10 Principles to Reduce Casting Defects

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In the production process, foundry enterprises inevitably encounter casting defects such as shrinkage, bubbles, segregation, etc. This will result in low casting yield, and re-reflow production faces a lot of manpower and power consumption. How to reduce casting defects is a problem that has always been concerned by casting professionals.

For the problem of reducing casting defects, John Campbell, a professor from the University of Birmingham in the United Kingdom,  have experienced many battles and has unique insights on reducing casting defects. As early as 2001, Li Dianzhong, a researcher at the Institute of Metal Research of the Chinese Academy of Sciences, carried out the organization simulation and process design of the thermal processing process, which was completed under the guidance of Professor John Campbell.

Hope the list of ten guidelines for reducing casting defects by international foundry master John Campbell is helpful to colleagues in the foundry industry.

1. Good castings start from high-quality smelting

We must prepare, inspect and process the smelting process before pouring the castings. If required, the lowest acceptable standard can be used. However, a better option is to prepare and adopt a smelting plan that is close to zero defects.

2. Avoid turbulent inclusions on the free liquid surface

This requires avoiding excessively high flow velocity at the front free surface (meniscus). For most metals, the maximum flow rate should be 0.5m/s. Meanwhile, for closed gating systems or thin-walled parts, the maximum flow rate will be increased appropriately. This requirement also means that the drop height of the molten metal cannot exceed the critical value of the “static drop” height.

 

3. Avoid laminar inclusions of surface condensate in molten metal

This requires that during the entire filling process, there should be no front end of any metal flow to stop the flow in advance. The liquid metal meniscus in the early stage of filling must be kept in a movable state, and not affected by the thickening of the surface condensate, which will become part of the casting. Thereupon, to achieve this effect, the front end of the molten metal can be designed to continuously expand. In practice, only the “uphill” ante bet can achieve a continuous ascent process. (For example, in gravity casting, flow upwards from the bottom of the sprue). This means: bottom injection gating system; no “downhill” form of molten metal falling or slipping, no large-area horizontal flow and no front-end flow stop of molten metal due to dumping or waterfall flow.

 

4. Avoid air pockets

Avoid air bubbles generated by the pouring system from entering the cavity. It can be achieved by the following methods: reasonable design of stepped sprue cups; reasonable design of straight runners to fill up quickly; reasonable use of “dams”; avoid using “well” or other open gating systems; use small cross-section runners or the sprue uses ceramic filters near the junction of the runner; uses a degassing device; do not interrupt the pouring process.

 

5. Avoid sand core pores

Avoid the bubbles generated by the sand core or sand mold from entering the molten metal in the cavity. The sand core must ensure a very low air content, or use proper exhaust to prevent the sand core pores. Unless you can ensure complete drying, you can not use clay-based sand core or mold repair glue.


6. Avoid shrinkage

Due to the influence of convection and the unstable pressure gradient, castings with thick and large cross-sections cannot achieve upward feeding. Therefore, it is necessary to follow all the feeding rules to ensure a good feeding design. At the same time, use computer simulation technology for verification, and actually cast samples. Control the flash level at the junction of the sand mold and the sand core, the thickness of the mold coating (if any), and the alloy and mold temperature.

 

7. Avoid convection

Convection hazards are related to the setting time. Both thin-walled and thick-walled castings are not affected by convection hazards. For medium-thickness castings: reduce convection hazards through casting structure or technology; avoid upward feeding; turn over after pouring.

 

8. Reduce deflection

Prevent segregation and control it within the standard range, or the area allowed by the customer to exceed the limit. If possible, try to avoid channel segregation.

 

9. Reduce residual stress

Do not quench the light alloy with water (cold water or hot water) after solution treatment. If the casting stress does not seem large, polymer quenching media or forced air quenching can be used.

 

10. Given reference point

We must give all castings a positioning datum point for dimensional inspection and processing.

 

Yide casting is a leading casting foundry in China, with 27 years’ experience, produces top quantity ductile iron castings. If you are interested in our casting fitting, please send us a drawing file, and feel free to get a quite quote.

The History and Development of Heat Exchangers

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  •  History and development

Plate heat exchangers appeared in the 1920s and mainly in the food industry. The heat exchanger made of plate instead of tube has compact structure and good heat transfer effect. Therefore, it has gradually developed into various forms.

In the early 1930s,

Sweden made the spiral plate heat exchanger for the first time. Then the British used brazing to produce a plate-fin heat exchanger made of copper and its alloy materials. And it usually appeared in the heat dissipation of aircraft engines.

In 1926,

the British Alston Chun used the indoor return air and outdoor fresh air which is positively intertwined. Due to the temperature difference and water vapor partial pressure difference between the airflows on both sides of the flat partition, simultaneous heat and mass transfer between the two air streams, causing a total heat exchange process. Through heat exchange to achieve indoor and outdoor air circulation, built-in blower and exhaust fan. The two-way equal amount takes place of the built-in blower and exhaust fan. Thus suppress the change of room temperature and keep enough fresh air indoors.

