The open gear has a simple structure, is easy to process, and has good ventilation and heat dissipation. It is suitable for transmissions with large loads and long-term operation under harsh conditions or under shock load conditions. In large mines such as mines, cement, metallurgy, etc. The crusher, dryer and mine shovel have been widely used.
Lubrication mechanism of open gear
The open gear is powered by the interaction and relative motion of each pair of meshing flank in the gear mechanism. In the gear transmission process, there are two forms of sliding friction and rolling friction between the teeth that are in contact with each other. When the teeth start to mesh, the root of the driving gear is in contact with the tooth tip of the driven gear. Due to the different tangential speeds of the root and the top, a speed slip is generated between the two tooth surfaces, and sliding friction is formed. As the meshing progresses, the slip gradually decreases to zero at the pitch circle, and the slip direction is opposite and gradually increases to disengage after the pitch circle. The moment of the moment of engagement and engagement is the largest, the sliding friction is also the largest, and the slip difference at the pitch circle is zero.
Becomes rolling friction and produces the largest rolling friction
. If the open gear is not effectively lubricated, the frictional force and contact stress between the meshing teeth will increase the temperature of the tooth surface microprotrusions which are in contact with each other, causing the two tooth surfaces to stick or even weld, resulting in gear fatigue and Wear, most
Eventually the teeth are broken. Germany Wollhofen et al
The investigation found that the cause of the damage of the open gear transmission was due to poor lubrication.
In general, depending on the gear load and working conditions, the lubrication can be divided into different lubrication states such as fluid dynamic lubrication (HL), elastic fluid dynamic lubrication (EHL), mixed lubrication (ML) and boundary lubrication (BL). . Since the contact of the gear is a line contact, and at the same time there is a form of sliding friction and rolling friction, it is difficult to determine in which kind of lubrication state the gear is in practice.
It can be seen from the formula that the thickness of the oil film is affected by various factors such as viscosity, temperature, rotation speed and load of the base oil. When the tooth surface roughness is constant, increasing the minimum oil film thickness hmin can increase the oil film thickness to improve the tooth surface lubrication state.
NicholasSamman et al
It is considered that when the oil film is thicker than the thickness of the oil film, the surface of the root is separated by a sufficiently thick fluid or elastic fluid lubricant film, and the viscosity of the lubricant plays a leading role in the lubrication effect. The oil film thickness is smaller than the tooth surface roughness, the tooth surface peaks collide with each other, and the gear is in a boundary lubrication state. At this time, the load-carrying effect of the lubricating oil is reduced, and the task of reducing friction and avoiding wear is mainly undertaken by the extreme pressure anti-wear (EP/AW) additive. The EP/AW additive and the metal surface are capable of forming a physical, chemically adsorbed film that prevents dry friction of the tooth flanks. When the contact surface temperature is high enough, the active elements such as phosphorus and sulfur contained in the EP/AW additive react with the metal surface to form a solid reaction film. The critical shear strength of the solid film is lower than that of the base metal, and the friction pair slides. The shearing action is carried out in a solid film to prevent gluing or scratching of the metal surface. When 1<>, the gears are generally in a mixed lubrication state, with elastic hydrodynamic lubrication and boundary lubrication. At this time, the oil film thickness of some parts of the tooth surface is smaller than the tooth surface roughness, the tooth surface convex peak will collide, and the tooth surface load is shared by the oil film and the convex peak. Within this range, the lubricant of appropriate viscosity and the matching thereof A suitable additive system is particularly important. Lubrication failure analysis of open gear
The open gear has low processing precision, rough tooth surface, and is in a state of low speed, heavy load and continuous operation for a long time, which brings many adverse effects to gear lubrication. Failure of gear lubrication often results in tooth surface wear and even biting or breaking of the teeth. Depending on the mechanism, wear can be roughly classified into adhesive wear, abrasive wear, fatigue wear, and corrosion wear. For open gears, the main manifestations are wear and tear, gluing and pitting.