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Instructional Handbook
Frequently Asked Questions (FAQ)

Mixing and Measuring Adhesives

Re-stir all products before weighing or dispensing. Carefully weigh out resins and hardeners or powders and  binders into separate containers before mixing. (Use a minimum mix of 25 grams to insure a homogenous mixture.) Mix both parts of the adhesive system thoroughly before using.

Improper measuring or mixing can cause: materials not to cure, soft spots, air voids on the surface, sticky surfaces, softening at elevated temperatures, changes in chemical or electrical resistance.

Bonding Dissimilar Materials

Select an adhesive with a thermal expansion coefficient that closely matches the materials to be bonded. When possible select a flexible epoxy. Clean dirt, oils, greases and mechanically roughen the surfaces prior to bonding. Cure the materials at room temperature for 4-16 hours and at 250F for two hours.

Recommended Bond Line Thickness for Adhesive Bonding

For standard epoxy and ceramic adhesives a bond line thickness of 5-8 mils (0.005" - 0.008") will produce excellent results. for Cotronics' non-sag putties (epoxy or ceramic) bonds of 0.020" or more can be used. To form a thick layer, or section, apply putty in several layers curing between each application.

Joint Design and Bond Strength

Butt joints are usually the weakest, inserted joints (tongue and groove, rod in a tube) are considered to be mechanically reinforced and the strongest type of joint design.  For repairing difficult applications use a metal or ceramic cloth buried in the glue line for additional reinforcing.

Bonding to Teflon, Nylon, Polyolefin and Similar Plastics

Specific surface treatments and/or etching are required for bonding these plastics. Cotronics offers flexible (4538) and activated epoxies (7050) that form strong adhesive bonds to many of these difficult-to-bond materials.

Preventing Flow of an Adhesive From a Joint

Select an adhesive with high viscosity or with thixotropic properties and use just enough adhesive to completely fill the gap between the two surfaces to be bonded.

Thinning Adhesives for Application

Adhesives sometimes require thinning in order to ease flow, create a thinner bond line or facilitate encapsulation. Epoxy formulations can be thinned with mild heat or epoxy thinner 105RT. Ceramic adhesives can be thinned with the corresponding thinner for the particular adhesive. Thinning ceramic adhesives should be done at a minimum to prevent cracking or weakening of the material. 

Removing Bubbles in Potting Materials

You can reduce the amount of entrapped air by warming epoxies prior to application or by vacuum degassing. (Apply pressure of 29 inHg for 2 minutes, repeat 2 more times if needed).

Working with Electrically or Thermally Conductive Adhesives

Electrically and Thermally conductive adhesives will provide optimum results after a post cure for 2 hours at 250F. Electrically conductive materials are also available in flexible versions to accommodate bonding substrates with different thermal expansions.

Cracking in Ceramic Adhesives and Castable Ceramics

Cracked and weak castings, encapsulations, or adhesive bonds can occur when using ceramic materials if excess activator or additional water has been added to the uncured mixtures. Check the mix ratio that was used when mixing the materials. Castable Ceramics will achieve optimum strength after heat treating.

Accelerating Cure Times

The best way to shorten the cure cycle is the raise the temperature. Typically most systems can be quickly cured at 250F. Check the data sheet or the product label for specific curing directions for the material you wish to use.

Modifying Existing Formulations

Cotronics can adjust formulations to provide variables as viscosity, gel times, curing characteristics as well as lap shear strength, peel strength, flexibility, chemical stability, heat resistance, impact strength, color, etc.

Special Packaging for Production Applications

Cotronics can supply materials in pre-measured units and in bulk quantities to facilitate the use of these systems in any production facility or field application.