What is chemical corrosion of metals

How to Unscrew a Rusted Bolt

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Many men, when repairing a car, or simply in everyday life, have encountered “stuck” bolts and nuts. Sometimes you have to struggle with rusty fasteners for hours, and the technician often runs the risk of breaking everything and also getting a bunch of bruises. How to avoid this and learn how to easily and simply unscrew old bolts, see our review.

1. Patience

The first and most important thing you need to have in such a situation is endurance and patience. If a stuck bolt does not give in, you should not use extra force to immediately move it. This way you can break off the head and delay the repair, as they say, with your own hands. There are many effective means that will help unscrew problematic fasteners. Read more about them in the following paragraphs of our review.

2. Remove rust

To make it easier to unscrew a bolt or nut, you need to remove all dirt, rust and paint. A stiff wire brush works best for this. Particular care must be taken to remove rust from threads.

3. Tool selection

To unscrew a stuck bolt or nut, you need a spanner or socket, preferably with 6 edges. A regular open-end wrench is likely to slip, smear the edges, and can cause injury. It is undesirable to use 12- and 18-sided tools, as there is a high probability of slipping.

If the fasteners are already licked off, you should get a special head, which is called “for torn edges” or an extractor.

4. Direction of rotation

Most people are accustomed to the fact that all screws are tightened clockwise and unscrewed counterclockwise. But in cars, fasteners with a reverse thread direction are often used, for example, left-hand wheel studs. Those who don’t know this will probably “play around” for a long time.

5. Lubricate rusty threads

On nuts and bolts that do not come loose easily, you can use one of many lubricants. Penetrating oil like WD-40 is very popular among car enthusiasts. By the way, this is a very useful drug in solving other everyday problems .

Apply penetrating oil generously to the mating surfaces of the parts and leave for some time. If the bolt or nut is very rusty, you can leave the chemical to work overnight.

You can also moisten rusted parts with kerosene, solvent, plain water or Coca-Cola. These remedies also help a little.

6. We are looking for a longer lever

The larger the handle of the tool used to remove a stuck bolt, the more likely it is that it will give in. True, if the parts hold tightly, then we move on to the next step.

7. Warm up the part

If you cannot unscrew the fastener even with a head with a long lever, then the connection should be warmed up. Professionals use an acetylene cutter for this. But if you don’t have it at hand, a mini gas burner, which you can buy on the market, is also suitable.

By unscrewing the pin from the aluminum cylinder block, we heat the block itself around the threads. At the same time, periodically tap the pin in a circle. And if you need to unscrew the nut, then heat it on one side and also tap it with a hammer on all sides.

8. Last resort

If even heating does not help, then the rusted fasteners most likely cannot be saved. Pneumatic or electric impact tools are very effective, but impact wrenches often break off the heads of "difficult" bolts.

Unscrewing problematic nuts also often ends with their mechanical removal. To do this, cut the nut into pieces with a saw or grinder; you can also drill with a drill in several places. Sometimes two notches on opposite edges are enough, and the nut begins to rotate. And the easiest way to quickly split an old nut is to use a special device known as a nut cutter or nut splitter.

When removing a stuck nut using the methods listed above, the thread is sometimes damaged. To “align” it, it is enough to drive away the damaged studs with a die.

Source: https://moy-instrument.ru/masteru/kak-otvernut-zarzhavevshij-bolt.html

The most popular brands of antifreeze

Antifreeze is an engine cooling liquid that is constantly present in the car. Leading specialists from the Autostat agency conducted a study and compiled a list of antifreeze brands that are in greatest demand among our car enthusiasts.

TCL

TCL antifreezes have a carboxylate base with the addition of certain anti-corrosion and anti-foam additives and components that extend the life of the engine and pump. The temperature range starts from -50°C and ends at +120°C. Most suitable for use in Japanese car brands.

TLC coolants must not be mixed with others. This may lead to loss of their properties.

Liqui Moly

The German company Liqui Moly produces antifreeze based on monoethylene glycol, which combines several types of acids and organic carbon additives. It not only protects the car system from overheating and freezing, but also saves metal parts from oxidation.

Suitable for almost all car brands. The temperature range of use ranges from -40°C to +109°C. Service life is 5 years, unless there is a need for replacement earlier. Compatible with other antifreezes, except liquids without silicates in the composition. High price.

