In vivo kinematics after a cruciate-substituting TKA. Clin Orthop Relat Res. In vivo comparison of kinematics for non-implanted and implanted knees. Orthopedic Research Society. Bicruciate-stabilised total knee replacements produce more normal sagittal plane kinematics than posterior-stabilised designs. In vivo kinematics and kinetics of a bi-cruciate substituting total knee arthroplasty: a combined fluoroscopic and gait analysis study. J Orthop Res.
The influence of contemporary knee design on high flexion: a kinematic comparison with the normal knee.
JBJS Am. Epub Jun Bicruciate substituting total knee replacement: how effective are the added kinematic constraints in vivo? Knee Surg Sports Traumatol Arthrosc. This paint offers the ease of use of other one-component technologies with the performance of a two-component paint.
Moisture-cured polyurethane technology is a rapidly growing example of this technology. Volatile Vehicles Solvents A solvent is used to dissolve the resins and additives in order to reduce the viscosity of the mixture to provide application consistency and allow the paint to flow out properly. In every case, it is designed to evaporate from the film during or after application. Solvents are also used in waterborne dispersions and latexes. At some point in either the manufacture of the resin or the paint, solvents are added to soften the resin.
During the drying of the paint film, the water evaporates. The dispersion of latex particles come into contact and flow together to form a continuous film. Finally the solvent evaporates from the film. This process, called coalescence, would not take place without the solvent. Resins that are hard enough to produce through tough films are too hard to coalesce without the solvent. Waterborne coatings are gaining interest by specifiers because they are perceived as being environmentally friendly.
Although many waterborne coatings do have low levels of solvents, some waterborne paints contain solvent in amounts equivalent to those in high-solid, solventborne coatings. Environmental concerns are forcing raw material suppliers and paint producers to lower the solvent content of the products they supply in order to reduce the amount of volatile organic compounds VOCs released into the atmosphere.
Coatings suppliers select the type of solvent suitable for each type of coating formulation. The choice of solvents is made based on the optimum paint viscosity and evaporation rate that result in proper paint flow and thus, the intended appearance and adhesion. Coating applicators may need to add solvents during application to control viscosity over the various temperature ranges encountered in the field. The wrong choice of solvents can jeopardize an application. If the chosen solvent evaporates too fast, bubbles caused by the vapor pressure of the solvent may appear in the surface.
If the coating is spray applied, the solvent may "flash out" of the spray mist before it reaches the surface, and the spray may become too dry for the paint particles to flow together. This effect is called dry spray. A solvent that is too slow to evaporate may remain in the film too long, causing sags and runs and resulting in a film that is soft and has other altered performance properties. The applicator must also take care not to add thinning solvent beyond that recommended by the manufacturer, because the paint viscosity may be so slow that the wet films will sag and run.
Over-thinned paint that is applied at too low a film build may result in films that are too thin and have no hiding power. Additives Additives make up only a small proportion of any paint. Yet without these chemicals the paint could not deliver all of its potential performance. Paint additives are used to aid pigment grinding, stabilize resin and pigment dispersions, break foams, aid flow, prevent film surface defects, catalyze chemical reactions, prevent oxidation, enhance adhesion, provide slip and abrasion resistance to the film surface, prevent corrosion, and to improve weathering resistance and enhance color retention.
These additives can be inexpensive or can be the most expensive component on a per pound basis of any ingredient. In these days of cost competition, it is not unusual for a paint manufacturer to cut costs by leaving out one of these vital ingredients. Sometimes the effects may not be known until years after the paint application.
For example, in a high performance polyurethane topcoat, it is usual practice to add antioxidants and UV absorbers to enhance the weathering resistance. If theses additives are left out of the formulation to lower cost, instead of the ten years of gloss and color retention, only one or two years might be expected.
It is imperative that expected paint performance be listed in the job specification. The English started with the idea of using zinc dust in organic vehicles to provide a zinc-rich coating. A completely different concept was started in Australia where the inorganic zinc-rich materials were developed.
