The usage of die casting depends on the melting temperature

sand casting is suitable for a small number of major components and metals melt at high temperatures. But it is a disadvantage that every time you need a new model. As a result, the technique is quite uneconomic for low melting point metals. For low melting temperature metals are other suitable casting technique. Die casting. The use depends on the die-casting metal melt temperature being tasted. (Bronze & brass door handles are made from the technique- As certain types of cases complextransmission car wheels, and carburetor parts can be produced by die casting.)

Properties die-casting:

1) Can a large number of small, Casting light produced with great precision.

2) Little surface finishing is required.

3) Standing model (can be used again and die)

Simplestmethod of die-casting gravity die-casting. It is pouring directly from the label; external pressures or forces involved. Mainly Magnesium (Mg) suitable for this technique. Before pouring the metal powder called french chalk put into the death of cast iron of the metal sticking prevention. Magnesium is continuously heated during the process to keep right ingredients thermal and maintain fluidity of magnesium and has kept flask to prevent contact with air (02) to prevent explosive properties and the during pouring Mg reason, once the surface is being powdered. This keeps powdering result in an inert gas (S02) heavier than air, to prevent explosive reactions and also the metal surface clean and shiny. Mg is ideal for making wheels rising by using gravity die-casting, because it is tight and strong.

Low-pressure die-casting:

In this technique death is surrounded by a gas burner to keep heat right ingredients. One of the major advantages of this process; there is no need to remove the riser and runner, so to minimize waste. A little final machining is required. Aluminum is suitable for this process because it is not easily react with oxygen gas, so it is easier than Mg work (can be shaped, and easily). Solidification starts at the edges of the edge and moves inwards to the center. To check whether any cracks, the casting is painted with blue color engineering. In the airplane industry Xray technique is used instead.

High Pressure die-casting:

In high pressure die casting to shorten the time Don metal solidified and increase the output of metal into water cooled infected die under high pressure and pressure twice. Between each injection of metal, metal is sprayed with oil-based graphite, metal sticking to prevent to the death. Due to high pressures safety regulations should involve obeyed with great precision.

The metal injection:

1) Metal in the plunger, the closure of the pouring hole.

2) Move the metal into the die.

3) Fill the cavity of the metal.

4) intensification of the metal concentration and reduce the cavitations (applying high pressure).

Operation speed depends on the cooling rate. In this technique carefully die design is important and justified usually die used steel output High output quality. Injection plunger makes metal into the die. The metal is injected into two identical die simultaneously produce two identical castings, which increases output. High melting point metal being tasted, lower the life of the die. Provides high-pressure die-casting good surface and good die dimensions. It is suitable for all nonferrous alloys. This technique is successful in thin walled structures also. Ideal for mass production.


Effect of mould expansion on pattern allowances in sand casting of steel

For steel castings produced in sand molds, the expansion of the sand and have a significant impact on the final size and shape of the casting. Experiments performed using a cylindrical solutions to study the effect to various sand (silica and zircon) and various sand binder systems (phenolic urethane and sodium silicate). Has a significant impact on the final solution features the type of sand, especially because he can not expand the silica sand to be irreversible. The effect is enhanced by the presence of sand expanding sodium silicate binder. In addition, the size of the heart, as in experiments at the controls of the amount of steel in the mold and thus the heat input to the model, affected strongly the internal and external aspects of the solutions as a result. And stress simulation solutions combined code used to predict the dimensional changes of the castings. In some cases, the allowances pattern successfully predict both free and blocked contraction cases. Possible disagreements between simulation and measurement results can be attributed the fact that the model does not account stress irreversible nature of the expanded silica sand, which is important when silica sand is heated to temperatures above y1200uC; and the outer mold sand of the solutions, which can cause inaccuracies when there is significant early expansion model, hindrance, or move. Dimensional errors can of castings can be divided into those due to random reasons and those due to errors pattern. Random errors are the cumulative result of many intermediate stages of production solutions, such as core making, mold making, assembly of cores into the mold, the final mold, pouring, heat treatment, cleaning and grinding.