Mobile

Mobil is a concentrated coolant mixture and requires dilution with water. It consists of a solution of ethylene glycol with the addition of salts of organic acids, silicates and corrosion inhibitors, but does not affect metal, plastic, rubber parts in the car’s cooling system.

The American manufacturing company also introduced mineral components into its concentrate that increase the antifreeze’s resistance to temperature changes, which can range from -45°C to +150°C. Suitable for all cars with cast iron or aluminum engines, ensures stable operation of the system without losing its properties for 4 years. In addition to providing protection against solid deposits, corrosion and carbon deposits, it is very cost effective.

Coolstream

Coolstream antifreeze is a budget coolant. When creating it, they used a Belgian-made concentrate with additives that make it possible to bypass the standards for crystallization and boiling points. Operates from -42°C to +120°C. Can be mixed with other antifreezes, but only those based on monoethylene glycol.

Recommended for use in all domestic and foreign cars, as it complies with all European standards. When poured into a new car, it will last a standard 5 years.

Castrol

Castrol is produced by a British company. It is a coolant concentrate with a recommended dilution ratio of 1:1 with water. With this proportion, all additives retain their properties, but its freezing temperature is within -36 ° C, which will not allow the use of Castrol in northern regions.

It consists of a silicate base that lubricates and envelops the system parts and thereby protects them from wear. The organic additives included in the composition stop the process of destruction of existing corrosion. Replacement interval - 3 years, suitable for gasoline and diesel engines.

SINTEC

Source: https://autozam.ru/interesnie-zametki/samye-populyarnye-marki-antifrizov.html

Anodizing technology for aluminum profiles. What is anodized coating - My site

Modern devices made of metal are very different from those made 30-50 years ago. They have become lightweight, resistant to harmful influences, and minimally dangerous to life. Anodized aluminum occupies one of the leading places among the metals that are used for the manufacture of such devices.

Anodized aluminum has long and firmly taken the place of steel and cast iron where, in addition to strength and resistance to external influences, other main qualities are required - lightness and ductility. It is much lighter than steel, so it has successfully replaced it in tens of thousands of products used in a variety of fields - industry, medicine, tourism, sports.

With the advent of anodizing technology, the remarkable properties of aluminum were supplemented by the results of chemical modification - high corrosion resistance and resistance to mechanical stress.

What is anodizing

The anodizing process is an electrolytic chemical reaction of a metal with an oxidizing agent. A thin layer of oxide is applied to a metal surface, which acts as an anode during the reaction.

Due to polarization in an electrolytic conducting medium, both pure metals and various alloys can be coated with a thin oxide film. The oxide layer effectively protects against corrosion and fading when exposed to direct sunlight.

The most in demand in industry are anodized alloys of aluminum and magnesium.

The ultimate goal of anodizing is to create a so-called AOP - anodic oxide film - on the surface of an aluminum sheet. It performs two main functions:

1. Protection from external influences;
2. Decoration.

In the second case, dyes of various colors with a strictly defined chemical composition are added to the conducting medium.

Engineers from the UK were the first to introduce industrial anodization of aluminum into production. The light and durable metal created in this way began to be used in the aviation industry. Later, a standard for metal anodization appeared, which is successfully used in modern aircraft construction. It has the nomenclature marking DEF STAN 03-24/3.

The coating consists of two components:

• organic;
• anode-chromium.

Paint applied in accordance with the standard is very resistant to abrasion and other mechanical damage.

Anodizing technology

Today, the most widespread process is aluminum sulfate anodization. Its essence is as follows:

1. The part and the cathode, made of lead, are placed in a bath with an electrolyte - sulfuric acid H2 SO4 - to remove impurities and oils. Indicators of physical quantities: solution density – 1,200-1,300 g/l; current density during anodizing process – 10-50 mA/cm²; source voltage – 50-100 V; electrolyte temperature – 20-30 °C (for subsequent painting – no more than 20 °C).
2. A final rinse is carried out in a caustic solution.
3. A thin oxide layer is created on the surface of an aluminum part.

The growth rate of the anodic layer on the metal surface is uneven and very low. The optimal amount of colored oxide is applied when the current density reaches 1.5-1.6 A/dm². At lower values, the layer turns out to be almost colorless.

Large values ​​of cathode density (the ratio of the size of the cathode to the size of the surface being processed) cause difficulties when processing massive parts - the appearance of burnouts and etching.

