The zero displacement design and the selection of the displacement coefficient are fixed because the center distance of the pair of gears used on the machine is fixed, and only the zero displacement design can be used. There are various methods for selecting the coefficient of displacement, such as the "line position" method, the German standard DIN3992, the British standard BS.PD6457 and the Swiss standard VSM15525. In the "Mechanical Engineering Handbook", "Gear Handbook" and other books, the main recommendation is the "line position" method proposed by Wang Zhixing in the late 1970s. This method is superior to other methods.
The check of the contact strength still only considers the situation of the large gear. In the calculation formula of the contact stress ÏƒH, only the coincidence degree Îµ changes due to the change of the displacement coefficient, thereby causing a change in the coincidence coefficient ZÎµ, while other parameters remain unchanged. Similarly, in order to simplify the calibration process, a relatively comparative method can be used: from ÏƒHZÎµ, ÏƒH can be obtained / before ÏƒH = 1.02. That is, the contact strength of the gear remains substantially unchanged after the displacement.
Gear tooth tip thickness check In the gear transmission design, in order to ensure sufficient strength of the tooth top, the tooth top thickness Saâ‰¥(0.15-0.4)m (m is the modulus of the gear), standard gear and negative displacement gear The thickness of the tooth tip can always meet this requirement. Zhang Yuegang et al.  proved that the thickness of the tooth tip of the positive displacement gear must be small. Therefore, it is necessary to check the thickness of the tip of the positive displacement gear. According to the calculation formula of the tooth thickness on any circumference, where: Sk is the tooth thickness on the circumference of radius rk; S is the tooth tooth index circle tooth thickness; rk is the radius of any circumference of the gear teeth; r is the gear index circle Radius; Î±k is the circumferential pressure angle of radius rk. It is calculated that the pinion of the pinion has a Sa=9.03mm, which is equivalent to 0.645m (m is the modulus of the gear), which fully meets the requirements.
The effect and summary of the outer diameter of the displacement gear wheel blank should vary with the amount of displacement. When the displacement is positive, the outer diameter of the wheel blank is equal to the outer diameter of the standard gear wheel blank plus twice the displacement; The bit is subtracted. When the tooth height coefficient h* remains unchanged (h*=1), the change of the outer diameter of the tooth tooth just offsets the displacement amount, and the relative positional relationship between the tool and the outer circle of the wheel blank is the same as when machining the standard gear. Therefore, The standard gear can be used to machine the displacement gear without the use of non-standard tools.
After the pair of gears are assembled, the distance between the tooth surfaces is 0.200.25mm and the pitch of the tooth tips is 3.5mm, which meets the design requirements. The gears are meshed normally during the test run, and there is no impact during operation. In the past two years, The equipment is in good condition. If you replace the original pair of new gears, the cost of accessories will be 35,000 yuan, the freight and travel expenses will be about 10,000 yuan, a total of 45,000 yuan, and the method of using the displacement design will cost only 8,000 yuan to save the enterprise. A certain amount of money. The maintenance was planned in advance, specially arranged in the secondary maintenance period of the annual production line, and the external processing did not take extra time.
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