DE814231C - Process for cleaning and pickling of metals and device for carrying out the process - Google Patents

Description

CWiGBl. P. 175)

ISSUED SEPTEMBER 20, 1951

p 30282 VIa j 48a D

Bagnac, Lot (France)

There are already numerous methods of cleaning ferrous metals and annealing them Metals generally known. Certain of these processes use electrolytic treatment, the piece to be treated being immersed in a bath made up of solutions of various Products is formed, e.g. B. phosphates, fluorides, etc. and in which it is used as a cathode. These known methods do not make it possible to obtain a completely clean surface of the treated pieces, and moreover, their efficiency is not such that the grate is removed from the smallest spaces can be.

The present invention relates to a method of this type which makes it possible after treatment to obtain a piece of perfectly clean and shiny appearance, no matter which one Showed the oxidation state of the piece before the treatment. The efficiency of the process is such, that the rust removes from the smallest cracks or gaps in the pieces being treated will.

The method according to the invention allows not only to remove the rust from ferrous metals, but also also fully permits tartar, calamine, cement, nickel, chromium, cadmium, paint, Email, in short to remove any products that may stick to the surface of ferrous metals. It is also suitable for copper, lead and their alloys without affecting their physical properties and their chemical composition have the least harmful effect.

The method of the invention allows pieces of any size to be treated, from Pieces weighing a few grams up to the largest locomotive boilers and possibly even more larger pieces; the application limit depends solely on the dimensions of the available standing material. The efficiency of the process is such that one rusted on a bolt Screw slightly off after treatment

ίο it can be twisted off, with the two parts in turn have taken on a completely new look. The process allows the grate to be removed from any To take out gaps or cavities where it cannot be removed, neither by working with sand, or by any other method.

According to the present invention, the piece to be cleaned or derusted is carefully degreased and rinsed with warm water and as

ao electrode used in an electrolytic bath, which is formed essentially from a solution of suitable density and which contains a mixture of alkali hydroxide and alkali cyanide, preferably with the addition of an alkali metal halide salt and

As of a suitable peptizing salt, then that Piece rinsed with warm water, drained and then immersed in a bath of protective oil and drained again.

An alkaline metasilicate or an alkaline aluminate, for example, can be used as the peptizing salt will.

The relative amounts of the various constituents of the electrolytic bath depend on different ones Factors and in particular on the speed with which the work is ahead of you should go, also on the amount and type of rust to be removed, on the amount and type of Precipitation to be removed, because possibly different at the same time on an existing piece If products are to be taken away, the composition of the bath must necessarily be such be that it can be used within the broadest possible limits, but the ingredients to be used are themselves by the economic conditions and by the cost of the necessary chemical Products limited.

It can be beneficial to add a wetting agent to the bath to be added, which allows the treatment liquid into the smallest spaces penetrate, thereby improving the effectiveness of treatment; the wetting agents can expediently of the sulfonate or of the sulfonated fatty alcohol genus, the appropriate concentration between 0.05 and 0.5 percent by weight or about 0.5 g to 5 g per liter of Solution can be.

In the course of the treatment, the cyanide can partially decompose and form complex iron salts with some of the oxides to be removed, so the composition of the bath should be monitored and salts should be added from time to time, which give it the necessary effectiveness.
The treatment is carried out at ambient temperature with a low direct current voltage, the current density generally being of the order of 3 to 3.5 amperes per dm ² . The piece to be cleaned or derusted, which is immersed in the electrolyte, is initially connected to the negative pole of the system, and the bath is stirred vigorously, for example by a compressed air distributor, which is provided in the lower part of the container. After this first treatment, the current is preferably reversed and held for a period approximately equal to ¹ Z _{5 of} the time during which the piece forms the cathode. Then it is washed, drained, and covered with a layer of a material which prevents it from oxidizing.

In the following description, reference is made on the drawing shows an embodiment of the invention to which the invention but is not limited.

