Cleanliness is next to stickiness.
Consisting of a resin and a hardener, a two-component epoxy can be formulated to offer a range of mechanical, thermal and electrical properties. While mix ratios differ, all offer the ability to cure at ambient temperatures or elevated temperatures for faster cures. Here are a few tips to help mix and apply a two-part epoxy:
Materials. First, get all the materials and safety equipment in place. These include:
- Disposable gloves
- Safety glasses
- Weight scale or volumetric cups
- Mixing stick (preferably metal)
- Part A and part B epoxies.
Surface preparation. Surface preparation is as important as the epoxy adhesive itself. Make sure the surfaces to be adhered are free of contaminants. The biggest problem with adhesives is substrate cleanliness. Whenever possible, the surfaces should be abraded or wiped down with a cleaning solvent before epoxy is applied. Oil on the surface of steel or even oil from fingerprints can ruin a bond. For added adhesion, plastic surfaces can be abraded or flame/corona-treated to remove any plasticizer.
Mixing. Several methods exist for proper mixing. Three include:
- Hand mixing is typically used for prototypes or low-volume production. This method is not recommended for medium to higher levels of production. When hand mixing, it is best to pour the resin (part A) into the mixing vessel first. The product should be weighed to the nearest gram. The hardener (part B) should be added next, using the same weighing procedure. Using a stir stick, mix the product for at least three minutes, scraping the sides and bottom of the vessel frequently. Avoid whipping the material to minimize air being introduced into the mix. After the epoxy has been thoroughly combined, the mixture should be poured into the mold or used in the adhesive step. When hand mixing, choose an epoxy with a long open time (pot life) to allow plenty of time to mix and pour into the application.
- Cartridge mixing is used for medium to large production runs. This method requires the two-part epoxy to be prepackaged in side-by-side cartridges. Adhesive or encapsulant formulas in 1:1 or 2:1 volume ratios are ideal for side-by-side cartridge packaging. Among the more common sizes for side-by-side cartridges are 50, 200, 400 and 1500ml. When choosing a cartridge size, consider shot size, pot life, quantity of parts to be processed and ergonomics of the job. Cartridges above 600ml have higher dispense pressures. A pneumatic gun is highly recommended for ease of use.
- Meter mix equipment is used for high-volume applications. There are several equipment manufacturers in the industry. When choosing equipment, ensure the plumbing is compatible with the epoxies. The epoxy manufacturer can confirm if any types of plastics or metals can negatively affect the material.
Curing. Two-component epoxy will cure by exothermic chemical reaction when properly mixed. Mixed epoxy will cure at room temperature, or under heat for a faster process. Cure rates are usually stated at a certain temperature and certain mass of material (e.g., 25 min. in a 100g mass). If working with a larger mass, the cure time will be shorter. Lower masses and thin films take much longer to cure.
When properly mixed and cured, two-part epoxies can add a great deal of protection to a product.
Albert Hernandez is sales manager at HumiSeal (humiseal.com); This email address is being protected from spambots. You need JavaScript enabled to view it..
