Jewelry casting. Casting from silver and gold to order Studio of artistic casting from silver

Jewelry casting is formally a type of lost wax casting. At the same time, jewelry casting has a number of specific features and represents one of the leading areas of artistic casting. Therefore, the authors of the textbook considered it possible to devote a separate chapter to it.

High surface quality and precision in reproducing the openwork pattern are ensured by the use of elastic rubber molds, finely dispersed molding materials with a gypsum binder, and forced filling of the molds with metal.

In the CIS countries, the leading developer and manufacturer of specialized equipment for the production of jewelry is the design bureau SKTB-6 of JSC Russian Gems (St. Petersburg).

8.1 MASTER MODELS

The first stage of serial production of jewelry is obtaining a master model. The artist sculpts or carves it from thermoplastic materials (Table 8.1).

The composition of materials subjected to mechanical processing includes paraffin, shellac wax, ethylene vinyl acetate copolymer, ceresin.

Modeling materials include wax, rosin, paraffin, and oxidized polyethylene wax.

The wax model made by the artist goes through the entire cycle of technological operations necessary to obtain the master model (see Chapter 7). Master models of jewelry castings are usually made

They are made from copper-based alloys (bronze, brass, nickel silver). Sometimes the master model is electroplated with a corrosion-resistant tin-nickel alloy.

8.2 Elastic molds

When making jewelry of complex configurations with particularly thin elements, elastic molds made of special vulcanized rubber are used. To do this, blanks of raw model rubber are placed in a metal cage. A master model, the internal cavities of which are filled with pieces of raw rubber,

placed on the prepared layer. The remaining rubber blanks are laid on top of the model. Then a punch is inserted into the holder. The clip is placed in a vulcanizing press.

Vulcanization occurs at a temperature of 150-160° C for 30-45 minutes. The temperature is maintained within the set limits automatically.

The desktop small-sized vulcanization press D159 (Fig. 8.1) consists of two heating plates, a traverse mounted on two columns, a screw pair with a flywheel, and a thermal control system.

Technical characteristics of the D159 press

Nominal pressing force of mold covers, kN

(at least) ........................ 5

Size of heating plates, mm............... 110x140

Maximum distance between plates, mm....... 70

Maximum heating temperature of plates, ° C........ 175

Temperature control error, ° C....... ±5

Supply voltage, V................ 220

Power consumption, kW (no more) ........... 0.8

Vulcanization time, min................... 30-45

Press weight, kg (no more) .................. 22

In addition to the D159 SKTB-6 press, a PV-1 vulcanization press with heating plate dimensions of 142x172 mm has been developed.

After cooling in water, the rubber mold with the master model sealed in it is cut, forming a complex relief of the connector in order to prevent the halves from moving relative to each other when obtaining wax models. In some cases, additional inserts are cut out to make it easier to remove the waxes. To improve the filling of thin sections, punch-out cuts are made in the mold cavity.

The rubber used for the manufacture of molds must not cause corrosion of the master model, not stick to the model composition and have high physical and mechanical properties (elasticity, resilience, etc.).

These requirements are met by materials based on polar rubbers and a mixture of SKI-3 rubber, which has high elasticity, with polar nitrile butadiene rubber.

Rubbers for the manufacture of molds, in addition to rubbers, include a filler (silicon dioxide, titanium white, carbon black, etc.), a plasticizer (paraffin and petroleum oils), and a vulcanizing agent.

Peroxides of organic compounds can be used as a vulcanizing agent (Table 8.2).

Rubbers based on SKN-40M rubber have fairly high elasticity and resilience, but are distinguished by high hardness. They provide high quality surfaces of products, almost do not stick to the model composition and can be used in the manufacture of massive products. Rubbers based on a mixture of SKI-3 rubber and butadiene-nitrile rubber are not inferior in physical and mechanical properties to imported “Gold label” rubber.

For the manufacture of small plastic and souvenir and gift items, you can use the unvulcanized rubber mixture of the Red Triangle LPO, which has the following properties:

Conditional tensile strength, MPa, not less......... 12

Elongation at break, %, not less....... 750

Residual deformation after rupture, %, no more....... 20

Hardness TM-2, arb. units, no more......................... 42

These properties are ensured under the following vulcanization mode: temperature 150± 5°С, time 45±5 min, pressure 10 MPa.

In the manufacture of jewelry of relatively simple configurations and souvenir and gift items, molds made from vixint, a rubber sealant, are also widely used. At the same time, the best performance was achieved in the case of using siloxane sealant Viksint U-1-18, which exhibits the following properties:

Vitality, h........................ 0.5-6.0

Conditional tensile strength, MPa, not less....... 2.1

Elongation at break, %, not less..... 160

Shore hardness, arb. units .................... 50-60

To make vixint molds, U-1 paste and catalyst No. 18 are used. The paste is thoroughly mixed with the catalyst and applied to a metal master model with a brush. For 100 parts by mass of U-1 paste, you need to take 0.4 parts by mass of catalyst No. 18. The duration of vulcanization is 72 hours at a temperature of 25 ° C.

