What is Degreasing process of pretreatment Process, Chemical Reaction of during Degreasing Process ,Testing of after degreasing process ,purpose of degreasing process ,

Degreasing Process :- 

The degreasing process is a critical step in the pre-treatment stage of painting. It involves removing oils, grease, dust, and other contaminants from the surface of metal components to ensure proper paint adhesion and corrosion resistance.

Purpose of Degreasing:-

  1- Remove oil, grease, and waxes left from manufacturing processes (like stamping, machining).

  2- Eliminate dirt, fingerprints, and other surface contaminants.

  3- Ensure strong adhesion of primer or paint.

 
  4- Improve corrosion resistance and surface finish.

Types of Degreasing Methods:-

1. Solvent Degreasing:-

   1. Uses organic solvents (e.g., mineral spirits, chlorinated solvents)
   2. Suitable for manual cleaning or small parts.
   3. Not eco-friendly; risk of fire and health hazard.

2. Alkaline Degreasing (Hot):-

                (a) Uses alkaline solutions (like sodium hydroxide, phosphate-based cleaners).

                (b) More common in automated spray or dip systems.

                (c) Removes oil and dirt effectively.

Emulsification 

Used for mineral-based industrial oils (most common in factories)

      1-Surfactants in the degreasing chemical attach to oil molecules.

      2-They form micelles: tiny droplets of oil surrounded by surfactant molecules.

      3-These droplets are suspended in water as an emulsion.

      4-Oil can now be washed off easily during rinsing.

 Micelle Action:

• Hydrophobic tail → sticks to oil
• Hydrophilic head → sticks to water

Degreasing Process Flow in Paint Shop (Spray or Dip):-

1. Loading

    (a) Material is loaded on racks or conveyor.

    (b) Ensure no excessive oil dripping.

2. Degreasing (Spray or Dip)

   (a)- Tank temperature: 50–60°C

   (b)- Chemical: Alkaline-based degreaser (Fine Cleaner 4449 , Gardoclean444, etc.)

   (c) -Concentration: 2–5% by volume

   (d)- Time: 3–5 minutes

   (e)-  Action: Removes oil, grease, dirt.

3. Water Rinse – I

• Removes degreasing chemical + oil residues.
• Water: DM or Soft water preferred.
• Overflow-type tanks keep water clean.

Tests for Degreasing Effectiveness:-

1. Water Break Test:

(a) After rinsing, spray DI water on the Panel Substrate .
(b) If water runs off in a sheet → Clean.
(c) If beading/droplets form → Still oily.

      2. White Cloth Wipe Test:

(a) Rub with clean cloth.

(b) No stains or oil marks = Clean. 

      3. PH and Titration:

(a) Check chemical concentration using titration.

Common Problems and Troubleshooting:-

Issue	Cause	Solution
Poor paint adhesion	Incomplete degreasing	Check temp, concentration, or increase time
Foaming in tank	Contaminated water or wrong surfactant	Use defoamer, replace bath
Rusting after Degreasing	Prolonged rinse or delay before phosphating	Minimize time gap, use water displacement
Sticky surface	Chemical not rinsed	Ensure proper rinsing stages
Foul smell	Oil contamination or microbial growth	Refresh bath, use biocide

Why Remove Oil & Purpose of Degreasing Process:-

(a) Oil acts as a barrier between the metal and the paint.
(b) If not removed, it causes:

1. Poor paint adhesion
2. Peeling, flaking
3. Corrosion under the paint film
4. Poor electrical contact in CED coating

Function of an Oil Skimmer in a Degreasing Tank :-

An oil skimmer is used in a degreasing tank to remove floating oil, grease, and contaminants from the tank surface. Its main functions are:

1. Removes Free Oil & Grease
   During degreasing, oil and grease separate from components and float on the surface. The oil skimmer continuously collects and removes this layer.

2. Maintains Cleaning Efficiency
   By removing surface oil, the degreasing chemical remains effective and does not get saturated with contaminants.

3. Prevents Re-contamination
   Floating oil can stick back to parts during immersion or spraying. The skimmer avoids this problem and ensures clean surfaces.

4. Extends Bath Life
   Continuous oil removal reduces chemical breakdown and increases the working life of the degreasing solution.

5. Improves Coating Quality
   Clean, oil-free parts improve phosphating, CED, powder coating, and paint adhesion.

6. Reduces Sludge Formation
   Less oil in the bath means lower sludge generation at the tank bottom.

7. Supports Easy Maintenance & Cost Saving
   Fewer bath dumps, lower chemical consumption, and reduced downtime.

Disc Type Oil Skimmer – Function & Working (Degreasing Tank):-

A Disc Type Oil Skimmer is widely used in degreasing and pretreatment tanks to remove floating oil and grease from the liquid surface.

Working Principle

1. A slow-rotating disc (usually SS or polymer) partially dips into the degreasing solution.

2. Oil adheres to the disc surface due to oleophilic (oil-attracting) nature.

3. As the disc rotates upward, scraper blades remove the oil from the disc.

4. Collected oil flows into a collection tray or drain line.

5. Clean solution falls back into the tank.                                                                  

                                           

                              

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