As a widely used packaging product, HDPE bottles (High-Density Polyethylene Bottles) are mainly used for storing food, daily chemicals, pharmaceuticals, cosmetics, and small-volume chemicals (such as reagents, additives). They have the advantages of light weight, good toughness, corrosion resistance, non-toxicity, tastelessness, and recyclability. According to the application and capacity needs, they can be divided into small HDPE bottles (100mL-500mL), medium HDPE bottles (500mL-2L), and large HDPE bottles (2L-5L), with low load-bearing requirements (dynamic load 0.05t-0.2t, static load 0.1t-0.5t). HDPE bottles must meet core performance requirements such as excellent hygiene, reliable sealing, uniform wall thickness, light weight, impact resistance, and compliance with industry hygiene and safety standards. The production process puts strict requirements on the extrusion stability, molding precision, hygiene performance and production efficiency of extrusion blow molding machines. Specifically, it can be divided into the following core dimensions, taking into account both equipment performance and the special hygiene and lightweight needs of HDPE bottle production.
I. Extrusion System: Ensuring Hygienic Melt and Uniform Plasticization
The extrusion system is the core of the extrusion blow molding machine for HDPE bottle production, which directly determines the plasticizing effect of food-grade/medical-grade HDPE raw materials, the uniformity of the melt, and the final hygiene, strength and sealing performance of HDPE bottles. Due to the small volume, thin wall and high hygiene requirements of HDPE bottles, the extrusion system must meet strict standards for hygiene, stability and precision.
1. Screw Configuration Adapted to Food-Grade/Medical-Grade HDPE Raw Materials
The mainstream raw materials for HDPE bottle production are food-grade, medical-grade or daily chemical-grade HDPE, which require non-toxicity, tastelessness, no impurities and good processability. Some special HDPE bottles (such as those for oil or corrosive small-volume chemicals) adopt modified HDPE with enhanced oil resistance or corrosion resistance. Most HDPE bottles are single-layer structure, and a small number of high-end products (such as barrier bottles for edible oil) adopt double-layer co-extrusion structure. Therefore, the extruder screw must be adaptively designed:
- Screw Parameters: The length-diameter ratio (L/D) should be controlled between 28:1 and 32:1, which is suitable for the plasticization of HDPE raw materials, ensuring sufficient plasticization without melt degradation, and ensuring that the melt has excellent toughness and uniformity; The screw diameter is adjusted according to the HDPE bottle capacity. A screw of Φ50-65mm can be selected for small HDPE bottles (100mL-500mL), a screw of Φ65-80mm for medium bottles (500mL-2L), and a screw of Φ80-90mm for large bottles (2L-5L), with corresponding plasticizing capacity (100-300kg/h) to meet the melt supply needs of HDPE bottles of different specifications and ensure high-efficiency mass production.
- Screw Structure: A gradual compression ratio screw with mixing section is adopted, and the compression ratio is controlled between 3.5:1 and 4.5:1. The mixing section is added to enhance the dispersion effect of additives (such as anti-oxidants, anti-UV agents) and avoid uneven distribution of additives leading to reduced performance of HDPE bottles; For double-layer co-extrusion HDPE bottles (such as HDPE + EVOH barrier layer), two sets of screws are configured to realize synchronous extrusion of different functional layers, ensure tight bonding between layers (bonding strength ≥1.2MPa), and prevent material penetration. The screw adopts a low-shear design to avoid HDPE degradation caused by excessive shearing, which affects the hygiene and toughness of the bottle.
- Screw Material: High-wear-resistant, corrosion-resistant and food-grade alloy material (such as 38CrMoAlA) is selected, and the surface is subjected to deep nitriding treatment (nitriding layer thickness ≥0.5mm) and polishing, with a surface roughness Ra ≤0.4μm, to avoid raw material contamination caused by screw wear and ensure the hygiene performance of HDPE bottles. The screw and barrel contact surface is smooth and free of dead corners, avoiding raw material retention and degradation.
2. Barrel and Head Design Meet Hygiene and Thin-Wall 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℃. The temperature of each section can be accurately adjusted according to the performance of HDPE (the barrel temperature is controlled at 160-200℃), 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 ≤1mm/m) —— which is crucial for the wall thickness uniformity and appearance quality of thin-wall HDPE bottles.
