As a key safety component of automobiles, automotive fuel tanks are mainly used to store fuel (gasoline, diesel, etc.), and their performance directly relates to the safety, reliability and environmental protection of automobiles. According to the vehicle type, they can be divided into passenger car fuel tanks (50L-80L) and commercial vehicle fuel tanks (100L-500L). They need to meet strict core performance requirements such as oil resistance, leakage prevention, impact resistance, static resistance, light weight and dimensional precision. The production process puts more stringent requirements on the extrusion stability, molding accuracy, structural adaptability and safety performance of extrusion blow molding machines. Specifically, it can be divided into the following core dimensions, taking into account both equipment performance and the special safety and performance needs of automotive fuel tank production.
I. Extrusion System: Ensuring High-Quality Melt and Oil-Proof Layer Integration
The extrusion system is the core of the extrusion blow molding machine for automotive fuel tank production, which directly determines the plasticizing effect of modified raw materials, the bonding quality of multi-layer structures and the final oil resistance and leakage prevention performance of the fuel tank. Due to the special requirements of fuel tanks for material performance, the extrusion system must meet the following strict standards.
1. Screw Configuration Adapted to Modified HDPE Raw Materials
The mainstream raw material for automotive fuel tank production is modified HDPE (High-Density Polyethylene), which is added with anti-static, oil-resistant and environmental stress crack resistance (ESCR) additives. Some high-end fuel tanks adopt multi-layer co-extrusion structure (such as HDPE + EVOH barrier layer), so the extruder screw must be adaptively designed:
- Screw Parameters: The length-diameter ratio (L/D) should be controlled between 32:1 and 35:1, which is higher than that of ordinary water tanks, to ensure sufficient plasticization of modified HDPE and uniform dispersion of additives, avoid melt degradation caused by excessive shearing, and ensure that the melt has excellent oil resistance and mechanical strength; The screw diameter is adjusted according to the fuel tank capacity. A screw of about Φ70-80mm can be selected for passenger car fuel tanks (50-80L), and a screw of Φ90-110mm should be selected for commercial vehicle fuel tanks (100-500L), with corresponding plasticizing capacity (250-450kg/h) to meet the melt supply needs of fuel tanks of different specifications.
- Screw Structure: A gradual compression ratio screw with mixing section is adopted, and the compression ratio is controlled between 4:1 and 5:1. The mixing section is added to enhance the dispersion effect of anti-static, oil-resistant additives and barrier layer materials, avoid uneven distribution of additives leading to reduced fuel tank performance; For multi-layer co-extrusion fuel tanks (2-5 layers), multiple sets of screws (2-5 sets) need to be configured to realize synchronous extrusion of different functional layers (such as HDPE base layer, EVOH barrier layer, adhesive layer), ensure tight bonding between layers, and prevent oil seepage between layers.
- Screw Material: High-wear-resistant and corrosion-resistant alloy material (such as 38CrMoAlA + plasma spraying) is selected, and the surface is subjected to deep nitriding treatment (nitriding layer thickness ≥0.5mm) to resist the wear of modified HDPE and additives, avoid screw wear leading to uneven melt extrusion, and ensure the stability of long-term mass production.
2. Barrel and Head Design Meet High-Precision Molding Requirements
- Barrel Temperature Control: Adopt high-precision zoned heating (feeding section, compression section, homogenizing section, mixing section) and cooling design, with temperature control accuracy reaching ±0.5℃ (higher than that of water tank production), which is 0.5℃ higher than that of water tank production. The temperature of each section can be accurately adjusted according to the performance of modified HDPE (when producing modified HDPE fuel tanks, the barrel temperature is controlled at 170-210℃), to avoid melt degradation caused by excessive temperature and insufficient plasticization caused by too low temperature, ensure stable melt extrusion, and effectively control parison sagging (the sagging amount is ≤2mm/m), which is crucial for the wall thickness uniformity of irregularly shaped fuel tanks.
- Head Structure: For single-layer fuel tanks, a center-fed accumulator head with high-precision flow channel is adopted, and the accumulator capacity is adjusted according to the fuel tank weight (for example, the accumulator capacity of 80L passenger car fuel tank model needs to reach 50L), which can stably output the parison and avoid parison fluctuation and deflection; For multi-layer co-extrusion fuel tanks, a multi-layer co-extrusion head is adopted, with independent flow channels for each layer, and the flow rate of each layer can be precisely adjusted (adjustment accuracy ±1%), to ensure the uniformity of the thickness of each functional layer (the thickness of EVOH barrier layer is controlled at 0.1-0.3mm). The die gap is driven by a servo motor with high precision (adjustment accuracy ±0.01mm), combined with the parison program control system, to realize precise control of the axial and circumferential wall thickness of the parison, compensate for the uneven stretching of irregular parts (such as oil filler neck, mounting bracket) during blow molding, and preset corresponding wall thickness parameters to improve the structural strength and leakage prevention performance of the fuel tank.
