Thread measurement of bolts, screws, and studs, material requirements, heat treatment requirements, and mechanical property requirements Industry Solutions

Thread measurement of bolts, screws, and studs, material requirements, heat treatment requirements, and mechanical property requirements Industry Solutions

1. Fastener thread measurement

A thread ring gauge or plug gauge measures general standard threads. As there are many thread parameters, it is impossible to measure each thread parameter individually. Usually, we use a thread gauge (thread ring gauge, thread plug gauge) to make a comprehensive judgment on the thread. This kind of inspection belongs to the acceptance method of simulated assembly, which is convenient, reliable, and comparable with the precision requirement of common thread, so it has become the most common acceptance method used in actual production.

2. Measurement of fastener thread (center diameter)

In the thread connection, only the size of the center diameter determines the nature of the thread fit, so correctly determining whether the center diameter is qualified is critical. Based on the median size, it should ensure that the most basic performance of the thread is achieved; the standard provides for the median qualified judgment principle: "The role of the actual thread median can not exceed the maximum entity tooth type median. And the single center diameter of any part of the actual thread cannot exceed the center diameter of the smallest solid tooth type."

Measurement of the single center diameter is currently more convenient: using the thread center diameter micrometer or the three-pin method.

3. Fastener thread fit grade:

Thread fit is the size of the looseness or tightness between the screwed threads, and the grade of the fit is the prescribed combination of deviations and tolerances acting on the internal and external threads. For uniform-inch threads, there are three thread grades for male threads: grades 1A, 2A, and 3A, and three for female threads: grades 1B, 2B, and 3B, all of which are clearance fits. The higher the grade number, the tighter the fit. In imperial threads, the deviations are specified only for grades 1A and 2A, with zero deviation for grades 3A, and the grade deviations for grades 1A and 2A are equal. The larger the number of grades, the more minor the tolerance.

(1) Grades 1A and 1B are very loose tolerance grades, which apply to the tolerance fit of internal and external threads.

(2) Grades 2A and 2B are the most common thread tolerance grades specified for the imperial series of mechanical fasteners.

(3) Classes 3A and 3B, which screw together to form the tightest fits, are for fasteners with tight tolerances and are used in safety-critical designs.

(4) For external threads, grades 1A and 2A have a fit deviation; grade 3A does not. Grade 1A tolerance is 50% greater than grade 2A tolerance and 75% greater than grade 3A. Grade 2B tolerance is 30% greater for internal threads than grade 2A tolerance. Grade 1B is 50% greater than grade 2B and 75% greater than grade 3B.

For metric threads, there are common thread grades for external threads: 4h, 6e, 6g, and six h, and there are common thread grades for internal threads: 6G, 6 H, and 7H (Japanese standard thread accuracy grades are divided into three levels, I, II and III, and usually in the condition of grade II). In metric threads, the fundamental deviation of H and h is zero. The primary deviation of G is positive, and the fundamental deviation of e, f, and g is negative.

(1) H is a commonly used tolerance band position for internal threads, generally not used as surface plating or with a skinny phosphating layer. g position fundamental deviation is used for special occasions, such as a thicker plating layer, but is generally seldom used.

(2) g is commonly used to plate 6-9um thin plating. For example, if the product drawing requirements are six h bolts, they are plated before the thread using a 6g tolerance band.

(3) Thread fit is best combined as H/g, H/h, or G/h. For bolts, nuts, and other fine fastener threads, the standard recommends a 6H/6g fit. This is the medium-accuracy class for common threads.

Nut: 6H Bolt: 6g Medium accuracy class for threads with thick cover layer

Nuts: 6G Bolts: 6e High accuracy class.

Nuts: 4H Bolts: 4hsix 6h

4. Specialized threads common to fasteners

Thread fit is the size of the looseness or tightness between the screwed threads, and the grade of the fit is the prescribed combination of deviations and tolerances acting on the internal and external threads.

For uniform-inch threads, there are three thread grades for male threads: grades 1A, 2A, and 3A, and three grades for female threads:

1B, 2B, and 3B grades, all of which are clearance fits.The higher the grade number, the tighter the fit. In imperial threads, the deviations are specified only for grades 1A and 2A, with zero deviation for grades 3A, and the grade deviations for grades 1A and 2A are equal. The larger the number of grades, the smaller the tolerance.

