molding. When the bottle mouth is smaller than the bottle body, it is blown with a hollow molding machine, and the bottle mouth larger than the bottle body is injection molded by an injection molding machine.

Compared with the finished product properties of injection molding, hollow molding has the advantages of higher strength, lighter weight, lower machine and mold cost, and multi-layer integrated molding, but the accuracy of the finished product is not as good as injection molding.

The following table lists the differences between them:

The following table lists the differences between them:

Compare:Blow moldingInjection Molding
Product strength:highmiddle
Product weight:lowmiddle
Product accuracy:middlehigh
One-piece multi-layer:feasiblenot feasible
Machine price:middlehigh
Mold price:lowhigh

Differences in how it work

blow molding

Mass production is combined with continuous extrusion and mold rotation in the blow molding process. In the process of the blow molding machine, the plastic is continuously extruded into a tube shape, and the mold is cut and blown out with compressed air (the shuttle motion of a group of molds is commonly used, and each mold takes turns to grab a point and shuttle to another section) to form a bottle shape, cooled and formed.

Injection molding

Injection molding is a process of producing parts made of thermoplastics or thermosets. Under the pressure of the plunger or screw, the molten plastic is compressed and moved forward, and then through the nozzle at the front end of the barrel, it is injected into the closed mold with low temperature at a fast speed. plastic product.

Differences in the mold

The internal mold core part is made of air by hollow blow molding; the internal mold core part is made of iron rods by injection molding.

Is blow molding expensive?

According to the mold requirements, costs and uses of hollow molding, the scrap rate of the finished product affected by the mold is lower than that of injection molding and extrusion molding, because the mold only accounts for about half of the key factor for the stability of the finished product, and the other half is other machines. set, so blow molding is not expensive.

Advantages and disadvantages of blow molding

Below is a short summary of our conclusions for reference:
Advantages: lower cost, variety of products, high quality and high output, high flexibility in production.
Disadvantages: Requires finer operating skills, produces residual material (burrs) in the process

What are the advantages of blow molding?

1. Lower cost

Compared with the injection molding machine, the blow molding machine does not need high-precision machinery, and the loss rate of the finished product has nothing to do with the quality of the mold. Therefore, under the condition of not demanding machinery and molds, it is possible to obtain high-quality finished products at a lower cost.

2. Diverse products

Blow molding molds are not limited by the size of the bottle mouth, allowing mold designers to experiment with creating a variety of different applications and designs, resulting in more hollow types of products.

3. High quality and high yield

Automation technology has been used in the field of blow molding, allowing machines to increase production capacity with shorter production cycles, to automatically recover all residual materials during production, and to automatically check bottles or products after output to ensure quality.

4. Highly flexible production

Blow molding machines can be used to produce products in a variety of industries such as food and beverage, medical, manufacturing, and pharmaceuticals. If you want to produce a series of products, the blow molding machine only needs to replace part of the mold, and you can get products of different volumes or different appearances. If you need to adjust the weight or thickness of the finished product, you only need to operate the thickness controller without modifying the mold. This highly flexible process, which can quickly adapt to various products, is very beneficial for modern production of small quantities and various types.

What are the disadvantages of blow molding?

1. Requires finer operational skills

The key factors for the stability of the finished product of the blow molding machine, and the precision of the mold are relatively low, and most of it depends on the machine setting. For example, the shell of the finished product after blowing out is uneven, resulting in fine cracks or ripples. The thickness of the finished product is also related to the operation setting of the machine, and it has high requirements for the professional skills of the personnel.

2. Residual material (burrs) generated during the process

The finished product produced by the hollow molding machine will have additional plastic material attached to the outer edge of the product after the initial output. It must be cut off in one more process to obtain a usable product, and the cut part needs to be recycled. to reduce material costs.


Whether it is injection molding or hollow molding, there are products and advantages and disadvantages that they are suitable for production. If it is an enterprise with a small number of products, and it is specialized in hollow products or continuous shape products, it is recommended to use a hollow molding machine. , then the injection molding machine is a machine that can control the quality of the product and can also meet most of the needs.