| Start of section
| Stealth Master
| Secrets of the cosmos
Secrets of the Earth
Secrets of the Ocean
Map of section
|Use of the site materials is allowed subject to the link (for sites - hyperlinks)|
TECHNOLOGY OF METAL CASTING IN HOME CONDITIONS
To make a small detail of a relatively simple form of low-melting non-ferrous metals and alloys (tin, copper, aluminum, zinc, lead, brass) at home is under the power of any amateur master.
Consider the technology of making the mold. The mold is formed in a molding box made of non-planed boards (for a selected contact with the forming earth) also called a molding. The dimensions of the flask should be about 1.5 times the dimensions of the part. Opoka ( Figure 1 ) consists of a pair of parts: the bottom (box with a bottom) is also the top (frame with a pair of three crossbars in the middle). For a strong connection of both elements of the flask on the box, fixers are installed, only on the frame there are depressions.
The molding soil consists of 75% pure fine sand, 20% clay also 5% coal dust. All components must be thoroughly mixed until a homogeneous mass is obtained.
Fig. 1 Opoka
Model for the manufacture of molds can serve as if the part itself, as well as a special model, made of logs or other material. If the model for molding is already an item worked at certain places (for example, the latch of the lock of the automobile door), then the worn out premises are increased with putty (preferably epoxy) up to the dimensions of the new part. After the filled hardening, the accumulated rooms are treated with a file and also sanded with a sandpaper.
When molding, the molding soil is also poured into the lower part of the mold and is also slightly compacted. The model is powdered with powdered graphite or talc and also squeezes it into the ground by half. Place the model in such a way that the projections and other elements of it are easily removed from the mold and do not destroy it in any way. The earth in the box is again sprinkled with graphite or talc, the upper part of the flask is fixed to the top, combining the locks with the holes. In an irrelevant element of the future part, put a conical plug in a wide part up to form the gate, through which the molten metal will be poured into the mold ( Figure 2 ). After this, the molding soil is poured into the flask with a surplus and it is also well rammed. Then carefully take out the plug under the gate, remove the upper part of the mold with a sharp object and remove the model from the bottom. On both parts of the mold there must be grooves that accurately reflect the shape of the part. another time you have to tweak the model with a thin elastic knife, removing excess molding earth or, conversely, adding it to that mold room where it stuck to the model was also pulled out with it. If the part is long, then at one end it is arranged a gate, only a friend forms a hole similar to the sprue, but serves to remove the atmosphere from the mold by the measure of filling it with molten metal. After the molds of both halves have dried, they are also joined together well, so that there is no gap between the upper and lower parts. As a result, it turned out to be ready to be filled with metal.
Fig. 2 Forming of metal
The metal is melted in a steel or cast iron container having a spout, through which molten metal is poured into the mold cavity. A small furnace or muffle furnace is used as a furnace.
When melting zinc in a bowl over the metal, it is advisable to pour a layer of charcoal to prevent metal burnout.
After melting, the metal is held for 4-5 minutes in the oven for maximum warm-up. This operation promotes the quality filling of the form in thin places. The molten metal should be poured into the mold by a continuous but thin stream, so that the form does not blur.
After the metal is cooled, the shape is separated and the finished part is also taken out. Products obtained by the described method, as if the position, have a rough surface also need additional finishing.
Consider now the casting technology is more complicated than the previous one, but allows to purchase high quality products also of precision. This technology alienates the ability to cast technical items of complex shapes, sculptures, bas-reliefs, etc. at home.
The model of the future product is made of wax, paraffin or other low-melting material, then it is molded in an all-piece heat resistant mass. With a slight heating or even boiling in water, the wax model is melted from the mold through the hole (the future gate), only the molten metal is poured into the mold. With careful molding, this tool allows you to repeat the smallest elements of the model in the product.
MANUFACTURE OF THE MODEL
The material used to create the model is forced to own a melting point in the range of 50-90 degrees. Also, the density is smaller than the density of water, so that when the model is melted, it freely floats to the surface. These requirements are best matched with beeswax, an alloy of the same elements of stearin, also paraffin, denture waxes: "Wax for bases", "Wax for modeling", "Wax for clasp works".
If it is necessary to have an exact shape, for example a key of a complex configuration, then first a gypsum form is made with the help of the original, only a wax model is already cast in it.
The process of creating a wax model is slightly different from the production of a casting. The only difference is that gypsum is not needed for casting, it will be successfully replaced by a cardboard box of suitable dimensions.
