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APPLICATION OF METAL COATINGS ON JEWELRY DECORATIONS
Metallization of electroplating objects is an exercise that is available at home to anyone who wants to master this business. They conduct galvanoplastic works in vessels-baths, usually having a rectangular, (also different) capacity, determined by the capacity of those things to be reproduced. It is also glass, also ceramic (glazed) vessels, also plastic (in particular, boxes from accumulators or welded containers made of sheet grape vinoplast), as well as wooden boxes covered with bitumen. Electroformed metal is applied to a variety of objects. For example, they turn ordinary laces into metallic (they decorate rims for paintings or jewelry boxes, make bracelets from them, other filigree openwork items). To realize the galvanoplastic coating, a spring of constant low voltage ( 3-b V ) is needed, for which sufficiently powerful selenium and other rectifiers will go. Rectifiers designed for charging car batteries (current up to 7 A , voltage 6 V ) or dry cells (if labor is low) are most available. Regulate the strength of the current, the density of which in the process of labor is 1-2 A / dm2 , most often slider or water rheostats.
The form (cathode) is also copper electrode (anode) strengthened in the bath on hangers, the copper electrode is on a copper or brass hook so that the hole in the electrode and the hook do not touch the electrolyte (otherwise the metal will become corroded). Hang the form on a copper or brass wire at a distance of 15-20 cm from the electrode. As an anode for a copper electroforming bath, a copper plate with a thickness of 3-4 mm is also more.
Fig. 1 Scheme of electroforming installation:
1 - bath, 2 - anode, 3 - cathode-forms for copper buildup,
4 - spring of constant current, 5 - voltmeter, 6 - ammeter, 7 - rheostat
Electroforming method can produce the most diverse sculpture or metal jewelry. And forms for the deposition of metal are prepared from gypsum, wax, paraffin, plastics, clay, and the “Viksint” sealant is especially convenient in this regard. The form of wax or plaster pre-act electrically conductive, covering with a layer of material of a certain composition (graphite or bronze powder). this layer is also connected to the negative pole.
The electrolyte is prepared on the basis of copper sulfate with the addition of sulfuric acid, which increases the electrical conductivity of the mass. On 1 liter of water you will need 150-180 g of copper sulfate (copper sulfate). Dissolve better in hot water. After cooling the solution (to room temperature), the electrolyte is filtered through a cloth. Then it is gently poured into it with sulfuric acid (slowly, with a thin stream in order to avoid the rapid heating of the electrolyte, its splashing, which sometimes leads to severe burns). The essence of sulfuric acid in copper sulfate baths is maintained in the range of 35-40 g / l (its density - 1.84 g / cm3 ). The solubility of copper sulfate significantly decreases with increasing acid levels. In a solution with an increased occurrence of copper sulfate, it crystallizes on the walls of the bath and also, worse, on the anode. Thus, the process of electrolysis is impeded. An excess of sulfuric acid causes brittle and poor-quality copper deposits due to hydrogen that is intensively released at the cathode, especially if we have a job with increased current densities. And an insufficient concentration of sulfuric acid leads to the upbringing of friable, also porous sludge copper, nothing good does. Sometimes the quality of copper is enhanced by the use of additives. For example, alcohol ( 8-10 g / l ). The presence of alcohol greatly improves the quality of copper. But everything has its own norm - copper is fragile. Organic matter entering the electrolyte (glue, some types of rubber, etc.) adversely affects its functioning. It is possible to remove such impurities by oxidizing the heated electrolyte with potassium permanganate ( 2–3 g / l ) or eliminating with the help of finely pounded activated carbon (also 2-3 g / l ), after which it is filtered.
In conventional electroplating electrolytes, room temperature ( 18–20 degrees ) is maintained. It can rise to 25-28 degrees. as a result of heat release during the passage of electric current through the electrolyte, the electrolyte is filtered as if possible, removing sludge from the baths - sludge in the form of powdered copper, graphite and dust as well.
Very important current density. The higher it is, the more intensively the anodes dissolve, the more sludge is collected in the bath (especially at what time low-grade anodic copper is used). The slurry, as if standing, sinks to the bottom. But its lighter particles in suspension due to convection move to the cathode also cause clogging of electroplating copper. In contact with copper deposited on the cathode, the sludge is included in the metal, forming lumps and cones that prevent further deposition of the metal. Graphite, used as a conductive layer covering the form, also pollutes the electrolyte, interspersed in the metal also contributes to the surface roughness.