II. Blow Molding System: Ensuring Irregular Shape Molding and Leakage Prevention Performance
Automotive fuel tanks have irregular shapes (adapted to the installation space of automobile chassis) and extremely strict requirements on leakage prevention and dimensional accuracy. The blow molding system, as the core link of molding, must meet the requirements of precise molding, uniform wall thickness and no defects.
1. Parison Control Accuracy Reaches Automotive Component Standards
The automotive fuel tank has extremely strict requirements on wall thickness uniformity (the deviation should be controlled within ±0.05mm), which is stricter than that of water tanks. Uneven wall thickness will lead to weak local structure of the fuel tank, uneven cooling shrinkage, easy deformation and oil leakage, and even potential safety hazards under high temperature and pressure. Therefore, the parison control must meet:
- Equipped with a high-precision parison wall thickness control system (up to 150 control points), which can accurately adjust the axial and circumferential wall thickness of the parison. For the parison sagging problem that is easy to occur in long parisons (for commercial vehicle fuel tanks), compensate by optimizing the extrusion speed curve and increasing the initial thickness of the upper part of the parison, so as to ensure that the wall thickness difference between the upper and lower parts of the fuel tank is ≤0.03mm.
- The parison weight is accurately controlled (control accuracy ±0.5%), and the maximum parison weight should match the fuel tank weight (for example, the parison weight of 80L passenger car fuel tank can reach 35kg), to avoid insufficient parison weight leading to too thin wall thickness and insufficient strength of the fuel tank, or excessive weight causing raw material waste and affecting the lightweight of the fuel tank.
2. Stable and High-Precision Blowing System
- Blowing Pressure and Flow Rate: Adjust according to the shape complexity and wall thickness of the fuel tank. The blowing pressure of passenger car fuel tanks is controlled at 0.6-0.8MPa, and that of commercial vehicle fuel tanks (with larger volume and more complex shape) needs to be increased to 0.8-1.0MPa. Multi-stage pressure control technology is adopted. A lower pressure is used in the initial stage to avoid local excessive stretching and material damage, and the pressure is increased after the material contacts the mold to ensure that the irregular parts (such as mounting holes, oil filler neck) are fully formed; The blowing flow rate is stable (flow rate fluctuation ≤5%), to avoid fuel tank defects such as depression, bulge and pinhole caused by pressure fluctuation. The blow-up ratio is controlled between 2.5:1 and 4.5:1, which is slightly higher than that of water tanks, to adapt to the irregular shape of fuel tanks while ensuring the wall thickness and strength.
- Blowing Timing and Cooling: The blowing timing is accurately matched with the parison extrusion speed (response time ≤0.1s), too early or too late will affect the material distribution, avoid the parison being too cold to blow up or deformation due to untimely cooling after blow up; The blowing medium adopts dry, clean and oil-free compressed air (moisture content ≤0.01%, oil content ≤0.001%), to avoid bubbles, oil stains and scratches on the inner wall of the fuel tank caused by moisture and oil stains in the air, which affect the oil resistance and leakage prevention performance. After blowing, inert gas (such as nitrogen) can be filled to prevent the melt from oxidizing and affecting the service life of the fuel tank.
3. Mold Adaptability and Efficient Cooling System
- Mold Adaptability: The mold size is accurately matched with the designed size of the fuel tank (dimensional tolerance ±0.1mm), which meets the precision requirements of automotive components. The mold cavity surface is polished with high precision (surface roughness Ra ≤0.8μm), smooth and free of burrs, to ensure the fuel tank has a flat appearance and no scratches; The mold has excellent sealing performance (air leakage rate ≤0.01L/min) to avoid air leakage during blow molding, leading to incomplete fuel tank molding; The mold is designed with a built-in exhaust groove (distributed according to the shape of the fuel tank) to discharge the residual air in the mold cavity, avoid pinholes and bubbles in the fuel tank; The equipment should be compatible with fuel tank molds of different vehicle types (passenger cars, commercial vehicles), with a mold thickness adjustment range of 800-1500mm to improve equipment versatility.
- Cooling System: A multi-circuit, high-efficiency cooling system is adopted to independently control the temperature of different areas of the mold (especially irregular parts), and the temperature difference on the mold surface is controlled within ±3℃, which is stricter than that of water tanks, to avoid fuel tank shrinkage and deformation caused by uneven cooling; The cooling water circuit is designed according to the shape of the fuel tank, with dense cooling points in thick-walled parts and reasonable layout in thin-walled parts. The cooling efficiency meets the production cycle requirements. The cooling time of passenger car fuel tanks is controlled at 40-80s, and that of commercial vehicle fuel tanks needs to be extended to 100-200s, to ensure that the fuel tank is quickly solidified after molding, improve production efficiency, and ensure the dimensional stability and structural strength of the fuel tank. The mold is also equipped with a temperature feedback device to realize dynamic adjustment of cooling temperature.
