Surface welds are primarily used to restore worn surfaces, increase corrosion resistance, and improve the mechanical properties of a material. They provide an additional layer on existing structures, extending their life and durability. This process is often used in industries such as manufacturing and construction for maintenance and repair tasks.
What is coming up soldering ?
Surface welding is a process in which a wear-, corrosion-, and heat-resistant layer of metal is deposited on the surface or edge of a workpiece.
Surface welding can extend the service life of parts, optimize material usage and improve product performance.
Different workpieces and coating electrodes require different coating techniques.
Surface welding is typically used to repair worn or cracked parts.
Related Reading: The Ultimate Guide to Welding
Application scope of surface welding equipment:
Automated surface is commonly used for cement equipment such as vertical mills, roller mills, screw conveyors, fans and rotary kilns.
For iron and steel equipment, automated coating can be used for converters, rollers, blast furnaces, continuous casting machines and conveyor wheels.
When it comes to power equipment, automated lining is often employed on coal mills, grinding rollers, boiler tubes, turbines, drain pipes and gears.
To illustrate the surface welding process, let me share some examples with you. Let's dive right in.
Case:
Rollers are a critical spare part in the rolling mill and consume a significant amount of steel during the rolling process.
With an annual steel production of more than 600 million tons in China, the value of consumed rolls exceeds 17 billion yuan.
Therefore, using coating methods to repair old rolls and extend their service life has become an important measure for steel rolling companies in China to reduce production costs and improve economic benefits.
When an original roller reaches the end of its useful life, it can be repaired by surface welding.
Surface welded rollers have the advantages of low cost, long service life and excellent performance. They are widely adopted by steel rolling companies and are in line with China's fundamental policies of energy conservation, clean production and circular economy.
The image below shows an old roller that has been repaired through surface welding.
Old roller repaired with surface welding
As science and technology continue to advance, mechanical equipment for various products is evolving into larger, more efficient designs with higher parameters. As a result, the demand for reliable, high-performance products is increasing.
Surface coating of materials, as a branch of welding technology, is an effective means of improving the performance of products and equipment and extending the service life.
In addition to metals and alloys, ceramics, plastics, inorganic non-metals and composites can also be used as coating alloy materials.
As a result, coating technology can give parts a number of special properties, such as wear resistance, heat resistance, corrosion resistance, high temperature resistance, lubrication, insulation and much more.
At present, coating technology is widely used in mechanical manufacturing, metallurgy, electrical power, mining, construction, petrochemical and other industrial sectors.
Automatic Submerged Arc Strip Surface Welding
Characteristics of the weld surface
Surface welding is a process in which materials with specific properties are deposited onto the surface of a part using welding methods.
Related Reading: 10 Different Types of Welding You Should Know About
The purpose of surface welding differs from that of general welding methods.
Instead of connecting workpieces, surface welding modifies the surface of the workpiece to obtain a coating layer with specific properties such as wear resistance, heat resistance, corrosion resistance, or to recover insufficient size due to wear or processing errors.
These two applications in surface engineering are referred to as repair and reinforcement.
The following image shows the surface of a component after surface.
Surface of parts after surface welding
The advantages of surface welding over other surface treatment methods are:
- The metallurgical bond between the coating layer and the base metal results in high bond strength and good impact resistance.
- The metal composition and performance of the cladding layer are easily adjustable, and the commonly used arc welding cladding electrodes or flux core electrodes offer convenient formula adjustments. Various alloy systems can be designed to adapt to different working conditions.
- The thickness of the surface layer can be adjusted between 2-30 mm, making it more suitable for severe wear conditions.
- Surface welding results in cost savings and good economy. When the workpiece substrate is made of common materials and the surface is welded with high alloy, not only the manufacturing cost is reduced, but also a large amount of precious metals can be saved. Reasonable selection of coating alloy and surface repair on the surface of a part damaged during maintenance can greatly extend the service life of the part, extend the maintenance cycle, and reduce production costs.
- Coating technology is highly operable because it involves increasing or restoring the size of parts by welding or obtaining an alloy layer with special properties on the surface of the parts. Those with experience in welding technology can easily perform this type of work.
Electroslag Strip Automatic Surface Welding
Classification of surface welds
Surface welding technology is a type of fusion welding that can use all methods belonging to fusion welding.
The following table illustrates the classification of common surface welding methods.
Currently, the two most commonly used methods are electrode arc coating and oxyacetylene flame coating.
