The detection method of large gray iron castings

Quenching, the detection method of large gray iron castings, is generally divided into three stages: vapor, boiling and convective heat transfer.

When the hot gray iron casting is put into the quenching medium, the medium around the casting is immediately heated to the boiling point and vaporized. Thus forms a superheated steam film on the surface of the castings to separate the casting from the quenching medium.

Due to the poor thermal conductivity of the steam film, the casting surrounded mainly depends on radiation and steam conduction. At this point, the casting cools slowly until the steam film ruptures and disappears, entering into the boiling stage.

Due to the presence of carbon nanotube particles, the oil-based carbon nanotube fluid breaks the formed bubbles, reduces the time of vapor stage, and enables different parts of the grey iron cast to enter into the boiling stage almost simultaneously with a high cooling rate. In the low-temperature stage of the cooling process, the cooling rate is relatively low. This greatly reduces the transformation stress of the martensite structure and the quenching cracking and distortion rate of the workpiece.

 

 

For the reasons mentioned above, the hardness of the sample in the oil-carbon nanofluid is significantly greater than that in 30# engine oil.

The failure modes of the cavity surface layer are mainly thermal fatigue cracks. The working characteristics of the low-pressure casting mold are affected by thermocycling. After each liquid metal is formed, the mold cavity is cooled by water, steam, air and other media. The working state of the mold cavity is repeated heating and cooling. As a result, the surface metal of the mold cavity undergoes repeated thermal expansion and contraction. That is, repeating tensile and compressive stress, resulting in cracks on the surface of the mold cavity.

Therefore, hot die steel needs high thermal fatigue resistance. The main factors affecting the thermal fatigue resistance of steel are as below:

1. Thermal conductivity of steel

The high thermal conductivity of steel can reduce the heating of the metal on the surface of the mold. Thereby it can reduce the tendency of steel to thermal fatigue. It is generally believed that the thermal conductivity of steel is related to the carbon content. The higher the carbon content, the lower the thermal conductivity. Therefore, it is not appropriate to use high carbon steel for hot die steel. Generally, we chose medium carbon steel (Wc=0.3%~0.6%) in production. If the carbon content is too low, the hardness and strength of the steel will decrease.

 

2. The critical point of steel

The higher the critical point (Ac1) of steel, the lower the tendency of steel to thermal fatigue. Generally by adding alloying elements such as Cr, W, Si, etc. to increase the critical point of steel.

 

The test result is invalid for the following causes:

1. Improper installing of the sample on the test machine, or improper operation of the test machine.

2. The surface of the sample has casting defects or improper processing of the sample (such as transition fillet, surface roughness and unsatisfactory size, etc.).

3. the tensile sample breaks outside the gauge distance.

4. obvious casting defects on the tensile sample port.

In the above cases, we should re-sample on the same test block or from the same batch of poured test blocks and test again.

 

If you want to know more about grey iron casting, you are welcome to visit our Yide Casting factory – JM casting.

If you are looking for an excellent grey iron casting for automobile engine cylinders iron cast, gears gray iron cast, speed grey iron cast wheels, casting gray iron brake discs and iron cast grey casting drums, and grey cast iron large machine tool bases, forklift casting, pipe grey iron parts, manhole over grey cast iron, Yide casting is a good choice for your casting parts manufacturing, please feel free to contact us for more details.

How to Manufacture Quality Cast Steel

As we all know, the price of the steel cast is higher than the iron casting. But why?

If cast iron vs stainless steel, the mechanical properties of stainless steel casting are higher than that of cast iron, but its casting performance is worse than that of cast iron. However, the manufacturing of cast steel is more difficult than cast iron, thus its cost is higher.

Stainless steel casting belongs to investment casting or precision casting, with a relatively high melting point, and the molten steel is easily oxidized, due to poor fluidity of molten steel and large shrinkage rate. From a practical perspective, stainless steel casting is suitable for casting of various types and alloys.

I will show you how to produce quality cast steel as follows.

1. Poor liquidity of the molten steel.

Firstly, due to the poor liquidity of the molten steel, the wall thickness of the steel castings should not be less than 8 mm, in order to prevent the cold shut and misrun.

