For optimum 2-part epoxy bonding, it is essential that the two components, resin and hardener, (often referred to as Part A and Part B), are combined in the appropriate ratios and adequately mixed prior to dispensing and applying to the product.
When manually measuring out the quantities of separate bulk packages of Part A and B, an accurate weight scale with suitable resolution (depending on the total quantities you are preparing) is necessary. An electronic scale with a “tare” function is helpful. Suitable ratios of each part can be measured into a suitable clean cup, and mixed with a clean, dust / lint / splitter-free mixing stick.
Epoxy packaged in bi-packs are by far the most commonly used in professional fiber optic connector termination scenarios. Bi-packs are a single plastic sleeve containing accurately-measured ratios of Part A and B. These are separated by either a clip or a burst-seal to prevent the two parts from coming into contact until you are ready to use. This is very handy in the production line, as it obviates the need for measuring on the production floor and reduces operator handling of the epoxy components.
The epoxy components are often “hazardous materials” that can pose health risks if not properly handled with suitable PPE (gloves and eye protection). To mix the two epoxy components in a bi-pack, the separator clip is removed, or the burst-seal is broken, and a roller (such as a typical lamination roller) is used to mix the two components together within the closed plastic sleeve.
Bi-packs can also be mixed by machines built specifically for this process, which helps ensure consistent and repeatable mixing. They often are designed for smaller (2.5 – 10 gram) bi-packs, so be sure to verify that your desired bi-pack size is compatible with such equipment.
Epoxy also can be packaged in “dual-tube” cartridges using a purpose-built dispensing gun similar to how a typical caulk or silicon sealant gun is used. Instead of one tube, there are two tubes, Part A and B, usually of different diameter to help ensure proper ratios are dispensed. A mixing-nozzle is attached to the dispensing end, and the two parts are pushed through the mixing nozzle as the gun plunger pushes from the back.
If mixing with a stick, as with bulk-packaged epoxy, or with a roller, as with bi-pack packaged epoxy, air bubbles are inevitably introduced to the mixed epoxy, and MUST be removed prior to injection into connectors.
De-gassing the epoxy after mixing and prior to applying is very important and failure to do so can result in serious long-term reliability risks to the product (air bubbles trapped within cured epoxy can present permanent stress to the delicate fiber within the connector). De-gassing is most commonly done by use of a centrifuge. Epoxy can also be de-gassed by subjecting the mixed epoxy to the vacuum in a vacuum chamber, though this is less common and un-necessarily complicated for most epoxies used for connector termination.
Variable-speed centrifuges are available, but single fixed-speed centrifuges are more common and usually sufficient. Most epoxies can safely be de-gassed with fixed centrifuge speeds in the 2500-3500 RPM range. Be aware that if you are using epoxies with additives, such as dyes for coloring, excessive RPM can separate out heavier additives, leading to a non-homogeneous epoxy mix which can significantly degrade your epoxy bonding characteristics.
Vacuum de-gassing is commonly reserved only for epoxies which cannot be easily de-gassed via centrifuge. An example would be very thick, high viscosity epoxies which are not common in normal termination applications.
The Fiber Optic Center Technical Team provides consultation on the exact type of centrifuge and mixing equipment best suited for specific applications and the viscosity of the epoxy being used. Choosing the correct method as well as proper centrifuge and mixing equipment will impact the quality and reliability of the finished fiber optic product.
