The screw is the core component of the extrusion system of an extrusion blow molding machine (EBM machine), and its diameter is one of the most critical parameters affecting the production capacity, plasticizing effect and product quality of the equipment. For beginners in the plastic processing industry, choosing the right screw diameter is crucial to ensuring production efficiency and reducing production costs. This article will elaborate on the relationship between screw diameter and EBM machine performance, and provide practical selection suggestions based on raw material types and product requirements.
What Is the Screw Diameter of an Extrusion Blow Molding Machine?
The screw diameter of an EBM machine refers to the outer diameter of the screw (usually denoted by D, unit: mm), which is a fixed parameter of the screw and directly determines the volume of the material channel between the screw and the barrel. Common screw diameters of EBM machines on the market range from 30mm to 150mm, and different diameters are suitable for different production scenarios. It should be noted that the screw diameter is different from the inner diameter of the barrel; the gap between the screw diameter and the barrel inner diameter is small, which ensures that the raw materials can be fully sheared and plasticized.
The Impact of Screw Diameter on EBM Machine Performance
The screw diameter directly affects three core performance indicators of the EBM machine: production capacity, plasticizing quality and product size range. Understanding these impacts is the basis for rational selection.
1.Production Capacity
Production capacity is the most direct impact of screw diameter. Under the same screw speed and length-diameter ratio, the larger the screw diameter, the larger the volume of the material channel, and the more plastic raw materials that can be conveyed and plasticized per unit time, resulting in higher production capacity. For example, an EBM machine with a screw diameter of 80mm can produce about 500-800kg of products per hour, while a machine with a screw diameter of 50mm can only produce about 100-300kg per hour. It should be noted that the production capacity is not only determined by the screw diameter, but also affected by the screw speed, length-diameter ratio and raw material type.
2 Plasticizing Quality
Plasticizing quality refers to the uniformity of melting, mixing and temperature of the plastic raw materials after passing through the screw. The screw diameter affects the plasticizing quality by changing the mechanical shear force and heat transfer effect. Generally speaking, a smaller screw diameter can generate larger mechanical shear force under the same speed, which is more conducive to the melting and mixing of raw materials, and the plasticizing quality is better; a larger screw diameter has a larger material contact area with the barrel, which is more conducive to heat transfer, but the mechanical shear force per unit volume is smaller, so it is necessary to match a reasonable length-diameter ratio to ensure plasticizing quality. For example, when processing high-viscosity raw materials (such as HDPE), a smaller screw diameter can improve plasticizing uniformity; when processing low-viscosity raw materials (such as LDPE), a larger screw diameter can avoid over-shearing and decomposition of raw materials.
3 Product Size Range
The screw diameter determines the maximum and minimum size range of the parison that can be extruded, thereby limiting the size of the final product. A larger screw diameter can extrude a parison with a larger diameter and thicker wall thickness, which is suitable for producing large-sized hollow products (such as 200L chemical barrels, automotive fuel tanks); a smaller screw diameter is suitable for extruding small-diameter and thin-walled parisons, which is suitable for producing small-sized products (such as 500ml shampoo bottles, 1L edible oil barrels). If the screw diameter is too large for small products, it will lead to low production efficiency and waste of raw materials; if the screw diameter is too small for large products, it will be difficult to extrude a parison with sufficient wall thickness and diameter, resulting in product defects.
Key Factors for Choosing Screw Diameter
When choosing the screw diameter of an EBM machine, it is necessary to comprehensively consider three core factors: product size and weight, raw material type, and production capacity requirements. The following is a detailed analysis:
1 Product Size and Weight
Product size and weight are the primary factors for choosing screw diameter. It is necessary to match the screw diameter according to the maximum diameter and wall thickness of the product:
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Small-sized products: Products with a volume of less than 5L (such as small bottles, small cans) usually require a parison diameter of less than 100mm and a wall thickness of less than 2mm. It is recommended to choose a screw diameter of 30-50mm, which can ensure the uniformity of the parison wall thickness and improve production efficiency.
