Electric Arc Spraying
Due fili (electrodes, cathodes and anodes) are pushed to the end of a gun, body where an electric arc which merges them into droplets which are then accelerated by the compressed air or gas and fired on the support.
Solid wires normally used
Applications Zinc and its alloys
|Al/Mg||Coatings resistant to corrosion in marine atmosphere|
|In||Coatings with excellent adhesion|
|Steels 13% Cr||Wear-resistant coatings, insufficient resistance to corrosion|
|Fe Cr Al||Excellent corrosion resistance at high temperatures|
|Mo||Coatings excellent fretting fatigue|
|Ni Cr 80 20||Corrosion-resistant coatings and binder for ceramic tiles surface|
The zinc coatings are excellent for the protection of steel from corrosion because zinc is resistant to basic solutions and atmospheres with low acidity (pH 5-12). There are many industrial applications such as: tubi di ghisa, iron bridges, torri eoliche, capacitors which creates an electrical contact between the laminae of the co-metallized film.
Aluminum and its alloys
Al is resistant to acidic and basic atmospheres (pH 2-10), for which it is used in the protection of the food industry, for marine structures and pipe evaporators liquid gas tanks. The oxygen content (2,5-3%) electric arc causes a higher resistance to corrosion than spraying gas, whose oxygen content is 0,4%.
The bequeaths AlMg 5% presents an excel-lent corrosion resistance of offshore structures and those in the atmosphere marine. Membership is 20-30 MPa, greater pure aluminum.
Each aluminum-based coating must be sealed to prevent the migration of corrosive vehicles through the pores of the surface.
The addition of small percentages of Al alloys of copper increases the resistance to corrosion due to the oxides of Al formed during the spraying and coating. The addition of Ni and Fe to the bronze / aluminum increases the corrosion resistance. In salt water they are more resistant brass and bronze.
Nickel and its alloys
They are used as corrosion of components in desalination and marine atmosphere. The coatings NiCu30Fe show excellent resistance to corrosion in oxidizing or reducing fluids.
Are comparable to steel and enamel coatings are recommended to repair damaged NiCu30 Fe.
The coatings NiCr80-20, employing argon as gas atomization, are excellent against corrosion by moisture. Test in NaCl solutions 5% and oxidizing fluids (1NH2SO4) confirm the excellent corrosion resistance, comparable to that of steel plated.
Are based on tin and bronze (p.e. CuAl18 – CuSn6) show a low rate of friction and excellent rub resistance. These coatings can be machined on a lathe. Those at the pond should be applied when the rotating shaft is not hardened, while the toughest coatings based on Cu can withstand higher pressures (a greater number of turns and higher static loads). Their range of application is 200/300 ° C.
NiTi alloys and NiAl have a high degree of adherence (for ceramic coatings and other materials with a thickness of a few millimeters, etc..)
Due to the exothermic reaction of Al with Ti and oxygen atomizing air, the fused particles are superriscaldate and when impacting on the substrate forming microscopic welding points.
The coatings NiAl 95-5 the arc show a greater adhesion than plasma, no major differences in hardness.
They are usually employed various hard steels such as those martinsitici (Cr13%,Co0,3-0,47%)(p.e. coatings of carbon steel on the levers of Al).
Due to the combustion of carbon and chromium in the electric arc, the finish of this steel is less harsh in the same heat-treated alloy. It is advisable in this case to use wireless animating containing Co and Cr to integration.
anti-wear coatings in corrosive atmospheric-ra
In many industrial applications, where the materials are subject to wear and corrosion, a coating with standard materials (p.e. steel wire 13% Cr) fails to ensure a long life. It is therefore necessary to use flux cored wires (as tungsten carbides). Coatings with hardness 500-600 HV0, 3 obtained from cored wires FeCrBSi (Cr 28%) instead of Cr 13%, applied on the rollers of the paper have not submitted to the test of incision visible traces of corrosion, while the mild steel support was highly corroded.
Mild steels and high-alloy steels are used to reconstruct trees motor-generators or cylinders for the paper or for re-housing and sealing rotating shafts worn. The bronzes and alloys based on tin can be sprayed liners to repair marine engines.
Corrosion preventive coatings from high temperature
Against corrosion and / or the simultaneous erosion of evaporators and pipes for transport vapors at high temperature, in coal-fired boilers and waste incinerators must apply coatings with cored wire NiCr and FeCr with high chromium content. E 'need to know to choose the suitable parameters (nozzles for spraying and distances, pressure atomization, voltage), in order to reduce the burning of chromium and its oxidation.
Effect of Chromium Metal
The Cr metallic form an oxide film on the surface of the coating, even in the presence of gas at low oxygen content.
