Method for separating a cooling lubricant agent from a bearing lubricant

Abstract

The present invention relates to a method for reconditioning bearing lubricants that can be used in equipment for metal working, in which cooling lubricant that can be used in equipment for metal working is separated from the bearing lubricant. In addition the invention relates to a bearing lubricant for use in the method according to the invention.

Claims

1. Method for reconditioning bearing lubricants that can be used in equipment for metal working, wherein the cooling lubricant that can be used in equipment for metal working is separated from the bearing lubricant wherein a. as bearing lubricant there is used a bearing lubricant whose flash point at 1 atmosphere is at least 150 C. and lies at least 50 C. higher than the flash point of the used cooling lubricant, the bearing lubricant contains at least one oxidation inhibitor with a flash point at 1 atmosphere of at least 150 C., and the bearing lubricant contains at least one synthetic oil selected from polyalkylenglycol; b. as cooling lubricant there is used a non water-miscible cooling lubricant according to DIN 51385 that at 40 C. has a kinematic viscosity according to DIN 51562-T1 of at most 10 mm.sup.2/sec; and c. the separation of the cooling lubricant from the bearing lubricant is carried out by means of a distillative method which is carried out at a temperature of at most 150 C.

2. Method according to claim 1, wherein the distillative separation of the cooling lubricant is carried out at a pressure of less than 5 mbar.

3. Method according to claim 1, wherein the distillative separation of the cooling lubricant is carried out by means of thin-film distillation, short-path distillation and/or by means of a falling film evaporator.

4. Method according to claim 1, wherein as bearing lubricant there is used a bearing lubricant whose flash point lies at least 70 C. higher than the flash point of the used cooling lubricant.

5. Method according to claim 1, wherein a cooling lubricant is used that is soluble in an amount of at least 5% in the bearing lubricant and/or that a bearing lubricant is used that is soluble in an amount of at least 5% in the cooling lubricant.

6. Method according to claim 1, wherein the separation of the cooling lubricant is carried out in the side steam.

7. Method according to claim 1, wherein the polyalkylene glycol is selected from polypropylene glycol and butanol-initiated polypropylene glycol.

8. Method according to claim 1, wherein a non water-miscible cooling lubricant according to DIN 51385 is separated.

9. Method according to claim 1, wherein a cooling lubricant that consists at least 80% aliphatic hydrocarbons is separated.

10. Method according to claim 1, wherein a cooling lubricant that at 40 C. has a kinematic viscosity according to DIN 51562-T1 of at most 5 mm.sup.2/sec is separated.

Description

(1) This object is achieved according to a further teaching of the invention by the provision of a bearing lubricant that contains at least one synthetic oil comprising carbon and oxygen with a kinematic viscosity of 60 to 220 mm.sup.2/sec, preferably of 70 to 150 mm.sup.2/sec, at 40 C. measured according to DIN 51562-1, a ratio of oxygen to carbon of at least 1 to 12, preferably at least 1 to 10, and a mean molecular weight of 1200 to 3500 g/mole, as well as at least one oxidation inhibitor with a flash point at 1 atmosphere of at least 150 C., preferably of at least 170 C. and in particular of at least 190 C.

(2) The bearing lubricant according to the invention has a sufficient compatibility with the products normally used as cooling, lubricant, for example hydrocarbon mixtures, which is advantageous especially in the event of a leakage from the bearing lubricant and cooling lubricant circuits.

(3) In addition the products normally used as cooling lubricant can be separated in a simple way from this bearing lubricant by the method according to the invention.

(4) The bearing lubricant according to the invention is in particular especially suitable for a thermal separation of cooling lubricant from the bearing lubricant. Above all however the bearing lubricant according to the invention can be removed from the cooling lubricant in a simple manner, preferably by a cooling lubricant filtration, in the case of contaminations of the cooling lubricant by leakages of bearing lubricant. This possibility arises insofar as for the cooling lubricant filtration filter aids are used on which the bearing lubricants according to the invention are adsorbed. This applies in particular to the use of filter aid mixtures containing inter alia also filter aids based on bleaching clays.

