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Control of alkali etching treatment for aluminum profiles
Content source: http://huichenglawyer-sy.com Author: military general, release date: 2020-05-07 09:29; times of reading: 1245 Click collection

one Control of etching quantity

An important control point in alkali etching is the amount of aluminum profile etched. In the process of alkali etching, the following requirements are required: first, remove the impurities and passivation layer on the surface of aluminum profile; second, the etching on the surface of aluminum profile is the least, especially for the processing of profile; for the processing of aluminum profile, it is calculated by ton per day, and the thickness of material is 0 1mm The total effective area is seven hundred and forty /t If etched five μ m The etched aluminum profile is as high as 10kg The total etching amount of the surface treatment of the profile is less than five μ m Only one side etching is required to be less than two point five μ m In general, most alkali etching will exceed this etching amount, which does not include the surface decorative etching after alkali etching; in this way, the etching amount in the alkali etching process cannot exceed one point five μ m This requires that the concentration of sodium hydroxide in alkali etching solution and etching temperature should be strictly controlled, and the addition of sodium hydroxide can effectively prevent the corrosion Aluminum profile For the etched additive, it is necessary to have a higher concentration of aluminum ions here;

 Heavy duty industrial aluminum profiles

The control of etching amount is not limited to the etching of aluminum profiles. All aluminum alloy materials requiring surface treatment hope to have as little etching amount as possible in the etching process;

(1) Formula selection: in the case of no special requirements, the process formula with low etching speed should be selected as far as possible, for example, the formula with sodium carbonate as the main body or the formula with low sodium hydroxide concentration can be selected;

(2) Temperature selection: alkali etching with sodium hydroxide as the main body, etching temperature should be controlled at 40~55 For alkali etching with sodium carbonate as the main body, the etching temperature should be controlled at ℃ 50~65 The temperature is suitable;

(3) Selection of etching time: etching time can be determined by experiments, generally based on the minimum time required for surface quality to be achieved by alkali etching, and then appropriately extended on this time benchmark 5~20s For aluminum profile products with short alkali corrosion time, alkali corrosion time can also be divided into two stages in actual operation, namely alkali corrosion( 1/2 Time) → water washing → alkali corrosion( 1/2 Time) → water washing;

 

two : texture and luminosity after alkali etching

Another control point in alkali etching is the state of the etched surface, which includes two aspects

(1) Surface texture: after alkali etching Aluminum profile The surface texture is uniform and there is no mechanical grain and material grain. No matter the plate or profile is corroded by alkali, all kinds of unacceptable texture may appear. The mechanical texture can be removed by mechanical polishing, polishing or sandpaper grinding. However, the material texture is caused by improper process control or uneven distribution of impurities or alloy elements in the material during the forming process of aluminum profiles The grain can be solved by heat treatment; however, it is difficult to eliminate the material grain by etching or reselection of operating conditions. In this case, the material grain can be disappeared or reduced to a level acceptable to customers through the texture etching or polishing process described later;

 

(2) In order to obtain a more clean surface, it is better to carry out two kinds of etching, such as etching and polishing, which is not conducive to the surface of the product For texture etching, alkali etching provides a clean surface without passivation layer and a reference luminosity, but this luminosity is not very important because the necessary reference luminosity needs to be provided by polishing; for electroplating and electroless plating, alkali etching only provides a clean surface, and the luminosity is mainly provided by electroplating or chemical plating;

 

For aluminum profiles directly anodized after alkali etching, on the one hand, alkali etching should provide a clean and uniform surface, on the other hand, it should also provide a luminosity, and this luminosity is an important control index, which determines whether the aluminum profiles meet the requirements of customers after alkali etching. In this case, the profiles after alkali etching should be compared with the samples approved by customers, Of course, in comparison, it should be noted that the surface luminosity of the oxidized aluminum profile will change with the thickness of the oxide film; when the material is the same (different material models, the degree of change of the light intensity after oxidation is different), the thicker the oxide film thickness, the more the luminosity will decrease. If the customer provides the luminosity deviation plate, the luminosity with the middle value or the middle value about higher can be regarded as the pre oxidation The judgment criteria of the system are as follows;

 

