<P> Vacuum furnaces is a relatively economical method of oxide prevention and is most often used to braze materials with very stable oxides (aluminum, titanium and zirconium) that cannot be brazed in atmosphere furnaces . Vacuum brazing is also used heavily with refractory materials and other exotic alloy combinations unsuited to atmosphere furnaces . Due to the absence of flux or a reducing atmosphere, the part cleanliness is critical when brazing in a vacuum . The three main types of vacuum furnace are: single - wall hot retort, double - walled hot retort, and cold - wall retort . Typical vacuum levels for brazing range from pressures of 1.3 to 0.13 pascals (10 to 10 Torr) to 0.00013 Pa (10 Torr) or lower . Vacuum furnaces are most commonly batch - type, and they are suited to medium and high production volumes . </P> <P> Silver brazing, sometimes known as a silver soldering or hard soldering, is brazing using a silver alloy based filler . These silver alloys consist of many different percentages of silver and other metals, such as copper, zinc and cadmium . </P> <P> Brazing is widely used in the tool industry to fasten' hard metal' (carbide, ceramics, cermet, and similar) tips to tools such as saw blades . "Pretinning" is often done: the braze alloy is melted onto the hard metal tip, which is placed next to the steel and remelted . Pretinning gets around the problem that hard metals are difficult to wet . </P> <P> Brazed hard metal joints are typically two to seven mils thick . The braze alloy joins the materials and compensates for the difference in their expansion rates . It also provides a cushion between the hard carbide tip and the hard steel, which softens impact and prevents tip loss and damage--much as a vehicle's suspension helps prevent damage to the tires and the vehicle . Finally, the braze alloy joins the other two materials to create a composite structure, much as layers of wood and glue create plywood . The standard for braze joint strength in many industries is a joint that is stronger than either base material, so that when under stress, one or other of the base materials fails before the joint . </P>

Low melting alloy used to join pieces of metal together