US3810786A

US3810786A - Method for cleaning (degreasing) web material

Info

Publication number: US3810786A
Application number: US00134742A
Authority: US
Inventors: B Lindgren
Original assignee: Nyby Bruk AB
Current assignee: Nyby Bruk AB
Priority date: 1970-04-15
Filing date: 1971-04-16
Publication date: 1974-05-14
Anticipated expiration: 1991-05-14
Also published as: GB1332557A; FR2097751A5; AT312389B; DE2118347A1; SE338221B

Abstract

IN DEGREASING STEEL ARTICLES AN IMPROVEMENT IN OVERALL COST AND IN CONVENIENCE IS REALIZED BY DISPLACING OILY SUB: STANCES FROM THE STEEL BY THE USE OF DETERGENTS HAVING A HYDROPHOBIC BALANCE OF 10 AND ABOVE, RESULTING IN THE FORMATION OF A LABILE EMULSION.

Description

May 14, 1974 B. LINDGREN 3,310,786

METHOD FOR CLEANING (DEGREASING) WEB MATERIAL Filed April 16, 1971 United States Patent Ofice 3,810,786 Patented May 14, 1974 3,810,786 METHOD FOR CLEANING (DEGREASING) WEB MATERIAL Boris Lindgren, Eskilstuna, Sweden, assignor to Nyby Bruks Aktiebolag, Nybybruk, Sweden Filed Apr. 16, 1971, Ser. No. 134,742 Int. Cl. B08b 7/04 US. Cl. 134-9 8 Claims ABSTRACT OF THE DISCLOSURE In degreasing steel articles an improvement in overall cost and in convenience is realized by displacing oily substances from the steel by the use of detergents having a hydrophobic balance of and above, resulting in the formation of a labile emulsion.

At the rolling of web material, particularly of stainless steel, necessarily oil is used. After completed rolling, this oil must be removed very carefully from the web surfaces as otherwise, particularly at subsequent annealings, surface reactions would occur which result in a partial or total rejection of the material.

The conventional method, which at present is the only possible one, comprises in principle the steps of removing the oil in a chemical and mechanical way by washing the surfaces in a liquid, usually water, which advantageously is heated and to which grease or oil solving chemicals are added. For intensifying the solvating effect of chemical agents, the chemical attack is combined with a mechanical effect which, for example, most easily can be achieved by brushing. Thereby the solvent is brought into a more intimate contact with the impurities. This operation usually is followed by flush cleaning and drying. The conventional method has several disadvantages, of which by way of example the following ones may be mentioned:

1) The addition of detergents or solvents provides the emulsion of water and oil with a high stability, i.e. the oil cannot be separated. This means frequent changes of the washing solution.

(2) For reducing the number of washing solution changes, very large quantities of washing solution are to be applied in order thereby to be able to clean large amounts of web material until that concentration of oil and impurities is obtained at which the effectiveness of the detergent decreases. Said large quantities require voluminous, bulky means-i.e. vessels-with high space requirements, particularly in their longitudinal extension, and also large and power demanding auxiliary equipment, for example for brushing, pumping etc. A further consequence is the problem connected with taking care of heavily polluted washing solutions at their discharge.

(3) The detergents used in relatively large quantities include large amounts of alkali, phosphates, silicates, hydrates and carbonates. These detergents are chemically labile, i.e., they disintegrate and thereby lose their solvating effect and constitute a heavy load for the efliciency degree of installation. This applies particularly to the polyphosphates, which have a very high thermolability. This implies that these polyphosphates disintegrate to orthophosphates and lose their solvating effect. Their emulsifying effect, however, results in emulsions of oil and water of high stability.

(4) The high stability of the resulting emulsion impedes the separation of the oil from the emulsion. This in its turn renders it impossible to utilize a circulation system with a theoretically unlimited use of the washing solution, i.e. if it were possible to reduce or eliminate the very rapidly increasing degree of pollution and the concentration of oil.

(5) For achieving an effective cleaning, usually about 3% of a very expensive detergent, counted on the relatively large water quantity, must be added. The high concentration implies that large amounts of emulsion and detergent remain on the surfaces of the cleaned webs and are to be removed by washing and flushing, in many cases by means of brushes. The result is satisfactory only in a few cases, because the degree of cleanliness obtained is not perfect. This involves the disadvantage that remainders of detergent and oil may react with the web surface. It is therefore necessary to apply much flushing water, which in its turn requires pumping systems and installations for mechanical cleaning (brushing installations) as well as means for the supply and removal of said large flushing water quantities. It is particularly the alkali content in the solvent which is dangerous for the surface of the cleaned web. Alkali remaining after the flushing constitutes a risk of corrosion.