(5) According to a preferred embodiment of the invention the bearing lubricant according to the invention contains a corrosion inhibitor.

(6) Conventional corrosion inhibitors are suitable as corrosion inhibitors. Preferably the corrosion inhibitors have an initial boiling point at 1 atmosphere of at least 150 C., preferably of at least 150 C. Thus, for example, nitrogen compounds are suitable, preferably basic nitrogen compounds such as tertiary amines and their salts of benzoic, salicylic or naphthenic acids, esters of fatty, naphthenic or dicarboxylic acids with triethanolamine, alkaline earth phthalylalkylamides, aminodicarboxylic acids, dicyclohoxylamine as well as diamides of heterocyclic hydroxyamines and imino esters, amides, amidoximes and diaminoethane derivatives.

(7) Also suitable are fatty acid amides in particular amides of saturated fatty acids with alkanolamines, alkylamines, sarcosine or imidazolines.

(8) Also suitable are phosphoric acid derivatives, in particular diaryl phosphates and thiophosphoric acid esters or neutral salts of primary n-alkylamines (C.sub.8-C.sub.18) or of cycloalkylamines with dialkyl phosphates.

(9) Also suitable are sulphonic acids or other sulphur compounds. Also suitable are combinations of Ba sulphonates and polyoxyethylated alkylphenols, reaction products of dipentene with sulphur in the presence of activated aluminium, combinations of Ba octytphenol sulphide, Ca and Na petroleum sulphonate, alkylmercapto- and alkylsulfinyl acetic acids, as well as mixtures of oil-soluble alkali or alkaline earth metal sulphonates, fatty acids with ethylenediamine (sarcosines) or diethylenetriamine.

(10) Also suitable are carboxylic acid derivatives, in particular napthenic acids, calcium naphthenates, zinc salts, hydroxy- and ketocarboxylic acids, dicarboxylic acids, maleic acid, unsaturated fatty acids, hydroxy fatty acids as well as esters of all of these acids, pentaerythritol and sorbitan monooleates and O-stearoyl-alkylolamines, polyisobutenyl succinic acid derivatives, mixtures of the dicarboxylic acid and its mono-2-hydroxyisopropyl ester, p-alkyl-phenoxycarboxylic acid, in particular acetic acids.

(11) The amount of the corrosion inhibitor that is used may vary. Particularly advantageous are amounts of less than 5 weight %, and in particular amounts of 0.1 to 2 weight %.

(12) In addition the bearing lubricant may contain conventional additives such as high-pressure additives/high-pressure agents, antiwear additives, friction-reducing agents, adhesive agents, viscosity indes improvers, detergents, demulsifiers, emulsifiers, non-ferrous metal inhibitors and/or antifoaming agents, preferably in an amount of less than 5 weight %, and in particular in an amount of 0.1 to 2 weight %. It is particularly preferred to use additives that have a flash point at 1 atmosphere of at least 150 C., preferably of at least 170 C. and in particular of at least 190 C. In this way the thermal separability of the bearing lubricant and of the cooling lubricant from the additives is not adversely affected.

(13) The bearing lubricant according to the invention contains at least one oxidation inhibitor. The known oxidation inhibitors are suitable as oxidation inhibitors so long as they have a flash point at 1 atmosphere of at least 150 C., preferably of at least 170 C. and in particular of at least 190 C.

(14) Thus, for example, sulphur compounds, in particular dialkyl sulphides, polysulphides, diaryl sulphides, modified mercaptans, mercaptobenzimidazoles, thiophene derivatives, xanthogenates, zinc dialkyl dithiocarbamates, thioglycols and thioaldehydes. Of the alkyl aromatic S compounds, dibenzyl disulphide should be mentioned. Alkylphenol sulphides are also suitable. 4,4-thio-bis(2-tert.-butyl)-5-methylphenol is particularly suitable. Also suitable are 2-mercaptobenzimidazole mercaptotriazines, reaction products of benzotriazole-alkyl-vinyl ethers or esters, 10H-phenothiazine and its alkyl derivatives and also 3,3-thio-bis-(propionic acid dodecyl ester) and bis-(3,5-di-tert.-butyl-4-hydroxybenzyl)-malonic acid bis-(3-thiapentadecyl) ester. Also suitable are sulphoxides, preferably in combination with aromatic amines.