After the first layer has vulcanized, it is covered with a gauze pad to strengthen the walls of the mold and the next layer is applied. The number of layers depends on the configuration of the master model and is selected experimentally.

Looking at the windows of expensive jewelry stores, we are delighted with the beauty of the products and the skill of the jewelers. The art of turning a precious metal into a luxury item in the imagination of many people is a kind of sacrament, a special skill that not everyone can master. How are rings that beckon with their beauty born? What path does a precious metal take from a sketch to its implementation in an expensive piece of jewelry? What is a flask in jewelry and what is it used for?

Features of the jeweler's profession

The profession of a jeweler requires not only a creative approach. A jeweler must be careful and patient. There are many nuances in this matter, the observance of which requires utmost precision. A jeweler works with high temperatures and hot metal; the danger of this profession requires endurance and physical strength. A jewelry master is not only a designer who comes up with sketches and works with a file under the bright light of a lamp. This is also a foundry worker, managing hot furnaces and molten metal, lifting heavy plaster molds and ensuring that technology is followed. The arsenal of a jewelry master is full of unusual devices that the average person has never even heard of. For example, flask. What is a flask and what is this device used for? Our article will talk about this.

Opoka in jewelry making

Despite all the innovations and high level of technology for making jewelry, many of the jeweler’s working methods remain unchanged since ancient times. The ring casting process, for example, has changed little. To answer the question of what a flask is, you should find out how the jewelry casting process occurs.

To make a ring from a precious metal, a jeweler uses a special fireproof cylinder into which hot metal, molding compound and wax blanks are placed. This is the flask.

This device serves to hold the molding sand while it is compacted during the process of obtaining a casting mold into which the precious metal is poured. You can make a flask yourself, the main thing is that it is made of fire-resistant material. Some craftsmen make a flask from a piece of pipe or roll it from a sheet of iron. The photo shows a modern metal flask.

This flask is already filled with molding mass, inside of which there are wax blanks. The next step is calcination of the flask in a hot furnace; this procedure takes place in the foundry.

Application of flasks in a foundry

No matter how sophisticated the jewelry is in the end, it goes through a very harsh path through the hot furnaces of the foundry. This is what the casting process looks like:

1. Products enter the foundry in the form of wax blanks, which undergo a molding process.
2. The wax blank is placed in a special fireproof metal cylinder - a casting flask.
3. Then the flask is placed in a hot oven for calcination. The temperature in such a furnace can reach 1000 degrees. The wax from the flask is melted, and in this form there is a place for the precious metal.
4. After the flask is calcined and the mold is formed, metal is poured into it. The process of casting jewelry takes place in a vacuum, preventing the formation of voids and the entry of foreign debris into the mold.
5. At the final stage, the caster removes the jewelry from the jewelry mold and begins its final processing and polishing.

Gypsum flasks for making jewelry

What is a gypsum flask? In shape it does not differ from the more common metal one. Its only difference is the material and the need for stepwise heating. Gypsum flasks are most often used for small jewelry casting, rather than industrial casting. In order for the casting process using a gypsum flask to be successful, the temperature regime must be observed, otherwise the mold will crack and become unusable. It is most convenient to do this in a special electric annealing furnace, since the temperature can be adjusted there. Annealing of gypsum flask is carried out in several stages:

1. Heating at temperatures less than 100 °C. The mold must be kept at this temperature for at least an hour.
2. The mold should then be kept in the oven at 250°C for two to two and a half hours.
3. After this time, the temperature should be raised to 450 °C and the investment ring should be annealed for another hour and a half.
4. Only after this can the temperature be raised to a maximum of 750 °C and the mold annealed for about three more hours.

The annealing time depends on the size of the flask: the larger it is, the longer it takes to anneal.

Disposable flasks

Having learned what a flask is and how it is used, it is easier to understand the intricacies of the process. It no longer seems so complicated, but rather interesting and simple. Modern technologies allow you to try to make your own jewelry almost at home. The Chinese market offers a wide range of disposable molds with ready-made molds. All that is needed to work with such a form is the required amount of precious metal and the ability to melt it. They are used both by jewelers who do not have their own foundry, and by freelance craftsmen who make custom-made jewelry.

The 3D Avtozavod company offers custom jewelry casting services from gold and silver. When working with silver, we can use our own certified materials or the client’s raw materials. For gold products, exclusively customer-supplied raw materials are used. All our products are of impeccable quality, as we are constantly improving technology. The stability of the alloy composition is achieved with the help of the latest equipment and the use of alloys from well-known global manufacturers.

Features of casting from silver and gold

Gold and silver have excellent technical characteristics. Exclusive jewelry, original souvenirs, and interior items can be cast from these precious metals. When casting precious metals, there are standards for production losses:

• for purity - 1.8%;
• for scrap - 3.5% (if the weight of gold is less than 30 grams, then losses during casting can be up to 5%).

