[tintuc]Procedcure of resfurbishing the grinding table liner and roller tires of vertical mill (Loesche, Fuller, Pfeifer, Polysius…)

Wear is a natural problem in the process of grinding hard and highly abrasive materials. Under high grinding pressure, hard (highly abrasive) material particles are pressed together with a gap just enough for the particles to be crushed. In most cases, this force is carried out by 2 metal surfaces with the material particles in the middle, in some cases the material particles are under the action of 3 surfaces. 2 Details (surfaces) of the pressed metal surface break the material in the middle into smaller particles, the shape of the material particles will be formed based on the direction of the force and the contour of the pressed surface. In parallel with that process, the metal surface (even though it is made of hard alloy material) will also have its elements gradually cut by the material particles.

ASTM G-65 measures the wear resistance of a metal surface using a grinding wheel. However, the characteristics and conditions of the abrasive are not the same as those of the actual abrasive. Therefore, the standard is only a reference for evaluating the quality of the weld deposit and the alloy in the wire used. The values ​​given by the standard do not fully assess the life of the weld deposit in practice.

However, some softer and tougher materials will last longer than harder materials in grinding applications. These alloys include austenitic manganese, martensitic, and some other carbides (usually smaller carbides, such as: Titanium Carbide). In conditions where there is very little impact, materials with a high-Chrome Carbide or/and Complex Carbide are the optimal choice.

1. Preparation for buildup and hardfacing:

Usually, in the process of welding the grinding rollers, the surface of the grinding rollers & grinding table is very hard and difficult to machine. Therefore, Carbon Electrode Blowing is the optimal solution that can be used to remove the old weld layer (if any) on the surface of the rollers & grinding table. The carbon blowing method also separates and minimizes the heat-affected area of ​​the weld layer while still maintaining the good weld layer on the surface. The advantage of carbon blowing & surface grinding is to create a smooth surface, control the width of the weld (blowing) to create the best weld layer. The grinding rollers & grinding table plate can be done while still inside the grinding machine or removed from the working position and transferred to the supplier's factory. In the case of performing the welding work on the grinding table roller at the supplier's workshop, the roller will be performed on the roller turntable to rotate at the rotation speed condition. The installation must ensure the centering of the roller and strict control during the welding process to ensure the contour of the roller. For the grinding table. There will be a specially designed system for the welding torch to rotate along the circumference of the pads. The penetrant testing method (PT) must be performed to detect defects before starting welding. 

2. PT (Penetrant Testing)

Non-destructive testing with penetrant material (Penetrant Test) is a mandatory requirement in the process of performing the welding work on the roller and grinding table pad. PT normally only works on smooth surfaces (such as casting surfaces). Therefore, the surface must be ground and cleaned before performing. PT is a testing method to detect surface discontinuities and cracks. PT is especially effective on austenitic alloy materials. Because these materials cannot be tested for magnetic properties. ASTM E 165 is the standard for this test method. 

3. Pre-heating

Normally, cast iron materials with 19.25% chromium do not require heating. But in some cases (especially in very low ambient temperatures), heating to narrow the temperature difference and remove moisture can be used. The maximum heating temperature can be 65 degrees Celsius. During the process, the temperature between welds should not exceed 150 degrees for cast steel and 100 degrees Celsius for cast iron. No heating is required when performing size compensation welding and welding of carbide composite welding wire. 

The chemical composition of the base material and the filler material is an important factor in determining the heating requirement & temperature control between welds. In the case of conventional brazing the material is a martensitic alloy. Brazing materials for brazing (specifically high chromium carbide alloys and high chromium steels) are not included in the above material category because the surface hardness of the layer is formed by very hard microstructures in a flexible crystal lattice, and it is independent of the quenching process. Martensitic alloys form their surface hardness and wear resistance through quenching at high temperatures or large differences between the lines. This is an important factor in understanding and determining the heating requirements and heat control during brazing.

Maintaining the temperature throughout the weld overlaying of the grinding table liner and roller tires is a very important factor affecting the quality and safety of the weld deposit. In the case that the temperature of the weld deposit falls below the interpass temperature before the weld deposit is finished, the hardening process begins to occur, an increase in the volume of the microscopic particles, the extent of which depends on how far the temperature has fallen from the interpass. Why is this? In fact, we do not want the surface of the weld deposit to harden before welding the next weld deposit onto it. When we weld the next weld deposit onto the hardened surface, the temperature of the additional weld deposit will soften the hardened material. The final weld deposit will be hard according to design, but the weld deposits below will be soft and unstable. This can easily create problems such as cracking after the machine runs. Therefore, maintaining the temperature of the weld layer within the interpass temperature range and cooling under ambient temperature conditions is extremely important to create a layer of a uniform, rigid and hard-to-harden weld layer according to the design thickness.

Refurbishment (Build-up and Hardfacing)

Build-up and hard-facing welding are based on the equipment conditions and the form of implementation (in the service shop or inside the mill). The choice of which type of welding material for each welding layer (build-up and hardfacing) is based on the properties of the base material (roll, mill table pad) and the required level of the build-up layer after welding. 

• ·Buffer layers
• ·Buildup layers
• · Hardfacing layers

In case the base material of the roller and the grinding table lining is high Chromium cast iron or Ni-Hard IV, the welding materials for both layers are the same. High chromium carbide wire (e.g. D100), or carbide combination (e.g. D200) can be used.

In case the base material is made of ordinary cast steel, it is necessary to add a backing layer to create a connection between the base material and the buildup layer. The materials that can be used are ER 309 or ER 307 welding wire.

Note: In all cases, the total thickness of the buildup layer should not exceed 65mm.

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[tintuc] FAQ of hardfacing wear plate

Q: What is the hardfacing of wear plate?

A: Hardfacing Wear Resistant Plate

Wear resistant steel plates are high-strength materials, typically made up of alloy steels, quenched and tempered steels, or carbon steels. These plates' most common alloying elements are chromium, manganese, nickel, and molybdenum.

Q: What is the purpose of a wear plate?

A: What are wear plate and where are they used | Cutting Edges

Wear plate play a critical role in the protection and longevity of earthmoving, mining and other industrial equipment. The outcome of using fit-for-purpose wear plates is threefold: Reduced cost of replacement parts. Reduced cost of maintenance.

