Sintered tungsten rod

Technological process
The preparation process of sintered tungsten rod is mainly as follows: static pressing of tungsten powder – pre sintering – vertical melting sintering
1. Molding process: powder molding is carried out by static pressure. The density of the briquette after molding is generally 60-65% of the theoretical density. See the table below for typical forming process.

2. Pre sintering: put the formed blank in the hydrogen molybdenum wire furnace at 1200 ℃ for pre sintering for 120 minutes, cool to 250 ℃ and then exit the furnace. Through pre sintering, a large part of adsorbed gas can be eliminated, so as to improve the strength, which is conducive to material handling and subsequent vacuum sintering.

3. Vacuum sintering: the purpose of sintering is to improve the purity and strengthen the density and lightness. Sintering is a diffusion process. Sintering temperature, atmosphere and holding time are three main factors that affect the quality of the final product. At 1650 ~ 1700 ℃, the metal impurities and interstitial elements can be exerted. Cut off the power and cool down after holding the highest sintering temperature. It takes about 10 hours to vertically melt a 45 mm diameter tungsten rod.

Pass rolling process

The billet is heated in the hydrogen molybdenum wire furnace, the temperature is 1500-1550 ℃, the first heat preservation time is 90 minutes, the remaining heat preservation time is 15 minutes, the final rolling temperature cannot be lower than 1300 ℃, the heating temperature is too high, the surface will crack. If the temperature is too low, the mouth will crack. So strictly controlling the heating temperature is the key to rolling smoothly.

According to the high temperature plasticity and rolling mill capacity of vertical melting sintered tungsten bar, the pass processing rate can be increased, but if the pass processing rate is too large, the bar will appear “ears”, which is not easy to bite. If it is too small, the surface of the bar will be deformed, and usually there will be 20 ~ 30mm shrinkage cavity in the tail.

The density is 90-95% of the theoretical density, and the number of grains is 200-400 / mm2.