Porosity is the name for the issue that occurs when oxygen get into the weld pool during the welding process. If porosity occur in the weld, the weld will appear to look like blackened peppercorns instead of a clean, silver bead of weld material. Improper flow of the shielding gas typicaly causes porosity.
The ceramic cup that control the flow of the shielding gas must allow for the shielding gas to flow in a steady stream. If the shielding gas isnt allowed to flow in a steady stream, then the oxygen will enter the weld pool and ruin the structural integrity of the weld joint. The sizing system for ceramic cups employ sixteenths of an inch as the unit of measurement for the size of the ceramic cup.
Stop Holes in Welds with the Right Ceramic Cup and Gas Flow
Therefore, if the ceramic cup is labeled with a number, that number refer to the number of sixteenths of an inch in the diameter of the opening in the ceramic cup. For instance, if the ceramic cup is labeled as a number four, the opening in the ceramic cup will be four sixteenths of an inch in diameter. The size of the ceramic cup will dictate both the amount of shielding gas that can pass through the ceramic cup as well as the size of the area that will be covered in shielding gas.
Small ceramic cups are used in situations where the welding job require the shielding gas to be more focused on a smaller area. Small ceramic cups allow the welder to better localize the heat of the welding process and to better focus the shielding gas. Ceramic welding cups can be made from a variety of different material.
One of the most common materials for welding ceramic cups is alumina ceramic. Welders often select this type of ceramic for welding ceramic cups because it is relatively inexpensive and can handle high temperature. An alternative to ceramic cups is to use a clear Pyrex glass cup.
These types of cups allow the welder to better view the welding process and the weld pool through the ceramic cup. However, Pyrex glass cups are less durable than alumina ceramic cups because they are more likely to crack if they are exposed to high temperatures. For heavy industrial welding job, some welding professionals prefer to use Lavite ceramic cups.
Lavite is a volcanic stone that has a resistance to thermal shock that is more greater than that of alumina ceramic materials. The size of the ceramic cup must be matched to the size of the tungsten electrode that is to be used for the welding process. It is impossible to effectively weld with thick tungsten electrode in a ceramic cup that has a small opening for the welding rod.
If the tungsten electrode is too large to fit within the ceramic cup, the shielding gas may become turbulent. Turbulence in the shielding gas will tend to pull air into the weld pool. The diameter of the ceramic cup should be at least twice as large than the diameter of the tungsten electrode to avoid this issue.
In addition to the size of the ceramic cup, the gas flow rate also should be adjusted according to the size of the ceramic cup. Using a large ceramic cup with a low flow rate for the shielding gas will create gap in the shielding gas. Using a high flow rate of gas through a small ceramic cup will create a venturi effect that will likewise pull air into the weld pool.
It is important, therefore, to balance the flow of the shielding gas so that it is powerful enough to push the air out of the weld pool yet not so powerful as to create turbulence in the shielding gas. Many professional in the welding field use a gas lens in place of a ceramic cup. Standard ceramic cups may limit the welder’s view of the welding process.
Gas lenses use a mesh screen that straightens the shielding gas that emerge from the ceramic cup. Because the gas is straightened, welders can extend the tungsten electrode beyond the ceramic cup without losing the shielding gas’ protective quality for the weld tip. Furthermore, welders can better view the weld pool when using a gas lens instead of a ceramic cup.
The distance that the tungsten electrode extends beyond the ceramic cup is referred to as the tungsten stick-out. If the tungsten stick-out is too large, the shielding gas will not be able to protect the tungsten electrode from becoming contaminated. The stick-out should be such that the length of the tungsten electrode that extend beyond the ceramic cup is of the same length as the inside diameter of the ceramic cup.
Using such a length of tungsten electrode will maintain a stable arc in the weld pool and keep the shielding gas from being disrupted.
