Sintered Tungsten Rod
The manufacturing processes include: tungsten powder press forming→presintering→vertical sintering.
1.Moulding process: the density of the press block made by powder compacting is the 60~65% of theoretical density.
2.Presintering: under the temperature of 1200℃, the blank is put into hydrogen molybdenum wire furnace for 120min. After cooling to 250℃, move it away. After a presintering process can eliminate most of the adsorbed gas, thereby increasing the strength of th eproduct, which is conducive to the transport and the follow-up processes of sintered tungsten rod.
3.Vacuum sintering: sintering purpose is to increasing the purity and density, a sintering is a process of diffusing. Sintering temperature, atmosphere and holding time are the three main factors that affect the final product quality. If the product can be kept at 1650 ~ 1700℃, the metal impurities and gap elements would volatilize. Sintering a tungsten rod with diameter of 45mm takes about 10 hours.
Heating temperature of Rod blanks in a hydrogen molybdenum wire furnace is 1500 ~ 1550℃, holding time of the first fire is 90 minutes, holding time of the rest of the fire is 15 minutes, finishing temperature should not be lower than 1300℃, if the heating temperature is too high, surface would have cracking phenomenon. So, strictly control the heating temperature is the key to the rolling. 90~95% of theoretical density, the number of grains of 200~400 of a sintering tungsten rod has a better high temperature plasticity.