1.Why is the adhesion of the original cold-rolled coil poor?
Low surface energy: Clean metal surfaces have high surface energy, but during storage and transportation, a very thin oxide layer forms on the surface of cold-rolled coils, which also absorbs grease, dust, and moisture, reducing the actual surface energy and making it difficult for adhesives to fully wet and spread.
Surface contamination layer:
Rolling oil/rust inhibitor: Residual grease after cold rolling is the biggest enemy of adhesion.
Dust and impurities.
Unstable oxide layer: The initially formed oxide layer has a loose structure and low strength.
Overly smooth surface: The surface of cold-rolled coils is very flat, lacking the microscopic roughness required for mechanical bonding.
2.How to perform surface treatment to enhance adhesion?
**Cleansing and Degreasing (Basic Requirement):**
Use organic solvents (such as acetone, isopropanol) or specialized alkaline degreasers to thoroughly remove oil and grease. This is the foundation for all subsequent treatments.
**Mechanical Treatment (Improving Mechanical Adhesion):**
**Grinding/Roughening:** Use sandpaper, wire brushes, etc., to create micro-roughness, significantly increasing surface area.
**Sandblasting:** One of the most effective methods, thoroughly removing oxide layers and contaminants, and obtaining a uniform, robust rough surface, greatly improving adhesion.
**Chemical Treatment (Forming a Highly Active Surface Layer):**
**Phosphating:** The most classic and effective metal pretreatment method. It forms a porous phosphate crystal film on the steel surface. This film bonds firmly to the metal substrate and has a large surface area and strong polarity, enabling it to form strong physical adsorption and chemical bonds with adhesives. Widely used in automotive, structural bonding, and other fields.
**Passivation:** Primarily used for stainless steel, and also effective for cold-rolled carbon steel, forming a dense and stable oxide film.
Coating treatment (altering interface properties):
If the cold-rolled coil has already been galvanized, painted, or powder-coated, then the adhesion target becomes these coatings. In this case, a specialized adhesive optimized for these coatings needs to be selected.
3.How to choose the right adhesive?
Structural Bonding (High-Strength, Load-Bearing Components):
Epoxy Resin Adhesives: Extremely strong adhesion, high hardness, and good chemical resistance.
Reactive Acrylic Adhesives (e.g., AB glue, acrylic structural adhesives): High strength, good toughness, and impact resistance.
Polyurethane Structural Adhesives: Excellent flexibility and fatigue resistance.
Non-Structural/Sealing Bonding:
Silicone Sealants: Moderate adhesion but excellent elasticity and weather resistance; commonly used for sealing.
High-Performance Pressure-Sensitive Adhesives (e.g., VHB double-sided tape): Good adhesion to clean surfaces, easy to apply, and shock-absorbing.
4.What are the considerations for its application in medical wheelchair accessories?
Durability and Safety: High-standard surface treatments (such as phosphating and spraying) and high-strength structural adhesives are essential to ensure no delamination under long-term vibration, load, and cleaning/sterilization conditions.
Process Reliability: Adhesive bonding processes (cleaning, applying adhesive, curing) require strict control and are more dependent on process stability than mechanical fastening (screws, welding).
Comprehensive Solution: In actual production, adhesive bonding is often combined with mechanical interlocking (such as slot designs) or spot welding to provide multiple layers of safety.
5.What are the conclusions and recommendations?
Raw condition: Poor. Never apply adhesive directly to untreated cold-rolled coils.
Treatment condition: Can be achieved in excellent condition, meeting the highest requirements for industrial applications.
Best practice path:
Thorough cleaning and degreasing -> Sandblasting or phosphating -> Proceed to the next step as soon as possible (within hours).
Select a suitable industrial-grade adhesive based on the bonding requirements (strength, elasticity, temperature resistance, media resistance).
Strictly follow the adhesive's process requirements for application, assembly, and curing.
For critical safety components, always perform adhesion testing (e.g., ASTM D4541 pull-out test).