Application of technology to lost foam steel casting

Lost Foam casting has the advantages of simple process operation, low material consumption cost, surface gloss knot, high dimensional accuracy,  less environmental pollution, etc., which gained great popularity  application in the late 1990s in China.

However, there is  much successful experience in the use of Lost Foam on steel castings, especially in the case of low carbon steel. The main reason is that the surface of Lost Foam cast steel is easy to increase carbon, resulting in the defect of chemical composition deviation.

Briefly introduce the application features of Lost Foam process on steel castings:

1. Prevent carbon gain

Lost Foam steel casting is prone to carbonization defects, which are mainly caused by carbon contained in the Foam material,  the free carbon decomposed by Foam combustion during pouring enters the molten steel.There is a certain amount of carbon increase

The regularity is that the surface of casting increases carbon, but the heart hardly increases carbon.There is little carburization near the internal sprue,  the further  the internal sprue, the more serious the carburization.(1) Choose foam materials with low carbon content, which is the key.

At present, the materials used for epc mainly include EPS, STMMA  EPSMMA,  their carbon content is reduced in turn. Among them, EPS is characterized by high carbon content, but it has small air capacity  is  easy to pour

Spray back,  the price is cheap, in cast iron  cast steel requirements are  high applied more;EPSMMA is characterized by its low carbon content, but its large gas emission is easy to cause the phenomenon of backspray,  the material price is expensive

Generally used in low alloy steel more.STMMA has the advantage of both. It has the advantage of less carbon in air  is the preferred material for steel casting in Lost Foam.(2) According to leaving the inside gate

The farther the casting is, the more serious the carbonization is. The riser is set at the farthest end  the inner sprue  at the highest point of the casting, so that the heavily carbonized molten steel entering the casting first enters into the riser. At the same time, the riser also collects slag.

The action of collecting gas.By using this process, the carbon content of the casting as a whole can be within the range of process requirements.(3) the density of appearance is very important, as long as the surface is bright  clean, the density is low, can bring to increase carbon low  the amount of gas

The benefits of.

2. Prevent backspray

Return spray is a common phenomenon in Lost Foam casting. If the return spray is serious, it may endanger the safety of the caster. To reduce the return spray phenomenon, the following measures can be taken: (1) The Foam shape density should be low

Under the premise of ensuring foam surface quality  model strength, the foam mold should be made as light as possible to reduce the air output during pouring.(2) Foam appearance must be dried before the paint, each batch of foam model

The weight change of the drying process should be sampled before use,  the baking weight change curve chart is made. The coating can be applied only under the circumstance that the weight no longer changes.(3) Casting system, especially straight runner  cross runner

The way should  be coated, so that the gas generated when pouring can be quickly  fully removed, but also save paint consumption.(4) Cover the top of the pouring cup with a baffle to spray back the molten steel

Block, so that it can  splash out, endangering the site operators.

3. Appropriate coating performance  correct coating  brushing process

The coating plays a very important role in the casting process of Lost Foam. The coating can avoid direct contact between molten steel  sand  ensure the surface quality of the casting.It can also improve the strength of the foam mold to make it in the handling process

Medium no deformation;The gas produced during pouring is mainly discharged through the coating.Therefore, the coating of Lost Foam coating should have certain strength  good air permeability.Coating process  coating drying

Attention should also be paid to the dry process.Coating coating brush had better  be a complete, a complete coating is bound to be thicker, easy to crack coating.Should go up two to three floors.The overall thickness of the coating should be controlled at about 1mm

The principle of coating thickness is that the coating should be as thin as possible on the premise that the casting does  stick sand, so that the gas can be discharged through the coating as soon as possible.After finishing each coating must be dried, can undertake next round besmear is brushed

modeling, if the coating is  thoroughly dry, the molten steel during pouring will produce a large amount of gas, resulting in backspray, in addition, the coating is  thoroughly dry, paint permeability is poor, gas can  be discharged in time, easy to make the casting

Gas hole, slag hole.

4. Prevent box collapse

When there are too many series castings in a box, the vacuum degree of each model is insufficient due to simultaneous gasification, which is easy to cause collapse of the box. Precautions to prevent collapse of the box should be noted:(1) keep enough stable vacuum degree in the sand box.(2) Control pouring well

At the same time, the casting speed should be consistent with the gasification speed of the model as far as possible, so as to prevent too slow pouring, which may lead to cold isolation  lead to collapse of the box.