English
I. Purpose of the Process
When the old paint film on workpieces suffers from coating defects, transportation damage or aging damage and re-hot-dip galvanizing is required, the old paint film must be removed. Old paint removal methods fall into three categories: mechanical method, flame method and chemical method.
II. Three Types of Old Paint Removal Methods
1. Mechanical Method
It includes manual/power tool grinding, high-pressure water jetting and shot blasting (sand blasting), which can effectively remove old paint.
2. Flame Method
A kerosene blowtorch or oxyacetylene flame is used to burn the paint film to make it char, soften and blister, followed by scraping with a scraper.
Advantages: Fast paint stripping speed.
Risks: Improper control may easily cause thermal deformation and burning of workpieces.
3. Chemical Method, divided into alkaline solution method and paint remover method.
(1) Alkaline Solution Method
Principle: The alkaline solution corrodes, penetrates, swells and degrades the paint film, weakens the adhesion between the paint film and steel, and the softened paint is scraped off and cleaned with warm water.
Application: Workpieces are immersed in an alkaline solution tank, or paint stripping paste is prepared and applied to the surface of the paint film.
Features: Simple operation; long time consumption, usually several hours.
(2) Paint Remover Method
It is a solution or paste compounded of strong dissolving solvents, paraffin wax, cellulose, etc., divided into two major categories:
Type I (T-1, T-2): Emulsions of ketones, alcohols, esters and paraffin wax; T-1 is suitable for oil paint, ester gum paint and phenolic paint; T-2 has stronger paint stripping capacity and can treat oil-based paint, alkyd paint and nitrocellulose paint.
Type II (T-3, etc.): Mainly composed of dichloromethane; faster paint stripping speed, applicable to epoxy paint, polyurethane paint and other coatings.
Operation: Soak or apply at room temperature, and scrape off after the paint film swells and softens.
Advantages: High paint stripping efficiency and low corrosion to metals.
Disadvantages: High cost, toxicity, high volatility, and dichloromethane is flammable.