US2373727A - Compositions for the prevention of the formation or accretion of ice on exposed surfaces - Google Patents

Description

tim Apr. 17 1945 COMPOSITIONS FOR THE PREVENTIONQOI THE FORMATION OBACCRE'I'ION OF ICE ON EXPOSED SURFACES Harry Longhurst West and Alexander Robert Ogston, London, England, assignors to Intava Ltd,. Westminster, London, it-British company No Drawing. Application March 20, 1942, Serial N0. 435,552. In Great Britain All!" 10, 1941 v Galina. (01. 106-13) This-invention relates to compounds for application to aerofoils and like surfaces subjected to high'relative speed air currents and ice forming conditions to prevent or reduce the formation and/or accretion of ice thereon.

' It is known that certain parts of aircraft flying in certain weather conditions tend to become coated with formations of meat different types depending upon the particular conditions and that'often these formations of ice build up or the parts in question'which add consider ly to the gross weight of the machine and may cause this to rise over the safe load. Furthermore,

' such accretions of ice on the various parts of the aircraft alter considerably the aerodynamic properties of certain parts which interferes more or less seriously with the operation of the aircraft and in some cases the secretions of ice may be such as'to prevent the movement of some parts in'which movement is. necessary for the control and manoeuvrability of the aircraft. and such accretions will therefore interfere serioush' with the safe and efiicie'nt operation of the said air- 7 craft. It is therefore extremely desirable that means should be provided either to prevent or 10 accrete and form substantialcoatings of lo over immiscible liquid or for flowing a cryoscopic' liquid over thejsurface of the parts in question have the disadvantage that they entail the use of mechanical devices which again add to the weight of the aircraft and reduce its useful loading capacity besides utilising considerable power. Such mechanical devices. also .require considerable maintenance and have a liability to fail at the time when they are most needed and often occupy areas which are required for other more important'equipment. It has also been suggested. to coat the parts likely to be ailected with a com- 7 pound containing a cryoscopic substance capable of lowering the freezing point of ice coming into contact with it and maintaining a liquid I film between the solid surface and theice so that the ice does not adhere to the surface and may be swept "away by the air currents passing over the said parts. One suchcompound comprises a reduce the formation of such coatings of ice, or

to enable such coatings of ice which may be built up on the parts to'be easily detached and removed.

Several methods of attacking this problem have already been" suggested and various devices and compounds'have been proposed for application to, he parts most liable to become coated with such-coatings of ice, either to prevent the occurrence. of ice or to remove the same as soon as it is formed. Among such methods are meth-" which the surface is coated with a liquid or solid quickly thanan uncoated-surface. 1

jelly of a gelatinous material and glycerol or glycol or mixtures thereof.

Such mixtures have been found to be not entirely satisfactory in that the ice is not very readily'detached from the surfaces coated with the material, and under such con'ditionsmore ice rapidly builds up on that already formed and may give rise to dangerous conditions more It has now been found that these can be largely overcome by incorporating in such a mixture of gelatine and glycol and/or glycerol a proportion of a'suitable liquid which is m miscible with the aqueous solution produced by the melting ice.

The present invention accordingly comprises a composition for application to parts. of air-' mation and/or accretion of ice on such parts -r comprising a ielly base consisting of gelatinous cryoscopic substance which reacts with the ice 1 to melt the same when in contact with it. and

maintain a film of melted ice water between the ice and the surface. and'such methods have included means for causing a'fifm continuously over the surtace, e. ggrhy pumping The arrangements iormaintaining aliilm of of liquid to flow prise avp'roportion of a'w craft and the like to prevent or inhibit the formaterialand glycol or glycerol or homologu'es thereof or polyglycols or polyslycerols, e. g., di-. ethylene gh'col or tri-ethylene glycol or mixtures thereof containing a proportion from 5-20% by weight of a liquid which is immiscible with ice or water and remains liquid at temperatures downtol0l". M

In addition to the glycol or glycerol compounds above referred to, the composition may alsov comr soiuble. 'nmnohydric alcohol such alcohol.

, Examples oi'iili'iuids immiscible withwater which may be; incorporated in the Jelly base are mineral, vegetable and oils including essential oils, such 1 as petroleum lubricating. oils; castor oil and pine oils, synthetic'oils. the, water disadvantages immiscible alcohols and in general any liquid which is immiscible with water and remains liq uid at temperatures below F.

It is found that the incorporation of such liquids in the gelatine-glycol base is not. always simple, and it has been found necessary to add to the mixture a small proportion of a dispersing agent to assist in dispersing the oil through the jelly base. Examples of such dispersing agents are soaps, for example, alkali metal or organic base soaps of fatty acids such as steaiic acid or oleic acid, naphthenates, sulphonic acid salts including those obtained from the residues from the treatment of mineral oils with strong sulphuric acid, commercial soaps and monohydric alcohols.

the glycol and/or glycerol.

The compositions are prepared in a simple manner by dissolving the gelatinous material in the glycol or glycerol with the aid of gentle heat and stirring the waterimmiscible liquid and the dispersing agent together into the mass. In certain cases the oil and dispersing agent may be I mixed or combined together to form a homogeneous composition before addition to the .Eelatine mixture.

