Keywords: blow molding, stretch bottle making, frequency conversion
Abstract: One-step injection stretch blow molding plastic hollow molding is the world's advanced stretch bottle making technology, which uses high pressure and high speed injection of preforms, axial stretching of the preforms, bidirectional blow molding, cooling and shaping. The injection, stretching and blow molding processes are completed sequentially on a single device, which is the "one-step" bottle making process.
One-step injection stretch blow-molded plastic hollow molding is the world's most advanced drawing bottle making technology. It adopts high-pressure and high-speed injection of preforms, axial drawing of the preforms, bidirectional blow molding, cooling and shaping. The injection, stretching and blow molding processes are completed sequentially on a single device, which is the "one-step" bottle making process.
After the plastic bottles are stretched, the comprehensive mechanical properties such as transparency, surface stiffness, impact resistance, and gas permeability are greatly improved, the production efficiency is high, and the inherent quality and dimensional accuracy of the products are easily guaranteed.
1. Brief introduction of one-step injection stretch blow molding process equipment
The main unit of the one-step injection stretch blow molding process equipment is an injection stretch blow molding plastic hollow molding machine and its injection stretch blow mold, which is mainly composed of an injection device, a lifting index device, a stretch blow molding device, a demoulding device, a hydraulic system, and a pneumatic system , Electronic control system, microcomputer automatic control system, frame, safety cover, injection preform mold, stretch blow molding mold and other parts, integrated injection and stretch blow special control computer, frequency conversion controller, electro-hydraulic proportional control system, Some advanced technological equipment such as hot runner molds.
Auxiliary machines for one-step injection stretch blow molding equipment mainly include plastic dehumidification dryers, air compressors, air dehumidifiers, mold coolers, etc. It is an integrated high-end technical equipment integrating "machine, electricity, liquid, gas, and microcomputer". The project innovatively and comprehensively uses some advanced technologies such as PID temperature control technology, frequency conversion technology, microcomputer automatic control technology, hot runner mold technology, etc., which are two steps in common with the extrusion blow molding machine, injection blow molding machine, injection stretch blow molding currently used in China. Compared with French equipment, it has obvious technical advantages in many aspects such as degree of automation, yield, energy saving, and waste reduction. It is suitable for the production of high-end plastic bottles with bottlenecks, high precision, good transparency, non-toxic, and good preservation of the contents. It is widely used in processing PET, PEN, PP and other high-end industries such as pharmaceuticals, health products, food, cosmetics and chemical industries Packaging bottles.
2. Equipment and technical characteristics
2.1 Three-station
Including injection preform station, stretch blow molding station, demolding station, see Figure 1.
Figure 1 Schematic diagram of three stations
2.2 One-step process
The preform injection molding, preform stretching, bottle blow molding and other processes are completed sequentially on this machine.
2.3 Application of frequency conversion and electro-hydraulic proportional speed regulation technology
The patented technology of frequency conversion and electro-hydraulic proportional compound speed control applied to the injection stretch blow molding process is the first in the world, and has achieved great results. Compared with the past, variable pump oil supply, double pump oil supply or double pump group supply Oil has many advantages. Mainly reflected in the small flow and high pressure working conditions:
(1) When dual pumps supply oil, the flow change time between each working condition is within 3s, and the time from the pump starting from zero speed to the rated speed is about 3s, so the machine cannot be stopped at high pressure and small flow Large pumps can only supply oil at full flow and unload the valve, causing energy consumption.
(2) When supplying oil to the double pump set, under the condition of high pressure and small flow, the small pump supplies high pressure oil and the large pump unloads, but the pump still supplies oil at full flow, and the overflow valve drains oil, causing energy consumption.
(3) Variable pump oil supply can achieve automatic control of the pump's oil supply flow, and reduce the flow when the pressure is high, thereby maintaining control of the output power, so the energy consumption is low, the degree of automation is high, but the cost is high, Domestic use is still relatively small.
