Common LSR Injection Molding Defects: Causes & Solutions-Iota

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News > Dynamic industry > Common LSR Injection Molding Defects: Causes & Solutions

Common LSR Injection Molding Defects: Causes & Solutions

Liquid Silicone Rubber (LSR) is widely used in medical, automotive, and electronic applications thanks to its excellent performance and fast curing. However, its low viscosity and rapid addition-curing reaction can also lead to molding defects if the process or materials are not properly controlled.

Here's a quick troubleshooting guide to the most common problems.

1. Air Bubbles

Problem: Internal voids or bubbles on the surface, reducing sealing performance and transparency.

Possible Causes

Injection speed is too high, trapping air inside the mold.
Poor mold venting or blocked vent grooves.
Air enters the A/B mixing system.
Moisture in fillers vaporizes during curing.

Solutions

Reduce injection speed and improve mold venting or vacuum assistance.
Check the sealing of the feeding system.
Dry fillers thoroughly.
Use low-volatility vinyl silicone fluid for better processing stability.

2. Flow Marks

Problem: Ripple marks or uneven surface gloss.

Possible Causes

Mold temperature is too low.
Injection pressure is insufficient.
Silicone base has poor flow properties.
Vinyl and hydrogen silicone fluids are not properly matched.

Solutions

Increase mold temperature and injection pressure.
Choose vinyl silicone fluids with good flowability.
Optimize the Si-H to vinyl ratio for a more uniform curing network.

3. Flash or Burn Marks

Problem: Yellow edges, burned parting lines, or excessive flash.

Possible Causes

Cure temperature is too high.
Clamping force is too low.
Platinum catalyst reacts too quickly.

Solutions

Lower curing temperature and adjust curing time.
Increase clamping force.
Select an LSR grade with a suitable pot life for your process.

4. Poor Bonding (Overmolding)

Problem: Weak adhesion between LSR and substrates such as PC, PA, or metal.

Possible Causes

Poor substrate surface preparation.
Mold temperature is unstable.
Insufficient adhesion promoter or silicone resin.

Solutions

Clean or plasma-treat the substrate.
Keep mold temperature stable.
Add suitable silane coupling agents or modified silicone resins to improve bonding.

Quick Troubleshooting Guide

Defect	Process Adjustment	Material Check
Air Bubbles	Reduce injection speed, improve venting	Check moisture and feeding system
Flow Marks	Increase mold temperature and pressure	Optimize vinyl silicone fluid and curing ratio
Flash/Burn Marks	Lower curing temperature	Check catalyst activity
Poor Bonding	Improve surface treatment	Verify adhesion promoter or silicone resin

High-quality LSR parts depend on the right combination of materials, formulation, and processing conditions. Proper troubleshooting can significantly improve production efficiency and product reliability.

If you're looking for vinyl silicone fluids, hydrogen silicone fluids, modified silicone resins, or technical support for LSR formulations, we're here to help.

Website: www.siliconeoil.net
E-mail: zyf@siliconeoil.cn

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