What are fasteners?
Fasteners are a class of mechanical parts that are used for fastening and are widely used. Fasteners, used in a wide range of industries, including energy, electronics, electrical, mechanical, chemical, metallurgy , mold , hydraulic and other industries, in a variety of machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments , chemical, instrumentation and supplies, etc., can see a wide range of fasteners, is the most widely used mechanical basic parts. It is characterized by a wide variety of specifications , different performance uses, and the degree of standardization, serialization, and generalization is also extremely high. Therefore, some types of fasteners with existing national standards are also referred to as standard fasteners , or simply as standard parts.
|Application of Fasteners||Parts of Fasteners|
|Standard of Fasteners||Types of Bolts|
|Type of Nuts||Main Materials|
|Correct selection and use of fasteners||Analysis of China’s Fastener Market|
Fasteners are a class of mechanical parts that are used for fastening connections and are extremely versatile. A wide variety of fasteners can be found on a variety of machinery, equipment, vehicles, ships, railways, bridges, buildings, structures, tools, instruments, meters and supplies. It is characterized by a wide variety of specifications, different performance uses, and the degree of standardization , serialization , and generalization is also extremely high. Therefore, some types of fasteners with existing national standards are also referred to as standard fasteners, or simply as standard parts. Fasteners are the most widely used mechanical foundation. As China joined the WTO in 2001 and entered the ranks of international trade powers. China’s fastener products are exported to the world, and fastener products from all over the world are also pouring into the Chinese market. As one of China’s large import and export products, fasteners are in line with international standards, and it is of great practical significance to promote the Chinese fastener enterprises to the world and promote the full participation of fastener enterprises in international cooperation and competition. Strategic significance. Due to the specifications, dimensions, tolerances , weights, performance, surface conditions, marking methods, and specific requirements for acceptance inspection, marking, and packaging for each specific fastener product.
- Bolt : A type of fastener consisting of a head and a screw (a cylinder with an external thread ) that is to be fitted with a nut for fastening two parts with through holes. This type of connection is called a bolted connection. If the nut is unscrewed from the bolt, it is possible to separate the two parts, so the bolt connection is a detachable connection.
- Stud : A type of fastener that has no head and only has threads on both ends. When connecting, one end must be screwed into the part with the internally threaded hole, the other end is passed through the part with the through hole, and then the nut is screwed, even if the two parts are fastened together in one piece. This type of connection is called a stud connection and is also a detachable connection. It is mainly used for the case where one of the connected parts has a large thickness, requires a compact structure, or is not suitable for bolting due to frequent disassembly.
- Screw : A type of fastener that is also composed of two parts, the head and the screw. It can be divided into three categories according to the purpose: machine screws, set screws and special purpose screws. The machine screw is mainly used for a tightly threaded part and a tight connection with a part with a through hole. No need for a nut fit (this type of connection is called a screw connection and is also a detachable connection; Fitted with a nut for a secure connection between two parts with through holes.) The set screw is primarily used to secure the relative position between the two parts. Special purpose screws such as eyebolts are used for lifting parts.
- Nut : With internal threaded hole, the shape is generally flat hexagonal column shape, but also has a flat square column shape or a flat cylindrical shape. It is matched with bolts, studs or machine screws for fastening two parts to make it One whole.
- Self-tapping screws : Similar to machine screws, but the threads on the screw are dedicated self-tapping screws. It is used to fasten and connect two thin metal members to make them a whole. The components need to be made into small holes in advance. Because of the high hardness, the screws can be directly screwed into the holes of the components, so that the components are Forming a response internal thread .
- Wood screws : also similar to machine screws, but the thread on the screw is a special wood screw thread that can be screwed directly into the wooden component (or part) for a metal (or non-metal) with a through hole. The parts are fastened together with a wooden component. This connection is also a detachable connection. 