Fig. Ι is a view of the treatment tank, with part broken away to show internal arrangement; Figure 2 is a top plan view corresponding to Figure 1;

Fig. 3 shows on an enlarged scale the arrangement of the anodes and the air inlet tube inside of the container and also the connecting rods, which are provided outside and which with the other Pole of the power source are connected;

Fig. 4 is an end view of one of the terminals of the connection cables to the rods, which are provided on the outside of the container;

FIG. 5 is an illustration, partly in elevation and partly in section, of that shown in FIG TeUs;

Fig. 6 shows the end of a connection cable, which is provided with an end piece, which the connecting terminals and to adapt the connecting organs to the items to be treated, with certain Parts are shown in section for the sake of clarity of description;

Fig. 7 is a clamping screw;

Fig. 8 shows another type of bracket which ^{is fastened 1 (} 55 on the piece to be treated by means of a bolt;

Figure 9 is an end view of the part shown in Figure 8;

Fig. 10 is a view with the 1 * 0 again in section given ends of a rod which is fastened above the container and which allows it to be attached to it hanging items that are easy to handle;

Figs. 11 and 12 show a side view and a Clear plan view of a basket that can accommodate small items to be treated;

Fig. 13 shows in vertical section part of the rust removal container, which is equipped with a gas heating device is provided;

Fig. 14 is a section through line XIV-XIV of Fig. 13;

Fig. 15 is a general representation of the plant; Fig. 16 is a top plan view of the same plant.

The pieces to be derusted are first carefully degreased so that the electrolyte in all parts of the ias Can wet the piece. This degreasing as well as all

other operations of the method are carried out in a container of suitably sized dimensions, which can be made of any material that will withstand the liquids it is intended to contain. The temperature of the bath degreasing takes place in a warm 4o ° / ₀ sodium carbonate solution, of a wetting agent, or even can not be added, the container containing this solution can be prepared by any suitable device heated, which allows to about 80 °, the bath is constantly stirred during the treatment.

After remaining in the degreasing bath for 15 to 30 minutes the piece is for 5 to 10 minutes in a similar container as the one described above washed off with warm water, then it is immersed in a cleaning or rust removal bath that is formed by a solution of 30 ° Be, a mixture of salts in the following proportions.

Sodium hydroxide NaOH 55 to 8 ₅ o / _o Sodium cyan NaCN 9 ■ Sodium silicate SiO ₃ Na ₂ 5 - Sodium chloride NaCl 0 - - 25% ■ 8%

to which 0.05 to 0.5 percent by weight of a suitable wetting agent is added, for example a sulfonated one Fatty alcohol.

If the water used to make the solution is hard water, it may be useful be to soften it beforehand by adding a suitable softening agent, e.g. B. Sodium metaphosphate in a ratio which does not exceed ι kg per 900 l solution.

The various components have the following tasks:

First of all, it is important to have a high concentration in caustic soda in order to obtain a strong release of hydrogen and oxygen at the electrodes ^{during electrolysis at a current density of 3.5 amperes per dm 2.} This release causes a strong mechanical dissolving effect on the rust or the precipitates and also facilitates the emulsifying and saponifying effects on any greasy residues that might be present on the surface of the pieces.

The main job of cyan sodium is to cloud the treated surfaces to be eliminated, for all the oxidized layers are easily dissolved in the solutions of the cyannatiium.

The radical chlorine is important in those cases in which the chlorine has a strong, dissolving effect on the Rust and the oxides did, however, especially in the nascent state, as it is present in electrolysis due to the strong dissolving effect it exerts on the containers or their linings, the percentage of sodium chloride must be relatively low and can be the same if necessary Be zero.

The silicate or the aluminate of sodium is used because of its peptizing effect by it provides an element that remains in semi-colloidal form; Silicon, silicon hydroxide or silicon containing Acid for a silicate, aluminum hydroxide for an aluminate, an element which is mechanically known as Abrasive detergent works when it is dispersed in the solution.

The role of the wetting agent is to reduce the surface tension and thus the effect of the To facilitate rust removal products. The sodium phosphate that has been added to hard water has the main purpose of softening this water and keeping the calcium salts and magnesium salts in Keeping solution, giving the best possible distribution or dissolution of the chemical products used allowed. '

While the piece to be derusted is used as a cathode, it can be assumed that in addition to the mechanical effect that results from the rapid formation of hydrogen on the surface of the metal and enables the largest oxide particles to be separated, a reduction of the iron oxides by the hydrogen according to Formula Fe ₂ O ₃ + 6 H = 2Fe + 3 H ₂ O takes place, so that a metallic precipitate forms on the piece.

