Glass Fiber Cloth Inspection

Glass fibre fabric inspection mainly conducts scientific testing and analysis on mass per unit area, tensile breaking strength, warp and weft density, width and length, moisture content and combustible matter content, 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

Mass per unit area: In accordance with the relevant standards (such as GB/T 7689.1), specimens of the specified size are cut, and weighed with an analytical balance with an accuracy of not less than 0.001 g. By calculating the mass per unit area (grams per square metre), the uniformity, thickness consistency and conformity with the product specification requirements of the glass fibre fabric are evaluated. It is the basic indicator for cost control and performance estimation.

Tensile breaking strength: A constant-rate-of-extension (CRE) strength testing machine is used to test the tensile properties of the warp and weft specimens respectively. The specimen is clamped in the grips until it breaks, and the maximum force is recorded. This item is the core for measuring the mechanical properties of the glass fibre fabric, and is directly related to the load-bearing capacity and structural stability of composite products.

Warp and weft density: Using a fabric density glass or the decomposition method, the number of warp and weft yarns within a specified length (such as 10 cm) is counted in the effective range of the specimen. The warp and weft density is the key structural parameter affecting the thickness, strength, resin infiltration and surface flatness of the glass fibre fabric, and has a decisive influence on the performance of the final composite material.

Width and length: Using a steel ruler or tape measure with the accuracy meeting the requirements, under the tension-free state, the width is measured at multiple positions evenly along the length direction of the roll, and the whole roll length is rechecked. The dimensional accuracy directly affects the efficiency of the downstream cutting and lay-up processes and the material utilization rate, and is a basic item of the delivery acceptance.

Moisture content: The specimen is placed in an oven at a specified temperature (such as 105 ℃±2 ℃) and dried to constant weight, and the moisture content is calculated through the mass difference before and after drying. An excessively high moisture content will affect the interface bonding performance between the glass fibre and the resin, and may cause defects such as bubbles and delamination in the composite products.

Combustible matter content: The dried specimen is placed in a high-temperature muffle furnace and burned at a specified temperature (such as 625 ℃±20 ℃) until all the organic substances (such as the sizing agent and binder) are completely burnt off. The content is calculated through the mass difference before and after burning. This indicator directly affects the bonding strength between the resin and the fibre and the final performance of the composite material.

Appearance quality inspection: Under a standard light source or specified illumination, the inspection is carried out by visual inspection or with a low-power magnifying glass. The items include defects such as broken warp, broken weft, stains, holes, thin and dense places and skewness. The appearance quality not only affects the aesthetics of the product, but may also become the structural weak points of the composite material.

Testing Scope

Glass fibre fabrics of different base materials: The testing scope covers the fabrics woven with glass fibres of different chemical compositions such as E-glass, C-glass, S-glass and AR-glass. The fabrics of different base materials differ significantly in the mechanical properties, corrosion resistance, electrical insulation and cost, and their key indicators need to be tested in a targeted manner.

Glass fibre fabrics of different weave structures: Including plain weave, twill weave, satin weave, unidirectional fabrics and various mesh fabrics. Different weave structures affect the softness, drapability, anisotropic strength and resin infiltration channels of the fabric, and the inspection needs to pay attention to the performance corresponding to their structural characteristics.

Glass fibre fabrics with different surface treatments: Inspection is carried out on the fabrics treated with different coupling agents such as silane and chrome types. The type of the surface treatment (sizing agent) directly affects the interfacial bonding strength between the fibre and the resin, and is the key to determining the interlaminar shear strength and environmental aging resistance of the composite material.

Glass fibre fabrics of different grammages and thicknesses: From the thin fabrics of tens of grams per square metre to the thick mats or composite mats of nearly one kilogram per square metre. The inspection needs to adjust the sampling method and test parameters (such as the clamp pressure) according to the grammage range, ensuring that the data accurately reflect the performance of the full series of products from light and thin to heavy and thick.

Glass fibre fabrics for specific fields: Including the ultra-thin fabrics for electronic grade copper clad laminates, the high-strength high-modulus fabrics for aerospace, the high-temperature-resistant corrosion-resistant fabrics for filtration, and the mesh fabrics for building reinforcement. For different application fields, the testing scope needs to be extended to their special properties, such as the electrical properties, high-temperature strength retention rate and acid and alkali resistance.

Glass fibre fabrics at each stage of the production process: The testing runs through the whole process from the inspection of the raw yarns, the control during the weaving process to the final inspection of the finished products. It includes the linear density and twist inspection of the yarns, the on-line defect detection during the weaving process, and the comprehensive performance verification of the finished rolls.

