Design criteria and calculation process of double circular arc gear in rolling mill

The use of steel is very extensive, and its role in the national economic system is crucial. With the rapid economic growth, the level of iron and steel production is an important indicator to measure the four modernization levels of a country’s industry, agriculture, national defense and science and technology. In the process of iron and steel production, a very small part of the steel is made by casting and other methods. The remaining 90% of the steel is rolled by rolling mill. What’s more, some of the steel is not produced directly by the steel casting workshop, but the billet is also provided by the rolling mill. Therefore, in the modern iron and steel industry, as the last link of steel production, steel rolling reflects its vital role, and the application of the rolling mill occupies a crucial position in the national economic system. The rolling mill is the equipment to realize the metal rolling process. It generally refers to the equipment to complete the whole rolling production process, including main equipment, auxiliary equipment, lifting and transportation equipment and auxiliary equipment. The driving mechanism of rolling mill includes gear base, reducer, flywheel, coupling shaft, coupling and other parts. In the working process of rolling mill, the use of double circular arc gear plays an important role. Compared with ordinary involute gear, double circular arc gear has more advantages. First, the load-carrying capacity of double arc gear is relatively large, because the structure is more reasonable, the tooth root bending strength and tooth surface contact strength of the gear are relatively high, and the same size and material can bear more load; second, the double arc gear has good lubrication performance, and it is easier to form dynamic pressure oil film on the tooth surface in the transmission, which can improve the service life of the gear; finally The double arc gear has no undercut phenomenon, so the size can be smaller. Therefore, the design and research of double circular arc gear of rolling mill is of great significance.

Double circular arc gear is an important part of the transmission system of heavy equipment. It has the characteristics of high transmission power, strong bearing capacity, strong transmission stability and small structure space. In recent years, it has been widely used in some high-speed, heavy-duty and high-power gear transmission. However, in the traditional design process of double circular arc gear, the calculation of gear design is large, the process of manually checking the chart and selecting parameters is complex, and the rationality is not guaranteed. Often, in order to ensure the volume of the transmission system, the strength of the gear is not enough, or to ensure the strength of the gear, the volume of the transmission system is too large. In the whole design process, the workload is often calculated repeatedly, which greatly reduces the work efficiency of engineers, thus affecting the timeliness of products. In order to solve this problem, a set of double arc gear design is developed for the transmission system platform of rolling mill.

Design criteria of double circular arc gear

The main failure forms of double circular arc gear are bending fracture, pitting, gluing and plastic deformation. Due to the complex stress situation of double circular arc gear, its strength calculation is mostly based on three-dimensional stress analysis and a lot of experimental research. In 1992, the national standard “calculation method of bearing capacity of double circular arc cylindrical gear” (GB / T 13799-1992) was formulated in China. At present, the design criterion of double circular arc gear is based on the standard, mainly including the calculation method of bending strength and contact strength.

During the design, some known parameters need to be determined according to the design requirements, such as: transmission power and revolution number of pinion, full load working time, transmission ratio, gear accuracy grade, tooth shape and gear material, etc., gear distribution and tooth surface hardness selection, gear use environment and lubrication conditions selection, and other values are temporarily taken according to the empirical values.

Calculation process of double circular arc gear drive

(1) Select the gear material and parameters, and calculate the coincidence degree ε β (integral part μ ε and tail part Δε) according to the known conditions and provisional values;

(2) According to the bending fatigue strength of the tooth root, the modulus Mn is initially determined;

(3) Initial gear transmission parameters, such as center distance a, helix angle β, pinion diameter D1, tooth width b, etc;

(4) Check the bending fatigue strength of tooth root;

(5) Check the contact fatigue strength of tooth surface;

(6) The main parameters and geometric dimension calculation include: normal modulus Mn, end modulus MT, number of teeth Z1 and Z2 of big and small gears, helix angle β, diameter of pitch circle D1 and D2 of big and small gears, diameter of top circle DA1 and DA2 of big and small gears, diameter of root circle DF1 and df2 of big and small gears, center distance a, and tooth width B.

In the above process, the workload and calculation involved in chart checking are relatively large, and a little negligence will cause parameter errors, which need to be verified and corrected continuously, and then rechecked.

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