- Head Structure: For single-layer HDPE bottles, a small-sized center-fed accumulator head with high-precision flow channel is adopted, and the accumulator capacity is adjusted according to the weight of HDPE bottles (for example, the accumulator capacity of 5L large HDPE bottle model needs to reach 5-30L), which can stably output thin-wall parison (parison thickness 1-3mm) and avoid parison fluctuation, deflection and uneven thickness; For double-layer co-extrusion HDPE bottles, a double-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 ±0.5%), to ensure the uniformity of the thickness of each functional layer (the thickness of EVOH barrier layer is controlled at 0.1-0.2mm). The die gap is driven by a servo motor with high precision (adjustment accuracy ±0.005mm), 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 the bottle mouth, bottle body and bottom (key sealing parts) during blow molding, and preset corresponding wall thickness parameters to improve the structural strength and sealing performance of HDPE bottles. The head flow channel is polished with high precision (Ra ≤0.4μm) and free of dead corners, ensuring no raw material retention and meeting hygiene requirements.
II. Blow Molding System: Ensuring Sealing Performance and Thin-Wall Uniformity
HDPE bottles are mostly used for storing liquid or powdery products, and have extremely strict requirements on sealing performance, wall thickness uniformity, appearance quality and dimensional precision. The blow molding system, as the core link of molding, must meet the requirements of precise molding, uniform thin-wall, no defects and reliable sealing, while ensuring high production efficiency.
1. Parison Control Accuracy Meets Thin-Wall and Hygiene Standards
HDPE bottles have extremely strict requirements on wall thickness uniformity (the deviation should be controlled within ±0.05mm). Uneven wall thickness will lead to weak local structure of the bottle, uneven cooling shrinkage, easy deformation, leakage and breakage, and affect the service life and appearance of the bottle. Therefore, the parison control must meet:
- Equipped with a high-precision parison wall thickness control system (up to 100 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 thin-wall parisons, 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 different parts of the HDPE bottle (bottle mouth, bottle body, bottom) is ≤0.03mm.
- The parison weight is accurately controlled (control accuracy ±0.3%), and the maximum parison weight should match the HDPE bottle weight (for example, the parison weight of 5L HDPE bottle can reach 500-800g, and that of 100mL small bottle is only 10-20g), to avoid insufficient parison weight leading to too thin wall thickness and insufficient strength of the bottle, or excessive weight causing raw material waste and affecting the lightweight of the bottle.
2. Stable and High-Precision Blowing System
- Blowing Pressure and Flow Rate: Adjust according to the size, wall thickness and sealing requirements of HDPE bottles. The blowing pressure of small HDPE bottles (100mL-500mL) is controlled at 0.3-0.5MPa, and that of large HDPE bottles (2L-5L) needs to be increased to 0.5-0.6MPa. 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 bottle mouth, thread and sealing groove (key parts) are fully formed; The blowing flow rate is stable (flow rate fluctuation ≤3%), to avoid HDPE bottle defects such as depression, bulge, pinhole and incomplete thread caused by pressure fluctuation. The blow-up ratio is controlled between 1.8:1 and 3:1, to adapt to the cylindrical, square or special shape of HDPE bottles while ensuring the thin-wall, strength and sealing performance.
- Blowing Timing and Cooling: The blowing timing is accurately matched with the parison extrusion speed (response time ≤0.08s), 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 food-grade dry, clean, oil-free and dust-free compressed air (moisture content ≤0.01%, oil content ≤0.001%), to avoid bubbles, oil stains and scratches on the inner wall of the HDPE bottle caused by moisture, oil stains and impurities in the air, which affect the hygiene, sealing performance and appearance quality. After blowing, air cooling is mainly adopted, and auxiliary water cooling can be used for large HDPE bottles to accelerate the cooling speed, ensure the bottle shape is fixed quickly, and improve production efficiency.
3. Mold Adaptability and Efficient Cooling System
- Mold Adaptability: The mold size is accurately matched with the designed size of the HDPE bottle (dimensional tolerance ±0.05mm), which meets the packaging size standards for food, daily chemicals and pharmaceuticals. The mold cavity surface is polished with high precision (surface roughness Ra ≤0.6μm), smooth and free of burrs, scratches and dead corners, to ensure the HDPE bottle has a flat surface, transparent or uniform appearance and no defects; The mold is designed with a built-in thread and sealing groove (consistent with the bottle cap specification) to ensure the sealing performance between the bottle body and the cap; The mold has excellent sealing performance (air leakage rate ≤0.005L/min) to avoid air leakage during blow molding, leading to incomplete HDPE bottle molding; The equipment should be compatible with HDPE bottle molds of different capacities (100mL-5L) and shapes (cylindrical, square, special-shaped), with a mold thickness adjustment range of 300-800mm to improve equipment versatility. The mold material adopts food-grade corrosion-resistant alloy, and the cavity surface is treated with anti-sticking technology to avoid material adhesion and ensure the hygiene and appearance of the bottle.
