Tinning is widely used in such industries as aviation, radio engineering and electrical engineering. Products used for the preparation and storage of food are also subjected to this process. What is tinning, what is it used for and how is this operation carried out correctly, and we will consider this article.
What is tinning done for?
Tinning 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 half-time.
The tinning procedure consists in preparing the surface and then applying half the surface on it. The surface is prepared depending on the requirements that apply to the product and the method of coating with tin. 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 to it of other materials.
Fluxing agents
Substances that are used to clean the surface of the product before tinning are called fluxes. To do this, apply:
- Ammonium chloride is a white solid, odorless, and soluble in water. Technical name - 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. Work with the substance only with gloves and goggles.
- Soda ash is a powder in the form of crystals, it dissolves in water with the release of heat. For storage use glass containers with a tightly closed lid. If air gets in, a coating forms.
All these substances qualitatively clean the surface of metal products from the oxide film to conduct tinning.
Chemical and physical properties of tin
Tin - a metal of silver-white color with a blue tint, refers to plastic and malleable materials. Its density is 7.3 g / cm 3 . A bar of pure tin, when bent, makes a characteristic sound that resembles the creaking of snow underfoot. When some impurities are contained in it, this property disappears. In nature, material is found 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 turns into a liquid at a temperature of 232 degrees. In its pure form, the metal inactively reacts with oxygen and therefore retains 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 acid, however, it interacts weakly with dilute acid.
Tin and Tin Alloys
According to the chemical composition, all tin is divided into four grades:
- 01 - contains impurities of 0.1%;
- 02 - 0.5%;
- 03 - 1, 65%;
- 04 - 3.75%.
For tinning, the first two brands are most often used. O1 - for tin and other metals, 02 - for kitchen utensils. The tin-coated products are highly resistant to deformation, withstand bends and bends. What is tinning - is the coating of the entire surface of the product with a layer of tin, which reliably protects the metal from rust. To process non-food items, lead or zinc is added to the tin. Such alloys well protect it from corrosion and are cheaper than tin. To obtain a white shiny midday, bismuth compositions 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;
- tin mites - hold parts;
- scrapers and hair brushes - clean products;
- blowtorches - heat the surface.
The process of applying tin to objects without these simple devices is impossible.
Training
What is tinning? This is the process of coating a thin layer of molten tin on the surface of a product to protect it from corrosion. This procedure will be more successful the better the surface of the part will be cleaned. Before tin coating, the following treatment is carried out:
- Scale and dirt removal. To do this, use brushes and scrapers.
- Remove all irregularities with an abrasive wheel or sandpaper.
- Chemical degreasing. Produced by caustic soda, dissolving 10 g of powder in a liter of water. The component is lowered into the boiling solution for 15 minutes.
- Mineral oils are removed with kerosene or gasoline.
- Brass, steel and copper products are cleaned with heated sulfuric acid, lowering the product into 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 for hot tinning products that are prepared in advance for this procedure:
- Tinning by grinding. A flux is applied to the surface of the product, in which zinc chloride is used, and the product is uniformly heated with blowtorches to the melting temperature of the tin deposited from the bar. From contact with a heated product, it melts. Then tow sprinkle with powdered ammonia and rub the heated surface with it until the even distribution of midday. After tinning, the product is cooled, rubbed with wet sand, then washed with water and dried.
- Tinning by immersion. After processing the part in 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. Finding a product in a liquid solution depends on its size and thickness of the material from which it is made. The process on average takes from 30 seconds to 1 minute. It is necessary that the level of tin fluid is 40 mm higher than the workpiece. Excessive midnight remove tow with powdered ammonia. After that, the treated object is washed with clean water and dried.
Small products are tinned by immersion, and large products are rubbed.
Tinned Tip
Cable lugs are used to terminate cables and wires. In the clamps, it is intended to prepare the end of the cable for alignment and fixation with the core. For industrial conditions, tips are made of copper and aluminum and their alloys. Aluminum is corrosion resistant and tinned to increase the life of copper products. Tinned copper, unlike a copper tip, is suitable for use in adverse climatic conditions.
In addition, such devices have increased resistance to aggressive chemicals: hydrochloric, nitric and sulfuric acid. They are not oxidized during long-term storage and operation, and are resistant to moisture.
Conclusion
With products processed by the tinning method, people meet 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 parts of the radio equipment from oxidation, is used to protect cables and wires, the manufacture of tin. In addition, the tin coating provides plasticity to the material, it is easily processed by stamping, rolling, drawing and soldering.