Lubricant method and compositions

Abstract: This invention concerns the lubrication of crosshead diesel engines, for example marine slow speed crosshead diesel engines. Lubrication is effected with a lubricant composition comprising a major amount of base oil and minor amounts of an anti-wear additive and of an extreme pressure additive. Good lubrication is achieved between metal surfaces at elevated temperatures and high contact pressures. Preferred compositions of the invention have a synergistic effect and include an anti-wear additive of formula X=P(OR) , where X represents an oxygen or a sulfur atom, and each R, which can be the same or different, represents a phenyl, tolyl or xylyl group, a halogenated derivative of such a group, tritolyl­ phosphate, trixylylphosphate or triphenylphosphorothionate, the extreme pressure additive being an organic sulfide.

Description: This invention concerns the lubrication of crosshead diesel engines, for example marine slow speed crosshead diesel engines. The lubrication of crosshead diesel engines, and in particular the cylinder liners and piston rings of such engines, presents problems since the temperatures and pressures involved during their operation can lead to breakdown of the film of lubricant on the internal walls of the cylinder liners. When this occurs it leads to excessive cylinder liner and/or piston ring wear. Various additives have been proposed for lubricant compositions for engines for the purpose of reducing engine wear. Anti-wear additives, for example, have been proposed but although they are effective at low temperatures, they tend to become ineffective at the temperatures encountered at the top of the cylinder liners of crosshead diesel engines. Extreme pressure additives have also been proposed which function as the lubricant film breaks down between metal surfaces when they slide under high pressures. They are in particular proposed for use in gear oils. The disadvantages of using such additives in lubricant compositions for crosshead diesel engines is that under the temperature conditions at the top of the liners of such engines, cylinder liner and piston ring wear can still occur, and indeed it can be enhanced even though lubricant film breakdown does not occur. According to the present invention there is provided a lubricant composition for lubricating a crosshead diesel engine, the composition comprising a major amount of a base oil and minor amounts of an anti-wear additive and of an extreme pressure additive, the anti-wear additive being a compound of formula X=P(OR) 3 , (where X represents an oxygen or a sulfur atom, and each R, which can be the same or different, represents a phenyl, tolyl or xylyl group, or a halogenated derivative of such a group) and the extreme pressure additive being a sulfurised olefin containing from 25 to 55 percent by weight of sulfur, the weight ratio of anti-wear additive to extreme pressure additive being from 0.2:1 to 10:1, and the total base number being at least 40 (as measured by ASTM D2896 in mg of KOH/g of composition). The invention further provides a method of lubricating a crosshead diesel engine, the method comprising lubricating the engine with a composition in accordance with the invention. Compositions in accordance with the present invention have enabled good lubrication to be achieved between metal surfaces at elevated temperatures and high contact pressures when compared with lubricant compositions consisting of a bas oil containing either the anti-wear additive or the extreme pressure additive alone. Particularly good and unexpected lubricant properties at elevated temperatures and pressures can be achieved in crosshead diesel engines using compositions in accordance with the present invention. Examples of particular anti-wear additives which can be used with advantage in accordance with the invention are the phosphorothionic acid esters described in British Patent Specification 1018307, and the analogous phosphoric acid esters having an oxygen atom in place of the sulfur atom of these esters. Specific anti-wear additives which can be used include tritolylphosphate, trixylylphosphate or triphenylphosphorothionate. The sulfurised olefins used as extreme pressure additives in accordance with the invention contain from 25 to 55 percent by weight of sulfur. Particularly preferred extreme pressure additives contain from 35 to 45% by weight of sulfur. The olefinic portion of the sulfurised olefins can be derived from one or more olefin, and the olefins can be straight or branched chain, or cyclic. Furthermore, the unsaturation