Introduction of Black Oxidation Process for CNC Machining Stainless Steel Parts

Anodizing is the electrochemical oxidation of metals or alloys. The process of forming an oxide film on the stainless steel product (anode) due to the action of the external current under the corresponding electrolyte and specific process conditions. Blackening is a chemical surface treatment. The principle is to produce an oxide film on the metal surface to isolate the air and achieve the purpose of rust prevention. Blackening treatment can be used when the appearance requirements are not high. The surface blackening treatment of steel processing parts is also called blue. This article mainly talks about the introduction of black oxidation process for CNC machining stainless steel parts.

What is oxidation blackening?

Black anodizing is a special type of anodizing. The dyeing method of black anodizing is to use inorganic salts made of metal to blacken the metal. The second method is to use organic black dyes; organic dyes usually provide limited benefits. One of the main advantages of this anodizing is that the black dye performs better in areas with high light and high heat.

Clamping problem of black anodized CNC machining stainless steel parts

Improper clamping position:

It should be noted that there are obvious white spots, which affects the appearance quality. This is due to the improper selection of the position of the stainless steel parts to be processed by the clamping. As a result, the contact parts of the stainless steel parts and the fixture are covered by the fixture and cannot form an oxide film.

Deformation of CNC machined stainless steel parts:

The clamps to prevent the deformation of the stainless steel parts during clamping are not the same as the hangers, and the clamps have a certain degree of elasticity. When clamping and deforming the CNC machined stainless steel parts, pay attention to avoiding excessive force to cause deformation of the CNC machined stainless steel parts.　

The fixture is too loose:

When the clamping of the CNC machined stainless steel part is too loose, the current between the fixture and the CNC machined stainless steel part will be on and off from time to time. In this case, it is likely to burn the part.

Clamping method:

The CNC machined stainless steel parts that need to be dyed are clamped one by one, and some small parts are wrapped with screen cloth or other methods before anodizing. Although this method can save man-hours and improve efficiency in certain occasions, it can only be used for some natural anodizing with low quality requirements. Even if a small number of CNC machined stainless steel parts cannot generate an oxide film at the mutual covering part, it is not easy to be identified. But for CNC machined stainless steel parts that require black anodization, this clamping method is not acceptable. It must be clamped one by one to ensure the anodized quality of the CNC machined stainless steel parts.　

Fixture cleaning

Cleaning the fixture to remove the film During the anodizing process, the fixture will also produce an oxide film. For this reason, the oxide film must be removed before using the used fixture again. The film removal can be carried out in the degreasing solution of stainless steel. It is also possible to file off the oxide film on the contact part between the fixture and the processed stainless steel part with a file. This method can prolong the service life of some fixtures.
 

Control of black oxidation process conditions for CNC machining stainless steel parts 　

The relationship between the temperature and time of the anodizing solution The lower the temperature of the solution, the longer the anodizing time required. This is because when the solution temperature is low, the formation rate of the oxide film is slow. When the temperature of the solution increases, the rate of formation of the oxide film increases.

At this time, the anodic oxidation time should be shortened, otherwise the film will dissolve due to the increase of the outer resistance of the oxide film, and the size of the CNC machined stainless steel parts will change, and the surface will be rough and the film will drop. The above measures are only emergency measures taken without cooling equipment and heating devices.　

The relationship between the temperature of the solution and the voltage is within the rated range, the lower the temperature of the solution, the higher the voltage required, because when the solution temperature is lower, the oxide film formation speed is slower and the film layer is denser.

In order to obtain a certain thickness of oxidation For membranes, the anodizing process needs to increase the voltage. When the temperature of the solution is high, the dissolution rate of the oxide film increases, and the resulting oxide film is loose. At this time, reducing the voltage can appropriately improve the quality of the oxide film.

Matters needing attention in the black oxidation process of machining stainless steel parts

After the CNC machined stainless steel parts are taken out of the anodizing tank, they must be fully rinsed, especially the slits, blind holes, etc. of the CNC machined stainless steel parts, otherwise the residual acid and alkali will flow out slowly during the dyeing process, causing the pH value of the dyeing solution to deviate In the normal range, the color of the residual acid-base parts is obviously different from that of the clean parts, and even corrodes the oxide film to show white.

CNC machined stainless steel parts should be dyed immediately after anodizing. If the CNC machined stainless steel parts are exposed to the air for too long after anodizing, the pores of the film will shrink and may be stained with dirt, which will cause difficulty in dyeing. If the dyeing tank is too small and it needs to be dyed in batches, the parts to be dyed should be soaked in water.

Common applications of black anodized stainless steel machining parts:

Black anodized stainless steel machining parts have a wide range of uses in different industries. The reason for this is not far-fetched. This finishing process provides the required corrosion resistance, strength, and basic functions required. It is a universal finish for many different materials.

1. Military application components: must meet specific specifications, such as gun components and shotgun magazines;

2. Auto parts: such as fasteners under the hood and oil filter tank;

2. Medical parts: medical equipment parts and ventilator parts;

3. Assembled hardware tools: such as fasteners, cutting tools, gauges, shafts, bearings, springs, etc;

4. Electronic parts: electronic product housings, such as knives, gears for timers and electrical switches, and wire strippers.

Summarize

Black oxidation is a special type of anodizing. Before using it, you need to consider whether you need this process. Different from other anodic oxidations, black oxide has the effect of metal non-reflective and heat, so as to better prepare metal.