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Silicones from Dow Corning
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Basics of Processing

Dow Corning ® brand silicone gels are easily applied by a variety of methods.  A general overview of these processes is given below. For more specifics, please refer to the Tutorial on Processing Gels and Encapsulants.

Some gels are supplied in bladder paks that avoid direct air contact with the liquid gel components. This allows the use of air pressure over the pak in a pressure pot for dispensing. Air pressure applied directly on the liquid gel surface, without the Bladder pak, is not recommended since the gel can become supersaturated with air. Then as the gel is dispensed bubbling can occur.  The Bladder paks not only solve this, but also have the benefits maintaining cleanliness and avoiding contamination in the gel.

In general the gels are supplied as two-part products that are mixed in a 1:1 ratio (Part A & Part B). There are one-part gels available which eliminate the need for mixing. Gels can be dispensed manually or using one of the many different types of meter mix equipment available. Typically the two components are of matched viscosity and are readily mixed with static or dynamic mixers. Automated meter-mix is normally used for high volume processes. In low volume, manual weighing and simple hand mixing may be appropriate. 

For assistance in designing a process tailored to the needs of your application, contact Dow Corning’s technical experts in the Application Center.

Hand Mixing

The two components are added in the proper ratio to a clean container and then hand stirred gently but thoroughly. For some products, the two parts are different colors to help judge adequate mixing. If air entrapment is a problem, it may be necessary to de-air the material after mixing to ensure that the cured material is bubble free. The mixed material is then poured into the unit to be encapsulated. The filled unit can also be vacuum de-aired before curing to remove any last air. Take care during any de-airing process since foaming and significant expansion of the mixed material can occur.

Automated Meter-Mix

Automated meter-mix equipment is typically used for higher volume production processes. These systems consist of a separate feed reservoir and pump for each component. The systems are set to achieve the desired 1:1 ratio of the two components. The materials are then fed through a dispense head attached to a static mixer which is used to achieve a uniform mix. The dispense head is used to control the amount of material that is dispensed into the part. Static mixer tubes may need to replaced or cleaned when the process is shut down for long periods to avoid having the gel cure in the mix tube. If air entrapment in the cured material is a problem, it may be necessary to de-air the material in the feed reservoirs or in extreme cases, deair the material in the parts. 

Manual Mixing and Dispense 

Manual dispense units have separate chambers for each component which connect to a common static mixer tube. Applying pressure to the plungers on the chambers pushes the material through the static mixer. This can be done manually by squeezing a hand trigger or can be gas powered. Static mixers are typically disposable one-time use units and may need to replaced or cleaned when not being used for long periods to avoid having the gel cure in the mix tube. These units can be supplied pre-filled and ready to use or can be loaded with mixed and de-aired material immediately before use.

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  1. Gels Tutorial

  2. Key Gel Characteristics

  3. Gel Applications

  4. Specialty Gels

  5. Basics of Processing

  6. Curing Methods

  7. Repairability of Gels

  8. Packaging and Storage Considerations

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