- Washer : A type of fastener that is oblate in shape. Between the support surface of the bolt, the screw or the nut and the surface of the connecting part, it increases the contact surface area of the connected part, reduces the pressure per unit area and protects the surface of the connected part from damage; another type of elastic washer, It also acts to prevent the nut from loosening.
Metric screw threads are identified by the capital letter M, followed by the nominal diameter which can be further defined by the thread pitch. If no thread pitch is specified the thread is assumed to be coarse thread.
|Metric Coarse Thread||Metric Fine Thread|
The pitch is the distance from one crest of the thread to the crest of the next thread.
For metric fasteners there are usually 2 pieces of information.
- A manufacturer marking which simply indicated the company that manufactured the fastener.
- The strength class which consists of two numbers separated by a decimal point. Common classes are 4.8, 8.8, 10.9, and 12.9. The number of the left indicates 1% of the tensile strength in MPa, or N/mm2. The number on the right indicates the proportion of the yield strength in relation to the tensile strength.
|Example for Class 12.9|
|Left Digit 12 (Tensile Strength)||Right Digit .9 (Yield Strength)|
|12 x 100 = 1200 MPa = 1200 N/mm2||.9 x 1200 = 1080 MPa = 1080 N/mm2|
Conversion factor for psi = 145
1200 MPa x 145 = 174000 psi
Conversion factor for psi = 145
> 1080 MPa x 145 = 156600 psi
Also known as a “coach” bolt, has a domed or countersunk head. The square section under the head grips into the part being fastened preventing the bolt from turning when the nut is tightened.
Din No ：DIN 603 ,DIN 608
Hex Head Bolts
Hex tap bolts, hex cap screws, trim head hex cap screws, and hex serrated flange bolts fall under this category. They share a hexagonal head and are driven with a wrench. Referred to as both bolts and screws.
DIN NO :DIN 933 ,DIN 931 ,DIN 960 ,DIN 961
Shoulder bolts (also known as shoulder screws or stripper bolts) are machine screws with a shoulder between the thread of the screw and the head of the part. Once installed, the non-threaded portion extends out of the surface of the application site, allowing the bolts to act as dowels or shafts for moving parts. They can be installed by hand or with a socket (allen) driver.
Socket Cap Screws
Socket cap screws are available in button socket, button flange socket head, flat socket, and socket cap. Driven with a socket wrench or a hex allen key. The term socket head cap screw typically refers to a type of threaded fastener whose head diameter is nominally 1.5 times or more than that of the screw shank diameter.
DIN NO :DIN 912
Square Head Bolts
Square Head Bolts have are similar to hex cap screws but with a 4 sided head. This head style allows for a wrench to grip more easily onto the head of the bolt. The head also provides a larger gripping area as compared to a standard 6 sided hexagonal head.
Hex Lag Screws
Lag screws, also called lag bolts, are large wood screws. The head is external hex and are driven with a wrench. Used for lag together lumber for framing, machinery to wood floors, and other heavy duty applications
DIN NO :DIN 571
Wood screws are partially threaded with large cutting threads and a smooth shank. They are designed to slide through the top piece of wood and tightly pull all boards together.
Bolts common hardness index
Bolt hardness indicates the ability of a material to resist the intrusion of a hard object into its surface. It is one of the important performance indicators of metal materials. The higher the general hardness, the better wear resistance. Commonly used hardness index Brinell hardness, Rockwell hardness and Vickers hardness.
Brinell hardness (HB) to a certain load (usually 3000kg) to a certain size (diameter is generally 10mm) hardened steel ball pressed into the surface of the material, to maintain a period of time, to load, the load and its indentation area ratio , That is, Brinell hardness value (HB), in kg / mm2 (N / mm2).
Rockwell Hardness (HR) When HB> 450 or the sample is too small, can not use the Brinell hardness test instead of Rockwell hardness measurement. It is a 120 ° angle of the diamond cone or a diameter of 1.59,3.18mm ball, under pressure in the measured material under pressure, the indentation from the depth of the hardness of the material. According to the hardness of the test material, divided into three different scales to represent:
- HRA: hardness obtained with a 60 kg load and a diamond cone press, for very hard materials (eg cemented carbide, etc.).
