Metal Wire Woven Mesh Testing

Metal wire woven mesh inspection mainly conducts scientific testing and analysis on the mesh count testing, wire diameter testing, aperture size testing, mesh thickness testing, material composition analysis and surface quality inspection, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Mesh count testing: Refers to the number of the apertures per inch or per centimetre of length, and is the core parameter for measuring the weaving density of the metal wire woven mesh. During the testing, at least 3 different positions need to be selected in any direction on the mesh surface, and a magnifying glass with a scale or a mesh count measuring instrument is used for the counting, ensuring that the measurement areas contain the complete warp and weft wires. The average value is calculated to evaluate the weaving uniformity.

Wire diameter testing: That is, the diameter of the metal wires constituting the woven mesh, directly affecting the strength, open area and filtration precision of the mesh. A micrometer with the precision not lower than 0.01 mm or a laser diameter measuring instrument is usually used for the measurement. The measurement should be carried out at the different positions of each tested wire (avoiding the nodes) for multiple times, taking the average value, and the warp and weft wires should be distinguished and recorded separately.

Aperture size testing: Refers to the net distance between the opposite sides inside the aperture, and is the key indicator determining the filtration and screening performances. The testing methods include the use of a reading microscope with a scale, projector or dedicated aperture measuring instrument. Multiple apertures need to be measured, and the maximum, minimum and average values are counted, to evaluate the uniformity of the aperture size distribution.

Mesh thickness testing: Refers to the overall thickness of the metal wire woven mesh in the natural flat state. A flat plate and dial indicator or digital thickness gauge are used for the measurement, and the probe diameter should be larger than the aperture size to avoid sinking into the holes. Multi-point measurements need to be carried out in the different areas of the mesh surface, to evaluate the flatness and uniformity of the weaving.

Material composition analysis: Used to confirm whether the material of the metal wires used for the woven mesh meets the requirements, such as the stainless steel, brass and low-carbon steel. The spark identification method can be used for the preliminary judgement, and the precise analysis requires the use of a spectrometer or chemical titration method, detecting the contents of the key elements such as the carbon, chromium, nickel and molybdenum.

Surface quality inspection: Checks whether there are the defects affecting the use on the mesh surface, including the broken wires, parallel wires (two wires together), skipped wires (weaving missing), corrosion, oil stains and serious wavy edges. This testing mainly relies on the visual observation, and a magnifying glass can be used when necessary. The allowable degrees of the defects are judged according to the relevant standards.

Testing Scope

Industrial screening meshes: Applied to the particle classification and screening in the industries such as the mining, building materials and chemicals. The testing needs to emphatically focus on the precision of the aperture sizes, wear resistance and the overall structural strength, ensuring the long-term screening efficiency and life under the high-frequency vibration and material impact.

Precision filter meshes: Used for the liquid or gas filtration in the fields such as the fuel, hydraulic systems, food and beverages and pharmaceuticals. The testing core lies in the absolute filtration precision (maximum passage size), cleanliness (particulate pollutants) and the corrosion resistance of the material, and the strict hygiene or safety standards must be met.

Protection and decoration meshes: Such as the machinery equipment guardrails, building decoration grilles and speaker grilles. The testing focuses on the flatness, beauty, mesh uniformity and sufficient mechanical strength of the mesh surface, and the quality of the edge treatments (such as the edge wrapping and edge welding) also needs to be checked.

Meshes for the aerospace and special fields: Used for the extreme environments such as the rocket engine filter meshes and satellite antenna shielding meshes. The testing scope is extremely strict. In addition to the routine items, the high-temperature/low-temperature performance testing, fatigue testing and the corrosion resistance testing for the specific media also need to be carried out.

Test sieves: The standardized tools used for the particle size analysis of the powder and granular materials in the laboratories. Their testing must comply with the standards such as GB/T 6003.1 or ISO 3310-1, with the extremely high precision and consistency requirements for the aperture size deviations, average wire diameters and welding quality.

Meshes of the different weaving forms: Covering the various forms such as the plain weave, twill weave and Dutch weave (dense mesh). The methods need to be adjusted according to the weaving characteristics during the testing. For example, the Dutch weave mesh needs to distinguish the different wire diameters and densities of the warp and weft wires, and measure and evaluate them separately.

