Service HotlineIn terms of inner hexagon, there are two versions of the national standard, one is GB70-76, the 76-year version, and the other is GB70-85, the 85-year version, most of which implement the DIN912 standard, so you should pay attention to the difference in actual business operations: GB70 -85 completely coincides with DIN912, so there is no difference in the use of the new standard, mainly the difference between GB70-76 and DIN912: for M8 series hexagonal products, the diameter of the round head of GB70-76 is 12.5MM, It is smaller than 13.27MM of DIN912. For M10 series inner hexagon products, the round head diameter of GB70-76 is 15MM, which is smaller than 16.27 of DIN912. For M12 series inner hexagon, the round head diameter of GB70-76 is 18MM. It is smaller than the opposite side 18.27 of DIN912, and the round head diameter of the inner hexagon GB70-76 of M16 and M20 series is 0.33MM smaller than that of DIN912, which are 24MM and 30MM respectively. DIN912 is 24.33MM and 30.33MM respectively. In addition, the width of the inner hexagon between the old standard and the German standard is different due to different standards. The inner side of GB70-76 is smaller, and it should be paid attention to in business operations.
The Greek mathematician Arkutas once described the principle of screw, screw, screw. In the first century AD, the Mediterranean world had begun to use wood screws, screws, and screws in screw presses that could press olive oil from olives, or make wine from grapes. Before the fifteenth century, metal screws, screws, screws were rarely used as fasteners in Europe. Rybczynski (Rybczynski) proves that hand-held screwdrivers and screwdrivers existed in the Middle Ages (at the latest AD 1580), but it was not until the eighteenth century that threaded fasteners were commercialized and began to be widely used. . Before threaded fasteners were widely used, there were many different ways of tightening. Mostly related to woodworking and forging, and less to machining, concepts such as dowels and pins, wedges, tenon and tenon, dovetails, nails, forge welding, and others are tied with leather or fiber and tied together. Before the mid-nineteenth century, ships were built with cotter pins, pin bolts, or rivets. There were also adhesives, but not as many as they are here today. Metal screws, screws, and screws became commonly used fasteners after the use of machine tools in the 18th century to mass-produce screws, screws, and screws. This technology developed around the 1760s and 1770s, along two separate processes. Approaches, but quickly converged: wood screws, screws, screws (metal screws for wood fixing, screws, screws) are machined with single-purpose, high-yield machines, and low-volume, mold shop style production V-Thread Machine Screws, Screws, Screws, can choose from a variety of different pitches.
The blind rivet is realized by pulling the core head. With the help of a force from the inside to the outside, under the action of the unidirectional pulling force, the pulling screw is pulled upwards, which causes the outer collar material to expand and deform, resulting in a sexual tightening force. , After the riveting is completed, the tension screw in the middle part breaks and falls out. Since a large pulling force is required to cause the rivet to expand and deform, the tensile screw is longer and accounts for about 60-80% of the total length of the rivet. At the same time, due to the limitation of the deformation mode, it is difficult for the blind rivet to be made into a hexagonal structure like a rivet nut, so the torsion resistance of its connection is low.
In specific implementation, the axial three-dimensional shape of the nut and the screw head is in the shape of a pentagonal frustum, the elastic surface of the screw is parallel to the center line of the bolt, and the upper contour line is arc-shaped; the screw can be full or partial thread; the top of the screw head The shape is round.
The performance grade 8.8 of stainless steel bolts refers to the material's tensile strength limit of 800MPa and yield limit of 640MPa. The performance grades of stainless steel bolts, studs and studs are divided into 10 grades: from 3.6 to 12.9. The number before the decimal point represents 1/100 of the tensile strength limit of the material, and the number after the decimal point represents 10 times the ratio of the material's yield limit to the tensile strength limit. There are 7 grades of performance grades for nuts, from 4 to 12. The numbers roughly represent 1/100 of the minimum stress that the stainless steel nut is guaranteed to withstand. For unified inch threads, there are three thread grades for external threads: grades 1A, 2A and 3A, and three grades for internal threads: grades 1B, 2B and 3B, all of which are clearance fits. The higher the rating number, the tighter the fit. Classes 1, 1A and 1B, very loose tolerance classes, which are suitable for tolerance fits of internal and external threads. Grades 2, 2A and 2B are the most common thread tolerance grades specified for inch series mechanical stainless steel fasteners. Grades 3, 3A and 3B, screwed together to form the tightest fit, suitable for tight tolerance stainless steel standard parts, for safety critical designs. Metric threads, there are three thread grades for external threads: 4h, 6h and 6g, and three thread grades for internal threads: 5H, 6H, 7H. Thread fit is best combined into H/g, H/h or G/h. For bolts, stainless steel nuts and other refined fastener threads, the standard recommends 6H/6g fit. Carbon steel: The strength grade is marked by ? It consists of two separated numbers. The meaning of the number part before the ? in the marking code represents the nominal tensile strength, for example, 4 in grade 4.8 represents 1/100 of the nominal tensile strength of 400N/MM2. The meaning of the ? and the number part after the point in the marking code represents the yield-strength ratio, that is, the ratio of the nominal yield point or the nominal yield strength to the nominal tensile strength. For example, the yield point of grade 4.8 products is 320N/mm2. The strength grade mark of stainless steel products consists of two parts separated by —. The symbol before — in the sign code indicates the material. Such as: A2, A4 and other signs — indicate strength, such as: A2-70 Carbon steel: The mechanical properties of bolts can be divided into: 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9 in total 10 performance levels
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