- HRB: is the use of 100kg load and diameter 1.58mm hardened steel ball, the hardness obtained for the hardness of the lower materials (such as annealing steel, cast iron, etc.).
- HRC: 150kg load and the use of diamond cone press into the hardness obtained for a high hardness of the material (such as hardened steel, etc.).
Vickers hardness (HV) to 120kg within the load and the vertex angle of 136 ° diamond cone press into the material surface, with the material indentation surface area divided by the load value, that is, the value of Vickers hardness HV). From the above description shows, Vickers hardness is one of the surface hardness. It has a conversion relationship with other hardness units. Expansion bolt hardness refers to the surface hardness, the material is no hardness within the requirements. Only the mechanical properties (tensile strength, yield strength and impact toughness).
Bolt inspection methods
Bolts: mechanical parts, with cylindrical nuts with threaded fasteners. A type of fastener consisting of a head and a screw (cylindrical body with external threads) is to be fitted with a nut for fastening the connection of two parts with through-holes. This type of connection is called bolting. Such as the nut from the bolt on the spin down, and can make the two parts apart, so the bolt connection is a removable connection. Bolt inspection can be divided into two kinds of artificial and machine, the following Chinese fastener network for you respectively detailed.
Artificial is the most primitive is the most common use of consistent detection. In order to minimize the outflow of non-performing goods, the general production staff by visual means of packaging or shipping products to be tested to exclude defective products (including tooth injury, blending, rust, etc.).
The other ways for the machine automatic detection, mainly magnetic particle testing.
Magnetic particle inspection is the use of bolt defects in the magnetic field and magnetic leakage interaction, for the possible existence of bolt defects (such as cracks, slag, mixture, etc.) permeability and steel permeability difference, these materials are not continuous magnetization The magnetic field at the part of the magnetic flux leakage will occur at the surface of the workpiece leakage magnetic field generated to attract the formation of magnetic defects in the formation of magnetic powder defects – magnetic marks in the appropriate light conditions, showing defects in the location and shape, The accumulation of these magnetic powder to observe and explain, has reached the purpose of removing bad products.
How to test bolt?
Bolts :mechanical parts, cylindrical threaded fasteners with nuts.A fastener consisting of two parts of the head and the screw (the cylinder with the external screw) shall be fitted with the nut to tighten the connection of two parts with a pass hole.This form of connection is called bolted connection.If you screw the nut from the bolt, you can separate the two parts, so the bolt connection is a removable connection.Bolt detection can be divided into two kinds: artificial and machine.
Artificial is the most primitive and the most commonly used uniform detection method.In order to minimize the bad product outflow, average production enterprise personnel treat packing or delivery of products by means of visual inspection, to eliminate non-conforming (bad tooth injury, mixing, rust, etc.).
Special head bolts ,SS socket head bolts
Another method is automatic detection of machine, mainly magnetic particle inspection.
Magnetic particle inspection defect of the leakage magnetic field is the use of bolt and the interaction of magnetic powder, bolts for possible defects (such as cracks, slag inclusion, mixing, etc.) permeability and steel permeability difference, these materials after magnetization of the magnetic field discontinuity battery change will occur, forming part of the magnetic flux leak occurs on the surface of work piece leakage magnetic field, so as to attract the magnetic powder form of defect magnetic powder – magnetic mark, under the condition of appropriate lighting, showing defects location and shape, to observe the accumulation of magnetic powder and explanation, has reached to weed out the purpose of the defective product.
Type of Nuts
Used with cotter pins to prevent loosening, a castellated nut, also called a castle or slotted nut, is a not with slots cut into the top. Used in low-torque applications such as holding a wheel bearing in place.
A coupling nut is a threaded fastener used for joining two male threads, most commonly threaded rod. The outside of the fastener is a hex so it can be driven with a wrench.
