RECOVERY AND REUSE OF ARYL PHOSPHATE
ESTER HYDRAULIC FLUID
Rex A. Hunter, Chemist
Environmental Research
Armco Inc.
Middletown, OH 45043
INTRODUCTION
The classical steps in the production of flat rolled steel strip are to melt and refine pig
iron in a furnace, pour the refined steel into molds to form ingots in a process known as
teeming, allow these ingots to cool prior to stripping away the molds, reheat the ingots and
roll them into slabs, allow the slabs to cool and then reheat them for rolling into strip or
sheet steel. Drawbacks to this process are the amount of handling involved, the amount of
energy lost, and the amount of waste created. The process known as continuous casting
takes molten steel from a refining furnace (usually a basic oxygen furnace or electric furnace)
and casts the metal directly into slabs. This eliminates a lot of handling, one cool down and
reheat cycle, and some of the waste incurred in the teeming process.
In a continuous caster, hydraulic cylinders are used to position the series of rolls necessary for giving the cast slab the appropriate thickness and width. Because several slabs are
cast from one ladle of steel, cutting torches, hydraulically positioned, are used to cut each
slab to the desired length at the exit end of the caster. Any leakage of hydraulic fluid from
these operations would come into direct contact with very hot metal and/or cutting torches.
Hence, the fire resistance of the hydraulic medium is of utmost importance and conventional
mineral oil hydraulic fluids are not suitable for this application.
The continuous casting unit studied was the one at Armco's Middletown (Ohio) Works.
This is a dual (two slabs side-by-side) or two-strand caster rated at 5 ton/min. It was built
as part of a major expansion of the capacity of Middletown Works and placed into service
in January 1972.
CHEMICAL NATURE OF FIRE RESISTANT HYDRAULIC FLUIDS
Fire resistant hydraulic fluids are classified into four types: pure phosphate ester (PE)
fluids, phosphate ester-mineral oil blends, water-glycol mixtures, and invert (water-in-oil)
emulsions. This study is concerned with pure phosphate ester fluids, but most of the results
could be applied to ester-oil blends as well.
Phosphate esters are petroleum-derived chemicals that have as their basic structure three
organic molecular groupings bound to a phosphorus atom through oxygen (ester) linkages.
They can be depicted as in Figure 1.
0
Rn_0-p-0-R
I
0
R*
Figure 1. Schematic representation of a phosphate ester molecule.
The organic groupings (R, R ', R ') can be in any combination depending on the reactants
used to form the compound. One of the more typical compounds is tricresyl phosphate. This
is shown in Figure 2.
115