Project Description
Degreasing is the pre-treating of aluminium profile before anodizing. Although some aluminium extrusion such as aluminium heat-sink, PC boards, NEV (New Energy Vehicles) etc. do not require anodize surface treatment, however, degreasing process is very necessary.
The statistical results show that the surface quality problem of aluminum profile anodized coloring is more than 60% caused by poor pre-treating, in which the unqualified alkali corrosion is the majority. It shows the importance of pretreatment.
What Is Degreasing?
Degreasing is also called removal of grease, oil removing. The aim is to remove natural oxide film, process oil, rust-resistant oil, hand sweat and dirt that sticks together with oil. In order to guarantee that the surface of alkali erosion can be uniformly corroded, and protect the cleaning of alkali erosion groove.
If the grease is not removed, alkali corrosion will not be uniform, and there are dark patterns and uneven surface defects after oxidation and coloring. This is one of the causes of corrosion during alkali corrosion. In China, the non-lubrication extrusion technology is mostly adopted, and the surface oil and dust are reduced, and chemical degreasing method is generally adopted.
Alkali Chemical Degrease:
Alkaline chemical degrease has low cost, and do not pollute alkali etching liquid, so the application is more extensive.
The essence of alkaline chemical solution is the result of saponification and emulsification. In addition to caustic sodium, alkaline degreasing fluid also includes detergent phosphate, buffer carbonate and emulsifier such as water glass and OP. Generally, alkaline chemical degreaser mainly uses anionic and non-ionic surfactant compared with acidic degreaser using cationic surfactant.
The normal temperature quick degreasing agent sold on the market is mostly neutral or weakly alkaline. The former is mainly composed of a variety of low-foaming and efficient surfactant with different properties. While the latter is composed of auxiliary lotion and surfactant. No matter which one choose, if using in the below 20 ℃, the degreasing time must be greater than 10 min, and the best use effect under 35 ~ 45 ℃.
Acidic Chemical Degrease:
Acid solution is only suitable for LD31 aluminum alloy, now it is more applied than alkaline method. The reason is that this method can make full use of the waste acid of aluminum oxidation and the waste acid of light removal from the pollution. So as to make the best use of the product and reduce the cost.
Commonly Used Acid Solution:
| Solution | Concentration | Operation Temperature | Immersion Time |
|---|---|---|---|
| Sulfuric Acid – H₂SO₄ | 10%~15% | 50~60℃ | 2~4 min |
| Nitric Acid – HNO3 | 15%~20% | RT | 2~4 min |
| Mixed Acid – H₂SO₄ and HNO3 | H₂SO₄-10%, HNO3-10% | RT | 1~3 min |
Summary:
The purpose of degreasing is to further remove the dirt on the surface, and thoroughly remove the natural oxidation film on the aluminum surface. So as to expose the pure metal matrix and provide a good foundation for the subsequent anodization.
