As we all know, only through nuts can the various parts and components be connected and fastened to constitute the host. However, in the host design process, some designs often focus on the structure, function, life, or operating rate of the mechanical equipment, and the connection and nut selection issues are not considered until the end. This may be a thing in the past, but this kind of thing does not need to exist. This type selection method was gradually attracted people's attention only after many mechanical and personal accidents occurred.
In the actual application selection, it is very important to choose the appropriate nut variety specification, accuracy and level. This is the experience gained at the expense of predecessors' life and blood.
When selecting nuts, first choose from the national standard varieties and specifications, and then choose in the industry. As a last resort, design according to the special needs of the host. Among the requirements, anti-loosening and anti-breaking are the two main considerations.
In the 1980s in Michigan, a local newspaper published a message saying that there are about 3 to 4 car out-of-controls in the state each week, causing casualties. It is suspected that these drivers were asleep or drunk. Later, after they had driven, the mechanical parts of the car were inspected, and it was found that 80% of the nuts were loose, including: bolts and nuts on the front suspension, rear suspension, and shock absorbers, and these devices are crucial to the control of the car. important. The report also pointed out that bolts and nuts are also loose on mechanical parts such as transmissions, differential systems, engine rocker covers, catalytic converters, and metal body members. In 1986, a passenger plane crashed in the rear of the tail section and caused 532 deaths. Later, an investigation was conducted on the same aircraft tails in various countries, and it was found that the nuts were loose and the bolts were broken. The strain at the tail of the aircraft exceeded the tightening force the nut could withstand. Second, internal displacements between the flanks of the engagement thread were also found.
Loosening of nuts is a common problem. There is only one nut for a pair of scissors. If it is loose, it can only be used if it is tightened. However, a large aircraft may have 300,000 nuts.
Industrial people in industrialized countries have realized that no problem is more troublesome to the industry than nuts, and no matter which problem is more important than solving the nut problem, this is their personal experience. Therefore, there is a "how to choose" nut that is safe, suitable and economical.
One. Selection according to different characteristics of nuts
Nuts are used in all areas of the national economy. According to the different uses of the nuts and the host, the application forms are also different. The following table summarizes the types and characteristics of general nuts.
There are many types of nuts and different characteristics. There are many specialized manufacturers. First of all, we must understand the domestic nut production and quality, such as the variety and specifications of nuts produced and the special uses of various products, such as stainless steel nuts, flange nuts, etc. They are used in many places, as well as mini-products, national-quality products, and brand-name new products or new, excellent, and special products of key enterprises. These products should be selected at the same time as the name, excellent new, and special nut products.
Second, the selection should be based on the applicable saving principle
Selection should be based on the characteristics of the nut. Nuts are small, but they are diverse. There are twelve major categories and more than 400 varieties according to major categories. There are nearly 100 varieties in 32 subcategories of bolts and screws alone. There are also 10 types of end types of rods class. Such a huge member of the nut family cannot be described one by one, and the selection should be based on the principle of economy. Now, the type of head is used as an example.
1. Hexagon nuts, such products are also equipped with a table, a hole, a boss, and a flange face. This kind of product does not have high mechanical properties, which is convenient for wrench tightening and can be applied with large tightening. The torque is widely used. The bearing surface has a convex or flange surface, which has the role of a washer, increases the pressure bearing surface, and has good anti-loosening performance. It can be used for the connection of steel structural parts and important host structures.
2. The square nut has a large head area, which is convenient for the wrench to tighten and rotate. It can apply a large tightening torque and is not easy to be bald. It is mostly used on relatively thick and frequently disassembled structures, but it is not suitable for moving parts.
3. Cover nut, head size, head slot, etc., is convenient for tool screwing, mostly used for products with low strength and low torque, generally used for small size host products such as household appliances. Below MIO, more than M6.