Process selection
1, to understand the performance of the workpiece itself: such as material, composition, surface condition, wear parts and wear area and depth.
2, to understand the workpiece conditions of use: the use of the environment (temperature, medium concentration and other main ingredients), stress (impact load or sliding fit, fit, failure (static) machining, wear, corrosion, etc.).
3, the following should be used in spraying process:
1) surface by static load or low sliding load, but wear resistance of coating and substrate with tensile strength requirements of not more than 50N/mm2 of the workpiece, coating hardness HV130 350 coating thickness from 0.3 to several millimeters, sprayed surface roughness Ra10 of 25 mu m coating after grinding surface roughness up to Ra0.8 - 0.4 m, such as various types of shaft bearing parts.
2) requirements for surface corrosion and erosion after processing roughness less than Ra0.4 m, such as the import of automobile crankshaft, crankshaft train, marine crankshaft etc..
3) made of copper alloy, aluminum and other non-ferrous metal or Aluminum Alloy, need to restore the size or improve the surface abrasion resistance.
4) spraying the best selection of copper based powder or aluminum in copper alloy, aluminum and other non-ferrous metal workpiece Aluminum Alloy.
5) used in corrosive medium, for coating is dense non porous, the workpiece should be based on the use of the environment, temperature, concentration and composition of medium choice can meet the conditions of the use of plastic, ceramic or metal coating corrosion resistance after using proper sealing agent on the coating of closed treatment.
6) the bonding strength of the coating layer: the traditional flame spraying layer is 20 30N/mm2 with tensile strength, Shaanxi Zhongke Surface Engineering Co., the latest development of ZK8032 powder production of multifunctional high-speed flame spraying gun used in ductile cast iron by sandblasting surface spraying aluminum nickel composite coating. The coating shear bond strength of 63.7N/mm2 coating; although as spray welding layer with high strength, but for the repair work in lubricated metal friction resistance failure parts are sufficient to meet the needs. After scientific research units, in the Jiefang CA141 car full load operation, the crankshaft seven shaft shear stress concentration in a spindle neck is only 15N/mm2; on the Dongfanghong 75 tractor is only 5.5N/mm2, this data is far lower than the shear strength of the coating layer.
7) coating wear resistance by spraying automobile crankshaft as an example, spraying the main journal and the new crankshaft has higher wear resistance than ever I sprayed the Japanese Hino automobile crankshaft main journal, overhaul repair after the inspection of wear quantity is 0.022 0.03mm, but without the main journal the wear amount of spray repair was 0.2 0.25mm, the wear rate is almost ten times the difference, from this example that coating has good abrasion resistance, even in the case of engine oil can still insist on running for several hours without burnt axle phenomenon.
8) spraying difference and spray welding:
1 spraying layer and combined spray welding layer and matrix metal formed different exothermic chemical reaction occurs by flame spraying beam heating nickel aluminium, after blasting to Sa3, forming RZ > 50 m steel surface micro metallurgical bonding layer and bottom work and "anchor" effect combined mechanical coating, combined with spraying layer and substrate is metallurgical bonding coating.
The spraying material, spray welding requires the use of self fluxing alloy powder, and the spraying of self fluxing powder is not high, and not necessarily self fluxing alloy powder, all kinds of self fluxing alloy powder can be used for spray welding and can be used for spraying, but do not have the self fluxing powder can only be used for spraying and can not be used for spray welding process.
The workpiece heating, spraying and spraying process, spray the preheating temperature of different workpiece heating effects, after spraying workpiece microstructure and properties are also different.
The different density of black coating, spray coating and spraying coating is dense, small pore.
The load bearing capacity, coating generally can bear large area contact in the surface lubrication condition, with the surface and other smaller stress conditions, spraying layer can withstand greater impact, extrusion stress or contact stress.
4, the following conditions should be selected spray welding process:
The surface of the workpiece loading of low alloy steel: carbon steel, large, especially by impact load, combined with the requirements of the strength in 350 450N/mm2 of the coating and the substrate, the hardness of HRC150 spray welding coating thickness is less than or equal to 65, from 0.3 to several millimeters, spraying layer after grinding surface roughness can reach Ra0.4 more than 0.1 M.
2 used in corrosive medium, require compact coating, no pore;
The workpiece surface original design by quenching, carburizing, nitriding, hard chromium plating process, the surface has a very high hardness.
The workpiece working environment, such as abrasive wear, erosion wear, cavitation strong etc..