1.1A and 1B grades are very loose tolerance grades, suitable for tolerance fits on internal and external threads.

2.2A and 2B, the most common thread tolerance grades specified for inch series mechanical fasteners.

3. Classes 3A and 3B, which screw together to form the tightest fits, are used for fasteners with tight tolerances for safety-critical designs.

4. For male threads, grades 1A and 2A have a fit tolerance, while grade 3A does not. Class 1A tolerances are 50% larger than Class 2A and 75% larger than Class 3A. Class 2B tolerances for female threads are 30% larger than 2A. Grade 1B is 50% larger than grade 2B and 75% larger than grade 3 B.

For metric threads, there are three thread grades for external threads: 4h, 6 h, and 6g, and three for internal threads: 5H, 6H, and 7H. (Japanese standard thread accuracy grades are classified into three levels: I, II, and III, and in normal conditions, grade II.) In metric threads, the fundamental deviation of H and h is zero. The primary deviation of G is positive, and the fundamental deviations of e, f, and g are negative. As shown in Fig:

1. H is the common tolerance band position for internal threads, generally not used for surface plating or with a skinny phosphating layer. The G position fundamental deviation is used for special occasions, such as thicker plating, and is generally rarely used.

2. g is commonly used for thin plating of 6-9um, such as product drawings requiring six h bolts and the threads before plating with a 6g tolerance band.

3. The best combination of thread fit is H/g, H/h, or G/h. The standard recommends a 6H/6 g fit for bolts, nuts, and other fine fastener threads.

Self-tapping, self-drilling threads of the main geometric parameters:

(a), large diameter/tooth outside diameter (d1) overlap for the imaginary cylindrical diameter of the top of the thread teeth. Thread diameter represents the nominal diameter of the thread size.

(ii), small diameter / bottom diameter (d2): The bottom of the thread teeth overlaps the imaginary cylindrical diameter.

(C), tooth distance (p): for adjacent teeth in the center of the meridian line corresponding to the axial distance between two points. In the British system, every inch (25.4mm) is within the number of teeth, indicating the pitch.

The following table lists the standard specifications of the tooth spacing (metric) number of teeth (imperial)

1. Metric self-tapping teeth: specifications ST 1.5 ST 1.9 ST 2.2 ST 2.6 ST 2.9 ST 3.3 ST 3.5 ST 3.9 ST 4.2 ST 4.8 ST 5.5 ST 6.3 ST 8.0 ST 9.5 ST

Pitch 0.5 0.6 0.8 0.9 1.1 1.3 1.3 1.3 1.4 1.6 1.8 1.8 2.1 2.1

2.British self-tapping teeth: specifications 4# 5# 6# 7# 8# 10# 12# 14#

Number of teeth AB teeth 24 20 20 19 18 16 14 14

Teeth 24 20 18 16 15 12 11 10

5. Material requirements, heat treatment requirements, and mechanical property requirements for bolts, screws, and studs

Fastener material selection: medium carbon steel, low carbon steel, alloy steel, stainless steel (including wire, bar, plate, tube, etc.)

5.1 Carbon Steel: Commonly used for general construction projects, offering good strength and moderate cost.

Stainless Steel: For applications exposed to corrosive environments, such as chemical plants or waterfront areas. -Alloy Steels: Used in general construction projects for good strength and moderate cost.

Alloy Steel: Used where high strength and abrasion-resistant environments are required. Choosing the correct type of thread (coarse or fine) reduces stripping and prevents vibration. Fine threads may be needed for precision equipment or structures that operate in high-vibration environments. Consider whether the stud requires additional surface treatment to enhance its corrosion or wear resistance. Typical treatments include hot dip galvanizing, electro-galvanizing, zinc spraying, or coating protection such as chrome plating or PTFE. Consider the operating conditions under which the stud will be used, such as high temperature, cold temperature, humidity, corrosive environments, etc., which may require a specific material or surface treatment. Carbon steel： Distinguish between mild, medium, and high carbon steels and alloy steels by the amount of carbon in the carbon steel stock.

