What are the three most common types of semi permanent fasteners
The three most common types of semi-permanent fasteners are rivets, cotter pins, and threaded inserts. Rivets can handle up to 50,000 lbs of shear force in aircraft, cotter pins lock nuts in place and withstand over 3,000 Newtons, and threaded inserts offer reusable threads in materials like plastic or wood.
Bolts and nuts
According to the International Standards Organization (ISO), more than 200 billion bolts and nuts are produced worldwide each year, mainly for machinery manufacturing, construction, automotive, furniture and other fields. In the automotive industry, about 1000 to 1500 bolts and nuts of different specifications are used per vehicle, and the bolts used for the connection of the engine and the frame are M10 or M12 specifications, with tensile strength up to 800 MPa, ensuring that the engine remains strong under long working hours and severe vibration.
Bolts used in the construction of steel structures are generally M16 to M24 specifications, and their load-bearing capacity can reach more than 5000 kg. Such bolts are generally made of high-strength carbon steel or alloy steel, and the tensile strength of bolts made of Q345 steel can reach 470 MPa, which is twice the strength of ordinary steel bolts. This type of bolt needs to be treated with a surface such as hot dip galvanizing to prevent corrosion when exposed to the external environment for a long time. The corrosion resistance of hot-dip galvanized bolts can extend their service life to 15-20 years in the Marine environment, significantly more than untreated ordinary bolts.
The price of ordinary carbon steel bolts is 8-10 yuan per kilogram, while the price of high-strength alloy steel bolts is more than 20 yuan per kilogram. The unit price of a carbon steel bolt in the M12 specification is about 1.5 yuan, and the alloy steel bolt is about 3 yuan. In large-scale use, the use of high-strength bolts, although the cost is higher, but its long life and high performance can reduce the user’s subsequent maintenance costs. In the construction of Bridges or power towers, the choice of high-performance bolts and nuts is a very economical and safe choice.
A2 class stainless steel bolts are widely used in highly corrosive environments, such as chemical plants or offshore platforms. The corrosion resistance of A2 stainless steel is much higher than that of ordinary steel, and its service life is about 30 years or more in the Marine environment, while ordinary steel bolts often fail due to rust in this environment in less than 5 years. A4 stainless steel bolts can also be used in more demanding environments, such as high temperatures and strong acids. The tensile strength of A4 stainless steel can reach 700 MPa, and the high temperature resistance is also better than other materials, which can maintain stable mechanical properties at 200 °C.
The optimal tightening torque for standard M10 bolts is usually between 50-60 Nm. If the torque applied is too small, the bolt may not be able to provide sufficient clamping force, and there is a risk of loosening; If the torque is too large, it may damage the thread or overstretch the bolt. In order to ensure the accuracy of fastening, torque wrenches are used for bolt installation in industrial applications. The torque wrench can increase the bolt tightening accuracy to ±10%, while the manual installation error is up to ±30%.
Screws
According to the global market statistics in 2023, the number of screws produced annually exceeds 500 billion, of which about 30% are used in the construction industry, 20% in furniture manufacturing, and 15% in automotive and mechanical equipment. Taking the construction industry as an example, gypsum board screws and wood screws are the two most commonly used types, the length of gypsum board screws is 25mm to 50mm, the standard diameter is 3.5mm to 4.8mm, the price is about 50 yuan per thousand, and the tensile strength of a single screw is 2000-3000 Newtons, which can easily meet the needs of daily home decoration.
Screws used in furniture are between 3mm and 6mm in diameter and 12mm to 50mm in length. Stainless steel screws are suitable for outdoor furniture, can resist corrosion and rust, and its life can reach more than 10 years. Compared with ordinary carbon steel screws, the price of stainless steel screws is higher, the price of ordinary carbon steel wood screws is about 8-12 yuan per kilogram, and the price of stainless steel wood screws can reach 20-25 yuan per kilogram.
The typical car uses more than 400 screws of different sizes, which are used to attach non-load-bearing components, such as the dashboard, seats, and interior panels. The screws for the instrument panel of the car are M5 specifications, 5mm in diameter, 15mm to 20mm in length, and 3-5 Nm (nm) in torque requirements. More than 5Nm of torque may cause the plastic material to crack, while too low a torque may loosen the screws, causing noise and shaking of the instrument panel.
