POWDER COATING

PRETREATMENT

Generally the meaning of pretreatment is to activate  the surface area of the object for the next process like coating or painting. Pretreatment is mainly 2 types.

     1. Phosphate

     2. Chromating

1. Phosphate

     Phosphate is also known as coating process. There are only 2 main type of phosphate found.

       I. Zinc Phosphate

      II. Iron Phosphate

I. Zinc Phosphate

        Zinc phosphate is a pretreatment process used on ferrous and galvanised material. In this process corrosion resistance and adhesion both are very high. Zinc phosphate in pretreatment system provide a very good salt spray corrosion protection in comparison to iron phosphate.

II. Iron phosphate

      Iron phosphate is a pretreatment process used on ferrous material. In this process corrosion resistance and adhesion both are good for coating process. The iron phosphate in pretreatment system provide good salt spray corrosion protection  but lower than in comparison to iron phosphate.

          PRETREATMENT PROCESS

Pretreatment process generally depends on few steps like:-

NOTE:- General all the steps of this process are in dip. Mainly all the material are dip in the tank of chemical. But in some cases according to the properties and size of material the process is done by spray also.

       Here the process tank volume are depends on the quantity and size and requirement of the material.

       In this process we use industrial water, DI water and DM water according to the chemical concentration and process.

a. WATER RINSE

  This process have not more work. By this process we remove surface impurities. So this process have very negligible work but we can't omit. When the material comes from one tank to other some chemical in liquid form are found in the surface area of the material. By which the chemical composition of the other tank will change. For this separation of chemical we used water tank.

b. DE GREASING

   The degreasing process based on removal of oil, grease and heavy rust from the surface area and make a degreasing layer coat on the object surface area. How ever this will affect the life of the life of coating layer. In any pretreatment process degreasing is one of the most important stage.

c.  DERUSTING

   Fabricated and machining material are storage for some day before come to pretreatment process. By which the material come in contact with atmosphere. In atmosphere iron-oxide is formed, when iron and oxygen react in the presence of water or moisture in the presence of air. Iron-oxide is very common, because iron reacts easily with oxygen in the air. so material got rust in surface. Before pretreatment we can use grease and oil to keep distance from rust. But after pretreatment we can't use grease or oil. In this process derusting chemical play a very important role. The desusting chemical make some derusting crystal. Because of cathode electro deposition process the crystal are make a bonding in surface area and make a derusting layer.

d.  SURFACE ACTIVATION

   Surface activation is used to obtain batter adhesion properties of a material. Surface activation increase the surface energy of the of the material. Surface activation is most commonly achieved by adding oxygen to the material surface.

e.  PHOSPHATING

   Phosphating process can start when all the above process are completed. In this process phosphating liquid formed a phosphate coat in the metal surface. Phosphate coat make the metal surface area more adaptive for future process.

f.  PASSIVATION

g. FREASH DM WATER RINSE

POWDER COATING

The general meaning of powder coating is cover with a polyester or epoxy powder, which is then heated to fuse into a protective layer.

       Powder Coating is a type of coating process, which is applied at the free matel surface area by dry powder. In this process liquid medium not required.

       The powder coating is typically applied electrostaticlly and then cured under heat. It's usually used to create a hard finish that is together a conventional paint.

  POWDER COATING PROCESS

       According to design complete part doesn't need powder coating. The surface area of the material which not need coating are covered by mask. The masking process is completed by the help of of high temperature tape, high temperature paper, caps and plugs. These are specially designed for powder coating. After masking the object is ready for powder coating.

       Now hang the object in hanger in a sequence in loading area. Now connect a iron wire from object to the hanger which is connected to earthing.


Generally powder application in powder coating to the object is to spray powder by the use of electrostatic gun or corona gun. The gun imparts a positive electrical charge to the powder, then accelerated toward the workpiece by powerful electrostatic charge through the spray nozzle, which is then sprayed towards the object surface by mechanical or compressed air pressure. Then the object should heated and the powder melts to a uniform film. The object first cooled to the room temperature and form a hard coating.

  

Modular Multicyclone

Post Filter

In powder coating process so many instrument are use.Modular Multicyclone is one of them. Modular Multicyclone use to reduce the wastage of  powder in powder coating. The capacity of collecting powder from the spray booth is very high.This system is fully Human friendly. 

Integration Concept

            Generally powder application in powder coating to the object is to spray powder by the use of electrostatic gun or corona gun. The gun imparts a positive electrical charge to the powder, then accelerated toward the workpiece by powerful electrostatic charge through the spray nozzle, which is then sprayed towards the object surface by mechanical or compressed air pressure. Then the object should heated and the powder melts to a uniform film. The object first cooled to the room temperature and form a hard coating.

