Why perform the full set of tests, including cross-cut, circle-cut, and pull-off methods, if the adhesion is clearly qualified?

 PART.01-First correction: there is no "universal adhesion", only "scene based adhesion"

The core pain point of coating adhesion: Different stress environments result in completely different ways of coating detachment.

Daily single adhesion screening can only verify basic adhesion, while in practical applications, workpieces will face multiple tests such as scratching, pulling, thermal shrinkage, and external tearing. Especially for thick coating systems of powder coatings and flexible coatings of water-based coatings, the stress characteristics vary greatly, and a single detection cannot avoid quality hazards.

Simply put, the grid drawing, circle drawing, and pull off methods comprehensively lock the adhesion of the coating from three dimensions: shear, local pulling, and overall tensile strength, covering all risks from conventional to harsh working conditions.

PART.02-Grid method: rapid screening, measuring the "basic fastness" of daily wear and scratch resistance

Core positioning: Qualitative rapid detection, industry entry-level screening standard

The grid method (hundred grid test) is the most commonly used adhesion testing method in the coating industry. According to the GB/T 9286 standard, it is easy to operate and highly efficient, suitable for batch inspection in workshops, sampling of finished products, and on-site inspection.

Testing principle: Cut a standard grid on the surface of the coating with a specialized tool, penetrate the coating until the substrate is reached, and then use standard tape to stick and tear it. Divide the grid detachment area into 0-5 levels to determine whether the adhesion is qualified.

Adaptation scenarios (with a focus on adapting our products)

• Water based thin coating: thin coating for hardware components and indoor equipment (≤ 60 μ m)

• Conventional powder coating: flat and thin coating workpieces for household appliance shells and decorative hardware

Advantages, disadvantages, and limitations 

✅ Advantages: Fast speed, low cost, on-site operation, suitable for large-scale daily quality control, able to quickly screen out defective products with poor coating adhesion.

❌ Shortcomings: Can only be qualitative, not quantitative. Only able to determine whether to detach, unable to measure specific tensile strength values; And it is not suitable for thick coatings and high hardness anti-corrosion powder coatings with a thickness greater than 120 μ m, which can easily lead to "false qualification".

Key conclusion: If the grid is qualified, it can only indicate that the coating is resistant to daily scratching, sticking and pulling, and may still peel off under strong stretching, cold and hot deformation, and heavy external forces.

PART.03：Circle drawing method: measuring the "crack resistance stability" of local stress

Testing principle: A sharp rotating needle draws overlapping circular rolling lines under the pressure of a weight, cutting through the paint film until the substrate is reached. The rating is based on the peeling of the paint film in the scratched area; Level 1 is the best, level 7 is the worst, suitable for flat single paint films on hard substrates (steel, aluminum, etc.), not suitable for soft substrates, thick coatings, and elastic coatings.

Adaptation scenarios (with a focus on adapting our products)

•Water based industrial coatings: mechanical equipment, hardware accessories, workpieces that can withstand local friction and slight pulling for a long time

•Medium thick layer powder coating: non super thick coating for outdoor hardware, fitness equipment, automotive parts and small components, etc

Core Values

•Domestic metal baking paint, anti rust primer, anti-corrosion paint, hardware coating, a large number of old standards, technical agreements, and acceptance clauses directly reference the GB/T1720 circle drawing method. Many customer drawings and warehouse inspections specify this method, which has compliance and contract matching value.

•Simulate the combined force of point pressure and shear, reflecting the anti peeling ability of the paint film by rotating the needle to roll and draw circles. It is not simply cutting, but a composite stress of compression, scratching, and tearing, which is closer to the working conditions of hard object collision and scratching. It is highly sensitive to hard and brittle paint films (epoxy, alkyd, amino baking paint), and can show the bonding strength between the paint film and the metal substrate.

PART.04-Pull open method: high-end quantitative measurement, measuring the "real adhesion strength" of extreme working conditions

Core positioning: Quantitative ultimate detection, high-end engineering, and strict anti-corrosion acceptance must pass the standards

The pull-out method is the "ceiling" of adhesion testing, and according to GB/T 5210 and ISO 4624 standards, it is also a mandatory acceptance item for many clients and engineering orders, which is completely different from the first two qualitative tests.

Test Principle

Adhere the standard test column firmly to the coating surface, and stretch it vertically at a constant speed through the equipment until the coating is damaged. Accurately measure the tensile strength per unit area (MPa), and define the adhesion level with specific values, rather than vague level determination.

Adaptation scenarios (with a focus on adapting our products)

Thick layer powder coating: steel structures, pipelines, engineering machinery, heavy-duty anti-corrosion equipment (coating thickness>120 μ m)

High end water-based anti-corrosion coatings: long-term protective coatings for outdoor steel structures, bridge fittings, and industrial equipment

All engineering projects that require the issuance of quantitative testing reports, bidding acceptance, and quality assurance accountability

By dividing and circling the core values, we can see the "surface detachment", and the opening method can directly hit the core: accurately distinguish whether it is due to insufficient coating adhesion, cracking of coating cohesion, or substrate pre-treatment problems. Many workpieces have a level 1 grid cut and no detachment in the circle cut, but the pull-out method value is low, indicating that there are hidden defects inside the coating. After cold and hot cycles and long-term weathering in the later stage, peeling and detachment will inevitably occur.

Key conclusion: Achieving the standard value of the pull-out method is the hardcore guarantee for the long-term durability and adaptability to harsh working conditions of the coating, and is the core proof of product high-end and engineering compliance.

PART.06-Manufacturer's expertise: Our company's standardized testing logic

As a professional manufacturer of water-based coatings and powder coatings, we never neglect quality control with a "single test qualified" approach. Instead, we have established a three-level adhesion quality control system to eliminate customer after-sales problems from the source Daily mass production: The grid method fully covers the batch inspection of each batch of products before leaving the factory, quickly screening for products with poor basic adhesion, and ensuring the use of regular workpieces. 2. Finished product verification: Precise re inspection using the circle marking method is targeted at medium thick coatings, irregular workpieces, and customized products, with a focus on detecting weak areas such as corners and seams to avoid potential local detachment hazards. 3. Engineering orders/high-end products: All heavy-duty anti-corrosion, outdoor long-lasting, and bidding engineering products must be quantitatively inspected using the pull-out method, and a pull-out method numerical report must be issued to accurately lock the long-term adhesion of the coating with MPa values, meeting the strict acceptance standards of Party A.

About Us

One stop water-based paint solution service provider

We are a source factory specializing in independent research and development and production of water-based industrial paints, deeply cultivating a full range of categories such as water-based amino baking paint, metal anti-corrosion paint, and hardware topcoat, The company adheres to craftsmanship and quality, aligns with international standards, continues to promote global layout, and is committed to serving the global market with domestically produced green coatings.

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