Improve the bearing capacity and service life of gears

Increase the center distance.

The center distance is one of the main parameters to determine the bearing capacity of the gear pair. The contact stress of the tooth surface is inversely proportional to the center distance of the gear pair. But it is often limited by the mill structure size. In view of the fact that the maximum roll diameter of the rolling mill has been increased from 540 m m to 580 mm in order to improve the rolling speed and prevent roll breakage in production, the center distance has been increased from 50 mm to 540 mm according to the technological requirements. In this way, the inclination angle of the quincunx joint shaft is reduced, the impact is gentle, the wear and noise are reduced, and the service life of the quincunx joint shaft is prolonged.

Reasonable material selection.

For heavy duty gears, high alloy steel with high strength, good hardenability and good comprehensive mechanical properties must be used to meet the requirements. Because of the bad working condition, large impact and high load of the gear base, 34CrNi3Mo high-quality gear steel is adopted. Medium hard tooth surface tempering technology is adopted. The bearing capacity of tooth contact strength is directly proportional to the square of hardness, and the bearing capacity of bending strength is directly proportional to the first power of hardness. Therefore, improving the hardness of gear surface is an effective way to improve the bearing capacity and prolong the service life of gear. The technology of hard tooth surface grinding after carburizing and quenching has been widely used in foreign countries. From the development direction of domestic heavy-duty gear, the hardened and tempered gear has developed to medium hard tooth surface. In the past, induction hardening treatment of gear surface will cause gear tooth deformation, which requires gear grinding and has high cost. For large module gear, due to the lack of quenching equipment, it is often replaced by flame quenching, and the quenching quality is not easy to guarantee, which makes the gear appear early pitting and peeling, and the bearing capacity and service life are not high. Therefore, it is decided to adopt the gear manufacturing technology of the final fine Hobbing with medium hard tooth surface hardening and tempering, and the hardness of the tooth surface reaches hb32o ~ 350.

Improve the accuracy of gear manufacturing.

The running in performance of hard tooth surface gear is poor, so it is necessary to improve its accuracy while improving its hardness. Because of the stress concentration and other reasons, the gears with low precision and high hardness are prone to early pitting and peeling, resulting in low bearing capacity and service life. So there is a undercut in the middle of the newly designed gear shaft, so that the hobbing can be used to improve the manufacturing accuracy and make it reach grade 8-8-7.

The new technology of gear shaping is applied.

It is a mature technology and widely used in foreign countries to carry out gear profile trimming (tooth top chamfering) and tooth profile modification. It is being actively promoted in China. It can reduce the impact and noise of gear engagement and improve the anti scuffing ability by trimming the top of gear. The modification of the tooth direction can be divided into two methods: chamfering at the tooth end and drum shaped at the whole tooth surface. The modification of tooth direction can improve the bad contact and uneven load in the tooth width direction which is thirsty for because of the elastic deformation, thermal deformation and manufacturing error of the gear transmission system. The contact rate of the gear modified in the tooth direction is significantly increased.

Select new lubricant.

It is necessary to choose the lubricant with high viscosity, good oil property and extreme pressure performance. As the contact stress of the gear base’s tooth surface has reached more than 800MPa, it is decided to choose N320 extreme pressure industrial gear oil with high viscosity, good extreme pressure wear resistance, anti emulsification, oxidation stability and anti Emei performance.

The new plum head cover is hot installed to the gear shaft end, adopting 35crm.

After quenching and tempering of alloy steel, surface quenching is carried out along the cavity of plum blossom head, and arc transition is added at the shaft shoulder of the cavity to reduce stress concentration, so as to avoid the whole gear shaft scrapping due to premature damage or fracture of the plum blossom head, and the plum blossom shaft head does not need frequent repair welding, which better solves the contradiction between high strength gear and rapid wear of the plum blossom shaft head.

The gear with soft tooth surface has low bearing capacity, but it is easy to manufacture and has good running in performance. It is mostly used in general machinery with no strict restrictions on transmission size and weight and small production. Because of the heavy burden of the small gear in the matched gear, the hardness of the small gear surface is generally higher than that of the large gear in order to make the working life of the large and small gears approximately equal.

The bearing capacity of hard gear is high, it is after gear finishing cutting, then quenching, surface quenching or carburizing quenching treatment, in order to improve the hardness. But in the heat treatment, the gear will inevitably deform, so after the heat treatment, it must be grinded, grinded or finely cut to eliminate the error caused by the deformation and improve the accuracy of the gear.