Flange Serrated Nuts
A flange nut is a nut that has a wide flange at one end which acts as an integrated washer that does not move or spin. The serrated flange distributes the pressure of the nut over the part being secured and creates a locking action to prevent loosening.
Hex Finish Nuts
Hex finish nuts are used for fastening to a hex cap screw, socket cap screw or bolt. The most common nuts, hex finish nuts are hex shaped with internal threads and driven with a wrench.
Hex Jam Nuts
A jam nut is often used when a nut needs to be locked in place without clamping to another object. Hex jam nuts are hex shaped with internal threads, but they are thinner than hex finish nuts.
Heavy Hex Nuts
Larger, heavier, and thicker than a standard hex nut. Heavy hex nuts are hex shaped, internally threaded, and driven with a wrench. Often used with hex cap screws and carriage bolts.
Hex Machine Nuts
A machine nut is hex shaped with internal threads. Smaller than a hex jam or hex finish nut, they are used with machine screws under 1/4″ diameter.
Nylon Hex Jam Nuts
A low profile lock nut is hex shaped, internally threaded with a nylon insert. The nylon material prevents loosening from vibration and cross threads to stop the nut from backing off of the fastener.
A four sided nut that may be flat or beveled on top. Square nuts provide a greater surface contact area which provides more resistance to loosening. Typically mated with square head bolts.
Structural Heavy Hex Nuts
Structural hex nuts are comparable to finish nuts but are made to be thicker and much stronger. They are typically used in steel to steel structural connections.
A t-nut or tee nut is used to fasten wood, particle or composite board leaving a flush surface. A long thin body with a flange at one end resembles a T in profile. T-nuts often have 3 or 4 prongs that sink into the surface providing better retention.
Wing nuts are threaded nuts with wings on each side of the body allowing for manual turning and installation. Easy hand assembly and used when the nut needs to be removed often.
Standard parts on the market mainly carbon steel, stainless steel, copper three kinds of materials.
(A) Carbon Steel Carbon steel carbon steel content to distinguish between low carbon steel, carbon steel and high carbon steel and alloy steel.
- Low carbon steel C% ≤ 0.25% Domestic commonly known as A3 steel. Abroad, basically called 1008,1015,1018,1022 and so on. Mainly used for 4.8 bolts and 4 nuts, small screws and other products without hardness requirements. (Note: Drill tail nail is mainly made of 1022 material.)
- Medium carbon steel 0.25%.
- High carbon steel C%> 0.45%. Currently not used on the market.
- Alloy steel: adding alloying elements in the plain carbon steel to increase some of the special properties of steel: such as 35,40 chromium molybdenum, SCM435,10B3
(B) Stainless steel Performance Level: 45,50,60,70,80.
The main sub austenite (18% Cr, 8% Ni) good heat resistance, corrosion resistance, good solderability. A1, A2, A4. Martensite, 13% Cr Corrosion resistance is poor, high strength, good wear resistance. C1, C2, C4 ferritic stainless steel. 18% Cr upsetability is better, corrosion resistance stronger than martensite. Currently imported materials on the market are mainly Japanese products. Mainly by grade SUS302, SUS304, SUS316.
(C) Copper commonly used materials for brass, zinc-copper alloy. The main market with H62, H65, H68 copper standard parts.
Bolt and nut matching
Bolts generally require the use of a nut. So when we choose a nut, how do we choose the matching of the bolt and the nut?
The matching of the bolt and the nut is firstly corresponding to the model, which means that the bolt of the M6 should correspond to the nut of the M6. The bolt indicates that the specification is usually the diameter and the length together, and the nut generally only refers to the diameter, that is to say the bolt of the hexagonal head. It is M6X20, the nut is M6; the flange bolt M8X20, the nut M8. If it is a fine or special threaded nut, the pitch is to be indicated, and the pitch is not the standard pitch.
