What are the methods for removing old coatings from steel surfaces?

Well... this is pretty much the same as the answer you got in your previous post about how to remove rust from steel surfaces. For small areas, manual or power sanders are used; for larger areas, sandblasting is employed. I guess that’s about it~

The removal of the old coating depends on the degree of damage to the coating film and the various requirements for the protective coating; it can be removed entirely or partially. The aforementioned manual, mechanical, sandblasting, and flame rust removal methods can all be used to remove old coatings. Furthermore, strippers are widely used to remove old coatings. For coatings with different film-forming substances, different stripping agents can be used; for example, old oil-based coatings are usually removed using alkaline stripping agents, while old coatings made of synthetic resin paints are typically removed with organic solvent-based stripping agents. However, due to the corrosive effect of alkali solutions, and if not controlled properly, they can easily damage the steel surface; therefore, organic solvent degreasers are commonly used for removal, with the choice of degreaser determined by the type of existing coating. For example, old coatings such as oil-based paints, ester resin paints, and phenolic resin paints can be removed using T-1 paint remover ； Old coats of alkyd resin paint and nitrocellulose paint can be removed using T-2 paint remover ； To achieve a faster stripping effect, T-3 stripper should be used, as its stripping performance is better than that of T-1 and T-2 strippers. For old coatings of epoxy resin and polyurethane coatings, although they can also be removed using T-3 striper due to their good adhesion and solvent resistance, the effect is poor; therefore, special strippers developed by the users themselves are usually employed. When using a paint remover to remove the old coating, first remove dust, moisture, and oil from the surface of the part to be treated. Then apply the paint remover to the old coating using a bristled brush, applying it in a thick layer; leave it there for about ten minutes (this time should be extended in winter). Once the old coating swells or softens, it can be gently removed using a spade. If the old coating is thick, it can be applied repeatedly to the surface left after removing the old paint, which may affect the adhesion of the new coating; therefore, it is essential to clean the surface with gasoline or similar substances.

The method for rust removal can be used as a reference; generally, mechanical methods are employed for coating applications, while sandblasting can be used if space and conditions permit. (1) Manual rust removal ； Remove rust using manual tools such as iron sandpaper, scrapers, shovels, and wire brushes. Some of these methods involve high labor intensity and low production efficiency, but they are simple and flexible to operate, and are still in use to this day. (2) Mechanical rust removal ； Rust is removed by utilizing the impact and friction of mechanical power; the most commonly used tools for this purpose are air brushes, rust removal guns, electric brushes, and electric grinding wheels. Small steel parts can be placed in wooden barrels filled with yellow sand or wood chips, and rotated at a speed of 40–60 revolutions per minute; the impact and friction resulting from this movement remove rust, enabling high production efficiency and good rust removal quality, which is why this method is widely used. (3) Jet rust removal: Using mechanical centrifugal force or compressed air, high-pressure water, etc. as power, abrasives (sand, gravel, or iron pellets) are ejected at high speed onto the surface of the workpiece through specialized nozzles. The impact and friction forces generated thereby remove contaminants (including damaged old paint) and rust, resulting in high production efficiency and good treatment quality. The surface of steel after sandblasting is slightly serrated, which enhances the adhesion between the coating and the steel surface. However, its roughness must absolutely not exceed 1/3 of the film thickness. Common sandblasting methods for rust removal include dry sandblasting, warm-air sandblasting, dust-free sandblasting, and high-pressure sandblasting. Dry sandblasting generates a lot of dust, which is harmful to the environment and poses risks to health.

