SAND MOLD CASTING
Sand casting method is one of the most used casting methods. It is preferred because of its low cost of mold and its application in parts of many different sizes. Sand mold casting method is divided into two as machine-assisted molding and manual molding. Gravity is utilized during casting and this method is suitable for single or small-scale mass production of castings. Thanks to sand mold casting, it is possible to cast parts from a few grams to 400 tons. Molding sand is given a variety by using various machines and is carried out by the effect of gravity force.
Green Sand Mold Casting
Sand mold casting is mostly carried out with green sand molds. green sand; It is a plastic mixture formed by SiO2 particles, clay, water and other additions. The term 'green' is given because of the moisture it contains, describing its difference from a dry sand mix.
Advantages of green sand mold;
It can be used many times by refreshing water and other additives,
It is the cheapest molding method.
Disadvantages of green sand mold;
Where the mold must have higher strength and erosion resistance
It is not preferred when higher dimensional accuracy and surface quality are desired.
The mold prepared with green sand is dried with air heated to 150C-350C in the oven to gain strength. Higher hardness and refractoriness are provided to the mold after drying. The time lost in drying is the main disadvantage. Moisture control is less critical than the green sand mold method. In addition, waiting for a while before casting does not cause problems such as drying and surface embrittlement as in green sand molds.
During the drying process, care should be taken to ensure that the temperature does not exceed 400 C. Otherwise; The loss of bound water will have a devastating effect on the strength properties of clays.
When drying is done not by itself in air but with a heat source, a significant local moisture concentration may occur in parallel with the temperature increase. At room temperature, moisture only escapes from the dried surface. However, at higher temperatures, the movement of moisture occurs in both directions. Therefore, in such partially established molds, casting should be started without wasting time.
WHAT IS SAND CASTING?
Sand casting is used to produce large parts (usually Iron, Bronze, Brass and Aluminum). Molten metal is poured into the previously formed sand (natural or synthetic) mold cavity. The sand blank is usually made of wood, sometimes with a metal mold, which is an approximate replica of the piece.
MATTERS TO CONSIDER IN SAND CASTING MODEL DESIGN
It should be ensured that the model is made without errors by reading the manufacturing drawing in the best way. The completeness of the measurement and the healthy molding of the casting part depend on the measurement accuracy of the model and the construction of the model according to the technological rules.
The modeler has to find the economical molding method and work accordingly. The model should be designed in such a way that it can be made simply and in a short time.
Even if the person who will mold the model by hand or on the machine is not qualified, it should be arranged in such a way that it can mold without defect.
The mold arrangement should be such that the molten metal flows easily into the mold and solidifies without defect.
It should be designed in such a way that there is no air gap and slag in the mold after casting.
TROWEL SURFACE SELECTION
Trowel surface: The parting surface of the mold is called the trowel surface. The trowel surface ensures that the mold is opened and the model comes out of the mold. Care should be taken to select the trowel surface from the surface or surfaces that will ensure the model is molded without defect. In addition, the shape of the part, the molding technique and the number of moldings are of great importance in the selection of the trowel surface.
NUMBER OF MOLDING
Models to be molded in small numbers are usually made of wood materials and handcrafted in a manner to be molded. The trowel surface is selected in a way that will ensure the most accurate and economical molding of the model, and if necessary, the model is made in parts from the trowel surface.
Models to be molded in large numbers (mass production models) are usually molded by hand or molding machines by attaching one or more models to the plate. These models are usually made of metal or polymer materials, while the plates are made of plywood, aluminum or cast iron.
SHAPE OF MOLDING
While making the models, the technical possibilities of the foundry that will make the molding and the molding technology should be taken into consideration.
Hand molding: It is the process of molding the models with metal or sand with the grades made by the modeler. Generally, metal sand melted in cupola or induction furnaces is poured into molds.
Machine molding: It is the process of molding mass production models attached to plates with standard grades with normal pressure molding machines. This process is done with high pressure molding machines in a more rapid and error-free manner.
The molding process is extremely fast and error-free in foundries working with a dizymatic system.