Thermal spraying

1、 Thermal spraying principle

• Thermal spraying is the use of various heat sources to heat and melt or semi melt inorganic coating materials;
• Then use high-speed gas to disperse and refine the inorganic coating material, and collide it with the substrate surface at high speed;
• The process of forming inorganic coatings.

2、 Schematic diagram of thermal spraying principl

3、 On site preparation:

In order to prepare for construction, the following conditions need to be met:

⑴ The construction space is sufficient for construction operations, ensuring that dust and sand particles do not harm people during work.

⑵ Ventilation conditions: Ensure smooth and good ventilation at the rear of the construction work surface, and ensure that the smoke and dust from sandblasting and spraying are promptly removed.

⑶ Before sufficient lighting facilities are available, ensure that the furnace can use a 36V safe power supply and ensure proper leakage protection

measures.

⑷ Engineering power supply 380V 80KW three-phase AC

Try to avoid cross construction as much as possible to ensure that there are no major cross operations during the construction process, so as not to affect the normal construction progress.

Construction scaffolding should be erected 10 centimeters above the bottom of the construction work surface. The floor height is 1.8 meters, and the width of the springboard is 50 centimeters less. Set up ladders between layers, with each level not exceeding 50 centimeters; Leave a distance of 100-200 millimeters between the scaffold and the water-cooled wall. Ensure the normal construction of the junction between the scaffold and the water-cooled wall.

The vertical height of sandblasting construction shall not exceed 25 meters. If it exceeds the height, the sandblasting machine needs to be lifted to the corresponding height position.

The distance between the spraying host and the workpiece should not exceed 15 meters.

Construction power supply: 380V three-phase AC power is provided by the owner to the power switch at the construction site of this project, and the construction power line is provided by our company's construction personnel.

Temporary venue

The construction equipment, toolbox, and material stacking site can be arranged on the boiler leveling ground, occupying an area of approximately 30 square meters. Please refer to the layout plan for details.

The quartz sand stacking site for construction B covers an area of about 15 square meters and is planned to be located in the equipment placement area for convenient construction.

The two sites mentioned above have a total area of about 50 square meters and both require rain and waterproof treatment by the engineering project department.

Two D sandblasting equipment occupy a total area of 6 square meters on the site, and the height needs to be adjusted according to the on-site construction, with a planned area of about 10 square meters for quartz sand.

The E spraying equipment occupies 2 square meters of the site, and the height will be adjusted according to the actual situation during construction.

F requires one domestic water point to meet daily hygiene needs.

G's vehicles for commuting to and from work need to temporarily occupy 12 square meters of space.

Appendix:

4、 Construction preparation:

① Set up scaffolding according to actual needs.

② Remove large pieces of coke, debris, etc. from the heated surface.

③ Conduct a comprehensive quality inspection of the parts of the pipe wall that require spraying, and promptly report any areas that require repair and reinforcement to Party A.

④ Utilize the existing conditions on site to carry out equipment positioning, electrical wiring, gas source pipeline connection, and abrasive recovery canvas laying work.

5、 Construction process:

1. Surface sandblasting:

1. The effect of sandblasting on the surface of the substrate

① Surface cleaning: Remove various pollutants from the sprayed surface, especially grease, dirt, scale, rust, and corrosive substances. The cleanliness of the working surface meets the Sa3.0 level specified in GB8923-88 "Rust grades and removal grades of steel surfaces before painting".

② Surface roughness: The bonding between thermal spray coating and substrate is mainly mechanical bonding, which requires substrate pretreatment not only to remove oil and rust, but also to roughen the surface, and the surface should have a certain roughness when used. The surface roughness reaches the Rz60-90 μ m specified in GB11373-89 "General Principles for Surface Preparation of Metal Parts by Thermal Spraying", and will not cause any damage to the thickness of the pipe wall.

The purpose of sandblasting treatment:

a、 Increase the contact area between the spray coating and the substrate to improve the adhesion of the coating.

b、 Increase the mutual embedding and interlocking between the coating material and the substrate surface, playing the role of an "anchor hook" and improving the adhesion between the coating and the substrate.