Q: What is a steel wear plate?

A: Wear plates or liners are used to prevent damage to the main machinery due to abrasion or impact and to increase the life of the machine. Examples of machines or components that might require wear plates or liners are: Crushers. Shredders. Casting equipment.

Q: What size are wear plate?

A: Wear Plate Dimensions :

Thickness : 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 8mm, 10mm, 12mm, 15mm, 18mm, 25mm- 32mm, 32mm-45mm, 45mm-51mm, 51mm-80mm, 80mm- 130mm. Width : 1000mm, 1500mm, 2000mm, 2500mm , cut widths provided. Length : 2000mm, 2500mm, 3000mm, 4000mm, 4500mm, 5000mm, 6000mm, Cut lengths provided.

Q: What are bucket wear plates made of?

A: Wear Plate is a duplex material consisting of a very tough and highly wear resistant alloy overlaid into a shock absorbing mild steel or chromium steel backing plate.

Q: What are the properties of wear resistance plate?

A: Wear Resistance Steel Plate is made of high-quality materials, which ensures that they will last for a long time. These plates are made from 100% steel, so they will not rust or corrode. The plates are also lightweight, so you can easily move them around. The steel plates are made of high-quality material.

Q: What are wear plates made of?

A: Produced out of a duplex material that generally consist of a tough, wear resistant alloy coating and a shock absorbing steel or chromium steel backing plate, these combined properties enable the product to perform under extreme conditions.

Q: What are the hardest wear plate?

A: Extreme is the world's hardest wear plate with a nominal hardness of 60 HRC and typical hardness of 650–700 HBW.

Q: What is the hardness of wear plate?

A: For this reason steel with hardness of around 400 Brinell is the most commonly specified and used. However hot rolled steel plate products for more exacting abrasive conditions are readily available in 500 Brinell hardness while even harder steel plates are also manufactured.

Q: What is the hardness of chromium carbide wear plate?

A: Hardness: Alloy layer macro hardness HRC57-63, carbide hardness hv1400-1800. Wear Resistance: low-carbon steel 20-25 times, stainless steel, High Manganese Steel 8-12 times, general high-carbon high chromium wear-resistant steel is more than 1.5 TIMES.

Q: What are bucket wear plate made of?

A: Wear Plate is a duplex material consisting of a very tough and highly wear resistant alloy overlaid into a shock absorbing mild steel or chromium steel backing plate.

Q: What are the uses of wear resistant plates?

A: Wear Resistant Steel Plates are used in the construction of buildings and bridges in addition to being used for kitchenware and appliances like cutlery and plates. Wear Resistant Plates can be used in a variety of materials, including cast iron, ductile iron, high-carbon steel, low-carbon steel, and stainless steel.

Q: What is the hardness of wear plate?

A: For this reason steel with hardness of around 400 Brinell is the most commonly specified and used. However hot rolled steel plate products for more exacting abrasive conditions are readily available in 500 Brinell hardness while even harder steel plates are also manufactured.

Q: What are the uses of wear resistant plate?

A: Wear Resistant Steel Plates are used in the construction of buildings and bridges in addition to being used for kitchenware and appliances like cutlery and plates. Wear Resistant Plates can be used in a variety of materials, including cast iron, ductile iron, high-carbon steel, low-carbon steel, and stainless steel.

Q: What is wear plate?

A: What are Wear-Resistant Steel Plates? Wear-resistant steel plates, also named abrasion-resistant plates (AR Plates), are used to reduce wear and tear on equipment surface caused by intense rolling abrasion and impact.

Q: What is a steel wear plate?

A: Wear plates or liners are used to prevent damage to the main machinery due to abrasion or impact and to increase the life of the machine. Examples of machines or components that might require wear plates or liners are: Crushers. Shredders. Casting equipment.

Q: Can wear plate be recycled?

A: Yes, steel wear plates can be recycled at the end of their service life, provided they are free from contaminants and processed correctly.

Q: What is the cost comparison between wear plate and other wear-resistant solutions?

A: While wear plates may have a higher initial cost, they can offer better value in the long run due to their durability and reduced need for frequent replacement. However, the total cost depends on the specific application and usage patterns.

Q: Can wear plate be used in high-temperature environments?

A: Some wear plates are designed to withstand high temperatures, but it depends on the specific material composition and heat-resistant properties.

Q: Can wear plates be customized?

A: Yes, wear plates can be customized to specific dimensions, shapes, and thicknesses to fit the requirements of different applications and equipment.

Q: What is special of D-Plate
A: D-Plate is a hardfacing steel plate manufactured by powder overlay process (POP) an abrasion resistant chromium carbide overlay and some other carbides to an impact resistant mild steel which is our standard base material. This can be changed to meet any customized requirements. in other word, D-Plate can be called POP Wear Plate

Overlay Material

D-Plate are overlaid by using high quality formulated powder and solid mild steel wire that is an austenitic chromium carbide iron. The microstructure consists of mainly M7C3 carbides in a carbide austenite eutectic matrix. Chemical composition of D-Plate’s overlay materials may depend on the application of operating environments of the customers.

More details at downloadable files: Test result of standard D-Plate

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[tintuc]D-Tech, part of BCC, is professional manufacturer of hardfacing wear plate, wear parts and refurbishment services applying for cement plant, power, mining etc since 2014. Since 2019, BCC invest in production line of welding electrode for future plan which will focus on metallurgical technology. D100e is the first product of hardfacing based on our research and development.

D100e hardfacing electrode which designed, tested and manufactured by BCC

Since April, 2022, we launched first product for hardfacing application. D100e is the chromium carbide covered electrode. The product was desgined for small size and daily hardfacing work. It means customer keep products at stock for all the time, then they can do the hardfacing at small size in order to keep machines operating in the best performance before closing for big shut down. 

Applications of D100e hardfacing electrode

D100e hardfacing electrode was suitable for hardfacing, repairing and refurbishing for equipment and machine at 

- Cement plants

- Coal-fired power plants

- Brick plant

- Sugar cane plant

- Mining

- concrete mixing plant

- Earth moving equipments

Some key factors of D100e hardfacing electrode

1. deposition efficiency

For normal welding electrode the efficiency is just about 45-55%. But for D100e, the efficiency can up to 76% which is almost closed to rate of flux cored wire.