The idea of incorporating zinc dust into an organic vehicle coincided with the time that the more sophisticated synthetic resins became available. Two categories of zinc-rich primers are available based on the binder chemistry.
Inorganic zinc coatings are composed of powdered metallic zinc mixed into a reactive silicate solution. Those formed from sodium silicate, potassium silicate, lithium silicate, colloidal silica, the various organic silicates, and even galvanizing, are reactive materials from the time they are applied. The second category is organic zinc-rich primers, the binders of which are based on organic or carbon-based compounds.
Organic vehicles include phonoxies, catalyzed epoxies, urethanes, chlorinated rubbers, vinyls, and other suitable resinous binders. One very important characteristic of inorganic zinc coatings is the electrical conductivity of the matrix. Electrons formed by ionization of zinc at any point within the coating can migrate to the steel substrate and provide cathodic protection to any steel area that may be exposed.
Particle-to-particle contact of the zinc pigment is not required for conductivity in inorganic zinc coatings since it is in a conductive, organic zinc-rich matrix. Organic rich coatings generally require a higher zinc loading to develop the zinc particle contact necessary for protection. Epoxy Epoxy binders are available in three types: epoxy ester; epoxy lacquer resin; and two-component epoxy.
The two-component epoxies are most commonly used for painting structural steel. Epoxy resins of this type can cure by chemical reaction. The epoxy is generally combined with either of two types of hardeners polyamine or polyamide to form epoxy-polyamine and epoxy-polyamide. Epoxy-polyamine blends are more resistant to chemicals and solvents and are often used for lining tanks.
Epoxypolyamide paints are the most popular of all epoxy binders for use on structural steel. When exposed to weathering, they chalk quickly, but retain excellent chemical and abrasion resistant properties. Acrylics Acrylics can be supplied as solvent- or water- based coatings with varying performance characteristics. They exhibit good color and gloss retention, are single package, relatively low in cost and easy to apply. Solvent and chemical resistance, however, is lacking. They are best for interior, non-corrosive environments.
Polyurethane Polyurethane binders are available in two types for painting structural steel:! Moisture-Cure Polyurethane Reacts with air moisture to cure. They produce the hardest, toughest coatings available in one package, and are increasingly popular due to the wide range of application and productivity advantages:!
Two-Component Polyurethane Polyurethanes can also be reacted with products such as polyols, polyethers, polyesters or acrylics to produce extremely hard, resistant durable coatings. These are commonly used as topcoats.
Alkyds Alkyds are available in both water dispersion and solvent-based formulations. Alkyd-oil vehicles can be formulated in flat and semi-gloss finishes over a wide compositional range.
Generally, alkyds have poor color and retention properties and tend to chalk when exposed to sunlight. Their primary advantage is low cost. Other coatings technologies can be considered. Consult your painting supplier for recommendations based on specific project requirements. They can provide fire ratings for exposed steel for up to three hours. Hot-D Dip Galvanizing There are several reasons for selecting galvanizing as a coating system.
For light fabrications and some medium structural applications, galvanizing can be the lowest cost coating system. It is usually also one of the lowest longterm cost coating system alternatives. Galvanizing does not adhere to the steel, but is actually metallurgically bonded to the base steelforming an alloy layer between the surface zinc and the underlying base metal.
Galvanizing is a tough coating system, providing high resistance to mechanical damage in transport, erection and in service.
Finally, galvanizing eliminates maintenance for relatively long periods of time. This can be a significant factor if maintenance of the facility requires shutdowns or the area to be maintained is not easily accessible.
There are several types of galvanizing processes that are used throughout the industry including electric, zinc plating, mechanical plating and hot dip galvanizing. Hot-dip galvanizing is one of the oldest and most common types and has been used to fight corrosion for more than years. Hot-dip galvanizing is a process in which a steel article is cleaned in acid pickled and then immersed in molten zinc that is heated to approximately Fahrenheit. This results in formation of a zinc and a zinc-iron alloy coating that is metallurgically bonded to the steel.
After the steel is removed from the galvanizing bath, excess zinc is drained or vibrated off the steel member. The galvanized member is then cooled in air or quenched in water.