(6) The large and space-requiring installation is difficult to operate in its entirety, it requires a relatively large operation staff and demands much service, etc. With respect to service, it is particularly the control of the chemical composition which has to be made continuously because of the different consumption of the different components in the solution. It is, thus, not the proportion of detergent in its entirety which is to be controlled, but the proportion of the different components in the detergent, in order to ensure a troublefree operation.

A further relatively effective method among those applied for the removal of the oil is the trichloroethylene degreasing method. This method, however, has the dis advantages as follows.

( 1) The installation costs are relatively high.

( 2) The health problems are difficult.

(3) The trichloroethylene remaining on the sheet metal surfaces gives rise to inconveniences at the heat treatment (carbon pickup). This applies particularly to stainless sheet metal.

(4) Trichloroethylene is an expensive product, and its consumption is high.

(5) The method of using trichloroethylene is not adapted for use at webs in motion, because it does not meet the requirement of perfect sealing.

The method and the apparatus according to the invention have as their object to eliminate the aforesaid disadvantages of the known conventional methods. The invention in principle is characterized by a displacement of the oil in a chemical-physical way, which displacement is effected by the use of detergents with a hydrophylic-lypophylic-balance (HLB) of 10 and above, which results in the formation of a labile emulsion, which by constructional means according to the invention very rapidly disintegrates to oil and water.

The method operates in principle with the characterizing features as follows.

The specially selected detergent can form with water and oil an emulsion only when energy is supplied and the energy level is maintained. As soon as the energy supply ceases, the emulsion reassumes its labile nature, the oil coalescence proceeds rapidly and totally, so that the oil is separated from the water and can be returned to a normal use, for example as fuel oil. Subsequent to the coalescence the detergent is regenerated automatically, and the washing solution free of oil can again be supplied into the process.

The apparatus for carrying out the method according to the invention is characterized by means for the supply of energy and an arrangement-the so-called rest roomwhere the quasi-stable emulsion due to the absence of energy reassumes its labile nature, so that the separation of the oil from the washing solution can take place.

In the following the construction of an installation and the function of the method is described by way of example, with reference to the accompanying figure.

From the working station (not shown) which may be, for example, a rolling mill, a grinding machine, polishing machine or the like, where oils or the like are applied to or develop on the surfaces, the web passes through a pair of doctor rolls 1, which under pressure remove rolling oil, for example, to such a degree, that the web only shows a coherent oil film without puddles and runnels. The doctor rolls are made, for example, of metal and coated with felt or plastic, but advantageously with rubber. Below the rolls is provided a collecting vessel (not shown) with flutes for the oil.

The web thereafter enters the degreasing zone 2 and passes in turn by a spray ramp 3 spraying a detergent solution onto both surfaces of the web, an energy supply means, which in the example shown is in the form of circular rotary brushes 4 vigorously agitating the washing solution on both surfaces of the web, and a spray ramp 5 for flushing both web surfaces with a clean detergent solution. The detergent solution includes water plus an addition of 0.05% by weight of a detergent with an HLB value at or above 10, for example nonyl-phenolethylene oxide adduct (which is a wetting agent with a relatively high HLB value and with a hydrophilic nature). As detergent there is used one (such as the mentioned nonyl-phenol-ethylene oxide adduct) having a non-ionic character, taken alone or in combination with an anionic and/or a cationic detergent. The amount of the selected detergent used in the aqueous solution is from 0.001% to 1.0% by weight; advantageously however, from 0.001% to 0.1% by weight and particularly to 0.05% by weight. The HLB value states the hydrophilic-lypophilic-balance in the chemical composition of a detergent and, thus, is a classification value for detergents with respect to the solubility in oil or water. The value is a limit value at which the detergents change their nature, i.e. change over from oil solubility to water solubility. This detergent solution advantageously may have a temperature of about 60 C., at which the solution speed is greatest, particularly when waxes or similar substances have been applied to the sheet metal surface at working (for example at polishing).