Classification of common surface methods
Table 9-1 Classification of Common Surface Welding Methods
| Surface welding method | Dilution ratio (%) | Deposition speed/(kg/h) | Minimum overlap thickness | Deposition efficiency (%) | |
| Oxyethylene flame surface | Electrode Wire Feed | 1~10 | 0.5-1.8 | 0.8 | 100 |
| Automatic wire feeding | 1~10 | 0.5-6.8 | 0.8 | 100 | |
| Powder surface | 1~10 | 0.5-18 | 0.2 | 85-95 | |
| Electrode arc surface | 10-20 | 0.5-5.4 | 3.2 | 65 | |
| Chlorine arc cladding with tungsten electrode | 10-20 | 0.5-4.5 | 2.4 | 98-100 | |
| Electrode Arc SurfaceTungsten Electrode Chlorine Arc Coating | 10-40 | 0.9~5.4 | 3.2 | 90-95 | |
| 15-40 | 2.3-11.3 | 3.2 | 80-85 | ||
| Arc Management Surface | Monofilament | 4.5-11.3 | 3.2 | 95 | 95 |
| Multifilament | 11.3-27.2 | 4.8 | 95 | 95 | |
| Series arc | 11.3-15.9 | 4.8 | 4.8 | 95 | |
| Monopole | 12-36 | 3.0 | 3.0 | 95 | |
| Multiband electrode | 22-68 | 4.0 | 4.0 | 95 | |
| Plasma arc surface | Automatic powder feeding | 0.5-6.8 | 0.25 | 0.25 | 85-95 |
| Welding Rod Powder Feed | 1.5-3.6 | 2.4 | 2.4 | 98-100 | |
| Automatic wire feeding | 0.5-3.6 | 2.4 | 2.4 | 98-100 | |
| Hot double filament | 13-27 | 2.4 | 2.4 | 98-100 | |
| ESW | 10~14 | 15~75 | 15 | 95-100 | |
Surface welding application
Surface welding technology, as a branch of the welding field, has a wide scope of application that covers various industries. It is widely used in manufacturing, including mining machinery, transportation machinery, metallurgy machinery, electrical machinery, agricultural machinery, automobiles, petroleum equipment, chemical equipment, construction and tool mold manufacturing and maintenance, and metal structures.
Surface welding is ideal for repairing metal parts and products with inferior appearance, and can also be used to manufacture bimetallic parts. Furthermore, it is an effective way to extend the life of parts, reduce costs and improve product design. This is particularly beneficial for the rational use of materials, especially precious metals.
The application of surface welding technology is mainly demonstrated in the following aspects based on the application and working conditions of the part:
(1) Restore part size using surface welding:
It is a prevalent problem for factories and mining companies that the part size is insufficient due to wear or processing errors. In these cases, surface welding is a common process method used to repair these parts.
Repaired parts can not only function normally, but also often exceed the service life of the original parts. This is because using new processes and materials in surface repair can significantly improve the performance of original parts.
Examples of such repairs include surface repair of cold rolls, hot rolls and profiled rolls, as well as surface repair of worn parts of agricultural machinery such as tractors, agricultural vehicles, transplanters and harvesters.
According to statistics, the amount of plating alloy used to repair old parts accounts for 72.2% of the total amount of plating alloy used.
Cold rolling repaired by surface technology
Roll tire and roll liner repaired by surface technology
(2) Wear-resistant and corrosion-resistant surface:
Wear and corrosion are the main factors that cause the failure of metallic materials. In order to improve the wear and corrosion resistance of metal part surfaces, meet the requirements of working conditions and extend the service life of the part, one or more layers of wear or corrosion-resistant material can be deposited on the surface.
Materials with different properties can be selected for the substrate and surface layer of the part, which can produce a bimetallic part. This is because only the surface layer of the part needs to have the special properties required in terms of wear and corrosion resistance. In doing so, it maximizes the role and potential of the material, saving a considerable amount of precious metals.
Wear-resistant coating or anti-corrosion layer I on the surface of the workpiece
(3) Create new parts
Bimetallic machine parts with comprehensive properties can be created by placing an alloy on a metal substrate.
The substrate and surface alloy layer of these parts have different properties, which can meet different performance requirements.
This approach fully unlocks the potential of materials.
For example, in the case of hydraulic turbine blades, carbon steel is used as the base material, and a layer of stainless steel is welded to the parts (mainly the bottom of the blades) that are susceptible to cavitation. This produces cavitation-resistant bimetallic blades.
When manufacturing metal abrasive tools, the matrix needs to be strong and tough. Therefore, carbon steel and low-alloy steel with relatively low cost are selected for the manufacturing process.
On the other hand, high-end molds require high hardness and wear resistance. The use of wear-resistant alloy surface in the cutting-edge mold can significantly reduce the consumption of precious alloy and significantly extend the service life of the mold.