can be terminal or internal. Preferably, the olefins contain up to eight carbon atoms. Particularly preferred extreme pressure additives are derived from olefins containing from 3 to 6 carbon atoms. Especially preferred sulfurised olefins which can be used as extreme pressure additives in lubricant compositions of the invention are described in British Patent Specification 1308894 and U.S. Patent Specification 4204969. The amount of extreme pressure additive should be sufficient to provide an extreme pressure effect. This will usually be provided by the presence of up to 5.0 percent of the additive based on the total weight of the composition. In general, at least 0.05 percent of an extreme pressure additive will need to be present, and compositions of the invention preferably contain from 0.05 to 0.2, more preferably from 0.1 to 1.5, and advantageously from 0.3 to 1.0 percent by weight of an extreme pressure additive based on the total weight of the composition. The amount of anti-wear additive present is based on the amount of extreme pressure additive present. The weight ratio of anti-wear additive to extreme pressure additive should be from 0.2:1 to 10:1, preferably from 0.2:1 to 5:1, and advantageously about 0.5:1. The relative amounts of these additives is preferably adjusted to provide the compositions with good anti-wear properties under high pressures but without excessive corrosion at elevated temperatures. The amounts of anti-wear and extreme pressure additives present in order to achieve this will often be less than would be expected to provide the compositions with satisfactory low wear at high temperatures based on the known properties of the anti-wear and extreme pressure additives used. The base oil, which can consist of a mixture of two or more oils, is preferably a hydrocarbon oil, and it can include one or more paraffinic or synthetic oils. In general, it is preferred to use a mixture of oils. The viscosity index of the base oil should in general be at least 50, and preferably at least 70, although it will not usually be more than 180, and preferably not more than 130. The base oil preferably has a viscosity index of from 95 to 105. Compositions used in accordance with the present invention will usually contain other additives, for example overbased additives, e.g. naphthenates, sulfonates, phenates, salicylates or carboxylates. The total base number (TBN) of the compositions should be at least 40, and preferably from 70 to 100 (as measured by ASTM D2896 in mg of KOH/g of composition). The TBN of the compositions is preferably not more than 150. The viscosity of the compositions is preferably at least 10, and more preferably at least 15 cSt at 100°C. However, the viscosity of the base oil will usually be not more than 35, and preferably not more than 30 cSt at 100°C. Advantageously the viscosity of the oil will be from 17 to 25 cSt at 100°C. The lubricant compositions can be prepared by known methods. Thus it is generally convenient first to heat the base oil, usually to a temperature of about 60°C, then to add any overbased additives with stirring, and finally to add the extreme pressure and anti-wear additives, again with stirring, preferably after allowing the mixture to cool. As will be appreciated, the compositions can contain various additives used in the lubricant art, for example dispersants, antioxidants and corrosion inhibitors. The following Examples are given by way of illustration only. All parts represent percentages by weight of the final lubricant compositions, unless stated otherwise. Example 1 58.96 parts of 500 SN mineral oil (viscosity index 95) and 13.0 parts of mineral oil brightstock (viscosity index 95) were blended and heated to about 60°C. 12.65 parts of overbased 250 TBN calcium phenate, 12.65 parts of overbased 300 TBN calcium sulfonate and 2.0 parts of polyalkylene succinimide were added to the blend with vigourous stirring. The resultant homogeneous mixture was cooled to about 50°C, and 0.50 part of sulfurised olefin (containing about 38% of sulfur) and 0.24 part of tritolyl phosphate (TTP) were added with stirring. The lubricant composition produced (TBN 70.6, viscosity index 97, and viscosity 17.2 cSt at 100°C) was then tested on a standard IP 239/85 test "Extreme Pressure Properties : Friction and Wear Tests for Lubricants : Four-Ball Machine" modified to operate from ambient to 200°C, the latter temperature being approximately that at the top of the cylinder liner of a slow speed crosshead diesel engine. The results obtained are shown in the accompanying Table, weld point and