What is tinning? Methods for protecting metal from corrosion

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

Tinning is widely used in industries such as aviation, radio engineering and electrical engineering. Products used for cooking and storing food are also subjected to this process. What is tinning, what is it used for and how this operation is carried out correctly, and we will consider in this article.

What is tinning done for?

Pinning is used to protect products from corrosion. For this procedure, tin or its alloy with lead or other components is used. The layer that is applied to the metal is called semi-dry.

The tinning procedure consists in preparing the surface and then applying half a day on it. The surface is prepared depending on the requirements that apply to the product and the method of tin coating. So what is tinning? This is the surface treatment of a metal product with a thin layer of tin or its alloys to prevent corrosion and subsequent soldering of other materials to it.

Fluxing agents

Substances thatused to clean the surface of the product before tinning are called fluxes. To do this, use:

• Ammonium chloride is a white solid material, odorless, highly soluble in water. The technical name is ammonia. Well cleans metal surfaces from fats and oxides.
• Sulfuric acid is a colorless oily liquid that mixes well with water. For dilution, the acid is slowly poured into water. In this case, a violent reaction occurs with the release of a large amount of heat. It is necessary to work with the substance only with gloves and goggles.
• Soda ash - a powder in the form of crystals, dissolves in water with the release of heat. For storage, use a glass container with a tightly closed lid. If air enters, a coating forms.

All these substances qualitatively clean the surface of metal products from the oxide film in order to carry out tinning.

Chemical and physical properties of tin

Tin is a silver-white metal with a blue tint, belongs to plastic and malleable materials. Its density is 7.3g/cm3. A bar made of pure tin, when bent, makes a characteristic sound, reminiscent of the crunch of snow underfoot. With the content of some impurities in it, this property disappears. In nature, the material occurs only in the form of compounds with antimony, copper, sulfur, iron and other metals. Some impurities (iron and bismuth) increase the brittleness of the metal, while others (zinc and copper) make it ductile. At what temperature does tin melt?

It easily liquefies at 232 degrees. In its pure form, the metal reacts inactively with oxygen and therefore retains its luster for a long time. Tin is very resistant to organic acids and perfectly resists precipitation. The metal dissolves well in sulfuric and concentrated hydrochloric, but interacts weakly with dilute acid.

Tin and tin-based alloys

According to the chemical composition, all tin is divided into four grades:

• 01 - contains impurities 0, 1%;
• 02 - 0.5%;
• 03 – 1, 65%;
• 04 – 3, 75%.

For tinning, the first two grades are most often used. O1 - for tin and other metals, 02 - for kitchen utensils. Products tinned with tin have increased resistance to deformation, withstand bends and kinks. What is tinning - this is the coating of the entire surface of the product with a layer of tin, which reliably protects the metal from rusting. For processing products not intended for food, lead or zinc is added to tin. Such alloys protect it well from corrosion and are cheaper than tin. To obtain a white shiny poluda, bismuth compounds are used - 90 parts of tin and 10 parts of bismuth. Tin-bismuth alloys are most often used for processing products of artistic value.

Tinning Tools

When processing products with tin, you must have the following tools:

• measuring instruments - used to determine the size of products;
• tinning pliers - hold parts;
• scrapers and hair brushes - clean items;
• blowtorches - heat surfaces.

The process of applying tin to objects without these simple devices is impossible.

Preparation

What is tinning? This is the process of coating the surface of an item with a thin layer of molten tin to protect it from corrosion. This procedure will be more successful, the better the surface of the part is cleaned. Before tin plating, the following treatment is carried out:

• Cleaning from scale and dirt. To do this, use brushes and scrapers.
• Remove all irregularities with an abrasive wheel or sandpaper.
• Chemical degreasing. Produced with caustic soda, dissolving 10 g of powder in a liter of water. The item is lowered into the boiling solution for 15 minutes.
• Mineral oils are cleaned with kerosene or gasoline.
• Brass, steel and copper products are cleaned with heated sulfuric acid, lowering the product into the solution for 20 minutes.

After processing, the parts are washed with cold water, cleaned with wet sand and only then washed in hot water. The preparation procedure ends with drying.

Hot tinning

There are two methods of hot tinning products that are prepared in advance for this procedure:

1. Rubbing tinning. A flux is applied to the surface of the product, which is used as zinc chloride, and the product is heated evenly with blowtorches to the melting temperature of tin applied from the rod. From contact with a heated product, it melts. Then the tow is sprinkled with powdered ammonia and the heated surface is rubbed with it until the half-day is evenly distributed. Having finished tinning, the product is cooled, rubbed with wet sand, then washed with water and dried.
2. Dip tinning. After processing the part in the flux, it is immediately lowered into the tin bath. It contains liquid tin, heated above the melting point of the metal to 270-300 degrees. The presence of a product in a liquid solution depends on its size and the thickness of the material from which it is made. The process takes an average of 30 seconds to 1 minute. It is necessary that the level of the tinning liquid be 40 mm higher than the object being processed. Excess poluda is removed with tow with powdered ammonia. After that, the treated item is washed with clean water and dried.

Small products are tinned by dipping, and large ones by rubbing.

Tinned tip

Cable lugs are used to terminate cables and wires. In clamps, it is intended to prepare the end of the cable for alignment and fixation with the core. For industrial conditions tips are produced from copper and aluminum and their alloys. Aluminum is resistant to corrosion, and to increase the service life of copper products, they are tinned. Tinned copper, unlike the copper tip, is suitable for use in adverse climatic conditions.

In addition, such devices have increased resistance to aggressive chemicals: hydrochloric, nitrogen and sulfuricacid. They do not undergo oxidation during long-term storage and operation, they are resistant to moisture.

Conclusion

People encounter tinned products every day. These are kitchen utensils: cutlery, kitchen utensils, cans and other products associated with long-term storage and transportation of food products. Tinning finds no less application in the spheres of the national economy. Tin protects the contacts of radio equipment parts from oxidation, is used to protect cables and wires, and to make tin. In addition, tin coating provides plasticity to the material, it is easily processed by stamping, rolling drawing and soldering.