What is the difference between pitting and spalling

It is typically caused by vibrations that occur when the bearing is in a static state, and therefore the depressions caused by false brinelling will have the same spacing as the rolling elements. You must be logged in to post a comment. You may also like: What are some considerations for linear actuators in contaminated environments? What happens when a bearing reaches the end of its…. These cracks may start at inclusions in the gear materials, which act as stress concentrators, and propagate below and parallel to the tooth surface.

Pits are formed when these cracks break through the tooth surface and cause material separation. Pitting appears as shallow craters at contact surfaces with a depth of, at most, the thickness of the work-hardened layer approximately l0 m. Spalling is chipping or flaking of a surface due to any kind of improper heat treatment or material dissociation.

Spalling leaves deeper cavities at contact surfaces with a depth of 20 m to m. What is the difference between scuffing and scoring Scuffing is localized damage caused by the occurrence of solid-phase welding between sliding surfaces. Gear scuffing is characterized by material transfer between sliding tooth surfaces.

Generally this condition occurs when inadequate lubrication film thickness permits metal to- metal contact between gear teeth. Without lubrication, direct metal contact removes the protective oxide layer on the gear metal, and the excessive heat generated by friction welds the surfaces at the contact points.

As the gears separate, metal is torn and transferred between the teeth. Figure 3. Figure 3 shows an example of advanced fatigue wear. The shaft in this tapered roller bearing was approximately mm in diameter and some of the advanced spalling from multiple sites is 30 mm across. Figure 4. Note at the sharper crater wall near the top edge of the spall in this micrograph there are several cracks associated with the spall. Though both spalling and pitting are the common forms of surface contact fatigue , spalling results in more rapid deterioration of surface durability when compared to pitting.

Spalling often induces early failure by severe secondary damage. It has been repeatedly reported as the more destructive surface failure mode for gear contacts. Such secondary damage can result in roller or race breakage, initiated from a severe spall on the contact surface, as well as friction- or heat-induced surface seizure, or complete spalling over all of the contact surfaces.

Figure 5. As shown in Figure 5, the contact point moves along a straight line DE through the pitch point P , which is tangent to the base circles. The line DE is called the pressure line because it is the common normal to the contact point for involute teeth. It reduces to zero at the pitch point pure rolling as in rolling bearings and then increases again to another maximum at the end of engagement.

Once the contact point moves into the vicinity of the pitch line, the number of gear pairs in contact becomes minimal, so that the normal Hertzian contact load is maximum on this region. Spalling is normally found in this region. Thus there is an intuitive similarity between the rolling bearing spalling and gear pitch line spalling phenomena. Figure 6. Pitch line surface fatigue spalling is illustrated in Figure 6. It is common for initial pitch line spalling usually labeled initial pitting to occur soon after gear drive commissioning and then stop suddenly and for the gears to continue a long life of service.

It is a relief mechanism for small-tooth geometry errors. In some cases, however, more severe geometrical errors can continue, leading to premature tooth cracking and early failure. The drive in Figure 6 has been operating with severe misalignment, which has the same detrimental effect as improper tooth geometry.

As a result, the crack tip was extended by the hydraulic pressure of the oil sealed between the crack surfaces. Bower performed a fracture-mechanics analysis of crack propagation in the presence of lubricating oil. Furthermore, the experimental results obtained by Cheng and others showed that the surface crack growth was very slow. According to Ding and Kuhnell, surface crack growth can only be in Mode II and can result only in shallow craters.

Fleming and Suh used fracture mechanics methods to analyze the propagation of subsurface cracks parallel to the contact surface. Kaneta and others studied the growth mechanism of subsurface cracks by numerically analyzing the behavior of a three-dimensional subsurface crack parallel to the contact surface. They concluded that the propagation of subsurface cracks is mainly by Mode II.

More recently, Ding and others studied the behavior of subsurface cracks beneath the pitch line of a gear tooth, focusing on developing a fundamental understanding of the mechanisms of spalling in gears. Using the finite element method, the potential modes of crack propagation and failure were analyzed and the values of the stress intensity factors SIFs of the subsurface cracks were below the critical SIF, Kc.

Consequently, ligament collapse at crack tips was hypothesized as the cause of spalling from subsurface cracks. Spalling primarily. Pitting occurs when fatigue cracks are initiated on the tooth surface or just below the surface. Usually pits are the result of surface cracks caused by metal-to-metal contact of asperities or defects due to low lubricant film thickness. Pitting can also be caused by foreign particle contamination of lubricant. Asked by: Cyndi Osante business and finance mechanical and industrial engineering industry What is the difference between pitting and spalling?

Last Updated: 16th April, Pitting is defined to be the formation of shallow craters mainly due to surface defects while spalling appears as deeper cavities mainly owing to fatigue crack propagation [43]. Spalling occurs as cracks reach to a critical size, which is usually followed by the release of large quantities of wear debris [45].

Chayma Quesnot Professional. What is scoring in gear? In gears , pitting occurs when continuous high-pressure forces act on the surface of the gear teeth. In high-speed operations, like aerospace gears , gear scoring occurs due to the vaporization of oil film and welding occurs between the gear teeth to form the scoring.

Robson Chula Professional. What causes gearbox failure? Here are some of the most common forms of gearbox failure. The major cause is inadequate lubrication caused by under filling, incorrect specification, mixing or incompatibility, incorrect lubrication and intervals, deteriorated grease or oil, water contamination and particulate contamination.

Satiro Tamaral Professional. What are the signs of gearbox going? Dashboard Warning Lights. Engine lights ignite on the dashboard for a reason. Leaking Fluid and Low Levels. This is possibly the easiest symptom on our list to spot. Smells and Odours. Audible Noises. Out of the Ordinary Behaviour.