Story by Piet van der Horst
Solid and cored wires are used for MAG welding. Both have their own properties and applications. The question I was asked very often is whether a cored wire is better or more economical than a solid wire. To give a clear answer to this question we first need to know what a cored wire actually is, what types there are and, not unimportantly, how they are made. Of course the differences in welding properties are also good to know.
You could say that a filled wire is actually an inverted coated electrode. With a coated electrode the coating is on the outside, with a cored wire the coating is in the wire in powder form. This powder can be rutile, alkaline or metal powder. What does not work with the coated electrode is possible with the cored wire; a metal powder filling does not form slag. This means that this type of wire has a higher efficiency. I will concentrate in two articles on the metal powder cored wire.
This first part is about the different types of cored wire and its properties. Part 2 will go deeper into melting speeds and application possibilities.
Types of cored wire
Roughly we can say that there are two types of cored wires, the folded cored wire and the tube or seamless cored wire.
The folded cored wire is based on a strip that is bent into a U-shape in which powder is deposited. After this the strip is folded shut and pulled to the correct diameter on tensile benches. The strip used for these wires is the same for most types, the quality of the weld metal is determined by additions to the powders. Characteristic of these wires is that they have a relatively thin wall thickness and therefore a large powder content. Another characteristic is that these are always blank wires. There are various types of folded cored wires; different manufacturers have their own production method.
The tube or seamless cored wire is based on a tube that is filled with powder and then rolled and pulled to the right diameter. A characteristic of these wires is that the wall thickness is greater than that of folded cored wire and that the powder content is therefore smaller. Furthermore, these wires are almost always copper plated. Another method is to weld a folded strip after filling, usually with laser, so that a tube is formed. These wires are also usually copper plated.
The diameter of a cored wire starts at 0.9 mm and goes up to 2.4 mm. Thicker cored wires are also available, but they are used in other processes such as submerged arc welding.
Solid wires are pulled from a thick wire of usually 6.3 mm. Solid wires are usually copper-plated to achieve a good current conduction. There are also blank solid wires and blank solid wires that have a special coating to improve the current conduction. The diameter of solid wires starts at 0.6 mm and goes up to 2.4 mm. It must be said that diameters 1.6 mm to 2.4 mm are very little used for MAG welding.
The welding properties of a solid and cored wire are totally different, although the seamless cored wire of pulled tube and thus with a thick wall comes close to the solid wire. The solid wire has a rather sharp arc and a finger-shaped penetration. A folded wire with a thin wall has a very soft arc that flows nicely and gives a nice penetration. Also here you see a finger-shaped penetration but not as sharp as with the solid wires. Wires filled with some metal powder form very fine spatter next to the weld that cannot be removed just like that. Sometimes it helps to adjust the welding parameters, but it can also be a property of the wire. Welded wires can, just like solid wires, also be welded in the short arc range.
Rules of thumb for the melting rate
There are a few rules of thumb for determining the melting rate, they represent the approximate melting rate in grams per minute.
When welding with a solid wire 1.0 mm in an 80%Ar/20%Co2 gas you can use the following guide values:
- In the short arc range 60 amperes to 160 amperes: 0.18 to 0.20 times the current (I)
- In the spray arc range 230 amperes to 280 amperes: 0.23 to 0.28 times the current (I)
- In the pulsed arc range 45 amperes to 240 amperes: 0.25 times the current (I)
For pulsed arc welding, the factor for the melting rate applies to the entire range of the wire/gas combination.
In case of cored wire, the rules of thumb for precipitation are as follows:
- Seamless cored wires from pulled tube: 0.30 to 0.32 times the current (I)
- Folded wires: 0.32 to 0.35 times the current (I)
These values only apply to the spray arc range.
Another easy way to determine the melting rate is to multiply the weight per meter of wire by the number of set meters per minute. Suppose you are welding with a wire speed of 12 m/min, a wire diameter of 1.2 mm and the weight of the wire is 8.87 gr/m. Then the gross melting rate is 12 x 8.87 grams = 106.44 gr/min or 106.44 gr x 60 min = 6.386 kg/h. The net melting rate will be slightly lower due to splash losses and evaporation of weld metal.
To apply this rule of thumb you must know the weight of the wire used. For solid wire the following standards apply per meter of unalloyed wire.
- 0.8 mm – 3.94 gr/m
- 1.6 mm – 15.77 gr/m
- 1.0 mm – 6.16 gr/m
- 2.0 mm – 24.65 gr/m
- 1.2 mm – 8.87 gr/m
- 2.4 mm – 35.48 gr/m
On a roll of 15 kg 1,2 mm solid wire is 15.000 : 8,87 =1691 meter wire.
Due to various production methods of cored wires it is not possible to give a standard weight per meter of wire. As a guideline we use 8 gr/m for a metal powder cored wire with a diameter of 1.2 mm.
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