（1）Low carbon steel C%; 0.25% usually called A3 steel. Model 1008,1015，1018, 1022, and so on. Mainly used for 4.8-grade bolts and 4-grade nuts, small screws, and other products without hardness requirements. (Note: Drill screws are mainly used 1022, 410, 416, etc.)

（2）Medium carbon steel 0.25%<C%0.45% Usually called No. 35, No. 45 steel, model 1035, CH38F, 1039, 40ACR, etc.. It is mainly used for 8-grade nuts, 8.8-grade bolts, and 8.8-grade hexagonal products.

（3）High carbon steel C%>0.45%. At present, the number of industrial manufacturing structural connections is relatively tiny.

（4）Alloy steel: Add alloying elements to plain carbon steel to increase some of its unique properties,

Such as 35,40chromium molybdenum, SCM435 and 10B38 .

The main components of SCM435 chromium-molybdenum alloy steel are C, Si, Mn, P, S, Cr, and Mo.

Stainless steel performance grade:

45, 50, 60, 70, and 80 main points austenitic (18%Cr, 8%Ni) good heat resistance, corrosion resistance, and weldability.

A1, A2, A4 martensite, 13%Cr poor corrosion resistance, high strength, good wear resistance. C1, C2, C4 Ferritic stainless steel. 18%Cr，18%Cr better upsetting and forging, stronger corrosion resistance than martensite. Currently, imported materials are mainly Japanese products on the market. According to the level of the main points SUS302, SUS304, SUS316.304M, 304HC, 316, three kinds of material are currently 300 series of austenitic stainless steel is one of the most widely used materials. The noticeable difference between each material is that after cold working, the material magnetism is 316<304HC<304M, 316 material resistance to chemical corrosion, pore corrosion, and seawater corrosion resistance relative to 304M and 304HC to be excellent.

Molding equipment:

Cold heading machines, cold extrusion molding machines, header machines, nail-making machines, 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, galvanizing line, Dacromet production line, etc.

Auxiliary equipment: grinding machine, milling machine, vibration plate, marking machine, etc.

Testing equipment and devices: hardness tester

A material tensile testing machine, microscope, etc

Bolt molding dies: cutting die, upper die (pre-punching die, fine blanking die, cutting edge die, etc.), lower die (cold heading concave die, shrinking die, ejector pin, etc.)

Nut forming dies: including cutting dies, punching rods, hole punching, hole dies, forming concave dies, ejector pins, etc.

Thread forming tools: thread rolling wheel, plate, tap, etc.

Surface treatment processes include electroplating, blackening, heat treatment, hot dip zinc, phosphating, mechanical plating, Dacromet, zinc-nickel alloy, environmental protection, zinc, and anodizing.

Auxiliary materials: brightening agent, cleaning agent, rust inhibitor, degreasing agent

Industry solutions for bolt performance grades:

The performance grade of bolts for steel structure connection is divided into 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9, and so on more than ten grades, of which the material of the bolts of grade 8.8 and above is low-carbon alloy steel or medium-carbon steel and heat-treated (quenched and tempered), commonly known as high-strength bolts. The rest are widely known as ordinary bolts. Bolt performance level labeling has two parts of the digital composition: the nominal tensile strength of the bolt material value and the flexural strength ratio value. For example, the performance level 4.6 grade bolts, the meaning is:

1. Nominal tensile strength of the bolt material up to 400MPa level;

2. Bolt material yield strength ratio of 0.6.

3. bolt material nominal yield strength up to 400X0.6 = 240MPa level performance level 10.9 grade high strength bolts, the material after heat treatment, can achieve:

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

2. Bolt material yield strength ratio of 0.9.

3. bolt material nominal yield strength of 1000X0.9 = 900MPa level bolt performance level of the meaning of the international standard, the same performance level of the bolt, regardless of the difference between its material and origin, its performance is the same, the design of only the performance level can be selected. Strength grade, 8.8, and ades refer to the bolt shear stress levels of 8.8GPa and 10.9Gpa.

