4 Paint Technology Handbook The disadvantage of phosphoric ac Part Preparation Processes and Equipment 5polymers, very low in surface. Modern paints and coatings offer an astounding variety of Paint Technology Handbook You have download access for this title. 1 Paint composition and applications — a general introduction explore various aspects of paint technology and its underlying science, whilst its lit-.
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Paint Technology Handbook. FIGURE Magnified zinc phosphate surface. CLEANING. Manufactured products have a variety of. How to Write a Better Thesis What Is a Thesis? David Evans†, Paul Gruba, Justin Zobel · Download PDF Chapter. Page. Coatings Technology Handbook, Third Edition. The second factor is time dependency. Some inks change viscosity over time even though a constant shear rate.
Upcoming SlideShare. Contents v 1. Waxes are often used on tubingas a rust inhibitor. Shopping Cart Summary. This is not agood surface condition for chemical bonding. This increases the capabilities of the chemicals by continu-ously replacing inactive, reacted product, with fresh chemical. Views Total views.
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Part Preparation Processes and Equipment 13 with a volume of water typically 3—5 gal overflowed to drain and made-up with fresh water to maintain relatively clean rinse water. The cleaner stage is usually heated to enhance the performance of the cleaning solution. Many of these soils can be effectively removed bymechanically abrading the surface. Mechanical methods, including wire brushing,abrasive blasting, grinding, and sanding, are used to smooth as well as clean surfaces.
Mechanical cleaning with a hand-held grinder or a manual blast system can be veryeffective, but it is very labor intensive. In-line blasting can be used to automate theprocess. Mechanical cleaning is sometimes the only way to remove excessive dirt,rust, or scale.
Blasting operations can be manual batch systems or automated in-line systems. Blasting systems can use high-pressure nozzles or a centrifugal wheel to deliver theblast media. Nozzle blast systems require compressed air for delivery of the media,while a wheel system uses centrifugal force. Even though the compressed air is anadded cost, it may be necessary to direct nozzles into hard to reach areas of a part.
The blast area must be enclosed to contain the blast media and dust. A blasted surface will create a very good anchor pattern for a coating. A blastsystem does not require as much space as a spray washer.
Adequate coveragewith the coating material is critical, if extended life is expected over a blast-onlysurface. Handheld air-blast systems are very dependent on the concentration of the oper-ator, and the quality may vary.
Blast cabinets are often suction-feed systems thatdraw particles into the spray gun by induced vacuum and accelerate the media with ametered stream of compressed air. Pressure-blast systems use a pressurized vessel todeliver the media, providing higher nozzle velocity that can clean the surface muchfaster than a suction system. Blast cabinets function similar to any booth designed for containment of over-sprayed material.
Negative pressure within the cabinet is maintained with a fan that The scrap material that is separated out of theairstream is collected for disposal in a container attached to a dust collector. Turbine-blast systems use high-speed turbine wheel with blades.
The media ismetered to the center of the wheel where it is fed onto the blades, which sling theparticles at the surface being blasted. Abrasive blasting is most often used for the preparation of heavy structural parts,particularly HRS welded components.
It does an excellent job of removing rust,smut, carbonized oils, and inorganic surface contaminants that are characteristicof this type of product.
It can also effectively remove organic soils as long asthe blast media is maintained to avoid a buildup of oil that can cause contamina-tion. The blasting dust needs to be washed away or blown off before the coating isapplied. Less aggressive media will remove most soils without cutting too deeply into themetal and leaving a visible texture on the metal surface. More aggressive mediacan be used to cut stubborn encrustations, such as red oxides, but it will leave moretexture on the surface.
A blast system requires less space than a spray washer that uses chemical clean-ing and it does not generate any wastewater. The degree of cleaning with the blast operation depends on the qualityrequirements of the surface. The principal four grades ofblasting endorsed by the SSPC are as follows: White metal blast: Removal of all visible rust, mill scale, paint, and foreign matter.
Used for conditions where corrosion resistance is very important and the environment is highly corrosive. Near white metal blast: Used for harsh environments where product is exposed to heavy usage.
