Depositing metal onto a surface
Reference Number: N 01-02
Inventors: Singer, Alfred R. E.; Davies, Gordon I.; Roche, Allen D.
According to the invention, there is provided a method of depositing metal onto a surface using an arc spraying process with a consumable electrode and a non-consumable electrode, characterised in that the surface is an internal cylindrical surface, the non-consumable electrode rotates about a first axis, the consumable electrode is fed in a direction generally parallel to the first axis but does not rotate about its own axis, an arc is struck between the electrodes and atomising gas is directed through the arc at an angle to the first axis to atomise molten metal in the arc and to carry it towards and deposit it on the surface.
The non-consumable electrode preferably describes a circle when it rotates about the first axis and the consumable electrode can be fed axially within the circle described by the non-consumable electrode.
The consumable electrode is moved in an axial direction as it is consumed. Apart from this axial movement, the consumable electrode can either describe a circle about the first axis, or can lie at all times on the first axis. Whichever alternative is used however, it is important to note that the consumable electrode will not rotate about its own axis.
In a preferred embodiment, the non-consumable electrode rotates about the consumable electrode, and the consumable electrode lies on the first axis whilst the non-consumable electrode rotates around the first axis.
An additive can be introduced into the atomised molten metal before the atomised metal is deposited on the surface.
The invention also provides apparatus for depositing metal onto a surface using an arc spraying process, the apparatus comprising a consumable electrode and a non-consumable electrode, characterised in that the surface is an internal cylindrical surface and the non-consumable electrode is mounted for rotation about a first axis, the apparatus also including a feed mechanism for feeding the consumable electrode in a direction generally parallel to the first axis, means for striking an arc between the electrodes and means for directing atomising gas through the arc at an angle to the first axis towards the surface.
The non-consumable electrode is preferably of tungsten, is water-cooled at its base and is shrouded by an inert gas. The electrode can be mounted in a head and directed towards the centre of the surface, the head being mounted for rotation such that the electrode maintains its direction towards the centre as it rotates. The head can include gas passages for directing the atomising gas through the arc towards the surface.
The apparatus may include means for feeding particulate material into the atomised metal before the metal is deposited on the surface, and the head may include passages for directing a gas with entrained particulate additives towards the surface.
Both electrodes can be axially movable relative to the cylindrical surface.