Surface treatment method of water-based industrial paint substrate!

Correct surface preparation prior to application of waterborne industrial paints is critical to a successful painting j.

Steel: The following briefly introduces some methods of surface treatment of ste.

Standard IS08504: 1992 (E): Surface treatment of steel-based materials before painting and related products - surface treatment metho.

The American Steel Structure Paint and Coatings Council Standard (SSPC): a full range of surface treatment standar.

Standards IS08501-1: 1998 (E) and ]: S08502-2: 1994: Cleaning of steel-based materials before applying paint and related products: Visual determination of surface cleanline.

Swedish standard SIS055900 (1967): Standard illustration of surface treatment of steel pre-coated par.

NACE Anti-Corrosion Engineers Association standards for surface treatme.

GB/IB923, GB/T13288, GB/T18839 series of standards for surface treatme.

Removal of contaminants: The surface state (roughness and cleanliness) of the coated steel has a great influence on the performance of the applied pai.

A) Surface dirt, including salt, oil, grease, drilling (cutting) fluid,e.

B) Rust and sca.

C) Surface roughne.

The main purpose of surface cleaning is to ensure that all of the above contaminants are thoroughly removed, reducing the likelihood of incipient corrosion and creating a surface roughness with good adhesion to the coati.

Oils and greases must be cleaned of all dredgeable salts, greases, drilling (cutting) fluids, and other contaminants from the surface prior to sandblasting or overcoati.

The correct way is to dry it with a clean rag three or four times, and use a clean rag each time to wipe it o.

Surface salts can be removed relatively easily with fresh wat.

Manual cleaning

The loose oxide scale, rust and aged coating on the surface of the steel plate can be removed by manual methods such as wire brushing, sandpaper or shov.

However, the cleaning of these methods is not thorough, especially the tightly attached thin rust layer is difficult to remo.

The manual cleaning method is described in SSPC-SP When used, it should meet the St2 level standard in IS08501-1: 198 Some types of coatings even need to meet the St0 level rust removal standard before painti.

Power Tool Cleaning

When it comes to removing loose scale, aged coatings and rust, power tool cleaning is better than manual and saves time and effo.

However, power tools cannot remove tightly attached scale and ru.

Commonly used power tools are power wire brushes, impact tools (such as needle guns), sanders and grinde.

However, it must be noted that when using a power wire brush, do not polish the metal surface, because this will reduce the roughness of the substrate surface and affect the adhesion of the coati.

Cleaning with power tools is covered in both SSPC-SP3 and SSPC-SP1 The SSPC-SP11 standard describes the use of power tool cleaning to obtain a certain roughne.

jet cleaning

One of the most effective methods for cleaning scale, rust and aging coatings is blast cleani.

The abrasives for blast cleaning include steel shot, steel grit, copper slag,e.

The level of surface preparation appropriate for a particular coating requirement depends on many factors, the most important of which is the type of coating system select.

The main standards used in this product specification are IS08501-1:1988(E) and ]:S08501-2:1994, ie the treatment of steel substrates prior to coatings and related products - visual identification of surface cleanline.

This standard is an extension of the Swedish standa.

The Swedish standard SIS055900 was developed by the Swedish Corrosion Institute, the American Society for Testing and Materials (ASTM) and the American Society for Protective Coatings (SSPC) and is used worldwi.

The general principle is: when the product is used in underwater or corrosive atmosphere, the required blasting treatment standard should reach Sa5 (IS08501-1: 1988) or SSPC-SP1 However, for products exposed to the general environme.

The blasting treatment standard should reach Sa2 (IS08501-l: 1988) or SSPC-SP6 lev.

Surface treatment Before blasting, the surface should be free of grease and welding sl.

If there is salt and grease on the surface, it needs to be thoroughly cleaned before sprayi.

It seems that these impurities can be removed by spraying, but this is not the case; although these things cannot be seen on the treated surface, the actual These contaminants still form a thin film in situ, which affects the adhesion of the coati.

Surface defects exposed during the blasting process, such as rough welds, laminations and sharp edges, must be grou.

