Upgrading Tungsten and Molybdenum Processing Equipment: Changing Selection Criteria for Mills and Hammers

A molybdenum plate travels from sintered billet to finished sheet through several rolling and annealing passes. With the same billet batch, a different equipment set will open a gap in yield and microstructural uniformity. In recent years, equipment upgrades at tungsten and molybdenum processing companies look on the surface like capacity expansion, but in substance they are aimed at shape, thickness tolerance and internal structure. Equipment selection therefore cannot compare tonnage and price alone; it has to be judged against process capability.

Three Checks to Settle Before Replacing Equipment

On the shop floor you often hear that the old mill can no longer press the material, but the problem frequently lies upstream: billet density fluctuation, uneven heating, an unreasonable pass schedule. The equipment merely amplifies the fluctuation. To judge whether the mill really needs replacing, start with three things: record the density distribution of the same billet batch, measure the temperature difference between the upper and lower surfaces of the billet after heating, and compile the thickness tolerance range of the existing mill. If all three are stable, then discuss equipment; if one is scattered, fix the process first. Inspection criteria can follow the dimensional and structural checks described under quality control.

Mills: Stiffness Matters, and So Do the Means of Shape Control

Molybdenum has high deformation resistance at temperature, and rolling force fluctuations show up directly in the roll gap. Where stand stiffness is insufficient, thickness tolerance accumulates pass after pass. Stiffness cannot be judged from the nominal value alone; observe the thickness consistency of the same specification billet across different pass schedules. Shape depends on roll crown configuration, roll bending means and reduction allocation, and thin sheet becomes more sensitive to shape in the later passes. Companies focused on wide thin sheet should spend time comparing the roll system and the response speed of the hydraulic screwdown; this is discussed in more detail under process technology.

Setting Hammer Tonnage and Striking Method

The hammer handles cogging and microstructural improvement, and tonnage selection relates to billet unit weight and the target deformation. If drop energy is insufficient, deformation stays at the surface; if energy is excessive and control is coarse, edge cracking is likely. Steam-air and all-hydraulic striking methods each have their application: the former has a fast rhythm and suits batch cogging, while the latter offers adjustable striking energy and better suits alloy billets that are sensitive to deformation rate. At selection, ask the supplier to trial-forge with your own billet and observe whether core deformation is achieved.

After sectioning a trial forging, hardness can be measured at three points through the thickness; a flat hardness curve shows that deformation has penetrated to the core, while a marked difference between surface and core means striking energy or the pass schedule still needs adjustment. Folds and hairline cracks in forgings mostly appear at the corners and are easier to identify after pickling; when found, review the anvil face condition and the billet heating record. A heavy billet cannot be penetrated in a single blow, and several lighter blows are often safer than one heavy blow.

Furnace Temperature Uniformity Is Easily Skipped

Heating and annealing between rolling and forging determine whether the structure is uniform. Where the furnace chamber temperature distribution is uneven, local coarse grains appear in the plate and the risk of cracking in subsequent rolling rises. When accepting a heat treatment furnace, look beyond controller accuracy and run temperature distribution tests in both empty and loaded states, recording the heating rate. Repeating the test after a change in load has more reference value than empty-furnace data alone.

Accepting Equipment and Process Together

After new equipment is installed, run a before-and-after comparison on the same billet batch, recording yield, thickness tolerance, grain size and the number of surface defects, to judge whether the upgrade is effective. Equipment parameters, process windows and inspection standards must be updated together; otherwise the new equipment will still be run by old habits. If you want your own billet conditions assessed together with an equipment plan, contact us.