Advantages and Disadvantages of Stainless Steel Casting Process

Advantages and disadvantages of stainless steel casting process

 

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

 

Advantages and disadvantages of the stainless steel casting process are as below:

 

First, 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. The structure of the pouring system strives to be simple, and the sectional dimension is larger than that of cast iron. Adopt dry casting or hot casting, and the casting temperature should be appropriately increased to 1520-1600 ℃. The fluidity can be improved since the casting temperature is high with 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 sand core. 3. Adopting hollow sand core and oil sand core to change the deformability and permeability of the sand mold and core.

bronze casting & brass casting pipe

The Smelting Process of Copper Alloy

Metallurgical Microscope for grey iron casting and ductile iron casting

The Density of Ductile Iron

The density of ductile cast iron is approximately 7.3 g/cm3, or 7.3 kg/liter, or 119.6 g/cm3. However, due to the material grade and shrinkage level, the density has a certain range of variation.

In other words, if the quality of pig iron used by the iron foundry is better and the shrinkage rate is smaller, then the density of ductile iron will be higher. Otherwise, the density of ductile iron will be lower. Therefore, it ranges from 7.1 to 7.3 g/cm3.

Iron foundries usually estimate the weight of rough castings by calculating the volume of ductile iron, so the density will be used. However, you cannot judge the quality of castings by density alone.

There are more factors that will affect it, such as spheroidization rate and cooling rate. Hence, it will be reasonable within this range.

2025 Made in China and ONE BELT, ONE ROAD Policy Impact on Iron Foundry

With the implementation of “Made in China 2025” and “One Belt One Road” construction, the rapid development of all walks of life will be promoted. At the same time, the scale of China’s metal casting enterprises is also increasing year by year.

 

With the rapid development of various application fields, industry concentration has gradually increased, and product quality has continued to improve. This shows that the foundry industry has entered a medium-to-high-speed development stage.

 

The China (Beijing) International Foundry Exhibition will continue to be held at the China International Exhibition Center (new hall). In this way, it promotes the innovation and development of the foundry industry and promotes in-depth cooperation and exchanges between enterprises.

 

As a foundry with a history of more than 20 years, Yide Casting will take this opportunity to meet the needs of different customers in countries along the “Belt and Road” with high quality, high technology and high quality. Use better cast iron products to show the world the capabilities of China’s manufacturing.

What Is Iron Casting?

What Is Iron Casting?

What Is Iron Casting?

What Is Iron Casting?

Gray iron is the most common type of iron casting. Its properties are good, making it the preferred material for a wide variety of applications. Its properties include high hardness, tensile strength, compressive strength, fatigue strength, and resistance to corrosion. While this type of iron casting is highly versatile, its disadvantages include low tensile strength and low elongation. It is a great choice for applications that require high tensile strength.

Yide Casting produces medium and heavy castings with sectional sizes up to four inches. It is the only iron foundry to cast the full range of test bar sizes. Inoculated irons are stronger than base iron bars and have a greater scatter of tensile strength values. A six-inch-diameter section at this foundry shows tensile strength values below the SAE line. The tensile strength data on this material are based on the center portion of the 6-in.-pediatric sections.

Gray iron is highly resistant to cracks. Its mechanical properties are related to the percentage of graphite, and the carbon-equivalent value. The cooling rate and eutectic solidification interval play an important role in the tensile strength of gray iron. The section size affects the tensile strength. The ASTM Specification A 48 requires the selection of the test bar. If the gray metal has an elongation value of less than 0.5, it will be stronger. The failure section should be as large as possible.

When choosing an iron casting foundry, it’s important to choose one that processes ductile iron separately from gray iron. The former is more malleable and durable than ductile. However, some foundries process gray and ductile iron from the same charge material. For example, if a foundry was to process internal recycled scrap gray iron, the sulfur would remain in the material. The solution would be to use a reducing agent, such as CaO, to remove the sulfur.

