Manufacturing of forms
The Form represents an exact relief from certain model with which help the demanded number of copies is made. Forms differ depending on a material of which the model, and quantities of demanded copies is made. The most widespread kinds of forms is the following: plaster draught (disposable), plaster pure (lumpy or reusable) and plaster semipure, elastic glutinous and formoplastovye, combined, cement, concrete, wooden and metal.
If it is necessary to make copies from plasticine or plaster models, the draught form is used . It is called as disposable as after reception of one casting it break.
For repeated use make the pure form which remove from firm models. Depending on their sizes this form can consist of several parts (pieces).
When the plaster model has many small openwork details, to casting is better to apply the elastic form .
Simple in manufacturing the draught form is Most. It consists of two layers which differ on a material a little. The first layer put directly on model, is called as colour plaster opleskom. It receive by cultivation 3-7 g a dry ink and a dense solution of quantity of a plaster powder necessary for reception in 1 l of water. Very important at paint addition to observe the specified proportions as its surplus will soften plaster that will strongly complicate process raskolotki forms. Models do not possess sufficient durability, and they can be damaged easily at form removal. Therefore the layer of plaster nearest to a surface should be painted and differ from the second, unpainted, a layer. At raskolotke forms, having reached the painted layer, it is necessary to operate especially cautiously not to spoil model.
For the second (supporting) layer of the form plaster more a coarse grinding undertakes. If the thickness of the first layer has to make 2-8 mm (depending on the size of model) the second layer should have a thickness not less than 30 mm, and for large models - not less than 50 mm.
At izgotovleny ornaments for facades it is enough to use the simple draught forms consisting of one integral part. .
Before the beginning formovki model strengthen in horizontal position on a board. Preliminary the board and a ground cover with greasing, and model slightly spray water. It is important, that clay was not washed away, and has got a matte shade and was a little softened. It is necessary to consider that dry clay quickly absorbs water and thus increases the volume. That such distortion of model has not occurred, it is necessary to collect a brush all water which remained in model deepenings. If the model before formovkoj is not humidified, dry clay will take away water from opleska, having dried up plaster ahead of time. It can strongly complicate form removal.
After model wetting on it quickly put the first layer of plaster, in regular intervals distributing it on all surface a hand or a shovel. Movements are necessary for making in strictly certain direction - from below upwards, differently it will be difficult to regulate a thickness of a layer. It is very important not to pass that moment when the solution will start to stiffen. Follows quickly protsarapat a surface that on it have appeared small bugorki. They will help the second layer to lie down more densely to the first, without seizing with it. The wire armature laid on hardening oplesok can increase durability of the form. If some ends of armature stick out outside it will facilitate branch of the form from model.
The Supporting layer should not lag behind the second at all, that is between layers should not remain empty space. Therefore the second layer of plaster is put only after full hardening of the first. The first portion of a solution put in the way nakidyvanija, and the others smear. .
As soon as the supporting layer will harden, the form needs to be removed from model accurately. For this purpose between it and a board cautiously insert wooden wedges and pour in a few waters to soften clay. Then it is necessary to try to loosen the form slightly. With that end in view it is possible to take out a wedge, to pour in the formed crack water and again to insert a wedge. After a while the form can be removed from model.
Now it is necessary to prepare the form for casting, At first from it clean the clay rests, clearing an internal surface a stack or a wooden scraper, and wash out under a water stream. If clay has left traces they are simple for removing on the form, having taken for a drive on them a lump of soft clay. Deep places of the form and thin details of a pattern should be cleared a soft brush to avoid damages. .
Long to store the received form it is not recommended, as it, drying up, can and warp. To facilitate branch of the form from casting, before use it is necessary to cover its internal surface spirit with a varnish and fresh birch shchelokom or kerasino-stearin greasing. The matter is that plaster, stiffening, forms a porous surface, greasing fills a time and, covering a surface with a thin fatty film, does its smooth. .
For manufacturing of flat ornaments - sockets and reliefs - use way of simple pouring at which the form fill with several layers of a plaster solution. At first in it fill in a few plaster. If the future product has fine details it is necessary to take care of that all deepenings of the form have been in regular intervals filled by plaster. Some time for a solution for this purpose is necessary to blow, simultaneously stirring up the form. At work with small forms it is more convenient to put a solution shchetinistoj or a hair brush. As soon as the solution will start to stiffen, it is necessary to give its surfaces a roughness. The second layer of plaster fill in in the form while the first has not fallen asleep yet. More dense solution in which in process of pouring place armature is for this purpose used. Plaster should fill all form to edges, and the superfluous solution is necessary for removing.
For full hardening of plaster it is required about two hours. After that it is possible to begin raskolotku the draught form ( fig. 34 ). At the given stage of work extra care as plaster casting is very easy for damaging is necessary. That it has not occurred, the form needs to be removed layers.
a Fig. 34. Clearing of model of the form
In top, unpainted, a layer easily enough it is possible to do small flutes, without getting more deeply colour opleska. Thus fallen asleep plaster appears divided into small slices which easily leave. Also process raskolotki will accelerate also presence in the form of armature - its each end at removal will remove a plaster slice. Having reached a thin colour layer, it is necessary to release model especially accurate, precisely calculated movements. To remove oplesok it is necessary tupilkoj necessarily from top to down, differently pieces of the form falling downwards can spoil plaster model. .
After casting clearing its surface will sweep off a soft brush. If all the same there was the model damage, the brought down sites can be closed up accurately liquid plaster, and beaten off details to attach into place. For this purpose damaged place is necessary protsarapat a knife a few to wet and impose on it a plaster solution.
The Cleared model should be processed a glass skin, to dry up at the temperature which is not exceeding 50 °s, and to varnish.
From the turned out product it is already possible to take off the reusable uniform, for example the glutinous.
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