As core equipment for the molding of hollow plastic products, blow molding machines are mainly classified based on parison manufacturing processes and molding principles. The mainstream types include three categories: extrusion blow molding machines, injection blow molding machines, and stretch blow molding machines, while special-structure blow molding machines are designed for customized scenario requirements. Various types of machines have significant differences in working principles, technical characteristics, application scenarios, cost control, etc. The following is a detailed comparison from multiple dimensions to provide a reference for equipment selection.

I. Detailed Description of Core Characteristics of Mainstream Blow Molding Machine Types

(I) Extrusion Blow Molding Machine (EBM)

Extrusion blow molding machines are currently the most widely used models. Their core structure is a combination of an extruder and a blow molding mechanism, equipped with key components such as a parison die, clamping mechanism, and thickness control system. Its working principle is as follows: thermoplastic plastic is melted and plasticized by the extruder, then extruded into a continuous tubular parison through the head die. During the extrusion process, the die gap adjustment and thickness control system can work synergistically to accurately control the wall thickness of each part of the parison; when the parison reaches the predetermined length (positioned by a photoelectric sensor or encoder), the clamping mechanism closes quickly to clamp and cut both ends of the parison. Subsequently, compressed air of 0.2-0.8MPa is injected into the parison through an air blowing needle, making the plastic parison inflate and cling to the inner wall of the mold. After cooling and shaping, the clamping mechanism opens, and the product is demolded by an ejection device to finally obtain the hollow product. According to the movement mode of the clamping mechanism, extrusion blow molding machines can be divided into translational type, rotary type, accumulator type, etc. Among them, the accumulator type is more suitable for the production of large thick-walled products because it can extrude large-volume parisons instantaneously.

In terms of technical characteristics, extrusion blow molding machines have strong versatility, which can adapt to various blow molding grade plastics such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), and polyvinyl alcohol (PVA). They can produce various hollow products with a volume range from 2.5ml (small daily chemical bottles) to 10⁴L (large water storage tanks), and are especially good at manufacturing large containers such as chemical drums, water storage tanks, automotive fuel tanks, and large hollow pallets. Its core advantages are: first, the mold development cycle is short (usually 20-45 days) and the cost is relatively low (the cost of a single set of molds is about 30,000-200,000 yuan), which is more suitable for small-batch and multi-variety production compared with other models; second, the product appearance design has a high degree of freedom, and complex products such as flat bottles, handle-equipped bottles, and irregularly shaped hollow parts can be produced through special-shaped dies. In addition, 2-9 layer co-extrusion technology can be used to achieve special packaging requirements such as high barrier properties, light protection, and fresh-keeping (for example, multi-layer co-extrusion pesticide bottles can block solvent penetration); third, the equipment operation threshold is low, and the maintenance cost is controllable. The limitations are manifested in: the products inevitably have parting lines (which need subsequent grinding treatment), the dimensional accuracy of the bottle mouth is relatively poor (the tolerance is usually ±0.1-0.3mm), 20%-30% of scrap will be generated in conventional production (mainly from the cut part of the parison), which needs to be recycled and reused, and it is difficult to produce thin-walled and high-precision products.

(II) Injection Blow Molding Machine (IBM)

An injection blow molding machine is composed of an injection molding mechanism (including an injection screw, barrel, and injection mold) and a blow molding mechanism (blow mold, air blowing system). The mainstream models are three-station (injection-blowing-demolding) or four-station (injection-cooling-blowing-demolding) rotary equipment. The core drive method is mostly hydraulic drive or electro-hydraulic hybrid drive, with high-precision positioning and synchronous control functions. Its core process is divided into four steps: the first step is resin plasticization and melting, where the plastic is heated to a molten state by the injection screw (the temperature is usually 200-280℃, adjusted according to the material); the second step is injection molding of the parison, where the molten plastic is injected into the space between the mandrel and the mold cavity of the parison mold at high pressure to form a tubular parison with a bottle mouth structure (the bottle mouth is formed in one step with high precision); the third step is transfer and blowing, where the mandrel with the high-temperature parison is transferred to the blowing station through the rotary mechanism. After clamping, compressed air of 0.3-1.0MPa is injected into the mandrel to make the parison inflate radially and cling to the inner wall of the blow mold; the fourth step is cooling and demolding, where the product is cooled and shaped by the mold cooling system (the water temperature is usually 15-25℃), then the mold is opened and the finished product is taken out. Compared with extrusion blow molding, its core difference is that the parison is formed by injection molding, so the dimensional accuracy and wall thickness uniformity are easier to control.