Graphite is another element used in iron casting. Its gray color is a result of a process known as investment casting. The investment-casting process produces pieces with thin walls and is usually used for ductile iron. Centrifugal casting, on the other hand, has the advantage of reducing porosity and sturdiness of the finished part. In addition, the material is also more resistant to corrosion, which is a positive feature for the investment-grade material.

The gray iron found in commercial castings is the most affordable of the two types of iron. This type of iron has a high modulus of elasticity and is suitable for structural components that must be stiff. On the other hand, it is prone to thermal fatigue, so it is not recommended for housing and machinery bases. Its high tensile strength and elasticity to make it the best choice for these applications. It is a great choice for those who want to save money.

Casting Defects – Sand Mold, Metal Casting

Today, I will introduce you to various metal casting defects and pictures found in the manufacturing process of yide casting. These are common sand casting defects on the surface and inside of cast iron and cast steel parts.

1. Blowhole and Pinhole

This is a void defect, which is also divided into pinholes and underground pores. Pinholes are very small holes, some can be seen on the surface. Underground air holes can only be seen after machining or grinding.

After machining or grinding, most underground pores can be found. If the surface is flat, our yide casting can inspect them by ultrasonic flaw detector.

Pinhole defect

2. Sand Burning Defect

This defect includes chemical burns and metal penetration. Usually, you will see excess metal material around the corner. This is because of poor sand. The metal has penetrated into the sand mold.

Sand burning defect

3. Sand Inclusion and Slag Inclusion

These defects are also called scab or black scab. They are inclusion defects. It looks like there is slag inside the metal casting.

Sand inclusion defects

4. Sand Hole Defects

Sand hole is a typical shrinkage defect. After sandblasting or machining, you will see voids. The sand falls from the sand mold, rolls into the liquid metal, and creates blisters.

This is a problem of the sand mold, or the flow rate of the metal is too high. This decfect can be solved by the foundry.

Sand hole defect

5. Cold lap Defect

Also called cold shutdown. This is a crack with rounded edges. The cold lap is due to a lower melting temperature or a poor gate system. This is not just a surface defect. Generally, this location may cause air leakage, and in addition, the material at this location will be of poor quality and therefore may be fragile.

Cold lap defect

6. Flash, Fin and Burrs

The joint flash is also called a casting fin, which is a thin protrusion on the surface of a metal casting. During the cleaning and sanding process, the joint burrs should be removed.

Sharp fins and burrs are similar problems with burrs. In fact, the large flash is a casting problem, the foundry should improve it by modifying the pattern. However, the small fins and burrs are not casting defects, the foundry only needs to grind and remove them.

Flash, Fin and Burrs

7. Mistrun defect

This is an incomplete casting defect, resulting in unfinished casting. The edges of the defect are rounded and smooth.

Mistrun defect

8. Porosity Shrinkage Defect

Shrinkage defects include scattered shrinkage, micro-shrinkage and porosity. For the large porosity on the surface, you can easily see them. However, for the smaller dispersion shrinkage, you can see them after processing. The figure below shows the shrinkage of porosity. The density of the metal is very poor, and many small holes can be seen after processing.

Porosity shrinkage defect

9. Shrinkage Cavities Defect

These are also called shrinkage cavities, which are a serious type of shrinkage defect, and you can easily see these holes on the rough surface of the metal casting. Foundries can improve their gates and ventilation systems, and then can solve these shrinkage problems.

Shrinkage defect

10. Shrinkage Depression

This defect is also a type of shrinkage defect, which looks like a recessed area on the surface of a metal casting. Although this defect is not as serious as shrinkage, it still leads to poor surface quality, and there may be some internal defects, so the foundry should try to solve or improve it.

Shrinkage Depression

11. Elephant skin defects

This is a surface defect that can cause irregularities or wrinkles on the surface. This defect is caused by the temperature difference of the molten metal or poor sand mold.

Elephant skin defects

12.Veins Defect

It is also called rat tail and looks like many small water traces on the surface of a metal casting. Sometimes this is caused by the low temperature of the molten metal or the improper gate control and exhaust system.

