What are the types of brazing gases in the furnace

There are three types of brazing gases in the furnace:

(1) Non combustible gas, non combustible gas will not burn in the air, and will not explode when it is mixed with air in any proportion and at the ignition temperature of combustible gas mixture. The typical nonflammable gases are nitrogen, argon, carbon dioxide and their mixture (also contain flammable gases such as hydrogen and carbon monoxide, but the content is lower than the combustible concentration).

(2) The low exothermic gas is a mixture of nitrogen and carbon dioxide, in which the content of hydrogen and carbon monoxide is very low, which is significantly lower than that at room temperature, and the minimum content of hydrogen and carbon monoxide that can be exploded by hot furnace elements, The mixture of various proportions of non combustible gas and air can be used in the furnace at will, which will not cause explosion due to heating or stopping heating of the furnace, and will not cause explosion due to ignition or non ignition of the pilot device. However, be careful when using carbon monoxide, because it is toxic. Attention should also be paid to gases with higher density than air, such as argon and carbon dioxide, which may escape from the furnace and stay in the pit or other low-lying places, suffocating people entering here.

（3） Carbon monoxide and methane (CH4) are common combustible gases in furnace gas. The prepared mixture gas containing carbon hydroxide, a small amount of methane and a certain proportion of non combustible gas includes: multi exothermic gas, purified multi exothermic gas and endothermic gas. The decomposed ammonia (75% H2, 25% N2) is a strong combustible gas.

Special attention shall be paid to the following situations when operating the furnace with combustible gas atmosphere.

① Introduce the combustible protective atmosphere into the furnace chamber; 

② open the cold chamber filled with combustible gas; 

③ remove the combustible atmosphere and let the air enter the furnace again; 

④ the combustible air entering the furnace during the normal operation is accidentally blocked, so that the air can enter.

What should be done if the combustible gas flow is blocked?

When the combustible gas flow to the furnace is blocked, the operator must immediately try to restore the flow. If it cannot be restored immediately, the furnace shall be purified by non combustible gas method or burn out method to restore the pressure and prevent air from entering. The type, location, air flow, temperature and flammability of the furnace all have an impact on the allowable time delay before purification, but the safety measure is to automatically start to use non combustible gas to clean the furnace immediately. When the combustible air flow is blocked, an alarm shall be given to let all personnel leave the site.

If the non combustible gas cannot be supplied in an emergency and the gas flow cannot be restored immediately, the burning method shall be used for purification. For intermittent box furnace or other through furnace, the gas ignition device with continuous combustion can be used as ignition source. If none of these methods can be used or invalid, the portable flame torch shall be used, or the rubbed newspaper or grease cotton yarn shall be placed on the whole width of the opening of the outer door, ignited, and then the door shall be fully opened. Before the residual gas is burned out, the pilot device, torch, newspaper or cotton yarn shall be burned continuously to ensure the safety of welding construction.