Wear-resistant coating or corrosion-resistant layer II on the surface of the workpiece
Coating application field
Mold making
- Roughening the surface of a plastic mold increases its aesthetic appeal and service life.
- To repair the dividing surface of a helmet plastic mold, surface welding is recommended.
- For the diffuser cone of an aluminum alloy die casting die, surface reinforcement is required.
- When a mold cavity becomes worn or scratched, or goes out of tolerance, it must be repaired and reinforced.
Plastic rubber
Repair of rubber and plastic mechanical parts, out-of-tolerance molded rubber and plastic parts, wear and repair.
Aerospace
- Repair of parts of aircraft engines, turbines and turbine shafts;
- The surface of the rocket nozzle is reinforced and repaired, and the aircraft's outer panel parts are repaired;
- Improvement or repair of artificial satellite shells;
- Local reinforcement by carburizing titanium alloy parts;
- Local strengthening by carburizing iron-based superalloys;
- The magnesium alloy surface is infiltrated with A1 and other anti-corrosion coatings;
- Repair of local defects of magnesium alloy parts by surface welding;
- Local surface repair of nickel/cobalt-based superalloy blade workpiece, such as wear of the damping surface of the blade crown and blade tip and ablation of the guide vane.
Manufacturing Maintenance
In the automotive manufacturing and maintenance industry, our services are used to compensate and repair various components such as cams, crankshafts, pistons, cylinders, brake discs, impellers, hubs, clutches, friction discs and exhaust valves. We also offer repair of defects in surface weld seams for automobile bodies.
Electrical power for ships
- Repair of electrical crankshafts, bearing bushings, bearing bushings, electrical components, resistors and other related equipment.
- Weld the connecting piece between the wheel of an electric railway locomotive and the lower line of the track.
- Production and welding of conductive rolls and copper-aluminum electrodes with metal oxidation properties at an electroplating plant.
Manufacturing maintenance
In the automotive manufacturing and maintenance industry, our services are used to compensate and repair various components such as cams, crankshafts, pistons, cylinders, brake discs, impellers, hubs, clutches, friction discs and exhaust valves. We also offer repair of defects in surface weld seams for automobile bodies.
Electrical power for ships
- Repair of electrical crankshafts, bearing bushings, bearing bushings, electrical components, resistors and so on.
- Welding of the connecting piece between the wheel of an electric railway locomotive and the bottom of the track.
- Production and welding of conductive rolls and copper-aluminum metal oxidation electrodes at an electroplating plant.
Machinery industry
Correction of out-of-tolerance parts and repair of machine tool guide rails, various shafts, cams, hydraulic presses, hydraulic press plungers, cylinder walls, journals, rollers, gears, pulleys, mandrels for forming springs, gauges plug, ring gauges, various rollers, rods, columns, latches, bearings, etc.
Foundry industry
Repair defects such as sand holes and air pockets in iron, copper and aluminum castings and resolve any wear on aluminum molds.
Technical skills and surface welding methods
1. Overview
Surface welding is a process that involves welding cladding materials with specific properties onto the surface of the welds.
The objective is not to join the weldment, but to acquire a metallic layer deposited on the weldment surface that has unique characteristics, including wear resistance, heat resistance and corrosion resistance. This technique can also be used to restore or increase the size of the weldment.
The surface method is widely used in manufacturing and repair processes.
2. Metal for cladding weld
In general, the metal deposited for surface welding must first meet the welding service conditions. After that, the selection of the surface metal with better weldability and greater economy is considered.
The following are some common surface metals used in various work environments:
- Cobalt-based hypoeutectic alloy and cobalt-based alloy containing intermetallic compound are selected for high-stress intermetallic wear.
- Low alloy steel is selected for low stress intermetallic wear.
- Most cobalt-based alloys or nickel-based alloys are selected for wear+corrosion or metal-to-metal oxidation.
- High alloy cast iron is selected for low stress abrasive wear, impact attack and abrasive attack.
- The carbide cutting edge is chosen for severe, low-stress abrasive wear.
- Cobalt-based alloy is selected for cavitation erosion.
- High alloy manganese steel is selected for severe impacts.
- Cobalt-based hypoeutectic alloy is chosen for severe impact + corrosion + oxidation.
- Cobalt-based hypoeutectic alloy and cobalt-based alloy containing intermetallic compound are selected for high-temperature intermetallic wear.
- Austenitic manganese steel is selected to chisel abrasive wear.
- Cobalt-based carbide alloy cobalt-based alloy is selected for thermal stability and creep resistance at high temperatures (540℃).