Veins Defect

13.Rough surface

A rough surface is also a surface defect. A normal rough surface cannot be considered a defect, but a surface that is too rough and uneven will be a defect.

Rough surface defects

14. Mismatch and displacement defects

This kind of mold defect is caused by the displacement of mold burrs. It will cause the parting line to be misplaced. Near the parting line, the left side may be a few millimeters lower or higher than the other side. The parting line is not a defect, but if the height on the left is different from the height on the right, it will be a casting defect. If there is no special requirement, a mismatch of less than 1mm is allowed. For the sand casting process, no mismatch is impossible.

However, if the mismatch affects the function of the casting, the foundry must control it, grind or machine it to meet the requirements.

Mismatch mold defects

 

15. Mechanical damage

This is not a casting defect, but a real casting quality problem you may encounter. This is damage during machining or delivery. Workers should pay more attention to this problem.

Mechanical damage defect

16.  Slag Inclusions Defects

This kind of defect is also called foreign inclusions, slag inclusions. Generally, slag is made of molten metal. During the metal melting process, the foundry should thoroughly remove dirt and inclusions, otherwise, these inclusions will be poured into the casting.

Slag inclusion defects

17. Raised Mold Defect

Due to the scattering of the liquid metal, the mold bottle is raised, causing the top of the casting to become higher or thicker than the lower part.

Raised Mold Defect

18. Crack defect

Crack defects usually occur inside metal castings. This defect will reduce the physical properties of the metal casting. There are also cracks on the surface.

Crack defect

19. Abnormal Nodulizing Defect

For many reasons, the spheroidization rate of graphite of ductile cast iron will be affected, resulting in poor spheroidization rate. Through the metallographic microscope, you can hardly see the graphite balls, but you can see many worm-like graphites.

This is a substantive issue. If so, its mechanical properties will not meet the standard requirements, which may cause damage to the cast product during use.

Abnormal Nodulizing Defect

20. Uneven hardness defects

This means that the hardness on the same surface is not uniform. The hardness is not uniform, and some parts may have extremely high hardness. When processing to a harder position, processing will become more difficult. The drill bit may be damaged.

This is a substantive issue. Locations with higher hardness may cool down faster than localized areas.

Uneven hardness

21. Sand Drop Defect

It is also called crushed sand. Some lumps of sand fall from the sand mold, which will result in similarly shaped sand holes or incompleteness. This is a problem of sand molds. The sand mold may not be tight enough.

Sand Drop Defect

22. Deformation problem

This problem will result in excessive flatness and straightness tolerances. For long castings and flat castings with thin walls, this is a very common defect. The reason is the natural deformation of the sand mold or the air during the cooling process. Sometimes, excessive sandblasting may also cause this problem.

Deformation problem

23. Welding Repair Problem

After welding repair, even after mechanical processing or polishing, welding traces are still visible. For unimportant casting surfaces, these marks should be acceptable if the customer allows welding repairs. However, for locations subject to high pressure, or the customer expressly prohibits any welding repairs, these marks will be considered defects.

Welding repair mark

24. Cold Iron Mark

Cast iron can effectively reduce the shrinkage of key parts, so it is very common to use cast iron in cast iron plants. However, the edges of the cold iron can be clearly found by visual inspection. If these marks do not affect the appearance, some customers will not need to grind them. However, customers may require the casting manufacturer to grind them in order to obtain a better surface appearance. Please be clear that these marks should not be considered as casting defects.

Cold Iron Mark

25. Casting chilling defects

It is also called “white iron”. The surface of the casting with this defect will be very white, shiny and smooth. Defective castings are fragile and brittle, so some edges and tips will break during processing. This defect is caused by the low temperature of the sand mold, and it leaves the sand mold prematurely, so the hot iron is quickly cooled. Appropriate annealing heat treatment on them can solve this defect.

