Liquid composition and its use as magneto-rheological liquid

Details Liquid composition and its use as magneto-rheological liquid Liquid composition and its use as magneto-rheological liquid

1999-06-25

2001-06-12

Koslow, C. Melissa (Department: 1755)

Compositions

Magnetic

Flaw detection or magnetic clutch

C252S062540, C252S062550

Reexamination Certificate

active

06245253

ABSTRACT:

The present invention relates to a fluid composition which is characterized by a low tendency towards settling of the particulate solid materials dispersed therein and to the use of said composition as a magnetorheological fluid (MRF).
Magnetorheological fluids are functional operating media the flow behaviour of which can be changed in a wide range by applying a permanent or variable electromagnetic field.
Magnetorheological fluids are useful in many different fields, such as hydrodynamic, hydrostatic, and lubricating applications. Examples of said applications include adaptive damping devices, clutches, and programmable brake systems, the fixation of antiwear agents, and sealants for moveable shafts.
Prior art experimental magnetorheological fluids generally consist of a carrier fluid, ferromagnetic particles and, optionally, additives for improving certain application characteristics of the desired products. Additives are particularly required for minimizing the sedimentation tendency or centrifugal separation of the specifically heavier magnetic particles. Examples of such additives are disclosed for instance in PCT/US 93/09939 (WO 94/10693).
Persuant to prior art, mostly synthetic media, such as silicones or polyglycols, are used as base fluids. However, said fluids are frequently incompatible with the mineral oil-based operating media mostly employed for industrial applications and, therefore, they are inappropriate for many uses.
In addition, said fluids require special additives which cannot be universally used involving higher cost and undesirable multifariousness of products.
The additive components employed for the synthetic base fluids referred to hereinabove do not sufficiently prevent from particle settling whenever the base fluids are hydrocarbons. Therefore, it was the object of this invention to eliminate the shortcomings described hereinabove.
Pursuant to this invention, the problem is solved. It was surprisingly found that when utilizing a special fluid composition, optimum fluid characteristics with respect to particle settling, flow, and magnetorheological properties can be achieved. Said fluid composition may be described as a stable suspension in which the particles are permanently dispersed.
The fluid composition according to this invention contains as
component A
a hydrocarbon as a base fluid, as
component B
one or more particulate solid(s), the
average particle diameter being less than
50 &mgr;m, and as
component C
a polyurea compound having at least 3 and
not more than 20 —NH—C(═O)—NH— groups as a
thickener.
Optionally, also the components D and E can be present.
Component D is a partially esterified polyol serving as a dispersant.
Component E is an acrylate polymer and/or methacrylate polymer used as a viscosity index improver.
The optional additive components D and E will correlate with the essential components A, B, and C and allow to adjust the flow behaviour in a controlled way and according to the desired application, while maintaining or further improving the antisettling stability.
The individual component concentrations in the additive base systems are dependent on the intended use and the respective magnetic particle content in the MRF. Besides component A, the composition advantageously consists of the following components which may be used in different quantities according to use.
Preferred Quantity
Component
10 to 95 wt. %
25 to 90 wt. %
B or
(particularly preferred
55 to 85 wt. %)
1 to 70 wt. %
2 to 40 wt. %
B if B is no
metallic powder
0.05 to 4 wt. %
0.1 to 3 wt. %
C or
(particularly preferred
0.1 to 2 wt. %)
0.5 to 40 wt. %
1 to 30 wt. %
C, referring to
(particularly preferred
addition of SRI/2
1 to 20 wt. %)
0 to 6 wt. %
1 to 4 wt. %
D and
0 to 20 wt. %
2 to 15 wt. %
E
These quantities refer to the fluid composition. Most advantageously, components A through E add up to about 100 (the preferred weight percentages are independent of each other).
Component A is a hydrocarbon utilized as a base fluid. A hydrocarbon compound within the meaning of this invention is a compound which predominantly (>90 atom %, more desirably >95 atom %) consists of carbon and hydrogen atoms. Examples of said hydrocarbon compound include mineral base oils or synthetic hydrocarbon oils which are miscible with mineral oils, such as hydrocrackates and polyalphaolefins, or long-chain esters (carbon chain=acid+alcohol>C12). Preferably, the base fluid or the mixture of base fluids will not readily evaporate and has a boiling point of higher than 100° C. Examples of said fluids include hydrogenated spindle oils (hydrocarbon mixtures, e.g. Tanex DN 7 of DEA company) or solvent raffinates (hydrocarbon mixtures, e.g. Panax 19 and Nepos 6, both of DEA). Furthermore, commercially available conventional hydraulic or transmission fluids of the ATF type (Automatic Transmission Fluid) are useful. They may partly contain the optional components D and E. Illustrative of said fluids are Deafluid 1585 (ATF type TASA), Deafluid 4011 (ATF type Dexron II D), Deafluid 3000 (ATF type Dexron III) and the experimental product DES 5999 (ATF type Dexron III), all of DEA company.
For example, hydraulic or transmission fluids of the ATF type have the following typical composition:
approx. 85 to 92 wt. %
solvent raffinate, paraffin base
approx. 2 to 6 wt. %
viscosity index improver based
on polymethacrylate with dispersant function
approx. 4 to 8 wt. %
of an additive package comprising antioxidants,
corrosion inhibitors, antiwear agents, friction
coefficient improvers, and approx. 0.5 to 3.5
wt. % dispersants having a similar effect to
that of component D.
Component B is one or more particulate solid material(s), the average diameter of the particles being less than 50 &mgr;m. In particular, said component is a transition metal and/or transition metal compound. Within the meaning of this invention, a transition metal compound includes alloys containing transition metals. Transition metals according to this invention are any elements having the atomic numbers 21 to 30, 39 to 48, 57 to 80 and higher than 89. Preferred transition metals/transition metal compounds are those in metallic or oxidic form. Transition metals and/or transition metal compounds having magnetic properties (paramagnetic, superparamagnetic, particularly ferromagnetic) are most desirable, particularly Fe, Co, and/or Ni. The particles preferably have an average diameter of from 0.5 to 20 &mgr;m. Iron powder/iron oxide powder are preferred. Said powders may for instance have a silicic acid coating. Carbonyl iron powders with a low carbon, nitrogen and/or oxygen content which have been aftertreated by reduction have proved to be particularly appropriate.
Examples of said carbonyl iron powders include products of BASF Corporation, such as those of the SQ or CN series, Whiskers A 234 (Fe-Whiskers), or ferrite materials of BASF or Kaschke KG, Göttingen (Sr, Mn, and Mn/Zn ferrite).
Besides these powdery metallic solids, other particles, too, can excellently be suspended in the fluid compositions of this invention, for example molybdenum disulphide or graphite. Such fluid compositions are useful as lubricants which may be used among others in combination with ferromagnetic particles.
Component C is a polyurea compound having at least 3 but not more than 20 —NH—C(═O)—NH—groups, preferably 3 to 8, most preferably 4 to 6. Said component acts as a thickener. Excellent sedimentation stabilities can be achieved when utilizing a commercially available thickener concentrate based on the polyurea compound described hereinabove. The polyurea compounds used in the present invention are present in quantities of from about 6 to 10 wt. % (generally about 8 wt. %) in a commercially available grease marketed by Chevron under the trademark SRI/2. are for instance commercially available as ingredients in SRI/2 lubricant (Chevron company) which contains the polyurea component to be used according to this invention in quantities of from about 6 to 10 wt. % (≈8 wt. %).
The polyurea compound of this invention is part

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