Locking or seizure often occurs on fasteners made of stainless steel, aluminum alloy and titanium alloy. These metal alloys have anti-corrosion properties, which will cause a thin oxide layer on the metal surface to prevent the surface from being damaged. Further rust. When the stainless steel fasteners are locked, the pressure and heat generated between the teeth will damage the oxide layer, causing blockage or shearing between the metal threads, and then sticking. When this phenomenon continues, the stainless steel fasteners will be completely locked and will no longer be able to be removed or remain locked. Usually a series of blocking_clip_adhesive_locking actions occur in just a few seconds, so correct understanding of the use of such fasteners can prevent this phenomenon.
1. Correct selection of fasteners
- A. Before using, confirm whether the mechanical properties of the product can meet the requirements of use, such as the tensile strength of the screw and the guaranteed load of the nut. The length of the screw should be properly selected to tighten the nut and expose the nut 1-2 teeth.
- B. Check if the thread is rough before use, if there is iron filings or dirt between the threads, these things often lead to locking.
- C. Lubricate the fasteners before use. It is recommended to use butter, molybdenum disulfide, mica, graphite or talc for lubrication. Generally, it is treated with dipping wax to prevent lubrication.
2. Correct use of fasteners
- A. The speed of the screwing should be appropriate. Don’t oversize too much. Use a torque wrench or a socket wrench as much as possible to avoid using a spanner wrench or an electric wrench. Too fast will cause the temperature to rise rapidly and cause lockup.
- B. The direction of the force, the nut must be screwed perpendicular to the axis of the screw. c. The use of gaskets can effectively prevent the problem of over-tightening.
How to deal with fastener burrs?
Fastener burr refers to the very tiny microscopic metal particles on the surface of fasteners, the particles we have become burr.
How fastener glitches occur when fasteners are cut, ground, milled, and other similar chips are formed. In order to improve the serviceability and service life of fasteners, it is necessary to remove the fastener burrs before using the fasteners. Fasteners are the most commonly used parts on mechanical equipment, but also important parts, so the surface, acute angle and edge are required to achieve high metal cleanliness. The main ways to remove burrs are: traditional mechanical processes, grinding, polishing and other processes with different degrees of automation.
A chemical process can also be used to remove the fastener burr so that the quality of the fastener can be better protected by soaking all the fasteners in succession in multiple containers, one of which contains a Cullygrat solution. Through a simple soaking will be able to remove all burrs, the workpiece surface smooth, smooth edges and corners, to bring users unprecedented high quality. Chemical deburring with Cullygrat is not only environmentally friendly but also saves a lot of production and personnel costs.
In recent years, China’s fastener overcapacity and raw materials soared, the survival of the fittest, and innovation, is a sign of the healthy development of the industry. Along with overcapacity and product saturation, cold-rolled steel wire rods continue to rise. In fact, the direction of raw materials is the influence of the international environment.
The fastener industry is an industry that relies on raw materials, and rising raw materials will naturally increase the cost of fastener production. In the current situation, fastener companies should timely adjust product mix, control investment scale, and reduce non-productive expenses, which is undoubtedly positive. Luo Baihui, secretary general of the International Association of Mould & Hardware Plastics Industry Suppliers, believes that the main reason for the steady increase in the price of raw materials in China is to control the production capacity of the steel industry, so that the relationship between supply and demand tends to ease, the state strengthens the macro-control of the steel industry, and the steel market ranks.
Secondly, the decline in steel imports and the increase in exports are conducive to price stability. Once again, market confidence has recovered, operators and production customers are optimistic about market demand, and dare to purchase and open positions.
In recent years, China’s fastener demand growth rate is 5%-10%, and the demand for fasteners in 2008 was 3.13 million tons, an increase of 9.5% year-on-year, of which the automobile industry is the largest user, followed by the maintenance industry market and the construction industry. Then there is the electronics industry. In order to stimulate domestic demand, the state has introduced a number of supportive manufacturing policies. In the government’s 4 trillion yuan investment plan, the key investment targets are railways, highways, airports, power grids, and affordable housing infrastructure. Luo Baihui believes that the most direct benefit is Equipment manufacturing, which will greatly stimulate the demand for fasteners. In particular, the demand for high-strength fasteners of 16-30mm size ≥10.9 will increase sharply. In addition, the development of aviation industry has also played a strong supporting role in fasteners. For example, Boeing plans to add 3,400 aircraft in the next 20 plans. This data will bring new development and demand opportunities to the fastener industry.
