How sturdy do the scissors really need to be? Or to put it another way: what do lubricants and scissors have in common?

The question may seem unusual at first, but it is actually very close to the main topic. Whilst lubricants are not directly about shearing, they do concern the stability of polymers – which are added to lubricants as required (technically referred to as ‘additivisation’) – in the face of mechanical shearing. Mechanical shearing refers to the shearing, cutting, fragmentation and destruction of polymers. These polymers must withstand shear loss under mechanical stress – as is the case, for example, in bearings, gearboxes or on sliding surfaces. Here, metallic surfaces interact with one another, and the shear stability of the polymer or the lubricant is crucial. 

What influences the shear stability of a lubricant? 

The shear stability of a lubricant is a complex topic that depends on several factors. To explain this in concrete terms, let us take hydraulic oils as an example. For the trouble-free operation of a hydraulic system, it is essential that the viscosity of the hydraulic oil is selected correctly (see also our technical article ‘Viscosity – the great unknown of hydraulic oil’). The lubricant must maintain its optimum performance over a long period of time – which means that the viscosity remains unchanged. 

However, there are factors that can influence viscosity: on the one hand, through oxidation or thermal decomposition (see technical article ‘Are high temperatures critical for lubricants?’) or on the other hand, through mechanical stress, which is directly related to the shear stability of the lubricant. 

Why is shear stability an issue with mineral oil-based hydraulic oils? 

Unlike synthetically formulated hydraulic oils, shear stability is a major consideration for mineral oil-based multigrade hydraulic oils. Mineral oils have a comparatively more limited temperature range. To extend this range, shear-sensitive viscosity index improvers (VII – Viscosity Index Improver) are used. The polymers contained in the VIIs tend to be sheared – in other words, ‘cut up’ – under mechanical stress. This means that the polymer chains are partially broken down, leading to a loss of viscosity and the multigrade properties. 

However, this effect can be minimised through the targeted use of stable (and often more expensive) VIIs in combination with high-quality base oils and inhibitors. 

Shear stability and the KRL test 

The shear stability of a hydraulic fluid is determined in a standardised manner using the KRL test (cone-roller-bearing test) in accordance with DIN 51350-6. This test determines the reduction in viscosity of the lubricant as a percentage (%). The lower the viscosity loss in %, the more stable the lubricant is in practical application. 

ROXOR TERRA CIRCULAR HV 46 and shear stability 

With ROXOR TERRA CIRCULAR HV 46, we have once again set new standards. We have succeeded in developing a mineral oil-based multigrade hydraulic oil which, thanks to sustainable ‘second-life’ base oils, highly specialised additive technology and perfectly balanced VIIs, achieves outstanding KRL shear stability of around 5 %. Conventional hydraulic fluids achieve KRL values of well over 20 %, which leads to a change in viscosity over the medium term. In such cases, it is necessary to change the oil regularly to maintain the efficiency and reliability of the hydraulic system. 

Conclusion: Sustainability and efficiency combined 

The gap between conventional mineral hydraulic oils and ROXOR TERRA CIRCULAR HV 46 is clearly evident here: While conventional mineral hydraulic oils only last for limited oil change intervals, ROXOR TERRA CIRCULAR HV 46 manages to extend the service life considerably whilst maximising the efficiency and reliability of the hydraulic system – sustainably and cost-effectively. 

SWISS OIL IN MOTION – We keep your machinery running sustainably. 

Disclaimer: These recommendations are based on the experience of LAEMMLE Chemicals AG and our customers, as well as the information they have provided to us. These have proven effective in practice; however, deviations in individual cases cannot be ruled out. It is essential that the manufacturer’s instructions are followed during use.