8.8 nominal tensile strength of 800N/MM2 nominal yield strength of 640N/MM2 . General bolts use "XY" for the strength of the bolt, X * 100 = tensile strength of the bolt, X * 100 * (Y/10) = the yield strength of this bolt (), because according to the marking provisions, the yield strength is the same, regardless of the difference in material origin, the design can only choose the performance level. According to the provisions of the logo, yield strength / tensile strength = Y / 10), such as the 4.8 level of the bolt's tensile strength is 400MPa yield strength of 400 * 8/10 = 320MPa. Another: stainless steel bolts are usually labeled as A4-70 and A2-70 material.

6. Types and construction of steel structure bolting

6.1 Overview of bolt connection for steel structure

Bolt connecting for steel structure (bolt connecting for steel structure) involves connecting more than two steel structure parts or components with bolts to form one connection method. Bolt connection is the easiest connection method in component preassembly and structural installation.

Bolted connections were first used in the installation of metal structures. High-strength bolts of medium- or medium-carbon alloy steel are 2 to 3 times stronger than ordinary bolts. High-strength bolt connections have the advantages of convenient construction, safety, and reliability. Please get in touch with our team if you need high-quality, high-strength screws& fasteners with more detailed specifications and related information.

Email:adelajonly@gmail.com,www.juxinfasteners.com.

6.2 Specification of bolts

Commonly used bolt specifications in steel structures are M12, M16, M20, M24, and M30; M is the symbol of the bolt, and the number is the nominal diameter. Bolts according to the performance level of 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9, 12.9, a total of 10 grades, of which more than 8.8 bolts made of low-carbon alloy steel or medium-carbon steel and heat-treated (quenched, tempered), commonly known as high-strength bolts, 8.8 or less (excluding the 8.8 level, the refined ordinary bolts also include 8.8 level) Commonly known as ordinary bolts.

The performance grade of the bolt is labeled by two parts of the number, respectively, indicating the bolt's nominal tensile strength and the material's flexural strength ratio. For example, the meaning of a bolt with a performance grade of 4.6 is:

The first part of the number (4.6 in the "4") for the nominal tensile strength of the bolt material (N / mm2) of 1/100, that is, that fu ≥ 400N / mm2;

The second part of the number ("6" in 4.6) for the bolt material yield strength ratio of 10 times, that is, fy/fu = 0.6; the product of the two parts of the number (4 × 6 = "24") for the nominal yield point of the bolt material (or yield strength) of the (N /) mm2) of 1/10, that is, fy ≥ 240N/mm2.

Joint bolts for steel structures can be divided into three grades according to the production precision: A, B, and C. A and B grades are refined bolts, generally used for mechanical products, and C grades are crude bolts. Except for special instructions, steel structure ordinary bolts are typically crude C-grade bolts with performance grades of 4.6 or 4.8.

6.3 Classification of bolts: Bolts have many names, screws, bolts and nails, standardized parts, fasteners and so on. Bolts include ordinary bolts, high-strength bolts, ground anchors, expansion bolts, chemical anchors, screws, bolts, and nails, etc.; narrowly speaking, bolts are divided into two kinds of ordinary bolts connection and high-strength bolts.

Ordinary bolts: Ordinary bolts are divided into crude and refined bolts according to the production precision. Ordinary bolts can be divided into hexagonal head bolts, double head bolts, countersunk head bolts, etc., according to the form;

Rough bolts: C-class bolts are generally rough bolts made of carbon structural steel; to make the bolt smoothly into the screw hole, the hole diameter should be larger than the nominal diameter of the bolt d 1.0 ~ 2.0mm for the II class hole. The bolt-hole spacing arrangement should make it easy to wrench-tighten the nut. When the crude bolts connect columns, beams, and roof frames, the connection structure should be used with pallets. The bolt is in tension, and the pallet bears its shear force.

The crude bolt's low strength grade limits its use in structural connections. However, it is still widely used to connect the secondary beam of the working platform with small shear force, wall-skin beam, roof beam, support, articulated support, etc. The crude bolt is also commonly used to connect plant components.

Roughing bolts are also commonly used in preassembling plant steel structures, pre-tightening riveted components before riveting, and temporary fasting of high-strength bolts before connection before assembly and welding mounting nodes. When crude bolts are used as permanent fixing bolts, they must be tightened, and anti-loosening measures are taken after the alignment.

