Metal forming lubricant

Description

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to lubricants for use in metal forming processes such as stamping and cutting sheet aluminum. More particularly, the invention relates to a lubricant having a reduced volatile organic compound (VOC) content and suitable for use in the fin press machines used for manufacturing the plate fins used in plate fin and tube type heat exchangers.

[0002] Plate fin and tube heat exchangers are commonly found in air conditioning, refrigeration and engine cooling equipment. The plate fins improve the thermal performance of the heat exchangers by increasing the amount of external heat transfer area. In air conditioning and refrigeration applications, the plate fins are usually fabricated from thin gauge aluminum sheet or strip. In large scale manufacturing operations, plate fins are produced by stamping, punching and forming the sheet or strip in a machine called a fin press. As with many metal forming machines and processes, lubrication of the metal feedstock before and during the fin press operations can lead to increased production output, end products of better quality and increased tool life.

[0003] One prior art lubricant used in fin presses has been mineral oil. Mineral oil of proper viscosity provides excellent lubricating properties. However, mineral oil remains as a residual coating on the plate fins after completion of fin press operations. This residue must be removed before subsequent manufacturing operations may be carried out The cleaning agents commonly used to remove the oil from the plate fins can present serious environmental problems such as ozone depletion and atmospheric and ground water contamination. Properly storing, handling and disposing of such cleaning agents can be difficult and expensive.

[0004] Another prior art lubricant, introduced to avoid the difficulties experienced with mineral oil lubricants, is mineral spirits to which have been added relatively small amounts of surfactants and lubricity enhancement agents. This type of lubricant evaporates rapidly after application without leaving a residue, thus eliminating the need for subsequent lubricant removal. On the other hand, the lubricating performance of such a lubricant is very poor. Even with the use of large quantities of mineral spirit based lubricant, the life of tools used in fin presses is greatly reduced when compared to the performance of presses using mineral oil. In addition, mineral spirits is a volatile organic compound (VOC). VOCs are now considered to be atmospheric contaminants whose discharge is strictly regulated and controlled.

[0005] What is needed is a lubricant for use in a fin press or similar machine that will provide greater lubricating performance, leave little or no residue on the press output and have reduced VOC content when compared to prior art lubricants.

SUMMARY OF THE INVENTION

[0006] The present invention is an improved lubricant for use in a fin press or similar machine that overcomes, to a large extent, the deficiencies present in prior art lubricants used in such applications.

[0007] The improved lubricant is a mixture of mineral spirits, a small quantity of surfactants and extreme pressure lubricity additives and one or more organic compounds selected from the group consisting of polyisobutenes and alkylene glycols. In a preferred embodiment, the proportion of mineral spirits is about 70 percent by weight, the proportion of surfactants and lubricity agents is about 10 percent by weight and the proportion of selected organic compounds is about 20 percent by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0008] The lubricant of the present invention is a mixture of mineral spirits, surfactants and lubricity additives and one or more organic compounds selected from the group consisting of polyisobutenes and alkylene glycols. The preferred proportions in the mixture are, by weight, about 70 percent odorless mineral spirits, about 10 percent surfactants and lubricity additives and about 20 percent selected organic compounds.

[0009] The selected organic compounds have the long chain molecular structure desirable in lubricants for good lubricating performance thus extending the life of the fin press tooling. In addition, they evaporate leaving only a small amount of residue. Those residues do not affect subsequent manufacturing operations but, if necessary, a residue may be easily removed using common water based cleaning agents. The polyisobutenes selected should have a molecular weight of from 320 to 460. The alkylene glycols selected should have one terminal hydroxyl group and a viscosity in the range of from 65 to 1715 Saybolt Universal Seconds (S.U.S.) at 100° C. Selected compounds having these characteristics are preferred because they are easily miscible in mineral spirits. It is not necessary that only a single selected compound be used in a particular lubricant batch but one, two or more of the selected compounds, in total adding up to the preferred weight proportion, will make an acceptable lubricant.

[0010] Polyisobutenes and alkylene glycols are relatively costly. The lubrication performance of these compounds, however, is far superior to mineral spirits. Therefore, as the proportion of the organic compounds increases in the lubricant mix, not only the performance but also the cost increases. Because of its greatly improved capability as a lubricant, the usage rate of a lubricant containing the selected organic compounds is significantly less when compared to prior art mineral spirit based fin press lubricants. The difference in total cost for lubricants used between the lubricant of the present invention and prior art lubricants is not so great as it may first appear and the total cost of using the lubricant may be even less.

[0011] A lubricant having proportions of 80 percent of the selected compounds, ten percent of other additives and the remainder mineral spirits will offer excellent lubricating properties, low usage rates and very low VOC emissions but will be relatively costly. In addition, the residue left on the press output may prevent painting of the metal without first removing the residue. Such a lubricant is suitable where lubricating performance and low usage rates are priorities, cost is of lesser importance, or where the press output will not later be painted.

[0012] Proportions of 20 percent of the selected compounds, 70 percent mineral spirits and 10 percent of other additives yield a good compromise when one considers lubrication performance, cost, VOC emissions and paintability without cleaning. A mixture of such proportions still contains a significant amount of mineral spirits. The usage rate for such a lubricant, because of its greatly improve lubricating performance, will be much less when compared to prior art mineral spirit based fin press lubricants. The total VOC emissions from manufacturing operations where the lubricant is used will be significantly less than before.

[0013] The lubricant is easily prepared using well known batch mixing processes. The extreme pressure lubricity additives and surfactants are the same as the proprietary additives contained in the 8191FR mineral spirit based fin press lubricant available from Chem Arrow Corporation International of Irwindale, California and made be obtained from that company.

Claims

1. A lubricant comprising a mixture of mineral spirits and one or more compounds selected from the group consisting of polyisobutenes having a molecular weight of from 320 to 460 and alkylene glycols having one terminal hydroxyl group and a viscosity in the range of from 65 to 1715 Saybolt Universal Seconds (S.U.S.) at 100° C.

2. The lubricant of claim 1 in which said mixture contains between 20 and 80 percent by weight of said selected compounds.

3. The lubricant of claim 1 in which the proportion of said selected compounds in said mixture is 20 to 80 percent by weight; there are eight to 12 percent by weight of other liquid additives and the remainder of said mixture is mineral spirits.

4. The lubricant of claim 3 in which said other liquid additives comprise surfactants and extreme pressure lubricity additives.

5. The lubricant of claim 1 in which the proportion of said selected compounds in said mixture is 18 to 20 percent by weight, there are eight to 12 percent by weight of other additives and the remainder of said mixture is mineral spirits.