Generally, the surface texture will not change under the specified formula and process conditions, and its final state depends on the nature of the material; if there is black line on the surface of aluminum profile after alkali etching, it is generally caused by two reasons, one is the material itself, such as Aluminum profile The hard skin on the surface of aluminum ingot is not cleaned up during calendering; second, the concentration of impurity zinc ion in alkali etching solution is high; for some wire drawing profiles, there are positive and negative colors in the dark box after alkali etching, which is mainly caused by the surface burn of aluminum profile during drawing process, which can be solved by secondary drawing treatment or adjusting the formula composition of alkali etching solution, or alkali etching treatment can be carried out before wire drawing; Under the specified formula conditions, there will be certain differences in the luminosity when the process conditions are changed. Generally, the luminosity will increase with the increase of sodium hydroxide concentration, high temperature and long time. However, when reaching the luminosity suitable for the formula, prolonging the time can not make the luminosity continue to increase. Therefore, the relationship between the luminosity control and the time should be paid attention to when alkali etching is carried out, otherwise it is easy to make the profile Over etching;

 

three : consequence of alkali corrosion anomaly

In the process of alkali corrosion, the irreversible quality problems are mainly excessive alkali corrosion, which makes aluminum profiles become thinner seriously and change the inherent mechanical strength of profiles. This quality problem is caused by high sodium hydroxide concentration, too high temperature, too long time and too many rework times. The profiles with such quality problems should be scrapped, but the profile surface after alkali etching should be scrapped There are mottling and imprinting caused by non-material reasons, which are caused by incomplete degreasing of aluminum profile before alkali etching, or secondary pollution or contamination of some stubborn marks caused by long standing time of profile after degreasing in the working room. If there are etch spots on the surface of aluminum profiles, they will also produce speckles or marks before alkali etching;

 

four : cost of alkali corrosion

Alkali etching accounts for a large proportion of the cost in the anodizing of aluminum profiles, especially for the profiles which are anodized only after alkali etching, the cost of alkali corrosion will account for 1/4 Even higher; the consumption in the alkali corrosion process mainly comes from two aspects: one is the consumption of aluminum corrosion in the alkaline corrosion process, and the other is the consumption brought out with the profile; the reaction process is very intense, and the reaction products generated at this time are easy to adhere to the profile surface, which is difficult to clean in acid pickling, and it is likely to remain Lower imprinting; when the profile is taken out from the alkali etching solution, a fast way is adopted to make the profile leave the alkali etching solution and put it into the water; therefore, the amount of the profile taken out is larger than the consumption of the alkali etching. If the profile is complex, the alkali etching time will be shorter, and the amount carried out will be more than the etching consumption; the methods to reduce the cost of alkali etching are as follows:

 

One is to put a recovery tank next to the alkali etching tank 50~60 If there is a recovery tank, the solution can be directly supplemented with the solution in the recovery tank. At the same time, the amount of carried out can be reduced and the pressure of wastewater treatment can be reduced;

 

Second, the degreasing and grinding work should be done before alkali corrosion to prevent multiple alkali corrosion caused by unclean degreasing or secondary grinding. Multiple alkali corrosion will increase the cost of alkali corrosion and increase the etching amount of aluminum profile, which will increase the size change of profile and even cause scrap of profile;

 

according to Aluminum profile Calculation of chemical formula in alkali etching solution, dissolution 1g Aluminum is needed in theory 1.482g Sodium hydroxide, but in actual production at least need 2.5g Sodium hydroxide: according to the shape and actual area of the profile, combined with the selected alkali etching process formula and operating conditions, the consumption of sodium hydroxide of an aluminum profile product can be estimated. This consumption should include the consumption in the etching process and the consumption when the solution is taken out;

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Contact APAs / contact us
Tianjin Aipu industrial aluminum profile Co., Ltd
Tel: 022-87920088
Fax: (avoid malicious advertising) please Contact the enterprise network administrator
Service hotline: 137021119190 (24-hour service hotline)
Q        Q: five hundred and thirty-four million nine hundred and seventy-three thousand nine hundred and six
Email address: lxc@apas.com.cn
Address: a3-2 Saida international industrial city, Xiqing Economic and Technological Development Zone, Tianjin
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