US2986526A - Metal cleaning - Google Patents

Description

METAL CLEANING Joan T. Crowther, Chicago, 111., assignor to Nalco Chemical Company, a corporation of Delaware The present invention is concerned with aqueous metal cleaning baths and cleaning compositions.

The cleaning of metals to remove such substances as oils, greases, buiiing compounds and fatty substances prior to painting, electriplating, hot metal dipping, phosphating and similar processes has been in common practice for many years. Failure to properly clean metal surfaces prior to coating processes of the types described, results in defective articles that are not satisfactory as items of commerce and industry.

Metals such as iron, steel, copper, brass, aluminum and zinc are often cleaned with hot solutions of alkaline cleaners. The process usually involves soaking the metal part or surface in a hot aqueous bath containing varying amounts and proportions of alkaline reagents. There are many commercial alkaline cleaning preparations available to the metal processing industries but they are often deficient in one or more respects.

The prior art alkaline cleaners, while performing satisfactorily in removing dirt from metal surfaces, tend to place on the cleaned surface chemical deposits which frequently interfere with subsequent processing operations such as heat treating, electroplating and the like. In some cases it has been observed that alkaline cleaners tend to precipitate from solution and form deposits on the equipment in which they are contained; such deposits interfere with heat transfer and require frequent cleaning to maintain the equipment in good operating condition. It is therefore an object of the invention to provide an alkaline cleaner which will remove dirt, grease and similar contaminants from metal surfaces.

Another object is to provide an aqueous alkaline bath for cleaning metal surfaces.

A further object is to provide an alkaline metal cleaner which will not place harmful deposits on surfaces cleaned therewith.

An important object is the furnishing of an alkaline metal cleaner which forms stable, non-precipitating solutions in aqueous liquids. Other objects will appear hereinafter.

In accordance with the invention it has been found that excellent alkaline metal cleaners are afforded by combining in certain critical proportions an alkali metal pyrophosphate and a higher aliphatic fatty alcohol which has been reacted with from 3 to 15 moles of ethylene oxide. It is recognized that phosphates and wetting agents have been combined previously in cleaning compositions but the particular combination of ingredients disclosed herein are superior and produce results not predictable from the prior art.

The alkali metal pyrophosphates may be selected from any of the sodium, potassium, rubidium or cesium salts of pyrophosphoric acid. Due to commercial availability and economic factors, however, the tetrasodium pyrophosphate and the disodium dihydrogen pyrophosphate are most suited for use. Tetrasodium pyrophosphate is not only an economically preferred ingredient but it gives the best results.

Patented May 30, 196i TABLE I Moles oi Ethylene Oxide Composition No. Fatty Alcohol Dodecyl alcohol.--" do Octyl alcohoL Hexadecenyl alcohol- Octadecyl alcohol. Octadecenyl alcohol l2-hydroxy octadecenyl alcohol. 0 ctyl alcohol The ingredients are combined in definite amounts to produce a single composition. Two general formulae are set forth below to illustrate typical combinations.

General Formula 1 Where the fatty alcohol-ethylene oxide reaction product is a solid it may be mechanically mixed with the alkali metal pyrophosphate to produce a unitary composition. If the fatty alcohol is a liquid and small quantities are used, the alkali metal pyrophosphate may absorb the material and a solid product will result. When excess liquids are present a paste may be prepared by using from 1% to 3% by weight of a water soluble binder such as carboxymethyl cellulose. A typical product containing the following ingredients was prepared.

Composition IX Ingredients Percent by Weight Tetrasodinm Pyrophosphate 99. 3 Composition I, Table I 0. 7

Composition 1, Table I, was a viscous liquid which was blended into the tetrasodium pyrophosphate. The finished material was a dry, pulverulent free-flowing, granular product.

Compositions of the type shown above, are dissolved in water to produce aqueous metal cleaning baths containing from 0.5% to 10% by weight of the compositions and preferably 2% to 3% by weight. The weight ratios of the fatty alcohol-ethylene oxide reaction product to alkali metal pyrophosphate are usually within the range of 1:9 to 1:199 with a preferred range being from 1:49 to 1:165.

To achieve maximum cleaning efiiciency it is usually necessary to adjust the pH of the treating bath from 8.0 to 11.5. Excellent results are achieved when the pH of the treating bath is between pH 9.0 and 10.0. When the tetraalkali metal pyrophosphates, especially tetrasodium pyrophosphate, are used, the pH of the treating bath will be within the preferred ranges specified. When acid pyrophosphate salts are used it is necessary to use alkaline bufiers to adjust the pH to the point of alkalinity desired.

dry and then examined. The efficiency of the cleaners were based on their grease and dirt removal efficiency, whether films were formed on the surface of the cleaning solution or whether precipitates formed and whether there was any foaming of the solutions in use. The forming of a film on the surface of the beaker meant that similar films would probably deposit on the surfaces of equipment contacting such solutitons. The results of these tests are reported below in Table II.

