Successfully developed a dual-position five-layer co-extrusion dual-mold hollow molding machine

Entrusted by the Guangdong Provincial Department of Science and Technology and hosted by the Shantou Municipal Science and Technology Bureau, the dual-station five-layer co-extrusion dual-die hollow molding machine developed has passed the provincial scientific and technological achievements appraisal. The Appraisal Committee has always believed that "this product is a domestic initiative and has reached the advanced technology level of similar foreign products."

1. The purpose and significance of project development

1. The needs of social progress and industry development

With the development of the plastic raw material industry and the continuous improvement of people's environmental awareness and quality of life, the food, agricultural and sideline products, medicine, chemicals, automobiles, machinery and other industries have an increasing demand for small multi-layer co-extruded plastic hollow molded products.

2. New requirements for products

The project is suitable for the production of small five-layers with good barrier, sealing, light protection, corrosion resistance, temperature resistance, antibacterial, non-toxic, quality preservation, antistatic, flame retardant, high strength, high toughness, impact resistance, etc., and complex shapes. Co-extrusion of plastic hollow molding products. The containers produced can replace glass bottles and are suitable for the technical requirements of various packaging industries; the project can also produce parts with complex shapes that cannot be formed by metal materials, such as motorcycle gasoline tanks (to reduce gasoline volatilization), car bellows, and collars , Windshield cleaning water tank, etc.

3. Save and rationally use petroleum resources

Plastic raw materials are derived from petroleum. The world's petroleum resources are seriously in short supply. The rational and economical use of resources is an important issue facing all countries. The project uses the advanced technology of plastic foaming to add foaming agent to the plastic raw materials used in any layer of the five-layer co-extrusion system with a special structure for micro-foaming, which can improve the insulation and impact resistance of the product. At the same time, the weight of products is reduced, the consumption of raw materials is reduced, and the limited human petroleum resources are saved and rationally used.

4. Current status of domestic equipment

Due to the slow start of domestic multi-layer co-extrusion technology and lack of core technology, the co-extrusion plastic hollow molding machine with more than two layers is in a blank state, and the product technology is backward, the control level is low, the degree of automation is not high, and it cannot meet the requirements of PA (polyamide, Commonly known as nylon), EVOH (ethylene-vinyl alcohol ethylene copolymer) and other high barrier raw materials processing. Before the project development, only a few plastic machine manufacturers in Germany, the United States, Italy and other countries could produce this kind of equipment. The equipment imported from abroad is about US$800,000 (excluding tariffs), and most manufacturers are unable to purchase them and are eager to supply domestic equipment to the market.

5. Five-layer co-extrusion plastic hollow molding machine

Single-layer plastic hollow molding machine products use a single raw material, simple formula, and products with high performance requirements must consume a lot of valuable raw materials. For example, in order to ensure the barrier performance of the entire product, all PA must be used; to improve the appearance of the product The degree of pearlescent must be 4-10 times higher than that of multi-layer co-extruded products. The cost of PA pearlescent is high, and production cannot be maintained.

The five-layer co-extruded plastic product has excellent barrier function. If it is used to package fresh milk, the shelf life is as long as 0.5 to 1 year (normal packaging is only 1 to 1.5 months), and the shelf life of packaged tomato juice is as long as 2 years. Above, meet the export packaging requirements. In addition, the cost of raw materials for five-layer co-extrusion and three-layer co-extrusion should be low, the strength should be high, and the structure design should be flexible and convenient.

2. Project development process

1. Determination of the technical plan

(1) The main structure of the project

2SPZADV～1 Double-station five-layer co-extrusion double die headHollow molding machineIt is mainly composed of 5 automatic feeders, 5 single-screw plastic extruders, hot runners, five-layer co-extrusion dual die heads, automatic parison wall thickness control, automatic tube blank sealing and cutting, blow molding, duplex displacement molds, and clamping Forming, hollow forming mold, residual blank removal, product automatic conveying, product online automatic leakage detection, hydraulic pressure (proportional pressure, proportional flow), pneumatic, frame and computer centralized control system.

