First, the thread is a shape on the solid outer surface or the inner surface of the cross-section, with a uniform spiral line convex shape.
According to its structural features and uses, it can be divided into three categories:
(1) Ordinary thread: The shape of teeth is triangular, used to connect or fasten parts. Ordinary thread is divided into coarse thread and fine thread thread according to pitch, and the connection strength of fine thread is high.
(B), transmission thread: teeth have trapezoidal, rectangular, saw-shaped and triangular and so on.
(c) Sealing threads: used for sealing connections, mainly pipe thread, taper thread and taper thread.
Second, thread matching level:
Thread fitting is the loose or tight size between the screw threads. The mating level is the combination of deviation and tolerance on the internal and external threads.
(a) For the united inch thread, the male thread has three thread grades:
Grades 1A, 2A, and 3A have three levels of internal threads: Classes 1B, 2B, and 3B, all with clearance fit. The higher the rank number, the tighter the fit. In inch threads, the deviations are only specified in levels 1A and 2A, the deviation in levels 3A is zero, and the level deviations in levels 1A and 2A are equal. The larger the number of grades, the smaller the tolerance.
1,
Grades 1A and 1B, very loose tolerance grades, apply to the tolerance fit of internal and external threads.
2,
Grades 2A and 2B are the most common thread tolerance grades for imperial series mechanical fasteners.
3,
Grades 3A and 3B, which are screwed together to form the tightest fit, are suitable for tight tolerance fasteners and are used for critical safety designs.
4, external thread, 1A and 2A
Level has a fit tolerance, 3A does not. Class 1A tolerances are 50% larger than Class 2A tolerances, 75% larger than Class 3A, and for internal threads Class 2B tolerances are 30% greater than 2A tolerances. Class 1B is 50% larger than Class 2B and 75% larger than Class 3B.
(b) Metric thread, external threads have three thread grades:
4h, 6h and 6g, the internal thread has three thread levels: 5H, 6H, 7H.
(The date mark threading accuracy grade is divided into I, II, III three grades, under the ordinary condition is the grade II) In the metric thread, the basic deviation of H and h is zero.
The basic deviation of G is a positive value, and the basic deviation of e, f, and g is a negative value. as the picture shows:
1. H is the common tolerance zone for internal threads. It is generally not used as a surface coating or an extremely thin phosphating layer.
The basic deviation of G position is used for special occasions, such as thick plating, and it is rarely used.
2, g commonly used to plate 6-9um thin coating, such as the product drawing requirements is 6h bolts, the thread before plating using 6g tolerance zone.
3, the best combination of thread into H / g, H / h or G / h, for bolts, nuts and other refined fastener thread, the standard recommended 6H / 6g with
Third, the main geometric parameters of self-tapping, self-drilling thread:
(a) Large diameter/dental diameter (d1) is the imaginary cylinder diameter where the crest of the thread overlaps. The large diameter of the thread basically represents the nominal diameter of the thread size.
(B), diameter / bottom diameter (d2): the imaginary cylinder diameter of the thread bottom coincide.
(c) Tooth pitch (p): The axial distance between two adjacent points on the midline. In the imperial system, pitch is indicated by the number of teeth per inch (25.4 mm).
The table below shows the number of teeth (metric) with common specifications (inch)
1, metric tapping teeth:
specification:
ST 1.5, S T1.9, S T2.2 S T2.6 S T2.9, S T3.3, S T3.5, S T3.9, S T4.2, S T4.8, S T5.5 , S T6.3,
S T8.0, S T9.5
Toothpitch: 0.5, 0.6, 0.8, 0.9, 1.1, 1.3, 1.4, 1.6, 1.8, 2.1
2, inch self tapping teeth:
specification:
4#, 5#, 6#, 7#, 8#, 10#, 12#, 14#
Number of teeth: AB teeth 24, 20, 20, 19, 18, 16, 14
A teeth 24,20,18,16,15,12,11,10
Fourth, the structural performance of steel bolts points
3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, etc. More than 10 grades, of which bolts of grade 8.8 and above are low carbon alloy steel or medium carbon steel and heat treated (quenched and tempered) For high-strength bolts, the rest are commonly referred to as ordinary bolts. Bolt performance grade labels are composed of two parts, which respectively indicate the nominal tensile strength value and yield ratio of the bolt material. For example: a bolt with a performance rating of 4.6 means:
1. Bolt material nominal tensile strength up to 400MPa;
2. The yield ratio of bolt material is 0.6;
3, the nominal yield strength of bolt material reaches 400×0.6=240MPa grade
Performance grade 10.9 high-strength bolts are heat treated to achieve:
1. The bolt material has a nominal tensile strength of 1000MPa;
2. The yield ratio of bolt material is 0.9;
3, the nominal yield strength of bolt material reaches 1000×0.9=900MPa grade
The meaning of the bolt performance level is an internationally accepted standard. Bolts of the same performance level have the same performance regardless of their material and origin.
The design can only use the performance level.
Grades 8.8 and 10.9 for strength grades refer to bolts with shear stress ratings of 8.8 GPa and 10.9 GPa
8.8
Nominal tensile strength 800N/MM2 Nominal yield strength 640N/MM2
The general bolt is the strength expressed by "XY", X*100=the tensile strength of this bolt, and X*100*(Y/10)=the yield strength of this bolt (because it is stipulated by the mark:the yield strength/tensile strength =Y/10)
Such as 4.8. The tensile strength of this bolt: 400MPa; yield strength: 400 * 8/10 = 320MPa.
Five, stainless steel bolts are usually marked A4-70 (usually refers to 316SUS), A2-70 (refers to 304SUS), the meaning of another interpretation
6. Measurement: There are mainly two kinds of length measurement units in the world today, one is metric system, and the unit of measure is meters (m), centimeters (cm), millimeters (mm), etc., which are used in European countries, China, Japan and other Southeast Asian regions. The other is the English system. The unit of measurement is mainly in inches, which is equivalent to the old market in China. It is used in many countries in the United States and the United Kingdom.
1, metric measurement: (decimal)
1m =100 cm=1000 mm
2, British measurement: (8)
1 inch = 8 cents
1 inch = 25.4 mm 3/8 inch × 25.4 = 9.52
3, 1/4 inch
¢ The following products are denoted by the number designation, such as: 4#, 5#, 6#, 7#, 8#, 10#, 12#