The zinc coating acts as a barrier that separates the steel from the environmental conditions that can cause corrosion. The galvanizing process precludes the possibility of coating improperly prepared steel surfaces, since the molten zinc will only react with clean steel.
Due to the immersion process, galvanizing also provides complete protection of all galvanized partsincluding recesses, sharp corners, and inaccessible areas. Today, almost any size item can be galvanized. Most galvanizing facilities have galvanizing kettles that are at least 30 ft in length. Larger kettles of up to 50 ft long are becoming common.
If an item is too long for total immersion at on time, it may still be possible to galvanize the item. If more than one half of the item will fit into the kettle, a process called "double dipping" may be incorporated.
Double dipping is a process where one half of the item is dipped in the kettle filled with molten zinc and withdrawn, and then the other half is dipped. The double dipping process provides a constant thickness of zinc coating similar to the total immersion process. Consult a galvanizer before planning to use a "double dipping" process. Sometimes it is necessary to prevent the zinc coating from bonding to a local portion of the steel article.
An example of this situation would be where something needs to be welded to the galvanized article, since the zinc coating could contaminate the welds. This concept would also apply to galvanized beams where the top flange must remain ungalvanized to receive shear connectors for a composite beam.
Today there is a technology that can incorporate the hot-dip galvanizing process while leaving predetermined areas of the article uncoated. This process can be applied in any location, on any size or shape of steel members.
Consult a local galvanizer for more information on this topic. If aesthetics are an important issue for the galvanized item, the architect should indicate suitable locations to the galvanizer. Since all of the material is immersed into the galvanizing kettles, chains, wires or other holding devices are needed to support the immersed articles.
Holding devices usually leave marks on the finished galvanized product. These marks are not necessarily detrimental to the coating, but could affect the desired aesthetics. Best results for galvanizing will occur when the architect and fabricator keep the nature of the galvanizing process in mind at all stages.
To minimize any warping that may result form the galvanizing process, the item to be galvanized should be fabricated so that it can be quickly and completely immersed in the kettle. Use of symmetrical sections in lieu of unusual angles or channels will minimize shape warping. For more information on galvanizing characteristics, consult a local galvanizing company. In any building there are many areas susceptible to corrosion that warrant special protection through galvanizing.
The two-page Figure 24 illustrates high potential corrosion areas on high-rise buildings where galvanized protection is advised. An example of a building design galvanizing checklist is also given in Figure Contact information for AGA is given in the Appendix.
Galvanized Steel Painted Duplex System Sometimes it is desirable to provide a coating system for steel that includes both galvanizing and paint systems. There are several reasons why it would be desirable to combine these materials: aesthetics, color coding, safety markings, ease of repairing, and low life-cycle costs are just a few. This combination of galvanizing and paint systems is known as a duplex system. The key to success of a duplex system is proper surface preparation and proper selection of a paint system.
Simply stated, the galvanized system must be clean, and the paint system must be compatible with zinc. Previous difficulties with paint adhesion on hot-dipped galvanized surfaces were related to three factors:!
Today, these difficulties can be overcome. The lack of surface profile can be overcome by brush-blasting or chemical etching treatments of the galvanized surface. The reactions between components of paint can be overcome by properly specifying paints that do not contain vegetable oil-based vehicles alkyds , which destroy the zinc bond. Finally, proper solvent washing prior to painting can control the surface contamination between galvanizing and paints. In many cases, a piece of steel that has been galvanized and painted can provide synergistic benefits in protection to the steel.
There is evidence that protection provided by painting galvanized steel is greater and lasts longer than the sum of the protection provided separately by zinc or paint alone. The protection is typically 50 percent greater than the additive effects of zinc and paint topcoating. If steel is galvanized and painted, any corrosion resulting from the eventual broken barrier is limited to the surface of the exposed areas and does not cause undercutting, blistering or flaking of the paint.
Actually, galvanized products retard further damage to the steel by sealing pores and cracks in the paint film. At the same time, paint actually extends the life of the underlying galvanized coating by postponing degradation of the zinc layer.