The removal of the old coating depends on the degree of damage to the coating film and the various requirements for the protective coating; it can be removed entirely or partially. The aforementioned manual, mechanical, sandblasting, and flame rust removal methods can all be used to remove old coatings. Furthermore, strippers are widely used to remove old coatings. For coatings with different film-forming substances, different stripping agents can be used; for example, old oil-based coatings are usually removed using alkaline stripping agents, while old coatings made of synthetic resin paints are typically removed with organic solvent-based stripping agents. However, due to the corrosive effect of alkali solutions, and if not controlled properly, they can easily damage the steel surface; therefore, organic solvent degreasers are commonly used for removal, with the choice of degreaser determined by the type of existing coating. For example, old coatings such as oil-based paints, ester resin paints, and phenolic resin paints can be removed using T-1 paint remover ； Old coats of alkyd resin paint and nitrocellulose paint can be removed using T-2 paint remover ； To achieve a faster stripping effect, T-3 stripper should be used, as its stripping performance is better than that of T-1 and T-2 strippers. For old coatings of epoxy resin and polyurethane coatings, although they can also be removed using T-3 striper due to their good adhesion and solvent resistance, the effect is poor; therefore, special strippers developed by the users themselves are usually employed. When using a paint remover to remove the old coating, first remove dust, moisture, and oil from the surface of the part to be treated. Then apply the paint remover to the old coating using a bristled brush, applying it in a thick layer; leave it there for about ten minutes (this time should be extended in winter). Once the old coating swells or softens, it can be gently removed using a spade. If the old coating is thick, it can be applied repeatedly to the surface left after removing the old paint, which may affect the adhesion of the new coating; therefore, it is essential to clean the surface with gasoline or similar substances.

There are many methods for removing rust from steel surfaces, and the commonly used ones include the following: (1) Manual rust removal: Using manual tools such as iron sandpaper, scrapers, shovels, and wire brushes to remove rust. This method requires high labor intensity and has low production efficiency, but it is simple and flexible to operate, and is still in use to this day. (2) Mechanical rust removal: Rust is removed through the impact and friction generated by mechanical power; the most commonly used tools for this purpose include air brushes, rust removal guns, electric brushes, and electric grinding wheels. Small steel parts can be placed in wooden barrels filled with yellow sand or wood chips and rotated at a speed of 40 to 60 revolutions per minute; rust is removed through collision and friction, resulting in high production efficiency and good rust-removal quality, which has led to its widespread use. (3) Jet rust removal: Using mechanical centrifugal force or compressed air, high-pressure water, etc. as power, abrasives (sand, gravel, or iron pellets) are ejected at high speed onto the surface of the workpiece through specialized nozzles. The impact and friction forces generated thereby remove contaminants (including damaged old paint) and rust, resulting in high production efficiency and good treatment quality. The surface of steel after sandblasting is slightly serrated, which enhances the adhesion between the coating and the steel surface. However, its roughness must never exceed 1/3 of the film thickness. Common methods for rust removal by sandblasting include dry sandblasting, wet sandblasting, dust-free sandblasting, and high-pressure water sandblasting. Dry sandblasting generates a lot of dust, which is harmful to the environment and poses risks to health ； Although the wet method produces no dust, moisture causes the surface to rust again. To prevent this, 1% to 1.5% of an anti-rust agent (such as trisodium phosphate, sodium carbonate, sodium nitrite, etc.) along with an emulsifier or soapy water is added to the water, so that the surface does not rust again for a short period of time; after that, a maintenance primer is applied. Dust-free sandblasting involves the continuous cyclic operation of adding sand, performing sandblasting, and recovering the sand within a closed system, in order to prevent dust from spreading. High-pressure water jetting is mainly used for large-scale rust removal, such as on ship hulls, oil tanks, storage tanks, boilers, etc.; passivators and soapy water are often added to the water as well. (4) Flame rust removal: Utilizing the difference in thermal expansion coefficients between steel and scale, an oxyacetylene burner is commonly used to heat the steel, causing the scale to flake off. It is mainly used for thick steel components and large castings, etc., and cannot be used for thin steel materials or small castings, as otherwise the workpieces will deform due to heat, affecting their quality. (5) Chemical rust removal: This method involves using acid solutions to initiate a chemical reaction with iron oxides, thereby dissolving and removing the surface rust layer to achieve rust removal. Therefore, it is also known as \"pickling\" for rust prevention. It is commonly used for rust removal on small workpieces and those with complex shapes. It’s very efficient. However, there is slight dissolution loss of steel and hydrogen embrittlement occurs. There are many formulas for chemical rust removal; typically, an aqueous sulfuric acid solution at 7% to 15% concentration (or with 5% table salt added) is used as the acid cleaning solution for rust removal. To prevent sulfuric acid from corroding steel, a small amount of corrosion inhibitors such as ribudin and thiourea can be added. In addition, different acid pickling and rust-removing solutions can also be prepared using phosphoric acid, nitric acid, hydrochloric acid, etc. There are many methods of pickling, with immersion pickling and spray pickling being commonly used. In addition, pickling paste treatment is also used, depending on the specific conditions.