Energy consumption will cause the system to heat up, and the pump will work at full flow for a long time, which will affect the running accuracy and service life of the pump. The use of frequency conversion and electro-hydraulic proportional compound speed control microcomputer control system to achieve the optimal control of pressure and flow according to the working conditions of the system, thereby greatly reducing the overflow loss of the hydraulic system, with significant energy saving and consumption reduction effects, compared with ordinary technology Save more than 30% electricity. When the machine is running under the control of the microcomputer, the microcomputer uses the displacement sensor to accurately measure and control the movement stroke and determine which working condition the machine is in the entire working cycle, and then sends the set frequency signal to the inverter according to the working condition requirements to control the motor without Step speed regulation, control the output flow of fixed pump.
The characteristics of this technology are: to avoid the power consumption and heating phenomenon caused by excessive oil supply overflow; the oil pump will not supply oil for a long time at full flow, and its life is greatly improved; the fuel supply amount adjustment is stepless adjustment, the conversion is stable, not It will cause shock phenomenon; especially in high pressure and small flow conditions, its advantages are more prominent and obvious. Through frequency conversion, it can be preset by frequency conversion parameters within a certain speed range, so that the motor provides the load required by the quantitative pump at low speed With oil pressure, the motor runs at a lower power output, which reduces energy consumption and heat generation of the system, making the operation of the entire system safer and more reliable; it can also make the motor soft start and reduce the impact on the power grid.
2.4 Using PET as the main raw material
The raw material of PET is semi-crystalline plastic, the crystallization point is 260 ℃, and its plasticization temperature is controlled at about 280 ℃; it has strong water sensitivity and is easy to absorb moisture and hydrolyze. It must be dried in dry air at 150 ℃ for more than 4h to make the moisture content less than 0.005 %; The preform temperature is stretch blow molded at 95 ° C, easy to form, and the quality is easy to control; at 170 ° C, the crystallization speed is the fastest, so it should be quickly cooled through the crystallization zone, and the slow crystallization rate should be selected. 85 ml / g.
2.5 Multi-cavity
A multi-cavity mold can be used when the equipment is formed, and continuous automatic production can be performed.
2.6 Hot runner mold design
Foreign advanced technology is already using computer software packages to perform precise design calculations on a multi-cavity hot runner mold. Advanced computer simulation technology is used to accurately simulate and analyze various factors such as plastic molding characteristics, medium cooling characteristics, heat transfer characteristics, flow channel parameters, and cavity stress changes.
In China, the design and manufacture of hot runner molds has become a bottleneck restricting the localization of the one-step injection stretch blow molding process equipment. People in the industry should find a breakthrough to focus on. In recent years, many manufacturers of plastic hollow molding equipment have also been paying attention to the progress of the one-step injection stretch blow molding process equipment, but the manufacturing process problems have rarely been involved. Relying on independent technology, Ningbo Qianpu Machinery Manufacturing Co., Ltd. worked closely with Zhejiang University and other colleges and universities to start the research and development of injection stretch blow molding process equipment in 2000. After successful product trial production, dozens of tests were carried out in the mold and molding process Exploration has achieved relatively obvious results.
2.7 Efficient PET plasticizing screw
The melting point of PET is 260 ℃, blow molding at about 95 ℃, temperature control should be relatively accurate to ensure stable molding. Since PET is a crystalline plastic, the preform injection molding process requires a rapid cooling method to quickly pass through the crystallization area, so the pressure-holding cooling time after the injection is only about 3s, and high-quality plastics must be completed in such a short time Chemical process, which requires PET plasticizing screw must be efficient. In recent years, China's PET plastic preform processing technology and equipment technology have been greatly improved, which has laid the foundation for the one-step method of PET injection stretch blow molding. The injection molding and one-step molding equipment for intellectual property will catch up with the world's advanced level.
3 Equipment advantages
The one-step process has higher production efficiency, lower labor intensity, and no secondary pollution than the two-step process.
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