October 11, 2018
Military vehicles endure extreme conditions during their lifetime. How can the steering systems of these vehicles take on temperatures as low as minus 40 degrees Celsius, without resulting in high torque steering? Here, Emma Cygan, design and development engineer at military steering system manufacturer, Pailton Engineering explains how environmental testing can alleviate these potential challenges.
It's not just low temperatures that are problematic for military vehicles, environmental testing also needs to account for the moisture and road debris faced by these vehicles and take this into consideration during the development process.
The testing process for steering systems needs to be bespoke to the vehicle and end application. For example, a military vehicle used for semi-submersed and wading applications will have different requirements to an armoured vehicle designed for warfare.
Using adaptability in the testing process means testing is not confined or restricted to standard tests, but instead, bespoke tests should be arranged based on the end application.
Every test is designed to replicate the real conditions a vehicle will face, to ensure the vehicle is fit for purpose. While all military vehicles can differ, when it comes to the environmental testing of military-grade steering components, there are some crucial parameters to consider that form three core tests:
Salt Spray Test
Pailton Engineering uses a salt spray test rig, where up to six steering parts at a time can be tested dynamically against salt spray, at varying temperatures. This rig is a large container with a rotary arm that controls the movement of steering components, normally at a rate of one cycle every three seconds—one cycle representing one turn of the steering wheel.
The salt spray test does not necessarily represent dirt or grit but represents any debris that could be on the road. This debris could enter a part and cause it to corrode or fail and the testing process is used to identify any potential problem areas. The test can use varying concentrations of salt, with higher concentrations being for the more extreme applications, as often seen in the military vehicle industry.
Salt spray tests can take on many forms, depending on the needs of the vehicle. For example, a test could check the effects of repetitive salt spray, with periodical temperatures of minus 40 degrees Celsius—this is the automotive industry standard for low temperature testing. The exposure to the requested temperature can vary depending on the customers’ requirements. This will ensure the steering system can withstand grit on the roads, even at low temperatures.
So, what can you expect to see from a test like this? The results will illustrate changes in torque, rate of corrosion, overall effect of grit on the vehicle and its steering system, as well as any potential for water ingression. Of course, the best possible result for this test to show is that these parts are capable of working in these conditions at low temperatures.
The same test rig can also be used to test the system against other factors, such as water. During rotary submersion, the parts are fully submerged in water. Ultimately, if a part can endure underwater movement at one cycle every three seconds, at varying temperatures, without corroding or failing, then the vehicle manufacture can be confident in putting those steering parts in a military vehicle for use in the end environment.
There are alternatives that can be explored to improve the performance of a part. From different finishes, to upgraded sealing and greases, there has been plenty of scope for development in recent years. With steering components taking on new and improved design features and passing rotary submersion testing, comes new opportunities for high performance extreme vehicles taking on deep water wading.
Low Temperature Evaluation
The importance of low temperature testing has been eluded to in both salt spray testing and rotary submersion, but it also forms a standalone test for military steering systems. Low temperatures can bring about issues with the viscosity of the fluid in lubricated component, which can have detrimental effects on steering torque, or even cause parts to lock up entirely.
Using a low temperature chamber, parts can be tested at as low as minus 40 degrees Celsius, for a set period of time based on the data of the end application. This low temperature could be applied constantly, or periodically for more dynamic testing. The parameters measured in this test include assessing changes to the part cause by low temperatures, checking rotation and measuring torque.
One customer's request lead to the production of the next generation of bevel boxes at Pailton Engineering, needed for vehicles carrying out long journeys at low temperatures with high levels of moisture and grit.
After improving on the design features of the previous bevel box, with a serration cover and alternative grease, the bevel box took on environmental testing. Operated at a rate of one rotary cycle every three seconds continuously and submitted to salt exposure and temperatures of minus 40 degrees Celsius for four hours every week, the new design features were certainly validated.
External validation showed the generation three bevel box conformed with ingress protection codes IP66 and IP67, which is great news for the military industry.
Those who don't opt for environmentally tested steering systems may face problems with water ingression, stiff steering and general maintenance. There are plenty of variables to consider when developing a steering system for military applications and the testing process should always be unique.
Emma Cygan is a design and development engineer Pailton Engineering Ltd. The company designs, tests and delivers steering systems, using CAD (SolidWorks), purpose designed and built test facilities, and manufacturing capability.