The optimal cathode area is x2 in relation to the size of the workpiece.

It is also very important to control the clamp and electrical contact of the part with the suspension.

In addition to sulfuric acid, other substances and compounds can be used as an electrolyte during anodizing:

• oxalic acid;
• organic compounds and mixtures;
• orthophosphoric acid.
• chromic anhydride.

The process technology does not change. The ultimate goal when choosing an electrolytic medium is to obtain a layer with certain physical characteristics before repainting.

Warm anodizing

The warm anodizing process is carried out at an ambient temperature of 15-20 °C. Parts processed in this way have two negative features:

1. Not very high anti-corrosion resistance. When in contact with a chemically aggressive environment or metal, the anodized layer is exposed to oxygen.
2. Low degree of protection against mechanical influences. It is quite possible to cause mechanical damage to the anodized layer with a sharp tip.

The warm anodizing process consists of six stages:

• cleaning the surface of the part from grease.
• fastening on a suspension.
• anodizing until a light milky color appears.
• rinsing with cold water.
• dyeing with a hot solution of aniline dye.
• allowing the anodized metal to sit for 30 minutes after painting.

The layers of film produced by warm anodizing are exceptionally beautiful. This type of aluminum is best used in structures that are not exposed to harsh external influences. In addition, the anodized layer is an excellent base for repainting due to its superior dye adhesion. The applied paint will last for a very long time.

Cold anodizing

The technology of cold application of the anodic layer involves processing aluminum at temperatures from -10 to +10 °C. The quality of metal processed in this way is incomparably higher than with warm anodizing.

Aluminum receives excellent physical characteristics:

• high strength.
• low rate of layer dissolution.
• greater film thickness.

When cold anodizing it is necessary to carry out the following procedures:

• degreasing the surface to be treated.
• placing the part on the hanger.
• anodizing until a dense shade is obtained.
• washing in water at any temperature.
• fixing the anode layer in steam or hot distilled water.

A distinctive feature of the process is the long forced cooling time. After this, the anodized aluminum layer becomes completely impervious to aggressive environments. Only titanium, after several decades, is able to slightly reduce the physical characteristics of cold-process anodized aluminum.

The coating is characterized by exceptional beauty and wear resistance. The technology has only one drawback: when repainting, you can only use inorganic compounds.

Why is aluminum anodized and how is it used?

The purpose of anodizing parts made of aluminum is to increase service life under exposure to various aggressive environments.

Given that pure aluminum has a high affinity for oxygen, its corrosion resistance is higher than that of many other light metals for structural purposes. Natural oxidation of aluminum occurs upon first contact with air. The process of anodic treatment further increases the tendency of both chemical elements to create oxides by reacting with each other.

The ability of the anodic film to perfectly absorb dyes of various chemical compositions makes aluminum processed in this way an excellent decorative material. It is widely used for external finishing of interiors of buildings and structures.

Aluminum structures are indispensable when creating:

• advertising structures for cultural and sports events, exhibitions and shows.
• information stands for mass actions, rallies, meetings.

The excellent reflective ability of anodized aluminum has made it an indispensable material in the manufacture of road signs. Thanks to interference, the information printed on the sign during anodization is clearly visible to motorists at night.

Amateur bicycle frames are also made from anodized aluminum alloys.

The special clothing worn by cyclists at night is coated with a thin film of aluminum oxide. Thanks to this, the silhouette is easy to see in the dark at a respectful distance.

For the same purpose, anodized metal is used in the manufacture of a reflective layer in floodlight installations.

The excellent properties of anodized aluminum allow it to be used for the manufacture of a wide range of parts and assemblies used in a wide variety of fields. We can safely say: if the decision is made to make something from metal processed in this way, the strength and lightness of the structure will not raise any doubts!

Source: http://ctroisys.ru/texnologiya-anodirovaniya-alyuminievyx-profilej-chto-takoe-pokrytie-anodirovannoe.html

chemical corrosion

The impact of an aggressive external environment without an electrochemical process on a metal surface leads to its destruction. Chemical corrosion begins. As a result, the metal loses its performance qualities.

What is the process of chemical corrosion and its types?

Any product becomes unusable over time, as well as under certain conditions. Metal is no exception. Chemical corrosion is classified as a type of destructive corrosion process.

Electric current as a source of influence is excluded here. In this case we are talking about an oxidative reaction.