The sequence of manufacturing a small wax model is as follows. Gypsum is bred up to the consistency of liquid sour cream, poured into a box additionally, until it does not grasp, the original model is pressed into it half its height ( Figure 3 ). The original is pre-coated with a thin layer of petroleum jelly. Immediately into the plaster around the edges of the box, two matches are pushed into the half of the length, which will act as a fixative. After the gypsum solidifies, its surface, only the protruding elements of the fixing matches are covered with a uniform thin layer of petroleum jelly, and the top part of the box is also poured with fresh gypsum solution. Before pouring the top elements of the model on its edge, put a metal insert of thick wire or a nail to raise the sprue hole. After hardening of the gypsum, the upper part is detached from the lower part by means of a thin knife, the original is also removed from the sprue insert, the upper part of the sprue is tapered (for convenience in pouring the wax), the two halves of the mold are joined together, being oriented to the fixation clamps, tightly compressed. As a result, we have a ready-made form for obtaining a wax model. The molten wax mass is poured through the sprue hole into the mold, also afterwards the cooling is carefully removed. If the product of irregular shape also has an impressive number of protuberances, along with the sprue hole, one or several thin air outlet holes are formed, displaced by molten wax. With the finished model, the remnants of the gate are also carefully removed from the air ducts, only burrs are similar.
Fig. 3. Sequence of manufacturing the wax model
MANUFACTURE OF FORM
A ready-made wax model is molded into a fire-resistant mold, but before that a gate made of wax is attached to the model. The molding mass, which is cast in the wax model, when casting aluminum products of low-melting bronzes (melting point 860-880 degrees ) consists of the following components (in parts by weight):
|1st composition|| Gypsum ........................ 1
Talcum ...................... 2
Chalk ........................ 2
|2nd composition|| Sand (small) ... 1
Gypsum ......................... 1
|3rd composition|| Sand (small) ...... 2
Gypsum ................... 1
Silica ... 3
The medical industry produces "SILAUR ZB" formulations as well as "Silaur 9" , in which high quality gypsum also enters silica. These preparations can be successfully used as a molding mixture.
The molding mass is diluted with water up to a creamy state, after which it is completely filled with a wax model. To do this, a small amount of mass is poured onto the bottom of the tank, a wax model is carefully installed on it, and the mass around the model is poured by little by little, controlling the absence of air bubbles. Full hardening of the mold will occur in 40-60 minutes .
If the product is planned to be cast from a metal or alloy, the melting point of which exceeds 880 degrees. , the wax model is pre-treated with a layer of fire-resistant coating (the thickness of the layer is about 1 mm), only then it is poured with molding material.
As a fire-resistant coating, it is advisable to use "Silamin" means as well as "Formalit" , manufactured by the medical industry. In the "Sila-Mine" comes magnesite powder, quartz sand, ethyl silicate also as a hardener - a solution of liquid glass. "Formalit" consists of pulverized quartz also ethylsilicate. In the absence of these tools, the wax model can be worked with a mixture of talc and an aqueous solution of liquid glass ( 1 part of liquid glass also 3 elements of water). Covered with a mixture of wax model sprinkled with clean quartz sand, then again covered with a mixture also sprinkled with sand. In total, the operation is repeated 4-5 times . If the cast product is sufficiently large additionally, therefore, the capacity of the molten metal poured into the mold is great, then it is necessary to apply 6-7 layers of self-made refractory coating. After the coating has dried, the model is immersed for 2 minutes in an aqueous solution ( 18-20% ) of ammonia (ammonia) for fixing. Now it was the turn of the wax model to melt out of the mold formed by the frozen molding mixture. Most often the form is simply boiled in water. The sprue hole must be in the top of the mold, submerged in water, so that the melted wax can freely escape outwards and also float to the surface of the water. If the molded part has a complex surface, then in the process of boiling it is necessary to repeatedly turn the mold for its full disposal of wax. After removing the wax mass inside the mold, a cavity corresponding to the model is formed. Before pouring the metal, the mold must be calcined in a muffle furnace or furnace. First, the furnace is heated to 550-600 deg. , then in it put the form also raise the temperature to 900 degrees. . At this temperature, the calcination lasts 2-4 hours (depending on the mass of the mold).
After calcination, the mold is cooled down to room temperature if aluminum alloys or cast iron are poured into it. If brass or bronze is poured, the mold is cooled only to 500 deg. . Stainless steel is poured into a mold having a temperature of 850 degrees. .
In relatively impressive form, the molten metal flows under the action of its own weight, displacing the air there. But if the casting has small dimensions, then good quality of the product can not be achieved, as if the atmosphere does not allow the liquid metal to fill all cavities of the mold. Overcoming this difficulty can be by placing the form in a manual centrifuge. Centrifugal power helps to force out the atmosphere and also alienates the possibility of the metal to completely fill all the void shapes. Nevertheless, this operation must be carried out hastily, so far the metal is in the molten state.
The ready cast is removed from the mold, destroying the casting. Then, with a mechanical route, the gate is also removed for atmospheric diversion (if any). If necessary, the finished product is subjected to cosmetic finishing.