Method of applying a wear-resistant coating on a yankee drying cylinder, such coatings and yankee cylinders with such coatings

Abstract

A method of applying a long lasting wear-resistant coating on a Yankee drying cylinder is described, whereby the method includes: providing a Yankee drying cylinder having a cylindrical shell with a circular cross-section and an outer surface; and performing a thermal spray operation to form a wear-resistant coating layer on the outer surface of the Yankee drying cylinder during which thermal spray operation coating feedstock is fed to at least one spray device, heated to become plastic and/or semi-molten and/or molten and sprayed onto the outer surface of the Yankee drying cylinder to form the wear-resistant coating layer. The coating feedstock for the thermal spray operation consists of a specific set of elements, by percent weight, with the remainder being iron and impurities. Coatings and Yankee cylinders with such coatings are also disclosed.

1 . A method of forming a wear-resistant coating with a diamond pyramid hardness (DPH) determined by ASTM E384-10, “Standard Test Method for Knoop and Vickers Hardness of Materials”, which is equal to or greater than 650 and equal to or less than 1004 on a Yankee drying cylinder ( 1 ), the method comprising:
 a step of providing a Yankee drying cylinder ( 1 ) having a cylindrical shell ( 2 ) with a circular cross-section and an outer surface ( 3 ); 
 a step of performing a thermal spray operation to form a wear-resistant coating layer ( 4 ) on the outer surface of the Yankee drying cylinder ( 1 ) during which thermal spray operation coating feedstock ( 6 ) is fed to at least one first spray device ( 5 ), heated to become plastic and/or semi-molten and/or molten and sprayed onto the outer surface ( 3 ) of the Yankee drying cylinder ( 1 ) to form the wear-resistant coating layer ( 4 ), the coating feedstock ( 6 ) for the thermal spray operation consisting of:
 0.0 to 2.1 weight percent Al 
 0.0 to 10.0 weight percent Ti, 
 0.0 to 10.2 weight percent Si, 
 1.7 to 10.1 weight percent B, 
 15.0 to 16.1 weight percent Mo, 
 9.5 to 11.4 weight percent V, 
 2.0 to 4.2 weight percent C, 
 0.000 to 0.050 weight percent Cr, 
 0.0 to 0.3 weight percent Mn, 
 0.0 to 0.2 weight percent Mg, 
 0.0 to 1.0 weight percent Ni, 
 0.0 to 0.5 weight percent Nb, 
 the remainder being iron and impurities. 
 
 
     
     
         2 . The method of  claim 1  wherein the step of thermal spraying the outer surface of the Yankee drying cylinder ( 1 ) is performed until the wear-resistant coating layer has obtained a thickness of 680 μm-2000 μm. 
     
     
         3 . The method of  claim 1  wherein the coating feedstock ( 6 ) for the thermal spray operation consists of:
 from 1.40 to 2.02 weight percent Al, 
 from 0.00 to 10.00 weight percent Ti, 
 from 0.10 to 10.08 weight percent Si, 
 from 1.80 to 10.00 weight percent B, 
 from 15.00 to 16.10 weight percent Mo, 
 from 10.00 to 11.36 weight percent V, 
 from 2.10 to 2.50 weight percent C, 
 from 0.000 to 0.020 weight percent Cr, 
 from 0.10 to 0.30 weight percent Mn, 
 from 0.00 to 0.10 weight percent Mg, 
 from 0.00 to 1.00 weight percent Ni, 
 from 0.00 to and 0.50 weight percent Nb, 
 the remainder being iron and impurities. 
 
     
     
         4 . The method according to  claim 1 , comprising the subsequent step of performing a grinding and/or polishing operation of the coated outer surface such that, after the grinding and/or polishing operation, the wear-resistant coating layer ( 4 ) has a thickness from 100 μm-1990 μm. 
     
     
         5 . The method according to  claim 1 , wherein the step of performing thermal spray operation to form the wear-resistant coating layer ( 4 ) is preceded by the steps of: performing an initial first grinding operation on the outer surface ( 3 ) of the shell ( 2 ); grit blasting the outer surface ( 3 ) after the initial first grinding operation; coating the ground and grit blasted outer surface ( 3 ) with a bond coating layer ( 10 ) having a composition different than the composition of the coating feedstock ( 6 ), and wherein the wear-resistant coating layer ( 4 ) is subsequently applied on top of the bond coating layer ( 10 ). 
     
     
         6 . The method according to  claim 5 , wherein the coating of the ground and grit blasted outer surface ( 3 ) with a bond coating layer ( 10 ) is performed by an initial thermal spraying operation during which a bond coating feedstock is fed to at least one spray device ( 13 ), heated to become plastic and/or semi-molten and/or molten and sprayed onto the ground and grit blasted outer surface to form the bond coating layer ( 10 ), wherein the bond coating feedstock constituting a Ni—Al mixture or alloy consisting of from 85 to 98 percent by weight Ni and from 15 to 2 percent by weight Al and unavoidable impurities. 
     
     
         7 . The method according to  claim 6  wherein the thickness of the bond coating layer is either:
 greater than or equal to 1.00 μm and less than or equal to 2000 μm; or 
 greater than or equal to 10 μm and less than or equal to 30 μm. 
 