Otherwise, the paint will flow away from sharp corners, resulting in a thin coating and reduced protecti.

It is almost impossible for a poorly formed spot weld to be uniformly covered with pai.

Uneven coating, in addition to weakening the adhesion of the coating, is also one of the main reasons for premature corrosi.

The surface roughness developed during blast cleaning is important and depends on the abrasive used, air pressure and blasting techniq.

Too little roughness and the coating won't adhere well; too much roughness can make the coating uneven on the crests and cause premature coating failure, especially with thin shop prime.

The table below shows the roughness obtained with different types and sizes of abrasives:

Abrasive Type Specifications Large Surface Roughness

Fine sand 80 mesh 37μm

Coarse sand 12 mesh 70^m

Iron shot 14 mesh 90S

Typical non-metallic copper slag5"Omni75-100 kim

Typical non-metallic iron sand .

G16200 Am

Sand blasting and rust removal

For previously coated or less rusted surfaces, it can be easily cleaned to Sa5 lev.

However, for heavily rusted or pitted surfaces, it is not easy to reach levelThe effectiveness and specifications of various types of abrasives have been tested in strictly controlled practical tes.

For corroded steel, the most efficient treatment is copper slag with a particle size of 3-
After sandblasting, the dust on the surface must be remov.

In the case of open air operations, dry compressed air can be used; in the cabin, careful cleaning is required, usually with a vacuum cleaner to remove all sand and du.

Local sandblasting and rust removal

This type of blast cleaning is often used for rusted and mottled structur.

It effectively removes rust and produces a surface clean to the specified standard (IS08501-1: 198
In actual operation, some things must be paid attention to to avoid coating quality problems:

The paint film around the local blasting area (especially the epoxy coating) may be cut due to the impact of the abrasive particles, and the paint film around the area may also loosen from the surface of the steel pla.

If this occurs, be sure to Use a disc sander to remove the warped edg.

The surface of the coating around the localized blasting area may be damaged by the grit, thus destroying the protective value of the original coati.

In order to obtain a good overall coating, the damaged coating around the blasted area must be properly repair.

Sometimes when crossing from one local blasting area to another > the gun does not stop blasting, the surface between the blasting areas may be damag.

Therefore, when blasting from one area to another, the gun must be stopp.

The resulting damage should be repaired as described abo.

It is recommended to mark the perimeter of the blasted ar.

sand sweeping

Sand sweeping is a surface treatment method that uses abrasives to sweep and clean the pre-coated surfa.

Its effect depends on the characteristics and state of the contamination on the surface of the steel plate, the type of abrasive and the size of the particles, and mainly the operator's ski.

A) Light sand sweeping

A quick blast removes surface contamination and loose coatin.

It can be used to roughen previously hard and smooth surfaces to improve the adhesion of the next co.

It is also good for removing rust from previously shop-primed steel surfaces, but not deeper ru.

To remove deeper rust, a "full spray" of 5 must be achiev.

The size of the abrasive particles is very importa.

If you do not want to damage the paint surface, it is more appropriate to use fine abrasives (sand size is2mm- 5.

B) Heavy sand sweeping

Used to remove old coating to shop primer or original ste.

Surface grade standards for raw steel plates may vary, but all standards are met once the scale has been remov.

Respray is also used to enhance the performance of the coating syst.

C) Sweeping cleaning of shop primer

Newly built ships often require full or partial removal of the original shop primer prior to formal painti.

The standard for surface cleaning shall be in accordance with JSRA Standard 198

Wet abrasive blast cleaning/mortar blast cleaning

Wet abrasive blast cleaning is the removal of rust with a slurry of water and abrasi.

This method can basically eliminate the harmful to health: dust, another advantage is that when the old, heavily corroded steel surface is washed with wet abrasive, many fusible contaminants of the steel surface pits can also be washed out, which will Greatly improve the performance of painti.

However, the disadvantage is that the surface of the cleaned steel part rusts quickly after the rust is remov.

Corrosion inhibitors are not recommended if wet abrasive blast cleaned, mortar blast cleaned steel structures are to be serviced in marine environments in the futu.

water jet cleaning

Blast cleaning is an advanced surface cleaning techniq.

