Regarding The "specifications" And "functions" of Fastener Products, You Must Know These Points

Fasteners, as a type of mechanical parts used for fastening connections, are widely used in industry and daily life. Their scope of use spans multiple industries, whether it is various types of machinery, equipment, vehicles, ships, railways, bridges, building structures, tools, instruments, chemical equipment, meters, or even daily necessities. , can be called the most widely used mechanical basic component.

The distinctive feature of fasteners is that their varieties and specifications are extremely complex, and their properties and uses are also different. At the same time, this type of parts has reached a very high level in terms of standardization, serialization and generalization. In view of this, people refer to the part of fasteners that have been incorporated into the national standard system as standard fasteners, or standard parts for short.

Fastener Product Specifications

Parameters that need to be indicated to describe fasteners are:

Product name (standard), specifications, material, strength level, surface treatment. Such as DIN912, M4-0.7x8, SCM435, grade 12.9, black.

◆1. Product name (standard): For screws that do not have standards and are non-standard parts, drawings need to be provided. For example, DIN912, the Chinese name is: hexagon socket cylindrical head screw, this is the product name. However, the most accurate way is to call it the standard, because GB70 also has the same product name; but the two standards have many differences in size.

The most influential standards in the world are: German standards (DIN), international standards (ISO), Chinese national standards (GB), American standards (ANSI), and Japanese standards (JIS).

◆2. Specifications: Generally, the name of the screw is the diameter of the thread * the length of the screw.

Tooth pattern name diameter, commonly used metric systems are: M2, M3, M4, M5, M6, M8, M10, M12, etc.;

Commonly used ones in the United States are: 4#-40, 6#-32, 8#-32, 10#-24, 1/4-20, 5/16-18, 3/8-16, 1/2-13, etc.

The screw length refers to the effective length of the embedded object. For example: the total length of countersunk head screws is loaded, the length of half the head is added to semi-countersunk head screws, and the length of cylindrical head screws does not include the head size.

For example: for specifications, it is best to add the tooth pitch in the full name. For example, M4-0.7x8, the outer diameter of the 4-finger tooth is 4mm, 0.7 means that the distance between the two tooth peaks is 0.7mm, and the effective length of the 8-finger tooth embedded in the object is 8mm.

For the sake of simplicity, the tooth pitch is not written, and the coarse teeth are defaulted to standard teeth because they are the most common; in this way, there is no need to mark them. This is only available in the metric system, and American products still have to mark the tooth pitch.

Here we focus on the specifications of American screws, such as 6#-32*3/8. 6# is the outer diameter of the thread, which is close to 3.5mm; 32 is the 32 threads per inch of thread length (equivalent to the threads of metric screws). distance); 3/8 is the length of the screw (specifically the same as the metric screw).

There are two formulas to remember here: tooth outer diameter A#=(Ax0.013+0.06)x25.4(mm), 1 inch=25.4mm.

Among them, 2#=2.2mm, 4#=2.9mm, 6#=3.5mm, 8#4.2mm and 10#=4.8mm are the data that must be memorized. The number of teeth corresponding to the screws of each specification must also be memorized: 2#-56, 4#-40, 6#-32, 8#-32, 10#-24, 1/4-20, 5/16-18 , 3/8-16, 1/2-13 (American standard teeth).

Note: US-made UNC teeth are standard teeth, and UNF are fine teeth. We default coarse teeth to standard teeth.

◆3. Material: The most common materials include: carbon steel, stainless steel, stainless iron, copper, aluminum, etc.

Carbon steel is divided into low carbon steel (such as C1008/C1010/C1015/C1018/C1022), medium carbon steel (such as C1035), high carbon steel (C1045/C1050), and alloy steel (SCM435/10B21/40Cr).

Generally, C1008 material is used to make ordinary grade products, such as 4.8 grade screws and ordinary grade nuts; C1015 is generally used to make eye screws; C1018 is generally used to make machine screws, and of course it is also used to make self-tapping screws; C1022 is generally used to make self-tapping screws. ; C1035 uses grade 8.8 screws; C1045/10B21/40Cr uses grade 10.9 screws; 40Cr/SCM435 uses grade 12.9 screws.