(2) The basic production process of the project

Automatic feeding → plasticizing extrusion → tube blank forming, parison wall thickness control → tube blank sealing and cutting → moving mold clamping tube blank, pre-blow molding → moving mold blow molding → mold opening → automatic product conveying → remaining blank removal →Automatic leak detection of products→Product collection.

(3) The main technical parameters of the project

Maximum product volume: 1L. Number of die heads: 2 pcs.

Co-extrusion layers: 5 layers. Number of stations: 2.

Maximum extrusion output: 55kg/h. Product layer structure: A/B/C/D/E.

Screw diameter: A, C, E layer ф40mm, B, D layer ф35m.

Screw length to diameter ratio: 25:1. Maximum screw speed: 65r/min.

Screw drive motor power: 5.5kW for A, C and E layers; 3kW for B and D layers.

Die structure: Five-layer co-extrusion double die.

Die Diameter: According to the product.

Automatic control point of parison wall thickness: 100 points.

Clamping force: 40kN. The power of the main oil pump motor: 11kW.

Oil pump type: high pressure and low noise double vane pump.

The working pressure of the large pump of the hydraulic system: 5Mpa.

The holding pressure of the small pump of the hydraulic system: 10Mpa.

Compressed air pressure: 0.4～0.7MP. Compressed air consumption: 65m3/h.

Nominal total heating power: 30kW. Nominal total power: 75kW.

Average energy consumption: 55kW. Dimensions (1xbxh): 3.872m×2.73m×2.67m.

Weight: about 12t.

(4) Applicable raw materials for the project

PA, EVOH, EVA, HDPE, PP, adhesive resin, pearlin, foaming agent.

2. The application of patented technology of the company's own intellectual property rights

The project applies 3 national patented technologies with the company’s own intellectual property rights, as detailed in the table below.

3. Key technical issues

1. Screw for high barrier resin

PA and EVOH are important raw materials for the production of multi-layer co-extruded plastic products with high barrier properties. In the ordinary screw processing process, these raw materials have to withstand high shearing action for a long time, and the material temperature will continue to rise, which will easily cause the extruded material to overheat and decompose, which will not only pollute the extrusion system, but also seriously affect the film’s performance. quality. In order to solve this difficulty, the company has its own intellectual property patent technology ZL 01 2 58204.2, a non-circular plastic extrusion screw, which not only ensures the full shear of the raw materials, but also allows the melt temperature to be controlled to ensure the cleanliness of the extrusion system. And product quality, solve the problem of key extrusion parts.

2. Five-layer co-extrusion dual die head

The five-layer co-extrusion dual die head is the key component of product molding. The design adopts the company’s own intellectual property patent technology ZL 00 2 272700.9 "a plastic multi-layer co-extrusion die device". The following key issues must be fully considered when designing the die: In order to pursue high productivity (economic benefits), the die is designed as a dual die structure (that is, two parallel die heads parallel to each other), which can simultaneously extrude two parallel die heads. In order to ensure that the extrusion length and weight of the two pipe blanks are equal, the size of the die runner must be the same, and the two die heads must maintain a high degree of symmetry. Due to the rich experience in melt runner design for various plastic materials, combined with melt runner design theory, it is clear that the main runner, branch runner, and material flow distribution runner design should have a certain compression ratio, and the inside of the die The pressure distribution must be reasonable to avoid dead corners in the runner design, and the runner must be smooth to make the material flow smoothly without undesirable phenomena such as material accumulation and avoid excessive decomposition of the melt to produce char material. Because the temperature of PA, EVOH, PE plus 2222 is very different, each die must be divided into upper and lower two levels, and at the same time, the heater of the die can be designed in sections to achieve the purpose of section heating of the die, which greatly reduces The effect of temperature on the extrusion materials in different die runners.