2. Productivity

Product was design for low-heat-input process, it means we use lower amps and volts for welding. Then we can increase the productivity easily whenever we increase the electricity factors.

3. Dilution and quality of hardfacing layers

with low amps and volts during welding, D100e can give low dilution which can the specifications of hardfacing layer in very first layer of deposit.

inside the manufacturing plant, processs of testing the weldablity and visual wear resistance

 Download introduction of Hardfacing Electrodes

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[tintuc]As a wear plate producer in Vietnam,D-Techs has a big advantage to do the fabrication job based on wear plate where we can optimize cost in order to have more competitve.

In July 2015, D-Techs has delivered the product to Nghi Son Cement (NSCC) which is a Japanses Cement Producer in Vietnam. NSCC is one of the best Cement Producer in Vietnam. Their product are using in most of important projects in Vietnam. They also is one of best company who are applying management process to control the production cost by using the cost-effective products.

BCC is prouded to become the supplier of NSCC to bring our best products in order to be a part of their production management.

Job Details:

·         Industry: Cement

·         Equipment: Vertical Roller Mill

·         Part: Guide Vane

·         Product: D-Plate 100

Some typical photos:

More details at downloadable files: D-Plate Introduction & Test result of standard D-Plate

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The deposited wear plate is a dual-metal steel plate which manufactured by overlay welding process. The wear resistant alloys were welded on the surface of Mild steel plate. This process is order to create a surface which can work at high wear conditions. It can be fabricated as the properties of mild-steel.

The overlay welding process can be  SAW, FCAW (Open arc), Sub-Arc Welding (The deposited layers can be made from calculated alloys using carbon electrode to melt weld pool). Depending each welding process, the width of welding seam will be difference.

The deposited wear plate can be fabricated by various process, such as bending, cutting, welding, studding etc. Plate just can be cut (thermal cutting) by Plasma flame.

The deposited wear plate can be applied at many difference industries which contains difference wear factors, such as: Abrasion, Corrosion, Heat, Impact, etc. By changing the welding consumable (alloys), we can create a new product which is suitable for specific application.

There are 02 processes to make the wear plate

Drum Process (round process): mild steel plate is bended to become a drum and installed on the the machine. The plate will be flattened back after welding.

The mild steel plate will be clamped on the flat position and make the welding on the surface.

Some typical industries: Cement, Coa-fired Power Plant, Mining, Quarrying…

Typical application of wear plate

More details at downloadable files: D-Plate Introduction & Test result of standard D-Plate

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With D-Tech™ Overlay Welding Technology, We provides a complete range of solutions for hard overlay welding. The following services are offered for vertical roller mills:

• Hard overlay welded grinding rolls and grinding tables 
• Welding consumables of alloys specifically matched for use in vertical roller mills 
• Portable welding system consisting of welding head, control unit and DC power supply which desgined and manufactured by BCM 
• D-Tech™ 3R Services can be done either at the 3R Workshop or at the mill plant site 

D-Techs™ 3R Offer the following Benefits:

• New grinding rolls and grinding plates made of hard casting with and without hardfacing to ensure long service life-time 
• Regeneration of grinding rolls and grinding plates to avoid the purchase of costly spare parts 
• Complete, cost effective services Supply of hard casting and hard overlay welding from a single source 
• Excellent references in the line of welding engineering 
• Experience in solving wear problems for many years.

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We, D-Tech, manufacture several types of D-Plate which are chromium carbide hardfacing wear plate in Vietnam and worldwide markets. D-Plate can be well used in various industries, such as cement industry, power station industry, steel industry and mining industry.

Wear plates and wear steel parts are used in many applications where friction between two parts or materials creates degradation.

Its wear-resistant chromium carbide alloys with 4.5 to 5% carbon added to sturdy carbon steel substrates. Wear plates are expendable items that are used to prevent excessive wear or damage to expensive equipment.

Abrasion resistant steel wear plate may bolt onto a machine that slides or rotates in a manufacturing process, while they can also be found where manufactured parts or minerals are regularly rubbing or abrasively contacting the surface.

Wear plate is commonly a type of abrasion resistant steel plate that is considered extremely durable, especially under harsh conditions.

However, various significant refinements and strategies have occurred. And as of present, the range of overlay wear plate accessible includes chromium and tungsten carbide grades, which possess excellent resistance to abrasion, impact, and erosion even at both ambient and elevated temperatures.

Meanwhile, in the more significant part of critical abrasion surroundings, the chromium carbide alloys are the primary profitable solution.

What types of material are wear resistant plate made of?

Alloy Chemistry

The highest ordinary used alloy facing is a high chromium iron consists of precisely 1/3 of Chromium and in surplus of 4% combined carbon.

D-Tech is making this to correlate to POP plate with the chemistry of Chromium of up to 34.0%, carbon of 5.4%, Manganese of 3.5%, and the others at 1.3%, Balance Fe.

Meanwhile, this standard alloy can be changed in many different ways; it can improve the abrasion resistance while lowering the toughness, or the other way round. On the contrary, the matrix can be made harder by reducing the manganese to 1%, with some reduction in firmness. Also, further refinement may be accomplished by the addition of other alloying elements.

Carbides

The substance that provides high chromium powder alloys with their capability to withstand abrasion is the establishment of primary carbides from a chemical compound of iron, Chromium, and carbon, or iron, Chromium, or carbide, which is also known as chromium carbide. Pure, high rate chromium carbide can be manufactured; however, it is costly for large-area preservation, so D-Techs makes use of mixed carbide, which involves both Chromium and iron. This makes up the primary carbide with the formula M7C3, where M specifies the mixture of metal and Chromium in the compound.

Hardness

A standard overlay alloy consists of a compound of chromium carbides in a matrix of a chromium iron-carbon alloy. The hardness of primary chromium carbides is proportionate of 1700HV correlate with. For instance, ordinary workshop steel files, with firmness of 600HV. In general, the hardness of these alloys can be calculated using a Rockwell hardness tester. Even though it neither measures the carbide or the matrix, it gives an agreeable general proof of the hardness of the alloy. An average value of being 54-60 HRC.