Commercial blast: Blast cleaning until at least two-thirds of the surface is free of all visible residues. For applications where tightly adhering contaminants are allowable on the surface; used for products with lower quality standards and noncorrosive environments. Plaster, H.
Brush-off cleaning: Acceptable in noncorrosive environments where long-term coating life is not expected. Some natural by-products arealso used for blasting, such as walnut shell or corncob. Other blast materials aremanufactured using a variety of metal and nonmetal compositions such as steel, iron,aluminum oxide, silicon carbide, plastic, wheat starch, and glass bead. The size of the media particles will affect the blast pattern. Other media selectioncriteria include how well it will cut, how well it will recycle, and how much it cost.
It is also important to know if there are any health and safety issues, such as lungproblems associated with silica, and if the media will leave by-products on the surface,such as oils from walnut shells. Table 1. In addition to the comparative issues listed in Table 1.
Hard grit media such as aluminum oxide will cut faster and deeper than soft,angular media such as plastic or agricultural grit. Mineral, ceramic, or metallic gritmedia are used in air-blast systems. Iron and steel media are more often used inturbine-blast equipment. Mineral slag 8—80 A 85— 7.
Steel grit 10— A 8. Steel shot 8— S 8. High 6—8 Med. Glass bead 10— S 85—90 5. High 8—10 Med. Wheat starch 12—50 A 90 2. Paint Technology Handbook The recirculated material will not be as effective, and the surface willvary widely after blasting.
They will remove the roughness anddried-on compounds that are often present on a cast surface or the burrs left behindon a sawed edge. Vibratory cleaning will leave some residue on the surface, and it isa good idea to spray clean parts after the vibratory polishing so that and residualcleaning compound is removed before coating. Chemical cleaningmethods include wiping the part with a rag, dipping the part into a solution, or usinga spray cleaning system.
The cleaner may be alkaline, acidic, neutral, solvent, oran emulsion. The particular cleaner and process used will depend on the soils to beremoved, the size and substrate material of the part, the type of coating to be applied,and the quality goals for the product.
A review of thevarious methods of applying a chemical cleaner helps to understand these strengthsand limitations.
This would normally involve hand-wiping parts with a solvent oraqueous water based cleaning solution. Manual cleaning can be somewhat effectivein terms of soil removal but is very costly in terms of labor and very slow in termsof production time.
Because of this, hand-wiping of parts is rarely done except on aspot basis. Hand wiping with a clean cloth does not require any capital investment, but it isnot very effective at soil removal; it has a high labor content, is inconsistent, and maycreate health and safety problems. Immersion systems can be either static still or agitated.
Immersion cycle times aretypically longer than spray cleaning methods, because spray systems have the addedcleaning power of mechanical energy from spray pressure. Systems with no agitationrequire longer cycle times, and they are not as effective. This aids in the overall speed ofreaction taking place between the cleaning compound and the soil. Agitation may beachieved in the tank through air addition or blade mixing. Some dip systems mayalso use a hoist to lift a basket of parts up and down in the tank to provide agitation.
Dip systems normally require higher chemical concentration than spray systems andlonger operation times, even with agitation.
Many systems use some immersion cleaning along with spray stations. Automotive systems often include some immersion stages to make sure that all ofthe surfaces of the product are fully wetted and dirt is loosened inside and outside ofthe part.
The use of immersion with spray stages can enhance overall performance. A manual operator has the time to focus attentionon stubborn soils and hard-to-reach areas, providing very thorough removal of soils.
Spray wands are often used for larger parts that cannot be easily transported throughautomated systems. The spray wand is used inside a booth. The booth encloses the process so thatthe water vapors is captured and exhausted to atmosphere.
High-pressure spray wands can use hydraulic pressure as the force to do thecleaning. This type of cleaning is done at pressures ranging from to psi. This type of washing is done with or without cleaning compounds. Steam generators are sometimes used to produce dry saturated steam for spraycleaning. In a coil-type, forced-circulation steam generator, water is forced into thecoil toward the discharge point.