Iron-based cladding metal is widely used because of its diverse products, wide range of performance capabilities, good balance between toughness and wear resistance, and low cost.
There are approximately four categories of iron-based surface metals:
(1) Pearlitic steel surface metal:
This type of alloy has good weldability, strong impact resistance, low hardness and is mainly used to repair mechanical parts such as shafts.
(2) Austenitic steel surface metal:
Manganese steel surface austenitic metal has high impact toughness and work hardening properties, but is prone to hot cracking. It is generally used to repair parts that are severely impacted by metal-to-metal and abrasive wear, such as mine cars and railroad sidings.
Chromium-manganese surface austenitic metal has better weldability, corrosion resistance, heat resistance and thermal crack resistance than austenitic manganese steel. It is mainly used to repair manganese steel and carbon steel parts that are severely affected by metal-to-metal wear.
(3) Martensitic steel surface metal:
The structure of this type of surface metal is mainly martensite. The hardfacing layer has high hardness, yield strength, high wear resistance, and can withstand moderate impact, but its impact resistance is lower than that of pearlitic and austenitic steel. It is mainly used to repair worn metal-to-metal parts such as gears and tractor chassis.
(4) Cast iron alloy surface metal:
This type of coating layer has high abrasive wear resistance, heat resistance, corrosion resistance, good oxidation resistance and light impact resistance, but it is prone to cracking during coating, so welding must be done with caution. It is mainly used to coat agricultural machinery, mining equipment and other parts.
Nickel-Based Surface Metal
The most used alloy among them is the nickel-chromium-boron-silicon series alloy. It exhibits excellent resistance to low-stress abrasive wear and metal-to-metal wear, and has good corrosion resistance, heat resistance and high-temperature oxidation resistance. However, its resistance to abrasive wear under high stress and impact is slightly weak. This alloy is typically used in corrosive media or occasions subject to low stress abrasive wear in high temperature environments.
Nickel-based alloys containing intermetallic compounds such as Ni-32Mo-15Cr-3Si exhibit high temperature hardness, excellent resistance to intermetallic wear and moderate abrasive wear, but low impact resistance. This alloy is best suited for gas tungsten arc or plasma arc cladding and is commonly used for coating the sealing surfaces of valves operating in severely corrosive media.
The price of carbide-containing nickel-based alloys is much lower than that of cobalt-based alloys. From an economic point of view, it has been widely used as a substitute for cobalt-based surface metals.
Cobalt-based surface metals mainly refer to cobalt-chromium-tungsten alloys, which can maintain high strength and hardness at about 650 ℃, have certain corrosion resistance and excellent adhesion wear resistance. Cobalt-based alloys have the best comprehensive performance among various plating metals and are commonly used for plating parts under high-temperature working conditions.
Copper Base Surface Metal
There are generally four types of copper-based plating alloys: bronze, brass, white copper, and pure copper. These alloys have good corrosion resistance, cavitation resistance and metal-to-metal wear resistance. They can be welded to iron-based materials to make bimetallic parts and can also be used to repair worn parts.
However, copper-based surface metals have poor resistance to sulfide corrosion, wear-resistant materials and high-temperature creep, low hardness, and are not easy to weld. They are only suitable for environments below 200℃. This type of metal coating is mainly used for lining bushings, sealing surfaces of low pressure valves and other similar applications.
Carbide Surface Metal
This kind of casing metal is mainly used for casing welding of oil well bits and road construction machinery parts under severe wearing conditions.
3. Welding process and coating method
Oxygen and acetylene surface
This method is mainly used to coat parts that require a smooth and high-quality surface, mainly small and medium-sized weldments produced in small batches, such as valves, oil well bits and plowshares.
Oxygen and acetylene equipment is simple to use, low in cost and can be used with gas welding equipment. However, the diameter of the welding torch nozzle orifice is larger than that of gas welding.
Hardfacing materials of any shape, including scraps, can be used. This method offers high visibility, allowing the coating to be carried out in a small area, producing a thin and smooth coating layer.
The dilution rate is low and the depth of the fusion layer can be controlled within 0.1mm, making it easy to guarantee the quality of the coating layer.
Using a reducing flame and a carbonizing flame for carburizing can reduce the toughness of the hardfacing layer, but can improve the wear resistance of the hardfacing layer with carbide as the primary wear-resistant phase.
This method is characterized by high labor intensity, low production efficiency and requirement for welders with certain technical skills.
Oxygen and acetylene surfacing typically involves the use of a carbonization flame, and the properties of the flame are related to the type of surface metal:
- Nickel-based alloys generally require a neutral flame, although a carbonizing flame may occasionally be used to improve the fluidity of the metal.