TABLE II Film For Test No. Cleaning Sol. Grease Dirt mation on Preclpltate Foaming Composition Removal Removal SurSIaee of Formation a t t O'-(1 a) A(1%)+B(0.1%)- A A C-(1%)+B(0.1%).. A- A A-(2%) A A A A A A A A A A A A A A Thus, sodium hydroxide, borax, sodium metabo-rate, ammonium hydroxide and similar alkaline materials may be used as buffering compounds. Care should be exercised in the choice of butter to insure complete solubility and freedom from precipitation under conditions of use. The most expedient buffering compound is sodium hydroxide. The buffers when used may be either blended int-o the solid compositions or they may be added separately to the treating bath.

The compositions of the invention are more soluble in hot water than cold. When the temperature of a treat ing bath is near boiling, viz. 200-210 F., as much as by weight may be placed into solution. This amount is generally not necessary for most cleaning operations and if local zones of cooling are encountered there is some danger of precipitation. Excellent cleaning may be afforded by using 2% to 3% by weight solutions which are stable at all temperatures encountered in conventional metal cleaning operations.

To illustrate the efiicacy of the invention the following are given by way of example.

EXAMPLE I The following chemicals were tested either alone or in combination with one another.

The test specimens were steel nails taken from typical production of a nail manufacturing machine. These specimens were caked with dirt and grease and in some instances were spotted with rust. The procedure consisted of heating solutions of the test chemicals in a beaker to 200 F. and maintaining the temperature between 200 F. to 212 F. The specimens were stirred in these solutions for two minutes, shaken in the air until 1 See us. Patent 2,674,619.

In Table II above, the designation A means satisfactory performance with the plus or minus signs indicating superior results in the case of pluses or unsatisfactory performance in the case of the minuses.

Test No. I shows that tetrasodiurn pyrophosphate while providing good dirt and grease removal left an oil film on the surface of the solution. Test No. II proved tripolyphosphate to remove dirt and not leave an oil film but grease removal was inferior. The combination shown in Test No. III passed the test but with the substitution of tripolyphosphate for tetrasodium pyrophosphate, grease removal was not satisfactory (Test N0. IV).

Tests V and IX indicate that when the concentration of tetrasodium pyrophosphate is increased, grease removal is improved but film formation is present.

Tests No. X through )GV demonstrate that the combination of anionic and cationic detergents with tetrasodium pyrophosphate prevent the film forming tendencies of the phosphate but grease removal is substantially impeded and heavy foaming occurs with the anionics.

Tests Nos. XV and XVII show that non-ionic detergents G and F in combination with varying amounts of tetrasodium pyrophosphate gives excellent cleaning results but precipitation formation and foaming renders the formulae unsuitable for use in commercial cleaning operations.

EXAMPLE H A manufacturer of nails was experiencing difiiculty in the cleaning and packaging equipment of his two nail making machines. These cleaning systems were of the recirculating type with the makeup of the cleaning solution being about 30 to 50 gallons per unit per turn. The temperature of the water was about 200 F. Heat was supplied through steam coils in the bottom of each unit. The cleaning liquid was an 8% to 10% by weight solu tion of a commercial alkaline cleanser which contained sodium metaphosph-ate, minor amounts of tetrasodium pyrophosphate and a wetting agent. As a result of this treatment heavy, adherent deposit accumulations were experienced throughout the entire recirculating systems of each unit. Cleanings were necessary from every one to two weeks, with such cleanings requiring at least 16 man hours. The nails so cleaned contained a visible film of chemical whichmaterially interfered with the heat bluing of the finished nails.

Composition IX was tested as the cleaner at a 2% by weight concentration for a period of several months with the following results being observed.

The expression carbonaceous deposits as used herein refers to all types of oils, dirt, greases or other types of deposits that commonly are found on unclean metal surfaces.

The expression wetting agent(s) and detergent(s)" are meant to be synonymous in meaning.

The invention is hereby claimed as follows:

The process of cleaning carbonaceous and other dirt from ferrous metal surfaces without leaving harmful deposits or an oil film on the metal surfaces, with no more than slight foaming of cleaning composition and without formation of precipitates in said cleaning composition or film at the surface thereof, which process comprises flushing said ferrous metal surfaces with an 0.5% to 10.0% by weight aqueous solution of a water soluble metal cleaning composition consisting essentially of:

Ingredients Percent by Weight A. Tetrasodlum pyrophosphate 98-99. 2 B. Dodeeylalcohol reacted with 8 to 12 mole of ethylene mrtdn 0.8-2.0

References Cited in the file of this patent UNITED STATES PATENTS 2,213,477 Steindorfi Sept. 3, 1940 2,508,035 Kosmin May 16, 1950 2,618,606 Schaeffer Nov. 18, 1952 2,733,215 Rufi Jan. 31, 1956 2,746,929 Wells May 22, 1956 FOREIGN PATENTS 490,285 Great Britain Aug. 11, 1938 683,383 Great Britain Nov. 26, 1952 OTHER REFERENCES Lesser: Metal Cleaners, Part I, Soap and Sanitary Chemicals, October 1952, pages 42-45, 169 and 171.

Fineman: NonionicsThe All Surface Cleaners, Part H, Soap and Sanitary Chemicals, vol. 29, March 1953, pages -53 and 114.