The rust removal takes 30 minutes to 3 hours, depending on the degree of oxidation. If this initial treatment period, during which is used to entrostende piece as the cathode completed, the direction of circulation of the current during a period of time is reversed, which is equal to about ¹ J ₅ of the previous period, wherein the piece under treatment then, the role of an anode plays.

During this last derusting phase, the chlorine ions discharge directly on the piece to be derusted, and the last oxide particles are quickly removed by the nascent chlorine: Fe ₂ O ₃ + 6Cl = 2 FeCl ₃ + 30. The attack on the piece is therefore extremely fast when the concentration of the alkali chloride exceeds the limits given above. During this treatment phase a slight oxidation of the iron, which was previously deposited by the electrolysis, may form, but the oxide formed is immediately dissolved by the cyanide and at the end of the treatment the pieces have a shiny appearance and are perfectly clean.

This dissolving effect, which the Alkalicyanid no in complex salts on the basis of Ferri- or Ferrocyanid converts, weakens the cyanide solution, so that it is useful to periodically add a new amount of this Add substance.

According to one embodiment of the method, from the moment the system is put into operation and a rust and paint stripping bath for a sufficiently long period, for example one year use and this new bath, the composition of which falls outside the limits given above is evident in the density, i.e. H. Maintain at 30 ° Be by giving it from time to time either adding water if the density is too high, or a mixture if the density is too low of suitable salts is added, which is referred to as regeneration mixture and which increases

Contains percentage of cyanur. The composition of this regeneration mixture can be between the following Limits are:

Sodium hydroxide NaOH 45 to 81 Cyan sodium NaCN 15 - 40 Sodium chloride NaCl 3 - 12 Sodium silicate SiO ₈ Na ₂ 0.5 - 3 Parts by weight

In this composition the percentage of cyanide is more important than in the composition of the new bath; the proportion of silicate is reduced. In the course of electrolysis, this product becomes as above indicated decomposes and gives a silicate in the semi-colloidal state, which by continuous movement of the bath is kept in suspension. Almost all of this silicate remains in the container without one To suffer decomposition.

ao After derusting, the treated pieces are washed with warm water, they must be in the The wash tank is left for a long enough time, not just to remove the last particles of the electrolyte, but also to keep them at a sufficient temperature

»5 to bring them to temperature so that they can be dried quickly. They are then immersed in an oil bath, which prevents them from oxidizing in the outside air. Such a bath may be formed by a solution of 2O ° / ₀ lanolin in kerosene. They are then dried off and can be used again soon.

This treatment method has such a complete effect that the nuts, bolts and threads and all connections which could not be separated from each other before the treatment and have been found to be unusable, have been cleaned and can be used again. In many cases can machine tools that are unusable and badly damaged by the weather can be used again without dismantling.

As a particularly advantageous embodiment of the invention, a fresh bath is formed by a solution of 30 ⁰ Βέ of a mixture of sodium salts according to the following formula:

Sodium hydroxide (NaOH) 77.20 0 /
/ 0 Cyan sodium (NaCN) 13.67 ° / o Sodium silicate (SiO ₄ Na ₂ ) 4.24 0 /
/ 0 Water and the like 4.89 0 /
/ ο-

This bath can be used for a sufficiently long period, about 1 year, provided that that it is regenerated from time to time by giving it the necessary amount of the following mixture, Called regeneration mixture, the following is added:

Cyan sodium (NaCN)

Sodium hydroxide (NaOH)

Sodium chloride (NaCl)

Sodium silicate (SiO ₈ Na ₂ )
Water etc.

33-09 ° / o
55.10%

9.27%
0.48%
1.96 · / ,.

This mixture is in a sufficient amount in the The aforementioned bath that has already been used is dissolved in order to bring its density to 30 ° Be.

