Ingenieurwissenschaften und zugeordnete Tätigkeiten
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South Africa and recently Nigeria are the only net exporter of cement in Africa, yet cements are imported into the country mainly on the basis of price competitiveness. This poses potential for scatter in the properties of the cements in the South African market as pricing seems to be the only determining factor that affects Portland cements imported. A survey of cements of grade 42.5N in the South African cement market was carried out to identify major players in the industry. The identified cements, which included four locally produced and one imported cement were then analysed for both chemical composition and physical properties in line with the Eurocode EN 196. Tests carried out include loss on ignition, chloride content, sulphate content, specific surface (Blaine), standard consistence, initial setting time, final setting time, soundness and flexural and compressive strength at 2, 7 and 28 days. The testing program was initiated as part of on-going Africa-wide cement testing competency program in partnership with BAM and PTB in Germany. The performance of the identified cements from the different local manufacturers and the imported cement were analysed and are presented in this paper. These results reveal some similarities and differences in the properties. Particularly of interest is the marked difference in the 28 days compressive strength of the cements. This paper shows that there is need for further tests across the cement industry as some of the cements failed to meet certain requirement as set by EN 196. The paper also recommends the use of proficiency testing schemes in the cement industry of the country to ensure the cement laboratories are providing results of high quality and at the same time act as a check to make sure these laboratories are not failing to meet standard requirements.
New interpretation approaches for seizure load tests on the translatory oscillation tribometer (SRV)
(2016)
When looking in detail at analyses of the tribological load-carrying capacity of high-performance lubricants, it becomes apparent that the stop of the machine of an exclusive evaluation of the development of the coefficient of friction cannot provide any sufficient criteria for determining the occurrence of adhesive failure. This is due on the one hand to the increasing complexity of lubricant formulae and sophisticated additive packages, and on the other hand to the increasing frictional power capacity of modern drive and control concepts in the design of tribometers. For this reason, it is urgently needed to examine the adhesive processes and their detection in more detail with the help of appropriate tribological values and criteria. The evolution of the friction can be coupled with the stroke, contact resistant and/or noise emission. Besides from new criteria for adhesive failure, which were compiled by the work group for the relevant ISO, DIN and ASTM standards, this contribution discusses the inclusion of additional parameters. Among other things, it provides guidance on what evidence the continuous recording of the original coefficient of friction and position signals, the electrical contact resistance, temperature, noise emission, frictional power input of the machine and further derived parameters help to identify adhesive failures or events.
„Cliff“-testing by using SRV
The identification in engine or gear tests of the induction time or off-set point („cliff“), after which wear and friction increased.
“Cliff” testing as auxiliary method supports the interpretation of engine tests, as it enhances the values of expensive engine tests, because it enables correlations between friction & wear, either from engine or in SRV tests, with additive depletion, oxidation, viscometrics and dispersancy/detergency.
Oil samples taken in discrete intervals and “Cliff” tested monitors the evolution of tribological and functional properties versus engine running time. “Cliff” testing by using SRV is a purposeful tool in order to secure and accelerate metallurgical developments and the development of lubricant formulations.
Actions from the meeting in April 2016: 1. Four SAC test methods are in place and were revised: SH/T 0721 (Grease, coefficient of friction and wear), SH/T 0784 (Grease, pass load/O.K. load), SH/T 0847 (Oil, coefficient of friction and wear) and SH/T 0882 released by 11-2014 (Oil, pass load/O.K. load). 2. New test method to evaluate anti-fretting properties of greases based was approved by SAC TC280 and will be released. 3. SAC TC280 accepted the project “Simulation of synchronizer by using SRV”. Draft text to be submitted by 03-2017. Discussions on a parallel ASTM test method. 4. A procedure for “Wear Volume” is under development for SAC TC280.
Tribological profile of hydraulic oils by using SRV. The determination of a set of critical, tribological by using different SRV-based test methods. The SRV-based concept of tribological profile generates the wear volumes on two triboelements (specimen), the extreme pressure properties and friction under different contact pressures.
Thus, the benchmark and validation of hydraulic oils bear on a wider range of tribological properties.
The RR2016 extends with six hydraulic oils to other base oil types including biodegradable fluids, which were all tested according to ASTM D7043 in order to consolidate the correlation between SRV and V104C.