Testing Methods

Standard reference method: The testing is mainly carried out in accordance with the international, national and industry standards. The commonly used standards include ISO 4602 (warp and weft density), ISO 4606 (tensile strength), the GB/T 7689 series (Test methods for woven glass fibre fabrics) and ASTM D579 (Standard specification for greige woven glass fabrics), ensuring the international comparability and reliability of the test results.

Sampling and specimen preparation: Following the standard provisions, representative samples are cut from the whole roll, avoiding the end parts and the obvious defect areas. The specimen size needs to be precisely cut, the edges should be neat without selvedge fringes, and the conditioning is carried out under a standard temperature and humidity environment (such as 23 ℃±2 ℃ and 50%±10% RH), to eliminate the influence of the environment on the test results.

Physical property test methods: The classical physical and mechanical test means are adopted. For example, a CRE electronic universal material testing machine is used for the tensile and tearing tests; the combination method of the balance and the area measurement is used to determine the mass per unit area; and a density glass is used for the warp and weft yarn counting. All the instruments and equipment need to be regularly calibrated.

Chemical analysis test methods: Used to analyse the composition and content of the material. For example, the combustible matter content is determined by the ignition loss method; the moisture content is determined by the drying and weighing method; for the fabrics with special requirements, the infrared spectroscopy (FTIR) can be used to analyse the type of the sizing agent, or the X-ray fluorescence spectroscopy (XRF) can be used to analyse the chemical composition of the glass fibre.

Non-destructive and appearance inspection methods: Including the manual visual inspection and the machine vision automatic inspection. The manual inspection is completed on a fabric inspection machine, and the inspectors judge the defects according to the standard photos or limit samples. The automatic inspection system uses industrial cameras and image processing algorithms to realize high-speed and objective defect recognition and classification.

Application simulation test methods: Some high-end or customized inspections adopt the tests closer to the actual application. For example, the glass fibre fabric is compounded with a specific resin system to make a laminate, and then the mechanical properties of the laminate are tested, to comprehensively evaluate the performance of the fibre fabric in the final use state.

Testing Standards

Domestic Standards:

1. GB/T 7689.1, Reinforcements — Test method for woven fabrics — Part 1: Determination of mass per unit area

2. GB/T 7689.2, Reinforcements — Test method for woven fabrics — Part 2: Determination of number of yarns per unit length

3. GB/T 7689.3, Reinforcements — Test method for woven fabrics — Part 3: Determination of width and length

4. GB/T 7689.5, Reinforcements — Test method for woven fabrics — Part 5: Determination of glass fibre tensile breaking force and breaking elongation

5. GB/T 18370, Glass fibre woven roving

International Standards:

1. ISO 4602, Reinforcements — Woven fabrics — Determination of number of yarns per unit length of warp and weft

2. ISO 4606, Textile glass — Woven fabric — Determination of tensile breaking force and breaking elongation by the strip method

3. ASTM D579, Standard Specification for Greige Woven Glass Fabrics

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

Electronic universal material testing machine: The core mechanical testing equipment, equipped with pneumatic or mechanical grips, used for the precise determination of the tensile breaking strength, elongation at break and tearing strength of the glass fibre fabric. The equipment should have a high-resolution force sensor and displacement measurement system, and can output the complete stress-strain curve.

Constant temperature and humidity chamber, oven and muffle furnace: The constant temperature and humidity chamber is used for the standard environmental conditioning of the specimens before the test. The forced-air drying oven is used to determine the moisture content, requiring high temperature uniformity. The high-temperature muffle furnace is used to determine the combustible matter content, and needs to precisely control the heating program and constant temperature, ensuring the complete ashing of the organic components.

Precision balance and sampler: An analytical balance with an accuracy of not less than 0.001 g is used for the weighing of the mass-related items such as the mass per unit area and moisture content. The circular or square sampler is used to quickly and accurately cut the specimens of the specified area, ensuring the consistency of the sampling size.

Fabric density glass and fabric inspection machine: The fabric density glass is equipped with a magnifying glass and scale, convenient for the operators to count the number of warp and weft yarns. The fabric inspection machine is a stand with lighting and winding devices, which can unfold the fabric at a constant speed, convenient for the inspectors to carry out the continuous and efficient appearance quality inspection and length recheck.

Standard light source colour matching cabinet: Provides the standard light source environments such as D65 and TL84, used for the comparison and assessment of the colour and colour difference of the glass fibre fabric, and providing a stable and flicker-free lighting condition for the appearance inspection, reducing the inspection errors caused by the light changes.

Coating thickness gauge and microscope: For the glass fibre fabrics with coatings (such as coated mesh fabrics), a non-contact or contact thickness gauge is used to measure the coating thickness. A stereo microscope or digital microscope is used to magnify and observe the fibre distribution, weave structure, surface defects and sizing distribution state, for the micro-morphology analysis.