Filler Neck on Fuel Tank

One of the important applications of brazing in the automotive industry is the brazing of filler neck on fuel tank. Fuel tank is found in all types of vehicles so the brazing of filler neck is a widely recognized process in the automotive sector. Brazing provides safe and secure joints, which is important for the fuel tanks so that the joints are leak proof.

Brazing Alloys
Different brazing alloys are used for brazing filler necks made of different material. In case the fuel tank is made of leaded sheet steel, then brazing alloys containing cadmium are suitable for use. For this process the working temperature should be around 610°C. However different brazing alloys are used if the parts to be joined are made of galvanized sheet steel.

Silver brazing alloys are considered best for the brazing of filler neck of fuel tanks. The common constituting elements are silver, copper, zinc, and cadmium. Other elements present in lesser amounts are aluminum, bismuth, phosphorous, silicon, etc. Silver constitutes almost 40% by weight and is the major constituent. Copper, zinc and cadmium are other major constituents each having 18 to 20 % by weight.

In case the fuel tank and filler neck are made of ordinary steel sheet, then a brazing alloy having slightly different composition is used. For this type of fuel tanks, the brazing alloys don't contain cadmium. Instead they contain tin (up to 5%). The flux used for brazing this type of fuel tanks are based on boron compounds and contain fluorides. The flux residues must be removed after brazing because it is highly susceptible to corrosion.

Brazing Process
Torch brazing is the most suitable brazing process for joining filler necks on fuel tank. The brazing is usually carried out using the gas flux method. Here, gaseous flux, which mostly forms from volatile liquid mixtures, is used for brazing with a torch flame.