Knowing this is important in order to have an idea of ​​why metal requires protection when used as the main material for the installation of various pipework, in other areas where it is applicable.

Metal destruction is classified according to two types of aggressiveness of external influence:

1. The occurrence of chemical corrosion in non-electrically conductive liquid media (non-electrolyte liquids).
2. Chemical gas corrosion.

Gas chemical corrosion

This type is considered one of the most common destructive corrosion processes. The metal is deformed when interacting with gases under the influence of elevated temperatures.

What should you think about right away? About the reinforcement used to strengthen the furnace masonry, reinforcing bars present in engines and turbines. In addition, the influence of ultra-high temperatures occurs during metal processing, when high pressure is present.

During heating before rolling and stamping of metal products, during forging, during thermal and other similar manufacturing processes.

The rate at which gas chemical corrosion develops depends on a number of indicators:

1. From atmospheric temperature;
2. From components contained in a metal alloy or metal;
3. On the parameters of the environment in which the gases act;
4. From the properties of chemical products that create corrosion.

Protective agent for gas corrosion - oxide film

One of the elements in chemistry that protects metal from chemical gas corrosion is an oxide film. The properties and parameters that are inherent in it allow it to be considered the most powerful protective factor that prevents rusting of a metal surface. Metal oxidation is divided into the following stages:

1. The adsorption process occurs. Oxygen molecules are concentrated on the surface of a metal element that is exposed to the external environment.
2. The interaction of oxygen molecules with gas allows the development of a destructive chemical reaction that occurs on the surface of the metal. The oxide film makes it difficult for this chemical process for the penetration of metal and oxygen reagents to each other.

Oxide films are classified into three types.

They can be:

• thin (they can only be seen with a microscope);
• medium, forming iridescent tarnish colors;
• thick when visible with the naked eye.

The oxide film has protective capabilities that inhibit the development of chemical corrosion. And sometimes they completely stop the formation of rust.

The oxide film helps to increase the heat resistance of the metal.

How fast does chemical corrosion develop?

The speed with which a metal undergoes destruction is directly related to the temperature. High temperature levels accelerate oxidation processes. Decreasing heating does not have any effect on this process.

Metals that are affected by the gas environment tolerate its effects differently with a corresponding difference in temperature fluctuations. We are talking about the difference in how metals perceive the components of a gaseous environment. For example, on a copper surface, corrosion forms quickly when the metal comes into contact with oxygen.

If instead of oxygen the source of exposure is sulfur oxide, then copper becomes resistant to chemical corrosion. Quite the opposite is the case with nickel.

The influence of sulfur oxide is detrimental to it, and in an oxygen environment or when exposed to carbon dioxide, resistance to corrosion occurs.

The rate of formation of chemical corrosion as a result of an oxidative reaction depends on the components of the metal alloy. Successful alloys in this sense are compounds of iron with cobalt, copper, beryllium and titanium. The chemical compound that creates the austenitic structure is more stable. In other words, high-temperature iron.

An additional factor influencing the rate of formation of chemical corrosion is the condition of the treated metal surface. If the surface is smooth, then oxidation occurs more slowly. On an uneven surface, rusting occurs faster.

The process of metal corrosion in non-electrolyte liquids

Liquids - non-electrolytes do not react with metals and corrosion does not develop. But when impurities are added, chemical corrosion may occur.

There are:

• Non-conductive liquid media of organic origin, such as benzene, oil, alcohols, kerosene and other compounds.
• And organic - sulfur, liquid bromine. 

Adding sulfur-containing impurities (hydrogen sulfide, mercaptan) to oil accelerates the onset of corrosion. Also, high temperatures and the presence of oxygen in the liquid contribute to the intensification of corrosion processes.

Liquid bromine is an element that can significantly accelerate the development of corrosion. The destructive effect occurs under normal temperature conditions in which high-carbon steel is located: aluminum, titanium. Iron and nickel are less susceptible to bromine. Increased resistance to corrosion due to liquid bromine is manifested in lead, silver, tantalum, and platinum.

The occurrence of chemical corrosion cannot be avoided unless protective methods are applied to the metal.

Among these:

• painting metal surfaces with durable protective paints,
• galvanic coating,
• adding elements to the alloy that increase its resistance to corrosion damage,
• reducing the aggressiveness of the external environment,
• use of electrochemical protection.

Source: https://prompriem.ru/korroziya/himicheskaya.html