Examples of compositions prepared according to this invention are:

l. 15% Isopropyl alcohol 72% Glycol 8% Gelatine 5% Oil 2. 23.5% of a mixture of glycerol, containing 3% sodium stearate 67.5% of a mixture of ethylene glycol, containing 10% gelatine 9.0% Mineral oil 3. 81% Ethylene glycol 9% Gelatine 5% Soap previously mixed to form a 5% Mineral oil homogeneous composition v 4. 81% Glycol 9% Gelatine 1% Tri-ethanolamineoleate 9% Oil 5. 58.7% Glycol 11.2% Gelatine 0.5% Gum t'ragacanth 19.6% Water 1.0% Soap 9.0% Oil 6. 63.0% Glycol 7.0%Gelatine 119.0% Water 2.0% Soap 9.0% Oil The above compounds whentested by the following method in the laboratory all showed useful results. The experiments were carried out in a'small wind tunnel installed in a refrigerated chamber and practical icing conditions were simthrough which currents of air at low temperature are driven, and spraying water on to the leading edge of the aerofoil with respect to the wind current.

By varying the conditions of experiment, all types of icing from the hard glassy ice to soft crystalline rime can be produced on the aerofoil.

Samples of the de-icing media described above, when tested'under these conditions showed that as the ice tendsto form, the oily or immiscible liquid content in the medium forms an oily interface having a very low adhesion for the ice which can thereore be readily removed by the air currents. Under very severe conditions the coating of the medium may become entirely covered with ice but this is held very loosely and would, in

all probability, become dislodged and removed under practical flying conditions.

In a particular test, an aerofoil treated with a compound according to formula 6 above; was tested under. severe icing conditions at a temperature of 28 F. in a wind current of miles per hour and at the end of five minutes, it was found that hardly any ice had formed on the treated surface, whereas in a control aerofoil alongside untreated with the compound, a coating of clear glassy ice inch thick had been formed. With continued exposure to still more severe icing conditions, an ice layer up to inch thick was formed on the treated aerofoil, whereas that on the untreated aerofoil was about inch,thick.

Further, in a comparative test between this type of compound and one which has already wide use on aircraft, in a period of 30 mins. the latter was coated with an irregular formation over 1 inch thick, whilst the former. had only a thin ice cap I; of an inch in thickness.

It was found in general on comparing the com! pounds prepared as above containing. the immiscible liquid or oil with similar compounds not containing oil, about 30% to 50% improvement was obtained.

These compositions are easily applied to the parts in question by melting the jelly to a viscous liquid and'then spraying or brushing. the same on to the parts to be treated. They form stable coatings which are not removed rapidly by the friction of the air-currents or slip stream over the parts in question and will retain their ice preventative properties for a considerable time in non-icing conditions, although, of course, underv conditions of icing or heavy rain, the effective life of the coating will vary with the severity of the conditions and the amount of cryoscopic liquid which is used up in melting and dissolved out by the water present.

The composition can frequently be-applied with advantage over many or the preparations and mechanical devices previously disclosed for thispurpose and gives a coating which has a greater emciency than any of the coatings or methods previously described, for example, it may be applied to the flexible shoes fitted to the leading edges of aircraft and intended to be flexed pe- 70 iilated by placing model aerofoils in the tunnel r-iodically to split of! ice formed thereon, or it may be applied as an upper or an under coatin in combination with any of the coating compositions previously described for this'purpose.

What-weclaim is:

' 1. A composition for application to surfaces exposed to the deposition of ice to prevent the formation or accretion 'of ice thereon, comprising a jelly base composed of from about 7 to 17 percent by weight of a gelatinous material and from about 83 to 93 percent by weight of an antifreeze material of the class consisting of glycol, glycerol, polyglycols, poly glycerols and their mixtures, having incorporated therein from about 5 manna": p

' posed to the deposition-otice to reduce the formation'snd accretion of ice-thereon comprising to 20 percent by weight of an organic liquid which is immiscible with ice and water and which remains liquid at temperatures below plus 10 l".'

2. Acomposit'ion 'occording to claim 1 in which the immiscible liquid is a mineral lubricating oil.

3. A composition =accordin'gto claim 1 in which the immiscible, liquid is a vegetable oil.

4. A composition according to claim 1 in which the immiscible liquid is an flllliml Oll.

5. A composition according to claim 1 containing'as a dispersing agent-l; soap or the class consisting of an alkali metal soap 0! a higher fatty acid and an organic base soap.

6. 'A composition according to claim l containing as a dispersing agent a low molecular weight alkyl monohydric alcohol.

7. A composition; comprising 23.5% of amixture of glycerol and 3% of its weight oi sodium stearate, 67.5% of a mixture or ethylene glycol and 10%. or its weight of gelatin and 9% y weight of mineral oil.

8.- .A composition ior application to surfaces ex- 81% by-weight ot a mixture of ethylene glycol cnd9% of its weight om gelatin and a mixture of 5% by weight of mineral oil end 5% by weight of map .9, A composition for application to Mouse:- posed to the deposition of ice to reduce the formation and secretion otiee thereon comprising 32% oi ethylene glycol, 15% of iso-propyl-clco 'mmiw ,mn'onms'r i iirinxs mnn noun-r ocis'mu.

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