Microstructure

In the extension of chemistry, the most significant characteristic of the alloy overlay is its microstructure. Hence, when checked out under a microscope, the carbides will take the form of white substance against a dark background, that that’s the matrix. A perfect microstructure, for more excellent abrasion resistance, must have a dense array of needle-like carbides that, in cross-segment, look as slender hexagons with a small hole in the middle.

Moreover, whenever you notice an appearance of uneven shaped spots or avenues of white. Such as either ladder, fish-bone patterns, or central poles with rungs on any of the sides. This is a sure sign that the carbon content is beneath optimum for high abrasion resistance, but it has also improved impact-resistant properties.

How we supply for wear resistant plate?

• Wear Resistance materials: We manufacture solid welding wire and formulated powder by our own selves, with strict rule on the alloy composition.
• Base Plates: We get all our base plates from China’s biggest steel Mills and are restricted to our strict quality assurance procedure.
• R&D Team: We provide an R&D team on both equipment and hardfacing technology.
• Customized Wear Products: We also supply customized Wear products in line with our customers’ demand.

What else should I know before I order my hardfacing wear plate?

You should know the what hardness of the plate is and what the intent is of the liner. The harder the plate that is used, the longer it will last in service, but there are trade-offs. For some parts, you will need a softer material that is intended to wear out before your primary surface.

More details at downloadable files: D-Plate Introduction & Test result of standard D-Plate

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Abstract:  Repair welding and surfacing are both considered in the field of maintenance welding and are covered together since they are both done by the same welders. Often it is extremely difficult to separate what is considered repair welding from maintenance welding, and surfacing can be included in both situations. The same basic factors apply to both weld repair and surfacing. Repaired parts may be more serviceable than the original part, since they can be reinforced and the weaknesses of the original part corrected. It is often more economical to weld repair since the delay in obtaining the replacement part could be excessive and the cost of the new part would normally exceed the cost of repairing the damaged part.

The need for weld repair and surfacing

There are probably more welders employed doing maintenance and repair welding than there are in any other industry grouping. The work done in the primary metal industry is primarily maintenance and repair. This is true also of the utility services category and by combining these with repair services you find that approximately 18% of the welders are engaged in this type of work. In addition, it has prime importance to welding since the earliest use of welding was for repair work. The most famous incident happened at the outbreak of World War I when German ships were interned in New York harbor. Their crews, hoping to make the ships inoperable, sabotaged the engines and machinery. However, by means of welding, repairs were quickly made and the ships were placed in transatlantic service to deliver material from the U.S. to Europe. Repair welding and surfacing are both considered in the field of maintenance welding and are covered together since they are both done by the same welders. Often it is extremely difficult to separate what is considered repair welding from maintenance welding, and surfacing can be included in both situations. The same basic factors apply to both weld repair and surfacing. Parts break and wear out continually. It may be impossible to obtain another part exactly like the one that broke or wore out. This is particularly true of older industrial machinery, construction machinery, agricultural machinery, machine tool parts, and even automobiles. Repaired parts may be more serviceable than the original part, since they can be reinforced and the weaknesses of the original part corrected. It is often more economical to weld repair since the delay in obtaining the replacement part could be excessive and the cost of the new part would normally exceed the cost of repairing the damaged part. Weld repair is commonly used to improve, update, and rework parts so that they equal or exceed the usefulness of the original part. This is normally attained, with the possible exception of weld-repaired cast iron parts that are subjected to heating and cooling. Weld repairs on cast iron parts subjected to repetitive heating and cooling may or may not provide adequate service life. The problem is that cast iron parts subjected to high-temperature heating and cooling, such as machinery brakes, furnace sections, etc., fail originally from this type of service and due to metallurgical changes the weld may fail again without providing adequate service life. Except for emergency situations, it is not wise to repair cast iron parts of this type. The metal that the part to be repaired is made of has a great influence on the service life of the repaired parts. Parts made of low-carbon and low-alloy steels can be repaired without adversely affecting the service life of the part. On the other hand, high-carbon steels may be weld repaired but must be properly heat treated if they are to provide adequate service life. It is absolutely essential that we know the type, specification, or composition of the metal that we are planning to weld. As mentioned above, it may be unwise to weld repair certain metals. But we should not weld on any metal unless we know its composition. The economics of weld repairing are usually very favorable and this applies to the smallest or the largest weld repair job. Some weld repair jobs may take only a few minutes and others may require weeks for proper preparation and welding. Even so, the money involved in a repair job may be less than the cost of a new part. A part made of any metal that can be welded can be repair welded or surfaced. In fact, some of the metals that are not normally welded can be given special surfacing coatings by one process or another. All the arc welding processes are used for repair and maintenance work. In addition the brazing processes, the oxy-fuel gas welding processes, soldering, thermit welding, electro slag welding, electron beam welding, and laser beam welding are also used. The thermal spraying processes are all widely used for surfacing applications. In addition, the various thermal cutting processes are used for preparing parts for repair welding. The selection of the appropriate preparation process and welding process depends on the same factors that are considered in selecting a welding or cutting process for the original manufacturing operation. In the case of repair welding, there are usually limitations, such as the availability of equipment for a one-time job and the necessity of obtaining equipment quickly for emergency repair work. This limits the selection and it is for this reason that the shielded metal arc welding process, the gas metal arc welding process, the gas tungsten arc welding process, and oxyacetylene welding and torch brazing are most commonly used. However, for many routine and continuous types of repair work some of the other welding processes may be the most economical. For example, submerged arc welding is widely used for building up the surface of worn parts. The electro slag process has been used to repair and resurface parts for hammer mills, for construction equipment, and for rebuilding rolls for steel mills. Thus there is a difference in the selection of the welding process for the routine, continuing types of repair and surfacing work versus the one-of-a-type or breakdown emergency repair job.

