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Lube-Tech


d) Pumpability of the lubricating greases can be simulated by different methods e.g. measurement of the flow pressure according to DIN 51805. Parameters such as consistency of the grease, polymer content, kinematic viscosity of the oil, pour point as well as the degree of the wax content in the base oil are the main parameters that can affect the mobility of the greases. In this study, we can eliminate parameters such as wax content and polymers so the main parameters that can affect the low temperature mobility of the greases are the thickener content, the viscosity and the pour point of the oils. Hence, good low temperature mobility for all greases at -20 °C has been noted. Nevertheless, the higher pressure needed for the BO 600 based greases should be attributed to the higher pour point.


2.3. Tribological study


The tribological study is based on four different methods; two oscillatory tests by using SRV instrument; ASTM D5707 (friction coefficient and wear test) and ASTM D7506B (step load test), and two rotational tests by using four-ball machine; wear scar test (ASTM D2266) and weld load test (ASTM D2596). The standard methods and the evaluation of lubricating greases on the SRV oscillation tribometer is described in literature [1] in detail.


2.3.1. SRV Apparatus & Measurements Modern tribometric test systems like SRV®


(Schwing


Reib Verschleiß) provide both suitable tools and test methods to get a deeper understanding of tribological and lubricity behaviour of the greases. In a previous study, some of the tribological aspects of neat lithium and neat lithium complex greases based on two of the oils that are used in this study (BO 400 and BO 600) were determined by using SRV®


[2]. However,


the frame of this work has been extended further by focusing on the additivated greases as well.


The focus of the investigation in this study was on the Figure 1: SRV® oscillation chamber


Wear values are estimated according to ASTM D5705 “Standard Practice for Determining the Wear Volume on Standard Test Pieces Used by High-Frequency, Linear-Oscillation (SRV®


) Test Machine”. Figure 1


shows the oscillation test chamber. Test specimen for SRV®


: Lower specimen:


Disk 24 x 7.9 mm, both surfaces lapped, according to DIN 51834, surface roughness 0.50-0.65 µm Rz, material: 100Cr6, hardened


LUBE MAGAZINE NO.165 OCTOBER 2021 31


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.136 page 3


following issues: 1) What will be the response of the additive package in various types of greases?


2) Can lower soap content (the greases contain different soap content but same consistency) create better opportunity for the additives to perform (since soap typically competes with additives on the available positions on the metal surfaces)?


3) Is the additive package going to perform equally on various grease formulations?


The following standards have been achieved by SRV®


for the investigation of different tribological performances of greases for decades: 1) Friction and wear performance - ISO 19291 / ASTM D5707


2) Load-carrying capacity (EP load) - ISO 19291 / ASTM D5706B


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