(15) Also suitable are phosphorus compounds, such as preferably triaryl and trialkyl phosphites, phosphoric acid/phenol derivatives such as 3,5-di-tert.-butyl-4-hydroxybenzyl-phosphonic acid dialkyl esters or also phosphonic acid dipiperazides.

(16) Also suitable are sulphur-phosphorus compounds such as metal salts of thiophosphoric acid compounds, in particular zinc dialkyl dithio phosphates. Also suitable are Zn and Ba dialkyl dithio phosphates. Also suitable are reaction products of P.sub.2S.sub.5 with terpenes (dipentene, -pinene), polybutenes, olefins and unsaturated esters, especially the terpene and polybutene reaction products.

(17) Also suitable are phenol derivatives, in particular sterically hindered monohydric and also dihydric and trihydric phenols, sterically hindered dinuclear and trinuclear and also polynuclear phenols. Particularly suitable are polyalkyl phenols, in particular methylene-4,4-bis-(2,6-di-tert.-butylphenol). Outstanding results are obtained with 2,6-di-tert-butyl-4-methylphenol. Bisphenols or trisphenols, and also esters of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid as well as 2,6-di-tert-butyl-4-(dimethylaminomethyl)-phenol are preferred at higher temperatures. The reaction product of alkylthiohydroquinone and butylamine is also suitable.

(18) Also suitable are amines, in particular oil-soluble amines such as diphenylamine, phenyl--napthylamine, p,p-tetramethyldiaminodiphenylmethane. Alkylated (C.sub.8,C.sub.9) diphenylamines and N,N-diphenyl-p-phenylenediamine are suitable especially at higher temperatures.

(19) Practical tests have shown that particularly good results can be achieved with high boiling point phenolic oxidation inhibitors with a flash point of at least 150 C., both as regards protecting the bearing lubricant against ageing due to thermal load in the bearing and in the thermal separation of bearing lubricant and cooling lubricant, and also as regards the efficiency of the thermal separation of bearing lubricant and bearing lubricant additives from the cooling lubricant.

(20) In addition practical tests have shown that particularly good results are achieved as regards protecting the bearing lubricant against ageing due to thermal load in the bearing and in the thermal separation of bearing lubricant and cooling lubricant, if a high boiling point amine oxidation inhibitor with a flash point of at least 150 C. is used in addition to a phenolic oxidation inhibitor. Preferably in a concentration of 0.1 to 3 weight %, in particular 0.5 to 1.5 weight %. The use of an alkylated diphenylamine in a concentration of 0.5 to 1.5 weight is most particularly preferred.

(21) The concentration of the oxidation inhibitor in the bearing lubricant is preferably 0.1 to 3 weight preferably 0.5 to 1.5 weight %.

(22) According to a preferred embodiment of the invention the bearing lubricant comprises a synthetic oil with a ratio of oxygen to carbon of 1 to 12 to 1 to 1, preferably of 1 to 5 to 1 to 2, and especially of 1 to 4 to 1 to 2.5. Such a bearing lubricant still has a sufficient compatibility with the products conventionally used as cooling lubricant, for example mineral oils. In addition cooling lubricants can be separated particularly easily from such a bearing lubricant. Most importantly however such a bearing lubricant can be removed in a simple manner, preferably by a cooling lubricant filtration using filter aids, in the event of contamination of the cooling lubricant by bearing lubricant. This applies in particular to the use of filter aid mixtures that contain, inter alia, also filter aids based on bleaching clays.

(23) According to a further preferred embodiment of the invention the bearing lubricant at 40 C. has a kinematic viscosity of 60 to 220 mm.sup.2/sec, preferably 70 to 150 mm.sup.2/sec.

