Nogas is briquette for plunging into Copper & Copper alloys to remove Hydrogen Gas. The solubility of hydrogen in copper and copper-base alloys decreases appreciably as the metal cools from the liquid to the solid phase. The metals normally alloyed with copper have varied effects on the solubility of hydrogen in copper.
Aluminium, zinc and tin additions decreases the solubility of hydrogen, while nickel additions increases it. Where solidification occurs over a range of temperature, the decrease in solubility from liquidus to the solidus is distributed over that range. The gas dissolved in the molten metal diffuses during solidification into the remaining interdendritic pools of liquid until, when these solidify, it is ejected as gas bubbles to form the familiar interdendritic gas porosity. Thus, NOGAS is a must use to prevent gas porosity defects arising due to Hydrogen Gas.
NOGAS briquettes are convenient to apply and most effective in removing dissolved hydrogen from molten copper and its alloys. A compacted degassing briquette is plunged beneath the metal surface to release a stream of scavenging gases from the decomposition which ensues.
The scavenging gases do not produce any objectionable or toxic fumes and the only equipment required is a suitably protected plunger rod.
NOGAS is supplied as strong, robust briquettes that can be safely and easily stored, handled and applied.
Degassing with NOGAS briquettes can be carried out in the furnace in the case of lift-out, tilting and high frequency furnaces. For larger units it is recommended that degassing should be carried out in the transfer ladle.
The NOGAS briquettes are so designed that they can be attached to or wedged on, to a variety of plunger rod shapes, etc. Perhaps the most suitable tool is a simple steel rod, furnished with a peg or stop to prevent the briquette riding up the rod, when plunged into molten metal.
The briquette may also be wired to a suitable plunger made from either steel or graphite or, if a suitable graphite rod is available, the end can be turned down into a cone shape and the briquette wedged on to it. This is the most satisfactory method since it leaves the largest surface area of the briquette exposed to produce the scavenging gases. For very large melts a dummy stopper rod is probably the best approach.
One piece to be plunged beneath the molten metal for 8 to 10 minutes for 250 to 300 Kgs of metal. In case of more than 300 Kgs, additional piece has to be fixed in plunger for every 250 Kgs of metal. Piece will not get dissolved but the chemicals inside it will get used in a single use only. (Plunger rod needs to be designed as per number of pieces to be used.)
