GB2023644A

GB2023644A - Improved Lubricant

Info

Publication number: GB2023644A
Application number: GB7841106A
Authority: GB
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 1977-10-18
Filing date: 1978-10-18
Publication date: 1980-01-03

Abstract

This invention relates to lubricants for use in connection with machining operations and especially in connection with such operations on metal. The invention is more particularly concerned with lubricants for turning and/or burnishing operations on platinum metal and platinum base alloys, as well as other platinum group metals and alloys thereof, whereby a high surface finish may be obtained and wear of the cutting and/or burnishing tool reduced. Specifically the lubricant according to the invention comprises gelatine and water.

Description

SPECIFICATION Improved Lubricant This invention relates to lubricants for use in connection with machining operations and especially in connection with such operations on metal. The invention is more particularly concerned with lubricants for turning and/or burnishing operations on platinum metal and platinum base alloys, as well as other platinum group metals and alloys thereof, whereby a high surface finish may be obtained and wear of the cutting and/or burnishing tool reduced.

By a "high surface finish" or "high finish" here and throughout the remainder of this specification is meant a polished or highly polished finish, often known as a "mirror finish", which is pleasing to the eye. This is generally associated with a surface configuration as measured by a Talysurf (registered Trade Mark) device, in which the maxiumum separation between the peaks and troughs in the surface is of the order of tenths of a micron.

A turning operation to produce a high finish is frequently called a "glossing" or "gloss turning" operation and, in general in such an operation, whilst part of the cutting tool is actually removing metal from the article being turned, a neighbouring part of the tool bears on that part of the surface of the article from which metal has been removed, either immediately or very shortly after its removal, so as to exert a burnishing or planishing action on the surface, and thereby to help produce the desired high finish.

A gloss turning operation is commonly used in the jewellery industry as a finishing step in the manufacture of rings. No problems are encountered in the gloss turning of gold rings (by "gold" here, of course, is meant a gold alloy, such a 9 carat gold, which is suitable for the manufacture of rings) and, typically, about 100,000 rings may be gloss turned using a diamond tool and a conventional lubricant, such as a mixture of paraffin and watch oil, before the tool needs to be replaced or re-sharpened.

When the same tool and lubricant are used for the gloss turning of rings made from a suitable platinum alloy, such as a 5% copper-platinum alloy, the number falls dramatically from about 100,000 to between 8 and 10. In addition the surface finish of the 8 to 10 platinum alloy rings so produced often leaves something to be desired.

One object of the present invention is to provide lubricant which has improved effectiveness when used in connection with a gloss turning operation as compared with currently known lubricants such as the paraffin and watch oil mixture previously referred to.

According to one aspect of the invention, a lubricant for use in a machining operation and especially a machining operation on a metal, comprises gelatine and water.

The relative proportions by weight of water and gelatine should preferably be between 3 parts of water to 1 part of gelatine and 100 parts of water to 1 part of gelatine.

A preferred composition comprises 35 parts by weight of water to 1 part of gelatine.

We have found that lubricants according to the invention are surprisingly effective when used in connection with gloss turning operations, especially with such operations on platinum metal alloys. The present of water in these lubricants, however, can lead to the formation of rust on the lathe on which the gloss turning operation is being performed and, in addition, they can in store develop mould spots especially at relatively high concentrations of gelatine.

The first of these disadvantages may be overcome by adding a rust inhibitor such as sodium benzolate to the lubricant and the second by the addition of a fungicide such as carbolic acid.

According to further aspects of the invention, therefore, a lubricant comprising gelatine and water may also contain a rust inhibitor or a fungicide or both.

A diamond tool for the gloss turning of gold when a conventional lubricant, such as paraffin and watch oil, is used, advantageously has a negative top rake of 1 50C, a front face clearance of 100 and a narrow, flat surface extending along the top of the front face away from the cutting point and inclined at an angle of 1.50 to the vertical. This is a so-called "glossing flat". In service, it bears against and exerts a burnishing or planishing action on the freshly cut surface of the metal being gloss turned.