The selection of a suitable painting system is critical for the successful painting of galvanized steel. Loss of adhesion often occurs when incompatible systems, such as alkyd resin-based paints, epoxy resin-based paints or acrylate. See sketch on next page. It is important to use compatible products primer, sealer and topcoat. There are a variety of manufactured paint systems that have unique characteristics and are appropriate for specific use with galvanized steel.
Specific paint system characteristics, however, are beyond the scope of this guide. Comments here relate only to generic paint systems and are based on overall understanding of industry experience. Contact paint manufacturers for additional information of specific paint applications. A paint system that is to be used over galvanized steel typically includes pretreatment, primers and topcoats.
Pretreatments are commonly used to condition galvanized surfaces for proper paint adhesion. In many cases, a topcoat will not adhere to galvanized steel without a primer. Therefore, a primer coat is a critical component of the system.
The primer acts as a tie coat to the galvanized steel, and provides other performance characteristics for the overall system. The topcoat must also resist dulling, fading, chalking, flaking, peeling and blistering in the environment in which the steel must function.
The Clean Air Act Amendment requires that volatile organic compound emissions be reduced for industrial maintenance coatings for field applications. The systems included herein have VOC levels up to 3. Coating Systems Paint systems used in the U. Some of the systems are listed as "Newer Technology. Tables 2a and 2b are an application guide showing the most effective use of the paint systems described in Table 1. These tables offer recommendations for the type of system that will be effective, based on the severity of the environment in which it will be used, and also indicate the systems that can be used to topcoat various types of existing paints.
Interior Structural Steel Before an appropriate coatings systems for a specific application is determined, it must first be determined whether or not a coating system is actually required at all. Currently, many architects specify all interior steel that is not covered with spray-applied fire protection to be shop primed, even though the steel will not be exposed to view or subjected to corrosive environments.
This specification is usually not appropriate and is generally not in the best interest of the owner. An examination of a number of buildings that had been in use for more than 50 years indicated no corrosion of any significance whether or not the steel was painted. Some isolated locations of severe corrosion had been found in these buildings, but only at localized spots where water had been allowed to seep in and remain in contact with the steel for long periods of time.
Results of this study led the American Institute of Steel Construction to conclude that structural steel hidden between the exterior cladding of a building and the interior finish need not be painted. Appropriate protection of the steel should be determined by the end-use of the building and the exposure of the steel structure.
The building's service requirements may determine that little or no protection of the steel is necessary at all. Steel does not rust except when exposed to atmospheres above approximately 70 percent relative humidity. Serious corrosion of steel occurs at normal temperatures only in the presence of both oxygen and water.
In dry atmospheres less than 70 percent relative humidity , non-painted steel can be exposed for extremely long periods of time with no evidence of rusting. If the steel is not painted, a thin transparent film of iron oxide forms on the non-painted steel, actually protecting the steel from further corrosion. Therefore, it is difficult to justify painting all interior steel members as a protective measure for the steel.
Table 1 Paint Systems. They should be specifically formulated for whichever use is intended. It is reasonable to conclude that painting is not mandatory for interior steel framing in low humidity environments, provided the structure remains water tight. The question then must be asked, why paint interior steel at all? If the steel of a building under construction is exposed to the elements for a normal period of time prior to enclosure, the minimal corrosion which occurs on the unpainted steel would not be considered to be structurally detrimental.
The issue then becomes a matter of aesthetics. The appearance of "raw" steel may not be desirable. Customers and building owners usually prefer the appearance of a painted surface to a rusty surface on exposed steel framing. Paint systems reference numbers see Table 1 shown in bold text are considered Newer Technology for either coating unpainted steels or topcoatings over existing paints. All other environments are considered at least mildly corrosive.
There are, however, disadvantages to painting interior steel that is not exposed to view. One disadvantage is the cost. Shop painting can be expensive, particularly if the steel fabrication shop does not have the appropriate painting facilities. For example, not including surface preparation by blasting or other means, a single coat of shop-applied primer can add percent to the in-place cost of the structure.
