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Blow molding machine operation principle/simple overview

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Note: According to the production method of the parison, blow molding can be divided into extrusion blow molding and injection blow molding. The newly developed multi-layer blow molding and stretch blow molding.

A blow molding machine is a plastic processing machine. After the liquid plastic is sprayed out, the wind blown by the machine is used to blow the plastic body into a certain shape of the mold cavity to make a product. This kind of machine is called a blow molding machine. The plastic is melted and quantitatively extruded in the screw extruder, and then formed through the mouth film, and then cooled by a wind ring, then a tractor is pulled at a certain speed, and the winder winds it into a roll.

Alias: Hollow blow molding machine
English name: blow moulding

Blow moulding, also known as hollow blow moulding, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of the thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state). After the mold is closed, compressed air is injected into the parison to blow the plastic parison It expands and clings to the inner wall of the mold, and after cooling and demolding, various hollow products are obtained. The manufacturing process of blown film is very similar in principle to blow molding of hollow products, but it does not use molds. From the perspective of plastic processing technology classification, the molding process of blown film is usually included in extrusion. The blow molding process was used to produce low-density polyethylene vials during World War II. 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 the hollow container can reach thousands of liters, and some production has adopted computer control. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The resulting hollow containers are widely used as industrial packaging containers.

According to the production method of the parison, blow molding can be divided into extrusion blow molding and injection blow molding. The newly developed multi-layer blow molding and stretch blow molding.

Energy saving effect

The energy saving of the blow molding machine can be divided into two parts: one is the power part and the other is the heating part.
Energy saving in the power part: Most of the inverters are used. The energy saving method is to save the residual energy of the motor. For example, the actual power of the motor is 50Hz, and you actually only need 30Hz in the production to be enough for production, and the excess energy consumption is in vain If it is wasted, the inverter is to change the power output of the motor to achieve energy saving effect.
Energy saving in heating part: Most of the energy saving in heating part is the use of electromagnetic heaters, and the energy saving rate is about 30%-70% of the old resistance coil.
1. Compared with resistance heating, the electromagnetic heater has an extra layer of insulation, which increases the utilization rate of heat energy.
2. Compared with resistance heating, the electromagnetic heater directly acts on the material tube to heat, reducing the heat loss of heat transfer.
3. Compared with resistance heating, the heating speed of electromagnetic heater is more than one-fourth faster, which reduces the heating time.
4. Compared with resistance heating, the heating speed of the electromagnetic heater is faster, and the production efficiency is improved. The motor is in a saturated state, which reduces the power loss caused by high power and low demand.
The above four points are the reasons why Feiru electromagnetic heater can save energy up to 30%-70% on the blow molding machine.

Machine classification

Blow molding machines can be divided into three categories: extrusion blow molding machines, injection blow molding machines and special structure blow molding machines. Stretch blow molding machines can belong to each of the above categories. Extrusion blow molding machine is a combination of extruder, blow molding machine and mold clamping mechanism, which is composed of extruder, parison die, inflation device, mold clamping mechanism, parison thickness control system and transmission mechanism. The parison die is one of the important components that determine the quality of blow-molded products. There are usually side feed die and central feed die. When large-scale products are blow-molded, the storage cylinder type billet die is often used. The storage tank has a minimum volume of 1kg and a maximum volume of 240kg. The parison thickness control device is used to control the wall thickness of the parison. The control points can be up to 128 points, generally 20-30 points. The extrusion blow molding machine can produce hollow products with a volume ranging from 2.5ml to 104l.

Injection blow molding machine is a combination of injection molding machine and blow molding mechanism, including plasticizing mechanism, hydraulic system, control electrical appliances and other mechanical parts. Common types are three-station injection blow molding machine and four-station injection blow molding machine. The three-station machine has three stations: prefabricated parison, inflation and demoulding, each station is separated by 120°. The four-station machine has one more preforming station, each station is 90° apart. In addition, there is a double-station injection blow molding machine with 180° separation between stations. The plastic container produced by the injection blow molding machine has precise dimensions and does not require secondary processing, but the mold cost is relatively high.

The special structure blow molding machine is a blow molding machine that uses sheets, molten materials and cold blanks as parisons to blow mold hollow bodies with special shapes and uses. Due to the different shapes and requirements of the products produced, the structure of the blow molding machine is also different.

Features and advantages

1. The screw central shaft and cylinder are made of 38CrMoAlA chromium, molybdenum, aluminum alloy through nitrogen treatment, which has the advantages of high thickness, corrosion resistance and wear resistance.

2. The die head is chrome-plated, and the screw spindle structure makes the discharge more even and smooth, and better completes the blown film. The complex structure of the film blowing machine makes the output gas more uniform. The lifting unit adopts a square frame platform structure, and the height of the lifting frame can be automatically adjusted according to different technical requirements.

3. The unloading equipment adopts peeling rotating equipment and central rotating equipment, and adopts a torque motor to adjust the smoothness of the film, which is easy to operate.

Operation Principle / Brief Overview:

In the process of blown film production, the uniformity of film thickness is a key indicator. The uniformity of the longitudinal thickness can be controlled by the stability of the extrusion and traction speed, while the uniformity of the transverse thickness of the film generally depends on the precision manufacturing of the die. , And change with the change of production process parameters. In order to improve the film thickness uniformity in the transverse direction, an automatic transverse thickness control system must be introduced. The common control methods include automatic die head (thermal expansion screw control) and automatic air ring. Here we mainly introduce automatic air ring Principle and application.


The structure of the automatic air ring adopts the double air outlet method, in which the air volume of the lower air outlet is kept constant, and the upper air outlet is divided into several air ducts. Each air duct is composed of air chambers, valves, motors, etc. The motor drives the valve to adjust the opening of the air duct Control the air volume of each duct.

During the control process, the film thickness signal detected by the thickness measuring probe is sent to the computer. The computer compares the thickness signal with the current set average thickness, performs calculations based on the thickness deviation and the curve change trend, and controls the motor to drive the valve to move. When it is thin, the motor moves forward and the tuyere closes; on the contrary, the motor moves in the reverse direction, and the tuyere increases. By changing the air volume at each point on the circumference of the wind ring, adjust the cooling speed of each point to control the lateral thickness deviation of the film within the target range .

Control plan

The automatic wind ring is an online real-time control system. The controlled objects of the system are several motors distributed on the wind ring. The cooling air flow sent by the fan is distributed to each air duct after constant pressure in the air ring air chamber. The motor drives the valve to open and close to adjust the size of the tuyere and air volume, and change the cooling effect of the film blank at the die discharge. In order to control the film thickness, from the perspective of the control process, there is no clear relationship between the film thickness change and the motor control value. The thickness of the film and the valve position of the valve change and the control value are nonlinear and irregular. Each time a valve is adjusted Time has a great influence on neighboring points, and the adjustment has hysteresis, so that different moments are related to each other. For this kind of highly nonlinear, strong coupling, time-varying and control uncertain system, its precise mathematical model is almost impossible Established, even if a mathematical model can be established, it is very complicated and difficult to solve, so that it has no practical value. Traditional control has a better control effect on a relatively definite control model, but it has a poor control effect on high nonlinearity, uncertainty, and complex feedback information. Even powerless. In view of this, we chose the fuzzy control algorithm. At the same time, the method of changing the fuzzy quantization factor is adopted to better adapt to the change of system parameters.
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