How to inspect the quality of iron castings?

Many buyers are not familiar with the inspection to iron castings, so they have no idea how to inspect and control the quality of their products. Sometimes, they will just request the suppliers to meet the standard on the drawings, but sometimes, they do not understand why their quality is not good although their suppliers have said they have met the standard.
As for the quality of iron castings, there are many aspects. Mainly include dimensions, tensile strength, hardness, surface and inside defects. There are many other aspects we will not talk about them in this article, such as heat treatment, smoothness of surface, pressure test, impact test, chemical component, coating and painting, packing etc. You could try to learn more about them by Dandong Foundry Blog. We issued more articles in this blog time to time.
Ok, let us start to learn about these main aspects and find out how to control them as a buyer.
Dimensions
Dimensions include the rough casting dimensions and machining dimensions. As a buyer, you could ask your suppliers to send you the dimension inspection reports. So, all dimensions are clear. For some tolerances denoted on the drawings, of course, you should control them strictly, but for some indicated tolerance, you could try to ask your suppliers to meet the general tolerance denoted on the drawings, but if your suppliers are difficult to meet some dimensions, you should talk about it with your clients to check if they could enlarge the tolerance. Some dimensions will not affect the application, so strictly control to them will increase the unnecessary production costs on suppliers.


Tensile Strength
Tensile strength is the main physical property for material. It will show if your suppliers have met the standard of material, and it will affect the application of castings. Many clients will request the compensation if the tensile strength is unqualified. It is because too low tensile strength will cause the danger in use. Especially for truck parts and machinery parts, unqualified material may cause very serous danger on your clients.
Most of large foundries could test the tensile strength by themselves. As a supplier, you need to ask your suppliers to issue the mill inspection reports to tensile strength, and if you doubt their inspection, you could cut some part from the body of products, and entrust the third party to inspect it. However, it is not easy to cut the test specimen from the casting body for small castings. In addition, test by the given test specimen from your suppliers is not authentic since you do not know if the test specimen is as same as your castings.
Hardness
Sometimes, if the designer has denoted the hardness on the drawing, then you should ask your suppliers to meet the range of hardness. Otherwise, the hardness is not necessary.
Most of metal foundries in China could inspect the Brinell Hardness by themselves.
Surface and Inside Defects
On the machined surfaces, of course, the defects such as sand holes, air holes, shrinkage are not allowable. You could check them by visual inspection. On the surfaces of rough castings, it is easy to inspect them without painting, but please do not request too high. For sand castings, few sand holes with max. 2mm diameter and max. 1mm depth should be allowable. Too strict requirement will be unreachable for your suppliers.
For inside defects, many buyers requested the ultrasonic inspection to all pieces. This is impossible and unreasonable for the most of products, unless you really think it is necessary. Ultrasonic inspection is not accurate for iron castings since the tester can not distinguish the sand holes, shrinkage and low density. Some level of shrinkage and low density should not be taken as defects. As for steel castings, ultrasonic inspection will be more accurate than to iron castings, but the result will still be debatable.
For some special iron castings, the X ray inspection will be very accurate, but the inspection cost is very high, moreover, most of metal foundries do not have X ray flaw detector.
As the buyer, if you really want to inspect the inside quality for some positions to your products, you could ask your suppliers to cut open them by electric saw, or you could cut open them by yourself or third party. It is easier and more accurate.
As for checking other aspects of iron casting quality, please check our following article "How to check the quality of iron castings - Part2"

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