Most people think that stainless steel will NOT rust, But actually, If the correct surface finish is not performed，Even stainless steel 316 will rust in the field or in your warehouse in few weeks or month.
Pickling solution for stainless steel castings
Traditionally, The most economical and convenient surface finish for stainless steel castings is acid pickling. Pickling solution means to immerse the stainless steel casting in an acid solution for about 20-30 minutes to remove the surface rust, then the casting surface has a dense passivation film.
But pickling can cause a lot of pollution, such as pickling sludge, etc. In the past, basically every Chinese foundry had its own pickling facility. At that time, pickling was very convenient and the cost was very low. Now, especially since 2016, the Chinese government has implemented strict environmental protection measures. The foundry does not allow to have its own pickling facilities. A city often has only a few qualified pickling plants, so it is very inconvenient to pickle now. The price is also high.
Alternative surface treatments for stainless steel castings
Because pickling is becoming more and more difficult now, people now think about several alternative surface treatments.
Some foundry now use shot blasting, although they use high chrome stainless steel shot (not the carbon steel beads)to clean the surface. But according to our experience, IT’S NOT ENOUGH. Because the shot blasting machine is made of carbon steels. so corrision may come from the carbon steel components of shot blasting machine.
The electropolishing is a very good surface finish for stainless steel casting parts, It is said to be 10 times more corrosion resistance than pickling. But electropolishing is too expensive, The electropolishing cost in China for stainless steel casting is about USD 0.6/Kg, And foundry also need to send the castings to the electropolishing factory, It’s not convenience.
We now use sandblasting as a alternative surface treatment for stainless steel castings, Mainly used for anti-rust treatment of internal structure of products, the advantage is as below:
1.The operation is very simple, the worker only needs few training. and foundry can do the sandblasting in their own place.
2. High corrosion resistant than pickling.
3. Competitive price, the cost for sandbalsting is between pickling to electropolishing
4. Environmentally friendly， Do not produce too much pollution.
5. Does not affect subsequent machining process.
The best anti-rust method for stainless steel castings is still pickling because of its low price, simple operation and good rust prevention. But as it causes a lot of pollution, sometimes, The government will close all pickling facilities for several days. In this case, we can use sandblasting as an alternative surface treatment.
As a leading stainless steel machining shop, We machine a wide range of stainless steel castings, If you are looking for stainless machining/casting services, please feel free to contact us