The oxygen acetylene flame spray welding alloy powder to strengthen or repair the surface of carbon steel and low alloy steel parts, but should pay attention to some of the features of parts and materials, when the substrate material linear expansion coefficient and alloy spray welding layer linear expansion coefficient difference is larger than 12 * 10-6/ greater than 12 DEG C c * 10-6/, should be used with caution in this process, so as to avoid the crack, if the base metal and oxygen affinity large elements such as tungsten and molybdenum content of more than 3%, aluminum, magnesium, titanium, cobalt, molybdenum content is more than 0.5% or more of total sulfur content in steel, would bring difficulties to spray welding, this is because these materials with oxygen easily generate dense and stable oxide film, wettability of molten alloy barrier on the matrix, when the liquid alloy is remelted bead like "sweat" as to tumble, so in the welding process, should pay attention to this work The adaptability of the material to the base material.
. without special treatment can spray welding metal materials:
Carbon structural steel the carbon content is less than 0.25%.
Alloy structural steel 2 Mh, Mo, V, Cr, Ni content of less than 3%.
In 18 - 8 stainless steel, nickel stainless steel, cast iron, malleable cast iron, ductile iron, low carbon iron, copper.
Characteristics of typical surface coating
Part geometry for spraying (welding) have a certain effect, such as the outer surface coating when spraying, cooling, shrink hold trend; the inner surface of a workpiece from the coating cooling trend, simple surface spraying powder easily deposited; some parts of complex surface spraying powder deposition is difficult to twist. So the research and mining of various parts surface spraying (welding), the correct use of spraying (welding) process, to ensure the quality of spraying is of practical significance.
, 1 shaft surface spraying technology:
(1) before spraying surface preparation to strict treatment, rough treatment to do according to the requirement of process, surface treatment is good to avoid moisture contact or touch.
(2) to strictly control the spraying norms, can not exceed 250 DEG C temperature rise control the workpiece, when the coating is thick, the small, continuous spraying temperature may exceed 250 degrees, should adopt the method of intermittent spray cooling, but the residence time is not too long, otherwise it will be caused by the pollution of coating layer with bad.
(3) excessive grinding angle and edge, shaft with hole or slot, the hole plugging and keyway edge grinding into a rounded, pay attention to spray a good edge.
(4) cylindrical surface of the substrate preheating temperature should be lower, should control the substrate temperature in the spraying process, thereby reducing the contractile force of the matrix.
, 2 plane spraying technology:
(1) note that fixed edge, edges and corners; the preheat requirement is uniform, large available at the preheating.
(2) to be sprayed powder from around the edge, and then lead the plane, repeatedly spraying, one should be the first one spraying direction perpendicular to each other.
(3) to prevent the coating edge, spraying before slotting on the edge, and the roughening can reduce stress.
3, rabbet surface spraying technology:
Spray spigot cylindrical part 1 spray, after spraying the plane part.
The direction of the spray gun along the circumferential direction of the workpiece at a 45 degree angle jet as well, this may make the powder deposition rate is low, but can be ejected clear edges spraying operation attention can not be perpendicular to the corner of mouth spray gun spraying, this will cause the corner coating loose or clip ash.
By spraying the edges as burrs and Alice, should be promptly removed and then spray.
4 points spraying process and local serious damage to parts of the:
: local damage to polished clean, gunning repair or by other methods, and then spray all the plane.
For the local defects may deep and wide, can also use wire fill, then fully spray.
The start and stop of the endpoint local defects with crack first to find a crack, and there lay a stop hole, groove, cracks will be completely clean and gunning or flat welding defects, then spraying the surface to be sprayed.
5, large equipment rail technology:
Repair machine guide, have a large area of oil leakage problems, the machine tool overall uniform heating oil is difficult to achieve, but also to the deep oil removed, if the heating temperature, and easy to make the guideway deformation, this can be the following.
2 flame temperature local baking temperature of the workpiece is about 80 - 100 DEG C, then wipe with baking grease, so repeated several times, and then use high power quick spray gun.
Using solvent cleaning or brush plating processing, and then use the flame gunning, again.
The as the rail strain, can be used to guide the repair glue or casting defect repair machine welding process.
6, outer surface spraying technology:
With the same shaft spraying, coating the coating contraction tight matrix, is conducive to the combination provided the strength of the dam to take lower temperature of the pituitary, the spraying process, the workpiece temperature more than 250 DEG C, must also indicate for shape, volume and position of different parts of spraying, should have different requirements of the workpiece temperature control. When the cylindrical parts of spraying small parts, avoid the workpiece temperature is too high, the cooling shrinkage stress, the workpiece, will cause the coating off or cause large deformation.