III. Clamping System: Ensuring Molding Stability and Operational Safety
Automotive fuel tank molds are complex in structure, high in precision and high in production frequency. The clamping system is responsible for opening, closing and locking the mold, and its clamping force, stroke and precision directly affect the fuel tank molding quality, production safety and mold service life.
- Clamping Force: Determined according to the fuel tank size, shape complexity and blowing pressure. The clamping force of passenger car fuel tank models needs to reach 800-1200KN, and that of commercial vehicle fuel tank models should not be less than 1500-2000KN, to ensure that the mold does not loosen or overflow during blow molding, and avoid fuel tank defects such as flash, burr and dimensional deviation. The clamping force is adjustable (adjustment accuracy ±10KN) to adapt to fuel tanks of different specifications.
- Clamping Stroke and Template: The clamping stroke is designed according to the maximum mold size and fuel tank shape, generally 1000-2200mm, to meet the needs of mold opening, closing and fuel tank taking out. The template size is matched with the mold (for example, 1500x1600mm template is suitable for passenger car fuel tank molds), and the template parallelism error is controlled within 0.05mm, to avoid wall thickness deviation of the fuel tank or mold damage caused by uneven force on the mold during clamping; The mold thickness adjustment range is 800-1500mm, which is compatible with fuel tank molds of different thicknesses and vehicle types.
- Operational Convenience and Safety: Equipped with automatic clamping, demolding and mold changing mechanisms. The automatic demolding mechanism is designed according to the fuel tank shape (with special clamping fixtures) to avoid fuel tank damage caused by manual demolding and reduce labor intensity; The mold changing mechanism adopts quick-change design (mold changing time ≤30min) to improve production efficiency when switching between different vehicle type fuel tanks. The clamping mechanism has good stability and durability, and can withstand high-frequency opening and closing actions (≥10000 times/month) for a long time, reducing the impact of equipment failures on production. At the same time, a safety interlock device is equipped to prevent accidental operation during clamping, ensuring production safety.
IV. Control System: Realizing Precise Regulation and Batch Consistency
Automotive fuel tank production is mass production of automotive safety components, which has extremely high requirements on the consistency of product performance and dimensions. The control system must realize precise regulation of all parameters, reduce inter-batch errors, and ensure that each fuel tank meets the standard.
- Control Accuracy: Adopt a high-precision PLC control system (such as Siemens S7-1500 series) with high-speed processing capability, which can accurately control key parameters such as extrusion speed, barrel temperature, head temperature, blowing pressure, clamping force and cooling time. The parameter adjustment accuracy is high (extrusion speed fluctuation ≤1%, temperature control accuracy ±0.5℃), and the response speed is fast (response time ≤0.05s), ensuring the coordinated stability of each process and realizing the consistency of mass production (inter-batch dimensional deviation ≤0.1mm).
- Automation Function: It has full-automatic production functions such as automatic feeding, automatic extrusion, automatic blow molding, automatic cooling, automatic demolding, automatic trimming (trimming of flash and burrs) and automatic inspection, reducing manual intervention (manual intervention rate ≤5%), lowering labor costs, and avoiding product defects caused by manual operation errors; Equipped with a real-time wall thickness monitoring and feedback system (adopting ultrasonic thickness measurement technology, measurement accuracy ±0.01mm), real-time monitor the wall thickness changes of the parison and fuel tank, feed the data back to the control system for dynamic adjustment, and further improve the wall thickness consistency. At the same time, it is equipped with an online leakage detection system (air pressure detection method, detection pressure 0.3-0.5MPa), which can automatically detect unqualified products and remove them, ensuring the qualification rate of products (≥99.5%).
- Fault Warning and Data Management: It has a complete fault warning and diagnosis function, which can timely detect problems such as extrusion abnormalities, temperature deviations, air leakage, clamping failures and leakage of fuel tanks, and issue audible and visual warning signals, and display fault points and handling suggestions, avoiding the generation of batch unqualified products; At the same time, it can record production parameters (extrusion speed, temperature, pressure, etc.), fault information and product inspection results, store data for ≥1 year, facilitate later problem troubleshooting, production process optimization and quality traceability, which meets the quality management requirements of the automotive industry.
V. Auxiliary System: Adapting to the Special Safety and Performance Needs of Fuel Tanks
In addition to the core system, the auxiliary system of the extrusion blow molding machine needs to be adaptively designed to the particularity of automotive fuel tank production, especially in terms of raw material processing, safety protection and environmental protection, to ensure the smooth progress of production and the performance of fuel tanks.