Analyze and develop rework procedure

The success of a repair or surfacing job depends on the thought and preparation prior to doing any actual work on the project. Many factors must be considered in making a thorough analysis. A thorough analysis as outlined may not be required in many situations. This is due to experience gained by welders and others in analyzing jobs, making repairs, and then checking on the service life of the repaired part. As experience is gained many short cuts can be taken, but it is the intent to provide a detailed method of analyzing jobs so that the repair will be as successful as possible. One of the reasons for such an investigation is to establish the cause of the failure in the case of a broken part or the cause of wear or erosion in the case of a part to be surfaced. The four points outlined are:

• Make a detailed study of the actual parts that failed.
• Learn the background information concerning the specifications and design.
• Make an investigation of the materials used.
• Make a listing of all of the facts so that at the conclusion the reason of failure will be as accurate as possible.

There are certain situations and certain types of equipment for which repair welding may not be done or may be done only with prior approvals. Certain types of containers and transportation equipment must not be weld repaired or may be welded only with special permission and approval. These include railroad locomotive and car wheels, high-alloy high-strength truck frames, and compressed gas cylinders. Most pieces of power-generating machinery, including turbines, generators, and large engines, are covered by casualty insurance. Weld repair on such machinery can be done only with the prior approval of the welding procedure by the insurance underwriters. In some cases, approval may not be granted. An example of this can be cast iron crankshafts in large stationary diesel engines. Certain weld repairs may be made but it is necessary to develop a written procedure which must be approved in writing by the underwriting company’s representative. Repairs by welding to boilers and pressure vessels require special attention. Pressure vessels that carry an ASME stamp or are under the jurisdiction of any state or province or government agency must be repaired in accordance with the National regulations issued by responsible authorities. Repairs by welding are limited to steels having known weldable quality. It provides a maximum carbon content of 0.35% for carbon steels and a carbon content of 0.25% for low-alloy steels. For welding high-alloy materials and nonferrous materials the work must be done in accordance with the ASME code. Welders making such repairs must be qualified based on the thickness of the material and the type of material being welded. Full-penetration welds are required with welding recommended from both sides. Permissible welded repairs are defined as cracks, corroded surfaces, and seal welding, patches, and the replacement of stays. A repair is the work necessary to return a boiler or pressure vessel to a safe and satisfactory operating condition. Alterations are also permitted and this is a change in a boiler or pressure vessel that substantially alters the original design and in this case work can be done only by a manufacturer possessing a valid certificate authorization from ASME. All alterations must comply with the section of code to which the original boiler or pressure vessel was constructed. A written repair procedure is required for doing either repair work or alterations. In the case of an alteration a record must be made and all alteration work must be approved. These records must be filed with the inspection agency or the jurisdictional agency, the National Board of Boiler and Pressure Vessel Inspectors, and all work must be inspected. Alterations on bridges, large steel frame buildings, and ships may be done only with special authorization. The alteration work must be designed and approved. The welders must be qualified according to the code used and the work must be inspected. Written welding procedures are required. Once the decision has been made to make a weld repair it is then necessary to establish why the part failed or wore out. This relates to the type of repair job since it also determines whether reinforcing may be required. Reasons for the part to fail or wear out can be among the following:

• Accident
• Misapplication
• Abuse
• Overload.

If the part failed because of an accident or an overload, it may be returned to service with the weld repair made to bring it back to its original strength. The same consideration applies if the part has been abused or misapplied. It may be necessary to reinforce the part so that it will stand temporary overloads, misapplication, or abuse. This decision should be made prior to the weld repair. In the case of poor workmanship, poor design, or incorrect material the weld repair should eliminate the poor workmanship that was responsible for the failure. In this case, the part would be returned to its original design. If failure is due to poor design, design changes may be required and reinforcement may be added. In a case of wrong material it will be assumed that the material was of a lower strength level which contributed to the failure. In this case reinforcing would be required. If the repair or alteration job is to modify the part, it is necessary that the modification be designed by competent designers who have the knowledge of the design conditions of the original part. This may require reinforcing to make sure the modification or alteration is satisfactory. Another important factor that must be considered is what results are expected of the repaired or reworked part. Should it be reinforced or should it be redesigned and altered to provide necessary service life? Finally, in the case of surfacing, what better surface could be provided to withstand the service that caused the premature wear or failure?

Rework Procedure

A written repair procedure is required for all but the most simple jobs. It is absolutely necessary that the type of material being welded is known. This can be found in several ways. If possible, refer to the drawing of the part and the specifications that are shown for the part or parts to be welded. If this is not possible, particularly in the field or at the maintenance shop, look for clues as to the type of metal involved. Analyze the application of the metal, for clues. For example, an automobile engine block is normally cast iron except for some which might be cast aluminum. Aluminum and iron are easily distinguishable. The spring of an automobile or truck would normally be high-carbon steel. The body structure of a car or truck would be mild steel. The appearance often helps provide clues. As a final resort it may be necessary to obtain a laboratory analysis of the metal. Filings or a piece of the metal must be sent to a laboratory capable of making such determinations. The normal method of selecting the welding process will be followed once the material to be welded has been identified. This involves the type of metal, the thickness of the metal, the position of welding, etc. This also leads into the question of filler metal to be used. After this, the normal method of filler metal selection is followed. This involves matching base metal composition, matching the base metal properties, particularly strength, and providing weld metal that will withstand the service involved. In surfacing, the surface characteristics desired for the finished job depend entirely on the service to which the surface will be exposed. This is based on knowledge and experience and on the fact that the surface has deteriorated to the point that it needs to be reworked or resurfaced. When wear is involved, surfaces can be rebuilt many times without reducing the strength of the part and the service life will be greatly extended. The repair procedure should be very similar to a procedure developed for welding a critical part. It should include the process and filler metal and the technique to be used in making welds.

Source: http://www.d-plate.com/welding-repair-surfacing/

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D-Tech succesfully  has applied our Hardfacing Technology to fabricate the Sliding Plate which a very important wear part in Vertical Roller Mill by Polysius for a Vietnamese Cement Plant.

Job Details:

• Customer: Ha Tien 1 Cement
• Industry: Cement
• Equipment: Vertical Roller Mill (Polysius)
• Part: Sliding Plate.
• Applied wire: Hardcored 101

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1. General

Hardfacing is applied in cases where the surface of engine parts is being subject to abrasion by wear, corrosion or heat. According to the definition hardfacing is applied when the surface is going to be damaged by wear due to hard minerals. 

