Spray welding technology
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Spray welding technology (Tech Center of Shanghai HY Industry Co., Ltd)

Spray welding is the preheated self-soluble alloy powder coating and then heated to 1000 ~ 1300 ℃, so that the particles melt, slagging up to the surface of the coating, generated borides and silicides dispersion in the coating, so that the particles and the substrate surface to achieve a good combination. z The final deposit is a dense metal crystalline organization and the substrate to form about 0.05 ~ 0.1mm metallurgical bonding layer, the bonding strength of about 400MPa, good impact resistance, wear resistance, corrosion resistance, mirror surface appearance.

Advantages

Compared with the spray layer, the advantages of spraywelding layer are significant. However, due to the remelting process, the substrate is locally heated up to 900 ℃, will produce a large thermal deformation. Therefore, the scope of use of spray welding is somewhat limited. Suitable for spray welding of parts and materials are generally.

  • by the impact load, requiring high surface hardness, good wear resistance of vulnerable parts, such as sand blasting machine blades, crusher tooth plate, excavator bucket teeth, etc..

  • large wearable parts with relatively simple geometry, such as shafts, plungers, sliders, hydraulic cylinders, chute plates, etc.

  • low carbon steel, medium carbon steel (containing less than 0.4% carbon), structural steel containing manganese, molybdenum, vanadium total <3%, nickel-chromium stainless steel, cast iron and other materials.

Self-fusing alloy powder for spray welding

Self-fusing alloy powder is nickel, cobalt, iron as the base material of the alloy, which adds the right amount of boron and silicon elements, the role of deoxidation slag welding flux, while reducing the melting point of the alloy, suitable for acetylene an oxygen flame to remelt the coating. Domestic self-fusing alloy powder varieties, nickel-based alloy powder has strong corrosion resistance, oxidation resistance up to 650 ° C, strong wear resistance; cobalt-based alloy powder Z is a good feature of the red hardness, can be at 700 ℃ to maintain good wear resistance and corrosion resistance; iron-based alloy powder wear-resistant grain wear better than the other two categories.

Spray welding process

The process of spray welding is basically the same as spraying, but the difference in the process of spraying powder increased the remelting procedure. Spray welding has a step spraywelding method and two-step spray welding method.

Before construction, attention should be paid to.

  • workpiece surface carburizing layer or nitriding layer, must be removed during pretreatment.

  • preheating temperature of the workpiece for general carbon steel 200 ~ 300 ℃, heat-resistant austenitic steel 350 ~ 400 ℃. Preheating flame with neutral or weak carbon flame. In addition, after the spray layer remelting, the thickness is reduced by about 25%, and this amount should be taken into account when measuring in the thermal state after spraying and melting.

One-step spray welding method

One-step method that is, after spraying a section that melts a section, spraying, melting alternately, using the same gun to complete. Can be used in small and medium-sized spray welding gun. After preheating the workpiece first spray 0. 2mm protective layer, and the surface is sealed to prevent oxidation, spray melt from one end, spray distance 10 ~ 30mm, sequential local heating of the protective layer to melt began to wet (can not flow) and then spray powder, and melting repeatedly until it reaches a predetermined thickness, the surface appears “mirror” reflection Then expand forward to reach the surface of all cover spray welding layer. If a thickness is not enough, can be repeated to thicken. One-step method is suitable for small parts or small area spraywelding.

Two-step spray welding method

Two-step method that first completed the spraying layer and then its remelting. Spraying and remelting are used with high-powered guns, such as SpH-E spraying, welding dual-use gun, so that the alloy powder is fully melted in the flame to produce a plastic deformation on the surface of the workpiece deposition layer. When spraying iron-based powder with a weak carbon flame, when spraying nickel-based and cobalt-based powder with a neutral or weak carbon flame.