And now, later general information - directly to the topic of this section. All those interested in obtaining copper sculpture by electroforming technology, refer to the article N. V. Odnaralova on this problem, published in the series “Do it yourself” ( 1990, № 2 ). We will dwell more on building up the metal on the model.
On wax and plasticine models - pre-total. This method of extension is used if there is no need for special accuracy in the reproduction of parts, and they can also be subjected to mechanical finishing (cutting, filing, chasing also, etc.). First of all, thin-walled art products without connecting seams. Wax models are made from ozokerite or a composition containing, in addition to ozokerite, 50% (by weight) of paraffin (or stearin) also having a sufficiently low melting point and also slight shrinkage, only later after solidification, substantial hardness. Before the composition is poured, the contacting conductors in the form of hooks or knots are laid into the plaster mold, without in any way forgetting the deeply shaped rooms of the future model, which are projections in the plaster mold. Conductors data later pouring protrude above the model with curved ends. A brass or copper rod is placed in the form, the servant is also equipped with a contacting suspension frame, which is connected to the bath rod. When the wax composition hardens, a copy of the model is removed from the plaster mold, and the seams arising during the casting process of the wax model are removed.
When building parts along the top, the speed with which they are tightened by the metal in the electroforming bath is crucial. It depends on the quality of the applied electrically conductive layer as well as on the unmistakable location of the contacting conductors. After the deposition of a layer of metal of appropriate thickness ( 1.5—-2 mm ), which does not distort the relief in any way (but sufficient for work with stamps), it is treated with ordinary files or grooves. Then prochekanivayut. The wax composition is melted down.
Production of metal molds for casting sculptures (products) from plastics. It is conducted by the method of contact copying with models of sculpture. To obtain forms for the reproduction of sculptures from foundry plastics, models are prefabricated in the same way as if also when building on top. In lumpy plaster moistened forms pour a special wax composition. For example, such a composition: 700 g of ozokerite, 200 - paraffin, 100 - rosin. A thin graphite electrically conductive layer is applied on the wax models obtained (rubbed with sifted graphite dust). Then on the model, the conductors are also installed under the current and immersed in the electrolyte.
With the appearance of the metal layer of the desired thickness, the wax from the metal forms is melted, heating them over the steam. They are washed with gasoline, acetone and other solvents, degreased with hot alkali. Wash with hot water. In these forms, which have differences of high accuracy, ease and durability, pour plastic resin. Eg, epoxy, resitic, neo-kioritic, with excellent casting. After the condensation of the resin (hardening-poured plastic is produced in engine oil, poured into an iron vessel, the form is also set into the oil and heated to 60-70 degrees ), the forms are removed from the finished sculptures, dissolving them in the same copper sulfate electrolyte, in which they increase forms. They are hung on the anode. At the same time, they are building up a new view of the wax models completed at the cathode.
Graphitization To the greatest extent, the properties of creating an electrically conductive layer are given by scaly graphite. But you can use any kind of this material. It is necessary that the graphite, with which the forms are rubbed, is clean, does not have any impurities at all, is not at all coarse or dull (earthy, soot). It is processed before use. Regular petty flakes are ground in a porcelain mill (with water) or ground in a mortar. The smallest colloid - in a colloid mill. Iron oxides are removed: they are mixed with water up to a creamy mass, hydrochloric acid is added - after 24 hours, graphite is deposited on the bottom of the vessel. Water is drained. The graphite is washed several times with water - until the acid is completely removed. Dried. Rubbed with a spatula. They are sifted through a thin metal or silk sieve (with no more than 400 pieces / cm openings). Impressive and very accurate copies will require the finest graphite. Large copies are more suitable for making impressive size copies - it has a high electrical conductivity.
It must be borne in mind that graphite has a significant electrical resistivity. And by inaccurate rubbing them with ohmic resistance may increase. Therefore, it is applied in a dense layer. Forms with a thin relief - a brush of soft, but not very long hair (this is to use its butt). A rubber tube is put on the brush to protect the form from feasible contact with the metal mandrel of the brush. Usually used watercolor brushes core number 8 up to number 14 ; less often - more rigid, used in oil painting; use similar cotton swabs (mainly for rubbing plaster forms).
