Introduction

In the modern plastics processing industry, accuracy, efficiency, and consistency are paramount. The initial stage of any production process, such as injection molding,rotational molding, blow molding, or extrusion, begins with the precise handling of raw materials. For materials like LLDPE, LDPE, HDPE, PP, and PET in powder form, a specialized Weighing Machine and Distribution System becomes the critical cornerstone for ensuring final product quality and optimizing operational costs.

Equipment and components

Storage Hoppers / Silos: For bulk storage of different plastic powders (LLDPE, LDPE, HDPE, PP, PET).

Weighing Hoppers / Scales: High-precision load cells are installed to measure the exact weight of the powder discharged.

Feeding Devices: Such as screw feeders, vibrating feeders, or rotary valves, which control the flow of powder from the storage hopper to the weighing hopper.

Distribution System: This could be a network of pipes, diverter valves, and pneumatic conveying systems that transport the weighed powder to the designated processing machine (e.g., mixer, extruder hopper).

Control System: A Programmable Logic Controller (PLC) and Human-Machine Interface (HMI) panel allow operators to set formulas, target weights, and manage the entire process.

Process and workflow

Formula Selection: An operator selects a production recipe on the HMI, specifying the type and weight of each plastic powder required (e.g., 50kg HDPE, 30kg PP).

Coarse and Fine Feeding: The system activates the feeding device for the first material. It starts with a high-speed “coarse feed” to quickly fill the weighing hopper. As it approaches the target weight, it switches to a slow “fine feed” to achieve pinpoint accuracy, preventing overfeeding.

Weight Verification: The load cells continuously monitor the weight in the hopper. Once the target weight is precisely achieved, the feeder stops completely.

Distribution and Discharge: The distribution system (e.g., a pneumatic conveyor) is activated. A diverter valve directs the flow, and the precisely weighed batch of powder is transported to the designated receiving point, such as a mixer or an extruder’s throat.

Cycle Repetition: The system then automatically repeats the process for the next material in the recipe until the entire batch formulation is complete.

Advantages for Handling Various Plastic Powders

Measurement level accuracy
Adopting high-precision sensors and closed-loop control to eliminate human errors. Ensure the precise execution of the formula and guarantee the consistency of key physical properties (such as mechanical strength and viscosity) of the product with the batch.

Material integrity assurance
By using low shear force conveying and a mild pneumatic conveying system, it is possible to avoid thermal degradation or compaction of plastic powders (such as thermosensitive materials) and maintain their inherent molecular structure and properties.

Excellent anti cross contamination measures
The system is equipped with mirror polishing, blind spot free flow channel, and automatic blowing function to ensure that residual between batches is minimized when switching materials (such as PP and PET), ensuring product purity.

Fully automated and efficient operation
Realize unmanned and continuous material distribution from storage to production line, liberate manual labor from tedious operations, improve overall equipment efficiency, and support 7×24 uninterrupted production.

Frequently Asked Questions

Why use a weighing and distribution system instead of manual powder handling for rotomolding?

Manual powder charging — an operator weighing powder on a scale and carrying it to the mould — introduces two main operational problems: weighing variability (individual batches vary by ±50–200 g depending on operator technique and fatigue) and cycle time loss (manual weighing and carrying adds 2–5 minutes per mould charge per cycle on larger moulds). On a rotomolding machine running 20–40 cycles per shift, this translates to significant resin waste from over-charging and lost cycle time per shift. An automated weighing and distribution system eliminates both by delivering a consistent pre-set weight to each loading point automatically, allowing the operator to focus on mould loading, demoulding, and quality inspection rather than powder handling.

What plastic powder types can this system handle?

The system handles free-flowing plastic powder at 20–120 mesh from any material ground on the PNMF pulveriser: LLDPE, LDPE, HDPE, MDPE, PP, PET, EVA, PS, ABS, nylon, and others. Powder with low bulk density (e.g. fine LLDPE at 80 mesh, bulk density approximately 350–450 g/L) requires conveying speed and pipeline sizing to be matched to the specific material — confirm with WANROOETECH at the design stage. For tacky or cohesive materials (high-VA EVA, soft PVC powder), the distribution system should be specified with a screw conveying mechanism rather than pneumatic conveying to prevent bridging or line blockage.

Can this system be retrofitted to an existing PNMF pulveriser installation?

Yes — the weighing and distribution system connects to the powder outlet of any existing PNMF installation, either at the cyclone discharge or the central collection bin outlet. The system does not require modification to the pulveriser itself. The distribution pipeline is routed to match the existing facility layout; WANROOETECH provides layout drawings for system integration during the quotation stage.

Video