2. Activated surface:

Sandblasting provides active surface capabilities for spraying, such as lattice defects and plastic deformation, generating a certain stress state to increase the adhesion between sprayed particles and the substrate surface, and improving the micro metallurgical bonding ability between sprayed particles and the substrate. The analysis of activation effect is as follows:

① Sandblasting creates a certain residual compressive stress on the surface of the workpiece after repeated impact by sand particles. Although the stress value is extremely small, it is beneficial for relaxing the thermal stress of the coating during the spraying process, improving the bonding strength of the coating, and also increasing the fatigue strength of the workpiece.

② Spraying can remove organic pollutants and oxide layers on the surface of workpieces, and can increase the plastic deformation of metal surface grains and cause lattice defects, making the substrate surface in a state prone to chemical reactions, which helps to enhance the physical and chemical bonding strength between sprayed particles and the substrate surface.

3. Explanation of damage to pipe wall thickness caused by sandblasting: Sandblasting only removes surface dirt and debris, with a pipe wall thickness of ≤ 15 μ m. This thickness is thin and will not affect the entire pipe wall thickness. Secondly, sandblasting operations will not cause tearing or blowing damage to the pipe wall. Thirdly, sandblasting operations are carried out uniformly, and the thickness reduction of the entire surface is consistent. In summary, sandblasting operations are only an effective method for achieving drying, cleaning, and activating the surface of the furnace tube, improving the bonding strength of the coating, and will not damage the pipe wall thickness.

So sandblasting treatment is extremely necessary before spraying the workpiece. And the sandblasted workpiece should be sprayed as soon as possible, the shorter the time, the better the surface activation effect, and the higher the coating quality.

A、 Sandblasting requirements: First, use 16-18 mesh brown corundum to perform rough spraying on the surface of the workpiece to achieve a surface cleanliness level of Sa3.0. Then, use 14-16 mesh brown corundum for surface roughening treatment to achieve a surface roughness of Rz60-90 μ m. The sand particles used must be clean and dry, and the sandblasting area must be enclosed and other recycling measures must be taken to ensure that it does not pollute the surrounding environment. Sandblasting can only be carried out after confirmation by the on-site engineer. Parts that do not meet the pre-treatment requirements need to be re sandblasted, and attention should be paid to protecting qualified parts during re sandblasting.

B、 Sandblasting machine selection: TS9015 high-efficiency sandblasting equipment

C、 Compressed air quality requirements: Self provided air compressor, exhaust flow rate ≥ 6m3/min, working pressure 0.55-0.8Mpa.

D、 Operation method: Sandblasting distance is 150-200 millimeters, and the sandblasting angle is 50-70 ℃ from the substrate.

E、 Operation sequence and inspection requirements: First, spray brown corundum twice to completely remove rust, oxide scale, coking, etc. on the surface of the steel, and expose a gray white metallic luster. The effect of spraying brown corundum is only to roughen the surface of the substrate to achieve the required surface roughness for spraying, without causing any damage to the thickness of the pipe wall. Use roughness samples for comparison and inspection. After sandblasting, the surface of the pipe wall should be dry, free of dust, oil stains, oxygen scale, rust spots, and other debris, and the surface of the substrate should present a homogeneous gray white metallic appearance.

F、 Before spraying, the pre treated surface should be inspected: if rust or non-conforming parts are found, they should be reprocessed,. If serious thinning or cracking is found, please request Party A to replace the pipe or reinforce it. Spray painting must be carried out within 2-4 hours after sandblasting is completed.

3. Supersonic arc spraying:

The TS500 supersonic arc spraying system consists of equipment such as power supply, wire feeder, supersonic arc spray gun, air compressor, gas storage tank, oil-water separator, etc. This technology is a new thermal spraying technology developed by our company through the introduction of advanced equipment and independent research and development. It has been listed as a key technology for surface engineering in the 21st century by developed countries such as the United States and Japan. This spraying technology uses an electric arc burned at the end of the wire to melt the uniformly fed wire, and the supersonic airflow accelerated by the Laval nozzle atomizes the melted wire into small and evenly distributed particles, which are sprayed onto the workpiece to form a coating. Melting particles are mainly combined with substrates through mechanical, physical, and metallurgical means, with a bonding strength of over 65MPa. Compared with ordinary arc spraying and flame spraying, supersonic arc spraying has higher particle flight speed, stronger bonding strength, lower porosity, higher coating uniformity, good density, and the workpiece will not deform when the sprayed particles reach the surface at a temperature below 80 ℃, which can obtain high-quality coatings.

