Plastic Filters Mould

The production process of plastic filters varies depending on the product type (such as household water purifier filters, industrial filter meshes, etc.) and the production method. However, the overall process usually covers key steps such as raw material preparation, molding processing, post-treatment, assembly and testing. Here is an analysis of the common production process of plastic filters:

1. Raw material preparation
Material selection
Common plastic materials include:
Polypropylene (PP): Resistant to chemical corrosion, high temperature (100-120℃), commonly used in water treatment filters.
Polyethylene (PE): Good flexibility, suitable for manufacturing flexible filter nets or filter core casings.
Polyvinyl chloride (PVC): Low cost, but attention should be paid to environmental protection, mostly used in industrial-grade filters.
Polytetrafluoroethylene (PTFE): Resistant to strong acids and strong alkalis, suitable for high corrosive environments (such as chemical filtration).

Auxiliary materials: Additives (such as antioxidants, flame retardants), fillers (to enhance strength), color mother (coloring).

Raw material pre-treatment
Drying: If the raw materials contain moisture (such as nylon), they need to be dried using a drying equipment (hot air dryer) to remove the moisture, to avoid air bubbles during molding. 

1. Injection Molding (applicable to structural components such as housings and frames)
Process:
Mold Design: Metal molds (such as fixed molds and moving molds) are fabricated based on the size and shape of the filter. The molds must include features like flow channels and gate points.

Injection Machine Processing:

• Raw materials are heated and melted (the melting point of PP is approximately 160-170℃), and then injected into the mold cavity through a screw.
• After cooling and setting, the mold is opened to remove the formed parts (such as the filter housing and end cover).
• Features: High production efficiency, suitable for mass production of regular-shaped components.

2. Extrusion Molding (applicable to filter elements, filter screens, etc. of slender structures)
Process:
Extruder Melt: The raw materials are heated and melted in the extruder, and then extruded into continuous tubular, sheet-like, or filament-like structures through the die head mold.

Forming and Cooling:

• If producing filter screens, they can be woven into nets by extruding flat wires;
• If producing filter elements, a porous plastic tube (such as honeycomb filter elements) can be extruded, or non-woven fabric filter elements can be manufactured through the meltblown process (see below).
• Application: Often used in the production of water treatment filter elements and air filter cotton base materials.

3. Meltblown Molding (applicable to high-precision filter elements) 

Principle:
After the polymer (such as PP) is melted, it is blown through a high-speed hot air stream (300-350℃) to form ultra-fine fibers and randomly stack into a net-like structure. After cooling, it becomes a filter-membrane-like meltblown fabric with filtering function.
Features: Fiber diameter can reach 1-5 microns, high porosity, often used in the core filtering layer of water purifier PP cotton filter elements and air filter elements.

4. Blow Molding (applicable to hollow housings)
Process:
The melted plastic is extruded into a tubular blank, placed in the mold, and compressed air is blown into it to make it expand and adhere to the inner wall of the mold, then cooled to form a hollow shell (such as the filter housing).
Application: Suitable for manufacturing large-volume, thin-walled filter housings.

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