The core advantages of this model are extremely high product precision. The dimensional tolerance of the bottle mouth and thread part can be controlled within ±0.02-0.05mm, the sealing performance is excellent (it can be directly adapted to standard bottle cap sealing), the surface is smooth and flawless (no parting line), the raw material utilization rate is as high as 98% or more, almost no scrap is generated, no subsequent processing is required, and it can meet the cleanliness requirements of the food and pharmaceutical industries (can be equipped with clean room-adapted models). It is suitable for the production of small-volume, high-precision hollow products, with a common volume range of 5-300ml. Typical products include medical oral liquid bottles, antibiotic bottles, cosmetic essence bottles, food-grade reagent bottles and other products with strict requirements on cleanliness, sealing performance and dimensional consistency. However, the limitations are relatively obvious: first, the capacity is limited. Due to the limitation of the injection parison molding capacity, it is difficult to produce products larger than 300ml, and it is impossible to form special-shaped bottles, flat bottles and other complex-shaped products; second, the mold cost is high and the development cycle is long. The cost of a set of injection blow molding molds (including parison mold and blow mold) is usually 200,000-600,000 yuan, and the development cycle is 45-90 days; third, the production efficiency is lower than that of extrusion blow molding machines. The output of conventional single-cavity models is 3,000-8,000 pieces per hour. Although the output can be increased through multi-cavity design, it will further increase the equipment and mold investment; fourth, it has high requirements on the fluidity of raw materials, and is only suitable for blow molding grade resins with good fluidity such as PE, PP, PET, and PS.

(III) Stretch Blow Molding Machine (SBM)

Stretch blow molding machines are high-performance models developed on the basis of extrusion or injection parisons. The core lies in improving product performance through “biaxial stretching”. They can be divided into two categories: extrusion stretch blow molding (EBSM) and injection stretch blow molding (IBBM). Among them, injection stretch blow molding is more widely used due to its higher precision. Its core process is to add an axial stretching step before blowing, so that the parison realizes synchronous axial and radial stretching within the glass transition temperature range (such as 80-120℃ for PET). The stretching ratio is usually 2-4 times in the axial direction and 2-5 times in the radial direction. Through biaxial stretching, the plastic molecular chains are oriented and arranged, which significantly improves the mechanical properties and transparency of the product. Its detailed workflow is as follows: the first step is preform preparation. Extrusion stretch blow molding produces tubular parisons through an extruder and then cuts them into sections; injection stretch blow molding produces preforms with bottle mouths through injection molding process (the precision is equivalent to that of injection blow molding parisons); the second step is preform heating. The preforms are sent to a heating furnace, and the heating temperature is accurately controlled by infrared heating tubes to ensure uniform temperature of each part of the preforms (temperature difference ≤±2℃), so as to avoid uneven thickness or damage during stretching; the third step is biaxial stretching. Axial stretching is performed by a stretching rod, and at the same time, compressed air is injected to realize radial blowing. The stretching and blowing actions need to be synchronized and coordinated (synchronization precision ≤0.1s); the fourth step is cooling and demolding. The inflated products are quickly cooled by the mold (cooling time is usually 3-8 seconds) and shaped, then demolded to obtain the finished products. The mainstream models are mostly fully automatic continuous production lines, integrating full-process automatic functions such as preform feeding, heating, stretch blowing, finished product inspection, and blanking.

