GB2382588A

GB2382588A - Slideway lubricant with anti-microbial additive

Info

Publication number: GB2382588A
Application number: GB0128502A
Authority: GB
Inventors: Christopher John Nettleship; Stephen David Chapman
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2001-11-28
Filing date: 2001-11-28
Publication date: 2003-06-04
Also published as: ATE496110T1; GB0215454D0; CN1735680A; DE60239008D1; CN1333058C; GB0128502D0

Abstract

A machine tool slideway lubricant comprising in a mineral oil or other lubricant base an oil-water partitionable anti-microbial, active against micro-organisms present in aqueous cutting fluids and degrading the lubricant base. Also disclosed is a method of metering an anti-microbial agent as an additive to cutting fluid by adding the anti-microbial agent to the slideway lubricant, and a method of operating a machine tool in which an aqueous cutting fluid is exposed to slideway lubricant.

Description

Field of Invention This invention relates to machine-tool lubricants, anti-microbial additives for cutting fluids and methods of adding such additives to cutting fluids.

Background to the invention In industrial metal-working machine tools the work piece and tooling are positioned and moved on flat bearings generally referred to as slideways. These surfaces require a lubricant-the slideway oil-to reduce the metal/metal contact therefore eliminating friction and'stick-slip'motion, and prevent wear on the slideways. This is essential to maintain the potentially very expensive machine tool in good condition and to ensure machining accuracy.

As most machining processes also utilise a water based cutting fluid to cool and lubricate the cutting zone the slideway oil is constantly washed off the surfaces of the slides. To combat this most machine tools automatically dispense oil onto the slides on a continuous or metered basis. Given the very low cost of the slideway oil this total loss system is the most cost effective method of ensuring that the performance of the machine is not compromised.

Whilst this method ensures that the machine stays in good condition it has the opposite effect on the cutting fluid. Being water based, cutting fluids provide an ideal environment for microbial growth. Although great efforts are made when formulating metal working fluids to exclude obvious sources of nutrients and to ensure that the fluids are as resistant as possible to microbial growth this is largely negated by the effect of the slideway oil. The oil seals off the fluids from the air so that they become anaerobic, and since slideway oils are generally based on refined mineral oils and contain additive elements such as sulphur and phosphorus (as anti-wear and anticorrosion additives), this provides ideal nutrients for micro-organisms. It is accepted throughout the metal working industry that one of the main causes of failure for cutting fluids is microbial growth promoted by excessive contamination with slideway oils.

Several attempts have been made to overcome the problem of slideway oil contamination these include: i) Use of synthetic, biologically-hard base fluids instead of mineral oil as the base for slideway oils. While this may reduce the overall level of nutrient for the microbes the key sulphur and phosphorus additives are still present.

Synthetic base fluids are also prohibitively expensive for'total loss'systems. ii) Use of the metalworking fluid concentrate as the slideway lubricant. Although this overcomes the contamination problem the primary function as a slideway oil is compromised. The ease with which these products can be washed away can leave slideways'dry'resulting in high friction and poor control of the tooling/work piece. The emulsification of this additional concentrate can also lead to the cutting fluid strength increasing to excessive levels. iii) Use of oil skimmers/separators. These can vary in both price and performance : The simplest and cheapest types are either belt or disc skimmers that are immersed directly into machine sumps and pick up free oil from the surface of metal working fluids. These are limited in their performance due to the fact that the oil will only separate from the fluid when there is no agitation (i. e. in 'dead'areas of the sump) or when the fluid is saturated with oil.

At the other end of the scale are stand alone machines that extract fluid from machine sumps and remove any oil contamination. These can either be static, dedicated to a single machine, or mobile to service multiple machines on a rota basis. Although they are effective at removing the contamination from the fluids the cost of these units can be tens of thousands of pounds each. This can mean a significant capital investment even for moderately sized engineering shops. iv) use of an anti-microbial as an additive to the cutting fluid, anti-microbial are dangerous chemicals, especially in concentrated form as an additive, and the anti-microbial needs to be added in correct dosages to maintain function.

