Easy and low cost.
The detachable connection of machine parts has various methods such as pin coupling, wedge coupling, threaded coupling, key and keyless coupling, among which the threaded coupling application is quite extensive. At present, there are two kinds of common thread standards used in countries around the world. In addition to the standard metric thread standard issued by China in accordance with the ISO standard, the world's major industrial countries such as the United Kingdom, the United States and the United States also use the metric system and the British standard thread standard.
Recently, when an enterprise repairs and maintains imported textile equipment, it is necessary to purchase or process a small number of inch-sized hexagonal hexagon socket head cap screws (thread 0.3125-18UNC-2A, see) due to damage to the original screws. The inch-type hexagon socket head cap screws in China are non-standard parts, which are generally not available for purchase and can only be processed. Since the quantity of demand is too small to be customized by the standard parts factory, the time is not economical. To this end we have envisaged a method of making an inch cylindrical socket head cap screw.
The technical problem of self-made screws is mainly the precision of the uniform thread and the shape and performance of the hexagonal hexagon socket. Refer to the English Unified Thread Manual (see Table 1). The accuracy grade 2A is the most commonly used standard thread for general purpose screws. The tolerance of the outer diameter of the external thread is 0.102mm (0.0040), which is equivalent to the level 5 of the thread precision class in China. Secondly, the shape and performance of the hexagonal head hexagon socket, with reference to China's standard, the hexagonal head hexagonal screw performance grade is 8.8 (GB70.1-2000 standard) material is medium carbon steel, fire and tempering, hardness 2232HRC, surface oxidation treatment . The experimental plant of the School of Mechanical and Electrical Engineering of Suzhou University is small in scale. If it is for a small amount of inch screw forging processing and then processing thread after heat treatment, the quality of the nail is not allowed to be guaranteed during the high cost period.
Table 1 British uniform thread parameters. h Nominal size and number of teeth per inch Thread series code External thread level Capacitance Large diameter limit Medium diameter limit Small diameter Maximum minimum and maximum minimum tolerance After research, we have envisaged a method of making English uniform threaded screws, that is, buying a small amount of M8x60 Standard cylindrical hexagon socket head cap screws (the screw thread length does not exceed L.=30mm), first use the turning tool to cut the thread part on the lathe to ensure the axial length of the cylindrical part is L=30mm, according to the maximum limit of the thread diameter in Table 1. Dimensions 7.907mm (0.3113"), minimum limit size 7.686 mm (0.3026" boring thread OD end face chamfer 1x45 ° and then turn the inch thread on the lathe or use the threaded chuck on the lathe tailstock (mounting thread 5 / The 16" die tool is galvanized and inch threaded to ensure L0=25mm. In the actual machining, we used the latter threaded chuck to cut the thread. Since the purchased screw material and heat treatment have met the requirements, only the processed inch screw surface will be processed. Oxidation treatment (blackening treatment) can be used.
The above method for manufacturing the inch-type hexagon socket head cap screws eliminates the steps of forging and heat treatment, and the end hexagonal shape of the original standard screw is only simple for cutting and processing the inch thread, the production time is short, the quality is good, and the cost is low. The actual use effect is ideal and meets the needs of use.
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