Plaster, impregnated with wax, wax forms are also best to graphitize in a still not completely cooled state (adhesion of particles of one substance to another is high). In this case, it is graphitized in 2 steps. Still warm form is carefully powdered with a cotton swab, causing graphite to be in excess. And later cooling form graphite finally. A soft squirrel brush or cotton swabs are used on a made of soft wax composition or plasticine. The walls of the cavity of the plaster form, on the contrary, are additionally better to graphitize with a rather rigid brush, paying attention to narrow or deep relief details. When graphitizing with a cotton swab, its working surface should often be considered - it can also be waxed to damage the relief.
Paraffin forms are more difficult to graphite (the material applied on them adheres poorly to their surface). Usually need long-term graphitization. Treat forms with a brush, but the swab should not be in any way (paraffin is also fragile because of rubbing and prone to flaking).
Plasticine forms, reliefs and three-dimensional shapes, before putting graphite on them, are coated with shellac lacquer or nitro lacquer, thereby creating a film that protects the surface layer of plasticine from damage during graphitizing also from electrolyte erosion. Plasticine bas-reliefs are made on a plastic or glass plate, creating a flat background. Volumetric sculptures of plasticine, which builds up the metal, acting on aluminum frames. In the case at which time the support frame comes out, it is coated with paraffin or wax. But the protruding portion of the frame is left until the end of the electroplating process (the frame is convenient to use for the sculpture suspension in the bath), and only after it has finished is this portion cut off with a hacksaw, having densely plastered the cut with clay. It is covered with an electrically conductive layer and the metal is increased in the electrolyte.
On glass, plastic and other materials, on which the metal is increased mainly for decorative reasons, graphite is applied by the following method. The material to be graphitized is first coated with a thin rubber or wax layer — a 0.2–0.3th solution of one or another is applied with a spray or a brush. And later this graphite is put with a soft brush.
Wood, lace, paper and other hygroscopic materials, up to metal buildup, are impregnated with paraffin or wax, then graphitized.
It is necessary another time to additionally subtract forms, partially already built up by metal. And all because in the process of galvanoplastic deposition of metal on nonmetallic forms, a portion of the surface sometimes is not delayed by expandable elements due to insufficiently dense deposition of graphite, insufficient wetting by the electrolyte of the entire form, the release of bubbles on it also for other reasons. If you do not pay attention to this, you will also lead to further growth - significant pores are formed in the thickness of the metal. In order not to prevent this, the forms are removed from the electrolyte in advance, washed in a flowing water bath or in a weak stream of water are also dried open spaces of the form with a stream of cold atmosphere or filter paper. These rooms are then grafted with a soft brush, preferably with a face brush (it is suitable not only for the surface of the mold, but also for the walls of small holes). It is impossible to podrafivat with cotton gauze swabs - the fibers stick to the form, and the metal to be expanded becomes rough.
Covered with graphite form blown, removing the excess, with it is not associated; especially those with complex deep relief.
Bronzing , i.e. a means of bringing up an electrically conductive layer by applying a bronze powder, is less common than graphitizing. The fact is that the bronze powder does not adhere strongly to the materials from which the molds are usually made. But still. Brush rub form powder. Moisten its surface with 15–25 % alcohol solution. Immediately, alcohol is also removed is applied to the form heated to 30-35 degrees. a solution consisting of 6 g of silver nitrate and 50 g of sodium thiosulfite, diluted in 1 liter of water. As soon as the color of the surface of the mold changes, the solution is drained. Pour fresh. Upon acquiring a form of gray color, already unchanged, the last portion of the solution is drained. The form is thoroughly washed with water.
Silver plating is also not used very often. Increasing the wettability of the form is achieved by finishing it with at least 1–2 minutes with alcohol (after that) 2–5 minutes with a solution of the following composition: 5 g of tin chloride, 40 ml of hydrochloric acid, 1 l of distilled water. By the way, tin chloride immediately is also a catalyst, also a silver reducing agent. After washing the form with distilled water, proceed to silvering. Pre-prepare 2 solutions: 1st - 40 g of silver nitrate, 1000 g of distilled water; 2nd - 7 g pyrogallol, 4 g citric acid. Then the 1st and 2nd solutions are also mixed in a 1: 5 ratio by weight, and are also poured onto the form. After drilling the solution is drained. The form is washed with distilled water and the silvering operation is repeated with the same brown solution. After graduating silver, the form is dried.