Casting chilling defects

26. Massive Free Carbide

On the metallographic photos, you can see many cemented carbides without fish bones. This is a serious defect of cast iron materials and usually occurs in ductile iron. Due to reverse cooling defects and poor inoculation, there will be qualityless carbides, which will lead to brittleness to ductile iron and poor welding performance. High temperature annealing heat treatment can improve its quality.

Massive Free Carbide

27. Cold short or short iron

This defect is also called internal sweating. There are iron beans in the casting. This is because of the unreasonable gate control design, causing some molten iron to suddenly become beans, and then these beans are wrapped in other molten iron. These are surface defects, but if they are located in critical locations, they can cause serious slurry problems.

Cold short iron

28. Stripping Defect

The iron sheet on the surface of the casting is very thin. Two floors. This is because the gating system is unreasonable, resulting in a very thin air layer. This defect is a surface defect, so it can usually be ground off. However, if it is not just on the surface, it should be discarded.

Stripping Defect

29. Cast Iron Graphite Floatation

This defect is a material problem. This is caused by low pouring temperature and high carbon content. This defect is very harmful and can lead to very fragile materials. On the fractured surface, you can see the obvious black surface caused by the defect.

Cast Iron Graphite Floatation

Surface Finish Degree (Smoothness) Comparison Table between Rz, Ra and RMS for Iron and Steel Castings

What standard can be used to express the surface finish or smoothness of steel castings?

The comparison table we made as below is for your reference. You can find the comparison of the new Chinese Ra and Rz standards with the American micron and micron inch Ra in this table. In addition, we have also borrowed from China’s old grading system for your reference. The old grade is still widely used in China. We usually call the downward-pointing triangle “hwar”. However, we usually do not recommend buyers to indicate the old grades of China on the drawings or inquiry sheets. The comparison is for reference only, not as an inspection standard.

This article is from www.yidecasting.com. Please keep this link! For more related articles, please refer to our blog.

China Old Grade China New
Ra
China New
Rz
USA micron
Ra
USA microinch
Ra
▽ 1 50 200
▽ 2 25 100
▽ 3 12.5 50
▽ 4 6.3 25 8.00 320
6.30 250
▽ 5 3.2 12.5 5.00 200
4.00 160
3.20 125
▽ 6 1.6 6.3 2.50 100
2.00 80
1.60 63
▽ 7 0.8 6.3 1.25 50
1.00 40
0.80 32
▽ 8 0.4 3.2 0.63 25
0.50 20
0.40 16
▽ 9 0.2 1.6 0.20 12.5
10
8
▽ 10 0.1 0.8 0.10

 

RMS (microinch) RMS
(µm)
RA (microinch) RA
(µm)
Grit Size
80 58
47
34
17
14
2.03 1.47
1.2
0.6
0.43
0.36
71 52
42
30
15
12
1.90 1.32
1.06
0.76
0.38
0.30
80 120
150
180
240
320

Casting flask, Moulding flask, Sand box, Moulding box

Casting flask is also called moulding flask, sand box or moulding box. It is an indispensable tool in the production of sand castings. At the same time, it also plays an important role in the casting process. A suitable sand box can improve the quality of casting and reduce the consumption of molding sand, thereby reducing production costs.

Casting flasks are usually made by welding steel plates. But it can also be made by sand casting process. In other words, the sand box itself can also be a sand casting. For the automatic molding line, the casting flask has a fixed size. Taking the FBO 3 automatic molding line as an example, the size of the flask should be 508 * 610mm.

If the iron foundry does not have a suitable casting flask, then they will have to make some casting flasks for production. There are many types and sizes of sandboxes. The small flask is suitable for the production of small metal castings, and the large flask is suitable for large castings. Their shapes include circles and squares. Sometimes, some reinforcing ribs are welded inside to fix the molding sand. During the casting process, all designs need to be considered to suit production. However, the flask of the automatic molding line cannot be changed. Only packaging boxes used for manual molding and resin sand molding processes can be used.

Generally, unless you want the iron foundry to speed up production, the purchaser of castings does not have to bear the cost of manufacturing the sand box. More flasks can greatly increase productivity.

