US2962401A

US2962401A - Cold deformation of metals

Info

Publication number: US2962401A
Application number: US721702A
Authority: US
Inventors: Roman D Guminski
Original assignee: Aluminium Laboratories Ltd
Current assignee: Alcan Research and Development Ltd
Priority date: 1958-03-17
Filing date: 1958-03-17
Publication date: 1960-11-29
Anticipated expiration: 1977-11-29

Description

United States 2,962,401 COLD DEFORMATION OF METALS No Drawing. Filed Mar. 17, 1958, Ser. No. 721,702

6 Claims. (Cl. 148-115) The present invention relates to the lubrication of the surface of aluminium during cold forming processes, such as the cold rolling of aluminium (including aluminium alloys) to form sheet or strip material or in the cutting out or blanking of circles or slugs from such material.

In all such processes a lubricant is employed to prevent damage to the surface finish of the material. It is the present practice in the cold rolling of aluminium to apply a lubricant which comprises a relatively light petroleum fraction base oil, to which is added a small proportion of a special load-bearing additive.

The additives at present used are generally long chain 3, aliphatic acids, such as lauric acid, and esters of such acids, such as lanolin or butyl stearate. When the sheet metal ,is annealed after rolling it is found that its' surface is discoloured by two forms of staining (a) white stain, and ('b) brown stain. The brown stain is particularly severe when, as in modern practice, the cold rolled sheet or strip is coiled into tightly wound coils which are annealed in this form.

White stain is produced by a surface etching of the aluminium by free acids which might be present in the form of acid additives or which might be produced by the decomposition of originally neutral additives, such as lanolin or other esters.

It is already known that the load-bearing capacity of alubricant which determines the percentage reduction in thickness which can be achieved during the cold rolling of a sheet of metal without the surface damage which results from the breakdown of the lubricant, is dependent on the chain length of the molecule of the load-bearing "additive and on its polarity.

It follows that the longer the chain length of the additive, the better its load-bearing capacity. It is found, however, that the greater the chain length of the additive used in cold rolling aluminium, the greater is the tendency for the aluminium to form brown stains, which mar the surface appearance of the rolled sheet on subsequent annealing. These brown stains can be removed by annealing the sheet at a higher temperature and for a lo'nger time than are required by strictly metallurgical requirements for softening the sheet after cold rolling.

Where the sheet produced with the aid of known lubricants has to be annealed at a relatively low temperature, as for example in the production of a part-hard sheet from fully hardened cold rolled sheet, it is impossible to remove the brown stains and the only way to obviate them is to remove the lubricant from the surface of the sheet before annealing is commenced.

It will be appreciated that the removal of the brown stains by prolonged heating or avoidance by removal of the lubricant are both expensive and wasteful procedures.

It is an object of the present invention to provide a method for cold deformation of aluminium employing a lubricant, which on subsequent annealing of the aluminium, does not form white stains and which has a re duced tendency to form brown stains as compared with atent O 2,962,401 Patented Nov. 29, 1960 a lubricant containing an acid or ester additive of the same load-bearing capacity.

The object of the present invention is substantially achieved by the use of a lubricant comprising a petroleum fraction base oil having low staining properties and a small proportion of a long chain saturated aliphatic alcohol as the load-bearing additive.

As with known additives the load-bearing capacity of these alcohols and their tendency to produce brown stains on the surfaces of the aluminium on heating to annealing temperature both increase with chain length.

However, with straight chain aliphatic alcohols up to lauryl alcohol and particularly with nonyl alcohol there is no staining due to the additive on annealing and, provided a specially refined non-staining base oil is employed, these alcohols can be used as load-bearing substances in the reduction of sheet for subsequent partial annealing with very satisfactory results. With nonyl alcohol in such a base oil there is no necessity to dry off the lubricant prior to low temperature partial annealing and this is a most satisfactory lubricant additive provided that only moderate reductions are employed. The use of nonyl alcohol as an additive to the lubricant oil does per mitof producing part-hard sheet commercially from fully-hardened cold rolled sheet without intermediate removal of the lubricant. This is a result not previously obtainable with the known additives.

