Blow molding machine is a plastic processing machine. After the liquid plastic is sprayed out, the wind blown out by the machine is used to blow the plastic body to a certain shape of the mold cavity to make a product. This machine is called a blow molding machine. The plastic is melted and quantitatively extruded in the screw extruder, then formed through the mouth film, and then cooled by the wind ring, and then pulled by a traction machine at a certain speed, and the winder winds it into a roll.
Blow molding introduction
Blow molding, also known as hollow blow molding, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of thermoplastic resin is placed in a split mold while hot (or heated to a softened state). After the mold is closed, compressed air is immediately introduced into the parison to inflate the plastic parison and cling to the inner wall of the mold. After cooling and demolding, various hollow products are obtained. The manufacturing process of blown film is very similar to that of hollow product blow molding in principle, 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. Blow molding technology began to be used to produce low-density polyethylene bottles 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 has been widely used. The volume of hollow containers can reach thousands of liters, and some production has adopted computer control. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc., and the resulting hollow containers are widely used as industrial packaging containers.
According to the parison making method, blow molding can be divided into extrusion blow molding and injection blow molding. The newly developed ones are multi-layer blow molding and stretch blow molding.
Energy saving effect
The energy saving of 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 them use frequency converters. The energy saving method is to save the surplus energy of the motor. For example, the actual power of the motor is 50Hz, but you only need 30Hz in production. The excess energy is wasted. The frequency converter changes the power output of the motor to achieve energy saving.
Energy saving in heating part: Energy saving in heating part mostly adopts electromagnetic heater, and the energy saving rate is about 30%-70% of the old resistance coil.
1. Compared with resistance heating, electromagnetic heater has an extra insulation layer, which increases the utilization rate of thermal energy.
2. Compared with resistance heating, electromagnetic heater directly heats the material tube, reducing heat transfer and heat energy loss.
3. Compared with resistance heating, the heating speed of electromagnetic heater is more than one-quarter faster, which reduces the heating time.
4. Compared with resistance heating, electromagnetic heaters heat faster, which improves production efficiency and keeps the motor in a saturated state, reducing the energy loss caused by high power and low demand.
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 be classified into each of the above categories. Extrusion blow molding machines are a combination of extruders, blow molding machines, and clamping mechanisms. They consist of extruders, parison die heads, inflation devices, clamping mechanisms, parison thickness control systems, and transmission mechanisms. The parison die head is one of the important components that determine the quality of blow molded products. There are usually side-feeding die heads and central-feeding die heads. Storage cylinder parison die heads are often used for blow molding of large products. The minimum storage cylinder volume is 1kg and the maximum can reach 240kg. The parison thickness control device is used to control the parison wall thickness, with a maximum of 128 control points, generally 20 to 30 points. Extrusion blow molding machines can produce hollow products with a volume range of 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 electronics and other mechanical parts. Common types are three-station injection blow molding machine and four-station injection blow molding machine. Three-station machine has three stations: preform, blow and demoulding, and each station is 120° apart. Four-station machine has one more preforming station, and each station is 90° apart. In addition, there are double-station injection blow molding machines with stations 180° apart. Plastic containers produced by injection blow molding machines are accurate in size and do not require secondary processing, but the mold cost is high.
Special structure blow molding machine is a blow molding machine that uses sheet, molten material and cold blank as a blank to blow a hollow body with a special shape and purpose. 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 center shaft and cylinder are made of 38CrMoAlA chromium, molybdenum and aluminum alloy treated with nitrogen, which has the advantages of high thickness, corrosion resistance and wear resistance.
2. The die head is chrome-plated, and the screw mandrel structure makes the discharge more even and smooth, and the film blowing is better completed. 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 rotation equipment and center rotation equipment, and adopts torque motor to adjust the smoothness of the film, which is easy to operate.
How it works
Brief Overview
In the production process of blown film, the uniformity of film thickness is a key indicator. The longitudinal uniformity of thickness can be controlled by the stability of extrusion and pulling speed, while the transverse uniformity of film thickness generally depends on the precision manufacturing of the die head and changes with the changes of production process parameters. In order to improve the transverse uniformity of film thickness, an automatic transverse thickness control system must be introduced. Common control methods include automatic die head (thermal expansion screw control) and automatic air ring. Here we mainly introduce the principle and application of automatic air ring.
Fundamental
The automatic air ring structure adopts a double air outlet method, in which the air volume of the lower air outlet is kept constant, and the circumference of the upper air outlet is divided into several air ducts. Each air duct is composed of a wind chamber, valve, motor, etc. The motor drives the valve to adjust the air duct opening degree and control the air volume of each air duct.
During the control process, the thickness probe detects the film thickness signal and transmits it to the computer. The computer compares the thickness signal with the currently 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 the film is thin, the motor moves forward and the air outlet is closed; on the contrary, the motor moves backward and the air outlet is increased. By changing the air volume at each point on the circumference of the wind ring and adjusting the cooling speed at each point, the lateral thickness deviation of the film can be controlled within the target range.
Control plan
The automatic air ring is an online real-time control system. The controlled objects of the system are several motors distributed on the air ring. The cooling air flow sent by the fan is distributed to each air duct after constant pressure in the air ring wind chamber. The motor drives the valve to open and close to adjust the size of the air outlet and air volume, change the cooling effect of the film blank at the die head discharge, and thus control the film thickness. From the control process, there is no clear relationship between the film thickness change and the motor control quantity. The thickness change of different thickness films and different valve positions and the control quantity are nonlinear and irregular. Each time a valve is adjusted, the adjacent points are greatly affected, and the adjustment has a lag, which makes different moments interrelated. For this highly nonlinear, strongly coupled, time-varying and control uncertain system, its accurate mathematical model is almost impossible to establish. Even if a mathematical model can be established, it is very complicated and difficult to solve, so it has no practical value. Traditional control has a better control effect on a relatively certain control model, but it has a poor or even powerless control effect on highly nonlinear, uncertain, and complex feedback information. In view of this, we chose the fuzzy control algorithm. At the same time, the fuzzy quantization factor is changed to better adapt to the changes in system parameters.
