Often, when buying self-tapping screws, they pay attention to the thread pitch or size. But many people do not even suspect that color also matters. Yellow, white, black is not just a decorative finish, but a special division of self-tapping screws according to their characteristics. Novate.ru will tell you why you need to take into account the color of self-tapping screws and for what purposes to use them.
White self-tapping screws
Self-tapping screws are made from hard steel grades. The products themselves are obtained in a light gray shade, which is commonly called white. White self-tapping screws are considered the cheapest because they contain stainless steel. The screws are resistant to corrosion, durable (they last for decades) and can withstand heavy loads. Self-tapping screws are used for interior work if the humidity in the room does not exceed 65%. Most often they are hidden under finishing materials because of their unattractive appearance.
There are also galvanized white self-tapping screws. They differ from ordinary ones in increased strength, since they are made of carbon steel. However, due to carbon, screws are prone to corrosion. To prevent rust from corroding self-tapping screws, they are electroplated with zinc. Galvanizing protects the screws from corrosion and gives the fasteners a silvery tint. Such self-tapping screws can be used for both indoor and outdoor work. But it is better not to fasten parts with them, which in the future may be exposed to excessive moisture.
Yellow self-tapping screws
The first type of yellow self-tapping screws is galvanized fasteners. Standard silver-gray screws are treated in a special passivating solution (inorganic substances with oxidizing properties). Chromic acid is one of the ingredients in the liquid, which is why the procedure is called chromate passivation. As a result, the self-tapping screws are covered with a yellow conversion film of 0.5 microns, which improves the anti-corrosion properties of the screws. Fasteners look good on hinges and other similar shades.
The second type is brass yellow self-tapping screws. They cost a little more and are made of a copper alloy, which includes iron, manganese, nickel, zinc, and lead. Compared to ordinary yellow screws, brass screws are more wear-resistant, do not rust without protective treatment, do not magnetise and even with prolonged exposure to low temperatures do not lose their properties. It is very easy to distinguish between galvanized and brass screws. The former shine and shimmer with gold, while the latter look simpler.
Black self-tapping screws
Black self-tapping screws are the most popular fasteners. However, be careful: screws painted in black without protective treatment are also sold. Be sure to check with the seller what the screws are made of and what properties they have. The correct screws are made from carbon steel, and the dark shade is achieved in three different ways.
The first is zinc plating. As a result of chromating, the thickness of the coating is obtained from 0.25 to 1 micron, providing a different degree of protection against rust. Choose screws that have gone through the oiling phase as they are more wear-resistant. Black galvanized self-tapping screws are suitable for harsh chemical environments and high humidity conditions.
The second is oxidation. An oxide film forms on the surface of the screw, which prevents corrosion. It protects against rust better than the chrome layer. Fasteners are designed for indoor use in rooms with low humidity. To use them in more aggressive conditions, you need to oil the self-tapping screws or make water repellents. Then a water-repellent layer forms on the products. Oxidized screws are a great option if you need paintable screws.
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The third is phosphating. As a result of the process, the screws are covered with a 2–15 µm protective film. The layer consists of iron phosphates and for its application Mazhef is used - a powder of phosphorus, manganese and iron. The coating is almost impossible to damage and paint perfectly lays on it. Phosphated self-tapping screws are a suitable option for fastening parts in high humidity conditions.
Reliability, strength and durability of the structure depend on the correct choice of self-tapping screws. Consider these tips when buying screws to waste your money. We also recommend reading about life hacks that will make working with a drill and screwdriver more efficient and varied.
A source: https://novate.ru/blogs/280121/57613/
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