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Electrocoat (Manufacturing Process (Coating))

Electrocoat (old)

Electrocoat is a kind of dip coat, in which the part is electrically charged and then dipped into a paint bath that has been given an opposite charge. This improves adhesion and permits use of water-based paints(which reduce fire and pollution hazards). (Mikell P. Groover; Fundamentals of Modern Manufacturing Materials, Processes, and Systems 3rd Edition; pg.682)

Electrocoat (new) (better)

Electrocoating covers all dip paintinting processes, where the paint precirpitates on the workpiece owing to chemical conversion and associated coagulation of the binder. These conversions are caused by an electric current flow from an external electrode via the conductive paint, to the workpiece. The advantages of the electrocoating process are follows:

- complete and uniform coating, also in cavities;

- very good corrosion protection;

- no formation of drops and runners;

- very low paint losses with the corresponding purging techniques;

-very good possibilities of process and quality control;

- electrocoat installations are fully automatic, and are constinuously operated.

(Automotive Paints and Coatings, Yazar: Hans-Joachim Streitberger,Karl-Friedrich Dössel, page:261)

Roller Coating (Manufacturing Process (Coating))

Roller Coating (old)

Roll coating is a mechanized technique in which a rotating roller is partially submersed in a pan of liquid adhesive and picks up a coating of the adhesive, which is then transferred to the work surface. Figure 32.14 shows one possible application, in which the work is a thin, flexible material (e.g., paper, cloth, leather, plastic). Variations of the method are used for coating adhesive onto wood, wood composite, cardboard, and similar materials with large surface areas.

(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 760)

Roller Coating (new)(better)

Roller coating is a highly mechanized and closely controlled process for coating flat stock. It provides a means for applying a fixed amount of liquid coating to one or both sides of any sheet or strip requiring an even coating. Tuhs, roller coating is used for applying photoresists to copper-laminate stock on which etched circuitry is subsequently formed, in applying solder maskants to printed wiring boards, and in applying thin dielectric films on metal foil in fabricating capacitors.

In roller coating, the liquid coating is transferred from a reservoir pan to the flat surface by means of a series of metering and printing rolls. The prining roll may be embossed to lay down a pattern or the metering roll may be lithographed top rint a functional or decorative design. After coating, the part is passed through the dring and curing zones of an oven, and the sheet are stacked or the strip is rerolled. Roller coating is widely used commercially for applying decorative coatings to metal stock for cans, bottle caps, toys, television parts, automobile instrument panels, and ligthening fixtures.

  (Coating Materials for Electronic Applications: Polymers, Processes ,Reliability,Testing , Yazar: James J. Licari, page:246)

Flow Coating (Manufacturing Process (Coating))

Flow Coating (Old)

Flow coating essentially involves saturating a part suspended from a moving rail by the use of two or more spray heads. The excess paint drains from the part as it moves through the spray booth and is collected and recycled. Compared with actually dipping the part in paint. it has the adventage of reaching corners without being impeded by pockets of entrapped air
(Weldon D.G., Failure Analysis of Paints and Coatings, 2009, 127-128)

Flow Coating (new) (better)

Flow cating is often employed for items that would be difficult to dip because of their size or shape, or as a means of avoiding the installation and operation of large dip tanks. A flow coating system operates by using high pressure sprays to flood the item with solvent-based paint. After spraying, the item is allowed to drain and the excess paint is recirculated. Since a considerable amount of bubling occurs due to spraying, the item is then passed through a solvent chamber where the solvent vapors allow the paint to reflow. Following this operation, the item is then oven-dried. The main disadvantage of flow coating is high solvent loss, which can be three times as large as for dipping and twice as great as for spraying.

(Metal-bearing Waste Streams: Minimizing, Recycling, and Treatment, Yazar: Michael Meltzer, Page:92)

Dip Coating (Manufacturing Process(Coating))

Dip Coating (old) (better)

Dip coating is one of the simplest and oldest methods of painting industrial goods. It is easy to use to automate, has a much higher material yield when compared with spray coating and low capital costs. The process makes use of the adhesion properties of viscous paints on the objects to be painted. Its disadvantages are the lack of prpcessing window with regard to film thicknesses and the defects associated with it, such as runs and blisters, the costs and the need for special precautionary measures to avoid explosions or fires when using solventborne paints. As a result of these dangers and corresponding incidents practically only waterbased dip coats are now used in the few still operating conventional systems.

(Artur Goldschmidt, BASF Handbook On Basics Of Coating Technology,p.478)

Dip coating (new)

Dip coatings are applied by dipping a heated object in liquid dispersions or solvent mixtures of plastics. The most common plastics used is polyvinyl chloride. For dispersions, a heating cycle is required to fuse or cure the plastics on the coated object. However, some dip coatings may harden by simple evaporation of solvents. Generally, 10 minutes of heating is needed for each milimeter of coating thickness. Curring temperatures range from 175°C to 190°C [350°F to 375°F]. Tool handles and dish-drainer racks are examples of the most common dip-coated products. Objects are limited by the size of the dipping tank.(Fig)

(Industrial Plastics: Theory and Applications, Yazar: Erik Lokensgard, page:296)

 

Curtain Coating (Manufacturing Process (Coating))

Curtain Coating (old)

In curtain coating, the momentum of the falling curtain aids in holding the coating liquid against the web and opposing air entrainment. Thus the velocity of the faling curtain, determined by the height of the curtain and also by the velocity of the liquid film leaving the slide, helps determine of the maximum coating speed. Also, as with both slide and slot coating, the flow rate itself is very important, aside from the need for a minimum flow to form the curtain. If the web stationary, the curtain on striking the web will split in the opposite direction. As the web starts moving, more of the flows goes in the direction of the web.Above some speed, all the liquids moves in the web direction. But even when all the liquid moves in the  web direction, at speeds just above the minimum, some liquid still goes backward a short distance before turning forward, to form a heel, as shown by Kistler(1984).

(Edgar B. Gutoff, Edward D. Cohen, Coating and Drying Defects: Troubleshhoting Operating Problems, p. 127) 

Curtain Coating (new) (better)

Curtain coating is used principally in the furniture industry to coat plane surfaces such as cupboard walls and door panels, etc. The process is also suitable for coating sheet metal and for paper and card. The coating is generally applied by transporting the workpieces on a conveyor belt through a curtain of coating material flowing from a narrow, adjustable slit (see fig.). 

 The coating material is continously recirculated and replenished, and also filtered and cooled as required. The thicness of the coating film can be adjusted by altering the width of the slit and the throughput rate of the workpieces. Film thicknesses are usually between 20 and 500

µm. With narrower film thicknesses the surface smoothness may not be adequate. In such cases vacuum feed heads have proved useful: reduced pressure in the feed head expands the slit and allows a more uniform coating tobe obtained.

Curtain coating is generally used with UV or electron beam curring coatings, but it is also suitable for two-component coatings (base and hardener are applied with different feed heads).

Curtain coating can produce a very good surface quality with almost 100 % yield, but it is only suitable for plane or very slightly convex components, or for profiles of a similar type.

(European Coatings Handbook,Yazar: Thomas Brock,Michael Groteklaes,Peter Mischke, page:277)