Surface Cleaning Using Visual Standards
- 27 April 2018
- Posted by: Stm Coatech
- Category: Educational Articles
Bir boya tabakasının dayanıklı olması için her şeyden önce boyanın metal yüzeyine sağlamca yapışması gerekir. Bu ise yüzey temizliğine bağlıdır. Eğer yüzeyde pas, toz, kir, çeşitli yabancı maddeler ve özellikle yağ varsa boya metal yüzeyine yapışamaz.
In order for a paint layer to be durable, it must first adhere firmly to the metal surface of the paint. This depends on the surface cleanliness. If the surface is rust, dust, dirt, various foreign materials and especially oil, the paint can not stick to the metal surface.
Surface cleaning is the basis of coating quality. If the paint layer does not adhere completely to the metal surface, water vapor, which is a pen from the surface, may be collected there. In addition, thermal effects and osmosis events cause the paint to quickly bloom in that area. The methods by which the metal surface is to be cleaned before painting and the cleanliness ratings of the surfaces have been standardized in detail by Steel Structures Painting Council (SSPC) and Standard Institution of Swedish (SIS). From the visual guides where these training programs are published, the closest photo to the initial state of the material to be cleaned is selected. In the selected initial condition, the appropriate cleaning type is selected from the section showing various cleaning grades and the selected operation is performed. When cleaning is finished, the photos are compared to the prepared surface to determine if the cleaning is compatible. It should not be forgotten that reference photographs will not be identical to the surface prepared for many reasons. Because the starting conditions of the prepared steel are different from the starting conditions that the reference photographs are based on. Similarly, the abrasive used will be different from the depth profile of the surface profile and the illumination reference photographs. It is considered suitable for commercial sandblasting as long as the staining remaining after cleaning is between 6% and 33%. It is not surprising that photographs never look identical to the Commercial Sandblast Cleaning surface, as the amount of dyeing can vary slightly with such a wide variety of dyeing. Accordingly, it is important to use photos as a guide for appearance, not as an absolute comparison. It is useful to compare the surface to all the images in the image, to estimate the image.
Metal Surface Cleaning Methods
The metal surfaces can be cleaned by one of the following methods before painting. The cleaning method can be selected according to the characteristics of the surface and tender. Gasoline and similar fuels should never be used in the solvent cleaning method, which is the simplest cleaning method. Because the oil and sulfur derivatives present in these types of fuels reduce the surface adhesion of the paint. Surface cleaning is done by the following methods.
– Cleaning with hand tools
– Spray cleaning
-Cleaning with Solvent
-Estimation Cleaning (Pikling)
-Cleaning with machined tools
Cleaning with solvent – SP-1
It is washed by spraying, brushing or dipping the surface with a suitable solvent to remove the oil on the surface.
Due to the contamination of the solvent, it is widely used due to its ease of application, as well as its short duration of use and its weaknesses such as fire and health hazards.
The oil, grease, etc., the foreign substances dissolved in the solvent are cleaned by washing with any solvent or immersing in the solvent. However, the solvent used for cleaning soon becomes contaminated. For this reason it is better to wipe the metal surfaces with a solvent-soaked ointment cloth. Even in this case, a thin oil film may remain on the metal surface of the solvent evaporation end. Finally, the metal surface may need to be washed with solvent.
With this method, it is not possible to remove oil and dirt as well as rust and inorganic substances adhered firmly to the surface.
Hand Tools Cleaning – SP-2
It is the simplest method for cleaning metal surfaces. Rusty and greasy surfaces may not give the desired finish. Old paint residues on the metal surface, soft foreign materials and rough rust layer can be cleaned using hand tools such as wire brush, scissors, blasters, chisels and hammer.
With this method, the foreign materials in the cracks and the thin rust layer in the pits on the surface can not be cleaned. In addition, hand tools can disrupt the smoothness of the metal surface, creating occasional ridges and pits.
Old paint residues on the metal surface, soft foreign materials and rough rust layer can be cleaned using hand tools such as wire brush, scissors, blasters, chisels and hammer.
Cleaning with Machine Tools – SP-3
Using electric or airborne wire brush, stone (disk), sandpaper, old paint residues, welding burrs and rust on the metal surface are removed by scraping.
Despite working with the machine, surface cleaning is very difficult with this method. Small surfaces, however, are used for this repair. The best method for rapid surface cleaning is sandblasting.
We are going to use machine tools to get rid of the harmful effects of sandblasting on the environment where it is not possible to apply the sandblasting method.
Spray Cleaning – SP-5, SP-6, SP-7, SP-10
The best surface cleaning can be done by sandblasting. In the past, a lot of hard and abrasive solid particles have been used instead of sand, although sand spraying is more advanced.
In this method, certain granulometride silica sand (or other hard particles) is sprayed with a gun at high speed (300-600 km / h) to the metal surface. Thus, rust on the surface and all foreign matter can be removed completely.
This method involves abrading and roughening the surface to be painted by bombarding hard materials sprayed with high pressure. As abrasive, steel shot (shot) or clit (grit) and sand are used. Spray cleaning is extremely clean, giving a suitable surface for paint.
The desired degree of roughness on the surface depends on the type, size, shape and application pressure of the abrasive material used.