The invention The present invention has these aspects :a) A machine-tool slideway lubricant comprising in a mineral oil or other lubricant base a oil-water partitionable anti-microbial additive, active against

micro-organisms that are present in aqueous cutting fluids and degrade the lubricant base. b) A machine tool having slideway lubricant and aqueous cutting-fluid feeds, where the slideway-lubricant feed contains a lubricant as above. c) A method of operating a machine tool in which an aqueous cutting fluid is used and is exposed to slideway lubricant, wherein to prevent objectionable growth of micro-organisms the slideway lubricant is a lubricant as above. d) A method of metering an anti-microbial additive to a machine having a slideway, a reservoir for a slideway lubricant and a reservoir or sump to which cutting fluid drains and from which cutting fluid is delivered to the tooling/work piece, comprising the step of adding a suitable anti-microbial additive to the slideway lubricant reservoir and using application of slideway lubricant by the machine tool to the slideway as a vehicle to meter the anti- microbial additive into the cutting fluid sump.

An anti-microbial additive is herein defined "as any ingredient imparting microbial inhibiting properties".

Slideway lubricants are specialised products normally containing, in the lubricant base, additives for anti-wear, tackiness (to control excessive washout) and demulsification (to limit harmful effects of emulsifying the slideway lubricant into the cutting fluid).

The present invention thus uses a slideway oil that incorporates an anti-microbial additive which, when the oil is washed into a metal working fluid, will transfer into the aqueous phase where it will maintain anti-microbial properties in the fluid. All of the primary functions of the slideway oil (lubrication, anti-wear, etc) are unaffected by the inclusion of the additive and no specialist equipment is required, the oil is used in the existing lubrication system on each machine.

This method of adding to the microbial resistance of the fluid is also'intelligent'.

Where there is a high degree of oil contamination more of the anti-microbial additive will be transferred into the fluid maximising its resistance. In cleaner systems where less oil is used there is less requirement for high levels of extra anti-microbial additive.

Details The anti-microbial additive for inclusion in the slideway oil can be any of the commercially available microbicides that would be familiar to anyone in either the metal working or biocide industries. Examples include formaldehyde releasing compounds such as triazine derivatives and oxazolidines, or non-formaldehyde products such as benzisothiazolinones and parachloro metacresol.

Factors in choosing the anti-microbial additive are: i) Compatibility with the slideway oil. The additive should not interfere with the primary function of lubrication. ii) Balanced oil and water solubility. The additive should be soluble in the slideway oil but also be sufficiently soluble in water to ensure that it is transferred into the metal working fluid. iii) Broad spectrum of anti-microbial activity. Metal working fluids can be contaminated by bacteria and fungi both of which can have deleterious effects. iv) Good toxicological profile. Metal working fluids commonly come into contact with skin therefore the anti-microbial additive should pose as little hazard as possible.

Following these criteria the preferred anti-microbial compound for the invention is 7aethyldihydro-lH, 3H, 5H-oxazolo (3,4-c) oxazol. This is commercially available from Angus Chemie under their trade name Bioban CS-1246. The properties of particular interest for this additive are: i) No detrimental effect on the lubrication characteristics of the slideway oil.

Experimental detail for specific examples is given later. ii) Octanol/water partition co-efficient (log Pow) of 0.28. Indicating primarily oil solubility but with adequate water solubility to allow transfer of the anti- microbial into the water phase. iii) Broad spectrum of anti-microbial activity indicated by the minimum inhibitory concentrations (MIC) for common spoilage organisms as follows: Organism MIC (parts per million) Bacterial:

Enterobacter aerogenes 250-300 Escherischia coli 450-500 Pseudomonas aeruginosa 800-850 Staphylococcus aureus 200-250 Fungal: Aspergillus niger 65-125 Fusarium moniliforme 125-250 Saccharomyces cerevisiae 16-33 iv) Low toxicity. As supplied the anti-microbial is harmful by inhalation and in contact with the skin, irritating to eyes and skin but is not a sensitising agent and is non-mutagenic. However at typical use dilutions there is no hazard with the product. This is indicated by its approval in Europe as a cosmetic preservative up to levels of 3000 parts per million.

The experimental details referred to above are :Four samples consisting of a mineral oil base, a commercially available slideway oil additive package (containing additives for anti-wear, corrosion inhibition etc), a tackiness additive (to promote adhesion of the slideway oil to metal surfaces) and anti-bacterial additive (Bioban CS 1246) were prepared as follows.

