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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Microcasting at home. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Ham Radio Technologies A lot of cast parts made of non-ferrous metals and their alloys are used in engineering, including quite complex and miniature ones, the serial production of which can only be afforded by enterprises with precision technology. However, it is quite possible to organize a single (or even small-scale) microcasting at home. Modern technology, it turns out, can compete with the ancient method of injection molding using a simple manual centrifuge. Almost everything that is needed for such microcasting can be made by hand. Costs are minimal. Indeed, the flask required for casting in this case is a segment of an ordinary steel pipe with a diameter of 50-60 mm and a wall thickness of 2-3 mm. For casting products of different sizes, it is good to have several flasks of different diameters, provided that each one fits freely in the centrifuge bucket. With such a set, you can cast a whole series of parts in turn. To match the flask in simplicity and centrifuge. Its wooden handle has a length of about 200 mm and a diameter of 20-30 mm. An M8 bolt is inserted into the axial hole of the handle. A metal earring is attached to it with the help of a locking nut so that both the handle and the earring rotate easily without interfering with each other. A bucket for the flask is suspended from the earring on a rocker made of 6 mm steel wire. The side of the bucket is made of a 60 mm piece of steel pipe 80x3 mm, and the welded bottom is made of a steel sheet 3 mm thick. The 200 mm high shackle is made of the same 6 mm steel wire.
the filling of the mold with the melt during the rotation of the centrifuge and the subsequent operations for extracting and finishing the finished product are not shown. In order to confidently use such a centrifuge, you must first practice a little, remembering how in your school years in the physical classroom you had to twist a bucket of water on a string when studying centrifugal force. True, now instead of a twine and a bucket of water in the hands of a home-made centrifuge with a bucket, on the bottom of which is a plastic (so as not to break) cup. But the water in it is usually naya, which was in school experiments in physics. And the action of centrifugal force is similar. Holding the handle firmly, it is necessary to rotate the entire chain (earring - rocker - bucket and a vessel of water) around the axle bolt, trying not to spill a drop. Having adapted, you can subsequently deal not with water, but with molten non-ferrous metal (or alloy), which will be pressed by centrifugal force through the gate channels into the casting cavity in the flask installed in a bucket instead of a plastic cup. Perhaps the most complex and time-consuming in micro-casting is the manufacture of a three-dimensional, life-size wax model. This is molded from wax by hand, using a heated eye scalpel or a hot darning needle. Even small details are worked out with the utmost care, because molten metal (as well as any alloy) does not forgive mistakes and slovenliness. What's more, the casting performed on a centrifuge under pressure reveals all the flaws of the model! In my practice, I use wax models that are no more than 40 mm high and 50 mm in diameter. At the same time, I try to observe proportionality so that the mass of metal in the casting does not exceed 40 g. The restrictions are mainly due to the low power of the burner I use for melting. Based on the prevailing proportions, I do not forget about the use of reference data. In particular, I cast silver figurines, focusing on the density of wax and silver. I put the wax model on the scales VLR-200. I multiply the readings of the scales by 12 and find out the mass of the future silver casting. I take the coefficient 12 as slightly overestimated, so 2-3 grams of metal in the rough semi-finished product will be superfluous. But such a reserve is quite justified, because it is better to have a small surplus (usually all of it goes to the inevitable "needles" that crystallize in the sprue channels), which can then be easily cut off from an already poured figurine, than not to get silver and ruin the product along with the model. In different places, I stick heated metal pins 1 mm thick and 60-80 mm long into the wax model. Typically, such (purely auxiliary) elements require from 5 to 8 pieces. The recommended material for them is polished stainless steel or nichrome wire. I connect the upper ends of the pins with a piece of wax. Considering the dimensions of the model, I select the flask. Its height is such that the distance between the imaginary bottom and the model is 10-15 mm, and in the upper part of the molding mass there is a gating bowl for melting metal. I prepare the molding mass from two parts of gypsum and one part of talc or carefully ground pumice. I mix the composition well, after which I fall asleep in water. The molding mass should have the consistency of sour cream. I put the flask on a flat sheet of plastic and pour molding into it. mass. Then I take the wax model by the pins and immerse it with a slight vibration (to remove air bubbles) into the “sour cream” that has not yet hardened. Not earlier than half an hour later, with a scalpel, I cut out (without removing the pins) the sprue bowl, it should subsequently, it is necessary to contain exactly as much metal as is necessary for the cast product. After making the sprue bowl, I carefully remove the now unnecessary pins with pliers. Gating channels remain in their place, fanning out from the center of the gating bowl, and each has its own exit to its own section of the model. To remove wax from the gypsum flask, I place it on an electric stove (gating channels down) and, loosely covering it with a ceramic plate, bring the temperature of the sintering molding mass to 1 ° C for 1,5-350 hours. After melting the wax, I do not stop heating. On the contrary, I continue to burn with a gasoline burner the flask, laid sideways on the asbestos sheet, until the wax is completely removed. Only with a thorough warm-up, characterized by a clearly visible reddening of the walls, do I transfer the flask to a manual centrifuge. I carefully put the right amount of metal into the gating bowl and start melting it. To do this, I use a gasoline burner with a flame temperature of at least 1200-1500 ° C. Of course, melting metal does not go into narrow gating channels by itself. To do this, you need a force pressing it to the bottom of the bowl. For example, centrifugal, which will occur during rotation in a centrifuge. And indeed. When the melt becomes like a moving mercury ball gathered in the gating bowl, I begin to quickly rotate the centrifuge - and the metal rushes into the mold. As a rule, twenty revolutions of the centrifuge are sufficient for the melt to fill the entire mold. To cool and extract the finished casting, I substitute a hot flask under a stream of water directed into the gating bowl. From a sharp temperature drop, the form immediately collapses. I carefully take out the casting from the wreckage, cool it completely, process it with fine emery cloth, polish it with GOI paste and bring it to a shine with an overcoat cloth. Author: A.Narvatov, Volsk, Saratov region
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