This happens in all domains of mechanical processing, where processes are realised at room temperature or increased temperatures, such as in crushing, conveying, mixing and separating in the field of mining, steel and iron industry, cement industry, coal power plants, overground and underground working, recycling and environmental protection.

In chemical industry it is applied in areas of sharp mineral dressing.

The objective of hardfacing according to DIN 50320 is to surface a layer onto the basebody, which is most beneficially resisting to the wear-causing mineral.

The meaning of hardsurfacing did significantly increase in the course of the last 10 years, as standstills do become more and more expensive for big factories, due to increased wages and salaries, but also for reasons of networking. Layers of between 2 mm and 200 mm thickness can be produced by application of the different hardfacing procedures, whereas the fusion-efficiency rate can vary between 0,5 and 50 kg/hour, with fusion penetrations of between 0,5 mm and 10 mm.

The welding procedures can be differentiated by the intensity of mixture with the base body, which is usually increasing along with an increasing fusion efficieny rate.

Nearly all kinds of weldable materials can be hardfaced and mostly all types of known wear- resistant metals in combination can be used as hardfacing materials.

Ceramic materials, which can only be coated by spraying-on thin layers, cannot be hardfaced.

2. Trends for Welding

2.1 Stick Electrodes and Filler wires 

Stick electrodes will be further used, before all for reparation in built-in condition, as they can be processed not only in tub position. Anyhow, their low fusion-efficiency rate, which results in costs of more than 50 Euro per kg, is a disadvantage.

Filler wires can be regarded as an absolutely necessary welding process, with regard to a consumption per buyer of more than 1 ton of material per year.

The fusion penetration per burner is usually between 3 – 6 kg per hour, so that the costs per kg welding material are decreased to an amount of about 20 Euro per kg.

But this processing can almost only be easily used in tub position. This means, that the engine parts to be protected have to be moved accordingly, so that welding in built-in condition is often impossible.

The results of fusion efficiencies of the latest developments in the sector of filler wires where up to 15 kg per hour, so that the costs per kg welding material decreased to 10 – 15 Euro per kg.

It is most important for tubular-wire welding that removal by suction is made very carefully. 

2.2 Plasmapowder-Hardfacing 

Plasmapowder-hardfacing made a triumphant march through hardfacing of valves for the motor car industry. A mechanical hardsurfacing at permanent operation was achieved, with very slight mixtures and good surface qualities, so that the material consumption was only half compared to the demand for continuous casting sticks as used before.

This procedure is also qualified for tungsten carbides, which are not added into the metal arc, but behind it, in order to have them gently inserted into the melt, without their dissolution, what is a second advantage. Thus a higher rate of tungsten carbides is achieved, which means a significantly better resistance to abrasive minerals compared to usual chromium carbides.

This processing, as a special procedure, is widely applied at Rheinbraun, but also for processing of oil sands and in oil mining. The trend for this area has not yet become obvious.

2.3 Submerged hardfacing

Submerged welding processes give us the chance of achieving fully mechanically even higher fusion efficiencies, compared to tubular-wire welding with open metal-arc, which often do achieve between 8 – 10 kg. 

But when applying this process, using wire or band, it is nearly impossible to produce high-quality hardfacings. Therefore this process, within the scope of hardfacing, is meant for big construction parts, such as cones of blast furnaces, but also for regenerating of earth shifting units, especially in the Far East, whereas in Europe it seems to be more economic to use new parts, which are scrapped after their wear reserve has been exhausted.

Hardfacing is a wage-intensive process, which is only to be applied, where operation costs in Western European countries, where wages costs are high, can really be decreased by applying this technology, or when operativeness cannot be guaranteed in another way. 

4 Application of prefabricated hardfaced plates

Instead of hardfacing the part by own production, semifinished hardfaced products are more and more used.

These polyburner-technology plates with a high fusion-efficiency rate can be produced much more economically than having them manufactured by own production.

Constuction parts, such as hoppers, chutes, screens, tubes, fans, separators or others, can be manufactures by plasma-cutting and forming of such plates.

3. Trends for Welding Fillers

3.1 Increased Application of titanium-carbide containing martensitic alloys

The main application of hardsurfacing was formerly the use of martensitic alloys with 400 – 600 Brinell, but nowadays such material contain titanium-carbide fortifications, although the removal of slag is quite difficult when using such addings. Especially when using these materials, or those where niobium is added to martensitic alloys, the application is recommended for wear problems of so-called high- pressure rollers in a wide range. 

3.2 Use of highly-chromium containing materials with higher carbon contents then those of filler wires

Compared to formerly used hardfacing materials as filler wires, normally of the alloy group 10 with 4,5% C and 30% Cr, there is a clear trend towards higher alloyed filler wires to be seen, as only when using these filler wires as a second and third layer a significantly longer lifetime will be achieved.

In general such materials do contain 5,5% C, 20% Cr and 7% niobium, at higher temperatures they do also contain molybdenum and tungsten. In a certain range these materials can also be applied for higher temperatures up to ca. 750° C, but they will lose their wear-resistance at higher temperatures due to transformation of the matrix.

3.3 Tungsten-carbide containing hardfacings

In former times such materials were only used in oil- mining due to reasons of costs, whereas their application did meanwhile considerably increase, not only for stick electrodes, but also for filler wires and PTA- welding and special-welding procedures, as the lifetime is significantly higher, whereas the wages costs are the same. did meanwhile considerably increase, not only for stick electrodes, but also for filler wires and PTA- welding and special-welding procedures, as the lifetime is significantly higher, whereas the wages costs are the same.

But meanwhile there is a clear trend towards iron- containing materials, which are, as a consequence, cheaper.

4. Trends for Applications

4.1 Hardfacing of Strips and Disks for Coal- and Cement-Crushing

Application for Vertical Roller Mills in Cement Plant

Generally such strips do consist of materials which are known from the literature as being unweldable, having a high carbon-, chromium- or nickel-content.