(24) Practical tests have shown that particularly good results can be achieved with polyalkylene glycol, carboxylic acid esters, preferably diesters and/or polyol esters, especially esters of a C.sub.4-C.sub.20 alcohol with a C.sub.6-C.sub.22 dicarboxylic acid and/or esters of a C.sub.2-C.sub.10 polyhydroxy alcohol with a C.sub.6-C.sub.36 monocarboxylic and/or dicarboxylic acid.

(25) An advantage of the use of polyalkylene glycol, for which the abbreviation polyglycol is often used in the literature, is that leakages of the cooling lubricant into the bearing lubricant can be removed in a simple way by means of the method according to the invention. It is particularly advantageous that in the event of leakages of the bearing lubricant into the cooling lubricant, the viscosity of the cooling lubricant, and also its compatibility with an optionally provided subsequent thermal treatment of the rolled strip, for example an aluminium rolled strip, is scarcely impaired.

(26) This is based on the fact that polyalkylene glycol contaminations in the cooling lubricant as a result of a leakage of bearing lubricant can be removed from the cooling lubricant in a particularly simple and effective manner via a cooling lubricant filtration. It is particularly suitable for this purpose to carry out a full flow filtration as precoat filtration, preferably using filter aids, preferably with the partial or complete use of filtration aids based on bleaching clays. In addition polyalkylene glycol has the advantage that in the thermal treatment of the rolled strip it decomposes, i.e. polyalkylene glycol is classed as annealing friendly.

(27) A further advantage of the use of polyalkylene glycol is that polyalkylene glycol has a particularly high viscosity index compared to mineral oils. A high viscosity of the bearing lubricant can thus be adjusted by the use of polyalkylene glycol, which has a positive effect on the temperature range that can be employed in a bearing lubricant system.

(28) In addition an interference of the operation of equipment for metal working, in particular the production of aluminium rolled products in aluminium cold rolling mills, due to the leakage of bearing lubricants, in particular bearing oils from the oil-flood lubricated bearings for roll necks, into the cooling lubricant can be reduced by the use of polyalkylene glycol. In particular polyalkylene glycol increases the process reliability of rolling processes, since with its use an increase in viscosity due to leakages can be kept low or can even be completely avoided. In addition the purity of the cooling lubricant can be improved by their, which meets the requirements demanded by customers. Finally, the costs of replacing or reconditioning of the cooling lubricant filling are reduced, and especially in the production of aluminium foils it is possible to shorten the subsequent thermal treatment, for example by means of a degreasing annealing.

(29) Particularly good results are achieved with polyalkylene glycol if it is used as bearing lubricant in lubricating circuits in equipment for metal working, for example in oil-flood lubricated bearings for roll necks in aluminium cold rolling mills. In particular in the case of these lubricant circuits a leakage from the lubricant circuit into the cooling lubricant and also a leakage of cooling lubricant into the bearing lubricant cannot be completely prevented according to the present prior art.

(30) If a bearing lubricant containing polyalkylene glycol is employed, then the use of polyalkylene glycol with a mean molecular weight of 1200 to 3500, more preferably of 1000 to 3000 g/mole, and in particular of 1200 to 2500 g/mole, has proved particularly advantageous.

(31) Outstanding results are achieved with polyethylene glycol, polypropylene glycol, polybutylene glycol, especially butanol-initiated polypropylene glycol, polytetramethylene glycol, and/or block polymers and/or copolymers thereof.

(32) In particular the polymerisation of ethylene and propylene oxide in a ratio of 0:1 to 4:1, preferably of 0:1 to 2:1, more preferably of 0:1 to 1:1 and especially of 0:1, is suitable for the production of the polyalkylene glycol.

(33) The miscibility with the cooling lubricant can be improved and thus the risk of the formation of two phases can be reduced by adjusting the ethylene oxide/propylene oxides (EO:PO) ratio. In addition the miscibility with the respectively employed cooling lubricant can be specifically adjusted by the choice of the EO:PO ration.

