Graeme Sharp
Aluminum
- Joined
- Jul 24, 2005
- Location
- Dorset, U.K.
Many of the more experience welders proably know that tig welding and magnetism do not go together, but I thought it might be intersting to relay my recent experience in this area, which was a first for me.
I had to refurbish a bottle capping head which is essentially two stainless steel discs, each containing very powerfull button magnets, approximately 22mm dia by 10mm thick. These magnets have to be handled carefully, as they are powerful enough when they jump together to trap a finger! One disc is driven by the milk bottling machine, and the other disc contains the claws which grip the botle top and screw it onto the bottle. The amount of torque applied is regulated by inserting teflon washers between the two parts.
The magnets are sealed into pockets in the discs with epoxy resin. After a period of time, the expoxy eventually allows moisture (from daily machine cleaning) to get to the magnets, which then corrode and expand and render the magnetic clutch inoperative.
A suit suggested that I should machine out the old epoxy and magnets, and fit new magents into the pockets. However instead of sealing them in with epoxy, if I would make stainless discs to cover the magnet pocket, the discs could be welded in place, thus hermetically sealing the magnet, and dispensing with the corrosion problem for all time.
One experienced welder expressed doubts due to the magnetism, while another said he would give it a go.
I witnessed the attempt at welding, and can only say that St Elmo's Fire would be a poor display in comparison. The arc was completely uncontrollable due to the effect of the magnetic field and after several attempts welder No 2 gave up, so it was back to sealing with epoxy resin.
The problem of tig welding close to a strong magnetic field is probably insurmountable, but I would be interested to hear if any members have been able to overcome this difficulty.
I had to refurbish a bottle capping head which is essentially two stainless steel discs, each containing very powerfull button magnets, approximately 22mm dia by 10mm thick. These magnets have to be handled carefully, as they are powerful enough when they jump together to trap a finger! One disc is driven by the milk bottling machine, and the other disc contains the claws which grip the botle top and screw it onto the bottle. The amount of torque applied is regulated by inserting teflon washers between the two parts.
The magnets are sealed into pockets in the discs with epoxy resin. After a period of time, the expoxy eventually allows moisture (from daily machine cleaning) to get to the magnets, which then corrode and expand and render the magnetic clutch inoperative.
A suit suggested that I should machine out the old epoxy and magnets, and fit new magents into the pockets. However instead of sealing them in with epoxy, if I would make stainless discs to cover the magnet pocket, the discs could be welded in place, thus hermetically sealing the magnet, and dispensing with the corrosion problem for all time.
One experienced welder expressed doubts due to the magnetism, while another said he would give it a go.
I witnessed the attempt at welding, and can only say that St Elmo's Fire would be a poor display in comparison. The arc was completely uncontrollable due to the effect of the magnetic field and after several attempts welder No 2 gave up, so it was back to sealing with epoxy resin.
The problem of tig welding close to a strong magnetic field is probably insurmountable, but I would be interested to hear if any members have been able to overcome this difficulty.