Where heavy reductions are required in each pass of the rolling mill an oil containing a longer chain alcohol -isemployed,.such aslauryl alcohol orvoctadecyl alcohol. Although .octadecyl alcohol has a definite tendency to produce brown stains on aluminium during annealing, the temperature and time required to remove these stains is substantially less than that required with known additives which have been found, moreover, to have a lower loadbearing capacity than octadecyl alcohol.

Lubricants containing additions of lauryl alcohol, the chain length of which is intermediate between that of nonyl alcohol and octadecyl alcohol, have been found to be useful in many applications involving the cold form ing of aluminium products which need to be annealed subsequent to working. Thus, in the production of alusheet material by cold rolling, where moderately heavy reductions are required at each pass of the rolling mill, an oil containing about 4% lauryl alcohol has been used with very satisfactory results, the staining produced on heating the cold worked material being insignificant. The use of lubricants containing higher concentrations of lauryl alcohol allow heavy reductions to be taken at each pass of the mill. Thus, in practice, a lubricant containing 6% of technical grade lauryl alcohol has allowed aluminium sheet, which remained stain-free on annealing, to be cold rolled with a reduction of 64% at each pass of the mill.

Further, a lubricant containing from 2 to 8% of lauryl alcohol has been found to have excellent characteristics when used as a lubricant in the punching out of circles or slugs, for use in impact extrusion of articles such as thin walled tubes, from thick aluminium or aluminium alloy sheet. Thus, a lubricant containing 4% lauryl alcohol has been found to have an adequate load-bearing capacity for this purpose and, moreover, to lead to a marked reduction in the brown staining which has been found to occur during the annealing of the slugs when these have been produced using known lubricants.

In its broadest terms the present invention comprises a method of cold deforming aluminium (including its alloys), characterised in that the lubricant employed between the aluminium and the rolls or deforming tool comprises a hydrocarbon base oil with a low inherent tendency to stain the surface of aluminium when heated in contact therewith and containing a small proportion of a saturated aliphatic alcohol having at least seven carbon atoms. Below heptyl alcohol the load-bearing capacity of the alcohol additive becomes rather low and the flash point of the alcohol drops to a point "which may be unacceptable from the point of vi'ew-of fire hazard. At the other end of the scale alcohols having more than twenty carbon atoms decrease in solubility in the base oil'so that it is impossible to maintain sufficient quantities of the additive in solution. With certain special rollings, however, it may be desirable to employ an alcohol containing more than 20 carbon atoms. In such case the mixture of alcohol and base oil is first heated to get the alcoholinto solution. 011 cooling, the alcohol separates out and forms very fine particles which remain suspended in the base 'oil for-considerable periods. If the lubricant is used in this condition, it has exceptional loadbearing capacity and very high reductions can be 'obtained in cold rolling, using such a lubricant.

For operation with a modern high speed mill having continuous flood lubrication in which for economic reasons it is desirable to be able to obtain the maximum possible reduction, a long chain alcohol such as octatlecyl alcohol is employed as the additive, in a base oil in quantities of about 1-4%, the oil preferably being maintained at a temperature sufiicient to hold the alcohol in solution. The base oil used must be one which has a low tendency to form brown stains, but several such oils are commercially available at the present time. A-s'r'nall proportion (about 0.1%) of a surface wetting agent is preferably added to the base oil to ensure the spread of the lubricant over the entire surface of the metal.

In apractical rolling test on commercial purity aluminium alloyed with l%% manganese, it was found that the maximum reduction obtainable in one pass 'with known lubricants without damage to the surface was 58%. On reduction beyond this figure, the surface of thealuminiu'm became damaged by reason of collapse of the lubricant film, bringing the aluminium into direct contact with the surface of the roll.

On the other hand; on carrying out a rolling test on tlie' same metal with a lubricant comprising a commercial base oil with 1.8% octadecyl alcohol and a small proportion of wetting agent, it was found possible to obtain a reduction of 63% on one pass. It is possible that this figure could have been exceeded, but the power available '-at the rolling mill was insufiicient to permit a greater reduction to be obtained.

