Electric heating – Metal heating – By arc
Patent
1993-02-05
1994-11-01
Shaw, Clifford C.
Electric heating
Metal heating
By arc
21913051, B23K 9073
Patent
active
053609611
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with a method of welding and includes a method of applying a metallic wear resistant coating to a metallic substrate, and is particularly concerned with applying a metallic wear resistant coating to an edge surface on a turbine blade shroud, and further includes a method of sealing a hole in a metallic substrate, for example a cooling passage in turbine blade or turbine vane.
It is known to supply metal into an electric arc formed between an electrode of a welding torch and a metallic substrate for depositing a weld deposit on the metallic substrate. It is also known to deposit a weld deposit on the metallic substrate to form a metallic wear resistant coating which is metallurgically bonded to the metallic substrate.
Conventionally the electric arc is a direct current electric arc. The use of the conventional direct current electric arc results in penetration of the electric arc into the metallic substrate causing elements in the metallic substrate to diffuse into the weld deposit with a consequential softening of the weld deposit. In order to overcome the softening of the weld deposit used as wear resisted coatings, it is known to deposit a first weld layer on the metal substrate, allow the weld deposit to cool, machine the first weld layer and then deposit a second weld layer on the first weld layer.
The conventional method of applying a metallic wear resistant coating to a metallic substrate is laborious and costly.
The present invention seeks to provide a novel method of welding, a novel method of applying a wear resistant coating to a metallic substrate which overcomes the above problems and a novel method of sealing a hole in a metallic substrate.
Accordingly the present invention provides a method of welding comprising forming an alternating current electric arc between an electrode and a metallic substrate, the alternating current having a square wave form, supplying metal into the electric arc for depositing a weld deposit on the metallic substrate, the square wave alternating current electric arc being self supporting and not requiring intercycle high frequency support, the square wave alternating current having a wave bias ratio equal to or greater than 90% normal current to 10% reverse current,
The wave bias ratio may be greater than 95% normal current to 5% reverse current.
The wave bias ratio may be greater than 96% normal current to 4% reverse current.
Preferably the wave bias ratio is 97.6% normal current to 2.4% reverse current, or is 98% normal current to 2% reverse current.
The wave bias ratio may be less than 99.5% normal current to 0.5% reverse current.
Preferably the alternating current has a frequency greater than 50 Hertz.
The alternating current may have a frequency less than 200 Hertz.
The amperage of the alternating current may be in the range of 1 to 50 amps.
Preferably the alternating current electric arc is formed between a non consumable electrode of a tungsten inert gas welding torch and the metallic substrate.
Preferably the metal is supplied into the electric arc 30 by a solid consumable metal welding member.
The metallic substrate may be a first portion of laminated material, the first portion of laminated material is welded to a second portion of laminated material.
The weld deposit may form a metallic wear resistant coating on the metallic substrate, the coating being metallurgically bonded to the metallic substrate.
The metallic substrate may be a metallic substrate of a turbine blade.
The metallic substrate may be the shroud of the turbine blade, the weld deposit is deposited on an edge surface of the shroud.
The metallic substrate may be premachined before the weld is deposited on the metallic substrate.
The thickness of the weld deposit might be at least 1.0 mm.
Preferably the thickness of the weld deposit is 1.8 mm.
The metallic substrate may comprise nickel or a nickel alloy.
The weld deposit may comprise a cobalt alloy.
The metallic substrate may be a previously applied weld deposit on a turbine blade, the weld deposit is deposi
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patent: 2697160 (1954-12-01), Williams
patent: 3068352 (1962-12-01), Correy
patent: 4180720 (1979-12-01), Barhorst
patent: 4219592 (1980-08-01), Anderson et al.
patent: 4861965 (1989-08-01), Stava
patent: 4904843 (1990-02-01), Hori et al.
Ingall Robert C.
Waumsley Julie
Rolls-Royce plc
Shaw Clifford C.
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