Micro Ceramic Nano Glide Compounds: Solution towards reducing Micro Pitting on Gear Teeth

Introduction

Fatigue occurs on a body where there is more cyclic or repeated rolling contact than sliding motion. The contact fatigue phenomenon is most prevailing in mechanical applications such as gear flanks, bearings, rails etc. The primary factors which affect the fatigue life of mechanical components are: Material, surface finish, lubrication, dimensions and the type of operating conditions [1]. Researchers reported that the surface finish and lubrication plays an important role in controlling the damages occurred due to fatigue [2]. The surface failures such as occurrence of micro pittings, geometric stress concentrations etc results due to the failure of lubricating films [2]. It has been reported that the formation of an elasto hydro dynamic regime is greatly influenced by [3] viscosity at atm.pressure, temperature viscosity coefficient, thermal conductivity, heat capacity per unit volume, frictional coefficient of EHL and compressibility. All these factors in turn affect the film formation between the mating pairs as seen from the Hamrock-Dowson Equation (Eq. 1).

where,

a,b,c are constants. R’ is reduced radius of curvature,  U is mean entrance surface velocity, k is depends on the type of geometry, W is contact load, α is pressure viscosity constant, 0 is viscosity at atm. pressure.

It is very important to prevent the situations leading to material fatigue in order to protect the mechanical components such as gear teeth, bearing etc from premature surface fatigue failures leading to micro pitting. The easiest method is to maintain a stable high strength lubrication film between the mating surfaces, thus separating the mating surfaces from repeated/cyclic loading situations. A high film strength will eliminate the chances of contact between the mating pairs and hence, reducing the chances of surface fatigue.

Now the question arises, how to increase the film strength? One of the ways is to increase the viscosity of the lubricant, which is not always the best solution. Another possibility can be introducing a concept which would help in forming a stable lubrication film: “Micro Ceramic Nano Glide Compounds”. The “Micro Ceramic Nano Glide Compounds” contains billions of nano sized spherical nanoparticles which act as ball bearing between the surfaces and do not allow the mating pairs to come in contact with each other. Additionally, these spherical nanoparticles get deposited on the surface defects of the mating pairs and mend the surfaces, thus enhancing the load bearing capacity of the mating pairs. Once a stable high strength lubricating film is produced between the surfaces the mating surfaces are protected from repeated loading, thus minimizing the chances of formation of Micro Pittings due to surface fatigue. 

Rolling Contact Fatigue Test

To understand the efficiency of “Micro Ceramic Nano Glide Compounds” in preventing Micro Pitting on bearing steel surfaces, Rolling Contact Fatigue tests were conducted as per IP 300 standards using a four ball tribometer [4]. The test consists of a specially designed ball pot where the three bearing steel balls (AISI 52100) rotate freely. The fourth bearing steel ball (AISI 52100) which is attached to the chuck is rotated at 1450 rpm. The hardness of the balls were 59-61 Rc and the diameter was 12.7mm. The initial roughness of all the balls were 0.14 microns. The test was initiated with 392N and after 30 seconds loads were increased to 5996N. The test ran till the balls failed due to the pitting. An accelerometer picks up the signal of the increased level of vibration due to the occurrence of pitting and sends it to the controller to stop the test. The data acquisition system records the number of cycles before failure which determines the L10, L50 and L 90 life of the bearing steel. The occurrence of the pittings are confirmed using an optical microscope. Figure 1 shows the experimental set up of the Rolling Contact Fatigue Test rig.

Understanding the role of Micro Ceramic Nano Glide Compounds in enhancing the life of the bearing steel by reducing the chances of Micro pitting

Rolling contact fatigue (RCF) is one of the primary modes of failures in mechanical elements. Considering a case of gear meshing which involves both rolling and sliding motion, a gear lubricant must provide protection from failures occurring due to sliding as well as rolling (rolling fatigue failure). This article considered commercially available 320 cSt mineral oil with and without Micro Ceramic Nano glide Compounds. 

Figure 2 shows the microscopic images of the surfaces of the bearing balls. It can be clearly seen that the ball surfaces which were with 320 cSt gear oil (without Micro Ceramic Nano Glide Compounds) had severe plastic deformation and surface cracks. No major damage was observed on the bearing ball surface in presence of Micro Ceramic Nano glide Compounds, thus making a strong point of high life cycles of bearing in case of Micro Ceramic Nano Glide Compound added gear oil.

Statistically using a Weibull plot it was found that the characteristic life of the bearing balls was enhanced by 43% with the addition of Micro Ceramic Nano Glide Compounds.

How Micro Ceramic Nano Glide Compounds Work?

Any maintenance engineer has the following questions to ask:

• How to reduce the temperature of the bearings and gear boxes?
• How to reduce the wear?
• How to reduce the power consumption?
• How will we quantify the effect of new lubricants?