Refined bolts: A-grade and B-grade bolts are refined bolts. The hole is generally Ⅰ holes, and the hole diameter should be larger than the nominal diameter of the bolt, 0.3 ~ 0.5mm. They refined bolt connections for some, which are often disassembled and can not be riveted to the structure of the connection. Refined bolts are generally used in mechanical products and rarely used in the construction of steel structures.

7. High-strength bolts

Bolts made of high-strength steel, or bolts that require a large preload, are called high-strength bolts. High-strength bolts apply pre-tensioning force and transfer external force by friction. Ordinary bolts rely on bolt shear and hole wall pressure to transfer the shear force, tighten the nut when the pre-tension is very small, its impact is negligible, and high-strength bolts, in addition to their high material strength, to the bolts to apply a lot of pre-tension, so that the connecting components between the extrusion pressure, which makes the perpendicular to the direction of the screw there is a lot of friction, and the pre-tension, the coefficient of anti-slip and the type of steel have a direct impact on the high strength bolts—load bearing capacity.

7.1 The working principle of high-strength bolts: high-strength bolts are divided into friction and compression types according to their force condition. According to the construction process, high-strength bolts are divided into twisted shear high-strength bolts and large hexagonal high-strength bolts.

7.2 Torsion and shear type high-strength bolts and large hexagonal high-strength bolts： Friction-type high-strength bolt connection, relying on the bolt to tighten the pressure to connect the plating layer tightly after the contact surface of the steel plate friction to transfer the external force. The component's surface is sandblasted to generate a red rust surface, which can obtain a more significant friction coefficient and reduce the number of connecting bolts. Friction type high strength bolt hole diameter should be larger than the nominal diameter of the bolt d 1.5 ~ 2.0mm. Pressure type high strength bolt connection is to make the friction generated between the component and the bolt center axis shear force and the bearing pressure of the element at the same time to transfer the stress of the role of the hole diameter should be larger than the nominal diameter of the bolt d 1.0 ~ 1.5mm. They were making holes and molding mold using a CNC drilling machine.

In short, friction-type high-strength bolts and pressure-type high-strength bolts are the same kind of bolt; the difference lies in the design of whether to consider the slip. Design, friction-type high-strength bolt friction surface can not slide, the screw does not bear the shear force; once the friction surface slip, it is considered to reach the design of the damage state, technically more mature, reliable; pressurized high-strength bolts friction surface can be sliding, the screw also bears the shear force, the final damage and the destruction of the ordinary bolt are the same (bolt shear insufficient or steel plate pressure terrible). Large hexagonal high-strength bolts, by a high-strength bolt, a nut, and two washers can be composed of high-strength bolts connecting vice. During construction, the structure is temporarily fixed with crude bolts. After the structure is installed and corrected, the crude bolts are replaced with high-strength bolts one by one from the middle of the bolt group. The initial screwing is carried out, and the re-twisting and final screwing is carried out after the initial screwing is carried out in turn. When installing large hexagon head high strength bolts, a washer should be added on each side of the bolt. Initial screwing torque value for the final screwing torque value of 50%, re-screwing torque value is equal to the final screwing torque value, the final screwing torque value formula: Tc = K * Pc * d. Where Tc is for the final screwing torque value, unit N - m; K is for the torque coefficient; Pc is for the construction of the pre-tensioning force, unit kN; d is for the diameter of the thread of high-strength bolts, unit mm. Torque correction should be carried out before each use. Torsion shear high strength bolts, a high strength bolt, a nut, and a washer form a torsion shear high strength bolt connection vice. Torque shear high-strength bolts, a high-strength bolt, a nut, and a washer.

7.3 Torsion and shear type electric wrench, torsion and shear type high strength bolt installation principle, for torsion and shear type high strength bolt connecting sub-installation, should only be in the nut side with a washer. Initial torque value formula: Tc = 0.065 * Pc * d. Where Tc is for the initial torque value, unit N - m; Pc is for pre-tension construction, unit kN is for the high-strength bolts thread diameter, and unit mm. Lastly, use special wrenches will be the end of the plum blossom head screwed off. Quality inspection should focus on supervision and inspection of the construction process.

