Tungsten sheet is essential to advanced technology manufacturing—a key constituent in a vast range of products requiring accuracy, stability, and reliability. And no attribute of tungsten sheet is more critical to providing those qualities than tungsten sheet flatness.
The number and type of products that benefit from tungsten sheet’s remarkable flatness to sustain precise tolerances of smooth, level, surface quality are nearly endless. Exceptional flatness assures optimal contact surfaces and superior thermal conductivity, making tungsten sheet ideal for use as heat spreaders and other thermal conducting parts. It also makes possible precise electron beam focus and transition in applications such as X-ray tubes. In addition, exacting flatness tolerance assures even coating distribution on tungsten sheets requiring coatings or additional surface treatments.
Recent Advancements for Improving Tungsten Sheet Flatness
Recent advancements in the production process of high-flatness tungsten sheet represent a major leap forward from traditional manufacturing methods. The newest methods allow medium size (5.5” x 10”) tungsten sheets with a thickness of 0.01 inches to be further refined to thickness tolerances of +/- 0.004” and flatness of 0.001”. This advanced process involves pre-heating of tungsten billets before rolling, implementation of electropolishing, and introduction of simultaneous annealing flattening.
Pre-Heating
Pre-heating the tungsten billet minimizes thickness inconsistencies. To ensure even heat distribution, the billet is first coated with a 15%-20% graphite emulsion, then uniformly heated in a box-type furnace equipped with hydrogen nozzles. This step also facilitates even rolling of the billet, thereby reducing work hardening and cracking risks during the rolling phase and enabling more precise control over thickness tolerances.
Electropolishing
After rolling, tungsten sheets undergo an electropolishing procedure to reduce surface roughness. This involves the gradual dissolution of minor surface protrusions by electrolysis: a tungsten plate serves as the anode, a titanium plate as the cathode. An electrolyte solution of NaOH, KCIO₃, and K₂CO₃, is stirred using compressed air.
Advanced Annealing and Flattening
The final production stage involves an enhanced, simultaneous annealing and flattening to further improve the tungsten plate’s flatness. Post-rolling, the thin sheets are subjected to an annealing treatment in a cylindrical vertical resistance furnace. The environment is filled with hydrogen to prevent oxidation. Temperature is meticulously monitored and controlled using thermocouples in the furnace and heating tank. The flattening process employs press blocks made from high-flatness TZM molybdenum alloy, with the tungsten sheets arranged between multiple blocks. Additional tungsten weights are placed atop the uppermost block. To ensure optimal flatness, the entire annealing and flattening process is conducted within a variable temperature regimen of 760℃ for 0.5 hours, followed by 1100℃ for 2 hours.