The technical advantages are reflected in the excellent comprehensive performance of the products: after biaxial stretching, the impact strength of the products is increased by 2-3 times, the tensile strength is increased by 1.5-2 times, the barrier properties (oxygen barrier and water barrier) are increased by 3-5 times, and at the same time, the transparency is high (haze ≤2%), the gloss is good, and lightweight production can be realized (reducing weight by 10%-30% compared with ordinary blow molding products), which significantly reduces the raw material cost. This model is especially suitable for polyester (PET) material molding, and can also adapt to stretch-grade materials such as PP and PVC. It is a special equipment for food packaging containers such as carbonated beverage bottles, mineral water bottles, juice bottles, and edible oil bottles. Among them, the production of PET beverage bottles almost all uses injection stretch blow molding machines. In addition, this model has an adjustable stretching ratio function (axial and radial stretching ratios can be adjusted independently), which can adapt to the production of products with different performance requirements (for example, carbonated beverage bottles need higher tensile strength, and juice bottles need higher barrier properties). It has a high degree of automation (the automation rate of the production line ≥95%), and is usually integrated with automatic part taking, finished product inspection (such as wall thickness inspection, liquid leakage inspection), and defective product rejection systems, which is suitable for large-scale continuous production (the output of a single production line can reach 10,000-60,000 pieces per hour). The limitations are high equipment complexity and large initial investment (the investment of a single injection stretch blow molding production line is usually 800,000-5,000,000 yuan), strict requirements on raw material performance (special stretch-grade resin is required, such as PET chips with a viscosity of 0.72-0.85dL/g), high difficulty in process parameter control (temperature, stretching speed, and blowing pressure need to be accurately matched), and it is mainly suitable for the production of standardized products of specific materials, and difficult to adapt to complex-shaped or large-scale products.

(IV) Special-Structure Blow Molding Machines

This type of machine is designed for special raw materials, special-structure products or extreme working conditions, and belongs to customized models. The core includes sheet blow molding machines, rotary blow molding machines (rotational molding machines), multi-layer co-extrusion blow molding machines, large hollow blow molding machines (volume >10m³), special-shaped structure blow molding machines, etc. Its structure and process have a high degree of customization according to production needs, and usually need to be equipped with special molds and auxiliary equipment. For example, the rotary blow molding machine (also known as rotational molding machine), its core process is “rotational molding”. After adding plastic powder or molten material into the mold, the mold rotates and heats around two vertical axes at the same time, so that the plastic adheres to the inner wall of the mold uniformly under the action of centrifugal force for molding, without the need for parison extrusion or injection steps. It is especially suitable for the production of large complex-structure products such as automotive fuel tanks, hydrogen storage bottle liners, large amusement facility components, and marine hollow containers. Through rotation, the material is evenly distributed, which can ensure the uniformity of product wall thickness (tolerance ≤±5%), and can form integrally molded complex structures (such as products with multiple interfaces and internal reinforcing ribs); the multi-layer co-extrusion blow molding machine plasticizes different materials through multiple extruders respectively, and composites them into multi-layer parisons through a special co-extrusion die, which can realize 3-9 layer composite material molding (such as PE/PA/PE, PET/EVOH/PET and other composite structures), significantly improving the barrier properties, corrosion resistance or light protection performance of the products. It is suitable for food fresh-keeping packaging (such as meat vacuum packaging trays), medical high-barrier packaging, chemical corrosive liquid packaging and other scenarios; the large hollow blow molding machine (volume >10m³) is designed for ultra-large capacity storage needs, using an ultra-large accumulator die and a heavy-duty clamping mechanism, with a clamping force of 1000-5000kN, suitable for the production of large water storage tanks, chemical reactor liners, sewage treatment equipment, etc. The core advantage of this type of machine is strong adaptability, which can meet the high-end customized production needs that conventional models cannot achieve. The product performance can be accurately matched to special working conditions (such as high temperature resistance, high pressure resistance, high barrier properties); the limitations are high equipment cost (the investment of customized models is usually more than 5,000,000 yuan), poor versatility, a set of equipment can only be adapted to the production of a few types of products, high mold development difficulty and long cycle (usually 90-180 days), and high requirements on the technical level of operators, which is only suitable for large-scale production or high-end customized production in specific fields.

