Injection Molding Screw Types: How to Select the Optimal Design for Your Material

Over molding threaded inserts isn’t just “inject plastic around metal” – it’s a science。

Discover 7 critical screw types for injection molding, their working principles, and material-specific selection guidelines to reduce defects by up to 40%.

Why Screw Design Dictates Molding Success

“Over 35% of melt-related defects originate from improper screw selection”

The injection screw performs three mission-critical functions:

  1. Plasticizing – Converts pellets to homogeneous melt
  2. Metering – Precisely controls shot volume (±0.5% variance)
  3. Injecting – Delivers melt at 300-1,500 bar pressure
M2 M3 M4 M5 M6…Brass screw inserts

7 Industrial-Standard Screw Types Compared

1. General-Purpose Screw

  • Geometry: L/D ratio 20:1, compression ratio 2.5:1
  • Best for: PP, ABS, HDPE (>75% of commodity applications)
  • Limitations: Unsuitable for filled materials (glass/carbon fiber)

2. Barrier Screw (Maddock-Type)

  • Innovation: Secondary barrier flight separates un-melted pellets
  • Applications: Medical devices, optical lenses

3. Mixing Screw

• Must Use When: ◦ Coloring masterbatches (ΔE <0.5 required) ◦ Blending regrind (>25% content) • Elements: Dulmage pins, spiral disruptors

4. Ball Check Valve Screw

  • Mechanism: Tungsten carbide valve seals during injection
  • Critical for:
  • ROI: Eliminates 90% of drooling defects

5. High-Speed Screw

  • Design Traits:
  • Output: 25% faster plasticizing rate for PET preforms

6. Low Compression Screw

  • Specialization:
  • Saves: TPU/TPE scrap rates by up to 18%

7. Venting Screw

  • Devolatilization: Removes 5-8% volatiles (moisture, VOCs)

Selection Matrix: Matching Screws to Materials

Material Family Recommended Screw Type Critical Parameter

Engineering Plastics Barrier + Mixing Melt temp control Filled Compounds Hard-coated Mixing Wear resistance Medical-Grade Polished Barrier Cleanliness Class Recycled Content Venting Moisture removal

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Our engineering team assists customers in customizing screw inserts to perfectly match their product’s structure and meet the required pull-out test standards.

Take an example of our made plastic display cover with SS screw inserts, This product is primarily intended for marine use and will often be installed outdoors, exposed to marine environments with harsh conditions. It must withstand saltwater, be waterproof, and be resistant to high and low temperatures, UV resistance, etc. The product must be smooth, flat, and free of defects to prevent water ingress. The storage temperature range is -40°C to +85°C, while the operating temperature range is -30°C to +70°C.

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¿Necesita piezas moldeadas por inyección de alta calidad?

Si tienes una gran idea, podemos ayudarte a hacerla realidad. Hemos hecho esto antes y nos gusta convertirnos en socios durante todo el proceso de creación del producto. Desde asesorarte en el proceso de adquisición del molde hasta entregar tu nuevo producto a los clientes, queremos trabajar contigo en cada paso del camino.

Una búsqueda interminable por mejorar

Nuestra fortaleza es nuestra flexibilidad y adaptabilidad. Combinamos nuestra experiencia con tus ideas para sacar productos que están un paso en el futuro.

Producción de calidad sin defectos

Nuestra visión no es solo entregar productos que superen las expectativas de los clientes, sino también ayudarlos a reducir costos trabajando con ellos en el campo del diseño de moldes. 

Entrega puntual de pedidos 

Deseamos asegurarnos de que los clientes reciban los bienes con precisión y completen la entrega en el menor tiempo posible.