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04

2023-08

Cold heading and hot heading of bolts

Cold heading refers to the stamping of raw materials at room temperature, and hot heading refers to the stamping of raw materials after heating. There are no special requirements for specific uses. Generally, cold heading is required, because of such surface finish and material structure. The composition will be closer, and larger workpieces are often processed by hot heading. Cold heading: It is to use the plasticity of the metal to apply pressure or cold drawing by cold mechanics to achieve the purpose of solid deformation of the metal. A forging method in which the top of a rod or wire is thickened at room temperature. Cold heading is mainly used to manufacture bolts, nuts, nails, rivets and steel balls and other parts. The forging blank material can be copper, aluminum, carbon steel, alloy steel, stainless steel and titanium alloy, etc., and the material utilization rate can reach 80-90%. Cold heading is mostly carried out on a special cold heading machine, which is convenient for continuous, multi-station and automatic production. The processes of material cutting, heading, accumulation, forming, chamfering, thread rolling, diameter reduction and edge trimming can be completed in sequence on the cold heading machine. The production efficiency is high, up to 300 pieces/min, and the diameter of the largest cold heading workpiece is 48 mm. The schematic diagram of cold heading bolt process is a typical process of cold heading bolt. Multi-station nut automatic cold heading machine is a multi-station nut automatic cold heading machine. The bar is automatically fed to a certain length by the feeding mechanism, and the cutting mechanism cuts it into blanks, and then sent to the accumulating and pressing station and punching station for forming by the clamp conveying mechanism.

04

2023-08

Bolt surface treatment

Blackening is a common method of metal heat treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. When the appearance requirements are not high, blackening treatment can be used. The surface of steel parts is blackened, and some are also called bluish. Bluing treatment is a kind of chemical surface treatment, its main function is to form a dense oxide film on the surface of the workpiece, prevent corrosion and rust of the workpiece, and improve the wear resistance of the workpiece. It is only a surface treatment and will not damage the internal structure. To produce any effect, it is not heat treatment, which is fundamentally different from quenching. The commonly used methods of blackening treatment are traditional alkaline heating blackening and room temperature blackening that appear later. However, the normal temperature blackening process is not very effective for low carbon steel. The main components of the blackening solution are sodium hydroxide and sodium nitrite. The temperature tolerance required for blackening is relatively large, and a good surface can be obtained between 135 and 155 ° C, but the time required is somewhat long.

04

2023-08

Bolt Strength Grade

The strength grade is divided according to the mechanical properties. According to relevant standards, bolt performance grades are divided into more than 10 grades such as 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, among which the bolts of grade 8.8 and above are made of low carbon alloy steel or medium carbon steel and have been heat treated (quenching, tempering), commonly known as high-strength bolts, and the rest are commonly referred to as ordinary bolts. The bolt performance grade label consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material.

04

2023-08

Germany, Japan, the United States, and South Korea are the main import sources of my country's hardware products in the first three quarters of this year

From January to September 2015, the cumulative imports of the national hardware industry are mainly concentrated in Germany, Japan, the United States, South Korea, Taiwan, China, Italy, Switzerland, Austria, Thailand, and other regions. Germany, Japan, the United States, and South Korea are the main sources of imports of hardware products in my country, and the four countries account for more than 10%. The third-ranked US import growth rate dropped significantly, as high as -24.77%. Among the top ten countries and regions, the growth rate of imports of Austria, Thailand and Italy also dropped rapidly, all exceeding 10%. Among them, Thailand was the highest, reaching -43.16%.

04

2023-08

Both imports and exports in the first 10 months of China were lower than expected

According to the import and export data released by the General Administration of Customs on the 8th, in the first 10 months of this year, my country's total import and export value was 19.93 trillion yuan, a decrease of 8.1% over the same period last year (the same below). Among them, exports were 11.46 trillion yuan, down 2%; imports were 8.47 trillion yuan, down 15.2%; trade surplus was 2.99 trillion yuan, an increase of 75.3%.

04

2023-08

Expert: It is unrealistic for every screw of C919 to be domestically produced

On November 2, the first domestically-made C919 large passenger aircraft developed by COMAC finally rolled off the production line. This is undoubtedly an exciting thing, but besides the excitement, we also heard various "different" voices, including voices of doubt, voices of dissatisfaction, and voices of worry.

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