7, hole spraying technology:
The inner hole and the shaft, spray layer during cooling contraction has a tendency to make the coating from the substrate, is not conducive to improve the strength of
In shallow and large hole, the outer circle can be used to take a gun, spray angle for spraying, spraying for parts of the inner circle, the outer circle mostly use the spray gun, but spray pretreatment using thread should pay attention to the "shielding effect", to prevent loose coating.
For deep hole spraying (diameter greater than 200mm), using long tube hole spray gun, but the hole depth should not exceed 2 times of the aperture, otherwise the spraying quality greatly, in order to prevent the hole lance long tube in high temperature, air cooling application 0.4 0.6MPa pressure.
The workpiece speed should be slightly faster than the outer circle of spray, coating to prevent overheating, the direction of rotation of the workpiece should be oriented to avoid spraying powder, scattered into the surface to be sprayed, the flame at the slightly higher work center line as well.
The workpiece is not higher than 250 DEG C temperature control 5 in the spraying process of thick coating can be used for intermittent spray.
The spray parts surface of the inner hole of the substrate due to shrinkage stress is close to the trend of the matrix coating, such as workpiece preheating temperature, the temperature is low, because of the coating and the substrate shrinkage stress difference is too large, resulting in coating off, so desirable in the preheating temperature limit, workpiece deformation conditions permit the case may be appropriate to increase the preheating temperature of the substrate, thereby increasing the matrix shrinkage force.
7 by two step spray welding, similar to spraying, spray welding points can be determined according to the specific situation of various parts of the combined spray welding process.
Key points of spray welding process 8, iron castings:
In vehicle and machinery equipment in a considerable number of parts made of cast iron, all kinds of problems inevitably arise in the process of manufacturing or in use by oxygen acetylene flame spray welding process is not only the effective method to strengthen the iron, but also repair defects and damage (such as casting casting sand wear or, in the use of stomatal and other damage) ideal means;
The spray welding defect of iron castings used for local repair, and defect sizes and shades, suitable to adopt one-step spray welding, according to the workpiece and welding repair parts, should try to use small power gun, this can reduce the amount of heat input on the matrix, generally used in the QH - 1 / h, QH 2 / h, QH / h - 4;
3 spray welding, cast iron parts due to poor weldability, priority should be given to the selection of nickel based alloy powder (Ni - B - Si Series), nickel base alloy powder melting point is generally 950 to 1050 DEG C, the matrix will not be melted during remelting, at the same time, low nickel powder spray welding layer hardness of carbon the low amount of water, good plasticity, stress relaxation can be sprayed to prevent crack, then the operation is not good is very important;
Choosing spray welding specification, should consider the size of cast iron, defective parts, working conditions and other factors, in the premise of ensuring the necessary fire energy, reduce the heat input to the substrate, oxygen, acetylene gas pressure limit is appropriate, dusting, remelting, adjust the spray, penetration distance control of heat input;
The welding local small defects, such as pores, trachoma, spray welding without preheating before, try to reduce the spray welding layer around the heating area, so that in the high temperature region as small as possible.
The spray welding defects on the small and deep repair for continuous spraying, the powder deposition rate, the thickness of fast growth, high efficiency, but requires skilled operation, the amount of powder and spray, melting speed, coordination, do spray penetration;
The area of defect large and deep, in order to prevent the substrate heating due to excessive thermal stress can be increased by batch method of spray welding, when necessary, can also be used welding, spray welding composite technology, filling the bottom electrode, the upper spray welding, such as casting wall thickness is larger, can be sprayed before planting silk that not only can increase the bonding strength, prevent the spray welding layer and base material stripping, and can eliminate a part of welding thermal stress;
Large complex casting hot the welding stress is large, spray to take measures to reduce the stress accumulation, such as the use of heat stress reduction method, piecewise symmetric method; preheat, slow cooling after welding, good results can be achieved;
To control the melting temperature, the melting temperature is too high, not only the loss of alloy elements, the matrix matrix is overheating, even lead to melting of cast iron carbon into the spray layer, the spraying layer in the carbon content increased, hardness, lower plasticity, and the matrix for carbon content decreased, prone to white the temperature is too high, but also cause high thermal stress, resulting in cracks, the remelting temperature is not too low, otherwise, easy to form a clip or not through the influence of ash melting, bonding strength, for the control of the remelting temperature, mainly by the operator to pay attention to the change of surface state of coating with the help of the observation process, the surface remelting reflection "to control, showing" mirror ", shows that the melting slag powder has been floating, at this time, the remelting gun should be immediately removed, remelting over the site should avoid heating.