II. Comparative Analysis of Core Dimensions of Different Types of Blow Molding Machines (Paragraph Version)

In terms of core processes, the extrusion blow molding machine adopts the mode of extrusion parison + blowing and shaping, and can be equipped with a closed-loop thickness control system, among which the accumulator type can produce large parisons; the injection blow molding machine completes the molding through injection parison (with bottle mouth) + transfer and blowing, the mainstream is three/four-station rotary equipment with high synchronization precision; the core of the stretch blow molding machine is preform heating + biaxial stretching + blowing and shaping, and the key lies in the synchronous coordination of stretching and blowing actions; the special-structure blow molding machine adopts customized processes, such as rotational molding, multi-layer co-extrusion, ultra-large volume molding, etc., to accurately adapt to special production needs.

In terms of product precision, the extrusion blow molding machine has medium precision, the bottle mouth tolerance is ±0.1-0.3mm, there is a parting line, and the wall thickness tolerance is ±8%-12%; the injection blow molding machine has the highest precision, the bottle mouth tolerance can be controlled within ±0.02-0.05mm, no parting line, and the wall thickness tolerance is only ±3%-5%; the stretch blow molding machine has high precision, the bottle mouth tolerance is ±0.03-0.08mm, the wall thickness uniformity is good (tolerance ±4%-6%), and the product transparency is high; the precision of the special-structure blow molding machine depends on customized needs, the wall thickness tolerance of large products is ±5%-8%, which can accurately match special performance requirements.

The applicable volume range varies significantly. The extrusion blow molding machine covers 2.5ml-10⁴L, and is especially good at producing large products >200L; the injection blow molding machine is limited to small-volume products of 5-300ml; the stretch blow molding machine is mainly for small and medium-sized standardized products of 50ml-2L; the special-structure blow molding machine is customized on demand, with a volume covering 0.5L-100m³, and can produce large complex products.

Typical application scenarios have their own focuses. Extrusion blow molding machines are mostly used for chemical drums (200L), 1-10m³ water storage tanks, automotive fuel tanks, daily chemical packaging bottles (such as laundry detergent bottles) and hollow pallets; injection blow molding machines are suitable for small-volume products with high requirements on cleanliness and sealing performance, such as medical oral liquid bottles, antibiotic bottles, cosmetic essence bottles, food-grade reagent bottles, and small perfume bottles; stretch blow molding machines are special production equipment for PET carbonated beverage bottles, mineral water bottles, juice bottles, edible oil bottles, and food fresh-keeping boxes; special-structure blow molding machines are used for high-end customized scenarios such as automotive structural parts (such as instrument panel hollow components), hydrogen storage bottle liners, >10m³ large water storage tanks, and high-barrier pesticide bottles.

In terms of raw material adaptability, extrusion blow molding machines have the widest adaptability, which can process various blow molding grade plastics such as LDPE, HDPE, PP, PVC, and PVA, and have low requirements on raw material fluidity; injection blow molding machines have medium adaptability, mainly suitable for blow molding grade resins with good fluidity such as PE, PP, PET, and PS; stretch blow molding machines have a narrow adaptability range, mainly focusing on stretch-grade PET, PP, and PVC, among which the viscosity of PET chips needs to reach 0.72-0.85dL/g; special-structure blow molding machines are suitable for specific materials such as engineering plastics, composite materials, and powder plastics, which are completely matched according to product needs.