Anyhow this is the second-largest application worldwide for hardfacing with chromium-containing hardfacing materials. Compared to casting materials, the achieved lifetime is twice or three times longer and the grinding result is much better for a long period of time.

In the same way the disk, on which the strip rolls, can thus be regenerated and the lifetime extended.

4.2 Sinter-crusher stars with cobalt-base alloys and inserted mixed carbides

Sinter crushers are a considerable wear problem in each iron and steel work worldwide. Generally their lifetime in hardfaced condition is about 2-4 months. Actually tests are made, in order to find out if the use of tungsten-chromium carbides can increase lifetime significantly, which are promising.

But with regard to bar frames (the counter-part) it already became obvious that with such materials a longer lifetime is not achieved, due to even higher temperatures.

4.3 Use of hardfaced Plates as semifinished Products

The main trend and most important application for hardfacing worldwide is the production of hardfaced plates in standard sizes, of which parts ready to be installed are being manufactured. Processes according to drawings of parts to be manufactured can be made of such hardfaced plates, using plasma- burners or water-jet.

Even complicated equipments can be made by cold- work, like some examples show. The cheap production of the semi-finished products is mainly interesting, whereas the welding mechanization is most important. This can be achieved by using special procedures with an extremely intensive fusion efficiency rate per burner, or by combining many burners, e.g. up to 10 burners for filler-wire weldings.

Wear Plate Producing

5. Trends as a Result of Environmental Protection Prescriptions

The environmental protection is a very important trend for hardfacing, which will cause much more problems in the future than it did the last 100 years. Steams are emerging whilst hardfacing, which are not that dangerous, as they do nearly not contain hexavalent chromium. The size of dust particles is dangerous, so that a good suction during work shall be ensured.

In addition, there are new trends coming up with regard to valuation of danger of nickel and manganese, which will probably afford high investments with regard to the suction of such welding-steams within the next 10 years.

For that reason we assume that in the future there will be a concentration of orders in less locations, where an excellent suction is guaranteed, or where in fully- enclosed cabins, supported by robots, the main hardfacing work will be done.

6. Summary

Hardfacing is a modern procedure, which nowadays is mainly applied for bigger construction parts, in order to extend the lifetime, instead of using massive solutions, such as castings. This “added value” makes the parts more valuable, and the demand for it will be constant, as the standstill of concatenated machines will become more and more expensive. 

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Hardfacing Frequently asked questions

At first glance, hardfacing can be confusing and troublesome; in reality, it isn't. Understanding some of the basics about hardfacing can go a long way toward instilling confidence in your hardfacing product selection.

The following 19 answers to frequently asked questions may help you select hardfacing products that are most appropriate for your application.

1. What is hardfacing?

Metal parts often fail their intended use not because they fracture, but because they wear, which causes them to lose dimension and functionality. Hardfacing, also known as hardsurfacing, is the application of buildup or wear-resistant weld metals to a part's surface by means of welding or joining.

2. What base metals can be hardfaced?

Carbon and low-alloy steels with carbon contents of less than 1 percent can be hardfaced. High-carbon alloys may require a special buffer layer.

The following base metals can be hardfaced:

• Stainless steels
• Manganese steels
• Cast irons and steels
• Nickel-base alloys
• Copper-base alloys

3. What is the most popular procedure used to apply hardfacing?

In order of popularity, the following procedures can be used:

• Flux cored arc welding (FCAW)
• Gas metal arc welding (GMAW)
• Shielded metal arc welding (SMAW)
• Submerged arc welding (SAW)
• Gas tungsten arc welding (GTAW)
• Oxyfuel welding (OFW) or oxyacetylene welding
• Plasma transferred arc welding, laser welding, thermal spray, and brazing

FCAW and GMAW may be interchangeable or the same in terms of popularity. However, the trend is toward use of semiautomatic and automatic welding procedures.

Procedure Deposition Rate (lbs./hr.) FCAW 8 to 25 GMAW 5 to 12 SMAW 3 to 5 SAW 8 to 25 GTAW 3 to 5 OFW 5 to 10

Figure 1

4. With so many welding processes available, which ones are the most economical?

Many factors affect the economics of hardfacing, but a major one is the deposition rate. Figure 1shows the estimated deposition rate for each process.

5. Wear is such an all-encompassing term. Can it be broken down into more manageable categories?

Yes. Many different categories of wear exist—too many to cover in one article—but the most typical modes of wear are as follows (percentages are estimates of total wear):

• Abrasion—40 percent
• Impact—25 percent
• Metallic (metal to metal)—10 percent
• Heat—5 percent
• Corrosion—5 percent
• Other—5 percent

Most worn parts don't fail from a single mode of wear, such as impact, but from a combination of modes, such as abrasion and impact. For example, a mining bucket tooth usually is subjected to abrasion and impact, and depending on what type of material is mined (soft or hard rock), one mode may be more dominant than another. This will dictate the welding product used.

Determining the wear mode can be challenging and may require trial and error when you select hardfacing products.

6. Is there a convenient way to categorize the many alloys when determining which hardfacing to use?

Yes. Iron-base alloys can be divided into three main categories:

• Martensitic. This includes all hardenable steels with Rockwell hardness from 20 to 65. This group, similar to tool steel, hardens upon cooling. They are good for metal-to-metal and abrasive wear. They also can withstand a great deal of impact.
• Austenitic. Austenitic alloys include work-hardening steels, such as manganese and stainless. This group generally is soft when it's welded and hardens only after the weld metal is worked. They have good impact properties and moderate abrasion resistance. The stainless steel family is good for corrosion resistance.
• Metal carbide. These alloys contain large amounts of metal carbides in a soft, tough matrix and are good for severe-abrasion applications. The alloys that contain large amounts of chromium and carbon are known as the chromium carbide family and are closer to a cast iron or white iron. Their hardnesses are from 40 HRC to 65 HRC. Alloys that contain large amounts of tungsten and carbon belong to the tungsten carbide family. Some contain small amounts of chromium and boron that form borides and are good for severe-abrasion applications.

7. Many hardfacing alloys crack. Is this normal?

It depends on the hardfacing alloy. Many chromium carbide alloys check-crack when cooled to moderate temperatures; this is normal. Others, such as the austenitic and martensitic families, don't crack when applied with proper welding procedures.

