5 Effects of 'Cereclor' on Metals

Transcription

1 'Cereclor' as an Extreme Pressure Lubricant Additive 1 Introduction 2 Properties 3 Uses 4 Applications 5 Effects of 'Cereclor' on Metals 6 References Page 1

2 1 Introduction 'Cereclor' is the trade mark for a range of products manufactured by Ineos Chlor Ltd. The different grades of 'Cereclor' are produced by the controlled chlorination of carefully selected paraffinic hydrocarbon fractions. 'Cereclor' is used as an extreme pressure additive in gear oils and metal working lubricants, as a secondary plasticiser in PVC, as a plasticiser for chemical resistant paints and as a flame retardant additive for plastics, rubbers and textiles. The typical properties of a selection of grades used as extreme pressure additives are shown in Table 1. Table 1 - Typical Properties of 'Cereclor. Grade of 'Cereclor' S LV 51L 56L 60L 63L 65L 70L Chlorine (%wt) Density at 25 C at 100 C Viscosity approx at 25 C (poise) at 40 C (cs) at 100 C (cs) at 210 F (SUS) Pour point approx C (IP15) Stability 4h 175 C (% HCl released) Properties In addition to the excellent extreme pressure performance for which 'Cereclor' is used, the following benefits are important in lubricant applications: 1 Very light colour. 2 Low odour. 3 Extremely low toxicity and low dermatitis hazard. 4 Non flammability. 5 Soluble in common decreasing solvents. 6 Non staining to yellow metals. Page 2

3 2.1 Extreme Pressure Additives In heavy duty industrial gears, automotive hypoid gears, metal cutting and allied operations where high pressures and rubbing action are encountered, hydrodynamic lubrication cannot be maintained; so Extreme Pressure (EP) additives must be added to the lubricant for satisfactory performance. Such EP additives customarily contain one or more of the elements chlorine, sulphur and phosphorus. 'Cereclor' chlorinated paraffins are effective extreme pressure additives. They can be used either alone or in combination with additives containing sulphur and/or phosphorus, according to the application. 2.2 How 'Cereclor' Works as an EP Additive The exact mode of action of EP additives is the subject of some controversy. It has been shown that under extreme pressure conditions micro-welds are formed between the asperities of metals in contact. Relative movement is thus only effected by breaking such micro-welds, and the friction can therefore be considered as a function of the shear strength of the metal (Ref. 1). It has been shown, however that in the presence of chlorinated EP additives, a chloride film is formed on the metal surface. This film has a lower shear strength than that of the metal itself, so the friction between the metals in sliding contact is reduced. This low shear strength, low friction film thus prevents surface damage in gears and gives improved surface finish and increased tool life in metal cutting operations. 'Cereclor' chlorinated paraffins have been formulated to have the correct degree of activity so that they function as extremely effective EP additives and at the same time have adequate stability at bulk oil temperatures. 2.3 EP Action in Cutting Oils It is generally considered that a surface film ceases to give protection at temperatures above its melting point. The melting point of iron chloride is about 350 C, whereas that of iron sulphide is about C, depending on the form of the sulphide. In the high speed machining of non alloy steels, very high temperatures are created between the tool and the metal. Sulphur additives can therefore be expected to be more effective than chloride additives particularly in preventing welding of the tool to the workpiece. There is considerable evidence, however, to substantiate the improvement in performance found by using mixtures of chlorinated additives and active sulphur compounds (Refs. 2-4). Page 3

4 Effect of Temperature on Kinematic Viscosity of 'Cerclor' Grades Kinematic Viscosity, Centistokes 20,000,000 10,000,000 5,000,000 2,000,000 1,000, , , ,000 50,000 20,000 10,000 5,000 2,000 1, L L 63L 10 51L 56L LV Temperature C Page 4

5 Iron sulphide films have been shown to be formed more rapidly from active sulphur additives than are ferrous chloride films from active chloride additives at temperatures above 200 C. The iron sulphide film, which is formed first, reacts very rapidly with the chlorine additive forming a complex film consisting mainly of ferrous chloride but containing some iron sulphide, part of which is probably in the form of FeSn. Thus a mixture of 'Cereclor' and an active sulphur additive gives maximum performance in high speed machining, as it causes the rapid formation of a low friction chloride film and at the same time prevents high temperature welding due to the presence of the sulphide (Ref. 5). In the case of alloy steels and non-ferrous alloys, and in slow speed machining operations, e.g. broaching and tapping, chlorinated additives are generally considered to be superior to sulphur additives. Because of the ease with which such metals work-harden, it is necessary to limit surface temperatures by reducing the speed of cutting. The slower speed of formation and the lower maximum effective temperatures of chloride films are therefore no longer limiting factors. In the cutting process Merchant showed (Ref. 1) that heat generation takes place by two mechanisms: 1 Plastic flow of the metal in forming the chip. 2 Rubbing friction between the chip and tool. Both sources of heat are shown to depend on the friction between the chip and tool. 'Cereclor' is very effective in reducing friction under EP conditions, and it follows that oils containing 'Cereclor' permit alloys to be machined at higher rates. Tool life also has been shown to be inversely proportional to the twentieth power of temperatures at the cutting zone (Ref. 6), and 'Cereclor' therefore gives increased tool life. Page 5

