Varvel SpA claims manufacturers’ data sheets are no longer the only official comparison term between oil and grease.
The company’s R&D Department, thanks to an infrared camera and integrated hardware-software system for gears and gearboxes vibrational control of recent acquisition, developed an experimental procedure to check the performances of seal greases and gear lubricants, in terms of efficiency and thermal features.
Temperature control of running gearboxes is an important requirement for users and manufacturers of transmission systems. Among the various related factors, the lubricant correct choice is certainly the major advantage of shaft/seal contact lubrication to get a friction optimization during sliding conditions.
Performing laboratory tests with a tribometer for a friction coefficient evaluation, takes plenty of time and they are not always significant of the real behavior of a contact geometry that is hard to simulate on test pieces, such as oil seal/shaft.
In this sense, monitoring via infrared camera allows to take advantage of the direct proportionality between friction and temperature for a fast and effective comparison to be carried out in real time and directly on the product.
Thermal maps of contact area are acquired by placing the camera at the motor shaft on the gearbox test bench, specially designed by Varvel’s R&D. The maps highlight local and sudden temperature increases in the contact area that are strictly dependent on the type of used grease and motor shaft speed.
The first important result of a systematic comparison process, made on the fast shaft oil seal of the RD series helical-gearbox, revealed that the use of Teflon-coated greases, compared to other mineral-based, leads to lower contact temperatures of at least 20 Celsius in the sealing area, for a speed range from 500 to 2000 rpm.
Besides a clear indication on the grease choice to be used for operational temperature control in this series of reducers, Varvel SpA has now an effective internal validation procedure for the greases to be used, of which the experimental results in terms of temperature values could be effectively integrated into the gear calculation software “KISSsoft”, to get a more effective and precise calculation of gearbox thermal power.
Further R&D progress relate gear oil lubricants for which promising results are expected thanks to the development of an ad-hoc procedure for performance check in terms of efficiency and wear resistance without a traditional brake-test.
In order to make performance comparisons among different types of lubricants on Varvel gearboxes, without being a burden on programmed test benches and without the need of fixtures or equipment to expressly design, accelerometers for vibrational analysis can be used to be directly fitted on the gearbox and with the only need to be ask for a standard motor.
The acquired signal is then analyzed with algorithms aiming at the calculation of the dissipated energy by meshing friction that is closely related to efficiency and affected by the lubricating action of the used oil.
Given the high creep component of worm/wheel train meshing, the method gave good results for this type of gearboxes, for which it has clearly emerged the difference in terms of dissipated energy between the use of a synthetic oil compared to a mineral-based. .
These initial results have laid a good foundation for experimental campaign investigations on innovative and advanced types of synthetic oil additives, developed by experts in the field of nano-particles to be used in applications requiring optimized efficiency.
Thanks to this alternative analysis technique, Varvel’s R&D was able to quickly perform numerous tests on worm gearboxes lubrified with synthetic oil in nano-additive different concentrations with the result of a first effective comparison on the additive efficacy in energy reduction dissipated by friction and thus proportionally on efficiency.
The nano-additive effectiveness has also been tested in terms of improving the wear resistance the worm gears.
Determining the gear tooth wearing through bench test requires very long testing times, so it becomes complex to perform comparative tests among different lubricant types in terms of response to this property.
Thanks to the partnership with universities and tribology experts, Varvel used a laboratory approach to simulate the contact geometry between screw and bronze wheel teeth by a Block-on-ring tribometer. An advanced profilometer at tests ending, made feasible to collect detailed maps of wear traces, left on the samples, thus allowing an effective quantitative comparison of the material wearing.
The tests have revealed a sharp bronze wear decrease thanks to the use of oil with the right concentration of nano- additives, thus opening up – quickly and with concrete results – the door to new applications with longer lifetime and improved efficiency.
“The steady quality improvement – the President, Francesco Berselli and the General Manager, Mauro Cominoli claim – is one of the various strategic actions undertaken by Varvel SpA, to which are added a logistics and a supply chain more and more efficient, in addition to the very high level of service in pre- and post- sales, ranging from design to customization. A concrete response to the needs of different markets and an utmost guarantee at international level”
