Rolling and Surface Quality Control of Molybdenum Foil

Once molybdenum foil is reduced to a few tens of micrometers, a thickness deviation of a few micrometers is enough to affect subsequent blanking and lamination assembly. During rolling, thickness, flatness and surface condition influence each other, and the final finishing pass alone can rarely make up for shortfalls.

Pass Scheduling and Thickness Tolerance

Molybdenum work-hardens quickly; an excessive reduction per pass makes roll force rise sharply, increases elastic deflection of the roll stack and widens thickness variation. A multi-pass, small-reduction sequence is normally used, with intermediate annealing scheduled once cumulative deformation reaches a certain level. Thickness control relies on roll gap setting, thickness gauge feedback and tension coordination, and uniform incoming thickness is the foundation; if the blank itself has a wedge or local thick spots, later passes can hardly roll it flat. Tolerance requirements should match the application, since tighter tolerances raise slitting and rejection costs.

Incoming inspection cannot look at thickness alone. Cross-thickness variation within a sheet, edge cracks and surface oxidation of the blank are all amplified in later passes, so a surface check and thickness sampling before rolling can reduce batch scrap.

The Role of Intermediate Annealing

Intermediate annealing restores ductility and removes work hardening so that subsequent passes can continue to reduce thickness. Annealing temperature and time must balance recrystallization against grain coarsening: too little leaves the material hard and prone to cracking on further rolling, while too much coarsens the grains and degrades the mechanical properties of the foil. The surface condition after annealing also matters; if the furnace atmosphere contains oxygen or has a high dew point, the surface discolors, and later rolling presses the oxide layer into the base metal to form defects that are hard to remove. Loading arrangement affects heating uniformity, and the inner and outer wraps of a coil may differ in structure.

Scratches, Oxidation and Flatness

• Scratches: mostly from roll surface damage, guide plate burrs and handling impacts; roll surfaces must be inspected and changed at regular intervals.
• Oxidation: determined jointly by the annealing atmosphere, storage environment and packaging seal, and humid seasons require particular care.
• Waviness and bow: uneven roll force distribution, improper tension control or poor incoming flatness.
• Indentations: foreign matter pressed into the roll gap; cleaning and protection must be handled on the entry side.

Lubrication plays a part in all of these defects. The viscosity, cleanliness and filtration accuracy of the rolling oil affect oil film thickness; too thin a film raises friction and roughens the surface, while too thick a film interferes with thickness control. Degreasing after rolling must be thorough, because residual oil film carbonizes during annealing and creates surface contamination.

Matching coiling tension to speed affects coil shape, and tension fluctuation leaves marks at the loosely wound sections. Coil changes, joins and stop-restart are the periods when thickness variation concentrates, so speed transitions should be softened in operation. The rolling schedule should group orders of the same specification and thickness to reduce flatness fluctuations caused by frequent roll changes.

Slitting and Pre-Delivery Inspection

In slitting, tool sharpness, tension and edge guiding determine coiling alignment and edge quality. Burr height after slitting can be judged roughly by touch and a magnifier, with instrument measurement for critical applications, and the first piece confirmed before moving to batch production. Before delivery, inspection usually covers multi-point thickness measurement, visual surface examination, coil diameter and number of joins, with mechanical property sampling where required. Packaging uses moisture-barrier materials with desiccant, and compression during transport should be avoided.