In terms of equipment cost, extrusion blow molding machines are at a low-medium level, with conventional models of 100,000-800,000 yuan, and large accumulator models of 800,000-3,000,000 yuan; injection blow molding machines are at a medium-high cost, with single-cavity models of 300,000-1,200,000 yuan, and multi-cavity models of 1,200,000-3,000,000 yuan; stretch blow molding machines have high costs, with a single production line of 800,000-5,000,000 yuan, and high-speed production lines (>40,000 pieces per hour) need 5,000,000-15,000,000 yuan; special-structure blow molding machines have high-extremely high costs, and the investment of customized models is usually 5,000,000-50,000,000 yuan, increasing with production capacity and complexity.

The production efficiency varies. Extrusion blow molding machines have high efficiency. The output of small-volume products of conventional models is 500-5,000 pieces per hour, and that of large products is 10-50 pieces per hour; injection blow molding machines have medium efficiency. The output of single-cavity models is 3,000-8,000 pieces per hour, and that of 8-cavity multi-cavity models can be increased to 8,000-20,000 pieces per hour; stretch blow molding machines have high efficiency. The output of a single production line is 10,000-60,000 pieces per hour, with automatic continuous production and a defective product rate of <0.5%; special-structure blow molding machines have medium efficiency, with large products of 1-10 pieces per hour and standardized customized products of 500-2,000 pieces per hour.

The core advantages have their own focuses. Extrusion blow molding machines have strong versatility, low mold cost (30,000-200,000 yuan), flexible product shapes, can produce large products, and are easy to maintain; injection blow molding machines have high precision, good sealing performance, high raw material utilization rate ≥98%, no subsequent processing, and are suitable for clean production; the products produced by stretch blow molding machines have high strength, good barrier properties, light weight and high transparency, high automation degree, and are suitable for large-scale production; special-structure blow molding machines are suitable for special needs such as complex structures, ultra-large volumes, and high barriers, with product performance accurately matched and integrally molded without splicing.

The main limitations are also obvious. Extrusion blow molding machines have 20%-30% of scrap, limited bottle mouth precision, and difficulty in producing thin-walled and high-precision products; injection blow molding machines have limited capacity, high mold cost (200,000-600,000 yuan), long development cycle, and lower production efficiency than stretch blow molding machines; stretch blow molding machines have large equipment investment, limited raw materials, complex process control, and are only suitable for standardized small and medium-sized products; special-structure blow molding machines have poor versatility, extremely high equipment and mold costs, long development cycle (90-180 days), and high requirements on the technical level of operators.

In terms of energy consumption level, extrusion blow molding machines are medium, with a unit product energy consumption of 0.8-1.5kWh/kg; injection blow molding machines are medium-high, with a unit product energy consumption of 1.2-2.0kWh/kg; stretch blow molding machines have high energy consumption, with a unit product energy consumption of 1.5-2.5kWh/kg (including heating and stretching energy consumption); special-structure blow molding machines have high energy consumption, with a unit product energy consumption of 2.0-5.0kWh/kg for large/complex products.

The maintenance difficulty increases gradually. Extrusion blow molding machines have low maintenance difficulty. The maintenance of core components (extruder, clamping mechanism) is simple, with few wearing parts, and can be operated by ordinary technicians; injection blow molding machines have medium maintenance difficulty, which need to maintain both injection and blow molding systems at the same time. The rotary mechanism has high precision requirements and needs professional technicians; stretch blow molding machines have medium-high maintenance difficulty. The maintenance of heating system, stretching mechanism and synchronous control system is complex, and a professional operation and maintenance team is needed; special-structure blow molding machines have high maintenance difficulty, with many customized components, no general maintenance standards, and need special operation and maintenance support from equipment manufacturers.

III. Core Suggestions for Selection

1. If producing large hollow products (such as >200L chemical drums, 1-10m³ water storage tanks, automotive fuel tanks) or needing to flexibly adjust product shapes (such as handle-equipped, flat, irregular special-shaped parts), priority should be given to extrusion blow molding machines. Among them, conventional translational extrusion blow molding machines (equipment cost 100,000-500,000 yuan) can be selected for small-batch and multi-variety production, and accumulator extrusion blow molding machines (clamping force ≥1000kN) are recommended for large-scale production of large thick-walled products; if it is necessary to produce high-barrier products (such as pesticide bottles, chemical solvent bottles), multi-layer co-extrusion dies can be equipped to realize 2-5 layer composite molding and improve barrier performance. At the same time, it is necessary to equip recycling and granulation equipment to process 20%-30% of the scrap and reduce raw material loss.