6 3 Uses 3.1 Gear Oils 'Cereclor' Is extensively used as an EP additive for formulating lubricating oils for hypoid, spiral bevel, worm and heavy duty industrial gears. It is usually used on conjunction with certain sulphur and phosphorus compounds, e.g. dibenzyl disulphide, zinc dialky! dithiophosphate and sulphurised or sulpho-phosphorised fatty oils. 3.2 Multi-Purpose Oils These lubricants are used on automatic lathes for the triple functions: Cutting Oil. Hydraulic Fluid. Machine Lubricant. 'Cereclor' is particularly useful for formulating such products because it does not stain yellow metals. 3.3 Metal Working Oils The formulation of cutting fluids and metalworking lubricants is complicated by the multitude of operations and metals Involved. Laboratory tests often do not correlate with workshop experience (Refs. 5, 7) and the best formulation for a particular job can only be determined by works trial. 'Cereclor' can be incorporated in oils for the vast majority of metal cutting and forming operations. It is not always possible to give fully detailed recommendations, but the main factors for its use, e.g. operation, material, temporary protection are detailed below Neat Oils The concentration of 'Cereclor' in neat oils can be varied to suit the severity of the operation. Whilst there are no hard and fast rules for this, suggestions are given in Table 2 which can act as a starting point for suitable formulations Soluble Oils Heavy duty soluble or emulsifiable oils contain EP additives to extend the range of operations and materials for which waterbased fluids can be used. They are increasingly being used to replace neat oils for economy, and to improve working conditions. 'Cereclor' is effective at low proportions (1%-5% in the concentrate) but for improved performance under arduous conditions, up to 25% has been successfully incorporated in concentrate blends. The preferred grade for ease of emulsification especially at higher proportions is 'Cereclor' 50LV; 56L, 63L can also be used. Suitable corrosion inhibitors must be incorporated in such formulations. Page 6

7 Table 2 - Cutting Oil Formulations containing 'Cereclor' Application Light duty Medium to heavy duty Very heavy duty Heavy duty broaching Comments 2-5%wt chlorine with the optional addition of up to 0-2% sulphur from a sulphurised fat and up to 5% fatty oil 5-10%wt chlorine with up to 0.5% sulphur from a sulphurised fat and up to 10% fatty oil Up to 30% chlorine plus up to 1.0% sulphurised fat and up to 10% fatty oil 60% 'Cereclor' 50LV plus 10% fatty oil 4 Applications 4.1 Broaching Broaching oils require a high chlorine content with low viscosity. The main advantage of 'Cereclor' 50LV for this application is that it can be used with low viscosity base oils to achieve the required viscosity. 4.2 Deep Drawing 'Cereclor' is incorporated into deep drawing lubricants to prevent pick up and damage to the die. Typical formulations contain up to 40% w/w chlorine in oil and may include a fatty or sulphurised oil. Alternatively 100% 'Cereclor', e.g. 50LV, 51L or 50L. The Swift cup test is a measure of drawability expressed as the limiting draw ratio (LDR). The LDR is the ratio of the diameter, 'D', of the maximum blank that can be successfully drawn to the diameter 'd' of the punch. The latter is 50mm in the standard test. 'D' or LDR is therefore a measure of drawability. Table 3 shows the results obtained by the Swift cup test on stainless steel with a range of different grades of 'Cereclor' and two oils formulated to contain 14% wt chlorine with a viscosity of 500 SUS at 70 F. Page 7