Spray powder thickness of each layer <0.2mm, repeated spraying to achieve remelting thickness, generally can be remelted at 0.5 ~ 0. 6 mm. If the spray welding layer requirements thicker, a remelting can not meet the requirements, can be divided into several spraying and remelting.

Spray welding technologyRemelting is the key process of the two-step method, immediately after spraying. With neutral flame or weak carbonization flame of high power soft flame, spray distance of about 20 ~ 30mm, flame and surface angle of 60 ° ~ 75 °, from about 30mm from the coating, the appropriate control of remelting speed, the coating heated until the coating appears “mirror” reflection for the degree, and then the next part of the remelting.

When remelting, prevent over-melting (i.e. mirror cracking), flowing of coating metal, or oxidation of surface due to long local heating time. In case of multi-layer remelting, the first layer should be cooled down to about 700℃, and after removing the surface slag, the second spray melt should be made. Remelting should not exceed 3 times.

Cooling of the workpiece. Low carbon steel, low alloy steel workpiece and thin welding layer, the shape of a simple cast iron parts in the air natural cooling. For the weld layer thicker, complex shape of cast iron parts, manganese, copper, vanadium content of large alloy steel parts, high cold hardness parts, to be buried in the lime pit slow cooling.

Spray coating and spray welding process differences

Spray coating layer and spray welding layer and base metal bonding formation is different, nickel clad aluminum by spraying flame beam heating exothermic chemical reaction, in the sandblasted rust removal up to Sa3 level, RZ>50μm carbon steel surface to form a micro-metallurgical bonding of the bottom layer and the work layer and produce “anchor hook” effect of mechanical bonding coating, and spray welding layer and the combination of the substrate Purely metallurgical bonding coating.

Spraying materials are different, spray welding requires the use of self-fusing alloy powder, while spraying is not high requirements for self-fusing powder, and not necessarily self-fusing alloy powder, a variety of self-fusing alloy powder can be used for both spray welding and spraying, but spraying powder does not have self-fusing can only be used for spraying and can not be used in the spray welding process.

The workpiece is subjected to different heat, spraying and spray welding process, the pre-heating temperature before spraying is different, the workpiece is affected by different heat, the organization and performance of the workpiece after spraying is also different.

The denseness of the coating is different, the spray welding layer is dense, and there are a few pores in the spray layer.

The ability to bear the load is different, the spray layer can generally withstand a large area of contact, more in the lubrication conditions of the work surface, with the surface and other less stressful working conditions, spray welding layer can withstand large impact, extrusion stress or contact stress, etc.

The following cases are suitable for the selection of spray welding process

(1) a variety of carbon steel, low-alloy steel workpiece surface load, especially impact load, the required coating and the substrate bonding strength of 350-450N/mm2 workpiece, spray welding hardness HRC150 ≤ 65, coating thickness from 0.3 to several millimeters, spray welding layer after grinding process surface roughness up to Ra0.4- 0.1μm or more.

(2) Used in corrosive media, the coating is required to be dense and non-porous.

(3) The surface of the workpiece is originally designed with quenching, carburizing, nitriding, hard chromium plating and other processes, requiring a very high hardness on the surface.

(4) The workpiece working environment is harsh, such as strong abrasive wear, erosion wear, cavitation, etc.

(5) oxy-acetylene flame alloy powder spray welding process to adapt to a variety of carbon steel, low-alloy steel parts of the surface strengthening or repair, but should be noted that some of the characteristics of the parts material, when the base material of the coefficient of linear expansion and alloy spray welding layer of the coefficient of linear expansion difference is less than 12 × 10-6 / ℃ greater than 12 × 10-6 / ℃, then this process should be used with caution, so as not to cause cracks, if Base metal and oxygen affinity for elements with high content such as tungsten and molybdenum content greater than 3%, aluminum, magnesium, cobalt, titanium, molybdenum and other elements with a total content greater than 0.5% or steel containing more sulfur, will also bring difficulties to the spray welding, this is because these materials and the role of oxygen is very easy to generate a dense and stable oxide film, blocking the molten alloy to the wetting effect of the substrate, remelting when the liquid alloy will be beaded like “Sweat beads” like rolling down, so when using the spray welding process, should pay attention to the adaptability of this process for the sprayed substrate material.