The method can be used with the aid of electrolysis tanks of any type, which are made of materials which withstand the aforementioned chemical agents. Various devices are shown in the drawings with which excellent results have been obtained. The containers can advantageously be lined with soft steel sheet, which are appropriately reinforced by angle iron according to the dimensions and the maximum weights of the pieces to be treated. They can be of the same type or of different types, the rust removal tank also having the necessary equipment for electrolysis and the degreasing and washing tanks having a heating device.
, Figs. 1 and 2 show a container that is suitable for the rust removal process. The container ι is made of sheet metal and its sides i ° are ^{welded to each other and to the bottom i 6} , it comprises an edge 2 on its upper part, on which pieces of wood or ribs 3 are attached, which are used as insulating means to the power supply rails 4 and 13 to wear. Inside the container, a conduit 5 for compressed air feeds through pipes 6 led down two manifolds 7 which are arranged on the lower part and which carry connecting pipes 8 which are inclined at 45 ° in both directions. A copper piece 9 is connected to one of the poles of the low-voltage system, which contains a changeover switch which can pass a maximum power, and on this piece 9 four running rails 4 made of copper are fastened, between which the anodes 11 are fastened, which by plates made of soft steel are formed (see Fig. 3). The fastening of the rods and the anodes can easily be fastened by means of screw bolts 10 which penetrate the ribs 3 and the rails 4 which are held by rings 12 at a suitable distance from one another. As can be seen from Fig. 2, the anodes are provided on the four sides of the container and are kept at a small distance from its walls, from which they are electrically isolated.

The second pole of the power source is connected to outer rails 13, which are only present on one side of the container and which carry a certain number of pieces 14 which form connecting terminals. These clamps are particularly shown in Figs. 4 and 5, they are made of brass or phosphor bronze and contain a body in which two slots 15 are incorporated, which can accommodate two and three running rails 13, a hole 16 allows the fastening on the rails 13 by means of a bolt. The receiving part for the stream, which is provided on the upper part, is formed by a projection 17 which is provided with a thread on the outside and runs conically at ιη ⁰ · in order to form the female part of the connection; the male part which is attached to the connecting cable 18 (Fig. 6) comprises a hollow rod

made of bronze or brass, in which the cable 18 Takes place; the rod ends at the other end by a cable 19 attached to the cone 17 ° of the female Part is assigned and which is provided with a shoulder 19 "at the point of its largest diameter which serves as an abutment of a locking screw 20 provided with an opening.

The same connection arrangement by male and female cones is on all of the parts provided which lead the current to the pieces to be treated. Because they have enough size dimensions you can connect them to the pole of the power source by attaching a bracket or clamp to them attached, which are reproduced by Figs. 7 to 9. The clamp bracket in Fig. 7 consists of a U, one leg of which is connected to a female connecting member as described above and a V-shaped notch 21 is provided, while the second leg is a nut for a fastening screw 22 forms. The clip of Figs. 8 and 9 is used on the under treatment Piece to be fastened by a bolt that twists in this part and includes a female Connecting part 17, which is firmly connected to a part 23 which has a bore 24, which for this purpose serves to guide the fastening bolt. The two parts 17 and 23 are at such a distance spaced apart to allow rotation of the nut 20 of the male part of the joint will.

A certain number of cross members can be provided above the container at a suitable height, for example, swell when the pieces to be derusted are heavy, and the current will move the pieces supplied directly by means of the brackets or clamps as described; if the Pieces are lighter, they can be formed by simple round bars 25 of suitable diameter, an example of which is shown in Fig. 10. These rods are at their ends with female connecting parts 17 are provided, and they may contain spacer rings 26 welded on. the Pieces to be treated are placed on these traverses by means of hooks in S-shape or by suitable chains suspended, and the rings 26 play an important role in the suspension by chains, because they prevent the chains from sliding during treatment.

If the pieces to be rusted are small in size, they are simply put in baskets Steel 26 "(fig. 11 and 12) arranged by welded Elements are formed and have a hook 27 on the upper part and a ring 28 at the bottom. In this way it is possible to hang several baskets, one above the other, in such a way that the entire height of the container is made usable.