3. Die cleaning channel

There are two common problems in the plastic processing process: one is that the die must be disassembled and cleaned regularly to remove the accumulated material stuck on the surface of the die runner. It is very troublesome to disassemble the die; the other is that the melt pressure of the die is relatively high. Low, it is inevitable to produce material accumulation, which will consume a lot of raw materials and time to squeeze out old colors and old raw materials when changing colors or formulas of products. After repeatedly improving the design and testing, the cleaning channel of the die is finally added at the melt joint of the die. The channel is usually closed with screw plugs. When changing the color of the product or changing the formula, just unscrew a large amount of old color and old raw materials through the channel to quickly extrude out of the die. The entire cleaning time is usually less than 20min. This technological innovation can not only extend the period of regular disassembly and cleaning of the die, but also greatly facilitate the equipment to change the color and formula of the product. This innovation reduces. Less die cleaning time 8-24h, saving 400-1300kg of raw material for extruding melt cleaning die.

4. Automatic control of parison wall thickness

Because the continuously extruded tube blank is in a molten state when it is extruded from the die, the melt in the molten state is affected by gravity, and the tube blank becomes thinner by itself. As the length of the extruded tube blank increases, the tube blank It will become thinner and thinner, showing a gradual phenomenon of lower thickness and upper thinness. The project sets the wall thickness curve of the tube blank through the automatic control device for the wall thickness of the parison with a control point of 100 points. The automatic control device for the wall thickness of the parison realizes automatic cyclic control according to the set wall thickness curve under the control of the computer. So as to achieve reasonable product thickness distribution, appropriate weight, save raw materials, and meet product quality requirements.

5. Duplex displacement mold and mold clamping forming device

Since it takes a certain time for the product to cool and shape in the forming mold, the length of time is related to the processing temperature of the raw material and the different thickness of the product. By increasing the extrusion volume of the extruder, it is equipped with duplex displacement molds and mold clamping devices. When the products in one station are cooled, the other station is used for mold shifting, mold clamping, and tube blank sealing and cutting, which is reasonable Utilize the working time of the equipment effectively to achieve the purpose of increasing the output of products.

The project adopts ZL01 235905. X "a hollow plastic appliance molding device" patented technology, through the connection of the ejector rod of the cylinder and the mold base, the linkage rod is added to form a balance that can transfer the reaction force received by the cylinder to the middle section of the mold base, thereby eliminating mold stress The problem of deformation due to unbalanced pressure.

6. Remaining blank cutting device

In the past, the remaining blanks, flashes, and the retaining wall of the handle hole after the hollow products were formed must be repaired manually, which resulted in low work efficiency and frequent work-related accidents. In order to improve the work efficiency and the automation level of the equipment, the project adopts an automatic residual blank cutting device. The remaining blank cutting device is composed of product conveying rails, product positioning and clamping, remaining blank shoveling, pneumatic system and so on. After the product is demolded, it enters the remaining blank shoveling station under the action of the automatic product conveying device, the positioning clamping device (commonly known as the fake mold) clamps the product, and the pneumatic system drives the remaining blank shovel to automatically shovel the remaining blank on the product. , Flash, and handle hole to block the wall, thereby improving the working efficiency and automation level of the equipment.

7. Tube blank automatic sealing and cutting device

Since the product forming tube blank is continuously extruded, a cutting knife must be used to cut the tube blank into a formed tube blank of a certain technological length. Generally, the hollow forming machine uses conventional technology to heat the cutting knife to cut the tube blank, but cannot be used for the bottom sealing treatment of the tube blank, and mainly relies on the hot red cutting knife to cut the tube blank. Although the hot cutter chooses a special heat-resistant alloy steel and a cutter straightening device is designed at one end of the cutter, it cannot solve the problem of long-term heating surface oxidation, heavy delamination, bending deformation of the cutter, short life, and tube blank. Defects such as irregular cuts. In order to solve these problems, the project uses a room temperature cutter that does not need to be heated. There are 2 cutting knives, which are installed on the front and rear knife holders. Under the action of the driving mechanism, they can simultaneously close to the center of the tube blank, just like the shearing machine shears the steel plate. In order to satisfy the pre-sealing of the tube blank, it is more conducive to the molding process of the product, the tool holder is equipped with a pre-sealing device with concave and convex grooves to automatically heat seal the bottom of the tube while the tube is cut. Since the cutter does not need to be heated, not only the surface of the cutter is not easy to oxidize, does not delamination, does not bend and deform, has a long service life, and the tube blank is cut neatly, but also reduces power consumption and reduces the production cost of products.

