The English word for screw is Screw. The meaning of this word has changed a lot in the past few hundred years. At least in 1725, it meant "mating".
In addition to the knowledge in the name, it took thousands of years for the small screw to be tightened clockwise and loosened counterclockwise from its invention. Why must the screw be tightened clockwise? Plato's friends invented the screw. The six simplest mechanical tools are: screw, inclined plane, lever, pulley, wedge, wheel, and axle. The screw is among the six simple machines, but to put it bluntly, it is just an axis and an inclined plane winding around it. Today, screws have developed standard sizes. The typical way to use a screw is to tighten it by rotating it clockwise (in contrast, loosen it by rotating it counterclockwise). Clockwise tightening is mainly determined by right-handed people. However, since the screws were all made by hand when they were first invented, the fineness of the screws is not consistent, and is often determined by the personal preference of the craftsman. In the mid-16th century, French court engineer Jaques Besson invented a lathe that could cut into screws, and it took 100 years for this technology to be popularized. In 1797, the Englishman Henry Maudsley invented the modern lathe, which significantly improved the fineness of the thread. Despite this, there was still no unified standard for the size and fineness of the screws. This situation changed in 1841. Maudsley's apprentice Joseph Whitworth submitted an article to the Society of Municipal Engineers, calling for the integration of screw models. He made two suggestions: 1. The inclination angle of the screw thread should be 55° as the standard; 2. Regardless of the diameter of the screw, the number of threads per foot should be standardized. Although the screw is small, it required n types of machine tools and n+1 types of tools to make it in the early days. The early screws were not easy to manufacture because their production process "required three types of tools and two types of machine tools." In order to solve the production and manufacturing problems of the British standard, American William Sellers invented a flat-top and flat-heeled thread in 1864. This small change made it only take one tool and machine tool to manufacture the screw. Faster, simpler, and cheaper. The threads of Sellers screws became popular in the United States and soon became the application standard of American railway companies. Characteristics of bolted joints Figure B: Characteristics of bolted joints The main variables in the tightening process: 1) Torque (T): the tightening torque applied, in Newton meters (Nm); 2) Clamping force (F): the actual axial clamping (compression) size between the connecting bodies, in Newtons (N); 3) Friction coefficient (U): the torque coefficient consumed by the bolt head and thread pair; 4) Angle of rotation (A): the thread angle that needs to be rotated to make the bolt produce a certain axial elongation or the connecting part compressed under a certain torque. Bolt calculation animation demonstration↓↓ Already followed Follow Replay Share Like Close Watch more More Exit full screen video loading failed, please refresh the page and try again Error code: 44 Refresh Video details Bolt tightening control method 1. Torque control method Definition: When the tightening torque reaches a certain set control torque, the control method of immediately stopping tightening. Advantages: The control system is simple and direct, and it is easy to use a torque sensor or a high-precision torque wrench to check the quality of tightening. Disadvantages: The control accuracy is not high (the preload error is about ±25%), and the potential of the material cannot be fully utilized. 2. Torque-angle control method Definition: A control method that first tightens the bolt to a small torque, and then starts from this point and tightens it to a specified angle. Advantages: The axial preload accuracy of the bolt is high (±15%), a large axial preload can be obtained, and the value can be concentrated near the average value. Disadvantages: The control system is more complicated, and two parameters, torque and angle, must be measured; and it is not easy for the quality inspection department to find an appropriate method to check the tightening results. 3. Yield point control method Definition: A method of stopping tightening after tightening the bolt to the yield point. Advantages: The tightening accuracy is very high, and the preload error can be controlled within ±8%; but its accuracy mainly depends on the yield strength of the bolt itself. Disadvantages: The tightening process requires dynamic and continuous calculation and judgment of the slope of the torque and angle curves, and the real-time performance and calculation speed of the control system have high requirements.