In tests designed to ascertain the tendency of lubricants to produce brown stains on annealing, which tests comprise the annealing under standard conditions of stacks of sheets cut from cold rolled aluminium strip, some of which were coated with lubricants containing what were previously believed to be the most suitable load-bearing additives, and some of which were coated with the lubricant containing as a load-bearing additive 1.8% octadecyl alcohol, only the sheets coated with this latter lubricant were found to be free from staining after annealing the sheets.

In the place of octadecyl alcohol, about 2% of cetyl alcohol can be employed as the additive where a slightly lower percentage reduction in each pass is acceptable. Mixtures of long chain saturated aliphatic alcohols, such as cetyl and octadecyl alcohols, may be employed as additives. Such mixtures can be obtained commercially more cheaply than the pure alcohols and give results very little inferior to the use of a pure alcohol alone.

Again it is found that a straight chain alcohol has better load-bearing characteristics than a branched chain alcohol of thesame number of carbon atoms, but economics may make it desirable to employ the less efiicient branched chain alcohol as the lubricant additive. Alcohols containing unsaturated groups are not satisfactory for the present purpose.

The improved load-bearing capacity of lubricants containing octadecyl alcohol enables greater rolling speeds to be achieved than are possible with known lubricants,

so giving economies in time and in power consumption.

Moreover, in some marginal cases, the use of the improved lubricants has made it possible to eliminate one pass in a rolling programme, so that where three passes were required to produce 'a given reduction in the thickness of the metal using known lubricants, the use of a lubricant containing octadecyl alcohol allowed the same reduction to be achieved in only two passes of the mill.

In such instances the new 'method results in considerable economies in rolling costs.

In ordinary cold rolling-of aluminum strip the cost of the base oil of the lubricant used is a factor which has to be taken into account, so that it is necessary to employ a petroleum fraction which does not require very special refining techniques for its production. Thus, an oil which is suitable as a base for octadecyl alcohol or lauryl alcohol for compounding -a lubricant to use in rolling aluminum strip which is subsequently fully 'annealed,-may itself have a low staining tendency and still be fully satisfactory for its purpose.

Such oils may be obtained commercially at satisfactory prices and an oil having the following properties is suitable=for the purpose:

Boiling"r'ange 250-350 C. (preferably 260420 0.)

Bromine number 0.4 maximum.

Sulfur content 0.08% maximum mum) Acidity: H J

Fresh sample'neutrali's'ed by 0.02 Sample aged for 24 hours at C. neutralised by 0.025 'nigm. 'KOHl'gm.

The lighter and less viscous the oilis, the better it will be. However, against this the fire hazard must beset. Ordinarily a flash point of C. is the minimum for ordinary acceptability, but where special precautions can readily be taken, an oil of lower :flash point will give good results.

Three commercially available base oils found very suitable for the present purpose are Mineral Colza, Fusus A and Kerosine 2675 6, which have the following properties:

(preferably 0.06% 2;

Fusus A Mineral Keroslne Colza 26756 Bci'i'tg range C 255-350 255-341 288-331 'lotal sulfur content ..p c-rcet 1t. 0. 08 0.075 0.08 Bromi'e numben; v V v 0.; I 0 37 H Viscosity in centstdkes at 20 0 7. 38 6. 406 8. 139

Farce .taig'e carbon atoms 'rtng structure per(ent-. V 30 32 27 Percentage carbon atoms in 'aro-' matie structure "percent" '4 L 8 4.8

Percentage carbon atoms in napht'teaic structure percent- 26. 27 22. 5

These base-oils have themselves some tendency to produce brown stains, but these are removed under the standard annealing conditions for octadecyl alcohol and lauryl alcohol and substantially stain-free 'anneaIed sheet can beproduced.

In finishrollingwhere'surface'appearance of "the product is of primary importance, his usual to employ moderate reductions, and in such cases the load-bearing capacity of the lubricant is not of primary-importance, whilst the tendency of the lubricant-'to-form 'stains is of great importance. --1n finish rolling it is therefore preferred to use a relatively'short "chain alcohol, such as nonyl alcohol, which itself has substantially no tendency to form white or brown stains when heated in contact with alu- -minium.