For stainless steel, SS302/SS304/SS316 are the most common. Of course, a large number of SS201 products are also popular now, and even products with lower nickel content are called non-authentic stainless steel products. They look similar to stainless steel in appearance, but their anti-corrosion properties are very different.

◆4. Strength grade: Strength grade mainly refers to carbon steel fasteners.

Common strength grades of carbon steel screws are: 4.8, 5.8, 6.8, 8.8, 10.9, and 12.9. Nuts are correspondingly: level 4, level 6, level 8, level 10, and level 12.

Generally, screws below grade 8.8 are called ordinary screws, while screws above grade 8.8 (including grade 8.8) are high-strength screws. The difference is that high-strength screws require quenching and tempering heat treatment.

◆5. Surface treatment: Surface treatment is mainly to increase the anti-corrosion performance, and some also take into account the color, so it is mainly for carbon steel products, which generally require surface treatment.

Common surface treatments include: blackening, galvanizing, copper plating, nickel plating, chrome plating, silver plating, gold plating, Dacromet, hot dip galvanizing, etc.;

There are many types of galvanizing, including blue and white zinc, blue zinc, white zinc, yellow zinc, black zinc, green zinc, etc., which are also divided into environmentally friendly and non-environmentally friendly. Each type of plating has a variety of coating thicknesses to meet different needs. Salt spray test effect.

Fastener product functions

1. Functional aspects:

Screw torque requirements: The external hexagonal screws can withstand a relatively large torque, the internal hexagonal screws can bear less torque, and the cross-recessed screws can bear even smaller torques (for this reason, such screws are usually ordinary grade screws).

Assembly of hexagonal bolts: When assembling hexagonal bolts, commonly used tools include adjustable wrenches, torx wrenches and open-end wrenches. Among them, the adjustable wrench is extremely versatile and is suitable for external hexagonal screws with various head specifications. However, its assembly efficiency is low; the torx wrench has the highest assembly efficiency, but its applicable scenarios have certain limitations, because a torx wrench can only It has two heads and can only be used for external hexagonal screws with two sizes of heads; the performance of the open-end wrench is similar to that of the torx wrench, and it can also be used with an extended socket. It should be noted that the smaller the size of the external hexagonal screw, the higher the requirements for the edge accuracy of the external hexagonal bolt. Otherwise, when the wrench is applying force, its head will easily slip. In order to save materials, Wenzhou people invented the external hexagonal cavity. Although the hexagonal screws outside the pocket are lighter in weight and have a thinner head, they are prone to slipping when stressed, and the head may even be screwed off.

Assembly of hexagon socket screws: Hexagon socket screws need to be assembled with an hexagon socket wrench, which requires extremely high accuracy for the hexagon socket holes. If the hole is slightly larger, the wrench will slip easily; if the hole is slightly smaller, the wrench cannot be inserted. The smaller the inner hexagonal size, the higher the accuracy requirements for the hole. For some large-sized hexagon socket screws, as long as one of the opposite sides of the hexagon is qualified, the wrench can be used to assemble normally; but for some extremely small hexagon socket screws, such as M2 hexagon socket set screws, the wrench will be inserted into the hexagon socket. It will easily slip when applying force, so as long as one of the opposite sides is too large, it does not meet the assembly requirements. Therefore, when assembling M2, M2.5, and M3 hexagon socket screws (especially tightening products), the wrench is prone to slipping.

Assembly of cross-recessed screws: Cross-recessed screws are assembled with a screwdriver. Since the assembly force required is not large, its strength can reach level 4.8. Occasionally, for some screws with high strength requirements, the carburizing heat treatment process can meet the requirements.

Suggestions for product matching: When using products together, we usually recommend that the screw grade be one level higher than the nut grade. This matching method is the most economical. For example, grade 8.8 screws can be used with grade 4 nuts, so the next time you replace them, you only have to replace the nuts.

