Fastener material and performance grade

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　　Classification of fasteners and related accessories

　　

　　1. Fasteners:

　　

　　Bolts, studs, nuts, screws, washers, wood screws, tapping screws, pins, rivets, retaining rings, assemblies and connecting pairs, welding nails, innovative and non-standard products;

　　

　　2. Equipment:

　　

　　Molding equipment: cold heading machine, cold extrusion molding machine, heading machine, nailing machine, etc.

　　

　　Thread forming equipment: thread rolling machine, thread rolling machine, tapping machine, etc.

　　

　　Heat treatment equipment: industrial furnace, tempering line, high and medium frequency induction heating equipment, material annealing furnace, etc.

　　

　　Surface treatment equipment: phosphating line, oxidation line, zinc plating line, dacromet production line, etc.

　　

　　Auxiliary equipment: grinding machine, slotting machine, vibrating plate, marking machine, etc.

　　

　　Testing equipment and devices: hardness tester, material tension and compression tester, microscope, etc.

　　

　　3, tooling:

　　

　　Bolt forming die: including cutting die, upper die (pre-die, fine die, trimming die, etc.) and lower die (cold upsetting die, reducing die, ejector pin, etc.)

　　

　　Nut forming die: including cutting die, punch, punch, hole die, forming die, thimble, etc.

　　

　　Thread forming tools: thread rollers, thread washboards, taps, etc.

　　

　　4, surface treatment:

　　

　　Surface treatment process: electroplating, blackening, heat treatment, hot dip zinc, phosphating, mechanical plating and dacromet.

　　

　　Auxiliary materials: brightener, cleaning agent, antirust agent and degreasing agent.

　　

　　5. Raw materials:

　　

　　Medium carbon steel, low carbon steel, alloy steel, stainless steel (including wire, bar, plate, pipe, etc.)

　　

　　2

　　

　　The meaning of bolt performance grade

　　

　　The performance grades of bolts used for steel structure connection 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 and 12.9. Among them, bolts of grade 8.8 and above are made of low-carbon alloy steel or medium-carbon steel and are heat-treated (quenched and tempered), which are generally called high-strength bolts, and the rest are generally called ordinary bolts.

　　

　　The bolt performance grade label consists of two parts of numbers, which respectively represent the nominal tensile strength value and yield ratio value of the bolt material. For example, a bolt with performance grade 4.6 means:

　　

　　1. The nominal tensile strength of bolt material reaches 400MPa;

　　

　　2. The yield ratio of bolt material is 0.6;

　　

　　3. The nominal yield strength of the bolt material reaches 400X0.6=240MPa, and the performance grade is 10.9. After heat treatment, the material can reach:

　　

　　1. The nominal tensile strength of bolt material reaches 1000MPa;

　　

　　2. The yield ratio of bolt material is 0.9;

　　

　　3. The nominal yield strength of bolt material reaches 1000X0.9=900MPa.

　　

　　The meaning of bolt performance grade is an international standard. Bolts with the same performance grade have the same performance regardless of the difference of material and origin, so only performance grade can be selected in design.

　　

　　The so-called 8.8 and 10.9 strength grades mean that the shear stress grades of bolts are 8.8GPa and 10.9Gpa.

　　

　　8.8 Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2.

　　

　　Generally, the strength of bolts is expressed by “X.Y”.

　　

　　X*100= tensile strength of this bolt,

　　

　　X*100* (Y/10 )= yield strength of this bolt.

　　

　　(Because according to the marking: yield strength/tensile strength =Y/10)

　　

　　Such as 4.8.

　　

　　Then the bolt’s

　　

　　The tensile strength is 400MPa.

　　

　　The yield strength is: 400*8/10=320MPa. In addition, stainless steel bolts are usually marked as A4-70 and A2-70, and the meaning is otherwise explained.

　　

　　three

　　

　　magnanimity; tolerance

　　

　　There are mainly two types of length measurement units in the world today. One is metric, with the measurement units of meters (m), centimeters (cm) and millimeters (mm), which are widely used in Europe, China and Japan, and the other is English, with the measurement unit of inch, which is equivalent to the old city inch in China, and is widely used in the United States, Britain and other European and American countries.

