TOPIC: CONTROLLABLE VARIABLES:
TYPE OF WELDING: SUBMERGED ARC WELDING:
A knowledge and control of the variables in submerged arc welding are essential if welds of good quality are to be consistently obtained. The variables, in the approximate order of their importance, are:
1. Welding current
2. Welding voltage
3. Welding speed
4. Width and depth of the layer of submerged are welding flux
5. Mechanical adjustments
These variables are discussed in the following paragraphs.
a. Welding Current: Welding current is the most influential variable. It controls the rate at which welding wire is burned off, the depth of fusion, and the amount of base metal fused. If the current is too high, the depth of fusion will be too great and the weld may melt through the backing. In addition to this, the higher heat developed may excessively extend the heat affected zone of the adjacent plate. Too high a current also means a waste of power and a waste of welding wire in the form of excessive reinforcement. If the current is too low, there is insufficient penetration and not enough reinforcement.
b. Welding Voltage: Next in importance to welding current is the welding voltage. This is the potential difference between the tip of the welding wire and the surface of the molten weld metal. The welding voltage varies with the length of the gap between the welding wire and the molten weld metal. If the gap increases, the welding voltage increases; if the gap decreases, the welding voltage decreases. The welding voltage has little effect on the amount of welding wire deposited; this is determined mainly by the welding current. The voltage principally determines the shape of the fusion zone and reinforcement. High welding voltage produces a wider, flatter, less deeply penetrated weld than low welding voltage.
c. Welding Speed: With any combination of welding current and voltage, the effects of changing the welding speed conform to a general pattern:
If the welding speed is increased-
If the welding speed is decreased-
In addition to this pattern, welding speed may have another effect on the finished weld. Normally, only welding current affects the penetration of the weld. However, if the welding speed is decreased beyond a certain point, the penetration will also decrease. This is because a good portion of the molten weld puddle will be beneath the welding wire and the penetrating force of the arc will be cushioned by the puddle. Conversely, if the speed is increased beyond a certain point, the penetration will increase since the welding wire will precede the weld puddle.
d. Width and Depth of Welding Flux: The width and depth of the layer of granular welding flux influence the appearance and soundness of the finished weld as well as the welding action itself. If the granular layer is too deep, a rough, ropy weld is likely to result. The gases generated during welding cannot readily escape, and the surface of the molten weld metal is irregularly distorted. If the granular layer is too shallow, the welding zone will not be entirely submerged. Flashing and spattering will be present; the weld will have a bad appearance, and may be porous. An optimum depth of granular material exists for any set of welding conditions. This depth can be established by slowly increasing the granular material until the welding action is submerged and flashing no longer occurs. The gases will then puff up quietly around the welding wire, sometimes burning. It is seldom that too narrow a layer is applied. The safest procedure is to apply a layer that is three times the width of the fused portion. In large welds, a greater allowance may be necessary. A layer that is limited by too narrow confines interferes with the normal lateral flow of weld metal resulting in reinforcement that is narrow, steep-sided, and poorly “faired in” the baseplate or the edges.
e. Mechanical Adjustments: The position of the welding wire must be maintained to control the shape of the weld and the depth of penetration. The wire may be guided mechanically or manually adjusted as the weld progresses. While the welding is going on, inspection will indicate whether the backing is tight against the underside of the joint. If it is not, too much metal may flow into the space, resulting in reduced weld reinforcement, undercutting, and a ruined weld.
TYPE OF WELDING: SUBMERGED ARC WELDING:
A knowledge and control of the variables in submerged arc welding are essential if welds of good quality are to be consistently obtained. The variables, in the approximate order of their importance, are:
1. Welding current
2. Welding voltage
3. Welding speed
4. Width and depth of the layer of submerged are welding flux
5. Mechanical adjustments
These variables are discussed in the following paragraphs.
a. Welding Current: Welding current is the most influential variable. It controls the rate at which welding wire is burned off, the depth of fusion, and the amount of base metal fused. If the current is too high, the depth of fusion will be too great and the weld may melt through the backing. In addition to this, the higher heat developed may excessively extend the heat affected zone of the adjacent plate. Too high a current also means a waste of power and a waste of welding wire in the form of excessive reinforcement. If the current is too low, there is insufficient penetration and not enough reinforcement.
b. Welding Voltage: Next in importance to welding current is the welding voltage. This is the potential difference between the tip of the welding wire and the surface of the molten weld metal. The welding voltage varies with the length of the gap between the welding wire and the molten weld metal. If the gap increases, the welding voltage increases; if the gap decreases, the welding voltage decreases. The welding voltage has little effect on the amount of welding wire deposited; this is determined mainly by the welding current. The voltage principally determines the shape of the fusion zone and reinforcement. High welding voltage produces a wider, flatter, less deeply penetrated weld than low welding voltage.
c. Welding Speed: With any combination of welding current and voltage, the effects of changing the welding speed conform to a general pattern:
If the welding speed is increased-
- Power or heat input per unit length of weld is decreased.
- Less welding wire is applied per unit length of weld.
- Consequently, there is less weld reinforcement.
If the welding speed is decreased-
- Power or heat input per length of weld is increased.
- More welding wire is applied per unit length of weld.
- Consequently, there is more weld reinforcement.
In addition to this pattern, welding speed may have another effect on the finished weld. Normally, only welding current affects the penetration of the weld. However, if the welding speed is decreased beyond a certain point, the penetration will also decrease. This is because a good portion of the molten weld puddle will be beneath the welding wire and the penetrating force of the arc will be cushioned by the puddle. Conversely, if the speed is increased beyond a certain point, the penetration will increase since the welding wire will precede the weld puddle.
d. Width and Depth of Welding Flux: The width and depth of the layer of granular welding flux influence the appearance and soundness of the finished weld as well as the welding action itself. If the granular layer is too deep, a rough, ropy weld is likely to result. The gases generated during welding cannot readily escape, and the surface of the molten weld metal is irregularly distorted. If the granular layer is too shallow, the welding zone will not be entirely submerged. Flashing and spattering will be present; the weld will have a bad appearance, and may be porous. An optimum depth of granular material exists for any set of welding conditions. This depth can be established by slowly increasing the granular material until the welding action is submerged and flashing no longer occurs. The gases will then puff up quietly around the welding wire, sometimes burning. It is seldom that too narrow a layer is applied. The safest procedure is to apply a layer that is three times the width of the fused portion. In large welds, a greater allowance may be necessary. A layer that is limited by too narrow confines interferes with the normal lateral flow of weld metal resulting in reinforcement that is narrow, steep-sided, and poorly “faired in” the baseplate or the edges.
e. Mechanical Adjustments: The position of the welding wire must be maintained to control the shape of the weld and the depth of penetration. The wire may be guided mechanically or manually adjusted as the weld progresses. While the welding is going on, inspection will indicate whether the backing is tight against the underside of the joint. If it is not, too much metal may flow into the space, resulting in reduced weld reinforcement, undercutting, and a ruined weld.
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