Selection of A wire material: KM99 ultra hard and wear-resistant spray coated wire material with a diameter of 2.0mm

Coating performance: The following description is given for the coating prepared by our company using KM99 superhard wear-resistant spray wire material and supersonic arc spraying:

The specific microstructure is: Cr3C2 and its mixed phase generated during the spraying process serve as hard points, equivalent to the skeleton in the coating structure; NiCrB has good ductility and corrosion resistance, serving as a carrier for hard spots. Hard points are embedded in the carrier and evenly distributed within the carrier.

Wear resistance requirement: Cr3C2 and its mixed phase generated during the spraying process act as hard points, becoming the skeleton in the coating structure and subject to erosion particle impact. As is well known, chromium carbides have a relatively high hardness and can fully meet the requirements of wear resistance.

Ductility requirement: Chromium carbides have a relatively high hardness, but the coefficient of thermal expansion differs greatly from that of the matrix, which requires the carrier to have good ductility, that is, a coefficient of thermal expansion similar to that of the matrix. The transition of NiCrB as a carrier with a bottom layer (NiAl) ensures the ductility of the entire coating and prevents cracking during temperature changes.

Corrosion resistance requirement: The coating works under conditions of corrosive media in flue gas, and NiCrB has good corrosion resistance to ensure that it will not cause the failure and detachment of hard points due to the corrosion of the carrier, which directly affects the wear resistance of the coating.

B Clean air path: Dry and clean compressed air can be obtained through an oil-water separator.

Selection of C spraying equipment: TS500 supersonic arc spraying machine, dedicated spraying power supply, and supporting wire feeding device are selected.

Selection of D spray gun: A supersonic arc spray gun is selected, with a particle velocity of over 470m/s, and the coating porosity can be controlled within 0.9%. At the same time, the bonding strength between the coating and the substrate has also been significantly improved.

E、 Spray coating process parameters:

Arc voltage: 32-34V

B Arc current: 160-200A

C atomization air pressure: 0.55Mpa

Spray distance: 150-200 millimeters

E KM99 ultra hard wear-resistant spray coating thickness: 0.6-0.8 millimeters

F、 Spray method: To prevent local overheating during the spray process, the interlayer temperature should not exceed 800C in actual operation. A transition layer should be designed at the junction of each construction area or daily construction area, and the coating thickness at the transition layer should be from thick to thin and clearly marked. In the specific construction, our company has decided to conduct sandblasting at night and spraying during the day. Adopting the cross shaped spraying method, layer by layer and zone by zone operation, spraying in local areas until the process design thickness is reached, and then moving to other areas to ensure uniform thickness and adhesion of the sprayed layer, and to prevent missed spraying. After the spraying is completed, the coating quality inspection should be carried out, and the thickness δ 2 should be measured. If δ 2- δ 1 is ≥ 0.6-0.8 millimeters, it is judged to be qualified and can enter the next process. Otherwise, the unqualified parts should be re sprayed.

G、 Precautions for operation:

Divide the work into sections, spray paint in some areas to the design thickness, and then move to other areas. Set identification marks at the overlapping parts. During operation, the interlayer temperature should not exceed 80 ℃.

A dedicated person is responsible for monitoring the wire feeding tray and wire feeding situation to ensure smooth wire feeding and prevent wire material from getting tangled. At the same time, insulation must be ensured between the two wires to avoid short circuits.

Before spraying, a trial spray should be conducted on the test panel to adjust the voltage, current, wire feeding speed, and compressed air flow rate. The flexible joints and hose joints of the air circuit should be checked for any air leakage. If unstable wire feeding, unstable arc combustion, severe gas leakage and other special situations are found on site, they should be checked and adjusted in a timely manner. When adjusting the voltage, the main circuit should be disconnected to avoid damaging the spraying power supply.

Note: Damaged conductive nozzles during the spraying process should be replaced in a timely manner, and conductive nozzles with unqualified processing accuracy are prohibited from use.

If unstable wire feeding, fuse breakage, or intermittent arc is found during the spraying process, the use of the conductive nozzle should be checked first, and the installation of the wire feeding tube should be checked again for firmness. If it is loose, it should be tightened in a timely manner.

Before construction

5. Quality Description

A、 Sandblasting quality:

① Select high-quality quartz sand with a grit of 16-20 to remove the oxide scale on the surface of the pipe wall, until the surface of the pipe shows a metallic luster, and the surface cleanliness reaches the Sa3.0 level specified in GB8923-88 "Rust Grades and Preparation Grades of Steel Surfaces before Coating".