(6) can be sprayed without special treatment of metal materials welded.

  • carbon content ≤ 0.25% of carbon structural steel.

  • Mh, Mo, V, Cr, Ni total content < 3% of the alloy structural steel.

  • 18 – 8 stainless steel, nickel stainless steel, gray cast steel, malleable cast iron, ductile iron, low-carbon pure iron, copper.

(7) Need to preheat 250 – 375 ℃ spray welding after the need for slow cooling of metal materials.

  • carbon content > 0.4% of carbon structural steel;

  • Manganese. Molybdenum. Vanadium. The total content of nickel > 3% of the alloy structural steel;

  • chromium content ≤ 2% of the alloy structural steel ;

(8) isothermal annealing treatment of metal materials after spray welding.

  • martensitic stainless steel with chromium content ≥ 13%.

  • carbon content ≥ 0.4% of nickel-molybdenum alloy structural steel.

After determining the use of spray welding process, and then according to the following circumstances to choose a one-step or two-step spray welding process:

(1) the workpiece to be partially repaired, and spray welding does not allow a large amount of heat input, such as the repair of various types of machine tool guide local scars, it is appropriate to use a one-step spray welding process;

(2) the surface of the workpiece is complex or irregular, such as sprockets, gear teeth, spiral feeder, etc., it is appropriate to use a one-step spray welding process;

(3) large workpiece heating difficulties as a whole, such as locomotives, mining wheels, etc., a one-step spray welding process is appropriate;

(4) can be rotated in the machine tool of general shaft parts should be used two-step spray welding process;

(5) the hardness of the resulting coating should be as close as possible to the original design of the surface hardness, such as the original design using quenching or chemical treatment process, so that the surface hardness of HRC ≥ 55 or so, then the so-called “hard surface coating” powder should be used, such as Ni15, Ni60, Fe65 or Wc composite powder;

(6) strong wear of the non-cooperative surface, such as the impeller of the sand pump, shell, rock loader shovel teeth, screw feeder spiral surface, etc., should be selected with high hardness such as Ni15, Ni60, Fe65 or Wc composite powder;

(7) need to be processed, but can not be on the lathe, grinder, only by hand with tools such as files to process the workpiece, such as the repair of local scars on the machine tool guide surface, can only use low hardness spray welding powder such as SH ? F103, Ni15, etc;

(8) spray welding process and the difference between arc overlay welding: spray welding layer and the combination between the substrate is dissolved diffusion metallurgical bonding, while overlay welding is melting metallurgical bonding, the substrate is not melted in the spray welding process, only the spray welding layer and the substrate between the dissolution effect, there is a diffusion of mutual solubility between the two. As the matrix insoluble material and therefore spray welding layer

will not be washed out by the base material, so the dilution rate is very low, to ensure that the good performance of the spray weld layer, overlay base melting, overlay layer dilution rate is high, the need to overlay very thick to ensure that the performance of the weld layer, and the part contour angles are difficult to ensure that common biting, angular collapse, and spray welding will not have such defects.

The following cases can not be used spray welding process

(1) materials below the melting point of the alloy, such as aluminum and its alloys, magnesium and its alloys, brass, bronze;

(2) The workpiece is a long and thin shaft or very thin plate and does not allow the deformation.

(3) The original design of the workpiece is very high, and the metallographic organization does not allow any change;

(4) Nickel-chromium-molybdenum alloy steel with high hardness.

(5) Martensitic high chromium steel with chromium content > 18%.

(PS: Long shafts with an outside diameter of 28 mm or more and a length of 8 meters or less can be spray welded with high precision)

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