Tips for Properly Purging Mild Steel Tubes

By: Krysty


Mild steel tubing can be difficult to work with, particularly when it is time to weld. If you are not a professional or have never welded steel tubes before now, here are some tips. Make certain you have a 1/8 wire to do the welding instead of a 3/3n inch rod, use sufficient amperage to avoid overheating and use brushes and files made specifically for working with stainless steel. Allow the mild steel to cool between passes with your welding rod but keep the tip of the rod hot and be certain to use argon for shielding. Trim the welding rod if it gets stopped up in order to keep the tungsten sharp.

Purging mild steel tubes with argon gas is absolutely necessary. It prevents granulation and sugaring. These two symptoms of severe oxidation can be detrimental to your project. In order to complete a mild steel weld, the steel must be purged with argon on the inside surface of the tubes. To purge tubes, cover one end of the tubing with aluminium duct tape, fill with argon gas and then cover the opposing end. This will trap the gas inside the tube long enough to complete the purging process. Use an oxygen analyzer afterward to check the thoroughness of the purge.

Before purging make absolutely certain the inside of the tube is completely dry. If there is any water left inside the tube it will ruin the purge. To ensure that a tube is purged completely, you can poke a small hole in the aluminium duct tape on one end of the tube. Then use this hole to allow a continuous stream of argon gas into the tube. Since argon is denser than air, it should be allowed to completely fill the tube, replacing the air as it fills. Because of its density, argon naturally has the ability to displace air. To ensure a high flow rate of argon gas, attach a diffuser to both ends of your argon hose. If you donít have a diffuser one can be engineered using steel wool, a small piece of sheet metal and a perforated stainless steel sheet.

Once purging is complete, remove the tape from both ends of the tube and apply the tacking. Allow the tack to cool then replace the tape. The tacks should be placed 180 degrees, or directly across from each other. Re-weld impenetrable areas if necessary.

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