It should be noted that the pieces to be treated the

Anode-forming plates 11 must not be too close and that they are kept at a distance should be at least 10 cm between the anodes and those under treatment Pieces is. It goes without saying that the pieces are attached to the attachment points of the brackets or connecting clamps carefully cleaned to allow easy passage of electricity.

The degreasing and rinsing tanks do not, of course, contain the electrolysis assembly, but they do must be heated to 1 grains to bring the temperature of the liquid to about 80 °.

Figs. 13 and 14 show an advantageous embodiment for heating the container by means of gas. Rows of burners 29 are arranged under the metallic container i °. At a short distance from the sides i ^{a of} the container, a sheet metal casing 30 with the walls i " forms a conduit for the hot exhaust gases, which release a large amount of the calories they contain to the side walls of the container 15 and 16. In this embodiment, the containers are arranged one next to the other in a cavity 35 such that the top edge of the container is approximately 1 m above the floor and between the containers and the third edges of the cavity Arranged playpen, which allow movement around the container.

In front of the rust removal container 1 are the degreasing container 31 and the first rinsing container 32, both are heated by gas by means of rows 29. The second rinsing container 33, which the The rust removal container follows, is designed like containers 31 and 32. Assuming the stay of the pieces in the containers 32 and 33 is of only a short duration, one needs for the two washing processes to provide only a single container. However, for the system to work well, it is preferable to have both Provide container.

When leaving the rinsing container 33 , the pieces must drip off. For this purpose, they can be arranged on a grid 36, below which an inclined plate 37 is provided, which is connected to the container 33 by a line 38 so that the liquid flowing out of the rinsed pieces returns directly to the container ^ 3. The protection after the treatment takes place in the container 34, and the final draining on the grid 39, which is designed similar to the grid 36, which is provided with the same device for collecting the drained liquid.

The system is served by a conveyor, which is at a suitable height above the various Treatment tank can circulate. The bottom of the cavity 35 is advantageously beveled and lined with an impermeable material so that liquids that converge here are drained off and which make cleaning easier.

The process and the substances described can be modified by exchanging technically equivalent means Of course, changes can be made without thereby departing from the scope of the invention to come out. In particular, the above can be used as examples of the preparation of the various baths specified sodium salts by similar salts from another alkali metal) z. B. Potassium to be replaced. The proportions given above can

can be modified to reflect chemical equivalents.

Claims (8)

