There are countless standard parts on the market, if you want to buy standard screws, there will be standard screws. Let's talk about screw standard parts first. Screws are usually called in the industry. Screws usually include screws and bolts. There are many standards in the general market: DIN912 (GB70-85) hexagon socket screws. Its minimum size can reach M2 (the screw diameter and thread length are not limited). For example: M2.5 M3 M4 M5 M6 M8 M10 M12 M14, etc. (the length is not limited).
What is the specification of the standard screw? It consists of the thread (the distance between the thread and the thread), the diameter of the threaded rod and the length of the threaded rod of the screw (excluding the head). Let us take the above standard part data as an example. For example: the minimum specification M2, its professional standard name is: M2-0.4X5 (0.4 is the pitch, M2 is the length of the screw, and 5 is the diameter of the screw). The materials of general standard parts are: 4.8, 8.8, 10.9, 12.9, etc. There are also stainless steel, S04 S16 and so on.
Note on the use of standard parts: stainless steel and carbon steel are essentially different. Stainless steel has good ductility. Improper use can cause the screws and nuts to loosen. Commonly referred to as "lockout" or "bite". The improvement of locking can be considered from the following aspects:
1. Correctly choose standard parts:
(1) Before use, confirm whether the mechanical properties of the product meet the requirements (such as the safety load and tensile strength of bolts and nuts);
(2) The length of the bolt should be selected appropriately, and the 1-2 pitch of the nut exposed after tightening shall prevail.
2. Reduce the friction coefficient of standard parts:
(1) The thread must be kept clean;
(2) Add lubricants (such as butter, 40# engine oil) appropriately before use.
3. Correct operation method of standard parts:
(1) The nut must be tightened perpendicular to the axis of the screw and cannot be tilted;
(2) During the tightening process, the force must be applied evenly, and the force must not exceed the safe torque value (with a safe torque meter);
(3) Use socket wrenches or torque wrenches as much as possible, and avoid using electric wrenches or adjustable wrenches;
(4) It must be cooled when used at high temperature. Do not rotate it quickly during use, otherwise the temperature will rise rapidly and cause lock-up (such as electric wrenches, etc.).
4. Reference table of safety torque for standard parts:
(1) Equipment used: torque wrench, vise, matching sleeve:
(2) Performance level of screws and nuts; A2-70, 304 material, tensile strength: 700N/mm², drop strength: 450 N/mm²;
(3) Operation mode: Clamp the screw head vertically on the bench vise, clamp the workpiece, flat washer and spring washer in the middle, and tighten the nut evenly. The force on the nut is as follows: After setting this value, the nut can no longer be screwed out smoothly.
(4) Standard safety torque table: unit: Nm size M20-2.5 M18-2.5 M16-2.0 M14-2.0 M12-1.75 safe torque 220 180 150 100 55 size M10-1.5 M8-1.25 M6-1.0 safe torque 40 40 9.
What is the difference between high-strength nuts and general nuts, in fact, you only need to understand their standards and other characteristics to easily distinguish them. The so-called high-strength nut is a special bolt with high strength and high fatigue resistance used in special equipment or engineering. Of course, generally high-strength nuts are used with high-strength bolts to achieve better application. We generally see that many bolts with M heads in the market are ordinary nuts, not high-strength nuts. The calibration side of the general hexagonal head nut is the following pattern M30, and M30 indicates the thread standard, that is, the inner diameter of the thread is 30mm. Grade 10 indicates the functional grade of the bolt, and tZn is the surface treatment method. Other types of bolts also have their own expressions, but generally threaded bolts have to use the original functional grade of "M": The functional level of the nut is divided into 3, 4, 4, 5, 5.8, 6...
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