2. When producing small-volume (5-300ml), high-precision sealed products (such as medical oral liquid bottles, antibiotic bottles, cosmetic essence bottles), especially when needing to meet the cleanliness requirements (dust-free, impurity-free) of the food and pharmaceutical industries, injection blow molding machines are the best choice. It is recommended to select the number of stations and cavities according to production capacity requirements: three-station single-cavity models can be selected for small-batch production (<500,000 pieces/month), and four-station multi-cavity (4-8 cavities) models can be selected for large-scale production (>2,000,000 pieces/month) to increase the output to 8,000-20,000 pieces per hour. When selecting models, focus on the positioning accuracy (≤0.02mm) and clean design (such as stainless steel body, sealed barrel) of the equipment, and at the same time, match high-fluidity blow molding grade resins to ensure product precision and surface quality.

3. For large-scale production of lightweight, high-strength, high-transparency standardized packaging containers such as PET beverage bottles, mineral water bottles, and juice bottles (production capacity >10,000,000 pieces/month), injection stretch blow molding machine production lines should be selected. When selecting models, the production line speed (10,000-60,000 pieces per hour) should be selected according to the target production capacity, focusing on the stretching ratio adjustment range (2-4 times in axial direction, 2-5 times in radial direction), the temperature uniformity of the heating furnace (temperature difference ≤±2℃) and the synchronous control precision (≤0.1s); if producing high-pressure containers such as carbonated beverage bottles, high tensile strength models should be selected to ensure the pressure resistance of the products (≥2.0MPa); at the same time, special stretch-grade PET chips (viscosity 0.72-0.85dL/g) should be matched to reduce the defective product rate.

4. For high-end customized scenarios such as automotive structural parts (such as instrument panel hollow components), hydrogen storage bottle liners, large amusement facility components, >10m³ water storage tanks, and high-barrier pesticide bottles, special-structure blow molding machines are required. Among them, rotary blow molding machines are recommended for large complex-structure products (such as automotive fuel tanks) to ensure uniform wall thickness and integral molding; multi-layer co-extrusion blow molding machines (3-9 layers) are selected for high-barrier packaging products, and composite structures (such as PE/PA/PE oxygen barrier, PET/EVOH/PET water barrier) are matched according to barrier requirements; large hollow blow molding machines are selected for ultra-large volume products (>10m³), focusing on clamping force (≥2000kN) and accumulator capacity. For this type of machine, it is necessary to communicate customized requirements with equipment manufacturers in advance, reserve sufficient mold development and equipment commissioning cycles (90-180 days), and equip professional operation and maintenance teams.

In summary, the adaptability of different types of blow molding machines is jointly determined by multiple factors such as product requirements (capacity, precision, performance), production scale, cost budget, and industry standards. In actual selection, it is necessary to first clarify the core needs: if pursuing cost and versatility, priority should be given to extrusion blow molding machines; if pursuing precision and cleanliness, select injection blow molding machines; if pursuing large-scale standardization and high performance, select stretch blow molding machines; if adapting to special scenarios, select customized special-structure blow molding machines. At the same time, with the advancement of intelligent manufacturing and green manufacturing trends, all-electric and servo energy-saving models have become the industry development direction (all-electric models reduce energy consumption by 20%-30% compared with traditional hydraulic models). When selecting models, comprehensive consideration can be given to energy-saving requirements, automation needs (such as integrating MES production management system) and long-term operation and maintenance costs. In addition, attention should also be paid to the technical support capabilities of equipment manufacturers. Especially for special-structure or high-precision models, perfect after-sales and operation and maintenance services are crucial to ensuring production stability.