The Operation Techniques for Oxygen-Acetylene Brazing of Tungsten Carbide and Steel
a) In order to prevent decarburization and over-sintering of cemented carbide inserts ,it usually takes carbide flame in brazing
b) It is good to keep the brazing temperature at 1000℃,that is to heat the cemented carbide insert into bright red color. If the insert’s color as dark red or white light ,it is unavailable to be brazed.As if the color is dark red ,it means the temperature is too low ,but if the color is white light ,it means the temperature is too high and will lead to over-sintering problem.
c) The welding blow lamp to heat the cemented carbide cutting tools from right to left ,left to right ,from top to bottom repeatedly, so as to make the cemented carbide cutting tool body heat uniformly .
d) The distance between welding tip and shaft is around 50mm ,meanwhile the tip tilts shaft with angle at 110°,in order to ensue effectively use flame and reach heating balance ,avoiding oxidization and pore emerged .
e) The brazing speed is decided by the size of cemented carbide insert. The brazing for grade 40 steel and YT15 cemented carbide turning insert must be finished within 1min,with this way can avoid cemented carbide decarburization and over-sintering .
f) After brazing ,the cemented carbide inserts have to be heated with flame ,and then move out the brazing tip and make them cool naturally ,so as to prevent cracking .
In the brazing process ,we have to control the brazing temperature correctly .If the temperature is too high ,will lead to oxidization of welding seam and the Zn in brazing alloy evaporated .On the contrary ,if the temperature is too low will result in overthicknes of welding seam due to bad flowing of brazing alloy, meanwhile there are a lot of porosities and slag existing in welding seams which is the main reason of desoldering.The brazing temperature has to higher 30~50℃ ,at this time the brazing alloy is available to flow freely with good penetrability ,which is easy to penetrate and cover all the welding seam. After melting of the brazing alloy ,you should use a copper pressure-adding rod to move along with the cemented carbide groove repeatedly 2~3 times ,so as to eliminate slag in the welding seam, in addition the moving distance is 1/3 of the cemented carbide length .
Cooling speed after brazing is also a very important factor to influence the brazing quality .The tensile stress is created instantly as soon as cooling ,the cemented carbide’s resistance of tensile stress is dramatically bigger that the anti-pressure stress .Especially for the cemented carbide grade such as YT60,YT30 ,YG3X etc with which the brazing surface is big but substrate is small ,you must pay more attention to the cooling speed after brazing .Generally ,the work-piece after brazed is put into lime or charcoal powder trough so as to cool them slowly and naturally .This way is very simple but unavailable to control tempering temperature .If condition available ,the brazed work-piece should be put into the 220~250℃tempering furnace for 6~8h.It is a good way to eliminate part of brazing residual stress ,reduce cracks and prolong cemented carbide tools service life by means of low temperature tempering process.
