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KRL Shear Stability Tests in Four Ball Tester (FBT-3)

November, 2021

Lubricant formulations which ensure a stable viscosity under high shear rates (~ 107 sec-1) are critical to ensure adequate film thickness to protect equipment from unacceptable wear and scuffing. Viscosity modifier used as additives are susceptible to degradation during  mechanical shearing. The KRL shear stability test (CEC L-45-99) is considered one of the most severe tests to estimate the permanent change in viscosity caused by mechanical stresses and correlates well with the field data for a 60 hour test. (Reference - "Impact of Viscosity Modifiers on Gear Oil Efficiency and Durability", 2013 SAE, Lubrizol).

KRL shear stability module (KRL-SST) has been newly designed (Figure 1) as an add-on attachment to the Ducom benchtop Four Ball Tester (FBT-3) thereby expanding its capabilities beyond wear preventive and extreme pressure performance evaluation. This new design has zero impact on the compactness and ease of operation of the existing FBT-3 system. The module complies with the CEC L-45-99 and DIN 51350-6 standards.

FBT-3 with KRL module delivers the highest levels of precision and ease of operation without compromising with legacy data in users lab. 


Figure 1. Ducom FBT-3 with KRL-SST module 

As shown in Figure 2, the major physical change in the FBT-3 unibody shell is an open slot (65 X 30 mm) on the side for coolant coolant pipes that connect KRL bearing pot (Figure 1, inset) with the temperature control module.

KRL-SST FBT-3 changes

Figure 2.  (a) KRL test oil cup with temperature sensor (b)temperature control unit (c) FBT-3 unibody open slot design

A tapered roller bearing (SKF32008XQ) for shearing the fluid replaces the standard four ball configuration (Figure 1, Figure 2a). A special lubricant cup with fast response temperature sensor and integrated cooling channels is connected with a proprietary closed loop temperature control unit to maintain the temperature of 60 ± 1 °C. This system uses ethylene glycol as a coolant for high precision temperature control for long duration tests lasting for hundred hours. The load and speed controls is enabled by automated loading and direct drive technology on FBT-3 (Figure 2).

Note: FBT-3 with KRL-SST module can connect to MOOHA digital tribolab assistant through WiFI network for anytime, anywhere access to live streaming test data and instrument health monitoring.

The performance of the KRL module has been extensively tested and validated using RL 209 oil (CEC L-45-99 reference oil for bearing qualification). Table 1 describes the test conditions as per CEC L-45-99.

Table 1. KRL shear stability  test parameters as per CEC- L-45-99  

Parameters Values
Load (N) 5000 ± 200
Speed (rpm) 1475 ± 25
Oil temperature (°C) 60 ± 1
Oil quantity (ml) 40
Total number of revolutions 1740000 ± 500
Duration (h / min) 19 h 40 min ± 20 min


Closed loop aumated loading, embedded encoder drives and proprietary temperature control units ensure that the loads, speeds and temperature during the 20h test are maintained with a much better precision than the prescribed CEC limits. (Figure 3). The viscosity loss for RL 209 reference oil (9.88%) was within the stated limits of 7.5 and 10.9%. (Figure 3)

KRL- SST FBT-3 test data-1

Figure 3. Load was stable at 5000 N, Speed was stable at 1475 rpm and temperature was maintained at 60 +/- 1 oC during a 20 hr test. 

The newly designed FBT-3 with KRL-SST module expands the capability of testing and development of high-performance lubricants while still offering the benefits of precision, easy testing experience and lower cost of ownership.

Note - Ducom's Stand-alone KRL-SST-1 is the first automatic shear stability tester designed to be in full compliance with CEC L-45-99 standard for 20h to 100's of hours of conitnuous testing. Recommended for users who perform KRL tests on a regular basis for and prefer the flexibility without blocking out the use of their Four Ball Tester.

What other features you would like to have in a FBT ? We are excited to hear from you. Drop us a note

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