We often see different materials used for welding torches and their consumables. Mostly you can see Brass and Copper or Copper alloy - depending on the needs. Since there are various Copper alloys, we focus on the Copper Alloy: CuCr1Zr. Remember also that Brass, which is known as an alloy from Copper and Zinc, has many variations, as well. We will work with an example here.
Welding Diffuser Material Factors
Factors for choosing the right material for their individual use are mainly:
- Heat conductivity
- Electrical conductivity
- Hardness
- Yield strength
So let's take a deeper look in the different material properties. For the measurements we use the following formulas:
- Heat Conductivity: (W / (m-K) )
- Resistance: ( (Ω-mm2)/m - at 20o C)
- Hardness (HV): Hardness - Vickers Scale
- Yield Strength: (N/mm2)
Material
Heat Conductivity
Resistance
Hardness
Yield Strength
Copper
384
.0179
110 - 115
200 - 360
Copper Alloy
310 - 330
.0230
165
200 - 420
Brass
123
.05 - .07
Up to 140
360 - 500
These data are strongly dependent on the used alloy. So, how does this impact welding torch effectiveness? You can reasonably say that Copper may be perfect with it's high heat conductivity and low electrical resistance. But, the low hardness and a faster softening with higher temperatures leads to a higher wear of this material. So, wear parts with this material are only recommended for lower ratings.
Copper Alloy Welding Diffusers
This Copper Alloy has also a high heat conductivity (even if it's a bit lower than copper) and a low electrical resistance. Due to the fact that it has a high hardness and is much more wear resistant (especially for abrasion caused by the moving welding wire), this makes the Copper Alloy tested here very useful for contact tips. For contact tips holders, Copper Alloy again seems to be favorable. Note: We use different Copper Alloys for contact tips and tip holders to prevent it from corrosion due to the same material combination.
Brass Welding Diffusers
Brass is an all-rounder. Because of the higher resistivity, lower heat conductivity and a "medium" hardness, you won't see it as a contact tip. But as a contact tip holder, it's likely to be used. But what's the advantage of Brass against Copper Alloy? On the one hand it's a matter of price. Brass is much cheaper, and so are Brass contact tip holders in comparison to Copper Alloy tip holders. On the other hand, it's also a matter of the yield strength. There is almost no wear of the contact tip holder due to abrasion caused by the welding wire. But the tip holder must withstand crashes and, more more commonly, the automated reamer cleaning. So the lifetime of the contact tip holder can be increased by Brass.
But how does it really impact welding performance? Well, we have tested many different kinds of materials due to design changes, material changes, etc.
When testing the heat behavior of the contact tip in a test with a tin bath, we used a Brass and a Copper Alloy as material for contact tip holders.
Measuring Point
Copper Alloy Tip Holder (Celsius)
Brass Tip Holder (Celsius)
Contact Tip
161
178
Inner Tube
102
98
Tin Bath
250
250
The Brass tip holder causes the contact tip to become hotter. That's because of the lower heat conductivity.
That's also why the inner tube stays cooler.
Summary
Brass as a contact tip holder is okay as a cheaper alternative that can withstand the effects of automatic reamer cleaning better. It's thermal and electrical behavior is good for the use as contact tip holder, but cannot be used as a contact tip material.
Copper Alloy is a very good material for welding. It can be used for tips and holders. It has a very good electrical and thermal behavior, which leads to lower temperatures and reduce voltage drops. It can withstand the abrasion of the welding wire very good. Lower contact tip temperatures lead to higher lifetimes and can prevent thermal overload of the wear parts. It's only weakness is the lower yield strength.
Typical Size Range & Tolerances
Outside Diameter6 – 10mmBore Diameter0.7 – 3mmTolerance for OD and bore+/-0.05mm
Welding Contact Tip Alloy Comparison
- Standard DHP (Regular Copper) – world wide standard excellent general purpose.
- CrZr – (Cr-Chromium Zr-Zirconium) a very hard alloy, has been around for years made for stainless steel and stiff, high column strength or abrasive wires such as Flux cored / Metal cored.
There are 2 main reasons a welding tip wears
1. Common physical wear or abrasion, if you were to place a tip on the wire before the feeder with NO electrical contact, that tip would eventually wear completely through.
2. Electrical erosion is similar to the brushes on an electrical motor or the spark jumping across the gap on a spark plug. As the wire is traveling through the Contact tip at say 300 IPM the electricity has to jump across from the copper tip to the Mig wire. (Hence the name “Contact Tip”) The inside bore of the tip / wire is in constant electrical arcing as this process is happening. Electrical erosion is melting of the welding tip ID.
If you are attempting to get a “sure start” you need to choose the best alloy whether for electrical or physical wear. The next reason a tip wears is to do with heat. As the tip heats from the welding process the properties of the alloys start to break down.
The ability of the tip to dissipate the heat (thermal conductivity) will aid in keeping the tip cooler. The (electrical resistance) of the alloy is also in direct inverse proportion to the electrical conductivity.
As we need a “sure start” and are attempting to jump the gap from the contact tip to wire these two factors play a critical role, if the tip has higher conductivity of electricity it will transfer the current easier (or with less resistance) which will also cause the tip to run cooler.
Resistance equals heat. The additional benefit to higher conductivity is that the arc transfer from the tip to the wire is easier.
Easier arc transfer means a superior “sure start” and less arc failure or wire BURN BACK, sputtering and spatter.
Copper Alloy DesignationComposition%Softening TemperatureElectrical Conductivity
%IACSHardness
HVThermal ConductivityElectrical ResistanceUSA
UNS
Chromium ZirconiumCu min 99+
Cr.65 Zr.08500°C7517033523CrZr
Phosphorous
DeoxidizedCu min 99.9
P 0.015-.040300°C8511533520DHP
Silver AlloyCu 99
Ag 0.8-1.2400°C9812539517CuAg
Understanding contact tip recess
Correct contact tip recess can reduce the opportunity for excessive spatter, porosity and burnthrough or warping on thinner materials. It can also help minimize radiant heat that could cause premature contact tip failure.
Contact tip recess directly impacts wire stickout, also called electrode extension. The greater the recess, the longer the stickout is and the higher the voltage, which can make the arc slightly less stable. For that reason, the best wire stickout is generally the shortest one allowable for the application; it provides a more stable arc and better low-voltage penetration. Typical contact tip positions are 1/4-inch recess, 1/8-inch recess, flush and 1/8-inch extension.
Extending contact tip life
Contact tip failure can result from a number of influences, including burnbacks, mechanical and electrical wear, poor welding operator technique and reflective heat from the base material, which is common in tighter access weld joints or confined areas.
The quality of the wire being used can also affect contact tip life. Poor quality wire often has an undesirable cast or helix that can cause it to feed erratically. To extend contact tip life, consider the following:
- Keep the contact tip free of spatter.
- Use the proper drive rolls to ensure smooth wire feeding.
- Select contact tips with a smooth surface to prevent wire snagging.
- Trim the MIG gun liner to the correct length so that the wire feeds through properly.
- Lower operating temperatures, if possible, to reduce electrical wear.
In some instances, it may be desirable to convert to a water-cooled MIG gun to help keep the front-end consumables, including the contact tip, cooler and running for longer.