What is the tolerance range of precision screws?
What is the tolerance range of precision screws?
The cylindrical pin is mainly used for positioning and can also be used for connection. It is fixed in the pin hole by means of interference fit. Cylindrical pins used for positioning are usually not subject to load or a small load, the number is not less than two, distributed in the symmetrical direction of the overall structure of the connected parts, the farther the better, the pin is in each connected part The length is about 1-2 times the minor diameter. Cylindrical pins can also be used as shafts, and a straight shaft can also be used as cylindrical pins or even centering pins. So what's the difference between a shaft and a pin? The shaft can be used to transmit torque, bear bending moment and torque, and the cylindrical pin can be used for positioning, bear extrusion force and shear force. In a sense (such as small equipment), cylindrical pins can also be used as shafts.
At present, the electrical control boxes of the market regulators all include a box body with built-in circuit board components and a box cover that is fastened together with it. The box cover is mostly fastened on the box body by self-supplied screws. The following problems are: First, there are many electric control lines on the circuit board in the box. When installing the self-supplied screws, the electric control lines may be damaged, which may easily cause a short circuit of the electric control, which is a potential safety hazard; Electric batch and other tools are inconvenient to install and disassemble, and the production cost is high.
An embodiment of Guangdong Yueluo Hardware Industry Co., Ltd. provides a screw slotting device, as shown in Figure 1, which includes a workbench 1, a vibrating plate 2 is arranged on the upper part of the workbench 1, and a conveying device 3 is arranged on the vibrating plate 2. Below the discharge port, the slotting device 4 is arranged on one side of the conveying device 3, and the slotting device 4 is provided with a reciprocating cutting wheel 42 that can slot the screws in the conveying device 3 when it extends out. The device 4 is also fixedly provided with a fixed wheel 48 for grinding the grooved screws. Using the screw slotting device, the screws can be automatically sorted by the vibrating plate 2, which improves the production efficiency. The reciprocating motion of the cutting wheel 42 can greatly reduce the probability of knife breakage. Sanding, fixes burrs and roughness.
Self-tapping screws were introduced into the industry in large numbers in 1914. The earliest design (essentially imitating a wood screw) was a thread-forming screw made of hardened steel with an A-ended end, mainly used to connect sheet metal channels for heating and ventilation systems. Therefore, it is also called: sheet metal screw. By the end of the 1920s, with the widening of the market and new applications, emphasizing new designs, its application performance was widely improved. The following introduces the four different stages of the development of self-tapping screws in 40 years: thread forming self-tapping screws, thread cutting self-tapping screws, thread rolling self-tapping screws and self-drilling self-tapping screws. 1. Ordinary self-tapping screws (thread forming self-tapping screws) Ordinary self-tapping screws are a direct product of early sheet metal screws. The principle is: when screwing it into a prefabricated hole, the internal thread connected to the screw is formed by the displacement of the material around the hole and the material is pushed into the space between the threads. 2. Self-cutting self-tapping screws (thread cutting self-tapping screws) Because ordinary self-tapping screws are formed only in very thin threads. And it can be easily realized on materials with good toughness. Develop and expand the use of self-tapping screws to thicker sections and harder, brittle and other materials with poor deformability. In this way, the self-cutting self-tapping screw is developed: a cutting groove or cutting edge is machined at the end of the screw shank. When this kind of screw is screwed into the prefabricated hole, the screw acts as a tap and actually cuts out the thread that connects with itself. 3. Self-Extrusion Self-Tapping Screws (Thread Rolled Self-Tapping Screws) In the early 1950s, fastener engineers began to recognize the potential advantages of self-tapping screws as structural rather than just lightly loaded attachments. This has led to the development of a new self-tapping screw thread rolling self-tapping screw (self-extrusion self-tapping screw). According to the design principle of cold forging taps, the thread and end are specially designed for this kind of screw, so that the screw can be formed by applying intermittent and periodic pressure on the crest of its thread instead of on the side of the entire thread. Internal thread for connection. By concentrating and limiting the forming pressure, the pressurized material next to the hole is made to flow more easily and to better fill (squeeze) into the flanks and roots of the thread of the self-tapping screw. Since the frictional resistance of screwing in is much lower than that of ordinary self-tapping screws, threaded rolling self-tapping screws (self-extrusion self-tapping screws) can be screwed into thicker sections. At the same time, it has better screw control and tightening torque, and greatly improves the connection strength and overall firmness. The engineering standard of this kind of self-tapping screw stipulates that the selection of materials, the mechanical properties of heat treatment and the working performance should be strictly controlled. 4. Self-drilling and self-tapping screws (self-drilling screws) People have done statistics: Among the ten expenses that constitute the total assembly cost, the highest one includes the processing of holes. In practical applications of self-tapping screws, prefabricated holes need to be processed. Moreover, in order to make the prefabricated holes have good effect in practical application, the size of these holes must be controlled within a fairly strict range. In the early 1960s, self-drilling and self-tapping screws appeared. A major step forward in reducing assembly costs by eliminating the need to machine prefabricated holes. In general, self-drilling and self-tapping screws realize drilling, tapping and tightening in one operation. These are the four main stages of self-tapping screw design and development. In addition, two newly developed products are also worthy of introduction. Both are screws with a special thread type. One is designed for plastic and other low-strength materials; the other is used in the construction industry to connect cement wall panels, so it is also called wall panel self-tapping screws.
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