(34) Outstanding results are also achieved with synthetic oils that have a content of ether groups, measured as the mass of the COC bonded oxygen referred to the molecular weight, of 20 to 40%, preferably of 20 to 30%.

(35) Good results are also obtained with synthetic oils that contain carboxylic acid esters, preferably diesters and/or polyol esters, especially esters of a C.sub.4-C.sub.20 alcohol with C.sub.6-C.sub.22 dicarboxylic acid and/or esters of a C.sub.2-C.sub.10 polyhydroxy alcohol with a C.sub.6-C.sub.36 monocarboxylic and/or dicarboxylic acid.

(36) In contrast to mineral oils, polyalphaolefins or polyisobutylenes such synthetic oils possess polar, oxygen-containing molecule groups and thus have the potential to be removed, in the event of a leakage into the cooling lubricant via the cooling lubricant filtration. In addition the synthetic mineral oils that contain polyesters also have the property that under thermal treatment they decompose in a nearly residue-free manner.

(37) In an advantageous modification of the bearing lubricant this preferably consists in an amount of more than 5% of synthetic carboxylic acid esters such as diesters, polyol esters or complex esters, in which in turn the cooling lubricant is more than 5% soluble.

(38) The bearing lubricant according to the invention can in principle have widely varying flash points. A separation behaviour of possible cooling lubricant contaminations that is advantageous for a thermal separation method can be adjusted by the choice of the flash point of the bearing lubricant. The boiling point of the bearing lubricant and also the boiling points of optionally admixed additives and further constituents are preferably chosen so that they do not have a temperature range that overlaps with the boiling point of the cooling lubricant.

(39) Preferably a bearing lubricant is chosen having an initial boiling point that is as far as possible significantly above the end boiling point of the cooling lubricant and the optionally present cooling lubricant additives. It is also preferred that the additives and further constituents that are optionally added to the bearing lubricant have a boiling point or an initial boiling point that lies significantly above the end boiling point of the cooling lubricant and cooling lubricant additives.

(40) It is particularly advantageous if the flash point of the bearing lubricant at 1 atmosphere is at least 150 C., preferably at least 170 C. and in particular at least 190 C. In this way the thermal separation method can be carried out particularly effectively.

(41) The amount of the synthetic oil in the bearing lubricant can vary within wide limits. Practical tests have shown that the amount of the synthetic oil in the bearing lubricant is preferably at least 5 weight %, preferably at least 50 weight %, more preferably at least 90 weight % and in particular at least 95 weight % to 99.5 weight %.

(42) It is also advantageous if the bearing lubricant decomposes substantially residue-free at temperatures from 250 C. to 350 C.

(43) The bearing lubricant according to the invention is outstandingly suitable as oil-flood lubricated bearing lubricant in equipment for metal working, in particular in cold rolling mills. It is particularly advantageous that cooling lubricant can be separated from the bearing lubricant in a particularly simple manner by means of the method according to the invention, and that bearing lubricants according to the invention can be separated from the cooling lubricant in a particularly simple manner via the cooling lubricant filtration.

(44) As regards further advantageous embodiments or advantageous effects of the bearing lubricant according to the invention, reference is made to the remarks about the separation method according to the invention.

(45) Series of tests of the exemplary use, which should not however be regarded as restrictive, of polyalkyleneglycol-based bearing lubricants in aluminium cold rolling mills with bearings with oil-film bearing lubrication systems have shown that a contamination of the bearing lubricant by cooling lubricant can be restricted to less than 1% when using the method according to the invention. At the same time the bearing lubricant could be restricted to residual contents of less than 0.5% in the cooling lubricants by using the cooling lubricant filtration based on filter aids.

(46) Thus, in exemplary laboratory tests it was possible by means of the method of short-path distillation to remove cooling lubricant from bearing lubricant based on polyalkylene glycol to residual contents of less than 0.5%. The short-path distillation was operated at a pressure of 5 mbar at temperatures of less than or equal to 120 C., in particular between 25 and 120 C., or at a pressure of 1 mbar at temperatures of less than or equal to 100 C., in particular between 25 and 100 C.