Again in cold rolling aluminum sheet to full hardness and subsequently drawing it back to partial hardness by low temperature partial annealing at temperatures of ISO-260 C., nonyl alcohol in amounts of l-5% is again the preferred additive for the lubricant applied to the metal during rolling, although lauryl alcohol has been successfully tested for the same purpose and other alcohols containing more than nine and less than twelve carbon atoms are also suitable. Because of the staining produced by known additives, it is the present practice to absorb the lubricant from the sheet by wrapping the rolled sheet in tissue paper before annealing. By using a lubricant containing nonyl alcohol as the load-bearing additive during the rolling step, this costly practice can be avoided, and the coiled strip or sheet can be annealed whilst still having a lubricant film coating its surface.

Although nonyl alcohol itself has practically no tendency to form stains, the commercially available light petroleum fraction base oils, used for the compounding of rolling lubricants, have some tendency to form brown stains, although this is slight compared with the commercially available additives. When using nonyl alcohol, therefore, as the load-bearing component of the rolling lubricant to secure the best results, it is necessary to employ a specially refined base oil which is itself practically non-staining. Such base oils are not commercially available and are therefore expensive and can only be used where their use results in other economies.

The characteristics of a suitable base oil for this purpose are:

Bromine number less than 0.2, preferably less than 0.1.

Total sulfur less than 0.02%, preferably less than 0.01%.

Acidity after ageing for 24 hours at 110 C. neutralised by less than 0.01 mgm. KOH/gm.

Colour water white.

The fraction should be very close out with only of the oil distilling over outside a narrow boiling range of 20 C. In order to keep an acceptably high flash point of the order of 250 C., the boiling range of the base oil should be 275295 C., with only 5% of the sample distilling over at temperatures below 275 C. and a further 5% at temperature above 295 C.

Using a base oil of these characteristics nonyl alcohol is added in the range 1 to 5%, preferably with the addition of about 0.1% of a wetting agent to form a lubricant for use in the cold working of sheet, which is to be subsequently partially annealed at a temperature of between 180 to 260 C. The amount of nonyl alcohol which is added will depend on the reduction to be etfected, but for ordinary service about 2% nonyl alcohol is employed.

Additions of laryl alcohol have been used with success in the rolling of very thin aluminium sheet or foil to produce a very high surface finish. It is usual in the production of such foil to employ a light petroleum fraction to which is added up to about 12% of various esters and fatty acids, including palm oil and coconut oil, and special treatments are required to minimise the staining produced when these lubricants decompose during annealing. It has been found that virtually stain free foil, having the desired high surface finish, can be produced by cold rolling the foil stock with a lubricant comprising a light petroleum fraction to which is added 3% of lauryl alco- 1101. However, for the production of foil having an exceptionally high finish, it is necessary to use a lubricant containing as the main load-bearing additive 24%, preferably 3%, of lauryl alcohol, to which is added 1 to 2% of palm oil. Using this lubricant virtually stain free foil, having an exceptionally high finish, can be produced without the necessity of employing special annealing treatments, involving times and temperatures in excess of those required to anneal the metal.

I claim:

1. In a process for the cold deformation of aluminum, the step of lubricating the surface of the aluminum with a composition consisting essentially of: (a) a hydrocarbon oil having not more than a slight tendency to produce stains on aluminum when heated in contact therewith, (b) an amount sufiicient to improve the load-bearing capacity of said hydrocarbon oil of at least one saturated aliphatic alcohol having at least 7 carbon atoms, (0) from zero to an amount at least sufiicient to ensure the spread of the lubricant over the entire surface of the metal to be deformed of a surface-wetting agent, and from zero to about 2% palm oil.

2. The process of claim 1, in which said aliphatic alcohol is a straight chain alcohol having 9 to 20 carbon atoms; and in which the amount of said alcohol used is from about 1% to about 8% by weight of said composition.