The screws used in smartphones are 1.2mm to 1.8mm in diameter and between 3mm and 6mm in length. An M1.6 screw for mobile phones weighs less than 0.1 grams, but its tensile strength can reach 200 Newtons. The price of this type of screw is about 100 yuan per thousand, although the price of a single screw is not high, but considering that each mobile phone needs to use at least 50 screws, the cumulative screw cost is still an important expense in mobile phone manufacturing. Mobile phone manufacturers often cut costs by buying in bulk, with the price dropping to about 60 yuan per 1,000 units.
The screws used for the connection of the steel structure of the bridge are high-strength screws with a diameter of M20 to M36 and a tensile strength of more than 1200 MPa. Taking M24 specification screws as an example, their diameter is 24 mm, the length is 150 to 300 mm, the weight of a single screw can reach more than 1.5 kg, the tensile force of more than 15,000 kg, and a medium steel structure bridge needs to use more than 200,000 high-strength screws of this specification.
In terms of price, the cost of screws for different materials and uses varies greatly. For example, the price of ordinary carbon steel screws is usually 8-10 yuan per kilogram, while the price of high-strength alloy steel screws reaches more than 20 yuan per kilogram. In addition, the price of stainless steel screws due to its excellent corrosion resistance, generally 30-40 yuan per kilogram.
Pin (e.g. cotter pin, cotter pin)
Cotter pin is one of the most common pin fasteners, widely used in mechanical equipment and vehicle maintenance. Their main function is to prevent the nut or bolt from loosening by inserting the hole and bending the two ends. In industrial machinery, M3 cotter pins are used for fixing small bearings and mechanical components. The diameter of M3 cotter pin is 3 mm, the length is 20-50 mm, and the price of each thousand pieces is between 50 and 100 yuan. Their tensile strength can reach about 2000 Newtons, which is suitable for locking operation of light mechanical equipment.
In automobile manufacturing and maintenance, cotter pins are often used to lock hub nuts to prevent nut loosening due to vibration during driving. Take the common M4 specification cotter pin as an example. It has a diameter of 4 mm and a length of 40 mm. When installing it, it needs to pass through the nut on the axle and bend both ends to lock the nut. According to the force data when the car is driving, the locking force of the hub nut needs to reach more than 3000 Newtons, and the tensile strength of the M4 specification stainless steel cotter pin can reach 3500 newtons, which is enough to cope with the high-speed driving and long-term use of the car. Each car uses about 10-15 cotter pins, the single cost is about 1 yuan, and the service life can reach more than 5 years, which greatly reduces the frequency and cost of car maintenance.
Cotter pin is often used in more heavy machinery and equipment, in the main hook part of a crane, need to use a diameter of 12 mm cotter pin to fix. With a length of more than 100 mm and a tensile strength of up to 12,000 Newtons, the M12 copper can withstand large gravity and vibration. The price of each M12 copper pin is about 20 yuan, although the cost is higher, but its superior strength and up to 10 years of service life, making it an indispensable fastener in large machinery.
In the engine installation system of aircraft, titanium alloy cotter pins and cotter pins of special specifications are often used. The commonly used titanium alloy cotter pin has a diameter of 8 mm and a length of 50 mm, and the tensile strength can reach 8000 Newtons, while the weight is only half of the ordinary steel pin. The cost of each titanium alloy cotter pin is about 100 yuan, although it is more expensive than ordinary materials, but its excellent performance makes it the first choice for the aerospace industry.
In bridge construction, the temporary support structure needs to use cotter pins to fix the key connection points. The open-end pin of the M16 specification has a diameter of 16 mm and a length of 150 mm, and the tensile strength of a single pin can reach more than 15,000 Newtons. In order to ensure the safety of bridge construction, each temporary support point is usually fixed with 2-4 cotter pins and removed or replaced with permanent fixed devices after the construction is completed. The M16 cotter pins cost about RMB30 each and have a service life of up to 20 years, which is enough to cope with long-term construction projects.
