Definition
A wirewound coating rod is a laboratory tool used to prepare uniform, controllable thickness wet film coatings on the surface of a flat substrate. It is typically constructed of a metal rod precisely wound with stainless steel or alloy wire, which quantitatively transfers liquid samples through the gap between the wire and the rod, resulting in a wet film of a specific thickness.
How it works:
The working principle of wire wound coating rods is based on gap metering. When the operator places the appropriate amount of sample at the front of the substrate and pushes the coating rod at a steady speed, the wire wrapped around the rod holds the sample up and forms a series of parallel gap channels between the rod and the substrate. The liquid passes through these gaps under the action of surface tension and shear force and is uniformly scraped on the surface of the substrate, and the thickness of the wet film is mainly determined by the diameter of the silk thread (i.e., the gap height). The relationship between wet film thickness (WFT) and wire diameter (d) can be approximated as WFT ≈ k × d, where k is the correction factor related to the rheological properties of the liquid.
Measurement method
After the coating is prepared using a wire-wound coating rod, the wet film is usually quantitatively evaluated. Common measurement methods include: multi-point measurement immediately after application using a wet film thickness comb gauge to check uniformity; After the coating is cured, the dry film thickness is measured by micrometer or film thickness meter, and verified by estimation of solid content. Visually inspect the flatness and defects of the coating under specific lighting conditions. The operation process strictly adheres to the environmental conditions, coating speed and pressure requirements specified in relevant international standards such as ASTM D823.
Influencing factors
The coating effect is affected by a variety of factors. In terms of coating rod parameters, the diameter of the silk thread, the winding spacing, the length and material of the rod are the key. Under operating conditions, push speed, applied pressure, and coating angle affect the uniformity of the coating. Sample properties such as viscosity, leveling, solids content, and wettability to the substrate also directly determine the film formation quality. Ambient temperature and humidity can alter sample flowability, which in turn affects the final film thickness.
Applications:
Wire wound coating rods are widely used in industrial R&D and quality inspection processes that require the preparation of standard thickness coatings. Typical applications include: the coatings industry to prepare test samples to evaluate coverage and weather resistance; Deposition of functional material layers in the field of printed electronics; The adhesive industry prepares uniform films to test bonding properties; and laboratory sample preparation in the fields of optical films, paper coatings, textile finishing agents, etc. The value lies in the ability to simulate the actual coating process quickly and repeatedly.
Key points of selection
When choosing a wire-wound coating rod, it is necessary to consider multiple technical parameters. First, determine the wire diameter specification series according to the target wet film thickness. The rod length should be slightly wider than the substrate. Corrosion resistance is a consideration, and stainless steel is suitable for most chemical samples. The winding structure should be uniform and tight, ensuring consistent clearance. In addition, ease of operation, such as the ergonomic design of the handle, is also evaluated. It is recommended to refer to the requirements for coating tools in relevant industry standards (such as ISO standards) and conduct verification tests in combination with actual samples.