- Raw Material Processing System: Equipped with high-precision raw material drying, screening and mixing devices. The modified HDPE raw materials need to be fully dried (moisture content ≤0.05%, lower than that of water tanks) to avoid bubbles and pinholes in the fuel tank caused by moisture, which affect the leakage prevention performance; The screening device (screen mesh size ≤80 mesh) removes impurities in the raw materials to avoid wear of screws and molds and defects of fuel tanks; The mixing device (mixing accuracy ±1%) uniformly mixes modified HDPE, anti-static agents, oil-resistant additives and other materials to ensure the uniform performance of the fuel tank. For multi-layer co-extrusion fuel tanks, independent raw material processing devices are configured for each layer of materials to avoid cross-contamination.
- Exhaust System: A high-efficiency exhaust system is set on the barrel, head and mold to discharge air, volatile substances and harmful gases generated during the plasticization of modified raw materials, avoid bubbles inside the fuel tank, ensure uniform wall thickness and dense structure of the fuel tank, and improve oil resistance and structural strength. The exhaust gas is treated by a purification device (purification efficiency ≥95%) before emission, meeting environmental protection requirements.
- Safety Protection System: Equipped with a complete safety protection device to meet the safety production requirements of the automotive industry. Protective railings, light curtains and emergency stop buttons are set in the clamping area, head area and feeding area to avoid operators contacting high-temperature melt, moving parts and high-pressure gas, ensuring production safety; The high-pressure blowing system and hydraulic system are equipped with pressure protection devices to prevent equipment damage or safety accidents caused by excessive pressure; The electrical system adopts explosion-proof design to avoid fire and explosion hazards caused by static electricity generated during production (especially for fuel tank production involving flammable raw materials).
- Environmental Protection and Energy Saving: The equipment meets national environmental protection standards, reducing waste gas, noise and waste emissions (noise controlled below 80dB, lower than that of water tank production equipment); Adopt energy-saving heating (electromagnetic induction heating, thermal efficiency ≥90%), cooling systems and variable frequency motors to reduce energy consumption. For example, the average power consumption of passenger car fuel tank models is controlled at 150-220kw, and that of commercial vehicle fuel tank models is controlled at 200-300kw, improving production economy. At the same time, the waste flash and defective products generated during production can be recycled and reused (recycling ratio ≤20%, to avoid affecting the performance of fuel tanks).
VI. Other Special Requirements
- Vehicle Type Adaptability: The equipment should be able to flexibly adjust parameters according to the fuel tank specifications of different vehicle types (passenger cars, commercial vehicles, new energy vehicles), compatible with the production of fuel tanks of different capacities (50L-500L) and shapes (irregular shapes adapted to automobile chassis). For example, the passenger car fuel tank model can be compatible with 50-80L fuel tanks, and the production efficiency is adjusted according to the capacity (20-25 pieces/hour for 50L fuel tanks, 15-20 pieces/hour for 80L fuel tanks); The commercial vehicle fuel tank model can be compatible with 100-500L fuel tanks, with a production efficiency of 8-12 pieces/hour, improving equipment utilization. For new energy vehicle fuel tanks (such as hydrogen fuel cell hydrogen storage tanks), the equipment can be adapted to special raw materials and molding processes.
- Special Performance Adaptability: Automobile fuel tanks need to meet strict automotive industry standards (such as GB 18296-2019 “Safety Performance Requirements and Test Methods for Automobile Fuel Tanks”, EU REACH and US EPA standards). The extrusion blow molding machine must be compatible with these standards, and the produced fuel tanks can pass tests such as oil resistance, leakage prevention, impact resistance, high and low temperature resistance and static resistance; If producing multi-layer barrier fuel tanks, the equipment must ensure the bonding strength between layers (bonding strength ≥1.5MPa) to avoid layer separation; For lightweight fuel tanks, the equipment can realize precise control of thin-wall molding (minimum wall thickness ≥1.2mm) while ensuring strength.
In summary, the core requirements of Automotive Fuel Tank production for extrusion blow molding machines are “precision, stability, safety and adaptability”. Compared with ordinary water tank production, it has higher requirements on plasticizing quality, molding precision, leakage prevention performance and safety protection. It is necessary to ensure the dimensional accuracy, structural strength, oil resistance and leakage prevention performance of the fuel tank through reasonable configuration of screw, head and clamping systems, precise parameter control, and complete auxiliary systems, meet the strict standards of the automotive industry, and realize stable mass production. At the same time, it should be compatible with fuel tanks of different vehicle types and specifications, improving production efficiency and product qualification rate.
