Moulds

We make our moulds in-house. Here are some insights about what you need to consider when making your moulds.

Types of moulds

• Flat moulds e.g. 6×1, 4×1, 4×1.5 inches
• Tubes e.g. 2×2, 3×3, 4×4, 5×5 inches
• Beams e.g. 7×7 inches
• Custom moulds e.g. S-shapes, L-shapes, V-shapes (used for boat making)

Mould design steps

• Identify the use of your mould
• Create a drawing with measurements
• Develop a template
• Determine the tools and resources needed to make your mould
• Purchase your materials
• Make your mould (never start to make a mould if you do not have a demoulding procedure)
• Extrusion trial – identify the time taken, test the integrity of your mould
• Approve for production

Mould material

There are many types of metal you can use for mould-making, depending on cost, availability, and durability.

Our choice: Mild/high-carbon steel

• Affordable and easily available in our region.
• Downside: It rusts easily.

The thickness needs to be adjusted to accommodate pressure and size. We found 1 inch steel works well for moulds up to 2×7 inches.
If using thinner materials, attention needs to be given to not over-pressurise, which leads to bending and breaking.

Other metal options

• Low-carbon steel – Strong but still prone to rust.
• Stainless steel – Rust-resistant, but more expensive.
• Aluminium – Lightweight and corrosion-resistant, but not as strong as steel.

The best metal for your moulds will depend on your budget, local availability, and the type of products you are making.

Mould swell

Mould swell happens when the mould deforms under pressure during extrusion.

This can cause distortion in the final product. You can mitigate this by increasing the thickness or your material, or adding ribs.

Types of moulds and their advantages

1. Welded moulds
   

    

   • Easier to demould.
   • Maintain their shape well.
   • Downside: If a profile gets stuck, it is very difficult to remove. 
2. Bolted moulds
   

    

   • Allow for excess extrusion, reducing porosity (air bubbles) in the final product.
   • Downside: If bolts are not evenly tightened, the plastic profile can be inconsistent.

The best choice depends on your production needs. Welded moulds offer better shape control, while bolted moulds help reduce air pockets in the plastic.

Modular design

Modular moulds allow one module to be used for multiple moulds. They attach to each other using flanges, making it possible to customise mould shapes and sizes.

Key considerations for modular moulds

1. Flange design – Flanges must be identical (like a universal die) to ensure a secure and accurate fit between moulds.
2. Cooling challenges –
   • These moulds cannot be cooled in a standard bath.
   • They must cool naturally, which takes longer and reduces daily production capacity.
3. Demoulding difficulties –
   • The mould design often includes bends, making it impossible to use a standard demoulding table.
   • More manpower is needed to manually remove the extruded product.

While modular moulds offer flexibility in production, they also require additional cooling time and labour for demoulding, which must be factored into workflow planning.

Extrusion metal work

Several metal components are essential for the extrusion process, ensuring that materials flow correctly and moulds stay secure.

• Nozzles – Guide the molten plastic into the mould.
• Mould stoppers –
  • Hold the mould in place on the extrusion and demoulding tables.
  • Prevent the mould from shifting during extrusion and demoulding.

These precision metal parts help maintain consistency and control throughout the extrusion process.

Demoulding challenges in extrusion

Demoulding is a critical step in the extrusion process, but several challenges can slow down production or damage equipment.

1. Uncooled moulds
   • If the plastic has not fully hardened, the hydraulic jack can puncture the material, ruining the profile.
2. Unaligned moulds
   • If the mould is not properly positioned, it can:
     • Break the metal demoulding bar.
     • Bend the hydraulic jack.
     • Cause injury to the operator.
3. Stuck moulds (caused by excess extrusion)
   • Too much extrusion can cause plastic to overflow, making the product stick inside the mould.
   • In severe cases, the mould may need to be broken open to remove the material, damaging the mould.
4. Manual demoulding
   • Takes more time and effort, slowing down production.
   • Reduces efficiency, as workers spend more energy on each mould.

How to avoid these challenges

• Ensure the mould is fully cooled before demoulding.
• Align the mould properly before engaging the hydraulic jack.
• Control excess extrusion to prevent plastic from sticking.
• Use proper demoulding equipment to reduce manual effort and increase efficiency.