8 Table 3 Swift Cup Test Lubricant Maximum Diameter 'D' (mm) Limiting Draw Ratio Neat 'Cereclor' Neat 'Cereclor' 50LV Neat 'Cereclor' 51L Neat 'Cereclor' 63L Drawing oil containing 'Cereclor' Drawing oil containing Neat 'Cereclor' 63L Blanking and Piercing 100% 'Cereclor' 51L is recommended, applied to the punch periodically. Where oil circulation is possible neat 'Cereclor' 50LV is recommended. 4.4 Wire, Tube and Bar Drawing 'Cereclor' grades can be incorporated in lubricants for many drawing operations according to severity. 'Cereclor' 42 and 48 are useful lubricants used neat for the drawing of bright stainless steel wire. 'Cereclor' T grades have been developed to eliminate metal staining caused by high temperature generation during high speed drawing of stainless steel tube. (See section on specially stabilised grades). 4.5 Cold Forging 100% 'Cereclor' 51L or 'Cereclor' 50LV is suggested as a lubricant in the cold impact extrusion (cold forging) of low carbon steel and the warm extrusion of stainless steel. 4.6 Rolling 'Cereclor' is suggested for use as an EP additive to prevent pickup with steel rolling oils. Page 8

9 5 Effects of 'Cereclor' on Metals 5.1 Aluminium It is well known that chlorinated solvents react with aluminium and that this reaction proceeds more readily if the aluminium surface is cut, producing an oxide free layer (Ref. 8). Experience has shown that, presumably because of this type of reaction, corrosion problems can result from the use of highly chlorinated oils for machining aluminium, particularly if 'Cereclor' 50LV is used. Where the normal practice is to machine several different metals, including aluminium and its alloys, using the same EP lubricant, Cereclor' 42, 'Cereclor' 63L and 'Cereclor' 48 are the recommended grades. The relative reactivities of the different grades of 'Cereclor' has been examined, by determining the minimum concentration of 'Cereclor' in a spindle oil, at which the reaction is observed at 100 C, when the aluminium surface is cut whilst immersed in the oil solution. The results are given in Table 4. Table 4 Concentration of 'Cereclor' in a Highly Paraffinic Spindle Oil at which Aluminium Reaction Occurs at 100 C 'Cereclor' Grade Concentration in Spindle Oil %w/w 50LV 30 56L 50 63L 70 51L The reaction can be controlled by adding inhibitors such as alkyl phosphates (triethyl phosphates, organic nitro compounds and acid acceptors such as epoxy compounds and over-based calcium or barium compounds used as crankcase oil detergent/dispersants. 5.2 Copper, Brass, Bronze Because of its non-staining properties towards yellow metals, 'Cereclor' is recommended for formulating cutting oils for machining copper, brass and bronze alloys. Page 9

10 5.3 Refractory Metals 'Cereclor' is recommended for formulating cutting oils for machining titanium, molybdenum, tantalum, tungsten and their alloys. 5.4 Ferrous Metals Steel, the most widely used engineering metal generally causes few problems and the EP performance of 'Cereclor' is well known. However, extreme pressure lubricants are by their nature chemically active and unwanted reactions may lead to staining or corrosion of tools, machinery and components. Much of the development work undertaken for 'Cereclor' in lubricant applications is based on the need to improve anti corrosion properties under difficult circumstances. The requirements fall into two basic categories as follows: 1 A lubricant containing 'Cereclor' can be required to act as a temporary protective for components in the presence of moisture or a humid atmosphere. 2 Unusually high surface or bulk oil temperatures may lead to instability of 'Cereclor' and hence metal staining. The standard 'Cereclor' grades are each stabilised to give the optimum performance for their normal applications, e.g. 'Cereclor' 63L has above average heat stability. Page 10

11 6 References 1 "Cutting Fluid Action and the Wear of Cutting Tools", M Eugene Merchant, Paper 99, Conference on Lubrication and Wear, Institution of Mechanical Engineers. 2 "Hypoid Gear Lubricants and Additives", J S Elliott, N E F Hitchcock and E D Edwards, J Inst Petroleum, 45, No 428, Aug 1959, p "A Technique for Investigating Reactions between EP Additives and Metal Surfaces at High Temperatures", F T Barcroft, Wear 3 (1960), "Mechanism of Actions of Organic Chlorine and Sulphur Compounds in Extreme Pressure Lubrication", C F Prutten, D Turnbull and G Dlouhy, J Inst, Petroleum, 32, , "Functions of Metal Cutting Fluids and their Mode of Action", J Beaton, J M Tims and R Tourret, Paper 20, Lubrication and Wear, Third Convention, The Institution of Mechanical Engineers, May "Testing for Machinability by Measuring Cutting Temperature and Tool Wear", H Schallbroch, H Schanmann and R Wallicks, Voltrage de Hauptersammiung der Deutschen Gesellschaft fur Metalikurde, 1938, 3438 (VDI Verlag, Berlin). 7 " Development Testing of Cutting Fluids", P M Holmes, Production Engineer, March 1965, p "Mechanical Activation- A Newly Developed Chemical Process", M C Shaw, Journal of Applied Mechanics, March 1948, pp Page 11