- Cooling System: A multi-circuit, high-efficiency cooling system is adopted to independently control the temperature of different areas of the mold (especially the bottle mouth, thread and bottom), and the temperature difference on the mold surface is controlled within ±2℃, to avoid HDPE bottle shrinkage, deformation and thread damage caused by uneven cooling (deformation will affect the sealing performance); The cooling water circuit is designed according to the HDPE bottle structure, with dense cooling points in thick-walled parts (bottle bottom, bottle mouth) and uniform layout in thin-walled parts (bottle body). The cooling efficiency meets the high-frequency production cycle requirements. The cooling time of small HDPE bottles is controlled at 10-30s, and that of large HDPE bottles needs to be extended to 30-60s, to ensure that the HDPE bottle is quickly solidified after molding, improve production efficiency (80-200 pieces/hour for small bottles, 30-80 pieces/hour for large bottles), and ensure the dimensional stability, structural strength and sealing performance of the HDPE bottle. The mold is also equipped with a temperature feedback device to realize dynamic adjustment of cooling temperature.
III. Clamping System: Ensuring Molding Stability and High Efficiency
HDPE bottle molds are small in size, high in precision, and require high production frequency (mass production). The clamping system is responsible for opening, closing and locking the mold, and its clamping force, stroke and precision directly affect the HDPE bottle molding quality, production efficiency and mold service life.
- Clamping Force: Determined according to the HDPE bottle size, wall thickness and blowing pressure. The clamping force of small HDPE bottle models needs to reach 300-600KN, and that of large HDPE bottle models (2L-5L) should not be less than 600-800KN, to ensure that the mold does not loosen or overflow during blow molding, and avoid HDPE bottle defects such as flash, burr and dimensional deviation (flash will affect the sealing performance and appearance). The clamping force is adjustable (adjustment accuracy ±5KN) to adapt to HDPE bottles of different specifications.
- Clamping Stroke and Template: The clamping stroke is designed according to the maximum mold size and HDPE bottle shape, generally 500-1200mm, to meet the needs of mold opening, closing and HDPE bottle taking out. The template size is matched with the mold (for example, 800×1000mm template is suitable for 5L HDPE bottle molds), and the template parallelism error is controlled within 0.03mm, to avoid wall thickness deviation of the HDPE bottle or mold damage caused by uneven force on the mold during clamping; The mold thickness adjustment range is 300-800mm, which is compatible with HDPE bottle molds of different thicknesses and capacities.
- Operational Convenience and Safety: Equipped with automatic clamping, demolding and mold changing mechanisms. The automatic demolding mechanism is designed according to the HDPE bottle shape (with soft clamping fixtures) to avoid HDPE bottle damage, scratch and deformation caused by manual demolding and reduce labor intensity; The mold changing mechanism adopts quick-change design (mold changing time ≤20min) to improve production efficiency when switching between different capacity or shape HDPE bottles. The clamping mechanism has good stability and durability, and can withstand high-frequency opening and closing actions (≥30000 times/month) for a long time, reducing the impact of equipment failures on mass 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
HDPE bottle production is large-scale mass production of packaging products, which has extremely high requirements on the consistency of product performance, dimensions, appearance and hygiene. The control system must realize precise regulation of all parameters, reduce inter-batch errors, and ensure that each HDPE bottle meets the industry standards.
- Control Accuracy: Adopt a high-precision PLC control system (such as Siemens S7-1200/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 ≤0.5%, 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 ≤0.05mm).
- 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), automatic bottle inspection and automatic packaging, reducing manual intervention (manual intervention rate ≤3%), 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 ±0.005mm), real-time monitor the wall thickness changes of the parison and HDPE bottle, 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 (vacuum detection method, detection pressure -0.08 to -0.06MPa, detection time ≥10s) and appearance inspection system, which can automatically detect unqualified products (leakage, uneven wall thickness, scratches, deformation) and remove them, ensuring the qualification rate of products (≥99.9%).
- 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 HDPE bottles, 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 food, daily chemical and pharmaceutical packaging industries.
V. Auxiliary System: Adapting to the Special Hygiene and Efficiency Needs of HDPE Bottles
In addition to the core system, the auxiliary system of the extrusion blow molding machine needs to be adaptively designed to the particularity of HDPE bottle production, especially in terms of raw material processing, hygiene protection, environmental protection and high efficiency, to ensure the smooth progress of mass production and the hygiene and performance of HDPE bottles.