PATENT CLAIMS: 1. Process for derusting or stripping ferrous metals, copper, lead and their alloys, characterized in that after the pieces to be treated are carefully degreased and drained are left, they can be used as electrodes in an electrolysis tank, the one aqueous solution of a mixture of alkali metal hydroxide and alkali metal cyanide with the addition of a smaller one Contains amount of alkali chloride and a peptizing salt, the electrolysis during a sufficient Duration is maintained in order to remove the last traces of rust or something to be removed Precipitation make the pieces disappear ao then drained, then dried and immersed in a bath of a protective oil. 2. The method according to claim 1, characterized in that that the piece for a duration which is between 30 minutes to 3 hours Depending on the size and nature of the precipitate to be removed, it can be used as the cathode, then the current is reversed, the piece can be used as the anode for a period of time which is exactly equal to ¹ ^ of the previous period of time. 3. The method according to claim 1, characterized in that that the peptizing salt by an alkali metal silicate or by an alkali aluminate is formed. 4. The method according to claims 1 and 3, characterized in that the electrolyte is an aqueous solution of 30 ⁰ Be is a mixture comprising 55 to 85 weight percent sodium hydroxide, 9 to 25 ° / ₀ sodium cyanide, from 0 to 12% sodium chloride, 3 to 8% sodium metasilicate containing with or without the addition of a suitable wetting agent in the order of 0.05 to o, 5 ° / _0th 5. The method according to claim 4, characterized in that the wetting agent of the genus of Is sulfonate or is formed by a sulfonated fatty alcohol. 6. The method according to any one of the preceding claims, characterized in that the bath is moved continuously during the electrolysis, for example by introducing compressed air. 7. The method according to any one of the preceding claims, characterized in that the electrolysis is carried out at the temperature of the environment.
8. Process according to claims 1 to 5, characterized in that in the case of use of hard water, this water is softened by adding sodium metaphosphate in a quantity ratio which does not exceed 1 kg per 900 liters of solution. 9. The method according to claim 1, characterized in that the degreasing of the pieces is carried out in a solution of 40 ⁰ Z ₀ IgCm caustic soda, which is kept at about 80 °, and the pieces for a period of 15 to 30 minutes in this solution be immersed. 10. The method according to claim 1, characterized in that that the rinsing after derusting is done in very warm water and that the pieces are in this water for a long enough time stay to a temperature that allows them to dry quickly after draining. 11. The method according to claim 1, characterized in that the protective bath after derusting by a mixture of 2o ° / ₀ . Lanolin is formed in kerosene. 12. The method according to any one of the preceding claims, characterized in that when Start of the operation of the system and a rust removal for a sufficiently long period of time. and a stripping bath is used, the density of which is kept at 30 ° Be, depending on whether this Density is too high or too low, either adding water or a mixture of suitable salts, wherein the regeneration mixture contains an increased percentage of cyanide to the Bring the main composition of the electrolysis bath within the desired limits. 13. The method according to claim 12, characterized in that this regeneration mixture 45-81% sodium hydroxide, 40 to 15% sodium, 3 to i2 ° / ₀ sodium chloride, 0.5 to 3 / contains ° ₀ sodium silicate the percentages being in weight expressed and the salts are assumed to be dry, or a mixture of similar salts of another alkali metal, the proportions of which have been calculated and for which the chemical equivalents have been taken into account. 14. The method according to claim 13, characterized in that that the fresh bath by an aqueous solution of 30 ° Be a salt mixture is formed, which 77.2 parts by weight sodium hydroxide, 13.67 parts by weight cyan sodium, 4.24 Parts by weight of sodium silicate, 4.79 parts by weight of water and basic salts which contain impurities form, wherein the regeneration mixture has the following composition: Sodium cyanide NaCN Sodium hydroxide NaOH
Sodium chloride NaCl Sodium silicate, SiO ₃ Na ₂ Water and impurities 33.09% 9.27%
0.48%
2.06% 15. Plant for performing the method according to the preceding claims, characterized characterized in that they have a heated container for degreasing the pieces, a heated one Container to drain off before treatment, in an electrolysis container with an electrolyte Constantly moving device, a low voltage, high power source of power contains which a device for the rapid reversal of the low-voltage current i «5 includes a heated rinsing container after Treatment, a draining device for the rinsed pieces, an immersion container that a Contains protective oil, a drip device for the oiled pieces and devices for transport the pieces from one end of the rig to the other end, and for dipping and lifting out of the parts, whereby the draining devices are preferably provided with inclined plates, which are provided below and with suitable lines, which the liquids to the treatment vessels feed again. i6. Installation according to claim 15, characterized in that that the electrolysis tank has a receptacle made of an impenetrable and the chemical products used are invulnerable to material and electrodes made of soft steel arranged vertically around the container at a short distance from its walls and are suspended directly on continuous poles which are connected to one of the poles of the Power source are connected, a line system, which is compressed with a storage container Air is connected and feeds two manifolds, which are horizontal in the lower part of the container are arranged, and these collecting lines are provided with inclined connecting pipes, so that the compressed air allows a continuous circulation of the electrolyte, and the second Pole of the power source is connected to a series of continuous rods, which on the one side of the container are provided and on these rods the connecting clamps for the Cables are attached, which connect the pieces to be treated with the power source. 17. Plant according to claims 15 and 16, characterized characterized in that insulated cross members at a suitable height above the electrolysis tank are arranged and that the pieces to be treated, which are connected to the electrical circuit connected by cables and which by brackets or connecting brackets on the pieces are attached, are suspended from these cross members. 18. Plant according to claims 15 to 17, characterized characterized in that metallic baskets containing the pieces to be treated on the traverses are suspended, which are arranged above the container and that one of the Pole of the power source is connected to these trusses. For this purpose 2 sheets of drawings O 1532 9.