In Australian underground mining, certain applications such as fluid couplings require the use of fire-resistant fluids. Until recently, the choice of fluid was limited to phosphate esters, the use of which has a major inhalation toxicity concern. When overheated, the fusible plugs are liable to blow, emitting distasteful fumes into the work area.
To address this problem, the New South Wales Department of Mineral Resources along with a major coal producer approached Quaker Chemical with a challenge to develop an alternative fluid that met stringent fire resistance requirements but had lower toxicity.
In response, Quaker Chemical launched Quintolubric 822-320, a phosphate ester-free fire-resistant hydraulic fluid based on polyol esters. The fluid was trialled for 18 months and is now available to the market.
According to Quaker’s Derek Hanna, safety is the stand-out benefit of the new fluid. “Polyol esters are readily biodegradable, have low toxicity and are easily separated from water. Furthermore, upon breakdown they do not release phosphoric acid like phosphate esters,” he said.
Hanna said the performance benefits of polyol esters included superior seal compatibility and wider operating temperature range.
The development of fire-resistant hydraulic fluids in mining has been a gradual one. Use of these fluids began earlier this century after mineral oil-related fires claimed several lives - in particular one fire in Belgium which killed 50 workers.
Initially, water-based fluids replaced mineral oils in applications considered to have a high fire risk. These fluids had good fire resistance by virtue of their water content, but the lower operating pressure and temperature the lubricants required limited their performance.
Increasing power and reliability requirements for mining equipment led to the introduction of phosphate esters as an alternative to water-based fluids. The fire resistance of these fluids was thanks to their unique chemistry of an ester containing phosphorus. While inferior to water as a fire-resistant medium, phosphate esters had several attractive attributes of fire resistance while not having the pressure and temperature limitations of water-based products.
Phosphate esters had high resistance to ignition and flame propagation, and furthermore, it rapidly self-extinguished by emitting dense smoke which displaced oxygen.
The use of phosphate esters in mining was limited to critical applications such as fluid couplings. The rapidly expanding longwall industry had engineered itself toward high water-containing fluids to power the roof support. This was due to their high leakage rates, requiring a fluid media with low applied cost and high fire resistance.
During the 1960s, the use of phosphate esters increased and concerns emerged over its occupational health and safety as well as its environmental compatibility. Certain types of phosphate esters in use in agriculture were banned as they were found to be neuro toxins. Suppliers of phosphate ester hydraulic fluids launched safer new-generation phosphate esters and polyol esters.
Polyol esters are based on low-toxic natural fats specially refined to deliver virtually equivalent lubrication performance to mineral oil hydraulic fluids but with higher fire resistance.
Even though polyol esters have inferior fire resistance to phosphate esters, the concept was rapidly adopted in the steel industry, in particular, where the use of phosphate esters has now largely been replaced by polyol esters. This first generation of polyol esters, however, did not meet the high fire resistance requirements of underground mining applications, where the use of phosphate esters continued.
The project by Quaker and its partners introduced the next generation of hydraulic fluids in 1999. Since then, BHP Billiton has put Quintolubric 822-320 into all its fluid couplings across its mining business.