Why does anodizing leave rack marks?

What is rack mark?

In the process of anodizing, the aluminum alloy workpieces are hung on the hanger for electroplating. The place where the part is in contact with the hanger and cannot conduct electricity to form an anodized layer is the rack mark.

The cause of rack mark – Hanger

Some people may think that a hanger is just a tool for hanging the workpiece, as long as the workpiece is hung firmly, it has little effect on the quality of the plating. But the fact is the opposite. The hanger plays a very important role in the quality and efficiency of electroplating. Whether the design, selection and use of the hanger are appropriate is directly related to the success or failure of the anodizing process.

However, the rack mark is inevitable. Sometimes we will determine the shape, position and quantity of the hanger according to the size, shape and hole/thread position of the workpiece. The hanger should also be designed to be more elastic so that the rack marks could not be too obvious.

In addition, if it is a workpiece with a large area, you can choose a few more hanging points to ensure a good power supply and avoid burning at the hanging position. The photo below is an aluminum slice sample that we tested for anodizing. There are too few hanging points and excessive concentration of electrodes leads to burning bad.

If the customers’ parts have appearance requirements, we will communicate with customers in advance to confirm the location and size of the hanging point. For example, the hanging points can be set in the hole/thread or the inner side without appearance requirements. They won’t be seen after assembly to avoid the results of anodizing being unacceptable.

You can find the photo display of the CNC machining parts made by us HERE!

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