The mold is the most important element that is used to process the molten metal in order to obtain a casting that meets all the requirements for size, roughness, structure, and product properties.
Shell Types
Currently, two fundamentally different types of forms are distinguished. The difference between them is in the production technology of the mold. There are multi-layer species that are produced by applying a suspension, as well as using subsequent processes of sprinkling and drying.
The second type is two-layer. The production of these forms is carried out by the electrophoretic method. The main requirements for the mold shell are hot, tough, gas-permeable, accurate, with a smooth contact surface, and also one-piece.
Multilayer shells
The process of obtaining a multilayer shell proceeds as follows: the surface of the mold is wetted by the suspension. This process is carried out by dipping the form into the necessary substance. After removing the block from the suspension, it is immediately sprinkled with a granular substance. The suspension adheres to the surface of the block, which makes it possible to recreate its configuration with great accuracy, and a granular material is necessary in order to fix the suspension on the surface of the mold, as well as to make its layer more dense and thick.
A freshly applied layer of suspension and granular material practically does not adhere to the surface of the mold. The only thing that prevents it from slipping is the wetting forces. Giving the necessary strength to this form is carried out in the subsequent drying process - chemical solidification. It turns out that for the manufacture of a multilayer mold it is necessary to carry out three stages - moisten the shell with a suspension, sprinkle it with granular material, and then dry it. Such a procedure is carried out on average from 4 to 6 times. However, if it is necessary to prepare a stronger shell, then the amount can increase up to 12 times.
Two-layer shells
The production of two-layer molds is carried out with fewer procedures. The first stage of mold preparation is no different from the production of multilayer molds. The block is wetted and sprinkled with a granular product. However, before you begin to apply the second layer, which is called phoretic, the first must again be moistened with a suspension, which necessarily contains electrolyte. For example, the composition may include hydrochloric acid, which is a conductor of the 2nd kind. In addition, the suspension must also contain a binder for the mold. And after wetting, again sprinkle with granular material.
After two layers have been applied to the block, the process of drying the mold is started. This is enough if it is necessary to obtain a shape whose wall thickness will not exceed 6-8 mm. If this indicator needs to be increased, then two more layers are applied.
Varieties
For the metal casting process, a mold is needed in which molten material is always poured. The main difference between these forms is disposable and reusable. However, these two different types of forms are also divided into several classes.
There are disposable sand casting molds. For the manufacture of foundry molds of this type, special siliceous sand is used, which is mixed in a special machine with water, as well as other binding elements. Forms from this category are used to produce parts of any configuration and size.
If the process of casting non-ferrous metals is carried out, then disposable shell forms are most often used. Gypsum shell molds (composed of gypsum and quick hardening polymer) are used for the molding process of the molding model. After the gypsum shell form dries, it is cut into two parts, which are dried again. After this, the mold is connected and metal can be poured into it.
Molten Model Casting
In order to successfully implement the process of casting using fusion models, shell molds based on silicon dioxide are used. This substance is a powder that is bonded to each other using various bonding elements. The use of such forms occurs if it is necessary to manufacture a part with a high melting point.
A fusible metal mold is filled with various elements. It can be paraffin or subsequently frozen mercury, or plastic. After the production of the model, it is lined with some refractory material. Vibration is used to seal the mold and the refractory layer. After the hardening process is over, the shell is heated, due to which the block melts and flows out, and the mold remains and can be used to fill metal into it.
Reusable forms
Molds, which are classified as reusable in terms of their use, are made from materials such as cast iron, copper, brass or heat-resistant steel. Reusable forms have found their application in non-ferrous metal casting. They are used for casting zinc, brass or aluminum alloys. In addition to them, forms of graphite material are also actively used. Such blocks can withstand up to several hundred castings. The manufacturing process of molds from graphite is carried out by mechanical action on the material. Most often, a design of this shape consists of several parts that are fastened together. The only open part of this mold is the hole through which the melt is poured.
Molds
If we talk about multiple forms used for casting, then you can also highlight the mold. These are open-type forms into which molten metal flows by gravity. Most often, the manufacture of a mold is carried out from cast iron. However, you should be aware that when casting metal into molds, certain rules must be strictly observed and some features taken into account.
- It is necessary to carefully monitor the purity of the mold before each subsequent stage of pouring metal.
- It is necessary to prevent splashing of metal on the walls of the mold at the time of its pouring inward.
After each casting process, they start cleaning the molds, and molding non-stick paints are always applied to the inner surface. The mold can withstand up to 100 castings before it becomes unusable.
Molding materials
The materials used for the manufacture of foundry molds are called molding.
For forming casting molds for single use, it is necessary to ensure that the material meets such requirements as strength, resistance to dynamic influences exerted on the mold, as well as the ability to withstand the hydrostatic pressure that the cast metal exerts.
In order to produce molds for reusable use, it is necessary to make higher demands on the material in terms of its strength. However, it is important to understand that for all the requirements that apply to these materials, they must have an affordable price. Otherwise, the manufactured parts in such forms will have a very high final cost. And the selling price will be even higher.