1. first understand the bolt, a brief introduction to the next bolt bolt:

mechanical parts,Nutof cylindrical threaded fasteners. A type of fastener consisting of a head and a screw (a cylinder with external threads) must be matched with a nut to fasten and connect two parts with through holes.

There are various types of bolts.
According to the stress mode of connection, there are common bolts and bolts for reaming holes. According to the shape of the head: hexagonal head, round head, square head, countersunk head and so on. According to the length of the thread, it is divided into two categories: full thread and non-full thread.

According to the thread tooth type, it is divided into coarse tooth and fine tooth. The coarse tooth type is not displayed in the mark of the bolt. Bolts are divided into eight grades according to their performance grade: 3.6, 4.8, 5.6, 5.8, 8.8, 9.8, 10.9 and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low carbon alloy steel or medium carbon steel and are heat treated (quenched and tempered). They are commonly known as high-strength bolts, and those below grade 8.8 (excluding grade 8.8) are commonly known as ordinary bolts. Ordinary bolts can be divided into three grades A, B and C according to the production accuracy. Grade A and B are refined bolts and Grade C is crude bolts. For steel structure with connecting bolts, unless otherwise specified, generally for ordinary crude grade C bolts. Of course, there are other special-shaped bolts and special purpose bolts, which will not be introduced. Let's take grade 10.9 high-strength bolts as an example to talk about bolts.

2. you want to make a bolt, you need to design a bolt first.

If you want to do a good job in something, you must first define its characteristic requirements. Here is the technical requirements. How to define the technical requirements is actually quite rare. You must know the connection between the functional requirements and the technical requirements. The technical requirements come from the functional requirements, and the functional requirements come from the requirements of the user or the use environment or other external conditions. Functional requirements analysis can be analyzed using quality function deployment (also known as quality house) techniques, which are not described here.

How can the functional requirements be converted into technical requirements? This requires a certain amount of technical accumulation. To give two simple examples, if you want the bolt to have better fatigue resistance, you must reasonably design the transition fillet of the bolt head, the fillet of the bolt root, the transition between the thread and the screw, and then reflect the designed information on the design drawings or in the technical requirements. For another example, in practical application, bolts are required not to be corroded for a long time in a relatively vicious corrosive environment. You need to select appropriate surface treatment or bolt materials to meet the requirements of the application environment according to the corresponding standards in the corrosive environment. In addition, the performance level of bolts, thread tolerance level, dimensional accuracy level, surface treatment method and so on are all factors to be considered in the design, and even the sequence of some processes needs to be defined in the design (such as thread rolling and tempering treatment, which has a certain influence on the fatigue strength of threads after the sequence is reversed).

Three, to make the bolt to meet the application needs, the material needs to be selected

In fact, when designing bolts, the materials should have been selected. I say it again here separately because the author thinks that the materials are really important. Most bolts are ordinary carbon steel or alloy steel, which is a common situation. However, bolts may be used in highly corrosive environments or environments with large temperature changes, or extreme temperature environments, so ordinary carbon steel or alloy steel is not suitable, for example, ordinary carbon steel materials will become brittle under extreme low temperature conditions, and it is easy to produce brittle fracture without warning. If it is applied to high temperature environment, ordinary carbon steel will produce creep, that is, in the case of thread is not loose, the bolt preload will be reduced, easy to produce loose or fatigue failure.

In addition, some bolts also require high creep resistance, good stress corrosion resistance, oxidation resistance and low notch sensitivity.