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Medium-sized products: Products with a volume of 5-50L (such as 20L chemical barrels, 10L edible oil barrels) require a parison diameter of 100-200mm and a wall thickness of 2-5mm. It is recommended to choose a screw diameter of 50-80mm, which can balance production capacity and plasticizing quality.
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Large-sized products: Products with a volume of more than 50L (such as 100L, 200L chemical barrels, automotive fuel tanks) require a parison diameter of more than 200mm and a wall thickness of more than 5mm. It is recommended to choose a screw diameter of 80-150mm to ensure sufficient parison output and wall thickness.
2 Raw Material Type
Different plastic raw materials have different physical and chemical properties (such as viscosity, melting point, thermal stability), which require matching screws of different diameters to ensure plasticizing quality:
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Low-density polyethylene (LDPE): It has low viscosity and good thermal stability. A larger screw diameter (50-100mm) can be chosen to improve production capacity, and over-shearing and decomposition of raw materials are not easy to occur.
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High-density polyethylene (HDPE): It has high viscosity and poor thermal conductivity. A smaller screw diameter (30-80mm) is recommended to generate larger mechanical shear force, which is conducive to uniform melting of raw materials. For large-sized products processed with HDPE, a screw with a larger length-diameter ratio can be matched to make up for the insufficient plasticizing effect of the large diameter.
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Polypropylene (PP): It has a high melting point and is easy to decompose at high temperature. A screw diameter of 40-80mm is suitable. It is necessary to match a precise temperature control system to avoid overheating and decomposition of raw materials.
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Recycled plastics: Recycled plastics have complex components and uneven particle sizes. A screw with a slightly larger diameter (50-90mm) is recommended to increase the material processing capacity and avoid blockage of the material channel. At the same time, a screw with a special thread structure can be chosen to improve the plasticizing and mixing effect.
3 Production Capacity Requirements
Production capacity requirements directly determine the minimum screw diameter. If the daily output requirement is high, a larger screw diameter should be chosen to ensure production efficiency; if the output requirement is low, a smaller screw diameter can be chosen to reduce equipment investment and energy consumption. For example, if the daily output requirement is 10 tons, a screw diameter of 80mm or more is recommended; if the daily output requirement is 2-5 tons, a screw diameter of 50-70mm is sufficient.
Common Mistakes in Screw Diameter Selection
Beginners often make the following mistakes when choosing screw diameter, which need to be avoided:
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Blindly pursuing large diameter: Some purchasers think that a larger screw diameter means higher efficiency, but ignoring the product size and raw material type. For small-sized products, a large-diameter screw will lead to low production efficiency, uneven parison wall thickness and waste of raw materials.
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Only focusing on product size and ignoring plasticizing quality: For high-viscosity raw materials, choosing a large-diameter screw without matching a reasonable length-diameter ratio will result in insufficient plasticizing of raw materials, leading to product defects such as bubbles and uneven wall thickness.
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Ignoring the compatibility of screw diameter with other components: The screw diameter needs to be compatible with the die head, clamping system and other components. For example, a large-diameter screw needs to be matched with a large-size die head to ensure that the parison can be extruded normally.
Summary of Selection Suggestions
Choosing the right screw diameter is a key step in configuring an EBM machine. The following is a summary of practical suggestions for beginners:
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First, determine the size, weight and raw material type of the main products to be produced, which is the basis for selecting the screw diameter.
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Calculate the required production capacity according to the production plan, and initially determine the screw diameter range.
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Comprehensively consider the plasticizing quality: for high-viscosity raw materials, prioritize a smaller diameter; for low-viscosity raw materials, prioritize a larger diameter to balance efficiency and quality.
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Consult the equipment manufacturer's technical team: the manufacturer has rich experience in matching, and can provide personalized screw diameter suggestions according to specific production needs, and match a reasonable length-diameter ratio and thread structure.
The screw diameter of the extrusion blow molding machine directly affects the production efficiency, product quality and production cost. Only by choosing the right screw diameter according to the actual production needs can we maximize the performance of the equipment and create more benefits. If you need to know more about the matching of screw parameters (such as length-diameter ratio, compression ratio) and EBM machines, our professional technical team is always ready to provide you with one-on-one consulting services.