The web passes after the degreasing zone again through a pair of doctor rolls 6, which under a relatively high pressure remove the film of detergent solution. Thereafter the web is ready for further working or reeling. With respect to the film of detergent solution remaining after the passage of the web through the doctor rolls, it may be mentioned that this film has no damaging effect at the further working, particularly at annealing.

The detergent solution is supplied from a sedimentation-storage tank 7 by pump 8 to the aforementioned spray system in the brushing and flushing zones. In both of said zones, a relatively high energy amount is supplied to the solution and thereby imparts to the solution a temporary emulsion stability (quasistability), which contributes to lifting the oil remaining on the web therefrom and emulsifying it. The emulsion is pumped, by pump 8, from a collecting vessel 9 in direct connection with the degreasing zone to the aforesaid sedimentationstorage tank, the so-called rest room. Heat is supplied to the rest room and through the degreasing operation, at between 30 C. and 80 0, preferably between 50 C. and 70 C., and suitably at about 60 C. through means (not shown) and facilitates, as mentioned above, the degreasing and also promotes the separation of the oil from the water. Within the tank proper are provided service means, such as an oil separator 10, level controls (not shown) with metering pump for detergents, thermostats and filters. In the drawing the oil separator is shown by its simplest embodiment, viz. as a partition wall. At

very high requirements on cleanliness, or for emulsions with very fine droplets as well as at highly limited liquid volumes, advantageously a coalescence filter is applied, either in combination with said rest room or without the same.

In connection with the example described, the following may be mentioned.

The detergent amounts to be added for bringing about the results characterizing the invention, are almost negligible (0.05 by weight) relative to the solution volume, The detergent is regenerated after the oil separation and, thus, is not lost, except for a certain very small waste. The volume of the washing solution is only a fraction of the volume required for conventional cleaning and need not be changed.

It is not necessary, either, to control the chemical composition. The need of flushing water is abolished completely. Therefore, the installation is relatively small and space-saving, which is of a decisive importance for planning or placing the installation in the buildings required therefor. Due to the complete absence of discharge, furthermore, the definite requirement with respect to environment protection has been satisfied, which according to the conventional methods would have involved a very high burden both from an economic and operationtechnical point of view. The price of the washing solution is not affected by the addition of the cheap detergent, i.e. the washing solution costs as much as normal water, contrary to the conventional method, at which trichloroethylene and the added detergent amounts (3%) command a high price which, of course, is increased substantially by the frequent changes of the entire washing solution.

The example described has as its only purpose to facilitate the understanding of the invention without, however, restricting the same.

What I claim is:

1. A method of environment protective degreasing of stainless steel web material which comprises the steps of,

mechanically removing impurities on the web surfaces; subjecting the surfaces to a treatment with a washing solution consisting of water plus a detergent having an HLB value of at least 10;

simultaneously supplying kinetic energy in the form of mechanically induced agitation to the web material and treating solution to form a labile emulsion of impurities in the solution;

transferring the emulsion to a separate settling space wherein said kinetic energy supply ceases;

heating the quiescent emulsion whereby the water detergent solution portion thereof is separated from associated impurities and the detergent solution is regenerated;

flushing the surfaces of the web material with a clean detergent solution; and

mechanically removing adhering film of clean detergent solution from the surfaces of the web material thus treated.

2. A method according to claim 1 characterized in that the flushing is carried out with a clean washing solution by spraying.

3. A method according to claim 1, characterized in that the separation of the emulsion takes place in a settling space, which simultaneously serves as a sedimentation and storage tank.

4. A method according to claim 1, characterized in that the treatment takes place in a closed circuit process by means of suitable pumps, for achieving the environment protective object, without discharge into air, ground or water.

5. The method defined in claim 1, in which the detergent used includes a detergent having a non-ionic nature.

6. The method defined in claim 1, in which the detergent used is a composition including both a nonionic compound and a detergent selected from the group consisting of anionic and cationic compounds.

7. A method according to claim 1, wherein the detergent quantity added to the water amounts to from 0.001% to 1.00% by weight.

8. The method defined in claim 1, wherein the temperatnre in the settling space andi'during'the entire process is between 30 C. and 80 C.

References Cited UNITED STATES PATENTS 2,158,694 5/1939 Fenton "134-9 6 Keogh 13410 X Groom 134-10 Croft 134-9 Quigley 134-9 Nachtman 134-9 U X US. Cl. X.R.