DRIVE GEAR BOXES

A well-designed gearing generates its pay back of the gearboxes and the centralized lubrication units from the
POWER SAVING ALONE.

The gearboxes and pinion stands are with EN24 Pinions and EN9 gears. The alloys EN24 and EN9 are made by forging out of ingots produced on arc furnace. The forgings are annealed, and heat-treated up to 300 BHN, maintaining a difference of 20 BHN between the pinion & gear.

The gears are profile corrected to enhance root strength. The profile accuracy is maintained to have the transmission efficiency well within 2% per stage loss. A Two-stage gearbox at the Roughing mill should transmit 96% power, the figure being 94% for the three-stage gearbox.

The casings are with sufficient ribs for rigidity for vibration less transmission. The surface area is maximized to have the matching thermal efficiency. Thermal efficiency is stressed upon because with an increase of only 20 degree centigrade the viscosity of oil reduces by 70%. To augment the thermal efficiency the centralized lubrication units are provided for continuous supply of filtered, de-aerated and cooled oil to the gearing. If any one of the parameters filtration, de-aeration or cooling is sacrificed the cost is more than paid in the life of the gearbox and the transmission loss.

MILL STANDS

The Mill Stands are designed keeping in mind:

(a) Minimum percent elongation on load (maximum rigidity)
(b) Best alignment of the stand windows and the base locating taper.

We stress for cast steel Mill Stand housing, chocks and rest bars, because ...

     - Cast Steel structure is more corrosion resistant against water compared to Cast Iron or steel fabricated. In case of mill stands the water is continuously poured on the rolls.

     - The mill stands are designed to reduce percentage elongation of post sections under load, so that the rolled bar conforms more accurately to cut grooves. The post thickness design and usage of cast steel housing with increased yield strength reduce this percentage elongation.

     - The roughing mill housing has projected lugs for 3 hi Mill stands at the middle Chocks to shift the support point towards the center thereby reducing chocks deflection on load and improving size control.

     - All mill stand windows are machined in pairs in one setting with angle facing attachments on horizontal boring machines, to achieve perfect window alignment. The stand windows are further lapped manually to reduce aberrations. The chock-fitting dimensions are so made to provide the desired fit after discounting thermal expansion in operation.

This again shall reduce the Roller/fiber bearing consumption and power consumption.

AUXILIARIES

Tilting tables are well balanced at the fulcrum points so that the least power if required in lifting.

The rollers are designed so as to compensate for the thermal expansion without camber and supported on anti friction bearings. The mountings are sufficiently rigid for vibration free transfer.

Shears are provided with in built lubrication system for continuous spray of oil onto the gears and all friction points. Being an intermittent operation flywheel is provided to reduce the installed power.

The V belts are installed on the high speed and the low torque side, with minimum ratios at the pulleys, for reduced transmission loss.