Dry abrasive blasting

In the most-commonly used blasting technique — dry abrasive blasting — velocity of the blasting particles is controlled by the pressure of compressed air. It is more or less a constant for any given dry blasting equipment the mass of the abrasive particle therefore determines its impact on the steel surface. 

Only heavy abrasives can be used in preparing steel surfaces for painting. Lighter abrasive media, such as apricot kernels, plastic particles, glass beads or particles, and walnut shells, are unsuitable for heavy steel constructions. Because of their low densities, they cannot provide the amounts of kinetic energy that must be expended upon the steel s surface to perform useful work. In order to be conunerdally feasible, an abrasive should be  

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Dry abrasive blast cleaning should be used on new steelwork where the main contaminant is mill scale. For heavily rusted and pitted steelwork, increased durability can be obtained by the use of wet abrasive blasting where this is practicable. The water will be more effective in removing the potentially destructive and corrosive soluble iron-corrosion products that form at the bottom of corrosion pits. 

Dry abrasive blast consists of a uniform blasting of the surface with a clean, fine, nonmetaUic grit such as flintstones, silica, silicon carbide, aluminum oxide, or glass beads. The particle size will vary with the surface and the material. The degree of blasting for metal substrates should be a white metal blast —complete removal of... 

The Swedish Corrosion Institute found similar results in a study on pretreating rusted steel [14]. In this study, panels of hot-rolled steel, from which the null scale had been removed using dry abrasive blasting, were sprayed daily with 3% sodium chloride solution for five months, until the surface was covered with a thick, tightly adhering layer of rust. Panels were then subjected to various pretreatments to ranove as much rust as possible and were later tested for chlorides with the Bresle test. Results are given in Table 4.4. 

Dry abrasive blasting will not disappear in the foreseeable future. However, other blasting techniques are currently of interest. Some are briefly described in this section dry blasting with solid carbon dioxide, dry blasting with an ice abrasive, and wet blasting with soda as an abrasive. 

Dry abrasive blasting with silica sand is banned or restricted in many countries because of its hnk to the disease silicosis, which is caused by breathing excessive quantities of extremely fine particles of silica dust over a long period. This section discusses ... 

It is possible to reduce the risks associated with dry abrasive blasting with silica. Efforts needed to do so can be divided into four groups ... 

Figure 14.32 Dry abrasive blasting of (a) a ship hull (b) a pipeline. (Courtesy of Barton Mines Co.)...

EN 2497 Aerospace Series - Dry Abrasive Blasting of Titanium and Titanium Alloys. 

Mechanically abrade with a wet or dry abrasive blast. Use a light abrading (approx. 50—100 microinches) to maintain a uniform adhesive thickness. This type of abrading can be obtained with an air- or air—liquid- abrasive blast. 

To reduce the amount of dust produced, water can be added to the abrasive from a circular water sprayer around the no22le. Chemical corrosion inhibitors must be dissolved in the water to prevent flash msting of the steel. Newer methods to reduce dust include the use of ice, soHd carbon dioxide (dry ice), or plastic beads as abrasives. Blasting with dry ice is inexpensive and effective, but the accumulation of carbon dioxide must be avoided in enclosures. Plastic beads are inexpensive, but the cutting efficiency is low and paint removal is slow the beads can be cleaned of paint particles and reused. 

Surface preparation depends on coating formulation and intended usage. This could vary on steel substrates from a commercial to a white metal blast. Profile is also essential to obtain ultimate adhesion. The depth of profile required is proportional to the total dry film thickness of the coating system. On concrete surfaces, the general requirement is to remove latents and contaminants and this can be accomplished by chemical preparation, scarifying or abrasive blasting. 

Grinding-. Emission capture when grinding on stationary machines takes place in a similar way as with abrasive cutting, i.e. via fixed fimnels into which the abrasive blast is directed. An enclosed work place is used for manual grinding and abrasive cutting. Extraction walls can then be applied in the housing. Air decontamination processes are cyclones, wet washing and dry filters... 

Abrasive treatments consist of scouring, machining, hand sanding, and dry and wet abrasive blasting. The abrasive medium can be fine sandpaper, carborundum or alumina abrasives, metal wools, or abrasive shot. Mechanical abrasion is usually preceded and followed by solvent cleaning. The choice is generally determined by available production facilities and cost. 

A good practice would be to apply a general use epoxy primer 3-5 mils dry film thickness (dft) (75-125 pm). If the surface cannot be abrasive blasted, a surface tolerant epoxy mastic may be used. 

B) Where lead containing coatings or paint are present rivet busting power tool cleaning without dust collection systems cleanup activities where dry expendable abrasives are used and abrasive blasting enclosure movement and removal. 

Mechanicaily Drilled -1 Wet Etched - 2, 3,6 Insulation Displacement - S Mechanically Punched -1 Dry Etched (Plasma) - 2 Conductive Paste Via 9 Laser Drilled -1,4, S Abrasive Blast - 3 Conductive Bonding Sheets 10 Photo Formed s, G, 7 Post Pierced -0... 

Abrasive blasting, both dry and wet processes, are effective on all substrates, but they require experienced mechanics to minimize damage to surfaces. Pressures used are usually between 20 and 110 Ib/in (140 and 760 bars), and working distances are from 3 to 12 in (7.6 to 30 cm). The abrasives are usually silica sand, but crushed slags and coal wastes are often used. The mesh sizes are very fine, either 0 or 00. Round particles are less abrasive and damaging than crushed grains. 

Mud cracking deep irregular cracks that resemble dried mud A relatively inflexible coating applied too thickly (especially inorganic zincs) Remove coating by abrasive blasting before applying at lesser thickness. 

Abrasive wet blasting is variation of abrasive particle-air blasting that involves introducing abrasives into a rapidly moving stream of water and air. The combination obviously cuts down on the atmospheric pollution experienced when using the dry abrasive alone. Inhibitors are often added to the water to reduce rusting of the "clean" steel before the prime coat is applied. 

For certain surfaces, it is only necessary to wipe the surface with a selected solvent to remove oil, grease, and loose dirt. The use of detergent solutions, isopropanol, ketones, and aliphatic and aromatic hydrocarbons for this purpose can be effective. The major requirement for the process is that the wipe shall not leave a residual contaminant, but rather a clean, dry metal surface. Such a cleaning procedure is used on previously cleaned steel, stainless steel surfaces, and old paint films before overcoating, or on dirty steel prior to abrasive blasting. 

Manual demolition Cleanup on dry, abrasive Abrasive blasting... 

Abrasive blast cleazung tech-niquest either wet or dry, are convenient for removing scale fiam a variety of titanium products, ranging fix>m massive ingots to small parts. Because it can be used at lower velocities and is less likely to be... 

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