The defect problem of lost mold casting and its solution

The defect problem of lost mold casting and its solution

Wrinkled skin defect

The defect of crumpled skin is that the polystyrene foam formed a large amount of carbon when it was pyrolyzed with high temperature metal, which was not enough to squeeze out the mold cavity and remained on the grinding ball. It was often found in the initial flow of the metal liquid or the cold end of the liquid flow, which was usually on the top of the grinding ball.Treatment route:

1) select suitable materials for foaming grinding balls.Low density forging public foam EPS gasification fast, less residue.

2) improve casting temperature and casting rate.If the casting temperature of the mill ball is improved by 50%-80%, the gasification can be accelerated.Improved casting rate can reduce heat loss.

3) vacuum degree of progress.Beneficial to exhaust, exhaust, improve the premise of gasification, residue, gasification products escape quickly.

4) improve the air permeability of the casting mold.Choose coarse sand and good air permeability coating.

Carbon black shortcomings

Carbon black is indirectly caused by the high carbon content in the nodular cast iron grinding ball, C%=3.3%~3.8% of the ordinary grinding ball.Will have this shortcoming.Treatment route:

In pouring and appearance of the same premise of the environment, the process should be taken wettability, breathability outstanding coating, pouring to increase the amount of extraction and the use of developable polymethacrylate resin beads EPMMA material, strict control of the amount of appearance binder, can be useful to avoid the formation of carbon black.

Assimilation and slag inclusion

Assimilation and slag inclusion are caused by:

1) the residual magnesium content in spheroidal cast iron is relatively high, which improves the natural temperature of spheroidal cast iron liquid oxide film, forming an oxide film at a higher temperature, and forming slag after secondary oxidation of molten iron during casting.

2) the original iron solution contains high sulfur, and there are more natural sulfide (MgS, Ce3S4, CeS), which promotes the formation of assimilation.

3) low casting temperature, bad luck in slag inclusion floating, broken roots.

Treatment route:

1. Guaranteed pouring temperature of >1300℃, which is beneficial to the accumulation and floating of homogenous compounds and convenient for root breakage.

2. Under the condition of guaranteed spherification, the residual magnesium content should be reduced as much as possible and the sulfur content of original iron solution should be reduced.

3. Rare earth magnesium alloy was used as spheroidizing agent to control the conjunctival temperature of the liquid iron oxide film.

4. Filter mesh collect bag is added to the runner when pouring.

Porosity defect

(1) the gas generation process when the die cracking, the gas into the casting and porosity.In the process of mold filling, turbulence occurs, or in the environment of top injection or side injection, the part appears to be surrounded by the metal liquid and cracked, and the gas can not squeeze out from the metal, pores will occur, such pores are large and many with carbon black.

Prevention method: improve the process, make pouring filling process layer by layer replacement, no turbulence, improve pouring temperature;Improved coating and sand permeability.

(2) appearance, coating layer boring bad cause air hole.Appearance contains water content, coating boring poor or foaming agent content is too high, pouring back when a lot of gas easy to occur reverse spray, this kind of environment is the most easy to occur stoma;If coating drying is not enough, moisture content is more, at this point is extremely easy to form an invasive stoma.

Prevention method: appearance must be boring;Coating must be boring.

(3) the appearance of adhesive excessive cause pores, such as the combination of bonding to take the amount of binder is too large, in the liquid metal pouring filling mold, part of a large amount of gas, can make the metal liquid in the filling process of churning, at this time the gas can not squeeze out in real time, casting will occur pores.

Prevention and treatment: choose low amount of appearance adhesive;Under the condition of secure adhesion, the less binder, the better.

(4) when pouring into the atmosphere to form air holes, die die forging casting process, direct sprue can not be full, will be involved in the atmosphere, these involved in the atmosphere, if not real-time extrusion, casting will occur.

Prevention method: adopt the closed pouring system, when pouring, even the cup with the inevitable metal liquid, to ensure that the sprue is full of conditions.

Adhering sand faults

There are two reasons for the defects of the casting:

a. Coating peeling or cracking, metal liquid while this penetration sand, easy to form machine sticky sand;When coating selection and metal liquid does not match, and there are insignificant particles of dust in dry sand, can form chemical sticky sand.B. Influence of the size of negative pressure on the activity ability of liquid metal during pouring.Negative pressure degree is bigger, metallic fluid activity is better, form stick sand more easily.

Treatment route:

As for the defects of sand adhesion of die casting, it can be generally found in different parts of casting under different conditions: in the absence of negative pressure, sand adhesion is more likely to be found at the bottom or side of casting, and hot spot and sand are not easy to be compactive.During negative pressure casting, all sides can appear, especially at the corner of the casting and the overheat of the casting.