[Note : All compositions are % weight/weight.]

Sample A Sample B Sample C Sample D 500 Solvent neutral 60. 45 62.95 66.45 67.95 150 Solvent neutral2 36.30 32.80 28.30 25.80 Hitec 5103 2.25 2.25 2.25 2.25 Hitec E1514 1. 00 1. 00 1. 00 1. 00 Bioban CS 1246 0.00 1. 00 2.00 3.00 paraffinic rnineral oil with a kinematic viscosity of approximately l00cSt at 400C 2 paraffinic mineral oil with a kinematic viscosity of approximately 30cSt at 400C 3 slideway oil additive package commercially available from Ethyl Petroleum Additives Ltd.

4 polyisobutylene tackifier commercially available from Ethyl Petroleum Additives Ltd.

These samples were then subjected to an anti-bacterial screening test against pseudomonas aeruginosa-one of the most common spoilage organisms found in cutting fluids.

The oil samples were placed in a 10 mm diameter''well"in the centre of an inoculated agar plate. The plates were then incubated for 48 hours and visually inspected. Any anti-bacterial activity of the samples is shown as a zone of inhibitionzero bacterial growth-around the original 10 mm diameter well, the diameter of which can be measured to give a semi-quantitative estimate of activity.

Sample Diameter of zero growth Inhibited zone A 10mm Omm B 14mm 4mm C 20mm 10mm D 22mm 11 mm [Note : To obtain the measure of anti-bacterial activity the original diameter of the "well"must be subtracted (10 mm is therefore zero inhibitions From these results it is evident that the optimum balance between biocide level and activity was reached with sample C.

One of the key criteria in selecting an anti-microbial is to ensure compatibility with the slideway oil. Two of the key measures of this are the anti-wear and demulsification properties of the oil. Sample A (untreated slideway oil) and Sample C were tested using industry standard test methods as follows: Hans Schmidt demulsification test (40 mls of oil and 40 mls of water are mixed together in 100 ml measuring cylinder. At 5 minute intervals the volume of water separated from the oil/water mix is recorded).

Time (minutes) Sample A Sample C 0 0 0 5 3 7 10 15 8 15 16 9 20 17 10 25 20 15 30 30 15 35 36 18 40 37 24 45 37 29 50 38 31 55 38 32 60 39 34 Although the rate of separation of water is slowed by the inclusion of the antimicrobial, demulsification does still occur. In practice the slightly slower rate of separation should provide a longer time scale for the transfer of the anti-microbial into the cutting fluid.

Shell 4-ball wear test (60 kg load run for 15 minutes) Sample A

Ball number Wear scar dimensions mm 10. 709 x 0.723 2 0. 728 x 0.709 3 0. 708 x 0.725 Mean scar diameter = @0.71/mm Sample C

Ball number Wear scar dimensions mm 1 0. 479 x 0.457 2 0. 463 x 0.444

3 0. 470#0.451 Mean scar diameter = 0.462 mm The improvement in anti-wear properties due to the inclusion of the anti-microbial is unexpected and, while not fully explained, may be due to catalysation of chemical reaction between the sulphur and phosphorus anti-wear additives present in the oil and the steel surface.

Claims

1. A machine tool slideway lubricant comprising, in a mineral oil or other lubricant base, an oil-water partitionable anti-microbial, active against micro- organisms that are present in aqueous cutting fluids and degrade the lubricant base.

2. A machine tool having slideway lubricant and aqueous cutting fluid feeds where the slideway-lubricant feed contains a lubricant according to claim 1.

3. A method of operating a machine tool in which an aqueous cutting fluid is used and is exposed to slideway lubricant, wherein to prevent objectionable growth of micro-organisms, the slideway lubricant is a lubricant according to claim 1.

4. A method of metering an anti-microbial agent to a machine tool having a slideway, a reservoir for a slideway lubricant and a reservoir or sump to which cutting fluid drains and from which cutting fluid is delivered to the tooling/work piece, comprising the step of adding a suitable anti-microbial to the slideway lubricant reservoir and using application of slideway lubricant by the machine tool to the slideway as a vehicle to meter the anti-microbial into the cutting fluid sump.