initial seizure values being in kg, and scar values in mm. Example 2 In a similar manner to that described in Example 1, 59.04 parts of 500 SN mineral oil (viscosity index 95) and 13.0 parts of mineral oil brightstock (viscosity index 95) were blended and heated to about 60°C. 12.65 parts of overbased 250 TBN calcium phenate, 12.65 parts of overbased 300 TBN calcium sulfonate and 2.0 parts of polyalkylene succinimide were added to the blend with vigourous stirring. The resultant homogeneous mixture was cooled to about 50°C and 0.45 part of the sulfurised olefin and 0.21 part of triphenylphosphorothionate were added with stirring. The lubricant composition produced (TBN 70.3, viscosity index 98, and viscosity 17.1 cSt at 100°C) was then tested as in Example 1, the results being shown in the accompanying Table. Example 3 A composition similar to that produced in Example 1 was prepared using 0.55 parts of tritolyl phosphate and 0.5 part of the sulfurised olefin, the amount of mineral oil being adjusted accordingly. The composition was tested as in Example 1, and the results are shown in the accompanying Table. Example 4 A composition similar to that of Example 1 was prepared using 0.25 part of trixylyl phosphate in place of the tritolyl phosphate, the amount of mineral oil being adjusted accordingly. The composition was tested as in Example 1, and the results are given in the accompanying Table. Examples 5 and 6 Two lubricant compositions were prepared using the method of Example 1 but with the amounts and types of extreme pressure and anti-wear additives shown in the accompanying Table, the amount of mineral oil being adjusted accordingly. The results of the tests carried out as described in Example 1 are also given in the Table. Note In the Table, the following apply:- Sulfide A - Sulfurised olefin containing about 38% of sulfur Sulfide B - Organic sulfide containing about 42% of sulfur TTP - Tritolylphosphate TPPT - Triphenylphosphorothionate TXP - Trixylylphosphate Example Extreme pressure/anti-wear additive Weld point Initial Load seizure Scar 1 hour wear at 200°C (scar) 1 0.05 Sulfide A 340 165 1.381 1.010 0.24 TTP 2 0.45 Sulfide A 370 160 0.756 0.985 0.21 TPPT 3 0.5 Sulfide A 370 170 1.641 1.085 0.55 TTP 4 0.5 Sulfide A 350 145 1.055 1.100 0.24 TXP 5 1.12 Sulfide A 460 155 0.691 1.363 0.53 TTP 6 1.57 Sulfide B 630 180 0.613 1.240 1.0 TTP

Claims: A lubricant composition for lubricating a crosshead diesel engine, the composition comprising a major amount of a base oil and minor amounts of an anti-wear additive and of an extreme pressure additive, the anti-wear additive being a compound of formula X=P(OR) 3 , (where X represents an oxygen or a sulfur atom, and each R, which can be the same or different, represents a phenyl, tolyl or xylyl group, or a halogenated derivative of such a group) and the extreme pressure additive being a sulfurised olefin containing from 25 to 55 percent by weight of sulfur, the weight ratio of anti-wear additive to extreme pressure additive being from 0.2:1 to 10:1, and the total base number being at least 40 (as measured by ASTM D2896 in mg of KOH/g of composition). A composition according to claim 1, wherein each R represents a 4-tolyl or 3,5-xylyl group, or a halogenated derivative of such a group. A composition according to claim 1 or claim 2, wherein each R has the same meaning. A composition according to any of the preceding claims, wherein the anti-wear additive is tritolylphosphate, trixylylphosphate or triphenylphosphorothionate. A composition according to any of the preceding claims, containing up to 5.0 percent of a sulfurised olefin. A composition according to claim 5, containing from 0.05 to 2.0 percent of a sulfurised olefin. A composition according to any of the preceding claims, having a viscosity of from 10 to 35 cSt at 100°C. A composition according to any of the preceding claims, wherein the viscosity index of the base oil is from 50 to 130. A composition according to any of the preceding claims, containing an overbased additive. A composition according to any of the preceding claims, having a total base number (as measured by ASTM D2896 in mg of KOH/g of composition) of from 40 to 150. A method of lubricating a crosshead diesel engine, the method comprising lubricating the engine with a composition according to any of the preceding claims.

Inventors: CARTER BRIAN HOWELL, GREEN DAVID, HUTCHINGS TIMOTHY, CARTER, BRIAN HOWELL, GREEN, DAVID, HUTCHINGS, TIMOTHY
Applicants: CASTROL LTD, CASTROL LIMITED
Application year: 1989
Main classification: C10M141
IPC codes: C10M141, C10M163, F02B3