As the superior performance of liquid silicone rubber (LSR) products becomes increasingly recognized, their application range continues to expand. However, due to various factors, the production of LSR products in China started relatively late, and the associated technologies are not yet fully developed. Consequently, various problems often arise in actual production. I have compiled some past data and summarized common issues and their solutions in LSR production, hoping to assist others in the industry.

1.Incomplete Curing of Products

(1) Temperature is too low

    LSR generally undergoes platinum-catalyzed curing at temperatures between 110°C and 150°C (with slight variations depending on the silicone material and product structure).

    Countermeasures: Measure the actual mold temperature and appropriately increase it.

(2) Insufficient curing time

    LSR curing time usually ranges from 60 to 300 seconds (varying significantly with the silicone material and product structure, based on actual conditions).

    Countermeasure: Extend the curing time as needed.

(3) Contamination in the injection lines or molds

    Some greasy contaminants can disrupt the curing structure of LSR. For example, lubricating oil from machinery, rust-preventive oil on molds, and oils or sweat from workers' hands can affect curing.

    Countermeasures: Clean the injection lines and molds. Workers should wear finger cots or gloves during operation.

(4) Silicone material is too cold

    Some companies refrigerate mixed silicone material to extend its shelf life when not in production, leading to the use of cold material directly in production later.

    Countermeasures: Allow refrigerated material to reach room temperature before use.

(5) Inadequate mixing of materials

    LSR consists of two components (A/B), requiring thorough mixing before curing.

    Countermeasures: Use branded mixing systems and adjust the mixer speed and pressure.

(6) Embedded material is too cold (plastic or metal)

    This issue mainly concerns overmolding products, especially those with thick embedded parts in cold workshop environments (mainly in winter).

    Countermeasure: Preheat the embedded items.

2：Product Surface is Incomplete (or Partially Incomplete)

(1) Problem with mold release agent

    LSR has various types, and even the same type from different manufacturers can exhibit different performance characteristics. Different mold release agents are used accordingly, typically silicone-based ones, as recommended by the manufacturer.

    Countermeasure: Change the mold release agent.

(2) Mold surface contamination

    Greasy contaminants might adhere to the mold during production (rust-preventive oil, lubricating oil, or sweat from workers’ hands).

    Countermeasure: Clean the mold with toluene.

(3) Contaminated embedded items (plastic/metal)

    Dust, grease, or other contaminants might adhere to embedded items during production, not adequately cleaned in subsequent processes.

    Countermeasures: Clean and dry the embedded items thoroughly before production.

(4) Air pollution

    During LSR production, air pressure (air gun) is typically used for demolding. If the air from the compressor is contaminated, it can dirty the mold and affect the product.

    Countermeasures: Check the air line, clean, or replace the air compressor filter and dryer.

3：Products Contain Impurities (or Color Spots)

(1) Dirty silicone material or molds

    Countermeasures: Clean the molds and use clean silicone material.

(2) Dirty gloves or air gun used by the operator

    Countermeasures: Regularly replace gloves and air gun nozzles.

(3) Inadequate mixing of silicone material

    Sometimes, small white or transparent gel particles can be seen in the products, usually due to inadequate mixing of the silicone material.

    Countermeasures: Adjust the mixer speed and back pressure. If necessary, add a mixing process using a dedicated LSR mixer.

(4) Inadequate mixing of color paste (or color paste dispersion, sedimentation)

    Different silicone manufacturers use different color pastes. It is best to use the color paste provided by the silicone material manufacturer.

    Countermeasure: Change the color paste.

4.Product Deformation or Shrinkage (particularly in overmolded silicone products)

(1) Deformation temperature of embedded items is too low

    LSR curing temperatures range from 110°C to 150°C, so the deformation temperature of embedded items should be at least above 150°C.

    Countermeasures: Use materials for embedded items that can withstand higher temperatures.