7.4 Ground anchor bolt, ground anchor bolt alias ground bolt, ground screw, ground wire, etc., used for steel structure column foot and concrete foundation connection components and generally used Q235 and Q345 round steel production. Different kinds of anchor bolts (diameter greater than 24mm should be used in the form of anchor plate), the installation by the steel frame to fix the anchor bolt group, and tied steel cage together with the installation, and then the concrete, the bolt head should be exposed to the concrete surface for a certain length. After the concrete reaches a particular strength, the steel column foot is installed, and finally, the bottom is grouted for the second time.

7.4 Chemical anchor bolt A chemical anchor bolt is a new type of fastening material composed of chemicals and a metal rod body. It is used to install other structural connectors on the completed concrete structure. It can also be used for various steel structures, curtain walls, marble dry hanging construction in the rear, and the installation of buried parts. It can also be used for equipment installation, highway and bridge guardrail installation, building reinforcement, renovation, and other occasions.

7.5 Chemical anchor bolt screw and agent chemical anchor bolt is a new type of anchor bolt after the expansion anchor bolt; it is through the unique chemical adhesive screw cementation fixed in the concrete substrate drilling to realize the fixed parts of the anchor composite parts. Because the chemical anchor bolt has a larger pull-out bearing capacity, it can replace the embedded anchor bar, commonly used in the coating site, where the steel structure embedded parts are installed. Still, the concrete has been poured, and the chemical anchor bolt embedded parts to remedy the situation.

8. The construction steps of chemical anchor bolts are as follows:

1) According to engineering design requirements, professional and technical personnel or on-site tests should determine drilling holes in the base material (such as concrete) in the corresponding position, hole diameter, hole depth, and bolt diameter.

2）Drill the holes with an impact drill or water drill.

3）Clean up the dust in the drilled holes with a particular air cylinder, brush, or compressed air machine; it is recommended to repeat not less than three times; there should be no dust and open water in the holes.

4）Ensure that the surface of the bolt is clean, dry, and free of oil masonry.

5）Confirm that the glass tube anchoring package has no appearance of damage, agent solidification, or other abnormal phenomena; put its round end outward into the anchoring hole and push it to the bottom.

6）Use an electric drill and particular installation fixture to insert the screw into the bottom of the hole with a strong rotation, and should not use the impact method.

7）When rotating to the bottom of the hole or the marked position on the bolt, stop rotating immediately, remove the mounting jig, and avoid disturbing the gel until it is fully cured. Overtime rotation leads to loss of gel, affecting the anchoring force. (Rotation time should not exceed 30 seconds, the rotation speed should not be less than 300 rpm, not greater than 750 rpm, the bolt propulsion speed of about 2 cm/sec, not allowed to use the impact method).

Expansion bolts: The role of expansion bolts is the same as that of chemical anchor bolts, which are used for anchorages with smaller forces. Expansion bolts of different specifications of concrete structures with cracks and parts prone to cracks and expansion bolts shall not be used. At the same time, the main load-bearing structures, critical pipelines and high-speed operation, impact loads, and vibration of the design of the expansion bolts should be calculated according to the design of the tensile force and the design of the design of the shear force of the choice of a large class of specifications.

9. Bolt arrangement and construction requirements: bolt arrangement is divided into two kinds of side-by-side and staggered:

Juxtaposition - simple, neat, compact connecting plate size is small, but the member cross-section weakening;

Staggered - The arrangement is not compact, and the size of the connection plate used is significant, but the weakening of the component cross-section is slight.

Force requirements: vertical force direction: to prevent the bolt stress concentration interaction, cross-section weakening too much and reduce the bearing capacity, bolt side distance and end distance can not be too small;

Shun force direction: to prevent the plate from being pulled off or sheared, the end distance can not be too small;

For pressurized members: to prevent the connection plate from bulging, the middle distance can not be too large.

Constructional requirements: The bolt's side and center distance should not be too considerable to prevent the plate from closing, as moisture invokes steel corrosion.

Construction requirements to facilitate the wrench to tighten the nut, bolts in the distance should not be less than 3do;