Plastic Blow Molding
The raw materials for plastic blow molding will be more diverse in order to meet the functional and performance requirements of blow molded products. The material properties required for extrusion, injection, and stretch blow molding are all different, but they all need to meet the characteristics of high strength, good heat resistance, aging resistance, corrosion resistance, etc.
Perform/Parison Manufacturing for Blow Molding Processes
Blow molding is a versatile manufacturing process used to produce hollow plastic products such as bottles, containers, and automotive components. This process involves inflating a molten plastic preform or parison inside a mold cavity, resulting in a final product that takes the shape of the mold. There are several types of blow molding processes, including new technologies such as stretch blow molding, extrusion blow molding, injection blow molding, and even 3D blow molding, each with its unique method of perform/parison production and specific applications.
Extrusion Blow Molding
Extrusion blow molding is one of the most common and widely used blow molding processes. In this method, a continuous hollow plastic tube, known as a parison, is extruded and then inflated inside a mold cavity to form the final product.
- Parison Manufacturing
The parison manufacturing process for extrusion blow molding involves the following steps:
- Resin Preparation: The plastic resin, typically in the form of pellets or granules, is dried and fed into the extruder hopper.
- Extrusion: The resin is melted and extruded through an annular die, forming a continuous hollow tube or parison. The parison is vertically extruded and supported by a mandrel or air cushion to maintain its shape.
- Parison Conditioning: As the parison is extruded, it may undergo conditioning processes such as cooling, heating, or sizing to achieve the desired temperature and dimensions for the subsequent blow molding step.
- Parison Cutting: The continuous parison is cut into individual lengths, typically using a guillotine cutter or a hot knife, to create individual parisons for each blow molding cycle.
The parison manufacturing process is a continuous operation, allowing for high production rates and efficient material usage. Common materials used in extrusion blow molding include polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).
Injection Blow Molding
Injection blow molding is a two-stage process that combines injection molding and blow molding. In this method, a preform is first injection molded, and then it is transferred to a blow mold where it is inflated to form the final product.
- Preform Manufacturing
The preform manufacturing process for injection blow molding involves the following steps:
- Resin Preparation: The plastic resin, typically in the form of pellets or granules, is dried and fed into the injection molding machine’s hopper.
- Injection Molding: The resin is melted and injected into a preform mold cavity, where it cools and solidifies into a preform shape. The preform typically has a threaded neck finish and a thick-walled body.
- Preform Ejection: Once the preform has solidified, it is ejected from the preform mold cavity.
- Preform Conditioning (Optional): Depending on the material and application, the preforms may undergo conditioning processes such as reheating or surface treatment before being transferred to the blow mold.
The preform manufacturing process is a cyclic operation, with each cycle producing a single preform. Injection blow molding is commonly used for producing smaller containers, such as those for pharmaceuticals, cosmetics, and personal care products. Common materials used in injection blow molding include polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE).
Multi-Layer Blow Molding
Multi-layer blow molding is a specialized process that involves the production of containers with multiple layers of different plastic materials. This technique combines the advantages of various materials, such as barrier properties, strength, and chemical resistance, into a single product.
- Perform/Parison Manufacturing
The preform/parison manufacturing process for multi-layer blow molding can involve either extrusion or injection molding, depending on the specific application and materials used.
- Extrusion Multi-Layer Blow Molding:
– In this process, multiple extruders are used to extrude different plastic materials simultaneously.
– The individual melt streams are combined and co-extruded through a multi-layer die to form a multi-layer parison.
– The multi-layer parison is then cut and transferred to the blow mold for inflation.
- Injection Multi-Layer Blow Molding:
– In this process, a multi-layer preform is injection molded using a specialized injection molding machine with multiple barrels and a multi-layer mold.
– The different plastic materials are injected sequentially or simultaneously into the mold cavity, forming a multi-layer preform.
– The multi-layer preform is then transferred to the blow mold for inflation.
The choice between extrusion or injection molding for multi-layer blow molding depends on factors such as the desired layer configuration, material compatibility, and production requirements. Common materials used in multi-layer blow molding include PET, polyamide (PA), ethylene vinyl alcohol (EVOH), and various barrier resins.
Stretch Blow Molding
Stretch blow molding is a specialized blow molding process used primarily for producing PET bottles and containers. In this process, a preform is first injection molded, and then it is stretched and inflated inside a mold cavity to form the final product.
- Preform Manufacturing
The preform manufacturing process for stretch blow molding is similar to that of injection blow molding, with a few additional considerations:
- Resin Preparation: The PET resin, typically in the form of pellets or granules, is dried and fed into the injection molding machine’s hopper.
- Injection Molding: The resin is melted and injected into a preform mold cavity, where it cools and solidifies into a preform shape. The preform has a thick-walled body and a threaded neck finish.
- Preform Ejection: Once the preform has solidified, it is ejected from the preform mold cavity.
- Preform Conditioning: The preforms are typically stored and then reheated to a specific temperature (typically between 90°C and 110°C) before being transferred to the stretch blow mold. This conditioning step ensures optimal stretching and blowing characteristics.
- Preform Transfer: The conditioned preforms are transferred to the stretch blow mold, where they are loaded into the mold cavities.
The preform manufacturing process for stretch blow molding is critical, as the quality and consistency of the preforms directly impact the final product’s performance and appearance. Strict quality control measures are implemented to ensure that the performance meets the required specifications.
- Considerations in Preform/Parison Manufacturing
Regardless of the blow molding process, there are several important considerations in the manufacturing of preforms/parisons:
- Material Selection: The choice of plastic material is crucial and depends on factors such as the desired properties (strength, barrier properties, chemical resistance), processing characteristics, and end-use application.
- Dimensional Accuracy: Precise dimensional control is essential during the preform/parison manufacturing process to ensure consistent wall thickness, neck finish dimensions, and overall geometry. This directly impacts the quality and performance of the final product.
- Surface Quality: The surface quality of the preform/parison can affect the appearance and functionality of the final product. Defects such as scratches, contaminants, or surface irregularities should be minimized or eliminated.
- Crystallinity and Orientation: For certain materials like PET, the crystallinity and molecular orientation of the preform/parison can significantly influence the mechanical and barrier properties of the final product. These factors are controlled through precise temperature and processing conditions.
- Automation and Quality Control: Modern preform/parison manufacturing processes are highly automated and incorporate various quality control measures, such as vision systems, weight monitoring, and dimensional checks, to ensure consistent product quality.
- Productivity and Efficiency: Optimizing the preform/parison manufacturing process for high productivity and efficiency is crucial, especially for high-volume applications. Factors such as cycle times, material usage, and energy consumption are carefully considered.
The manufacturing of preforms/parisons is a critical step in the blow molding process, as it directly impacts the quality, performance, and efficiency of the final product. Each blow molding process (extrusion blow molding, injection blow molding, multi-layer blow molding, and stretch blow molding) has its unique method of preform/parison production, tailored to the specific material requirements and end-use applications.
From the continuous extrusion of parisons to the precise injection molding of preforms, and the specialized multi-layer and stretch blow molding techniques, the preform/parison manufacturing process requires careful control and optimization. Factors such as material selection, dimensional accuracy, surface quality, and automation play crucial roles in ensuring consistent and high-quality products.
Related News
Applied’s expertise in modifying materials at atomic levels and on an ihdustrial scaleenables our customers to transform possibilities into reality.