In order to comply with the requirements of the current legislation on the casting of precious metals, special registration with the State Property Inspectorate is required. You can get all the necessary information about this from the specialists of our company.

The 3D Avtozavod company fulfills orders in the shortest possible time, since the entire production cycle takes place at the facilities of our enterprise. Gold and silver castings are tailored to the needs of jewelers, jewelry workshops and designers. We can offer a whole range of specialized services:

• 3D design and 3D printing before casting;
• Mold removal, electroplating and turnkey processing after casting.

The 3D Avtozavod company accepts orders for gold and silver castings of any volume. To submit an application, use the form on the website, write to us by email or call the contact number in Moscow.

Courses in casting artistic products at the Russian Academy of Crafts are of interest not only to jewelers. The technologies being studied will complement the professional arsenal of any craftsman who works with metal - a manufacturer of souvenirs, costume jewelry, original interior fittings, clothing or haberdashery. Jewelers will pay special attention to casting with stones, because this technology is taught in courses extremely rarely.

Practical classes take place in an equipped workshop, and students have time to produce several educational works. Some of the technologies being studied can be used at home, without special equipment, and used at leisure, for example, in the manufacture of knightly equipment or models of equipment. At the end of their studies, students complete a thesis and, based on the results of its defense, receive a qualification document.

What is included in the training program

The casting course program for jewelers provides knowledge about the properties of metals and alloys, introduces the tools and technologies used in casting artistic products. Students learn centrifugal and vacuum casting, sand casting, graphite, ceramic and metal molds, rubber molds, and low-temperature casting at home. Much attention is paid to safety issues during casting.

During practical classes, students go through the entire process of casting an art product step by step in several modes.

What will you be able to do after the course?

• Choosing the right casting methods for various materials and solving specific artistic problems.
• Make molds from rubber and silicone.
• Create stencils (wax models) and collect “wax trees” for lost wax casting.
• Operate a vacuum injection molding machine.
• Making molds for casting low-temperature alloys.
• Perform low-temperature casting at home.
• Clean castings and evaluate their quality.

Conditions of education

Training period: 72 academic hours.
In the group until 7 people.
Training materials are included in the course price.
Issued document: Certificate of profession “Foundry worker of art products” with the assignment of 2-3 categories.
To register, you must have your passport and a 3x4 photo with you. When registering for the course, you must pay 50% of the tuition fee. The remaining amount is due during the first two weeks of school.
Classes take place on the street. Kasatkina (metro station VDNKh)

To obtain high-quality silver or gold products, you need to create a Christmas tree. Yes, yes, this is not a mistake, because this is what jewelers call the blank used for casting. It got its name due to its appearance, because it resembles a spruce with branches sticking out to the sides, on which rings, pendants or earrings made of wax “grow”.

Wax prototypes are quite fragile, so assembling such a “tree” requires extreme care and caution. Models ready for casting arrive at the foundry, where they are truly magically transformed into real jewelry.

Stage No. 1. Making a casting mold

There is such a profession - foundry worker. He is the one who casts jewelry. Its primary task is the production of a special shape, that is, molding.

To do this, the foundry worker needs a flask - a metal cylinder with a rubber base. The wax tree is placed in it, and all the free space around it is filled with a molding mass of finely ground refractories, various additives and water. Whipped to a homogeneous mass, it fills all the voids, and the remaining air escapes during the process of compacting it on the vibrating table.

The foundry worker places the flask in the furnace and calcines it in two or three passes at a temperature of 900-1000°C, carrying out technological holding in between. When wax melts, voids remain, which are subsequently filled with one or another precious metal.

Stage No. 2. Pouring metal

To cast jewelry, the foundry needs another important equipment - a centrifugal casting machine. It allows you to obtain thin-walled openwork castings of high quality.

The installation has two tanks. In this case, one of them is intended for loading metal, and the second is for placing a cooled cylinder-flask. A vacuum is created in the internal space by pumping out air, which is replaced by helium.

After melting, the metal, under the influence of centrifugal force, enters the flask, where it occupies all the voids that were previously occupied by wax. At the end of the procedure, the mold is removed from the foundry unit and cooled first with a powerful air flow, and then with water. At the same time, the sintered molding mass is washed out.

Stage No. 3. Bringing it to condition

As a result of casting, a Christmas tree is obtained, but not wax, but made of silver or gold. It is thoroughly cleaned of remnants of the refractory composition, dried, and then jewelry blanks are carefully cut from it.

By the way, jewelry casting of some products can be done directly with cubic zirconia. The inserts are not damaged if the exposure temperature is properly adjusted.

All that remains is to weigh the resulting pieces and send them for finishing to give them a perfect look.

Jewelry casting is a universal method that helps our craftsmen create real masterpieces worthy even of royalty.