Arc Machines 307 - Manual (Page 151)

Arc Machines, Inc. Model 307 Orbital Tube Welder Training
Document No. 740096 Chapter 15. Page 4.
Rev. A
TAPER ANGLE
AND TIP SHAPE
TUNGSTEN TIP
DIAMETERS
TUNGSTEN LIFE
Taper Angle and Tip Shape
Taper angle affects the current/voltage characteristics of
the arc and must be specified and controlled.
Arc Machines, Inc. recommends an 18 o included angle for
the electrode tip for all tungsten diameters used in the
orbital tube and pipe weld heads. The tip shape has a con-
trolling effect on the shape of the arc and on the amount
and depth of weld penetration. A flat tip extends electrode
life and increases weld repeatability.
Tip Diameters
The Tip Diameters are specified for orbital fusion tube
welding. Tip diameters are typically based on wall thickness
with a finer tip used for thinner-walled materials. Tungstens
of a particular diameter may be ground to the users’ tip
diameter specifications.
Tungsten Life
Tungsten Life will vary with the application, quality of the
gas, and cleanliness of the metal. A great many more welds
per tungsten are possible on 1/4 inch tube than on larger
pipe. However, factors such as moisture or oxygen in the
shielding gas can have a serious detrimental effect on tung-
sten life. The use of mixed gases such as 95%Ar/5%H2 or
75%He/25%Ar, may also limit tungsten life. Similarly, oxi-
dation or other surface contaminants on the metal can
adversely affect tungsten wear. The rule of thumb is to
change the tungsten if the weld quality deteriorates. For
high-purity tube welds, tungsten is often changed after a
set number of welds for that particular application.
Formula for calculation
of Tungsten Length
and diagram of relation-
ship of Tungsten Length
to Rotor Diameter and
Arc Gap.