The concentration control method of degreasing tank liquid is to control the free alkalinity of the tank liquid. The aging degree of the tank liquid is determined according to the ratio of total alkalinity to free alkalinity. When the ratio of total alkalinity
to free alkalinity exceeds a certain limit, the tank liquid should be discarded. The determination of this value is related to the material of the pre coated coil, the type of solid impurities on the metal surface, and the treatment temperature. The
specific determination should be based on the actual situation and jointly determined with the user.
1. What are the cleaning requirements after degreasing?
After degreasing, the color coated board must be rinsed by one or more stages of hot water spray. The continuous overflow method is best used to maintain the effective rinsing effect.
2. What are the eneral requirements for the material of degreasing equipment?
Degreasing storage tank, jacket, pump, valve and pipeline can be made of low carbon steel. Nitrile rubber and polyethylene rubber are best used for sealing parts of circulating
pump or valve and related elastic materials contacting degreasing agent. 80 carbon steel pipe or similar material is best used for heating pipe. Polished stainless steel is best used for heat exchanger, and stainless steel is also used for nozzle. Attention
should be paid to the difficulty of brush roller made of nylon material To withstand temperatures above 60 ℃.
3. How to remove passivation film on passivated galvanized sheet?
Galvanized sheet can be divided into passivation plate and oiled
plate. The degreasing concentration of oil coated plate is generally controlled at 1.5-5%, and the best is 2-3%. The passivation film can be removed when the concentration of passivation plate is controlled at 1.5%.
4. What should be paid attention
to before degreasing agent mixing tank?
The cleanliness of the tank must be checked before the tank is prepared. If there are oil, dust, welding slag and other foreign matters, they should be removed in advance, or the solution of 0.4-0.6% concentration
prepared by strip degreasing agent can be used for cleaning.
5. What are the hazards of chromium to environmental protection and human body?
Cr6 + and Cr3 + are the main raw materials of traditional conversion liquid and passivator for strip.
Cr6 + is widely used in color coated sheet and continuous hot-dip galvanized sheet with good corrosion resistance and adhesion. However, Cr6 + has extremely serious harm to the environment and human body, which is reflected in the following aspects: 1)
seriously pollute the surrounding environment, the toxicity of Cr6 + is about 100 times higher than that of Cr3 +, which is a strong mutation substance; 2 Chromium is harmful to human health. The harm of chromium to human body is that it infiltrates into
cells in the form of Cr6 +, and then reduces to Cr3 + in cells to form carcinogen, which causes cell mutation and canceration.
6. What is he determination method of zirconium?
Zirconium content is expressed as "point", which is the milliliter
of 0.1mol/l EDTA standard solution consumed per 100ml solution.
The determination method of Zr is as follows: take 100ml of bath solution, put it into a conical flask, add 40ml deionized water and heat it, then add 13 drops of 25% ammonia water
until obvious and non vanishing precipitation appears, add 10ml of water, 1.5ml of 98% H2SO4 and 1g of aluminum nitrate (jiushui). After boiling for 3 minutes, dilute it to 200ml with 70 ℃ water. Cool to about 50 ℃, add 4 drops of xylenol orange, titrate
with 0.1mol/l EDTA standard solution, add 0.5g aluminum nitrate (jiushui) near the end point, and titrate until the solution is yellow.