Classification Method, Properties and Application of Castings

Castings are metal moldings obtained by various casting methods. That is, putting the smelted liquid metal into a pre-prepared mold by pouring, injection, inhalation or other casting methods. After cooling, it will undergo sand removal, cleaning and post-treatment to obtain an object with shape, size and performance.

• There are many classification methods for castings:

1. According to the metal materials used in the casting

Casting falls into steel castings, iron castings, copper castings, aluminum castings, magnesium castings, zinc castings, titanium castings, etc.

2. According to the chemical composition or metallographic structure of the casting

Casting is further divided into different types according to the chemical composition or metallographic structure. For example, iron castings include gray iron castings, ductile iron castings, vermicular graphite iron castings, malleable iron castings, alloy castings, etc.

3. According to the different molding methods

Castings falls into ordinary sand castings, metal castings, die castings, centrifugal castings, continuous castings, investment castings, ceramic castings, electroslag remelting castings, and bimetal castings, etc,. Among them, ordinary sand castings are most widely used, accounting for about 80% of all casting output. The non-ferrous metal castings such as aluminum, magnesium and zinc are mostly die castings.

• Properties and applications of castings:

Castings have excellent mechanical and physical properties. Castings can have a variety of different strength, hardness, toughness and comprehensive properties. At the same time, they can also have one or more special properties. For example, wear resistance, high and low temperature resistance, corrosion resistance, etc.

Castings have a wide range of weight and size. The light weight is only a few grams. While the weight can reach as heavy as 400 tons. The wall thickness can be only 0.5 mm, or exceed 1 meter. Besides, the length can be several millimeters to ten meters. This all make castings meet different industrial requirements for use.

The application of castings has a long history. Ancient people used castings as coins, sacrificial vessels, weapons, tools and some living utensils. In modern times, castings are mainly used as blanks for machine parts. Furthermore, some precision castings can also be used directly as machine parts. Casting occupies a large proportion of mechanical products. For example, in tractors, the weight of castings accounts for about 50-70% of the weight of the whole machine; 40-70% in agricultural machinery; and 70-90% in machine tools and internal combustion engines. Among all kinds of castings, mechanical castings have many varieties, complex shapes and large amounts, accounting for about 60% of the total casting output. Followed by ingot molds for metallurgy and pipelines for engineering.

The liquid forming process can be so widely used because it has the following advantages:

1. It is possible to manufacture blanks with complicated inner cavity and shape. For instance, various boxes, machine bed, cylinder block, cylinder head, etc.
2. Large process flexibility and wide adaptability. Such as the size of the liquid molded part is almost unlimited. And for cast iron with poor plasticity, liquid forming is the only way to produce its blanks or parts.
3. The cost of liquid molded parts is lower. Liquid molding can directly use waste parts and chips. And the equipment cost is low. At the same time, the processing allowance of the liquid formed parts is small, saving metal.

However, there are many procedures in liquid metal forming and it is difficult to accurately control the casting quality. Due to the loose structure and coarse grains of the liquid forming, many defects are easy to occur. For example, shrinkage cavity, shrinkage porosity, and pores. Therefore, we need to take special measures to avoid such internal defects in production process. We will introduce more to you in the following blogs. If you are interested, please make sure to subscribe our website: wwww.yidecasting.com

Castings are also closely related to daily life. For example, frequently used door handles, door locks, radiators, water pipes, iron pots, and gas stove racks are all castings.

 

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

Detection Methods and Difficulties of Steel Castings

Difficulties in detection

1. Poor ultrasound penetration

Coarse grains, uneven structure and other complex interfaces enhance the scattering of ultrasonic waves. And the energy attenuation is large, so that the detectable thickness is smaller than that of forgings.

2. Many interference clutter

When the sound wave is scattered on the uneven, non-dense structure and coarse grain interface, the intensity of the scattered signal is larger and is received by the probe. The rough casting surface will form clutter on the sound wave reflection. These will display on the oscilloscope screen as a messy forest-like echo (also called grass-like echo), which may flood the defect echo and hinder the identification of the defect echo.

3. Poor surface coupling conditions

The surface of the steel casting is rough, which is not conducive to the coupling of sound. At the same time, the surface hardness is large and difficult to polish.

4. Difficult to quantify defects

Due to the large attenuation of sound waves by steel castings and the complicated shape of defects, the quantitative evaluation of defects based on artificial defects has large errors. As a result, it is more difficult to quantify defects by calculation.

The above is exactly the difficulty of casting inspection. These difficulties make casting inspection subject to certain restrictions. But on the other hand, due to the lower quality requirements of castings, single defects are allowed. Meanwhile, the parts where casting defects appear are regular. Therefore, casting detection still has a certain value. 

 

 

• Detection methods

1. Small and medium size castings

For small and medium-sized castings (especially investment precision castings), which are small in size, light in weight, and less processed, they can be magnetized in at least two substantially perpendicular directions on a stationary magnetic particle inspection machine. It is best to use direct current or pulsating direct current, and use the wet continuous method for inspection. Direct energization method, rod-through method, flux method and coil method are all available.

2. Large and heavy castings

For larger and heavier castings, magnetize parts or zones in at least two substantially perpendicular directions. It is best to use a portable or mobile magnetic particle flaw detector with DC or half-wave rectification. And use the contact or yoke method, dry or wet continuous method to detect parts or zones of castings. Testing should generally be carried out in two mutually perpendicular directions.

3. Take the following measures to prevent burning of the castings in contact with the electrodes

when the contacts are not completely in contact with the surface of the castings, no current is connected; and remove the contacts only when the current has been disconnected. In addition, use sufficiently clean and suitable contacts. For smooth and clean surfaces that have been machined, use yoke method.

4. Due to the influence of casting stress, some cracks (cold cracks) of steel castings will delay cracking. Therefore, we should not carry out test immediately after casting, but after 1 to 2 days.

5. If the casting is rejected due to the defect exceeding the acceptance criteria, and digging (shoveling) and repair welding are allowed, the repair welding area should also pay attention to control the delayed cracks.

6. The inspection should be done with the naked eye. And magnifying glass less than 3 times can be used only in the inspection of 001 and 01 quality levels.

 

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