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 Please keep this link! For more related articles, please refer to our blog.

China Old Grade China New
China New
USA micron
USA microinch
▽ 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 0.1 0.8 0.10


RMS (microinch) RMS
RA (microinch) RA
Grit Size
80 58
2.03 1.47
71 52
1.90 1.32
80 120

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.