3. The process of claim 1, in which said aliphatic alcohol is lauryl alcohol, and in which this alcohol is present in an amount from about 2% to about 8% by weight of the entire composition.

4. The process of claim 1, in which said aliphatic alcohol is octadecyl alcohol, and in which this alcohol is present in an amount from about 1% to about 4% by weight of the entire composition.

5. A process for cold rolling aluminium foil stock to produce a foil having a high surface finish, characterised in that the foil stock is lubricated during rolling with a composition consisting essentially of a light petroleum fraction oil of low tendency to form brown stains on aluminium when heated in contact therewith, about 24% lauryl alcohol, and about 12% palm oil.

6. A process for the production of part-hard aluminum sheet material, comprising cold rolling aluminum, whilst lubricating it with a composition consisting essentially of (a) a close-cut hydrocarbon oil having substantial freedom from formation of brown stains when heated in contact with aluminum, (1)) an amount suflicient to improve the load-bearing capacity of said hydrocarbon oil of a straight chain aliphatic alcohol containing 9 to 12 carbon atoms as a load-bearing additive, and (c) from zero to an amount sufiicient to ensure the spread of the lubricant over the entire surface of the metal to be deformed of a surface-wetting agent; and subsequently annealing the rolled aluminum at a temperature in the range of about to 260 C. to draw it back to part-hardness.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,070 Story Jan. 12, 1932 2,119,114 Richardson et al. May 31, 1938 2,409,726 Winning et a1 Oct. 22, 1946 2,590,451 Perry Mar. 25, 1952 2,605,224 Jahn July 29, 1952

Claims

1. IN A PROCESS FOR THE COLD DEFORMATION OF ALUMINUM, THE STEP OF LUBRICATING THE SURFACE OF THE ALUMINUM WITH A COMPOSITION CONSISTING ESSENTIALLY OF: (A) A HYDROCARBON OIL HAVING NOT MORE THAN A SLIGHT TENDENCY TO PRODUCE STAINS ON ALUMINUM WHEN WHEN HEATED IN CONTACT THEREWITH, (B) AN AMOUNT SUFFICIENT TO IMPROVE THE LOAD-BEARING CAPACITY OF SAID HYDROCARBON OIL OF AT LEAST ONE SATURATED ALIPHATIC ALCOHOL HAVING AT LEAST 7 CARBON ATOMS, (C) FROM ZERO TO AN AOMOUNT AT LEAST SUFFICIENT TO ENSURE THE SPREAD OF THE LUBRICANT OVER THE ENTIRE SURFACE OF THE METAL TO BE DEFORMED OF A SURFACE-WETTING AGENT, AND FROM ZERO TO ABOUT 2% PALM OIL.

6. A PROCESS FOR THE PRODUCTION OF PART-HARD ALUMINUM SHEET MATERIAL, COMPRISING COLD ROLLING ALUMINUM, WHILST LUBRICATING IT WITH A COMPOSITION CONSISTING ESSENTIALLY OF (A) A CLOSE-CUT HYDROCARBON OIL HAVING SUBSTANTIAL FREEDOM FROM FORMATION OF BROWN STAINS WHEN HEATED IN CONTACT WITH ALUMINUM, (B) AN AMOUNT SUFFICIENT TO IMPROVE THE LOAD-BEARING CAPACITY OF SAID HYDROCARBON OIL OF A STRAIGHT CHAIN ALIPHATIC ALCOHOL CONTAINING 9 TO 12 CARBON ATOMS AS A LOAD-BEARING ADDITIVE, AND (C) FRO ZERO TO AN AMOUNT SUFFICIENT TO ENSURE THE SPREAD OF THE LUBRICANT OVER THE ENTIRE SURFACE OF THE METAL TO BE DEFORMED OF A SURFACE-WETTING AGENT, AND SUBSEQUENTLY ANNEALING THE ROLLED ALUMINUM AT A TEMPERATUER IN THE RANGE OF ABOUT 180* TO 260*C. TO DRAW IT BACK TO PART-HARDNESS.