Yide Machinery casting factory uses FBO automatic molding line to produce iron castings parts for vehicles, cars, trucks, tractors, plow points etc. The following are some casting flasks from Yide Casting.

Introduction of Iron Based Coated Sand Casting

Brief introduction of iron based coated sand casting:

Iron based coated sand casting is a casting production technology. In the 1970s, Chinese foundry workers developed a special casting technology method, which is based on the research of domestic and foreign foundry counterparts, and in combination with China’s national conditions. It is different from sand casting, lost wax casting, V-shape casting, permanent mold casting, shell mold casting, paraffin casting, ceramic casting, steel shot casting and other casting methods. This method uses a metal model, and the cast iron cavity that is close to the shape of the casting as the sand box iron mold. And then the near-shaped iron mold is covered with a layer of 6~10mm of coated sand to form a mold for pouring into a casting.

 

  • The process of iron based coated sand casting includes:

Machine modeling-checking and closing the box-placing the sprue cup in the lock box-pouring-unpacking the casting-sand cleaning-modeling.

 

  • Features of iron based coated sand casting:

1. Having the characteristics of sand casting

That is, having a rigid sand mold shell, which makes the sand mold high in overall strength without deformation. At the same time, it has wide adaptability, easy demoulding of castings, reliable positioning and high precision.

2. Having the characteristics of coated sand shell casting.

The modeling is convenient and fast. No matter what the casting sand mold is, the molding can be completed within two or three minutes. The sand density and surface hardness of the mold are guaranteed by the equipment and are always consistent. And do not need to apply any paint. The smooth casting is obtained, and the shape and dimensional accuracy of the casting are improved.

3. Having the characteristics of metal mold casting.

The iron mold has obvious chilling effect during the crystallization process of molten metal. This can refine the grain size of the casting, thereby improving the overall strength of the casting. The presence of sand tires avoids the shortcomings of metal mold casting. Castings will not produce white holes. For iron castings, it can produce various materials in the as-cast state without heat treatment.

4. High precision

The mold composed of iron mold and thin sand tire has high rigidity, small deformation and fast cooling after locking. Meanwhile, the obtained casting has high dimensional accuracy, small machining allowance and compact structure. It is especially suitable for the production of ductile iron. At the same time, the method use the graphitization expansion of ductile iron to self-feed, and produce castings with less and no risers. Thus to obtain high-quality castings. Because the iron mold cools quickly, it is effective for the production of high-grade pearlite substrates. Rod and shaft castings are particularly advantageous.

5. High hardness

Under normal circumstances the hardness of castings produced by iron based coated sand casting is about 20 HB units higher than those produced by ordinary casting methods.

6. Low investment

Using the waste heat of the cast iron mold to solidify the coated sand produced by recycling, not only reduces electricity consumption, but also the casting process presents a closed cycle production state. In the meantime, the production area is small, requiring no sand treatment equipment, low investment and quick results.

7. Reuse of the mould

Due to the chilling of the iron mold, the molding sand will not be overfired. Not only can the molding sand be reused, but also because of the roasting during the pouring process, the molding sand (quartz sand) undergoes a phase change, and the thermal expansion coefficient of the sand is reduced from 15 to 5. Therefore, the old sand produced in the production process can also be recycled, which is in line with the development of circular economy.

8. Low rejection rate

Iron based coated sand casting is particularly suitable for the production of large batches of medium and small castings. If there are few replacements, the overall rejection rate can be reduced to about 3%.

9. Long service life

The service life of the iron mold with sand-coated iron mold can reach more than 10,000 times. However, under the influence of long-term repeated thermal expansion and contraction and the casting environment, additional maintenance is required.

Small Cast Door

Small cast doors are small doors made of cast iron, also called small cast iron doors. Depending on the application, there are many types of cast iron doors. For example, cast doors used on boilers are called ash doors; and cast doors used on stoves, fireplaces and stoves called furnace doors. Small cast doors mean […]