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Fastener specification and function articles for fastener basics

Update:04-08-2019
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Fastener Product Basics (Specifications) First, describ […]

Fastener Product Basics (Specifications)

First, describe the parameters that need to be marked for fasteners: product name (standard), specifications, material, strength grade, surface treatment. Such as: DIN912, M4-0.7x8, SCM435, 12.9, black.

1. Product name (standard): Note: For screws without standard, if it is non-standard, you need to provide drawings.

For example, DIN912, the Chinese name is: Hexagon socket head screw, this is the name of the product.

However, the most accurate method is still to call the standard, because GB70 is also the same name; but the two standards have many different sizes.

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

2, specifications, the general screw name is the tooth pattern diameter * screw length.

The horn pattern is commonly used in the metric system: M2, M3, M4, M5, M6, M8, M10, M12, etc.

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

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

For the specification, the full name is best added with the tooth distance. For example, M4-0.7x8, 4 finger outer diameter is 4mm, 0.7 means that the distance between the two tooth peaks is 0.7mm, and 8 means that the effective length of the embedded object is 8mm.

For the sake of simplicity, without writing the tooth pitch, we defaulted the coarse tooth to the standard tooth because it is the most common; this way it is not marked. This is only the metric system, and the American products still have to be marked.

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

The two formulas to be remembered here are: 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, 10#=4.8mm are the data to be memorized. The number of teeth corresponding to each specification screw 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: The US UNC tooth is a standard tooth and the UNF is a fine tooth. We defaulted the coarse teeth to standard teeth.

3, material: material in the most common order: carbon steel, stainless steel, stainless steel, copper, aluminum and so on.

Carbon steel is further 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 materials are all grades, such as 4.8 screws, common grade nuts; C1015 general lifting ring screws; C1018 general machine screws, of course, also used to do self-tapping screws; C1022 is generally used for self-tapping screws ; C1035 hits 8.8 screws; C1045/10B21/40Cr hits 10.9 screws; 40Cr/SCM435 hits 12.9 screws.

Stainless steel is the most common with SS302/SS304/SS316. Of course, a lot of SS201 products are also popular nowadays, even products with lower nickel content. We call them non-authentic stainless steel products; the appearance looks like stainless steel, but the corrosion resistance is quite different.

4. Strength grade: The strength grade mainly refers to carbon steel fasteners.

The common strength grades of carbon steel screws are: 4.8, 5.8, 6.8, 8.8, 10.9, and 12.9. The nuts are correspondingly: 4, 6, 8, 8, and 12.

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

5, surface treatment: surface treatment is mainly to increase the anti-corrosion performance, but also some of the color, so mainly for carbon steel products, generally need to be surface treated.

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, such as blue and white zinc, blue zinc, white zinc, yellow zinc, black zinc, green zinc, etc., and they are also environmentally friendly and environmentally friendly. Each plating has a variety of plating thickness to meet different Salt spray test effect.

Basic knowledge of fastener products (function articles)

First, the functional aspects:

1. Screw Torque Requirements: The torsion force of the hexagonal screw is relatively larger, the torque of the hexagon socket screw is smaller, and the torque of the cross recess is smaller (so the screws are generally ordinary grade screws).

2. Assembling the hexagonal bolts is usually assembled with an adjustable wrench, a wrench and an open end wrench. The adjustable wrench has low assembly efficiency, but it is very versatile. It is suitable for all kinds of head bolts. The wrench has the highest efficiency, but it is not suitable for some occasions. Only one head of a plum wrench can only be used. Two types of head hex screws; the open end wrench is similar to a Phillips wrench, but it can be used with a long sleeve. The smaller the specification of the hex screw, the higher the angular requirement of the hex bolt, otherwise the head will easily slip when subjected to the (wrench) force. In order to save materials, Wenzhou people invented the hexagonal recess. The hex screw of the pocket is light and light, the thickness of the head is thin, the force is easy to slip, and the head may be screwed off.

3. The hexagon socket head cap screws are assembled with an Allen key. The requirements for the hexagon socket are very high. If the hole is larger, the wrench will slip and a small wrench will not be inserted. The smaller the hex specification, the higher the hole requirements. For some large hexagon socket screws, if the inner hexagon is qualified, the wrench can be assembled normally. For some small hexagon socket screws, such as the inner hexagon of the M2, the wrench is inserted into the force. The hex will slip, so a little one is too big to qualify. Therefore, the hexagonal screws of M2, M2.5, and M3 (especially the tightening products) are easy to slip during the assembly process.

4. The Phillips screw is assembled with a screwdriver. It does not need to use too much force, so the strength is only 4.8. Sometimes there are some screws that require high strength, as long as the carburizing heat treatment can be used.

5. In the product supporting use, we generally recommend that the grade of the screw be one level higher than the nut grade, which is the most economical. For example, the 8.8-class screw is used with the 4-level nut; this way, you only need to change the nut for the next replacement.

Second, heat treatment:

The heat treatment is mainly for carbon steel screws, mainly for quenching and tempering heat treatment and carburizing heat treatment to meet the screw strength requirements of different environments.

1. Quenching and tempering heat treatment: The products of grade 8.8 and above are graded and heat treated. This heat treatment is characterized by a uniform hardness inside and outside.

When the same material is heat treated, the higher the hardness, the worse the toughness. Therefore, it is necessary to have a safety match, and the toughness is also guaranteed while satisfying the hardness.

2, carburizing heat treatment: self-tapping screws type screws basically need this treatment, the characteristics are that the surface is very hard, and the core is relatively soft; because it is necessary to attack the hard iron plate.

Self-tapping screws are more risky. For example, self-tapping screws often encounter broken ends. The possible reasons are: 1 hydrogen embrittlement; 2 hardness is too high or too low to cause twisting; 3 cross groove is too deep; 4 head is too thin 5 head-neck joint without R angle causes stress concentration; 6 operation is not standardized;

Third, the risk of hydrogen embrittlement:

1. Under normal circumstances, products with hardness >32HRC have the risk of hydrogen embrittlement. Therefore, all products with a grade above 10.9 (including grade 10.9) and products that have been carburized and heat treated (self-tapping screws) will be exposed to hydrogen embrittlement.

2. Hydrogen embrittlement means that when the product is electroplated, H+ enters the inside of the metal to form bubbles, which causes the screws to be used on the spot, but delayed fracture occurs within 24 hours.

3, the product with hydrogen embrittlement risk within 4 hours after plating, need to be sent to the hydrogen furnace, stored at 200 degrees Celsius for about 8 hours; this is called dehydrogenation.

4, hydrogen embrittlement treatment can greatly reduce the risk of hydrogen embrittlement, but can not be completely avoided, so in the case of the need to ensure 100% no risk of hydrogen embrittlement, the use of electroplating products is strictly prohibited; and the use of Dacromet, sandblasting and other surface treatment processes .

Fourth, fastener performance and processing technology development direction:

1. High strength while ensuring toughness;

2, the same size can make the weight lighter;

3, the mechanical strength can be guaranteed to make the volume smaller;

4, the strength of the guarantee can strengthen the toughness;

5. The anti-corrosion ability can be enhanced under the condition that the appearance is satisfied;

6. Improvement in accuracy limit;

Any of the above existing high processing cost processes, new processes that can achieve the required requirements at relatively low cost, will open up a new atmosphere in our fastener industry.

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