For example, 6 atm. pressure and 8 mm. sprayed from the breast,
Coarse sand 70 micron Grit G-50 80 micron Shot S-230 75 micron
Fine sand 50 micron Grit G-1 6 200 micron Shot S-390 90 micron
Natural silica sand is preferred because of its low cost as an abrasive. However, when cleaning the surface with sand, dust is generated at a rate that will both disturb the working worker and the environment. For this reason, in recent years, various synthetic materials (aluminum oxide,
silicon carbide, etc.) have been used instead of sand as a closed circuit.
The surface cleaning grades obtained by the sandblasting method are described below.
Sa-1: All foreign soft materials on the surface of the steel and light sand that has been removed from the pass.
Sa-1: All foreign soft materials on the surface of the steel and light sand that has been removed from the pass.
Sa-2: Moderate sandblasting where approximately 80% of the rust layer on the steel surface is removed.
Sa-2½: Sand spray where approximately 95% of the rust layer on the steel surface is removed.
Sa-3: Sand spray where all rust and foreign materials on the steel surface are removed and white metal is obtained.
Pickling – SP-8
It is an extremely effective surface cleaning method especially for cleaning rust on metal surfaces. Foreign substances on the metal surface can also be cleaned by chemical pikling process.
Pickling is a method of cleaning the metal surface with various acid solutions. The method of cleaning with Pikling is as follows.
– The metal is first dipped into the hot caustic solution to remove oil and grease from the surface.
– Caustic residues are removed by washing with hot water.
– At 80 ° C and in 10% sulfuric acid solution, rust is removed by acid effect.
– Acid residues are cleaned by washing with hot water. In many cases pickling is ended here.
– In order to passivate the metal surface with phosphate, the metal is immersed in 5% phosphoric acid at 80 ° C.
– Wash with hot water and dry.
The lining layer must be applied immediately after the pikling process. Priming should be done before the metal surface is fully cooled. Otherwise, water may condense in the capillary spaces on the surface due to condensation.
During the pickling process, dissolution in the metal may occur due to acid effect. It is beneficial to incorporate a suitable inhibitor into the piquing solutions to minimize metal loss and reduce acid consumption.
Cleaning with Alkali:
It is a cleaning process by removing many oils and greases from metal surface by soaping with an alkali. Alkali materials such as soda, borax, sodium silicate are cleaned by spraying, brushing or dipping them on metal surfaces of hot solutions.
Oxygen-Acetylene or the like is sprinkled around the flame surfaces from a source. Oil, grease, old paint residues and other organic materials become carbonized at 300 ° C and become dust. In addition, the rust layer (iron oxide) is loosened due to the different expansion of the iron-steel. After the flame incineration process, the surfaces should be cleaned with a wire brush or similar mechanical method.
Steam or Water Jet Cleaning:
It is a surface cleaning process by spraying high-pressure steam or water on the surface to remove dust, dirt, old paint residues that are loosely adhering to metal surfaces. The metal surface can be removed by removing the soil, dust oil and grease from the surface by spraying steam at high temperature and pressure.
This method is simpler than cleaning with solvent and is more suitable for environment cleaning. With this method, however, it is not possible to
remove the rust on the surface.
Solvent Oven Cleaning:
It is a very effective degreasing system. A specially designed tank is required for the application. At the base of this tank there are heating coils to evaporate the solvent, and in the upper interior there are cooler coils arranged along the circumference.
To prevent steam losses, the coolant coils must be slightly below the top edge. The piece to be cleaned is hung in the middle of the tank. The solvent on the base evaporates due to heat and rises up, cleansing the part by dissolving grease and grease on the part while returning on the part and condensing on the cold part.
– Trichloroethane is the most widely used solvent in this system.
– The advantages of the trichloroethylene vapor cleaning method are:
– It is a very good solvent for oils and greases.
– The solvent is in its pure state and its vapors come in contact with the part, so the service life is long.
– It’s not flammable.
– It’s economical. Vapors are heavy with air and steam losses are low.
– The part coming out from the cleaning tank is completely dry and ready to be painted.
– If there are solid impurities such as dust or soil in the part to be cleaned, the solvent may be sprayed on the part at a certain pressure by adding a pump to the system to clean them.
STM Coatech, SSPC PCI (International Coating Enspektörlüg), and Corroder (MPA Group England), Turkey, Romania, Ukraine, Georgia, Russia, Azerbaijan, Turkmenistan, Kazakhstan, Iraq, Qatar, Kuwait, Oman, the Sudan and Algeria official licensors.
It is also authorized examination center of the country we have already mentioned above, especially Turkey. Corrodere Training Courses are listed below.
1.Icorr Level 1
2.Icorr Level 2
3.Icorr Level 3
5.Corrodere Hot Galvanizing
6.Corrodere Insulation Inspector
7.Practical Workshop Icorr 1,2,3
8.Corrodere Marine & Offshore Inspector
9.Transition to Icorr
KTA University, How to Use SSPC Vis Guides in Practice, Access Date: 20 April 2018, https://ktauniversity.com/using-sspc-visual-guides/
Mobile Sandblasting, Surface Preparation Standards, Access Date: 20 April 2018, http://www.mobilesandblasting.ca/surface.html
Ecelak, Metal Surface Cleaning, Access Date: 20 April 2018, http://www.ecelak.com/files/c_Metal%20Yuzey%20Temizli%C4%9Fi.pdf