- Iron-based alloys require a double flame excess of acetylene (with a ratio of internal flame length to flame core of 2:1) to surface.
- When coating with low melting point, high carbon coating alloy such as high chromium cast iron or cobalt base alloy, an excess flame of 3 times that of acetylene is required.
Most steel parts can be coated without flux. However, when coating cast iron, flux must be used and measures must be taken to avoid white microstructure and cracks.
Preheating and slow cooling can significantly reduce the possibility of cracking of the coating layer and also help reduce the dilution rate.
Small parts can be heated directly using a welding torch, while large parts are usually heated in an oven, giving enough time to ensure the temperature is uniform.
The maximum thickness of each surface welding layer should be around 1.6mm, and multi-layer surface welding can be carried out.
For oxygen and acetylene spray welding (spray fusion), self-fusing alloy powder is typically used.
The spray welding process can be divided into “one-step method” and “two-step method” based on the order of powder spraying and remelting.
The “one-step” spray welding method involves simultaneous powder spraying and remelting, where the fine powder is preheated, presprayed, and then sprayed onto the work surface before being melted.
In contrast, the “two-step” spray welding method involves two separate steps of powder spraying and reflow using a reflow gun after preheating.
Common oxygen and acetylene surface defects include lack of fusion and pores, which may be caused by improper operation or poor quality surface materials.
Electrode arc surface
Rod welding arc equipment is an inexpensive and versatile option suitable for field cladding.
Common power sources include arc welding transformers, arc welding rectifiers, arc welding generators, and arc welding inverters. This equipment is particularly suitable for coating irregularly shaped parts and difficult-to-reach parts.
The concentrated heat of the arc results in minimal deformation and high productivity. However, it also has a high penetration rate and dilution rate, which can reduce the hardness and wear resistance of the coating layer.
Generally, 2-3 layers are welded, and multi-layer welding is prone to cracking.
The electrode arc surface is mainly used for small batch production and repair of worn parts. Surface electrodes available in China include D10×-24×, D25×-29×, D30×-49×, D50×-59×, D60×-69×, D70×-79×, D80×-89×, and brief.
Electrodes with titanium-calcium type, ilmenite type and low hydrogen type coatings should preferably adopt DC reverse connection to the surface. Electrodes with graphite-type coatings should preferably adopt positive DC connection or AC power supply.
Before surfacing, the electrode must be dried at the temperature specified in the electrode manual. Acid electrodes should be dried at 150°C for 0.5-1 hour, and alkaline electrodes should be dried at 250-350°C for 1-2 hours.
The preheating temperature for coating mainly depends on the carbon equivalent. For example, with a carbon equivalent (%) of 0.4, 0.5, 0.6, 0.7 and 0.8, the preheating temperature (℃) is 100, 150, 200, 250 and 300 respectively.
Slow cooling after coating can be carried out in a furnace or asbestos, or can be achieved by adequate heating to ensure that the cooling process is slow.
See Fig. 1 for electrode arc surface process parameters.
Fig. 1 Surface welding process parameters of shielded metal arc welding
| Coating layer thickness mm | <1.5 | <5 | ≥5 |
| Electrode diameter mm | 3.2 | 4-5 | 5~6 |
| Number of surface layers | 1 | 1~2 | ≥2 |
| Surface welding current A | 800~100 | 140~200≥ | 180~240 |
Submerged arc surface
Submerged arc surface is an automatic production method with high current and efficiency. It does not emit light radiation, providing good working conditions. However, the heat from the submerged arc can be excessive, leading to a high dilution rate.
To guarantee the required performance, 23 layers of coating are normally applied. Preheating and slow cooling measures are often taken to prevent cracking.
Submerged arc surface is mainly used for horizontal surface and is more suitable for large parts that are not easily deformed, such as the surface of corrosion-resistant layers on the inner walls of large-diameter containers or the surface of wear-resistant layers on steel laminating rolls. Not suitable for small parts.
DC or AC power supply can be used for submerged arc surface. However, DC reverse connection is mainly used to improve coating quality and production efficiency.
Increasing welding current will lead to greater dilution rate, penetration depth and coating thickness. The influence of welding arc voltage on the dilution ratio is not significant. The arc voltage is normally set between 30-35V and the length of the welding wire extension is 8 times the diameter of the welding wire.
To reduce the dilution rate and improve the deposition speed, multiwire and strip (tandem) electrodes can be used to improve the electrode.
Other surface methods
There are various coating methods available, such as gas metal arc coating, argon tungsten arc coating, plasma arc coating, electroslag coating, laser coating, friction coating and others.