A thick coating of chromium oxide determines a longer life of the coated piece in many corrosive atmospheres.
Numerous researches show a corrosion resistance of coatings based on Cr203 FeNiCr better than those in the atmosphere with high presence of HCl and SO2 .
Effect of Boron and Silicon
Many coatings are made with NiFe-cored wires with the addition of Si or boron . Typically these two elements lowering the melting point of iron alloys and Ni. The reduced melting point determines a lower viscosity of the atomized particles to which these can expand more easily on impact with the surface of the substrate giving rise to dense deposits. The porosità (Browsing, ranging from the outside at the interface between coating and substrate) decreases with the thickness of the coating. However, the latter, if it is too often, may crack due to residual stress that is greater when the thickness is more important.
A longer component life (come caldaie o rulli) is obtained by replacing solid wires with animated ones with coal, chromium and aluminum.
Coatings with cored wires with tungsten carbide and nickel showed an excellent resistance to wear by abrasion. At a temperature of 982 ° C, the Ni-Cr-Al cored wires can be sprayed on the electric arc worn parts or deposits of ceramic.
Type flux cored wire – application
|Fe C Mn Si||high resistance to wear in a dry atmosphere|
|Fe Cr B Si||coating resistant to wear and tear, good resistance to corrosion, high adherence|
|Fe Cr B Si W C Co Cr||excellent resistance to high temperature corrosion, high adherence|
|Fe Cr Si||resistance to wear and corrosion at high temperature up to 900 ° C, high adherence|
|Ni Cr 50 50||corrosion resistance high temperature up to 900 ° C|
|Ni B Si + WC||high resistance to wear, good corrosion resistance|
|Ni Cr B Si||high resistance to corrosion in humid atmosphere,good resistance to wear|
The table shows the resistance of various coatings with flux cored wires to the wires than standard steel 13% Cr. The loss of coating material Fe28Cr3B1Si is about half of the coating 40 Cr 13.The 'further strengthening of the wires ani-mati Cr B Si with WC-CoCr powder increases its resistance to wear. Only the system HVOF WC-Co has a higher resistance.
LIST OF METAL WIRES COLIMET
|Type||HB durezza||day (mm)||Steel wire (analisi) %|
|30L||210-230||1,6||basso C||0,10C-1-1 80mn, 0if|
|55L||300-320||1,6||1,3% C||1,50C-1, 40Cr-0,6Mn-1, 0if|
|60L||300-340||1,6-2||Inox||0,45C-13Cr-1 0mn-1 0if-1 0Ni|
|62L||240-266||1,6||Inox||0,35C-17Cr-0,60Mn-0,50Si-1, 0Ni-1 1Mo|
|65L||380-440||1,6||High C||1,15C-1, 80Cr,2,0Mn-0,30If-0,20You|
|80L||220||1,6-2||Inox 18/8||0,40C-19Cr-1 80mn-1, 30Si-9 0Ni|
|85L||250-270||1,6||Inox 18/8||0,15C-18, 50Cr,7,0Mn-0,9Si-8 50Ni|
|95L||280||1,6||18/11/2||0,06C-17, 50Cr,2,0Mn-1, 0 if-12Ni,2,5Mo|
|Type||HB durezza||day (mm)||Wires other metals (analisi) %|
|70L||160-200||1,6||Monel||0,64Ni-32Cu-2, 50Mn-1, 5Fe|
|100L||480||1,6||Pure Molybdenum||99,99 %Mo|
|RniL||160||1,6||Pure Nichel||99,2% Or|
|NiAl / L||230||1,6||Nichel-Al||93,5Ni-5, 0Al-1, 5Si|
|PBz / L||1,6||Lega PBz||6,0Sn-Cu balance|
|Al / L||20-40||1,6-2-2,5||At Pure||99,5% To the|
|Sn / L||2-2,5||Sn Puro||Sn 99,9%|
|AlMg5 / L||2,5||Orientation Al-Mg||Mg-5% Al saldo|
|LMSn / L||2,5||Orientation||SN 89%, Sb7, 50%, 3.50% Cu|
|Ms / L||1,6||Orientation Cu-Zn||Cu63%-Zn saldo|
|AlBz9Mn / L||160-180||1,6||Super Orientation||8,5Al 2 Cu-50Mn saldo|
|Orientation Cu-Zn||1,6||Orientation||68% Cu-Zn 32% e ALTR tenor|
|Filo Zn||tutti||Zn puro||Zn > 99,995%|
|Filo Zn / Al||Orientation||85% Zn-Al 15%|
|Filo Zn / Sn||Orientation||80% Zn-Sn 20%|
|Gross Ella di Zn||Zn puro||Zn > 99,995%|