Touch-up painting in the field can also add substantial cost to the project, particularly if the required touch-up work is extensive and accessibility to the touch-up area is limited.
Painted surfaces can also be problematic if an item needs to be welded to the painted steel. The paint can contaminate a weld if all of the paint at the weld location is not completely removed. The architect should determine the most appropriate coatings for the various types of steel members on the project. They should also educate the owner about the appearance and maintenance of various steel finishes specified for the owner's facility.
The owner also needs to realize that interior coatings are not expected to protect the steel for extended periods of time prior to the enclosure of the building. This type of information will lead to greater client satisfaction.
In fact, inadequate surface preparation is the biggest single cause of coating failures. No matter how carefully a coating is formulated and manufactured, how sound the research on which it was based or how sophisticated the technology, the coating will fail prematurely in service if the surface to which it is applied was inadequately prepared. No coating can form a strong bond to a surface if there is contamination under the coating that is weakly bound to the substrate.
Peeling coatings, dirt, rust, mill scale, oil, wax, moisture or other foreign materials provide a poor foundation to hold a coating, sometimes even when the contamination is present in such small quantities as to be invisible to the eye. The eventual result will be loss of adhesion. Surface preparation must be considered as an integral part of the coating specification. The coating specification must include the following:! Specifications must be written for coatings systems that include these items as well as the expected performance properties of the entire system over the life of the protected steel.
Specifications Specifications and pictorial standards for surface preparation have been published by SSPC and are considered to be the supreme reference for the architect and maintenance engineer.
The complete specification for the above procedures may be found in Volume 2, "Systems and Specification", of the Steel Structures Painting Manual. Pictorial standards for these procedures are also available from this group. Following is a brief description of these specifications. Describes a method for removing all visible oil, grease, soil, drawing and cutting compounds, and other soluble contaminants from surfaces.
Solvent cleaning should be used prior to any of the other surface preparation methods for the removal of rust, mill scale or paint. If this is not done, containments such as oil or salt on the surface of rust or paint could be driven into the substrate and would be difficult, if not impossible, to remove.
Describes a method of preparing surfaces by using non-power tools. Before hand tool cleaning, remove all visible oil, grease and soluble welding residues, and salts by the method outlined in SSPC-SP1. Hand tool cleaning is intended to remove all loose mill scale, rust and paint. It is not intended that this process remove tight mill scale, rust and paint. Materials are considered adherent if they cannot be lifted with a dull putty knife.
Examples of hand tools are a wire brush and sandpaper. A specification that describes a method of preparing steel surfaces by using power-assisted hand tools. Before power tool cleaning, remove all visible oil, grease and soluble welding residue, and salts by the method outlined in SSPC-SP1. Power tool cleaning is intended to remove all loose mill scale, rust, paint and other foreign matter. It is not intended that this process remove adherent mill scale, rust and paint.
Examples of power tools include a rotary abrader, grinder and needle gun. Vacuum power tools should be specified to comply with OSHA regulations regarding emissions. Describes a method of cleaning surfaces by using abrasives.
Before white metal cleaning, remove all visible oil, grease and soluble welding residue, and salts by the method outlined in SSPC-SP1. When white metal cleaned surfaces are viewed without magnification, they shall be completely free of all visible oil, grease, dirt, dust, mill scale, rust, paint, oxides, corrosion products and other foreign matter.
Blast media can be metal shot or mineral grit. Describes a method for cleaning surfaces by using abrasives. When commercial blat cleaned surfaces are viewed without magnification, they shall be free of all visible oil, grease, dirt, durst, mill scale, rust, paint, oxides, corrosion products and other foreign matter, except for staining as described in Section 2. When brushoff cleaned surfaces are viewed without magnification, they shall be free of all visible oil, grease, dirt and dust.
Tightly adherent mill scale, rust and paint may remain on the surfaces. Materials are considered tightly adherent if they cannot be lifted with a dull putty knife. Describes a method of cleaning steel surfaces by means of chemical action, electrolysis or both. When pickled surfaces are viewed without magnification, they shall be free of visible mill scale or rust.
