At the Department of Fluid Technology at KTH, there was a laboratory spanning three floors, with a large basin in the basement where full-scale pump and turbine tests using water could be carried out while generating electrical power.
– When the expansion of hydropower began to slow down, the work shifted toward testing oils instead, and the department then took the name Fluid Technology, Bengt Hedengren explains.
Tested the effect of additives on hydraulic oils
He began there himself as a research assistant, and later as a researcher, after completing his degree in Fluid Technology. One of the research projects focused on testing the shear stability of hydraulic oils.
– We had an industry group linked to the project, and they had discovered that oils lost viscosity during operation. In the project, I compared hydraulic oils with and without different additives and found that additives caused viscosity to decrease when the hydraulic systems were running.
They saw that the molecules aligned in the flow direction and that, in a pump, the flow was then reduced, something referred to as temporary viscosity loss. After some time in operation, a permanent viscosity loss could also be observed.
– The reason was that the additive molecules were broken down inside the pump and in pressure valves, and the shorter the chains became, the lower the viscosity contribution was.
This means that it is the weight percentage of additives that determines how viscosity develops during operation.
– In tougher oil environments, such as gearboxes, the molecular size of the additives had to be reduced so that viscosity could remain reasonably stable over time. In hydraulic systems, the impact is normally somewhat smaller, so the molecular size of the viscosity improver is adapted to the system’s effect on it. The amount of additives then becomes decisive for the viscosity increase.
Conducted several filter tests
In another project, Bengt Hedengren tested filters in hydraulic systems and examined how many particles passed through the standard filters available at the time. It was the first Multi-Pass test conducted outside the United States.
– One of the larger manufacturers in Germany sent me their entire filter range and asked me to test the filters. The results showed that none of the filters performed particularly well.
He was quite worried when he sent the report to them and wondered how they would react.
– I became even more nervous when, after a while, we heard that both the owner and the CEO were coming to KTH to visit. I did not think they would be very pleased. All the more surprising was it when they arrived with a completely new generation of filters and asked us to test them, which we did with far better results, Bengt Hedengren recalls with a smile.
In the same area, he also studied oils with different additives from Nynäs Petroleum to examine why some of their oil quickly clogged the filters. The problems were primarily caused by reactions between additives and water that blocked the filters.
Conducted field tests on his uncle’s excavator
At that time, the cleanliness of hydraulic oil was determined by bottle samples taken from the hydraulic system, and the sample became the only basis for deciding the contamination level in the system.
– I was then given the opportunity to measure the contamination level in my uncle’s excavator online, and I carried out field tests and measured particles in the oil during different movements of the bucket. It turned out that particle levels increased significantly especially when the bucket struck the rocky ground. The conclusion was that the contamination level in an excavator varies greatly during operation; impacts and shocks from the bucket hitting the ground create a large number of particles, which are then gradually filtered out.
Variable flow creates problems for filters
He also carried out filter tests for Atlas Copco, which had also experienced problems with particle contamination in its large mining drill rigs.
– I then tested the high-pressure filter during operation by measuring online before and after the filter under the highly variable flow conditions in the system at Atlas Copco’s mine in Sickla.
During drilling, the drill head strikes the rock at high frequency. This means that the flow through the high-pressure filter varies at the frequency of the drill impacts, since the flow controls the drill rod.
– Our tests showed that the filter could not withstand this variable flow. The first solution was to install a more robust filter in the high-pressure line and better filters on the return line, so that most of the cleaning took place there. A separate filter flow can also be used for cleaning if the operating conditions for an inline filter are too severe.
Many teething problems in new applications
In the early development of forestry machines, there were major problems with contamination in the hydraulic oil and with the mixed range of components used in the hydraulic systems.
– That was not so surprising, since they were using machines that were not intended for forest operation. For example, the tyres, which were ordinary truck tyres, often punctured. We conducted tests on the hydraulic oil during operation and realised that the components in the machine were not designed for the harsh forest environment and the contamination levels in the systems, Bengt Hedengren says.
The simple solution was to test better filters, which resulted in both cleaner systems and better operation. It is one example of the teething problems hydraulic systems have had in new applications over the years.
Started courses for companies
To help increase companies’ knowledge of hydraulic systems, he began organising courses at the department and laboratory at KTH. The mornings were devoted to theoretical lectures and the afternoons to practical tests in the lab.
– We showed how filters functioned and also addressed problems we had seen with hydraulic hoses. There was often a great deal of debris inside them during assembly, and we showed how hoses could be cleaned before installation. All such measures contribute to cleaner hydraulic oil and longer service life.
Hydraulic fluid as a machine element
All the projects carried out in the laboratory at KTH demonstrated the importance of regarding hydraulic oil as its own machine element; it must be given the same priority as other components. Often, it is best to choose the hydraulic oil first based on the intended application of the system and then design the hydraulic system around the oil that has been selected.
– One project we conducted that never really caught on in the industry was when I tested the dirt sensitivity of different pumps. We added particles gradually in increasing sizes and measured how the flow from the pump changed. The idea was that one should be able to combine the dirt sensitivity of different pumps with requirements for filter efficiency in order to optimise function based on the components’ dirt sensitivity. But, as I said, the hydraulic industry never adopted that idea.
Has taken part in several stages of development
Bengt Hedengren was also involved in evaluating the performance of hydraulic oils at low temperatures in the cold room at Fluid Technology and in field tests.
– Before we carried out our project, oil viscosity was measured at 40 and 100 degrees, and those values were then simply extrapolated down to temperatures of minus 20 degrees. In reality, many oils solidified in the cold. That led to the development of hydraulic oils that could handle low temperatures. The Hydraulic Fluids Committee introduced a hydraulic oil, SHS 32, that was supposed to handle a cold winter morning followed by high operating temperatures in the hydraulic system. It later became a Swedish standard, he explains.
He was also involved in the development of environmental oils, which began when it was realised that hydraulic oils leaking from systems could release oil and unwanted substances into nature and rivers.
– At first, that development happened a bit too fast and in the wrong way. Oils had always been subject to technical requirements, and then environmental requirements were added. The problem with the first environmental oils was that they met the environmental requirements but not the technical ones. That led to a Swedish standard for hydraulic oils with defined requirements for both environmental adaptation and technical performance.
How synthetic ester oils entered the picture
One thing Mobil had noticed with the synthetic polyalphaolefin oils they initially tested in hydraulic systems was that these oils reduced operating temperature in the systems. Mobil therefore concluded that their hydraulic oil provided higher efficiency and lower losses in the system.
– At the time, I was working at FMV with responsibility for fuels and lubricants, and I was contacted by Mobil, which wanted support in a project they wished to start at Luleå University of Technology. They were going to compare the performance of mineral oils with their polyalphaolefin oil.
A rather amusing detail in that project was that they first wanted to compare only mineral oils with one synthetic polyalphaolefin oil, but then the doctoral student insisted that three different oils were needed for a correct evaluation, so they added a synthetic ester oil as well.
– The ester oil turned out to be the most functional oil. That is how synthetic ester oils entered the development of environmentally friendly hydraulic oils, Bengt Hedengren explains.