Testing Methods

Optical image measurement method: A tool microscope, projector or video measuring system is adopted to enlarge and image the mesh sample, and the software is used for the automatic or manual measurement of the mesh count, wire diameter and aperture sizes. This method is non-contact with the high precision and good repeatability, and can save the images as the records. It is suitable for the testing with the high precision requirements.

Mechanical contact measurement method: The measuring tools such as the micrometers, thickness gauges and pin gauges (used to detect the through-holes) are used for the direct contact measurement. The method is intuitive with the low equipment cost, but attention needs to be paid to the deformation of the soft materials or fine wires caused by the measuring force, and the measurement efficiency is relatively low.

Gravimetric method for calculating the open area: Through the precise measurement of the mass, dimensions, material density and wire diameter of the mesh sample, the percentage of the open area to the total area (open area ratio) is indirectly calculated. This method can be used as the verification of the optical measurement results, and is particularly suitable for the very densely woven meshes.

Tension and stiffness testing: A fabric tension meter or the simple drape method is used to evaluate the ability of the mesh surface to resist the deformation (stiffness) and the isotropic tension distribution. For the meshes used as the filters or screens, the sufficient stiffness helps to maintain the stable aperture shapes.

Corrosion resistance testing: According to the material and application environment, the salt spray testing (such as the neutral salt spray NSS and acetic acid salt spray AASS), copper-accelerated acetic acid salt spray testing (CASS) or acid and alkali immersion testing is selected. After a certain period, the corrosion, pitting or colour change of the mesh surface is observed, rating its corrosion resistance grade.

Cleanliness determination: Mainly for the precision filter meshes. The mesh sample is cleaned with the pure solvent (such as the ultrasonic cleaning), and then the eluate is filtered, dried and weighed, determining the mass of the residual particles on the mesh, or a particle counter is used to analyse the number and size distribution of the particles in the eluate.

Testing Standards

Domestic Standards:

1. GB/T 6003.1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth

2. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

4. GB/T 232-2010, Metallic materials — Bend test method

5. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

International Standards:

1. ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth

2. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

3. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Reading microscope and tool microscope: Equipped with the eyepiece micrometers, they are the traditional precision instruments for measuring the mesh count, wire diameters and micro apertures. The operators need to be trained and read through the calibrated scales. They are suitable for the precision measurement and defect observation in the laboratory.

Laser/optical projection measuring instrument: The mesh sample is projected onto the screen, and the fast measurement is carried out with the software assistance. Its advantages are the reduction of the human reading errors, high measurement efficiency, and the automatic scanning and statistics of some parameters. It is the commonly used equipment for the modern mesh material testing.

Digital micrometers and thickness gauges: Used for the contact measurement of the wire diameters and mesh thicknesses. The digital instruments have the intuitive readings, can carry out the statistical calculations (such as the average, maximum and minimum values), and can output the results to the computer through the data interfaces, which is convenient for the data management.

Material analysis spectrometer: Including the handheld X-ray fluorescence spectrometers and bench-type direct-reading optical emission spectrometers. They can carry out the fast, non-destructive qualitative and quantitative composition analysis of the metal wire materials such as the stainless steel and copper alloys, ensuring that the material designations meet the requirements. They are the key equipment for the incoming material inspection.

Environmental test chamber: Mainly the salt spray test chamber, used to simulate the marine or industrial atmospheric environments and examine the corrosion resistance of the metal wire woven mesh. The equipment needs to be able to precisely control the sodium chloride solution concentration, pH value, chamber temperature and spray amount, and the testing process needs to comply with the standards such as GB/T 10125.

Electronic balance and ultrasonic cleaning machine: The two are combined for the cleanliness determination. The high-precision electronic balance (precision 0.1 mg or higher) is used to weigh the mass difference of the filter membrane before and after cleaning; the ultrasonic cleaning machine can effectively oscillate and peel off the pollutants in the deep parts of the apertures and on the wire surfaces, ensuring the testing accuracy.