Random errors increase the variability of measurements solutions. Double errors occur when the resultant average dimension solutions different from the size specified feature. When designing a new pattern, the three-dimensional model changes and anticipated solutions. These changes are estimated then applied to the pattern as something called traditionally the shrinkage allowance or the rule shrink. The factor is referred to as pattern allowance (PA) in this paper indicate that more than shrinkage factors to account. Many are very interdependent physical processes responsible for steel castings are not the same features as the pattern from which the molds are made. A contraction of the steel on solidification and cooling to room temperature the primary reason for dimensional changes. However, the potential is resizing, before and after the metal poured the mold as well. The model can also curb the contraction of the metal during solidification.

When metal shrinkage free or unrestricted model and forms an air gap between the casting and the mold, the allowance may have unpredictable pattern easily as discussed below. However, parts of its solutions into core contract or parts of the mold. In these cases, development and emphasized the contraction depends solutions lead the mechanical and physical properties of the sand and solidifying steel. Contraction is blocked such features are restricted solutions smaller in size than shrinking free. Emphasis also develop due to non-uniform cooling of the solutions which can result in distortion solutions. The final elements of steel casting is also strongly affected by changes in volumetric model and core sand.

Can the high temperature steel pouring cause significant heating and thermal expansion near the sand mold. When most of the liquid metal and it offers little resistance to the sand can extend into the cavity. The extension is captured when solidified shell metal develops against the sand. Since sand aggregate good insulator, the heat affected zone is usually narrow mold material. The amount depends on the type of sand extend sand, along with the binder system used.


Sand Casting Process Plan

An ordinary sand casting process plan should include: selection of core method, the species in casting, pouring position ,type and sand core design .Sand casting method can be divided into two kinds:manual selection and machine molding .The two kinds of methods have significantly different requirements on the casting process.It should be based on the characteristics of casting structure,production batch, comprehensive workshop conditions .In many cases, the selection method is the premise of moulding wear-resistant castings.

wear-resistant castingsThe first method is manual modeling.The equipment of manual modeling is simple, flexible and convenient,which is the most basic method to mould wear-resistant castings. The production methods of wear resistance castings commonly include: two box styling, flaskless molding, box modelling (stack molding) etc. Manual modeling is widely used in single or batch productions , especially in the production of large and complex castings. But the manual modeling with low productivity , high labor intensity and poor production conditions require high technical level of workers, and the casting quality is not stable enough.

The second method is machine modeling.The characteristics of machine molding is that it takes template for the two box styling. The template is divided into single and double-side . The single template is most commonly used in modeling .Double template is used only for the production of small castings,.Machine modeling cannot design three box styling. Machine modeling should avoid live block because removing the block would greatly reduce the productivity . So in the design of mass production of sand casting and formulate sand casting process,these technological requirements of machine modeling must be taken into account.


How to improve the technology of sand casting

To improve the internal casting, external quality and reduce the machining allowance,and further extend the application of green sand casting process with air impact, high pressure, injection pressure, extrusion molding and other high degree of mechanization, automation, high density is the main developing direction for small castings production in the future . It is the key point to promote the application of green sand molding process to modify bentonite by nanotechnology,or improve the quality of bentonite by adding adhesive technology in it.

sand molding processFacing the situation of severe competition in international market after entering the WTO, industry of sand casting machine needs to combine production,research and innovation under the necessity of the situation in our country.If the industry of sand casting machine make great efforts to develop new productions with advanced,efficient,low consumption, practical benefits and independent intellectual property rights, this industry would break a small investment, quick shortcut to change most sand casting enterprise with backward technology.

It is necessary to develop the precision forming technology so that we can vigorously develop the visualization of sand casting technology, and promote numerical simulation technology of sand casting process based on CAE towards integrated,virtual,intelligent and practical technology. To further improve the modernization level of sand casting,the technology of CAD/CAM/CAE/RPM,reverse engineering, concurrent engineering, remote design and manufacture,intelligent and on-line operation should be in full swing.


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