CASTING

I have worked for years in iron and steel casting area, so always wanted to write an article to introduce all aspects for iron and steel casting, and hope this article could help casting purchasers to quickly understand all main issues about castings. Ok, let's get started!

Casting is a kind of metal part. We need to melt the iron or steel into hot liquid, then pour it into pre-made molds, after cooling, we remove the molds, then get the iron or steel parts, we call them as castings. You may understand some about casting, but start to wonder what are the molds? Please keep reading.

Casting Molds and Patterns

Many casting buyers may confuse about the molds and patterns. Molds usually means the things we use them to hold the hot liquid iron during cooling period. There are many types of molds, such as sand molds, metal molds, water glass molds, silica molds etc. Of course, there are many different types of sand molds, such as green sand, dry quartz sand, resin sand, pre-coated resin sand etc. These molds could resist high temperature, so they could hold the hot liquid iron. Then, there is a question now. How can we make the molds? The answer is the patterns. We use the patterns to make the molds. Firstly, we make the patterns according to the drawings, then use the patterns to make the sand molds. The patterns could be made by wood, resin and metal. Have you understood this issue? If not yet, please keep reading.

Casting Category

There are many types of castings. According to the materials, it can be divided into iron casting, steel casting, aluminum casting, bronze casting, brass casting, iron alloy casting, steel alloy casting, aluminum zinc alloy casting, plastic casting etc. Of course, each type can be divided into many types according to the specific materials.

According to the casting processes, casting can be divided into sand casting, investment casting, die casting, lost foam casting, metal mold casting etc. Moreover, sand casting can be divided into green sand casting, water glass sand casting, resin sand casting etc. Want to learn more about casting processes? You will know how to do now. Yes, keep reading!

Casting Process

Casting process means the casting method, by which we produce the castings. You have known that there are many types of casting processes, such as sand casting, investment casting, die casting, lost foam casting and metal mold casting. Herein, let's learn more about these casting processes.

For sand casting process, we use the sand as the main material for the molds. In other words, we use the pattern and mixed sands to make many sand molds, these sand molds are inside empty, so we pour liquid iron into the empty cavities, then liquid iron cool in the sand molds until become solid parts, then we break the sand molds, and clean the surface sands off, then get the rough castings.

For investment casting process, instead of sand, we use the water glass or silica as the main material for the molds. In other words, we use the metal patterns and water glass or silica to form many molds.

For die casting process, we have to use the die casting machines to inject the liquid metal into the heat-resistant metal patterns, then the liquid metal cool in the metal patterns. Usually, die casting process can be used to produce aluminum zinc alloy castings. Not suitable to produce iron or steel castings.

For the lost foam casting process, we need to make a metal pattern, then use this pattern to make many foam patterns, then use these foam patterns to make the sand molds. Then, pour the liquid iron into the sand molds. The interesting thing is, we do not take the foam patterns out from the molds, the foam patterns will vanish when they meet hot liquid iron. Lost foam casting process is not widely used in China, but it is really suitable to make large metal castings, and the surface quality is good.

For metal mold casting process, we need to make the heat-resistant alloy pattern, then pour liquid iron or steel into this pattern directly, and after cooling, we take the casting out of metal pattern. Therefore, for metal mold casting process, the pattern is the mold. Of course, the surface quality is good, and less defects, and no sand residue. However, the alloy pattern is very costly, and the production rate is very low.

If you are interested to the above content, please keep checking the update. We will complete the following content and keep updating all content from time to time.

Casting Characters

Why do the designers choose the casting process, not forging or welding process? It is because some special characters of casting. Casting process can produce very small and very large metal parts, and can produce very complex inside and outside structures. Casting could reduce the rough weight of metal parts as low as possible. Lighter rough weight will mean lower cost for raw materials, and so for lower costs.

Moreover, there are many types of alloy cast iron, gray cast iron, ductile cast iron and vermicular cast iron etc. These cast irons have different physical characters, such as abrasive resistance, high tensile strength, heat resistance and impact resistance etc. In many conditions, you could not get these properties by forging or welding process.

Casting Application

Casting is the base of industry. There are too many areas which need castings. It is useless to talk about the specific application. Herein, I just list some main areas such as automotive industry, machine tools, stove parts, pipe and pipe fittings, pumps and valves, agricultural and engineering machinery, marine industry. When you see something made by iron or steel, they are more likely to be made by casting process.

Casting Products

I used to try to list all casting products, but I gave up in the end. There are too many casting products, and nobody could list all of them. So, herein, I just list some common casting products for your reference. For example, stove burner, stove plate, stove grate, stove grill, cast iron pan, iron skillet, chimney tube, stove door, bracket, motor case, reducer shell, belt pulley, brake drum, gear box, flywheel, axle support, cast iron weight, pump body, valve body, pipe fitting, manhole and manhole cover, hand wheel, seal ring, flange, wheel hub, frame, hammer, machine bed, bearing seat, cylinder block, brake wheel etc.

Casting Main Defects

There are many types of casting defects, herein, I just list some main common defects.

1. Sand holes and air holes
Sometimes, it is difficult to distinguish sand holes and air holes, they look like similar defects, just small holes on the surfaces or inside. On the surfaces, you could see the few or many small holes or pits. As for the inside sand holes and air holes, after machining, you could see them. As for the sand holes on the surfaces, sometimes, they are allowable, but the for the inside holes, normally unacceptable.

2. Shrinkage
Shrinkage looks like few very large irregular holes or many very small irregular holes. Shrinkage is normally unacceptable.

3. Crack
As for the steel castings, the crack is common defect. After machining, crack will be visible. Since crack will seriously affect the physical properties of the castings, so it will be unacceptable.

These are very common defects, as for the other defects, you could check our another article Common Defects of Iron Castings.

Casting Tolerances

Casting tolerances include two aspects, one is rough casting tolerance, another is machining tolerance. As for the rough casting tolerance, you could refer our another article DIN 1686 Standard. As for the machining tolerance, you could refer ISO 2768 Standard. These two standards are commonly used for buyers and suppliers. However, although tolerance standards are useful, you should not take standards as the only yard for acceptance. Some key dimensions may need higher tolerance, and if some dimensions do not affect the use, and they are difficult to keep, you should consider to allow looser tolerance.

Casting Prices

All the buyers are caring about casting prices. The casting prices are mainly related with the weight of rough castings, the materials, the heat treatment, the complexity of structures, the suited casting processes, surface coating and painting, and the machining costs. The changes of casting prices will be mainly caused by the prices of pig iron or called materials, and the exchange rate of currency. For the average prices of iron and steel castings, you could check the website of Dandong Foundry. We update the casting prices there.

Casting Suppliers

As we know, there are four metal casting manufacturing bases in China. They are Liaoning, Shandong, Zhejiang and Hebei provinces. There are also many trading companies in China, who specializing to export the metal castings to overseas. Moreover, there are many machining workshops who has their own subcontractors for supplying the rough castings to them. So, all of them could be your supplier for metal castings in China.

Casting Standards

There are many casting standards, some for the tolerances of rough castings, and some for the machining tolerance, and some for the cast iron grades. These standards are the useful tools for buyers and manufacturers.

Casting Machining

Most of castings need some level of machining, rough machining or finish machining. Most of Chinese foundries could do the rough machining, but only some of them could do the high-precision finish machining.

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