Extrusion blow molding (EBM) is widely used to manufacture hollow plastic products such as HDPE chemical jerrycans, drums, bottles, and industrial containers. While the molding machine forms the product, stable production also depends on how raw materials are stored, blended, conveyed, and recycled.
For factories operating multiple blow molding machines, understanding the complete production process helps identify where better material handling can reduce manual work and improve production organization.
1. Raw Material Preparation and Storage
The extrusion blow molding process begins with preparing the required materials. Depending on the product and formulation, these may include virgin HDPE resin, recycled material, color masterbatch, and additives.
Materials must be stored and supplied according to production demand. In factories that rely heavily on manual bag handling, operators may spend considerable time moving materials between storage areas and production machines. Scattered storage can also occupy valuable floor space and complicate material management.
For larger production lines, silos can provide bulk storage for resin. Outdoor silos may be used for bulk materials, while indoor storage units can accommodate other materials according to the factory layout and production requirements.
A central feeding system for blow molding can convey materials from designated storage points to multiple blow molding machines, reducing the need for repeated manual transportation. The system layout should consider material consumption, conveying distance, machine quantity, and required storage capacity.
Project case: An HDPE chemical container factory installed a centralized material handling arrangement serving 17 blow molding machines, with a reported total capacity of approximately 4,300 kg/h. The project included six outdoor silos and three indoor silos to support material storage and supply.
2. Material Feeding, Dosing, and Blending
After storage, materials must be delivered to each machine in the quantities required by its production recipe. When virgin resin, regrind, color masterbatch, and additives are used together, accurate dosing and consistent blending are important for maintaining the intended formulation.
A central feeding system handles material transportation, while a gravimetric blender weighs and doses individual components according to configured settings before blending them. These are separate functions: inventory weighing, where installed, monitors the amount of material stored, whereas a blender controls the quantities of ingredients used in a production recipe.
When selecting a gravimetric blender for plastic processing, factories should consider the number of ingredients, the proportion of each component, required throughput, and the properties of the materials being processed.
In the 17-machine project, each blow molding machine was equipped with its own Gravimetric Blender. Because the factory had sufficient building height, the blenders were installed on a support platform to save floor space. This arrangement kept the dosing equipment separate from the main working area, while machine-side equipment remained close to the production machines.
A raised platform is not suitable for every factory. Available headroom, structural load capacity, maintenance access, and operator safety must be checked before adopting this layout.
3. Plasticizing and Parison Extrusion
Once the prepared material reaches the blow molding machine, it enters the extrusion unit. The screw conveys, melts, and plasticizes the thermoplastic resin before pushing it through an extrusion die.
The molten plastic emerges as a hollow tube known as a parison. Its dimensions and consistency affect how the material is distributed during the blowing stage.
The required extrusion conditions depend on resin properties, product dimensions, wall-thickness requirements, and machine configuration. Stable material supply supports the production process, but it does not replace the need for suitable temperature settings, screw conditions, and parison control.
4. Mold Closing and Blow Molding
When the parison reaches the required length, the mold closes around it. Compressed air is introduced to expand the hot plastic against the mold cavity, forming the product’s shape.
For HDPE jerrycans and drums, the mold design and process settings influence features such as the handle, neck, corners, and wall distribution.
Consistent production requires coordination among parison formation, mold movement, blowing pressure, and cycle timing. Material formulation and blending must also remain appropriate for the product’s requirements.
5. Cooling, Demolding, and Trimming
After the plastic conforms to the mold, it cools sufficiently to retain its shape. The mold then opens, and the formed product is removed.
Extrusion blow molding often leaves excess plastic around areas such as the neck and base. This excess material, commonly called flash or trim scrap, is removed during trimming. The finished container can then move to inspection and any required downstream operations.
The trimming stage also creates an opportunity to recover suitable production scrap. However, scrap should not automatically be returned to production without considering its condition, potential contamination, material type, and the permitted regrind ratio.
6. Regrind Recycling and Material Reuse
Where the process and product specifications permit, clean production scrap can be processed through a granulator and reused as regrind. This can help reduce material waste, but the recovered material must be managed consistently.
A machine-side granulator can reduce the distance between scrap generation and size reduction. A nearby storage bin can temporarily hold the processed regrind before it is incorporated into an appropriate material recipe.
In the 17-machine HDPE factory project, a granulator and a small regrind storage bin were positioned beside each blow molding machine. This layout shortened the local handling distance for recovered material and made use of the available production space. The regrind could then be managed as a separate component where the product formulation allowed it.
For factories reviewing their scrap handling arrangements, a plastic granulator may be one part of a broader regrind management setup. The choice of equipment depends on scrap dimensions, material properties, processing volume, and the required particle size.
The appropriate regrind proportion depends on product quality requirements, material condition, and the production recipe. Containers intended for chemical storage may have specific performance requirements, so reuse decisions should follow the applicable product specifications and quality controls.
7. Finished Product Inspection
After trimming and any required finishing operations, the containers are inspected against the factory’s quality criteria. Depending on the application, checks may include appearance, dimensions, weight, wall thickness, and leak resistance.
Defects can originate at different stages, including material preparation, extrusion, mold design, blowing, cooling, or trimming. Reviewing process conditions alongside material and quality records helps operators identify potential causes and maintain consistent production.
Conclusion: Connecting Material Handling with Blow Molding Production
The extrusion blow molding process involves more than melting plastic and forming a container. Raw material storage, dosing, blending, conveying, molding, trimming, and regrind management all contribute to an effective production workflow.
For factories operating multiple HDPE blow molding machines, a properly planned central feeding system can coordinate material supply from storage to individual machines. Gravimetric blenders support recipe-based dosing, while machine-side granulators and suitable storage arrangements can help manage reusable production scrap.
The best configuration depends on the number of machines, material consumption, material formulations, regrind requirements, and available installation space.
Planning a Material Feeding System for Your Blow Molding Factory?
If you are planning a new extrusion blow molding line or upgrading an existing factory, the material feeding layout should match your machine quantity, estimated material consumption, raw material types, regrind requirements, and available installation space.Contact our team to discuss your central feeding system for blow molding project. Share your machine quantity, material requirements, and factory layout to help us evaluate a suitable storage, conveying, dosing, and blending arrangement.