To answer these questions, we need to follow the best practices of Tribology. The minimum good practice includes maintaining a good health of the base lubricant with proper sealing conditions to avoid any contaminations, selecting the right lubricant and avoiding any kind of misalignment. However, in practical situations even after maintaining a proper sealing, selecting a correct lubricant and having a proper alignment, the end user faces the issues of high temperature, high power consumption and high wear in their gear boxes and bearings. So, the easiest solution is to enhance the lubricating properties of the lubricant in use. As mentioned earlier this article will help you to understand the future of lubrication and will show you the benefits of using Micro Ceramic Nano Glide Compounds in your gear boxes and bearing oils.

A commercial oil lubricant contains about 5%-10% of various types of additives. These additives are generally micro sized particles particularly the friction modifiers and extreme pressure additives. Apart from the chemical composition of the additives, the lubricity provided by these solid lubricants also depends on the sizes of the solid additives [5]. The smaller the size of the solid lubricants the easier they penetrate in the contact zone. Nanotechnology has been utilized by the material scientist to develop commercial nano solid lubricants with superior lubricating properties than their micro sized counterparts. In several instances, the micro sized particles interact before the EHL zone, resulting in a weak lubricating film [6]. On the other hand, the nano solid additives (due to much smaller size and high surface-volume ratio) can easily pass through the contact zone forming a high strength lubricating film between the mating pairs (Figure 3). 

A good lubricant should protect the mating surfaces from damages occurring from both sliding motion as well as damages from fatigue. Generally, all maintenance engineers perform oil analysis to determine the wear happening in the system. They also visually check the gear flanks for surface damages particularly the Micro-Pittings. However, the maintenance cost will be reduced if the lubricant can provide protection against both sliding wear as well damages due to fatigue. Generally, only a few lubricant suppliers reveal the capability of the lubricant to prevent wear due to fatigue which is an important parameter to be determined specially in gear boxes and bearings, where there is a lot of rolling contact involved resulting in surface fatigue (micro pitting).

Micro Ceramic Nano Glide Compounds not only protects the surfaces of the mechanical elements from sliding wear but also protects the life of the mechanical elements such as gear teeth, bearings, rails, wheels from damages due to fatigue, by forming a high strength film between the mating pairs. The nano sized spherical particles (110nm – 298 nm) act as nano ball bearings between the surfaces and prevent them from contact with each other. Additionally, due to their nano size they easily mend the surface defects by forming a layer and getting deposited on the defects resulting in enhanced load bearing capacity, further forming a protective film between the surfaces. 

The presence of Micro Ceramic nano Glide Compounds prevented less surface damages due to fatigue as compared to the surface damages in case of the commercial gear oil without the Micro Ceramic particles.

Summary:

The article clearly indicates that by adding Micro Ceramic Nano Glide Compounds the life of the bearing steel was increased. The failure due to fatigue was significantly reduced in presence of Micro Ceramic Nano Glide Compounds. The surfaces of the bearing balls exhibited less plastic deformations and damages when Micro Ceramic Nano Glide Compounds added commercial gear oil 320 cSt was used. Field results have indicated a significant reduction of temperature and wear particles with the addition of Micro Ceramic Nano Glide Compounds.

The above discussions make a strong point of adding the Micro Ceramic Nano Glide Compounds to existing mineral oils and PAO by the maintenance engineers to run their gear boxes, bearings , steel rails etc smoothly with less breakdowns.

References:

1. Fernandez Rico, J. E., Hernandez Battez, A., & Garcia Cuervo, D. (2003). Rolling contact fatigue in lubricated contacts. Tribology International, 36(1), 35–40.
2. Zaretsky EV, Andesron WJH. how To Use What We Know About EHD Lubrication. Mach Des 1968;:167–73.
3. Kassfeldt, E., Larsson, R. Base fluid parameters for EHL and friction calculations and their influence on lubrication capability. In Proceedings of 12th International Colloquium Tribology 2000 – Plus. Esslingen 2000. 1525-1536.
4. Bhaumik, S.; Paleu, V. Wear and Rolling Contact Fatigue Analysis of AISI 52100 Bearing Steel in Presence of Additivated Lubricants. Metals 2021, 11, 907. 
5. Dai, W., Kheireddin, B., Gao, H., & Liang, H. (2016). Roles of nanoparticles in oil lubrication. Tribology International, 102, 88–98.
6. Bhaumik, S., Datta, S., and Pathak, S. D. (2017). “Analyses of Tribological Properties of Castor Oil With Various Carbonaceous Micro- and Nano-Friction Modifiers.” ASME. J. Tribol. November 2017; 139(6): 061802.