　　

　　1. Metric measurement: (decimal system)

　　

　　1m =100 cm=1000 mm

　　

　　2. English measurement: (octal)

　　

　　1 inch =8 minutes 1 inch =25.4 mm3/8 00×25.4 =9.52

　　

　　3, 1/4 0 of the following products use serial numbers to indicate their address diameter, such as:

　　

　　4#5#6#7#8# 10# 12#

　　

　　four

　　

　　screw thread

　　

　　1. Thread is a shape with uniform spiral protrusions on the cross section of solid outer surface or inner surface. According to its structural characteristics and uses, it can be divided into three categories:

　　

　　(1) Ordinary thread: the tooth shape is triangular, which is used to connect or fasten parts. Ordinary threads are divided into coarse thread and fine thread according to pitch, and the connection strength of fine thread is higher.

　　

　　(2) Transmission thread: the tooth shapes include trapezoid, rectangle, saw and triangle.

　　

　　(3) Sealing thread: used for sealing connection, mainly including pipe thread, taper thread and taper pipe thread.

　　

　　Second, the thread matching grade:

　　

　　Thread fit is the size of looseness or tightness between screwed threads, and the level of fit is the prescribed combination of deviation and tolerance acting on internal and external threads.

　　

　　(1) For unified English thread, there are three thread grades for external thread: 1A, 2A and 3A, and three grades for internal thread:

　　

　　1B, 2B and 3B, all of which are clearance fit. The higher the grade number, the tighter the fit. In English thread, the deviation is only specified as Grade 1A and Grade 2A, the deviation of Grade 3A is zero, and the grade deviation of Grade 1A and Grade 2A is equal.

　　

　　The greater the number of grades, the smaller the tolerance.

　　

　　Classes 1, 1A and 1B, very loose tolerance classes, which are suitable for tolerance fit of internal and external threads.

　　

　　Grade 2, 2A and 2B are the most common thread tolerance grades specified by English series mechanical fasteners.

　　

　　Grade 3, 3A and 3B, which are screwed to form the tightest fit, are suitable for fasteners with tight tolerances and are used for the key design of safety.

　　

　　4. For external threads, there is a fit tolerance for Grade 1A and 2A, but not for Grade 3A. The tolerance of Class 1A is 50% greater than that of Class 2A and 75% greater than that of Class 3A. For internal threads, the tolerance of Class 2B is 30% greater than that of Class 2A. Class 1B is 50% larger than class 2B and 75% larger than class 3B.

　　

　　(2) Metric thread. There are three thread grades for external thread: 4h, 6 H and 6g, and three thread grades for internal thread: 5H, 6h and 7H. (The thread accuracy grade of Japanese standard is divided into I, II and III, which is usually Grade II) In metric thread, the basic deviation between H and H is zero. The basic deviation of G is positive, and the basic deviations of E, F and G are negative. As shown in the figure:

　　

　　1. H is the commonly used tolerance zone position of internal thread, which is generally not used as surface coating or extremely thin phosphating layer. The basic deviation of G position is used in special occasions, such as thick coating, which is rarely used in general.

　　

　　2. G is commonly used to plate a thin coating of 6-9um. For example, the bolt required by the product drawing is 6h, and the thread before plating is 6g tolerance zone.

　　

　　3. It is best to combine the thread fit into H/g, H/h or G/H. For refined fastener threads such as bolts and nuts, the standard recommends 6H/6g fit.

　　

　　(3), thread marking

　　

　　Three, the main geometric parameters of self-tapping and self-drilling thread:

　　

　　(1) The major diameter/tooth outer diameter (d1) is the imaginary cylinder diameter with overlapping thread crests. The major diameter of the thread basically represents the nominal diameter of the thread size.

　　

　　(2) Small diameter/root diameter (d2): it is the imaginary cylinder diameter with overlapping thread roots.

　　

　　(3) Pitch (P): refers to the axial distance between adjacent teeth corresponding to two points on the meridian. Pitch is expressed by the number of teeth per inch (25.4mm) in the British system.