A less elaborate tool is preferable, however, when it is to be used with a lubricant according to the invention. Indeed, present indications are that the lubricant is most effective in gloss turning operations on a platinum alloy if it is used with a tool having zero top rake, a 5--100 front face clearance and no glossing flat.

Tests with rings made of 5% copper-platinum alloy have shown that 35-50 rings may be gloss turned with such a diamond tool a lubricant according to the invention before the tool needs replacement or resharpening. Using a 50/50 paraffin, watch oil mixture as the lubricant, however, reduces the number of rings to between 1 5 and 20. A further point is that a better surface finish is in general obtained with the lubricant according to the invention and surfaces showing Talysurf (registered Trade Mark) readings having maximum distances between the peaks and troughs of less than 0,05y are easlily obtained.

An incidental advantage of the lubricant according to the invention is that the relatively simple configuration of the diamond tool makes it easy to provide the tool with two cutting edges so that the effective life of the tool before it needs to be removed for resharpening is doubled.

The reason why a lubricant according to the invention is so effective is not entirely clear but it probably has to do with the tenacity with which the lubricant clings to the work piece. It certainly appears that the cutting edge or corner of the tool penetrates the lubricant film at the point of contact with the metal but that elsewhere the film retains its integrity. It follows that a film of lubricant remains between the work piece and those parts of the tool next to the cutting edge which exert a burnishing or planishing action on the work piece and the presence of the film of lubricant in these regions probably improves the burnishing or planishing effect.

Certainly one result of the use of our improved lubricant is increase in the value of the tangential load on the cutting edge or point of the tool which is required for a certain finish on the work piece as compared with the load with a conventional lubricant. This is illustrated at the left hand side of graph in the attached figure 1 where tangential load is plotted against number of cuts made by the tool. The full line shows the results obtained with a lubricant comprising 35 parts by weight of water to 1 part by weight of gelatine whereas the dotted line shows the results obtained with a 50/50 paraffin-watch oil lubricant. Initially the gelatinewater lubricant load is significantly higher than the load with the other lubricant.As the number of cuts progressively increases, however, the former increases and then remains substantially constant as shown by the levelling out of the full line curve, whilst the latter, after a relatively short period during which it is constant, begins to increase progressively. This is probably due to the progressive wear and consequent loss of sharpness of the tool when used with the conventional lubricant.

We have found that a lubricant according to the invention is best prepared by dissolving a desired quantity of gelatine granules of the type sold by chemical supply houses in warm water and then adding rust inhibitor and/or fungicide if required.

We have also found that the highly polished mirror finish produced on work pieces with the aid of our lubricant, can be marred by small quantities of swarf and other detritus produced during the machining operation. It is therefore desirable for a jet or spray of lubricant to be played on to the work piece at the cutting point so as to wash away any undesirable solid products and to prevent them from being trapped between the work piece and the burnishing surface(s) adjacent to the cutting point or edge.

Although the lubricant according to the invention has been described with reference to the gloss turning of platinum alloy articles, it is by no means limited to this particular application. It is, for example, highly effective as a wire-drawing lubricant and can, inter alia, be used in any application where one surface bears heavily against another.

Claims

1. A lubricant for use in a machining operation on a metal, the lubricant comprising gelatine and water.

2. A lubricant according to claim 1 comprising between 3 parts of water to 1 part of gelatine and 100 parts of water to 1 part of gelatine.

3. A lubricant to claim 2 comprising 35 parts by weight of water and 1 part of gelatine.

4. A lubricant according to any one of claims 1 to 3 including a rust inhibitor.

5. A lubricant according to claim 4 wherein the rust inhibitor is sodium benzolate.

6. A lubricant according to any preceding claim including an antifungicidal composition.

7. A lubricant according to claim 6 wherein the said cmposition is carboxilic acid.

8. A method of machining a metal component including the step of lubricating the machining using a lubricant according to any preceding claim.

9. A method according to claim 8 wherein the metal is a platinum group metal or an alloy containing a platinum group metal.