② Select 14-16 mesh brown corundum for surface roughening treatment to increase surface area and improve bonding strength. The surface roughness should reach RZ60-90 μ m as specified in GB11373-89 "General Principles for Thermal Spray Metal Surface Preparation", and not damage the thickness of the pipe wall.

B、 Spray quality:

① Coating appearance: The coating surface must be uniform and free from defects such as peeling, bulging, coarse particles, cracks, chipping, missed spraying, and other defects that may affect the use of the coating.

② Coating thickness: The following measures are taken to control the thickness of the coating for defects in use: firstly, it is required to supervise the construction personnel to strictly follow the operating specifications during the operation process; The second is to control the coating thickness through the consumption of spraying materials; The third is to operate according to the preset parameters before construction, spray samples or take actual samples on site and measure and inspect them with calipers; Fourthly, after sandblasting the metal surface, a portable coating thickness gauge is first used to measure the thickness δ 1 at a large number of points. Then, after thermal spraying is completed and before sealing the hole, the thickness δ 2 of the pipe wall is measured at points, and the numbers are slightly corrected. The difference between the two average values is the coating thickness.

Nickel chromium carbide superhard wear-resistant spray coating thickness: 0.6-0.8 millimeters

③ Coating adhesion strength (coating and substrate): Use a special puller to inspect the longitudinal and transverse stripes on the sprayed layer in a "#" shape, and observe whether there are chip like peeling. During installation, friction with the bracket must not cause detachment or peeling.

④ After sales service: Arrive at the scene within 48 hours of discovering problems, and perform maintenance work at any time during minor repairs.

6. Applicable standards

GB/T11373-89 "General rules for surface pretreatment of metal parts by thermal spraying"

GB11375-89 "Safety of Thermal Spraying Operations"

GB8642-2002 "Determination of Bonding Strength of Thermal Spray Coatings"

GB8641-88 "Determination of Strength and Tensile Strength of Thermal Spray Coatings"

GB8640-88 "Metallic Thermal Spray Coating Surface Rockwell Hardness Test Method

Construction organization design

List of Main Construction Machinery and Testing Equipment

engineering department

The Engineering Department is the representative of our company on this project and is fully responsible for the implementation of the project contract. Responsible for implementing relevant laws, regulations, and policies related to the construction of thermal power generation projects; Implement various management systems of the enterprise; Strict financial regulations and strengthened financial management; Properly handling the interests of enterprises and individuals; Execute the various clauses in the project contract that the project manager is responsible for fulfilling; Effectively control the construction of engineering projects and implement relevant technical specifications and standards; Ensure project quality and schedule, achieve safe and civilized production, and strive to improve economic benefits.

project manager

I am the person in charge of the project department, representing our company to fully fulfill our responsibilities and obligations to the owner, accountable to our company, establish the corporate image, and create economic benefits.

Construction team leader

Fully responsible for the specific implementation of the construction of this project.

Safety Officer Engineer

Responsible for the supervision, evaluation, and construction safety inspection of engineering quality, and formulating on-site safety construction management measures.

QC engineer

In charge of technical and quality control, responsible for engineering surveying, technical guidance, handling construction and change procedures, collecting, filling out, archiving engineering technical data, preparing completion documents, etc.

construction scheduling

The sandblasting schedule of power plant boilers is generally affected by high-temperature corrosion caused by gas sulfur dioxide and abrasion caused by coal powder. Based on our company's construction experience in various power plants, each sandblasting equipment can complete M12 sandblasting treatment on the surface of water-cooled walls every day (12 hours). Therefore, we have decided to use a set of sandblasting equipment for sandblasting construction. According to this schedule, the sandblasting construction task can be completed within two days (two night shifts), and there is enough time to deal with other situations that may affect the construction of the project, thus ensuring the completion of the construction task according to the schedule.

