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Bolts With Low Cost, Good Corrosion Resistance

Bolts: Mechanical parts, threaded threaded fasteners with nuts. A type of fastener consisting of a head and a screw (with an external thread) is required to be fitted with a nut for fastening the connection of two parts with through-holes, which are bolted The If the nut is unscrewed from the bolt and the two parts can be separated, the bolt connection is a detachable connection.

The manufacturing process of high strength bolts

Made of high-strength steel, or need to impose a greater pre-tightening bolts, can be called high-strength bolts. High strength bolts are used for connecting bridges, rails, high pressure and ultrahigh pressure equipment. The breakage of this bolt is mostly brittle fracture. High-strength bolts applied to high-pressure equipment, in order to ensure the container seal, the need for greater prestressing. High strength bolts processing technology:

Hot-rolled wire rod - (cold dial) - Spheroidization (softening) Annealing - Mechanical descaling - Pickling - Cold transfer - Cold forging - Thread processing - Heat treatment - Inspection;

High strength bolts and ordinary bolt of the difference:

Usually high-strength bolts can withstand the load than the same specifications of ordinary bolts;

The material of the ordinary bolt is made of Q235 (ie A3). High strength bolts material 45 # steel, alloy steel (eg 20MnTiB, 35VB)

1) the shape of the screw head

      Generally, the process of cold forging the bolt head using a forging machine such as a top heading machine or a jacker is called "upsetting". The so-called cold forging, that is, at room temperature for processing, it is heated with the blank after the warm processing and thermal processing relative to the said.

     The process of forging is to cut the coil-like steel into the appropriate length, with several forging device for the material forging (one side of the material pressure, while the material deformation). As the basic processing of forging upsetting, deep drawing, reverse extrusion, dressing and other four. Upsetting is to squeeze the material from one end, to expand to the original diameter than the original processing; deep punch is the opposite, that is, the material from one end of the dead, to narrow the smaller diameter than the original processing; reverse extrusion is From the end of the material to the diameter of the material than the small die for extrusion, so that the material side out, while the perforation of the processing; dressing is to use the forging die to remove the excess thickness of the processing. Depending on the shape of the processed product, these processes may be used separately or in combination. The more complex the shape of the product, the more need to increase the processing of the process, slowly forming processing, but the ordinary bolts only 2-5 processing processes can be processed forming.

(2) thread forming process

     In the thread forming step of the bolt, the thread is subjected to cold forging using a roll forming machine called "rolling or rolling", and the forming method is the same as the forming method of the bolt head.

     The processing of the thread shape is to hold the blank between the two sets of forging die, one side of the two forging die, while the blank rotation, through the plastic processing into a thread shape. The forging die used for thread forming is called "roll forming die".

     The roll forming machine has three kinds of flat forging roll forming machine, round forging roll forming machine and planetary roll forming machine. The flat forging die forming machine is equipped with two ordinary roll forming forging dies, which fixes one side and let the other side move forward to roll the blank. The round forging roll forming machine rotates the two cylindrical roll forming dies in parallel in the same direction to roll the blanks sandwiched between the two forging dies. The planetary roll forming machine is a method in which a blank is sandwiched between a cylindrical forging die and a fan-shaped forging die and is rolled by a rotary cylindrical forging die.

(3) heat treatment

     Cold forged forming bolts are generally made of materials suitable for plastic processing. High carbon content or the addition of alloying elements due to their material hard, not easy to process, so some need to heat the material by annealing. Most of the material in the case of cold forging and can not meet the required strength. Heat treatment is carried out after cold forging, it can make the required strength and mechanical properties of bolts, bolt production process is the most important process.

     Bolts in accordance with the use of parts and uses can be divided into various strength levels. According to JIS, ISO and automotive manufacturers and other users of the respective standards, according to each strength level to specify the hardness and tensile strength and other mechanical properties. The heat treatment (quenching and tempering treatment) is carried out so that the formed bolts have their respective desired mechanical properties.

(4) surface treatment

     The bolts used in the automobile engine are often soaked with lubricating oil, so that they do not rust even if they are not subjected to surface treatment. However, this bolt is only a small part of the part of the bolt is used in corrosive environment, so if not surface treatment, will soon rust. Rusty bolts if placed on this, after corrosion will not be able to screw open, serious when the bolt will break into a big accident. Therefore, the use of bolts in corrosive environments requires surface treatment such as electroplating.

The surface treatment of the bolts can be roughly divided into two types of plating and coating. The most widely used is the electroplating method, which has the advantages of low cost and good corrosion resistance. In the case where the corrosion resistance is higher than that of the plating, the alloy plating such as galvanized iron and galvanized nickel may be used, or a zinc-aluminum composite film may be applied.

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