The removal of the old coating depends on the degree of damage to the coating film and the various requirements for the protective coating; it can be removed entirely or partially. The aforementioned manual, mechanical, sandblasting, and flame rust removal methods can all be used to remove old coatings. Furthermore, strippers are widely used to remove old coatings. For coatings with different film-forming substances, different stripping agents can be used; for example, old oil-based coatings are usually removed using alkaline stripping agents, while old coatings made of synthetic resin paints are typically removed with organic solvent-based stripping agents. However, due to the corrosive effect of alkali solutions, and if not controlled properly, they can easily damage the steel surface; therefore, organic solvent degreasers are commonly used for removal, with the choice of degreaser determined by the type of existing coating. For example, old coatings such as oil-based paints, ester resin paints, and phenolic resin paints can be removed using T-1 paint remover ； Old coats of alkyd resin paint and nitrocellulose paint can be removed using T-2 paint remover ； To achieve a faster stripping effect, T-3 stripper should be used, as its stripping performance is better than that of T-1 and T-2 strippers. For old coatings of epoxy resin and polyurethane coatings, although they can also be removed using T-3 striper due to their good adhesion and solvent resistance, the effect is poor; therefore, special strippers developed by the users themselves are usually employed. When using a paint remover to remove the old coating, first remove dust, moisture, and oil from the surface of the part to be treated. Then apply the paint remover to the old coating using a bristled brush, applying it in a thick layer; leave it there for about ten minutes (this time should be extended in winter). Once the old coating swells or softens, it can be gently removed using a spade. If the old coating is thick, it can be applied repeatedly to the surface left after removing the old paint, which may affect the adhesion of the new coating; therefore, it is essential to clean the surface with gasoline or similar substances.

1. Mechanical grinding, using a grinder or sandblasting； 2. Immersion and coating with chemical agents ； 3. Heat it to high temperatures to cause oxidation, such as by fire; that’s all I can think of

The removal of the old coating depends on the degree of damage to the coating film and the specific requirements for it; it can be removed entirely or partially. The aforementioned manual, mechanical, sandblasting, and flame rust removal methods can all be used to remove old coatings. Furthermore, strippers are widely used to remove old coatings. For coatings with different film-forming substances, different stripping agents can be used; for example, old oil-based coatings are usually removed using alkaline stripping agents, while old coatings made of synthetic resin paints are typically removed with organic solvent-based stripping agents. However, due to the corrosive effect of alkali solutions, and if not controlled properly, they can easily damage the steel surface; therefore, organic solvent degreasers are commonly used for removal, with the choice of degreaser determined by the type of existing coating. For example, old coatings that were originally oil-based paints, ester resin paints, or phenolic resin paints can be removed using T-1 paint remover ； Old coatings of alkyd resin paint and nitrocellulose paint can be removed using T-2 paint remover ； To achieve a faster paint removal effect, T-3 paint remover should be used, as it is more effective than T-1 and T-2 paint removers. For old coatings of epoxy resin and polyurethane coatings, although the T-3 striper can also be used to remove them due to their good adhesion and solvent resistance, the results are poor; therefore, specialized strippers developed by individual users are usually employed. When using a paint remover to remove the old coating, first remove dust, moisture, and oil from the surface of the part to be treated. Then apply the paint remover to the old coating using a bristled brush, applying it in a thick layer; leave it there for about ten minutes (this time should be extended in winter). Once the old coating swells or softens, it can be gently removed using a spade. If the old coating is thick, it can be applied several times to remove it. When using organic solvents to remove paint, the paraffin contained in them often remains on the surface after the old paint has been removed, affecting things such as the adhesion of the new coating; therefore, it is necessary to clean the surface with gasoline or similar substances. The role of paraffin in the paint remover is to slow down the evaporation of organic solvents, allowing it to act on the old coating for a longer period of time. When the temperature is too low, paraffin will precipitate, affecting the paint removal effect. Therefore, the paint remover should be placed in a place with a higher temperature, and used after it has melted evenly. Be sure not to use an open flame for heating! The entire operation should be carried out in a location free from open flames and with good ventilation, to prevent fires and poisoning.