What is the rust?
Rust is a chemical reaction. Iron rusts easily when it is left for a long time. Besides its active chemical properties, it also has a great relationship with external conditions. Moisture is one of the substances that make iron rust easily. However, water alone will not make iron rust. Only when oxygen in the air dissolves in water, oxygen reacts with iron in the environment with water, and then a kind of iron oxide is produced, which is rust. Rust is a brown color. It is not as hard as iron and easily falls off. After a piece of iron is completely rusted, its volume can swell eight times. If rust is not removed, this spongy rust will absorb water easily, and iron will rot faster.
Here’s a more scientific explanation from How Stuff Works:
Iron (or steel) rusting is an example of corrosion — an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When they flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust. Iron (or steel) rusting is an example of corrosion — an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When they flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust.
Why does the rust？
After a sufficient time, iron will be completely oxidized to rust with sufficient oxygen and water. The oxidation of aluminum is very slow, because oxygen forms a dense aluminum oxide film on the surface of aluminum, which is called passivation. Rust is a general name for iron oxide, which is usually red and is produced by oxidation-reduction reaction in the environment of iron and oxygen. Different forms of rust will be produced under different conditions. Rust is mainly composed of Fe2O3·nH2O hydrate and ferric hydroxide (FeO(OH), Fe(OH)3). Other metals are also oxidized, but they are not usually called “rust”. The most common rusting phenomenon is that iron products are exposed to the air for a long time and undergo oxidation reaction with oxygen, or are eroded into oxides by oxygen in water.
How do you get rust off a bit or saw blade?
Each of these methods can be used in conjunction with one another or repeated for particularly rusty blades. After removing the rust, I do recommend resharpening the blade after any method to ensure a sharp and safe blade.
- The manual derusting method
Tools: wire brush, sandpaper, grinding wheel, file, wire scraper, file, scraper, etc., which refers to the machining method of manually grinding with wire brush and sandpaper or grinding with Sichuan file and scraper to remove rust layer, scale and casting sand on the metal surface. For derusting the inner surface of steel pipe, it can be brushed back and forth with a round wire brush; Rust removal on the inner and outer surfaces must be thorough, and it is qualified to show metallic luster. Then clean it with clean waste cotton yarn or cloth, and finally blow it with compressed air. This method is the most primitive and commonly used derusting method, which is flexible and convenient, but has low production efficiency and high labor intensity.
Advantages: simplicity and low cost;
- The roller derusting method
Roller derusting means putting metal workpieces and pig iron castings without special-shaped angles and external threads in a slow-rotating hexagonal or round roller, and removing dirt such as rust and scale by means of friction and rolling impact due to the rotation of the roller. The number of workpieces to be cleaned loaded into the drum should be less than 2/3 of the volume of the drum. At the same time, the drum will be filled with angular iron sand, iron filings, carborundum, etc., and some chemicals such as sodium sulfite, soda ash, soap powder, water, etc., which can achieve the purpose of rust removal and oil removal at the same time. The rotating speed is generally not more than 40r/min. If the rotating speed is too fast, the surface of the workpiece will be damaged.
Disadvantages: It is only suitable for metal workpieces with low requirements on surface smoothness, and the rotating speed is not well controlled, and the solvent damages the workpiece surface.
- The mechanical polishing derusting method
This method is a widely used rust removal method at present, and its principle is to effectively remove rust and dirt by impact and friction. For example, emery cloth, sandpaper, grinding paste, wire brush, etc. are fixed on the wheel disc, and when the wheel disc rotates, the rusted parts of metal can be polished and polished, and then the rusted objects can be removed. Commonly used tools include electric grinding wheel, pneumatic brush, electric brush, derusting gun and needle beam derusting device, etc.
Advantages: high derusting quality and efficiency;
- The flame derusting method
Flame derusting is one of derusting processes. The main process is to shovel off the rust layer on the substrate surface, then bake or heat it with flame, and clean the heated surface with power wire brush. It is suitable for derusting steel structures and castings with a certain thickness. The principle is that by using the difference of thermal expansion coefficients between metal and scale, scale will break and fall off after heating treatment, while rust will break and loosen due to dehydration during heating.
Disadvantages: The degree of removing scale and rust by this method is not thorough enough. Old scale is often removed and new scale is generated. After treatment, other tools should be used to clean it immediately, resulting in low production efficiency and high energy consumption.
- Electric spark derusting method
Electric spark derusting is to remove rust by using different conductivity and thermal expansion rate of scale and steel plate. The metal workpiece to be cleaned is used as one electrode, and the round roller is used as the other electrode. When the round roller contacts with the workpiece, a short circuit occurs to separate the scale, and the rust is separated from the surface of the workpiece by means of mechanical impact force.
Advantages: simple and portable equipment, high derusting efficiency, no damage to workpiece surface, etc. It is suitable for plate derusting, large workpiece derusting, especially on-site derusting.
- Shot blasting (sand) derusting method
It is mainly composed of particle jet erosion to achieve surface cleanliness and proper roughness. The equipment includes open shot peening (sand) rust remover, closed shot peening (sand chamber) and vacuum shot peening (sand) machine. The open shot peening (sand) machine is widely used and can thoroughly remove all impurities on metal surface, such as scale, rust and old paint film.
Advantages: high derusting efficiency, high mechanical degree and good derusting quality.
- Laser derusting method
Using the characteristics of high energy, high frequency and high power of laser, the high energy is instantly deposited in a small area, and the oxide layer is burned by high temperature, which is also called laser cleaning.
Advantages: high efficiency, high speed and low cost; The heat load and mechanical load on the substrate are small, and the substrate is not damaged; No water or solvent is needed, and the waste is easy to collect and has no pollution to the environment; Safe and reliable, without damaging the health of operators; Wide application range, suitable for large-scale derusting.
- Chemical treatment derusting method
Also known as “pickling” rust prevention. Its principle is to make use of the chemical reaction between the acid liquor and the rust (oxide) on the cleaned metal surface to make it dissolve in the acid liquor. In addition, the hydrogen produced by the interaction between the acid and the metal makes the oxide scale fall off mechanically. It can be widely used for derusting and cleaning the surfaces of small workpieces, workpieces with complex shapes, oxidized metal parts (except copper, aluminum, copper-plated, aluminum-plated and zinc-plated products), mechanical equipment, etc. It can also be used for descaling the machined parts before coating, with high efficiency. At present, the good products on the market include the series of anti-oxidation cleaning agents developed by Yuman Industrial Co., Ltd., which have a good effect and fast speed in removing rust and oxide. Low odor, suitable for many occasions, safe and non-corrosive to most metals, different cleaning schemes for different metal materials, safe and convenient transportation and storage.
Advantages: good effect and fast speed in removing rust and oxide. Low odor, suitable for many occasions. It is safe and non-corrosive to most metals, and it is safe and convenient to transport and store.
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