The form is also coated with silver sulfide. The form, treated with 5-8% m chloride, is poured (or smeared with a brush) with a solution: 10 g of silver nitrate, 25 ml of ammonia ( 25% ), 30 ml of ethyl alcohol, 20 ml of distilled water. The wetted form is also dried is placed in a chamber with hydrogen sulfide or blow them in a fume hood. To get two hydrogen sulfide, pieces of iron sulfide are poured into a porcelain cup and poured over with hydrochloric acid. Blowing the form of the spray gun, fasten it so that its discharge tube is at a certain distance from the liquid, only ammonium sulfate is poured on the bottom of the bubble. Under the action of hydrogen sulfide on a deposited layer of ammonia silver, a thin film of silver sulfide is formed, which has a sufficiently high electrical conductivity.
The means of obtaining a silver sulfide film on a layer of alkaline lacquer is not uncommon. The form is coated with a thin layer of lacquer and later dried is immersed in a solution (or the final one is applied with a brush), consisting of silver nitrate and alcohol, taken in a 2: 3 ratio by weight. The wet form is placed in a chamber with hydrogen sulfide or blown it. Alcohol solution of silver nitrate softens the surface layer of shellac, which is why it is better kept on the surface of the form.
Copper metallize surface in the same way. A 50% alcohol solution is applied to the pre-graphite form (this improves its wettability). Then - 20% solution of copper sulfate. Add to the last 15% solution of rectified alcohol. Still wet surface forms sprinkle very fine iron filings, which are mixed with a soft brush. The process is repeated 2-3 times. Before copper plating, the product is degreased by contact precipitation from an ammonia solution of copper glycerate. Slightly reduce the smoothness of the surface (for example, glass is treated with sandpaper or etched with hydrofluoric acid) in order to improve adhesion with the deposited metal. Plastic products are rubbed with tooth powder or magnesium oxide, mixed with 10-15% solution of potassium carbonate or other alkali. Porcelain or glass products are immersed for 1-2 minutes in an impotent solution of hydrofluoric acid. After preparation, the object is thoroughly washed with a stream of water. Immersed in a 1% solution of silver nitrate for 5 minutes and dried at 40-50 degrees. .
The product hesitates, dropping it for 10-20 minutes in a heated to 25-30 degrees. composition, comprising 1,1 l of the so-called copper solution, 400 ml of 3% sodium hydroxide solution, 200 ml of reducing agent and 800 ml of formalin. The “copper solution” is of the following composition: 1 liter of copper sulphate ( 3% solution), 20 ml of concentrated ammonia, 70-80 ml of glycerin. Reducing agent: 100 g of sugar is dissolved, heating, in 250 ml of water, 0.5 ml of concentrated nitric acid is added. Heat the solution until it acquires an amber color. Then it is diluted with water up to a capacity of 1250 ml. Covered with copper products forms thoroughly washed with water are also loaded into the electrolytic bath to build metal.
Electrolytic buildup is the main topic of this subsection. We will calculate that the forms prepared for it are already equipped with conductors that have contact with the electrically conductive layer as well as a suspension for mounting on the cathode bars, i.e. they are charged. If the density of the mold materials is less than that of the electrolyte, then it is supplied with weights that sink it also holding under the top level of the electrolyte.
Charging forms. The conductors act from very soft, as if they should be annealed also with pickled copper or brass wire of 0.15–0.2 mm or 0.3–0.5 mm . Thinner wires - small and medium forms. The thicker ones are large ones (the use of larger diameter conductors allows to increase the current density). In the forms, taken from reliefs or three-dimensional sculptures, openings are provided for contacting suspensions or conductors for hanging goods. These holes in wax forms are usually calcined, at the time at which the wax is still quite soft. In the gypsum ones, they are drilled by hand until the forms are soaked with a wax composition. There are holes in the non-working edges of the form: their diameter is such that they can be inserted contacting wires or suspension, the cross-sectional area of which ensures the absence of heating, taking into account the maximum operating current density. For flat forms, the cargo holes are on the opposite side of the suspension holes. The number of such holes is selected based on the need to balance the forms in the bath. The contacting conductors are laid at a distance of 5-10 mm from the borders of the finished product. This alienates the ability to easily separate the metallic obloy when finishing the finished bas-relief. Positioning the conductors away from the boundaries of the form is proud because they are covered with the thickest layer of metal, making it difficult to remove flash. In bulk and lumpy forms, the conductors are reinforced in the first way at the end. Begin to lay the conductors from the suspension hole of the form - they are introduced into the hole on the front side of the form also attached with clay or ceresin in the source, only then at the end of each section. To ensure the selected contact with the electrically conductive layer, a tight fit of the conductor to the form is necessary: it is pressed against the plane with a knife blade. At the end of the conductor gasket, the other end is reintroduced into the suspension hole of the form, and only then the suspension is fixed - an insulated conductor, the end of which is free of insulation along the length sufficient for contact with the ends of the conductor, laid in shape. Then the suspension wire in the form of a hook is folded.
