Sandy-clay casting - laboratory

1. Description of the essence of sand-clay casting

Sand-clay casting is a common and relatively simple method of casting. Single sand-clay forms can be prepared either directly in the soil (in the floor of the foundry) according to templates, or in special support boxes according to models.

Casting into sandy-clay molds has its advantages. These include: the mass of the casting can reach the value of hundreds of tons (machine bed), sizes from several millimeters to tens of meters, can be made of any configuration and from any casting alloys. This method produces the vast majority of castings in machine building.

Moulding mixture is used to produce mold, which is multicomponent system, composition of which is determined by type and mass of casting, and nature of metal. The main components of the moulding mixture are quartz sand and moulding clay. The clay is a binder and at an optimal water content (45%) gives the molding mixture the necessary strength and ductility. The sand increases the porosity and hence the gas permeability of the molding mixture. In addition, anti-stick additives (coal-tar dust, graphite), protective additives (boric acid) and other ingredients are added to the molding mixture. For the production of rods, rod mixtures consisting of quartz sand and self-solidifying inorganic (liquid glass with an addition of 10% solution of NaOH) or organic binders are used.

Casting molds - the process of filling the cavity of the mold with molten metal from a ladle. Ladle with molten metal is transported from smelting furnaces to casting place by means of bridge crane or via monorail track.

It is important to select the casting temperature of the molten metal when casting molds. At an increased pouring temperature, the fluid flow of the metal increases, the nutrition of the castings improves, but the hot metal is more gas-saturated, oxidizes more, causes burning on the surface of the casting. While the low pouring temperature increases the risk of the mold cavity not filling, air gripping, the casting power is deteriorated. The casting temperature of the alloys is suitably set to 100150 ° C above the liquidus temperature.

Cooling of castings in moulds after pouring continues to knock-out temperature. Small thin-walled casts cool in shape for several minutes, and thick-walled (weighing 5060 tons) - for several days and even weeks.

To reduce the cooling time: the molds are blown with air; coils or pipes are laid into moulds during moulding, through which air or water and others are passed. At the same time, the quality of castings does not deteriorate.

Casting is the process of removing solidified and cooled castings from a mold to a certain temperature, while the mold is destroyed. Castings are knocked out at various knock-out units.

Cleaning of castings - the process of removing tart, residues of the molding and rod mixture from the external and internal surfaces of the castings.

First of all, castings are monitored visually to identify defects or castings to be corrected. The correct configuration and dimensions are checked by marking, the density of the casting metal is checked by hydraulic tests under water pressure up to 200 MPa. Internal defects are detected in specialized laboratories.

Casting in sandy-clay molds is the simplest and most common method of producing cast blanks. The disadvantages of such casting are large allowances for mechanical treatment, low productivity and poor sanitary and hygienic working conditions.

The purpose of this laboratory work is to design casting, casting mold and define allowances and tolerances.

Define material heat treatment modes

Based on the task, it is necessary to produce a steel casting of medium complexity, the difficulty group is second. In small-scale production conditions, the most economical manufacturing method is single sand casting. Method of moulding - machine moulding according to split model in two supports with level of compaction to hardness of mold not less than 70 units.

Analysis of the technical requirements and processability of the part design shows that it is a symmetrical body of revolution; external surfaces with diameter D = 95 mm, D1 = 75 mm, transition cone at an angle of 45 ° and the lower end of the part are not to be machined; the most accurate surface with diameter d = 55 mm (base A) is made according to the 7th accuracy quota, the upper end of the housing is connected to base A by an end run-out tolerance, the surface of the internal hole (d + a) = 65 mm is connected to base A by an alignment tolerance, unspecified limit dimensional deviations are made according to the 9th accuracy. The minimum wall thickness 7... 8 mm can be obtained by the selected casting method. Eight M10 holes make no sense to get cast, they are scary.

As rough bases of machining, it is advisable to take the lower end of the body and the cylindrical surface with diameter D1 = 75 mm, thus implementing an explicit mounting base at the end and a double support hidden base at the cylinder.

Mold Design

To make the mold, it is necessary to produce a lower support, upper support, model, rod with signs, runner system and spout.

Model - a product designed to form an imprint in the mold of the corresponding external configuration and size of the casting.

A rod is a mold element used to form a hole, region, or other complex contour in a cast.

Rod is manufactured together with rod marks

Rod signs are used to obtain alignment of upper support with lower one and for perpendicular of rod

Rods are produced in rod box

A block is an accessory for holding a molding mixture during the manufacture of a mold. The cap is a wooden plastic or metal box without a bottom. Two supports are used to produce casting.

The runner system is a system of channels and elements of the mold, which provides the supply of molten metal to the cavity of the mold and its filling, as well as feeding the casting during solidification.

The runner system consists of:

- runner bowl;

- riser;

- slag catcher;

- feeder.

Evaporation - reverse vertical columns designed for the exit of air and gases from the cavity of the mold during its pouring, as well as the outlet of the Foundry alloy.

Conclusion

During the laboratory work, the following tasks were completed:

Analyses the material properties of a part (cast).

Definition of type of heat treatment and purpose of casting heat treatment modes.

Definition of admissions, allowances and amount of casting.

Creates a cast drawing.

Calculation and development of runner system elements.

Mold development.

Development of process design map.