2. Simple structure requirement.

The structure of pouring system strives to be simple, and the sectional dimension is larger than that of cast iron.

3. The requirement of Suitable Casting Temperature.

We should adopt dry casting or hot casting, and the casting temperature should be at 1520-1600 ℃.

The fluidity can be improved since the casting temperature is high with a large superheat, thus the liquid stays for a long time.

However, if the pouring temperature is too high, it will cause defects such as coarse grains, hot cracks, pores and sand burning. Therefore, the casting temperature of small, thin-walled and complex casting should be at the melting point +150 ℃; and of large, thick-walled casting +100 ℃.

 

 

We must take these measures to prevent the occurrence of shrinkage holes and cracks in stainless steel castings.

1. Making the wall thickness uniform, and avoid sharp and right-angle structures.

2. Adding sawdust to sand mold, and coke to the sand core.

3. Adopting hollow sand core and oil sand core to change the deformability and permeability of the sand mold and core.

 

Yide Casting is a leading casting foundry in China, with 27 years’ casting experience, provides casting & machining service for our casting customer. Here, we have a steel casting foundry partner, which we have cooperated for many years. Yide casting machines casting products, such as reel steel cast, cast steel plate, 6 inch steel caster wheels, burner stainless steel etc. If you are looking forward to a professional casting manufacturer, please don’t hesitate to contact us, and welcome to visit our JM casting factory in China.

How to Distinguish Good Sand Molding for Casting

The material used to make molds for casting is called molding material. The molding material used to make sand mold is customarily called mold sand. And the material used to make sand core is called core sand. Generally, mold sand is made from a mixture of raw sand with 9% clay and 6% water. In some cases, adding a small number of additionals such as coal powder, vegetable oil and wood chips can improve the performance of mold and core sand. The quality of mold and core sand directly affects the quality of the casting. Bad quality of mold sand will cause defects such as pores, sand eyes, sticky sand, and sand inclusion in castings. The molding sand of quality should have the following properties:

 

1. The breathability of Sand Casting Molding

When the high-temperature metal liquid is poured into the mold, it will be filled with a large amount of gas, which must be vented out. Thus, a good sand mold for casting needs to have a good breathability,  which is a property of letting the gas go out through the cavity.

Otherwise, the casting will produce pores, misrun and other defects. The factors affecting the density of the mold includes grain size, clay content, moisture content and mold compaction. The finer the grain size, and the higher the clay, moisture content and mold compaction, the worse the density.

 

2. Strength of Sanding Casting Molding

Sand strength means the property of the sand resistance to external force damage. The sand must have sufficiently high strength in order not to cause a collapse in the process of modeling, handling and assembling, and not to damage the cast surface when pouring. The strength of the sand should not be too high, otherwise, it will cause defects due to the density and deformability decline.

 

3. Fire resistance

High-temperature melton iron poured into the casting produces a strong thermal effect. And thus the sand must have the property of resisting high-temperature thermal effect. If the molding material has poor fire resistance, the casting is prone to cause burn-on. The higher content of SiO2 and the larger the sand particle, the better the fire resistance.

 

4. Plasticity

Plasticity refers to the ability of mold sand to recover to its existing shape after deforming under the action of external forces. The mold operation will be convenient, if the plasticity of molding material is good, and the shape of the mold is accurate, the contour is clear as well.

 

5. Deformability

The volume of casting will shrink in the condensation process. Hence the molding sand should have a certain compression capacity. If the deformability of the sand is not good, the casting is prone to cause internal stress or cracking. The tighter the sand, the worse the deformability. Adding wood chips to the sand can improve the deformability.

Yide Casting produces casting irons via sand casting molding, equipped with two automatic production lines imported from Germany, which has a fully complete automatic system like automatic sand pressing machinery parts, automatic melton iron pouring system, etc. – a fully casting production system. Thus Yide Casting can provide high-quality casting products with fast production efficiency.

If you are looking forward to a professional casting plant from China, or you want an OEM service for your casting parts in machinery, please don’t hesitate to contact us for more details.