(2) Unreasonable product structure design

    Silicone has a higher shrinkage rate compared to embedded items (plastic/metal). The silicone part of overmolded products should be uniformly structured without excessively thick or thin areas.

    Countermeasures: Advise the client to modify the product structure.

(3) Uneven pressure on embedded items causing deformation

    The embedded items in silicone overmolded products must be reliably positioned in the mold, with the sealing area under appropriate pressure. Pressure must be evenly distributed.

    Countermeasure: Adjust the stress points on the embedded items.

（5）Insufficient Material or Dents in Products

(1) Injection port is too small

    LSR injection ports are typically designed between 1.0 and 1.5 mm but can be adjusted based on the hardness and viscosity of the silicone material.

    Countermeasure: Increase the size of the injection port.

(2) Insufficient material supply

    Countermeasures: Adjust the material injection volume and increase the injection pressure.

(3) Poor venting

    Poor venting design can lead to insufficient material, usually due to bubbles breaking on the product surface.

    Countermeasures: Design a reasonable venting structure, enlarge the venting port, and consider vacuuming the mold if necessary.

(4) Dirty mold surface

    Contaminants on the mold surface can lead to a high rate of defective products.

    Countermeasure: Clean the mold regularly.

6.Products Have Bubbles (Entrapped Air)

(1) Poor venting

    Poor venting design, with the venting position typically at the product’s endpoint.

    Countermeasure: Adjust the venting position and consider vacuuming the mold if necessary.

(2) Air in the silicone material

    Air can be trapped during the mixing process, especially in high-viscosity silicone materials. Manual mixing should allow settling time for air release.

    Countermeasure: Check if the mixer is properly sealed and add a mixing process using a dedicated LSR mixer if necessary.

(3) Poor injection port design

    Large silicone products may have multiple injection ports to improve material filling. Ideally, only one injection port should be used due to LSR's good flow properties.

    Countermeasure: Adjust the injection port position.

7：Products Have Flash (Overflow)

(1) Excessive material supply

    Countermeasures: Reduce the injection volume, lower injection pressure, and increase clamping force.

(2) Insufficient mold parting surface precision (or wear)

    Due to LSR's good flow properties, the overflow value is only a few microns, requiring high mold precision. Some manufacturers use microinjection techniques to control flash, effective for large products but not for small ones. Adding an overflow groove at the product end can help.

    Countermeasures: Increase mold precision, improve machine microinjection accuracy, and add an overflow groove.

(3) Mold wear

    This applies to self-demolding structured products. Some weak self-demolding structures can wear out easily.

    Countermeasures: Design a reasonable self-demolding structure and electroplate the mold surface to increase hardness.

8：Poor Adhesion of Products (mainly overmolded products)

(1) Dirty embedded items

    Countermeasures: Clean and dry embedded items before molding.

(2) Adhesive problem (primer)

    Silicone generally cannot directly bond to plastic, metal, or glass and requires a primer (adhesive) before molding. Various adhesives with different effects are available. Self-adhesive silicones are available that do not require priming but are more expensive and not widely used due to cost and adhesive quality concerns.

    Countermeasure: Change the adhesive and consider using self-adhesive silicone if necessary.

(3) Unreasonable product structure design

     Some overmolded products have structural designs that complicate subsequent production processes, significantly affecting product quality and delivery times. Early-stage development evaluation is crucial.

     Countermeasure: Consider the feasibility of mass production during product development.

(4) Problem with mold release agent

     Some mold release agents can chemically react with adhesives, rendering them ineffective. For overmolded products, avoid or minimize the use of mold release agents, or wait at least half an hour after application before production.

     Countermeasure: Change the mold release agent and consider surface treatment of the mold to improve demolding.

    Statement: The issues and solutions presented here may vary depending on different manufacturers' machinery, production processes, and product structures. Specific problems and solutions should be analyzed based on actual conditions.

   Disclaimer: This article is a network repost, and all rights belong to the original author.