When near-white cleaned surfaces are viewed without magnification, they shall be free of visible oil, grease, dirt, dust, mill scale, rust, paint, oxides, corrosion products and other foreign matter, except for staining as described in Section 2. Describes a method of cleaning surfaces to bare metal and retaining or producing a surface profile by using power tools. SSPC-SP3 requires only the removal of loosely adherent material and does not require the production or retention of a surface profile.
When SSPC-SP11 power tool cleaned surfaces are viewed without magnification, they shall be free of oil, grease, dirt, rust, mill scale, rust, paint, oxide and corrosion products and other foreign matter. Slight residues of rust and paint may be left in the lower portion of pits if the original surface is pitted.
These surfaces must also be prepared properly for coating. Concrete should be coated for the protection from moisture penetration and the resulting physical damage of spalling. There are several factors to consider when preparing concrete to receive coating. Laitance is a thin layer of fine particles on the surface of fresh concrete caused by the upward migration of water during the mixing and finishing process.
Because this layer has poor adherence to the main body of concrete, it must be removed before coating. Abrasive blasting or acid etching can accomplish this. Failure to remove this laitance layer prior to coating is the biggest cause of failure on new concrete. Efflorescence is the deposition of salts on the concrete surface caused by moisture release during curing or moisture migration through the concrete as it ages. These alkaline deposits act much like concrete laitance and must be removed.
Form oil is applied to concrete forms as a release agent prior to pouring the concrete, to ensure the easy removal of the forms after curing. Some form oils are transferred to the concrete surface as a contaminant and must be removed by detergent and water washing before acid etching or abrasive blasting.
Concrete hardeners are sometimes used to modify the strength and permeability of concrete. They tend to migrate to the surface and cannot be acid etched. They must be removed with abrasive blasting. The surface of the concrete is usually treated to promote adhesion of the coating system.
Either physical abrading or chemical cleaning methods are used. Physical abrading can be done with, for example, sandpaper or a power-abrading machine.
Chemical cleaning can be done with various chemicals such as trisodium phosphate or muriatic hydrochloric acid. After treatment, the surface must be dry and free from grit. Cast Iron. Cast iron is a porous material that is likely to absorb moisture or other liquids with which it comes in contact. These liquids must be removed prior to surface preparation and painting. The requirements of the paint system control the degree of blast cleaning.
The surface should then be etched with materials like mild phosphoric acid or ammonium hydroxide to give a rough surface profile suitable for the specified coating. If the zinc is allowed to weather naturally, the zinc oxide will provide a profile suitable for many coatings. Alkyd- or ester-based coatings must not be applied directly to zinc surfaces.
Zinc oxide is an amphoteric material that is capable of acting as either an acid or base. The result can be deterioration of film properties and loss of adhesion of the coating to the zinc surface. Copper and Brass. It is expected that coating technology will continue to evolve, allowing the development of coating systems that are even longer lasting and more economical. The use of metallic zinc pigmentation in today's coatings effectively eliminates under-cutting corrosion and subfilm corrosion through galvanic action.
Abrasive blast removal of mill scale in the fabrication shop improves longterm adhesion and helps the original coating tolerate maintenance overcoating without costly surface preparation. With an intermediate coat and topcoat applied, the first required maintenance should occur after approximately 25 years of service. At that time, with spot cleaning, spot priming and the addition of another topcoat approximately mils , you could expect another years of service life. At the end of that period, the same process would be repeated with the same anticipated results.
A shop may be either a permanent painting shop which may be part of a steel fabricator's plant , a separate painting shop, or a temporary shop constructed at or near the building site to repaint the steel.
A covered shelter does not necessarily constitute a "shop. New steel used as a construction item is the easiest to protect from corrosion because it probably has not been contaminated with salts that act as electrolytes for the corrosion cells. Because the salts may not be present, it will be easier to achieve the degree of surface preparation needed to protect steel.