QUALITY CONTROL

PRE_TREATMENT  QUALITY

            Degreasing:-

       Pointage.

● Take 10ml of degreasing bath sample.

● Add 2~4 drops phenophthlein indicator.

● Titrate against HCL(Hydrochloric Acid).

● Note the pointage when pink color converted to color less solution.

              Derusting:-

        Pointage.

● Take 10ml of derusting bath sample.

● Add 90ml DI water in taken bath sample.

● Take 10ml from the 100ml solution.

● Add 2~4 drops methyl orange indicator.

● Titrate against o.1N NaOH(Sodium Hydroxide).

● Take the pointage when orange color converted to yellow color.

                  Phosphating:-

             Pointage.

● Take 10ml phosphating bath sample.

● Add 2~4 drops phenophthlein indicator.

● Titrate against 0.1N NaOH(Sodium Hydroxide).

● Note the pointage when color less solution converted to pink color.

POWDER COATING QUALITY

     In powder coating quality control is most important. To verify the fulfillment of product quality and customer satisfaction we do quality. For which conducting some test and inspection is needed.

               ◎ Visual Color

               ◎ Dry Film Thickness

               ◎ Film Hardness

               ◎ Adhesion

               ◎ Visual Inspection

    Some other important test are:-

               ◎ NSS test

               ◎ Humidity test

               ◎ EMT test

      ◎ Visual Color

     After powder coating color variation is a very big problem. So according to the customer provide coated sample part color inspection is most important.

     Required Equipment:-

         1. Highly lighting area

         2. Properly coated panel

     Procedure:-

● Prepare a panel according to customer recommendation.

● Powder coat the panel and apply heating on it.

● Allow panel to cool to room temperature.

● Select the proper lighting area and then compare the panel with sample part.

     Result:-

   Report the result as pass or fail.

NOTE:: The proper light source depends on the customer requirement.

       ◎ Dry Film Thickness

      After powder coating we check DFT of the object. By DFT we check the thickness of the powder which is coated on the object surface.

     Required Equipment:-

          1. Properly coated object

          2. DFT Gauge

    Procedure:-

● Powder coat the object and apply heat on it.

● Allow the object to cool down to room temperature.

● Now check the thickness of the coating by using DFT Gauge and note down the result.

      Result:-

    Report the result as pass or fail.

NOTE:: The thickness of the film coat should be within a tolerance which should be provided by customer.

     for example: 70μ to 90μ

             ◎ Film Hardness

       To determine the hardness of coating on a substrate in terms pencil leads of known hardness.

     Required Equipment:-

          1. Properly Coated surface

          2. Calibrated Pencil

          3. Abrasive Paper

     Procedure:-

● Powder coat a object, apply heat on it and cool down to room temperature.

● Rub the lead against the abrasive paper at an angle of 90° to the paper until a flat, smooth surface is obtained.

● Repeat the process down the darkness scale until a pencil is found that will not scratch the coating.

       Result:-

   Report the hardest pencil that will not scratch the coating. Unless specified as a "gauge" test by the customer. It is assumed that the scratch hardness will be reported.

NOTE::         4B - 3B - 2B - B - HB - F - H - 2H - 3H - 4H

      This is calibrated pencil scale from softer to harder.

              ◎Adhesion

     To assess the adhesion of coating films to material substrates by applying and removing pressure sensitive tape over the cuts mate in the film.

      Required Equipment:-

             1. Properly coated panel

             2. Cutting tool

             3. Adhesion tape / Semi transparent pressure sensitive tape

       Procedure:-

● Prepare a panel according to customer recommendation.

● Powder coat the panel and apply heat on it.

● Allow the panel to cool down to room temperature.

● Applying cutting tool make 25 square oh 0.5MM², 1MM² or 2MM² each. According to film thickness.

● Put the semi transparent pressure sensitive tape over the grid and smooth into the place by finger.

● Remove the tape from the grid rapidly.

       Result:- If the paint remove from the grid then this is found to be not ok.

NOTE:: The cause of paint removal is Poor Cleaning, Heating Temperature and Heating Time.

QUESTION

1. What is the difference between thermoplastic and thermoset powder coating?

2. How do I spray powder? What make it stick?

3. Why we need spray booth? How is the powder reused?

4. What about curing ovens?

5. Can I touch up powder coating?

6. What is DI water?

7. What is DM water?

8. Why I do earthing?

9. Write the type of spray nozzle.

10. What type of problems are found in phosphating material?