Figure 2 Caption here.

8. What is check-cracking?

Check-cracking, or checking as it's sometimes called, occurs in the metal carbide families and can be seen as cracks that are perpendicular to the bead length (see Figure 2). They generally occur from 3/8 to 2 inches apart and are the result of high stresses induced by the contraction of weld metal as it cools.

The cracks propagate through the thickness of the weld bead and stop at the parent metal, as long as it's not brittle. In cases in which the parent metal is hard or brittle, you should select a buffer layer of a softer, tougher weld metal. The austenitic family is a good choice for a buffer deposit.

9. What is chromium carbide hardfacing?

Generally, these are iron-base alloys that contain high amounts of chromium (greater than 18 percent) and carbon (greater than 3 percent). These elements form hard carbides (chromium carbides) that resist abrasion. The deposits frequently check-crack about every 1/2 in., which helps relieve stress from welding. Their low friction coefficient also makes them desirable in applications that require material with good slip.

Generally speaking, the abrasion resistance increases as the amount of carbon and chromium increases, although carbon has the most influence. Hardness values range from 40 HRC to 65 HRC. They also can contain other elements that can form other carbides or borides that help increase wear resistance in high-temperature applications. These alloys are limited to two or three layers.

10. What are complex carbides?

Complex carbides generally are associated with the chromium carbide deposits that have additions of columbium, molybdenum, tungsten, or vanadium. The addition of these elements and carbon form their own carbides and/or combine with the present chromium carbides to increase the alloy's overall abrasion resistance. They can have all of these elements or just one or two. They are used for severe-abrasion or high-heat applications.

11. Can hardness values be used to predict abrasion resistance?

No, this isn't a good idea. A martensitic alloy and a chromium carbide alloy can have the same hardness, let's say 58 HRC, and perform vastly different under the same abrasive conditions. The metallurgical microstructure is a better measuring stick, but that isn't always available.

The only time hardness can be used to predict wear is when the alloys being evaluated are within the same family. For example, in the martensitic family, a 55 HRC alloy will have better abrasion resistance than a 35 HRC alloy. This may or may not be the case in either the austenitic or metal carbide families. Again, you have to consider the microstructure. You should consult with the manufacturer for recommendations.

Figure 3 ASTM G65 Test Apparatus

12. If hardness is unreliable, then how is wear measured?

It depends on the type of wear involved, but in the case of abrasive wear—by far the most predominant wear mechanism—the ASTM Intl. G65 Dry Sand Rubber Wheel Test is used extensively. This essentially is a test in which the sample is weighed before and after the test, and the result usually is expressed in grams of weight loss or volume loss.

A sample is held against a spinning rubber wheel with a known force for a number of revolutions. A specific type of sand, which is sized carefully, is trickled down between the sample and rubber wheel. This simulates pure abrasion, and the numbers are used as guidelines in material selection (seeFigure 3).

13. What type of gas is used in GMAW hardfacing?

Low penetration and dilution are the major objectives in hardfacing, so pure argon and mixtures of argon with oxygen or carbon dioxide generally will produce the desired result. You also can use pure carbon dioxide, but you'll get more spatter than you would with an argon mixture.

14. What is a ball, or globular, transfer, and why is it important?

Welding wires produce either a spray transfer or a globular (ball) transfer of molten metal across the welding arc. Spray transfer is a dispersion of fine molten metal drops and can be characterized as a smooth-sounding transfer. These wires are desirable in joining applications in which you require good penetration.

Ball transfer wires disperse larger molten metal drops, or balls. This type of transfer promotes low penetration and dilution, suitable for hardfacing. It has a noisier arc that produces an audible crackling sound and generally has a higher spatter level than spray transfer wires. Welding parameters such as electrical stickout, gas (if any), amperage, and voltage can affect the size of the ball and its transfer. Gasless, or open arc, wires all have a globular or ball transfer.

15. Must parts be preheated before hardfacing?

As a rule, you should bring all parts at least to room temperature. You can select higher preheat and interpass temperatures based on the base metal chemistry and hardfacing product you're using.

Manganese and some stainless steels and similar hardfacing products require no preheating, and welding temperatures should be kept as low as possible. Other steels usually require proper preheat and interpass temperatures. You should consult the manufacturer for the best combination to prevent cracking and spalling.

16. When is a cobalt or nickel hardfacing alloy used?

Cobalt alloys contain many types of carbides and are good for severe abrasion at high temperatures. They also have good corrosion resistance for some applications. Deposit hardness ranges from 25 HRC to 55 HRC. Work-hardening alloys also are available.
Nickel-base alloys can contain chromium borides that resist abrasion. They can be good particularly in corrosive atmospheres and high temperatures when abrasion is a problem.

17. Why are some hardfacing products limited to two or three layers?

Limited-layer products usually are in the metal carbide families, such as chromium carbide and tungsten carbide. You can apply martensitic and austenitic products in unlimited layers unless the manufacturer specifies otherwise.

The brittle nature of the metal carbides leads to check-cracking, and as multiple layers are applied, stress continues to build, concentrating at the root of the check cracks, until separation or spalling occurs between the parent metal or buffer and the hardfacing deposit.

18. What is meant by a buildup or buffer alloy?

These alloys often resemble the parent metal alloy and are applied to severely worn parts to bring them back to dimension or act as a buffer for subsequent layers of a more wear-resistant hardfacing deposit. If the hardfacing produces check cracks, then it's wise to use a tough manganese product as the buffer to blunt and stop the check cracks from penetrating into the base metal.

19. Can cast iron be hardfaced?

Yes, but you must take preheat and interpass temperatures into account. Nickel and nickel-iron products usually are suitable for rebuilding cast iron. These products aren't affected by the carbon content of the parent metal and remain ductile. Multiple layers are possible. If further wear protection is required, metal carbide products can work well on top of the nickel or nickel-iron buildup.

These frequently asked questions only begin to address hardfacing. Hardfacing product manufacturers and specialists can contribute to a greater in-depth understanding of hardfacing and help assist you in product and process selection for your application

Source: thefabricator.com

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