At the end of the 1930s,

Sweden produced the first plate and shell heat exchanger for pulp mills. During this period, in order to solve the heat exchange problem of strong corrosive media, people began to pay attention to heat exchangers made of new materials.

Around the 1960s,

due to the rapid development of space technology and cutting-edge science, there is an urgent need for various high-efficiency and compact heat exchangers. Coupled with the development of stamping, brazing and sealing technologies, the heat exchanger manufacturing process was further improved. This has promoted the vigorous development and wide application of compact plate heat exchangers.

Since the 1960s,

in order to meet the needs of heat exchange and energy saving under high temperature and high pressure conditions, typical shell and tube heat exchangers have also been further developed.

In the mid-1970s,

heat pipe heat exchangers appeared on the basis of research and development of heat pipes, so as to strengthen heat transfer.

heating part

  • Heat exchangers fall into three types according to different heat transfer methods.

1. Hybrid type

Hybrid heat exchanger is a heat exchanger that exchanges heat through direct contact and mixing of cold and hot fluids. Since the two fluids must separate in time after mixing and heat exchange. This type of heat exchanger is suitable for heat exchange between gas and liquid.

For example, in the cooling water towers in chemical plants and power plants. we usually spray hot water from top to bottom, while suck cold air from bottom to top. On the surface of the water film of the filling or the surface of droplets and water drop, hot water and cold air contact with each other for heat exchange. Then, the hot water is cooled, the cold air is heated, and then separated in time by the density difference between the two fluids.

2. Recuperative type

The cold and hot fluids of the recuperative heat exchanger are separated by solid partition walls and exchange heat through the partition wall. Therefore, it is also called surface heat exchanger. This type of heat exchanger is the most popular one.

3. Regenerative type

Regenerative heat exchanger is a heat exchanger that uses cold and hot fluid to alternately flow through the surface of the regenerator (filler) to exchange heat. For instance, the regenerator for preheating air under the coke oven. This type of heat exchanger is suitable for recovering and utilizing the heat of high-temperature exhaust gas.

 

Yide casting is a leading casting foundry in China, with 27 years’ experience, produces top quantity heat exchangers. If you are interested in our casting fitting, please feel free to get a quite quote.

When was Cast Iron Invented?

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The Cast iron was invented by the Chinese in the 4th century BC.

China had begun to use blast furnaces to cast iron in at least the 4th century BC. Meanwhile Europe did not have such similar technology in the 7th century. The highly developed cast bronze during the Shang and Zhou dynasties provided the premise for the invention of cast iron technology. The development of the casting industry manifested as the increase in production capacity. In the meantime, the strengthening of fossil fuel preparation, furnace building, and model manufacturing technology also give evidence to it.

The first iron castings were similar in shape to similar bronze castings.

Early cast irons were white iron with high carbon and low silicon, brittle and hard, and easy to break. With the development of agricultural production, ductile cast iron occurred in the early stage of the Warring States period. As a result, the production tools can be made by cast iron. Through decarburization and graphitization heat treatment, we can obtain black and white core ductile cast iron with incomplete decarburization respectively. After the middle Warring States period, cast iron tools gradually replaced other tools, such as wood, stone and copper. Therefore, cast iron tools became the main production tools. The unearthed objects included shovel, sickle, adze, axe, plow, shackle, chisel, etc.

Because of the large demand for ironware, cast iron also contributed to the invention of Tiefan (cast iron metal mold).

In 1953, Tiefan used to cast iron axe, sickle and vehicles was unearthed from the Casting Site in Xinglong, Hebei. These iron castings have uniform wall thickness, reasonable structure, uniform shape and casting outline. At the same time, some iron mold can cast two objects at a time. This shows that casting iron technology has reached a fairly high level during this period.

Iron castings was widely used as farm tools in the late feudal society.

In the 10th century, it was possible to cast extra-large iron castings weighing 50 tons. After the Five Dynasties, iron buildings increased, such as the iron tower of the Northern Song Dynasty in Dangyang, Hubei. During the Tang and Song Dynasties, the iron in Hunan, Guangdong, Hubei, Fujian was known for its excellent quality. Furthermore, iron smelting production developed rapidly. Foshan, Guangdong has become a well-known smelting and casting center. The iron pots are exported to Southeast Asia, and traditional cast iron techniques such as clay casting and casting pots are still used in modern times.

Cast iron is an important invention of the working people in ancient China. Cast iron played a major role in the development of Chinese civilization and had a considerable impact on later generations.

Yide casting is a leading casting foundry in China, with 27 years’ experience, produces top quantity ductile iron castings. If you are interested in our casting fitting, please send us a drawing file, and feel free to get a quite quote.