Adhesives for bonding transformer ferrites
Bonding ferrite halves for transformer coils
To help reduce component weight, parts, and reduce rattle and hum in transformers, adhesives can be used to join the ferrite halves instead of mechanical clips. Different types of adhesive can be considered for this application including structural acrylic adhesives, UV curable adhesives as well as two component epoxies. For many applications structural acrylic adhesives and UV curable are preferred due to the fast cure speed.
Specialist grades of structural acrylic adhesive have been developed for use on high speed transformer production lines. These adhesives give a very fast cure between the ferrites, fixing the two halves in 15-30 seconds. Due to their rubber toughening, structural acrylic adhesives easily pass drop tests, thermal cycling, and rigorous strength testing. There are special structural acrylic adhesives which are methacrylic acid free, this feature is particularly important when the adhesive will be in close proximity to sensitive electronic components.
A different way to tackle the same application is to assemble the ferrite halves and then place a raised dot of UV-curable adhesive over the joint and cure with a UV light in a couple of seconds. This is a very swift operation and is ideal for high speed production lines. The fact the adhesive is single component makes dispensing and application very easy to automate.
Bonding ferrite core / rod into coil
Depending on the assembly process and production line, several types of adhesive could be considered for this application.
Using a highly reactive grade of single part anaerobic on the copper helps get over the fact that ferrite material is quite passive to trigger anaerobic cure. If the copper has a lacquer coating then it would be necessary to dip the ferrite pins in activator before assembly. A batch of pins can be dipped and will remain active for days so not a huge ordeal on a production line. Cure speed of anaerobic adhesive on copper is normally only a couple of minutes.
Single component heat cure epoxies are easy to dispense with no mixing or activator required, they are less gap-sensitive and cure when exposed to heat. Induction heating cures the adhesive in 2-3 minutes and the size and shape of these little transformer critters mean this is an ideal way to cure the adhesive.
Encapsulating copper coils
Single part heat cure epoxies, low viscosity clear two part-epoxies, and even tack-free UV coatings could be considered for coating copper windings and coils.
For further help and information, please contact Permabond to discuss your application.