8. Hydraulic system

Due to the increase in extrusion output, the output of products is simultaneously increased, which brings about the obvious hydraulic shock phenomenon in the process of rapid mold removal, mold opening, mold closing, and mold clamping. In order to solve this problem, the project adopts the internationally advanced hydraulic circuit with proportional flow and proportional pressure (ie electro-hydraulic proportional circuit) to realize that the pressure, flow and speed of the system can be flexibly set and adjusted according to the position requirements of the executive components. Make the movement of mold moving, mold opening, mold closing, and clamping smooth, soft, coordinated, fast, and avoid the undesirable phenomenon of hydraulic shock.

9. On-line automatic leak detection of products

Generally, the hollow forming machine does not have an on-line automatic leakage test function for the product, and the product needs to be leak-tested offline, which takes up time and production space, which greatly increases the manufacturing cost. In order to solve the above problems, the project successfully added an online automatic leak detection device for products to the equipment

10. Computer centralized control

The control technology of domestic equipment is backward, the control precision is poor, and the program runs slowly. The project adopts a computer centralized control system, and specially designed automatic control software for the processing temperature, screw speed, melt pressure, melt temperature, parison wall thickness, tube blank sealing and cutting, mold clamping, mold clamping, mold opening, and mold shifting. , Blow molding, product online automatic leak detection, etc., carry out centralized computer control, and display and monitor parameters such as temperature, current, voltage, pressure, product production quantity, etc., and have automatic alarm and self-diagnosis functions. The system is easy to operate, clear and easy to understand, and the information is represented by graphics and charts, can alarm and provide fault reports in time, and implement intelligent on-site precise control, monitoring and remote parameterization. At the same time, the processing parameters of the products can be stored, which is convenient for operation and convenient for enterprise management. It can significantly improve the economic benefits of the production line and greatly improve the automation control level of domestic equipment.

4. Trial production results

1. The project adopts screws suitable for the processing of PA and EVOH raw materials, five-layer co-extrusion dual die heads, automatic parison wall thickness control, automatic tube blank sealing and cutting, blow molding, duplex displacement molds, clamping molding, hollow molding molds, and more Advanced technologies such as blank cutting, automatic product conveying, product online automatic leakage detection, hydraulic pressure (proportional pressure, proportional flow), computer centralized control, and patented technologies with own intellectual property rights.

2. The project has a number of innovations: (1) "Corrugated" screw suitable for processing high-barrier raw materials. (2) Multi-layer co-extrusion die head suitable for processing raw materials with large temperature difference. (3) The die head melts and merges the flow channel to clean the channel in the low pressure area. (4) Micro-foaming powder screw with small helix angle in the feeding section. (5) A linkage balanced mold clamping device is used to avoid unbalanced deformation of the mold under pressure. (6) Adopt the new technology of room temperature cutting knife (cold cutting knife) and blank bottom sealing. (7) On-line automatic leak detection device for products. (8) Special software for computer centralized automatic control. (9) The five-layer co-extruded products produced by the project are different from those produced by general equipment: there are many extrusion layers, the product structure design is flexible, and the raw materials are reasonably matched. It can produce three-layer barrier materials and products with complex shapes.

3. The prototype has been installed, debugged, and operated, and it is shown that the technical performance indicators of the project have reached the technical requirements of the original "Technical Tasks", with advanced performance and stable and reliable operation.

5. Future development direction

Continuously develop different technical grades and large-scale series of products, research and develop multi-layer co-extrusion, multi-cavity, multi-die plastic hollow molding equipment suitable for the production of products with different structures and different functions to meet the needs of users.