| CPC C23C 4/129 (2016.01) [B21B 27/02 (2013.01); C23C 4/02 (2013.01); C23C 4/10 (2013.01)] | 6 Claims |
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1. A method for obtaining rolling mill rolls with a coating of tungsten carbide alloy, characterised in that the following operational phases or steps are defined therein:
a) degreasing the surface of the mill roll
c) heating the surface of the mill rolls with a diameter greater than 500 mm between 40-50° C. and the mill rolls with a diameter of less than 500 mm between 80-100° C.
d) coating the mill roll with a tungsten carbide alloy comprising molybdenum borides or chromium carbides by means of thermal spraying wherein a powder of a tungsten carbide alloy is melted exhibiting a powder granulometry comprised between 30 μm and 15 μm in a combustion chamber, the molten material is transported to a spraying gun by means of a carrier gas and is sprayed on the mill roll by means of the gun with a supply flow at values comprised between 1 and 8 kg/h,
wherein:
thermal spraying is high velocity fuel-air thermal spraying wherein the fuel is materialized in propane with a pressure comprised between 593 and 614 kPa, air is applied at a pressure comprised between 552 and 579 kPa, nitrogen and hydrogen are applied at a pressure of the order of 496 kPa, using a nitrogen flow rate of the order of 23 l/min, and a hydrogen flow rate of the order of 15 l/min, setting the pressure of the combustion chamber at about 496 kPa,
the carrier gas is nitrogen, with a flow rate comprised between 20 l/min and 30 l/min,
the propane pressure is at least 14 kPa above air pressure,
the distance between the gun and the mill roll to be coated is comprised between 19 cm and 26 cm,
the transverse speed of the spraying gun is comprised between 2 and 3 mm/s; having envisaged that the linear movement of the mill roll moves at a speed of between 2000 mm/s for diameters less than 500 mm, 2500 mm/s for diameters comprised between 200 and 500 mm and 3000 mm/s for diameters less than 200 mm.
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