Green Lubricants for Automotive and Manufacturing Industries

In the automotive industry, one of the best ways to increase fuel efficiency is to reduce vehicle weight by using lightweight aluminum or magnesium alloyed parts. Forming these alloyed parts can be very difficult due to high friction, extreme pressure requirements, and the inability of conventional lubricants to prevent wear during metalworking. Also, most conventional lubricants are flammable and contain chlorine, phosphorus, and sulfur-bearing additives that are potentially hazardous: removing these lubricants from finished products and treating them for disposal is difficult and costly. Thus, it has long been recognized that metal forming operations have significant environmental impact. Despite several decades of research on the subject, lubricants used in forming operations continue to pose substantial technological and economic challenges to the tribological community. The present challenges primarily stem from various factors such as (1) Nearly all lubricants used in sheet metal forming are made from petroleum-based resources which are not environmentally friendly and are becoming substantially more expensive, (2) Forming lubricants often carry a health risk to humans both during primary use and in their disposal, (3) Over the past several decades, there has not been a novel lubricant introduced in the manufacturing community to significantly increase the formability. Thus, use of boric acid-based green lubricant has the potential to overcome these problems. Its exceptionally low friction coefficient prevents the metals from sticking or transferring to the die or roll surfaces. Boric acid greatly reduces the friction and wear of dies and molds and at the same time provides an ultra-smooth surface finish on final products. After metal-forming operations, parts can be rinsed in water to remove the excess lubricants—no toxic or flammable solvents are necessary. The use of boric acid can decrease the unit cost for automotive parts because the near-perfect finished products do not require secondary machining or grinding. Other potential automotive applications of boric acid include its use as a lubricant for gears and bearings. Boric acid may also be mixed with existing liquid and solid lubricants.

Efforts have been made to evaluate the interfacial friction characteristics of canola oil and boric acid lubricants in metal forming operations. To simulate their performance, a strip tensile friction simulator [16] was utilized. This apparatus has been shown to effectively model the strain behavior encountered in a deep drawing process and accurately replicates the frictional effects experienced during sheet bending. By means of the simulator, the friction coefficient between a die (carbon steel) and a steel sheet was measured for four different lubricant conditions: unlubricated, canola oil (viscosity of 33 cSt at 20°C), transmission fluid (viscosity of 0.028 Pa s at 40°C), and a combination of boric acid and canola oil (viscosity of 0.276 Pa s at 20°C). As shown in Fig. 10.6, a lubricant consisting of canola oil mixed with boric acid crystals (5 wt% and 100 im average particle size) significantly outperformed several other lubricants with respect to the measured friction coefficient in the specialized experiments. This lubricant had a steady-state friction

Fig. 10.6 Variation of coefficient of friction with sliding distance for various lubricants obtained in the metal forming experiment [16]

value that was 54% lower than the unlubricated condition and 44% less than the transmission fluid case. Such a finding indicated that the novel lubricant may be used in manufacturing processes where replenishment is not feasible and disposal of non-environmentally friendly lubricants is expensive.

Studies were also conducted to determine the relative performance of boric acid-based lubricants and other oil combinations in a commercial brake valve assembly [10]. Pin-on-disk experiments were performed under the same operating conditions experienced by the brake valve assembly. To represent the slide valve, in the experiments, the disk samples were prepared from copper alloy C84400. Likewise, to represent the bushing material, a pin was constructed from copper alloy C93200. Figure 10.7 shows the variation of coefficient of friction with sliding distance obtained in the pin-on-disk experiment. As depicted in Fig. 10.7, the base materials in the absence of a lubricant yielded the highest friction coefficients over the sliding distance tested. Figure 10.7 also demonstrates that boric acid alone was an ineffective lubricant for the operating conditions examined. The increase in friction in boric acid case is caused by the fact that the amount of boric acid in the contact interface gradually diminishes with time. It is important to note, however, that in terms of the final friction coefficient values, the boric acid was significantly lower than the unlubricated case. Although the boric acid did not maintain an optimal separation level within the contact interface, a better frictional performance was attained because a portion of the lubricious boric acid remained in the contact region. For the transmission fluid case, the coefficient of friction was found to increase over the sliding range tested. This increase was attributed to the degradation of the lubricant film over time. Further, a lubricant combination of

Fig. 10.7 Variation of coefficient of friction with sliding distance for various lubricants when copper alloy pins slide against copper alloy disks [10]

transmission fluid and boric acid (5% weight) was found to provide optimum friction properties as the friction coefficient actually decreased over a significant portion of the testing period. The friction coefficients in a combined boric acid and canola oil lubricant were comparable but slightly larger than the transmission oil and the combined boric acid and transmission fluid cases. The boric acid and canola oil case showed no degradation over the entire range of the sliding tests and demonstrated the lowest wear rate of any of the lubricants tested. In fact, the wear rate was nearly 50% lower than the combined transmission fluid and boric acid lubricant mixture. The better wear performance was attributed to the fact that the boric acid and canola oil did not degrade over the entire range of sliding experiments. Such a finding is extremely important as it indicates that the lubricant can be used in extended duration applications where replenishment is not feasible.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook


Post a comment