Since China’s fastener industry is spontaneously formed, it must have its own unique characteristics: First, its scale is small. With its flexible operation mode, the fastener enterprises quickly adapt to the ever-changing market demand and have developed rapidly. Second, the number is large. At present, there are more than 2,200 companies in the family workshop or husband and wife shop and small processing stalls. This is an incomparable number in any region, forming a huge industrial cluster. The third is the whole class. From the most primitive processing methods to advanced multi-station cold heading machines, from red to heat treatment and quenching and tempering automatic production lines, the fastener industry covers almost all products and processes of the entire industry. Fourth, the cost is low. All production plants are private enterprises. The business owners are both factory directors and technicians, salesmen, and the monthly salary of first-line workers is between 500 and 800 yuan. Enterprises from the management mechanism and cost accounting are unmatched by coastal enterprises.
After long-term development of fasteners, it has certain industrial foundation and advantages. The variety of fasteners, the fastener market includes most of the fastener products, thousands of varieties of various specifications and models. A market can purchase all the needs. The price is excellent, and the fasteners are famous all over the country for their low price. The production enterprises are all private enterprises, with low cost and flexible operation methods, which makes Yongnian fasteners have great competitiveness. The network is wide, there are tens of thousands of sales outlets, and the sales force is spread all over the country. Almost all the county-level listed towns in the country have Yongnian fastener operation points. Functionality, the fastener market includes logistics and distribution, catering, accommodation, finance, post and telecommunications, communication, convenient purchase, fast delivery.
A few days ago, the EU issued an official announcement to initiate an anti-circumvention investigation of China’s re-exported fastener products exported from Malaysia. According to the EU, since the anti-dumping measures against Chinese fasteners, the number of Chinese products that have been transferred to the EU market through Malaysia has increased and continued to be dumped at a low price, which has seriously weakened the effectiveness of the current anti-dumping measures.
In the past, Malaysia exported fewer fasteners to the EU. In recent years, there were five or six large-scale enterprises in China that set up factories in Malaysia and exported them to the EU through their ports, which increased the local exports to the EU by two to three times. The attention of the EU. In fact, the EU has a great demand for fasteners originating in China, and it is a blessing for Chinese companies to export their products to the EU.
The EU has recently conducted a survey of a number of related companies, including companies that have established factories in the area. Whether the product can obtain the “ID card” originating in Malaysia depends on whether the added value realized in the assembly process in Malaysia exceeds 25% of the production cost.
If the EU ruled that Chinese companies have anti-circumvention facts, they will impose the same anti-dumping duties and even punitive tariffs on similar products imported from Malaysia. If there is indeed a entrepot trade, it is also hoped that through negotiation and other means, some enterprises may not understand the local laws and trade rules. If you really set up a factory in the local area, there should be no problem. There is a company in Jiaxing that is produced in Malaysia, but the amount is small. At present, all countries are eyeing us. Although the company is still alive, it is very difficult to live. Going overseas to set up a factory can be regarded as the best way to avoid trade risks.
Today, when competition is so cruel, it is not an easy task for foreign trade-oriented enterprises to switch to the domestic market. This difficulty is not only caused by its inherent internal thinking, but also by the intensification of external competition and market changes. Export enterprise
In order to successfully expand in the domestic market, we must strengthen the construction of the marketing management system and enhance the marketing execution ability on the basis of giving full play to the advantages of our products, so that our quality products can be accepted by the domestic market. Build a sales channel, improve the R&D level and forge a superior domestic sales team, and then fully build a customer’s domestic sales operation platform.
Source: China Fasteners Manufacturer – Yaang Pipe Industry (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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