Older steel and specifically corroded steel may have soluble salts imbedded in the corroded pits and intergranular surfaces. Though the salts may be of a soluble type, they are difficult to remove even with the most rigorous cleaning procedures and tend to shorten the service life of coating systems when compared to the life of the same systems on new steel.
Mill scale is a hard, smooth, blue-black layer of iron oxide Fe that forms on steel during the hot-rolling process. Mill scale is very inert. When intact, it forms a very efficient barrier to protect steel from corrosion.
Unfortunately it has a different coefficient of expansion than steel and is very brittle. Because of this, it cracks and chips. The remaining mill scale then becomes cathodic with respect to steel, forming very efficient corrosion cells. The result is that mill scale must be removed before painting. Red rust, a form of mixed iron oxides, is a surface contaminant familiar to everyone. It varies in color form light red to dark brown and may be loose and powdery or hard and granular.
Red rust provides a weak foundation for paint, contributes to the formation of corrosion cells, and contributes to the destruction of coatings. In the case of light superficial rust, there are surface-tolerant primers that can be used to provide future protection of the steel. For example, steel that has been prepared and cleaned in the fabrication shop may develop superficial rust on the jobsite prior to the building being enclosed may be adequately protected by such primers. Requirements for Preparation of Bare Metal Surface preparation is the most critical procedure for successful performance of a coating system.
Surface preparation consists of cleaning the bare steel or previously coated surface. It includes establishing an appropriate pro-. Cleaning and surface profile are both critical to the performance of the paint system. Cleaning of the surface includes removal of all soluble salts, oils, grease, dirt, dust and any other contaminants, by whatever means necessary, that will adversely affect the adhesion of the paint coat to the surface.
Ensuring that recontamination does not occur, such as from airborne dusts, is also critical to a successful recoating project. When blast cleaning is used to prepare the surface, the compressed air used to propel the abrasive shall be tested periodically to ensure it is free from oil and moisture and sufficient volume and pressure to clean the surface in a productive manner to the required profile.
For inorganic zinc prime coatings, surfaces shall be cleaned to a level as obtained by SSPC-SP10 for new construction. Preparation Methods and Specifications Power washing. Consists of blasting the steel with water at a pressure of psi to 5, psi with the nozzle not more than 12 in. If residue containing hazardous substances is removed during the washing process, the water will have to be strained to remove the contaminants or disposed of as hazardous waste.
Any abrasives used shall be free of oil, moisture, hazardous substances i. Abrasives with "free" silica contents in excess of one percent should not be used. As surface profile is critical to paint system performance, it must be controlled at the time it is produced, i.
This can be accomplished by controlling the range of particle size and shape in the abrasive used for blasting. When using automated recycling blasting equipment with steel shot or grit, it is important to consider that a working mix is developed through use, then maintained by addition of suitable quantities of steel abrasive of the correct size range. This mixture of sizes is commonly called the work mix or operating mix. It is important to emphasize that this is indeed a mixture of a range of particle sizes, shape and hardness that is necessary to produce the correct profile.
Larger particle sizes are suitable for removing heavy build-ups of mill scale or rust. Smaller size ranges increase productivity of removal of corrosion products through an increased number of impacts.
When using abrasives, the "right mix" can be obtained through consultation with the supplier of the abrasive. Surface profiles. Profiles of steel surfaces shall be obtained using abrasive or equipment meeting the requirements herein. When repairs to previously applied coatings are required, the proper surface condition of the repair area shall be obtained by power tool cleaning, spot blasting or by other acceptable means. Surface profile is measured as the difference between the average depths of the bottom of the peaks to the average tops of the highest peaks created by the blasting.
The profile height is dependant upon the size, type and hardness of the abrasive, the particle velocity, and angle of impact and hardness of the surface.
Surface profile provides the "tooth" needed for adhesion and long-term. Mulai proses cracking… Cara menghindari seranganini adalah dengan membuat password yang sulit ditebak, yakni password dengan kombinasi huruf dan angka dengan minimal jumlahnya 8 karakter. Older Posts. Subscribe to: Posts Atom. Site Info. Komputer Kesehatan tips dan trik Berita.
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