It completely uses high-energy water flow to impact the surface of the substrate to achieve the purpose of cleaning the surfa.

Water jet cleaning does not require abrasives, so there are no dust contamination issues associated with dry abrasiv.

Water jet cleaning generally uses two different water pressur.

n The working pressure of high-pressure water jet cleaning is:

Between 680 bar (10,00

i) and 1,700bar (25,00

.

The working pressure of ultra-high pressure water jet cleaning is:

Above 1,700 bar (25,00
.

i) To name water cleaning at various pressures, the following generally accepted definitions are used:

n Low pressure water flushing: the working pressure is less than 68 bar (100
.

.

n High pressure water flushing: The working pressure is between 68-680 bar (1000-1000
.

.

n High pressure water jet cleaning: The working pressure is between 680-1700 bar (10000-2500
.

.

n Ultra-high pressure water jet cleaning: the working pressure is above 1700 bar (2500
.

i), and the working pressure of most of the machines is in the range of 20000-25000 bar (30000-3600
.

.

The ultra-high pressure fresh water jet cleaning standard is formulated according to the use of ultra-high pressure fresh water jet cleaning equipme.

This standard also applies to surfaces cleaned by water jets at various operating pressures, provided that the cleaning results of the equipment used can meet this visual inspection standa.

Surfaces cleaned with UHP water jets look different from those treated with dry abrasives or slurry abrasives because water itself does not have the same ability to cut or deform steel as abrasives do, so the cleaned surface does not oxidize until it oxidiz.

It looked rather bleak before it happen.

In addition, the surface of the steel plate with corrosion pits will be mottled after being cleaned by ultra-high pressure water jet, because after the corrosion products are washed out from the pits, a light spot will be left in its original place, and the surrounding of the spots will be a.

, brown to bla.

This situation is the opposite of the result after rust removal with abrasiv.

After abrasive rust removal, the pits that act as anodes tend to be dark because the rust has not been completely removed, but the surrounding area is brig.

"Flash rust" refers to a slight oxidation that occurs when a water-jet cleaned surface dries, which can quickly change from the condition seen at fir.

Small areas of "flash rust" can be removed with a wire brush, but the effect is poor; for large areas of "flash rust", a power rotating wire brush should be used for cleaning, which is better than manual metho.

"Flash rust" can affect the surface to the expected standard when cleaning large areas with UHP water je.

In order to overcome this problem, a small area can be tested before a large area is cleaned to determine the actual selection standard, and then the construction is carried out according to this standa.

The approach to ensuring that the remaining areas are cleaned up to standards will vary from project to proje.

Generally, corrosion inhibitors are not recommended for ultra-high pressure water jet cleani.

During the UHP water cleaning process, the temperature of the steel surface will rise for the following reasons:

A) The temperature of the water itself will increase during the process of being compressed to the jet cleaning pressu.

B) In the process of water impacting the steel, part of the kinetic energy will be converted into heat energy, the increase of the temperature of the steel will accelerate the drying and weaken the "flash rus.

An important feature of the UHP water cleaning process is the ability to emulsify and remove grease from metal surfaces, but this does not mean that proper grease cleaning to SSPC-SP1 standards prior to cleaning is not necessa.

Although UHP water cleaning can abrade the steel and cause metal loss, it does not create surface roughne.

The surface roughness of the steel plate cleaned by ultra-high pressure water is caused by the previous surface treatment or corrosi.

Galvanized steel surfaces should be clean, dry and free of grea.

Degreasing most galvanized surfaces is laborio.

Zinc salts should be rinsed with high pressure fresh water, or removed by scrubbing with fresh wat.

Even with common surface preparation methods such as sand sweeping, freshwater removal of soluble zinc salts is recommend.

Many non-saponified polymer coatings can be applied directly to surfaces treated as described abo.

If the steel sheet is passivated immediately after galvanizing, the galvanized sheet must be weathered outdoors for several months, or the surface must be ground before the formal coati.

In general, acid etching treatments have little effect on passivated galvanized shee.