How Is The Parison Formed During Extrusion Blow Molding

2026-09-24

A parison is a hollow tube of molten plastic that forms before the mold closes. During extrusion blow molding, stable plasticizing, accurate die-head forming, and proper wall thickness control help prepare the parison for the blowing process.

How Is The Parison Formed During Extrusion Blow Molding-Kingplas Machinery

Plastic Pellets Melt Inside The Extruder:

Parison formation starts with plasticizing. Plastic pellets enter the extruder barrel, where the rotating screw conveys the material forward and melts it under controlled heating conditions.

In an extrusion blow molding machine, the screw, barrel, and heating system work together to produce a stable plastic melt before the material reaches the die head.

The plasticizing process needs a suitable melt temperature and stable material flow. An unstable plastic melt can affect the parison shape and the quality of the final hollow product.

The Die Head Forms The Tubular Parison:

The molten plastic moves from the extruder into the die head and flows around the core rod. The material then exits through the die opening as a hollow tube. This hot, downward-moving tube forms the parison.

The basic process follows this sequence:

Plastic Pellets → Plasticizing → Plastic Melt → Die Head → Parison

The die-head adjustment system controls the parison diameter and wall thickness according to product requirements. Proper adjustment helps distribute the material evenly before blowing.

How Is The Parison Formed During Extrusion Blow Molding-Kingplas Machinery

Parison Dimensions Need To Match The Product:

The parison needs enough material to fill the mold cavity and form the final product structure. Manufacturers adjust its settings according to product size, weight, shape, and machine configuration.

Key factors include:

Parison diameter and length: Determines whether the material can cover the required mold area.
Melt temperature: Affects material flow and parison stability.
Wall thickness: Influences material distribution after blowing.
Product dimensions and weight: Determine the required amount of plastic material.

Large containers and complex hollow products may require different material distribution from small bottles or simple containers.

Wall Thickness Can Be Controlled Before Blowing:

During blow molding, different areas of a hollow product may stretch by different amounts. Parison control adjusts material distribution before the mold closes, helping manufacturers achieve suitable wall thickness in different product areas.

Kingplas applies multi-point parison control to selected machines for larger technical products. The actual control system depends on the machine model and molded part requirements.

Manufacturers can adjust parison thickness at different positions to manage material usage and maintain product consistency during production.

How Is The Parison Formed During Extrusion Blow Molding-Kingplas Machinery

Accumulator Systems Support Larger Parisons:

For larger hollow products, an accumulator-type extrusion blow molding machine collects molten plastic before releasing it through the die head.

Kingplas accumulator-type equipment handles products from 25L to 240L, including chemical barrels, automotive parts, tool cases, seats, and toys.

An accumulator-type extrusion blow molding machine stores enough molten material before parison extrusion. After the parison reaches the required length, the mold closes around it. Compressed air then expands the hot plastic against the mold cavity to create the final hollow product.

FAQ:

Q1: What is a parison in extrusion blow molding?

A: A parison is a hollow tube of molten plastic that forms before the mold closes.

Q2: How is the parison formed?

A: Molten plastic passes through the die head and exits around the core rod as a hollow tube.

Q3: Can parison wall thickness be controlled?

A: Yes. Manufacturers can adjust wall thickness according to the product structure and machine configuration.

Q4: What happens after the parison is formed?

A: The mold closes around the parison, and compressed air expands it into the required hollow shape.

Why Choose Kingplas Machinery?

Has 30 years blow molding experience. Our blow molding machine portfolio is designed to handle a wide range of thermoplastic materials, including HDPE, PP, PE, PVC, PC, and PETG, for containers ranging from 10ml to 1250L.

Automatic Extrusion Blow Molding Machines: High-speed continuous extrusion systems (Single/Double Station) for cosmetics, lubricants, and household chemicals.
Accumulator Head Blow Molding Machine: Robust solutions for large-scale industrial parts, such as 200L drums, IBC tanks, and automotive components.
Multi-Layer Co-Extrusion Technology: Advanced 2-to-6 layer systems that provide superior barrier properties for agrochemical and fuel tank applications.
Turnkey Solutions: Integrated production lines including precision mold design and auxiliary equipment.