According to the requirements of wear-resistant spraying technology for water-cooled walls of circulating fluidized bed boilers, our company has decided to use supersonic arc spraying of nickel chromium carbide superhard wear-resistant spraying wire. In actual construction, the deposition rate is relatively low. When the spraying thickness is 1-1.5 millimeters, each set of spraying equipment can spray about 20M12 per day (twelve hours) on average. During the spraying construction, a set of spraying equipment is arranged for simultaneous construction. Except for the transition area at the boundary, all pipe bundles that have been sandblasted and pre treated are sprayed and sealed. According to this schedule, the spraying task can be completed within four days (four day shifts). To ensure the normal progress of spraying, our company plans to prepare two sets of spraying equipment to ensure that both sets of spraying equipment can work normally at the same time, and even if there is a temporary malfunction of the equipment, it will not affect the spraying construction.

engineering department

The Engineering Department is the representative of our company on this project and is fully responsible for the implementation of the project contract. Responsible for implementing relevant laws, regulations, and policies related to the construction of thermal power generation projects; Implement various management systems of the enterprise; Strict financial regulations and strengthened financial management; Properly handling the interests of enterprises and individuals; Execute the various clauses in the project contract that the project manager is responsible for fulfilling; Effectively control the construction of engineering projects and implement relevant technical specifications and standards; Ensure project quality and schedule, achieve safe and civilized production, and strive to improve economic benefits.

project manager

I am the person in charge of the project department, representing our company to fully fulfill our responsibilities and obligations to the owner, accountable to our company, establish the corporate image, and create economic benefits.

Construction team leader

Fully responsible for the specific implementation of the construction of this project.

Safety Officer Engineer

Responsible for the supervision, evaluation, and construction safety inspection of engineering quality, and formulating on-site safety construction management measures.

QC engineer

In charge of technical and quality control, responsible for engineering surveying, technical guidance, handling construction and change procedures, collecting, filling out, archiving engineering technical data, preparing completion documents, etc.

Quality assurance measures

Spray coating construction should strictly follow the process flow and step-by-step quality control, and corresponding requirements should be put forward for materials, equipment, personnel quality, etc. to ensure comprehensive control of project quality.

Construction period guarantee measures

A scientific construction plan provides technical assurance for the quality and schedule of this project.

B's advanced construction organization and management provide management assurance for timely completion.

The practical and feasible project schedule provides a plan guarantee for timely completion.

According to the project situation, advanced and sufficient construction equipment, spare parts, and materials are allocated, and a complete logistics guarantee system is established to provide material assurance for the quality and quantity of the project to be completed on schedule.

Experienced construction personnel, including technical experts, project managers, and operators of various trades, provided personnel guarantees for the timely commencement and smooth completion of the project.

F Construction organization capability: Our company's construction team has more than 50 skilled and experienced operators, as well as more than 20 professional technical personnel. We have over 13 sets of arc spraying machines, 13 sets of sandblasting machines, 8 air compressors, and 5 vehicles of various types, which can carry out construction simultaneously in most locations across the country.

Safety assurance measures and civilized construction measures

1. Implement the norms of the power industry and adhere to the principle of "safety is paramount".

2. By encouraging and training, establish awareness of safety, health, and environmental protection among all employees.

3. Build a safe working environment and care for the physical and mental health of employees.

4. Comply with the relevant factory rules and regulations of Party A and the safety agreement signed by both parties. Any violation of discipline shall be dealt with strictly and severely by the relevant personnel.

5. Two full-time safety officers will be appointed on site, and a pre shift meeting will be held every day to provide safety education before starting work.

6. All construction personnel must undergo safety training and pass the exam before entering the site to participate in construction.

7. Construction personnel entering the site should wear safety helmets and insulated shoes, and safety belts should be worn during high-altitude operations. Set up clear safety signs on site.

8. During the construction process, the safety officer conducts an hourly on-site inspection and promptly corrects any violations found. Inspect the on-site scaffolding before starting work; Discover problems and solve them in a timely manner.

9. 36V explosion-proof lamps should be used for on-site lighting. Protective clothing should be worn during sandblasting, and protective goggles should be worn during spraying.

10. Pay attention to whether there are other personnel in the work area during cross operation, coordinate with other construction personnel, and take relevant safety measures.

11. Maintain good communication with Party A and handle work relationships with other construction units to ensure civilized construction.

12. The maintenance of electrical equipment must be operated by professional electricians. The venue shall not connect or pull the power supply without authorization, and the power supply shall be reliably grounded.

13. It must be carried out under the guidance of the technical personnel of Party A, and unauthorized use of Party A's equipment is strictly prohibited.

14. Civilized construction must be carried out, and during the construction period, the "three no's", "three no's", "three no's", "three no's landing" and "three no's disorder" must be achieved.

15. Clean up the site after the construction is completed, ensuring that the work is finished, the materials are clean, and the site is clean.