Bolt: A cylindrical threaded fastener used with nuts as a mechanical component. A type of fastener consisting of a head and a screw (cylindrical body with external threads) that needs to be matched with a nut to securely connect two parts with through holes. This type of connection is called bolted connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.
Classification of bolts
According to the force distribution method of the connection, it can be divided into ordinary and those with hinged holes. According to the shape of the head, there are hexagonal, round, square, countersunk, and so on. Among them, hexagonal heads are the most commonly used. Generally, countersunk heads are used where connections are required.
The English name for a saddle bolt is U-bolt, which is a non-standard component with a U-shaped shape and is also known as a U-bolt. It has threads on both ends that can be combined with a nut, and is mainly used to fix tubular objects such as water pipes or sheet objects such as the plate springs of cars. Due to its fixed object like a person riding on a horse, it is called a saddle bolt. Divided into two types based on thread length: full thread and non full thread.
According to the thread profile, it is divided into two types: coarse and fine. The coarse profile is not displayed in the bolt marking. Bolts are classified into eight grades based on their performance levels: 3.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium carbon steel and undergo heat treatment (quenching+tempering), commonly known as high-strength bolts. Bolts below grade 8.8 (excluding grade 8.8) are commonly known as ordinary bolts.
Ordinary bolts can be divided into three grades based on production accuracy: A, B, and C. Grade A and B are refined bolts, while grade C is rough bolts. For connecting bolts used in steel structures, unless otherwise specified, they are generally ordinary rough C-grade bolts. There are differences in the processing methods for different levels, and the corresponding processing methods are usually as follows: ① The bolt rods of grade A and B bolts are machined by lathes, with smooth surfaces and precise dimensions. Their material performance level is 8.8, and the production and installation are complex, expensive, and rarely used; ② C-grade bolts are made of unprocessed round steel with imprecise dimensions, and their material performance level is 4.6 or 4.8. The deformation is large during shear connection, but it is easy to install and has low production costs. It is mostly used for tensile connection or temporary fixation during installation.
Application of bolts
There are many names for bolts, and everyone's name may be different. Some people call them screws, some call them bolts and nails, and some call them fasteners. Although there are so many names, their meanings are all the same, they are all bolts. Bolt is the general term for fasteners. A bolt is a tool that uses the physical and mathematical principles of the inclined circular rotation and friction of an object to gradually tighten the mechanical components of the object.
Bolts are indispensable in daily life and industrial production, and they are also known as the rice of industry. The widespread use of bolts is evident. The application scope of bolts includes electronic products, mechanical products, digital products, power equipment, and electromechanical products. Bolts are also used in ships, vehicles, hydraulic engineering, and even chemical experiments. Anyway, bolts are used in many places. Such as the precision bolts used in digital products. DVD, Micro bolts used in cameras, glasses, clocks, electronics, etc; General bolts for televisions, electrical products, musical instruments, furniture, etc; As for engineering, construction, and bridges, large bolts and nuts are used; Transportation vehicles, airplanes, trams, cars, etc. use both large and small bolts. Bolts play an important role in industry, and as long as there is industry on Earth, the function of bolts will always be important.
The shape of the bolt
Generally, countersunk heads are used in areas where smooth surfaces without protrusions are required after connection, as countersunk heads can be screwed into parts. Round heads can also be screwed into parts. The tightening force of the square head can be greater, but the size is quite large. In addition, to meet the needs of locking after installation, there are holes in the head and rod, which can prevent the bolts from loosening when subjected to vibration. Some bolts without threads need to be made thin, called slim waist bolts. This type of bolt is beneficial for connecting under variable forces. There are specialized high-strength bolts on the steel structure, with larger heads and varying sizes. In addition, there are special uses for T-shaped groove bolts, which are most commonly used on machine tool fixtures. They have a special shape and need to be cut off on both sides of the head. Anchor bolts, used for connecting and fixing machines to the ground, come in many shapes. U-shaped bolt, as mentioned earlier. wait. There are also specialized bolts for welding, with threads on one end and no threads on the other, which can be welded onto the part and the other side can be directly screwed with a nut.
The stress mode of bolts
Ordinary and those with hinged holes. Ordinary main load-bearing axial forces can also bear lateral forces with low requirements. The bolts used for reaming holes should match the size of the hole and be used when subjected to lateral forces.
The meaning of bolt grade
According to relevant standards, the performance grades of carbon steel and alloy steel bolts are divided into more than 10 grades, including 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. Among them, bolts with grade 8.8 and above are made of low-carbon alloy steel or medium carbon steel and undergo heat treatment (quenching, tempering), commonly known as high-strength bolts, while others are commonly known as ordinary bolts. The bolt performance grade number consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield strength ratio of the bolt material. Stainless steel bolts are classified into A1-50 A1-70,A1-80,A2-50,A2-70,A2-80,A3-50,A3-70,A3-80,A4-50,A4-70,A4-80,A5-50,A5-70,A5-80,C1-50,C1-70,C1-110,C4-50,C4-70,C3-80,F1-45,F1-60. The first letter and number represent the group of stainless steel, while the second and third numbers represent 1/10 of the tensile strength.
Bolt inspection
Bolt inspection is divided into two types: manual and machine. Artificial is the most primitive and widely used method of consistent detection. In order to minimize the outflow of defective products, personnel in general production enterprises inspect packaged or shipped products visually to eliminate defective products (including tooth damage, mixing, rust, etc.).
Another method is fully automated machine testing, mainly magnetic particle inspection. Magnetic particle inspection is a process that utilizes the interaction between the leakage magnetic field at bolt defects and the magnetic powder. It aims to address the differences in magnetic permeability between possible defects in bolts, such as cracks, slag inclusions, and mixed materials, and the magnetic permeability of steel. After magnetization, the magnetic field at the discontinuous parts of these materials will undergo distortion, forming a leakage magnetic field on the surface of the workpiece where some magnetic flux leaks. This attracts the magnetic powder to form a magnetic particle accumulation at the defect site - a magnetic mark. Under appropriate lighting conditions, the location and shape of the defect are revealed, and the accumulation of these magnetic particles is observed and explained to achieve the goal of removing defective products.