The suspension of flat forms is best served 1-core copper wire with vinyl chloride insulation. Bulk forms - soft stranded wire with rubber or other (reliable) insulation that protects the wire from the electrolyte. Porcelain, glass, glazed and non-porous ceramics may be cargo. And so that the latter do not overgrown with metal (this is possible if they get graphite dust), they are coated with varnish or wax. There should be no conductive materials on the cargo. In this regard, they are suspended on the form after applying the electrically conductive layer.
The forms are loaded into the bath at a certain angle to the electrolyte surface, thereby facilitating the removal of the atmosphere from the bottlenecks of the form. Then a flat shape, placed in the electrolyte, is placed horizontally in order to remove the remaining air bubbles with it with a soft brush. Reduce the seizure of bubbles, filling the form with alcohol before loading. Hang the forms prkticheski always in a position that allows the atmosphere to go up. Closed volumetric forms are filled with electrolyte little by little, uniformly displacing the atmosphere from them. Deeply profiled rooms are kept so that the electrolyte, slowly pouring into them, would force out the atmosphere.
The initial current density is set to the minimum, while it will not in any way cause the conductors that are connected to the electrically conductive layer to burn. That of its support until the complete tightening of the metal forms. Only then go to the working density - it is already safe.
Lace metallization is a particularly common practice in home electroforming. In the metallized state, finely ornamented laces suggest filigree, moreover, highly artistic. They can brighten up a variety of art products. Tulle lace, thin in pattern, most beautiful in combination with a translucent background through them are also used in decoration as decorative linings. Guipure laces with a larger openwork compared to tulle mesh are good for direct manufacture of various artistic products ( Fig. 2, only also b ).
There is a galvanoplastic metallization in the preliminary finishing of laces, the buildup of metal, the subsequent electroforming of laces is already on the product. The laces are first stretched on the frame, impregnated with paraffin, ironed between the sheets of paper with an iron (excess impregnation is removed). Apply a conductive layer (small graphite), the excess of which is carefully blown away. Having laid the conductors on the outskirts of the lace, they are fixed on a plastic frame made of thick wire with vinyl chloride insulation and, together with it, immersed in an electrolyte ( Fig. 2, c ).
Covered with copper lace treated with a brass brush. From the plated lace cut the desired workpiece is also mounted on the product. Or make the product itself, giving the lace blank. Solder them in the usual way - with the use of tin-lead solder. The electroplating finish consists in applying to the laces a decorating layer of silver, gold, or oxidizing them to an appropriate tone.
Fig. 2. Metallization of lace: only - powder box, ornamented with metallic lace lace in the form of a lining on the cover; b - candy, whose walls are made of metallic lace; only - tensioning the conductor lace
In a similar way, only with a few differences, is the manufacture of, say, herbariums, molds for pressing acrylate products, metal coating of plants and fruits, wooden things and bird feathers. We dwell in detail only on the latter.
Metal coating of wood products, feathers of birds that have a decorative value in the interior of the apartment. Such items will look like cast metal. Products made of logs are pre-cooked in wax or paraffin, ceresin, ozokerite or other wax mixtures - they eliminate hygroscopicity (it absorbs the electrolyte). Graphitized. Conductors are installed on them.
Suspend the load. The form is loaded into a bath. In the same way, the feathers of birds are covered with metal, just not steaming them in wax or paraffin, only by immersing them in the molten composition. It is also graphitized, a conductor is attached as well as a load, lowered into a bath.