Electron Beam Services Ltd
The machine consists of two parts. The chamber where the component is manipulated and the gun where the welding beam is generated. Both parts are evacuated to a high vacuum 10-3 to 10-5 mbar. The electron beam is generated by passing current through a filament, applying a high voltage typically 40kv to 150kv and a control voltage to regulate the electron flow (beam current). The resulting beam can be focussed and deflected electrically onto the component joint. The component is manipulated under the beam and a rapid melt and resolidification process occurs which enables deep penetration to be achieved while minimally affecting the state of the surrounding material.
The process of heat treating within the vacuum environment means the component comes out clean after processing and ideal for finished machined components.
The components are put into the furnace cold and evacuated, the heating process is started and because it is in vacuum there is no oxidation even at elevated temperatures, at the end of the process inert gas is used to cool.
Brazing can be assembled and pasted (in jigs if required) and processed in the same clean environment resulting in clean and reproducible joints.
Shrink fitting of components is a common thing to do for gears and generally involves heating the outer ring to about 180 degrees and cooling the inner section sometimes in liquid nitrogen.
This a non destructive testing process useful for checking leak tightness after electron beam welding or vacuum brazing.
The method can only be used on objects where the joint area can be sealed off and vacuumed down, the joint area can then have helium gas applied, any area that is not fully sealed will allow the gas to enter the object and pumped out via the sensor, the machine will indicate the leak and the severity.
Particularly useful for checking sensors and bellows that may be part of a line where leak tightness is essential.
The typical leak tightness is of the order 2x10-8 cc/hr
which could permeate through cast material.
A section of the weld can be taken and etched to show the profile of the beam and joint , this is sometimes required before doing critical joints.