     
     
         8 . The method according to  claim 1 , wherein the method comprises applying an aqueous solution comprising dissolved mono ammonium phosphate or di ammonium phosphate over the surface of the wear-resistant coating layer ( 4 ). 
     
     
         9 . The method according to  claim 4 , wherein the grinding and/or polishing operation is performed until the surface of the wear-resistant layer ( 4 ) has obtained a surface roughness Ra in the range of 0.1 μm-1.2 μm. 
     
     
         10 . The method according to  claim 1 , wherein the coating feedstock ( 6 ) for the wear-resistant coating layer ( 4 ) comprises from 16.00 to 16.10 weight percent Mo, from 10.85 to 10.98 weight percent V, from 1.81 to 1.85 weight percent B, from 2.17 to 2.19 weight percent C, from 0.00 to 0.10 weight percent Ti, from 0.00 to 0.10 weight percent Mg, from 0.00 to 0.10 weight percent Ni, from 0.00 to 0.50 weight percent Nb, and from 0.000 to 0.005 weight percent Cr. 
     
     
         11 . The method according to  claim 10 , wherein the coating feedstock for the wear-resistant coating layer ( 4 ) comprises 16.00 to 16.04 weight percent Mo, 10.85 to 10.98 weight percent V, 1.81 to 1.85 weight percent B, 2.17 to 2.19 weight percent C, and from 0.000 to 0.010 weight percent Cr. 
     
     
         12 . The method according to  claim 1  wherein the coating feedstock for the wear-resistant coating layer ( 4 ) comprises from 15.00 to 15.20 weight percent Mo, from 11.26 to 11.40 weight percent V, from 1.80 to 1.90 weight percent B, from 2.19 to 2.29 weight percent C, from 0.00 to 0.01 weight percent Ti, from 0.00 to 0.01 weight percent Mg, from 0.00 to 0.03 weight percent Ni, from 0.00 to 0.03 weight percent Nb, and from 0.000 to 0.010 weight percent Cr. 
     
     
         13 . The method according to  claim 12 , wherein the coating feedstock for the wear-resistant coating layer ( 4 ) comprises 15.01 weight percent Mo, 11.36 weight percent V, 1.85 weight percent B, 2.24 weight percent C, from 0.00 to 0.01 weight percent Ti, from 0.00 to 0.01 weight percent Mg, from 0.00 to 0.03 weight percent Ni, from 0.00 to 0.03 weight percent Nb, and from 0.000 to 0.005 weight percent Cr. 
     
     
         14 . The method according to  claim 12 , wherein the coating feedstock for the wear-resistant coating layer of this embodiment consists of from 15.00 to 16.00 weight percent Mo, 1.40 to 2.02 weight percent Al, 0.10 to 0.30 weight percent Mn, 0.10 to 10.10 weight percent Si, from 0.10 to 10.00 weight percent Ti, from 0.00 to 0.10 weight percent Mg, from 0.00 to 1.00 weight percent Ni, from 0.00 to 0.50 weight percent Nb, and from 0.000 to 0.020 weight percent Cr with the balance being iron and impurities. 
     
     
         15 . The method according to  claim 1 , wherein, when the at least one first spray device ( 5 ) acts against a part of the outer surface ( 3 ) of the shell ( 2 ) to apply the wear resistant coating to that part of the outer surface, the at least one first spray device ( 5 ) is operated at a distance from that part of the outer surface ( 3 ) which is in the range of 50 mm-260 mm. 
     
     
         16 . The method according to  claim 1 , wherein, when the at least one first spray device ( 5 ) acts against a part of the outer surface of the shell to apply the wear-resistant coating to that part of the outer surface, the plastic and/or semiplastic and/or molten feedstock is sprayed onto the outer surface of the shell ( 2 ) at an angle of 30°-90° with respect to that part of the outer surface. 
     
     
         17 . The method according to  claim 5 , wherein the coating the ground and grit blasted outer surface is initiated within at most 90 minutes after the grit blasting has been completed. 
     
     
         18 . The method according to  claim 6 , wherein the initial thermal spraying operation is carried out at such a rate that the entire outer surface has been covered within at most 3 hours after the grit blasting has been completed. 
     
     
         19 . The method according to  claim 6 , wherein at least one, two, three or more spray devices ( 5 ) are used simultaneously during at least one of the thermal spray operations. 
     
     
         20 . The method according to  claim 4 , wherein the grinding and/or polishing operation that follows the forming of the wear-resistant coating layer ( 4 ) is initiated within at most 15 minutes after the thermal spraying operation to form the wear-resistant layer has been completed. 
     
     
         21 . The method according to  claim 1 , wherein the coating feedstock ( 6 ) for the at least one first spray device comes in the shape of two wires, each wire having a diameter equal to or greater than 1.1 mm and equal to or less than 3.8 mm. 
     
     
         22 . A method according to  claim 1 , wherein the at least one spray device ( 5 ) is an arc spray gun or a high velocity oxygen fuel (HVOF) device or a high velocity air fuel (HVAF) device or a plasma spray gun or a water stabilized plasma spray gun.