Wednesday, October 21, 2009

Pipes of Steel - Wait thats Titanium

Here is your metal shop welding info for the day;

Welding Titanium and stainless applications requires surrounding the weld area with inert gas ( non flammable stable gas such as Argon, which is used the most often because it is very easy to control. ) both front and back of the weld area building a micro atmosphere.

When welding bicycles as an example; both the inside of the tube needs to be completely filled with the inert gas and then use of a large gas cup is needed on your tig torch as to cover the complete weld zone on the front side and allow no atmosphere air to enter the weld area. Here is a glass lens on a tig torch, this is the one I use for all my Titanium or stainless work as it covers a large area but doesn't block your view.
If atmosphere air enters the weld zone it will react with the molten metal and create impurities, depending on what kind of air hits the molten weld area it can cause things such as underling cracks cause by hydrogen or it can mess up the grain structure of the weld area causing a weak zone. The easy way to tell on titanium, how your weld turned out and the FAA approved way by aerospace testing procedures is by color ( this only applies to titanium ), any color other then a light gold color called Hay is considered contaminated and needs to be removed or redone.
Here is a picture of " Stainless Steel Sugaring " - This is a term from the aerospace industry. This will happen on just about any metal that is welded but it is very very critical that it is not present when welding stainless or titanium. If it is present well start cutting it out and starting over!

If you have a lot of work to do or it is very windy ( as this might blow the inert gas from the weld area and cause a welding failure ) some people use these bad boys. They are expensive but super nice, it is a complete purge welding balloon and you can also get fixed boxes with windows for production runs.

Other ways titanium can develop color in the weld area is from oil or other chemicals. If you ever visit a shop that specializes in titanium for aerospace or other industries, the shops are cleaner then most hospitals with most employees using cotton or rubber gloves for everything in the shop.
Here is an example of a color code chart for titanium - as you can see all the color plates are bad, the top left is very good and had the correct purge but second to the left is on the edge of being accepted.

NOTE - IF any one of these plates was cleaned with steel wool or sanded the color would disappear and the weld would be perfect looking - beeeeeeeee VERY CAREFUL it is possible to fool even the most experienced welding inspector if it is lightly cleaned.

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