2. Heat treatment

Heat treatment is mainly for carbon steel screws, mainly including quenching and tempering heat treatment and carburizing heat treatment, aiming to meet the requirements for screw strength in different environments.

Quenching and tempering heat treatment: Products with a strength level of 8.8 or above adopt a quenching and tempering heat treatment process. The remarkable feature of this heat treatment method is that the overall hardness of the screw is relatively evenly distributed inside and outside.

When the same material is heat treated, there is a characteristic that the higher the hardness of the material, the worse its toughness tends to be. Therefore, in practical applications, it is necessary to find a safe and reasonable matching point between hardness and toughness to ensure that while meeting the hardness requirements, the toughness of the screw can also be effectively guaranteed to meet various performances in actual use scenarios. need.

Carburizing heat treatment: Self-tapping screws basically require carburizing heat treatment. This treatment method makes the screw have an extremely hard surface and a relatively soft core. This characteristic allows it to penetrate hard iron plates smoothly.

However, self-tapping screws carry higher risks during use. For example, self-tapping screws often break heads. Possible reasons for this problem include: hydrogen embrittlement; twisting due to too high or too low hardness; too deep cross recess; too thin head thickness; head and neck joint; The R angle is not set, which leads to stress concentration; and irregular operating procedures.

3. Risks of hydrogen embrittlement

Generally speaking, for products with a hardness greater than 32HRC, there is a risk of hydrogen embrittlement when electroplating. Therefore, all products with strength levels of 10.9 and above, as well as self-tapping nail products that have undergone carburizing heat treatment, may face the risk of hydrogen embrittlement during the electroplating process.

The so-called hydrogen embrittlement means that during the electroplating process of products, H⁺ enters the interior of the metal and forms bubbles. This will cause the screw to break not immediately when it is used, but to undergo delayed breakage within 24 hours.

For products with a risk of hydrogen embrittlement, they need to be placed in a dehydrogenation furnace within 4 hours after electroplating is completed and kept at 200 degrees Celsius for about 8 hours. This operation is called dehydrogenation treatment.

Hydrogen removal treatment methods can significantly reduce the risk of hydrogen embrittlement, but cannot completely eliminate it. Therefore, when it is necessary to ensure that there is 100% no risk of hydrogen embrittlement, it is strictly prohibited to use electroplated products, and surface treatment processes such as Dacromet and sandblasting should be used instead.

4. Fastener performance and processing technology development direction

While achieving high strength, it ensures excellent toughness and achieves an excellent balance of strength and toughness to meet the stringent requirements for fastener reliability under complex working conditions.

While maintaining the same external dimensions, through innovative materials and optimized structural design, the weight of fasteners is effectively reduced, assisting the process of product lightweighting and reducing the overall load.

On the premise of ensuring that the mechanical strength meets the usage standards, the product structure is refined and improved to achieve miniaturization, thereby saving space and improving space utilization.

On the basis of ensuring stable strength, the toughness is further enhanced, the fastener's ability to withstand dynamic loads and impacts is enhanced, and its service life in harsh environments is improved.

While meeting the appearance quality requirements, advanced surface treatment technology and protective materials are used to significantly enhance the anti-corrosion capabilities of the fasteners, allowing them to work stably and long-term in corrosive environments such as high humidity, strong acids and alkalis.

We are committed to making breakthroughs in the limits of accuracy, continuously improving the level of processing technology, achieving more precise tolerance control, ensuring that the dimensional accuracy and shape accuracy of fasteners reach higher standards, and meeting the high-end manufacturing field's demand for high-precision components.

summary

In summary, the development of fastener performance and processing technology is moving towards multi-dimensional optimization. These development directions not only comply with the modern manufacturing industry's pursuit of high performance, lightweight, miniaturization, long life and high precision, but are also a key force in promoting technological innovation and progress in various industries. With the continuous development of science and technology, we have reason to believe that new technologies and breakthroughs will continue to emerge in the field of fasteners, injecting continuous power into the high-quality development of global industry.