Development of a Biopolymer-Based Hydraulic Fluid with Plant Corrosion Protection Additives

 

In complex technical hydraulic applications, high demands are placed on biodegradable pressure transmission media. In many cases, water as the basic fluid cannot meet the requirements. Besides the corrosive effect on metals, the low viscosity is a particular disadvantage. The aim of the present project is on the one hand to enhance the ecological and economic advantages of water in HFC media by increasing the water content and on the other hand to replace the additives, which have so far been based on mineral oil, by plant-based additives.

 
Benefit Procedure
Development of a new, water-containing pressure medium Creating the requirement profile for hydraulic applications
Targeted adjustment of viscosity through carbohydrate-based biopolymers Study of the stability of biopolymer solutions in an ageing test bench
Fluid system from renewable raw materials (basic medium, thickener and additives) Tribometer and compatibility tests
Reduction of the disposal costs of hydraulic fluids Application test in the efficiency test bench
 

Fluid Requirements

Today's hydraulic fluids must comply with a large number of laws, technical standards and certificates in order to survive in the market.

A comprehensive fluid development takes into account the areas of system compatibility, sustainability and efficiency. System compatibility means the chemical interaction between the machine and its hydraulic fluid. Examples are sealing compatibility and corrosion protection. Sustainability considers the production and disposal of the hydraulic fluid. While the term "environmentally friendly" according to DIN ISO 15380 only defines biodegradability, the term "bio-based" according to DIN EN 16575 refers to the proportion of biomass in the raw material.

Especially the fluids of the HETG class are environmentally friendly and bio-based. Not least because of the Vessel General Permit, which came into force in 2013 and requires water-soluble, environmentally compatible lubricants for all territorial waters of the USA, research has recently been focusing increasingly on HEPG and HFC class hydraulic fluids. Hydraulic fluids of the HFC class are aqueous solutions of polymers. However, HFC fluids are neither bio-based nor biodegradable in the sense of the standards. The hydraulic fluid to be developed is also water-based and is added with a bio-based polymeric thickener. Therefore, a comparability with a conventional HFC medium is most likely. The minimum technical requirements for an HFC hydraulic medium are specified in DIN EN ISO 12922.

 

Fluid Ageing Study

CAD Model of a Fluid Ageing Test Bench Copyright: ifas CAD Model of the Fluid Ageing Test Bench

With regard to the polymer-based fluid to be developed, the first issue to be addressed is polymer stability under hydraulic load collectives. In accordance with the tasks of the first work package, a fluid ageing test rig was developed at IFAS. The test rig is shown in figure 1, which consists of two circuits. In each circuit the test fluid is delivered by two pumps through a pressure relief valve (DBV) and a throttle. The pressure reduction is carried out in two stages to avoid cavitation damage in the valves. This increases the static pressure on the low-pressure side of the DBV. In addition, the viscosity can then be continuously estimated from the pressure drop across the throttle during test operation. Especially in the DBVs as well as in the throttles high shear rates are achieved which act on the polymer.

  Viscosities over the Test Period Copyright: ifas Viscosities bove the test time of Berufluid 46a and Hydrostar Red

The test parameters selected for both circuits were 160 bar at 10 l/min and 30 °C operating temperature. Fig. 2 shows above the kinematic viscosity of the Berufluid 46a with higher corrosion protection content as well as that of Hydrostar Red over a test period of 600 h. Within the test period a slight viscosity drop can be seen with both fluids. In the lower part of the picture the viscosity was normalised with the thickener concentration in degrees Brix to take into account the viscosity changes resulting from the evaporation of the water. Since the normalized viscosity also decreases, a chemical change of the thickener due to the shear stress in the test rig is currently assumed. However, the decrease in viscosity in the Berufluid 46a is not significant compared to that of the Hydro-star Red. The polymeric thickener in the Berufluid 46a therefore seems to withstand the loads in the hydraulic system to a similar extent as a polyglycol (Hydrostar Red).

 

Cooperation Project

The project is carried out in cooperation with the Fraunhofer IVV, which is responsible for the development of a plant-based corrosion protection additive. Furthermore, the company Carl Bechem will be responsible for the provision of test media, formulation and additives.

 

Publications

Otto, N.: „Experimentelle Untersuchung nachhaltiger Hydraulikfluide auf Ester- und Wasserbasis“, 2018, Dissertation