- Raw Material Processing System: Equipped with high-precision food-grade raw material drying, screening and mixing devices. The food-grade/medical-grade HDPE raw materials need to be fully dried (moisture content ≤0.03%) to avoid bubbles and pinholes in the HDPE bottle caused by moisture, which affect the sealing performance and hygiene; The screening device (screen mesh size ≤100 mesh) removes impurities in the raw materials to avoid wear of screws and molds and defects of HDPE bottles, and ensure hygiene; The mixing device (mixing accuracy ±0.5%) uniformly mixes HDPE and food-grade additives (anti-oxidants, anti-UV agents) to ensure the uniform performance of the HDPE bottle. For double-layer co-extrusion HDPE bottles, independent raw material processing devices are configured for each layer of materials to avoid cross-contamination. The raw material storage and feeding system adopts closed design (stainless steel storage tank, closed conveyor) to avoid pollution of raw materials by dust, moisture and impurities, meeting hygiene requirements.
- 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 HDPE raw materials, avoid bubbles inside the HDPE bottle, ensure uniform wall thickness and dense structure of the HDPE bottle, and improve strength and sealing performance. The exhaust gas is treated by a professional purification device (purification efficiency ≥98%) before emission, meeting the environmental protection requirements and avoiding air pollution.
- Safety and Hygiene Protection System: Equipped with a complete safety and hygiene protection device to meet the safety production and hygiene requirements of food, daily chemical and pharmaceutical packaging. 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 equipment and raw material contact parts (screw, barrel, head, mold) are made of food-grade corrosion-resistant materials, and can be disassembled and cleaned easily, avoiding raw material residue and bacterial growth, meeting hygiene standards; The production area is equipped with dust removal and purification devices to ensure the cleanliness of the production environment.
- Environmental Protection and Energy Saving: The equipment meets national environmental protection standards, reducing waste gas, noise and waste emissions (noise controlled below 75dB, lower than that of other packaging production equipment); Adopt energy-saving heating (electromagnetic induction heating, thermal efficiency ≥92%), cooling systems and variable frequency motors to reduce energy consumption. For example, the average power consumption of small HDPE bottle models is controlled at 80-150kw, and that of large HDPE bottle models is controlled at 150-180kw, improving production economy. At the same time, the waste flash and defective products generated during production can be recycled and reused (recycling ratio ≤30%, to avoid affecting the hygiene and performance of HDPE bottles), reducing raw material waste.
VI. Other Special Requirements
- Capacity and Shape Adaptability: The equipment should be able to flexibly adjust parameters according to the capacity and shape requirements of HDPE bottles, compatible with the production of HDPE bottles of different capacities (100mL-5L) and shapes (cylindrical, square, oval, special-shaped). For example, the small HDPE bottle model can be compatible with 100mL-500mL bottles, and the production efficiency is adjusted according to the capacity (150-200 pieces/hour for 100mL bottles, 80-100 pieces/hour for 500mL bottles); The large HDPE bottle model can be compatible with 2L-5L bottles, with a production efficiency of 30-80 pieces/hour, improving equipment utilization. For customized HDPE bottles (such as with handles, spray nozzles, pump heads), the equipment can be adapted to special molds and molding processes.
- Compliance and Special Performance Adaptability: HDPE bottles need to meet strict international and national standards (such as FDA food-grade standard, GB 4806.1-2016 “General Safety Requirements for Food Contact Materials and Products”, GB 13113-2014 “Plastic Bottles for Food Packaging”, USP medical-grade standard). The extrusion blow molding machine must be compatible with these standards, and the produced HDPE bottles can pass tests such as hygiene, leakage prevention, impact resistance, high and low temperature resistance, tensile strength and pressure resistance; For HDPE bottles storing edible oil, the equipment must be compatible with double-layer co-extrusion technology to ensure barrier performance; For medical-grade HDPE bottles, the equipment and production environment must meet GMP standards, ensuring no pollution; For outdoor-used HDPE bottles (such as pesticide bottles), the equipment must be compatible with anti-UV modified raw materials, ensuring that the bottle does not age, crack or deform under long-term sunlight.
In summary, the core requirements of HDPE Bottle production for extrusion blow molding machines are “precision, efficiency, hygiene and consistency”. Compared with water tank, automotive fuel tank and hollow pallet production, it has higher requirements on plasticizing uniformity, thin-wall molding accuracy, hygiene performance and production efficiency, focusing on ensuring the hygiene, sealing performance, lightweight and batch consistency of HDPE bottles. It is necessary to ensure the dimensional accuracy, structural strength, hygiene and sealing performance of the HDPE bottle through reasonable configuration of screw, head and clamping systems, precise parameter control, and complete auxiliary systems, meet the strict standards of the food, daily chemical and pharmaceutical packaging industries, and realize stable and efficient mass production. At the same time, it should be compatible with HDPE bottles of different capacities and shapes, improving production efficiency and product qualification rate.
