The role of glass lubricants in the extrusion of seamless steel tubes

As early as 1925, people had already mastered that steel could be deformed by extrusion like non-ferrous metals. Due to the low cost of equipment and tools, and the abundance of product sections, the hot-forming method for such steels has received increasing attention. In 1941, SejournetJ, with the assistance of Renn Electric Furnace Corporation, successfully tested glass lubricants, made the development of hot extrusion of steel possible, and quickly promoted it throughout the world.
Traditional steel extrusion production uses graphite (a mixture of flake graphite with engine oil, tar, or grease) as a lubricant. However, the disadvantages of graphite lubricants are: 1) Large thermal conductivity, poor thermal insulation, large temperature rise of the tool, rapid wear, and difficulty in extrusion of long products. 2 It is easy to cause carbon increase in the product. When the stainless steel is extruded, it easily generates intergranular corrosion. Therefore, the carburized layer must be removed after the extrusion, resulting in increased metal consumption. 3 will often cause environmental pollution.
The advantages of glass lubricant compared with graphite, its advantages are: 1 glass thermal conductivity is small, can prevent the surface of the billet too fast cooling, but also can play a role in protecting the mold. 2 It has good lubrication performance, can use a large extrusion ratio and increase the extrusion speed, which can expand the range of products produced by the extruder. 3 Glass Lubricants are chemically stable and do not cause tissue defects. 4 can easily change the ratio of glass lubricants to obtain different physical properties (such as softening point, viscosity, etc.), in order to adapt to the needs of products extruded different materials. 5 It can be kept clean when using glass as a lubricant. In summary, the advantages of glass lubricants are significant. Many foreign research results indicate that the use of glass lubricants for steel extrusion works best.
The parts that must be lubricated when extruding a seamless steel tube are: an extrusion die, an extrusion cylinder, and a mandrel.
(1) Lubrication of Extrusion Dies: Lubrication of molds is a common method of pressing glass powder into a glass mat, that is, placing the glass mat between the mold and the blank before extrusion. In order to ensure that the glass mat can continuously soften on the friction surface, the shape of the glass mat is required to match the shape of the entrance cone of the die hole and the end of the blank. The outer diameter of the glass mat is generally 3 to 5 mm smaller than the diameter of the barrel. The diameter of the hole in the glass mat is less than or equal to the diameter of the die hole. The thickness of the glass mat generally takes 4% to 8% of the length of the blank.
(2) Lubrication of the extruder barrel and mandrel: The lubrication of the barrel and the mandrel should be done by using a glass powder with a low softening point and a small particle size to coat the inner and outer surfaces of the billet. In addition, it is also possible to wrap glass cloth around the surface of the blank and wind the glass cloth around the core rod.
(3) Removal of the glass film on the surface of the steel pipe: Due to the glass lubricant used in the extrusion, a glass film with a thickness of 20 to 50 μm remains on the inner and outer surfaces of the extruded steel tube, which is hard and brittle and harmful to subsequent processing and use. Must be cleared. Removal methods include mechanical and chemical methods. Mechanical methods include shot peening, water cooling, and tension straightening. When the glass film is removed by a chemical method, since the residual glass lubricant on the surface of the steel tube has a high chemical stability, it is necessary to use an alkali solution or an acid solution to remove it. The disadvantage of the pickling method is that it is highly corrosive to various steel pipe materials and may cause excessive pickling on the surface of the steel pipe, which is particularly corrosive to carbon steel, and therefore has limited application. Currently using acid-base joint removal method.
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UHP 550 Graphite Electrode

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Carbographite Industrial PTE.LTD ,

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