What performance indicators and testing standards should be noted for alkali-free chopped strand mat?
I. Key Performance Indicators: Six Crucial Parameters Determining Product Performance
The performance of chopped strand mat is determined by glass fiber, adhesive, and specifications. The following six key indicators must be considered, as they directly affect the product's performance.
1. Gram Weight per Unit Area
- Standard Requirements: Measurement must be performed according to GB/T 9914.3-2001. The standard value range is ±5% to ±8%. For example, for 300g/㎡ chopped strand mat, a tolerance of approximately ±20g is allowed.
- Product Quality: Excessive deviation in gram weight will lead to uneven thickness and insufficient tensile strength in the chopped strand mat. Products such as battery casings for new energy vehicles and fiberglass storage tanks require strict control over weight deviation to avoid uneven tensile strength that could affect product quality.
- Common Specifications: 300g and 450g are commonly used in fiberglass hand lay-up processes; 225g and 300g are commonly used for automotive interior parts; 450g and 600g are optional for high-requirement corrosion-resistant applications.
2. Tensile Strength
- Standard Requirements: Testing must be conducted according to GB/T 6006.2. Taking 300g chopped strand mat as an example: longitudinal tensile strength needs to be ≥100N/150mm, and transverse tensile strength needs to be ≥80N/150mm.
- Product Impact: Insufficient strength can lead to deformation, cracking, and other problems in the final product. For products requiring high impact resistance, such as bumpers for new energy vehicles and fiberglass ship decks, it is essential to choose alkali-free chopped strand mat with a higher basis weight to ensure that tensile strength and other requirements are met.
- Key distinction: Alkali-free chopped strand mat has higher strength than medium-alkali and high-alkali chopped strand mat, making it suitable for applications requiring high strength.
3. Combustible content
- Standard requirements: The content should be between 1.8% and 8.5%, tested according to GB/T 9914.2-2001.
- Impact on quality: Excessive adhesive content leads to poor adhesion to resins and other chemical additives, reducing the product's heat resistance; low adhesive content makes the fiberglass prone to breakage and causes shedding after finishing.
- Recommended selection: For interior parts of new energy vehicles, emulsion-type chopped strand mat (combustible content 3%~5%) is recommended, as it is lint-free and has high strength; for fiberglass and bathroom fixtures, powder-type chopped strand mat (combustible content 5%~7%) is recommended, as it is more flexible and suitable for hand lay-up processes.
4. Moisture Content
- Standard Requirements: Powder chopped strand mat must have a moisture content of ≤0.20%, and emulsion chopped strand mat must have a moisture content of ≤0.50%. Testing must be conducted according to the indicators specified in GB/T 9914.1-2001.
- Key Issue: Excessive moisture content can lead to unstable resin curing, easy bubbling, and insufficient strength. Special attention is needed during application in humid environments.
5. Mat Surface Coverability
- Thickness Requirements: Mat surface thickness should be measured according to GB/T 20309. For products, the corresponding thicknesses are: 225g~300g ≤4mm, 300g~450g ≤5mm, and 450g~600g ≤6mm.
- Impact on Quality: Poor coverability can cause wrinkling, blistering, and delamination when molding complex curved surfaces. Especially for irregularly shaped products such as battery pack covers for new energy vehicles, fiberglass, and bathtubs, special attention must be paid to the conformability of the felt surface to ensure a seamless, wrinkle-free, and crack-free fit.
II. Product Testing Standards: The Core Basis in Production
Chopted strand mat testing must be strictly conducted in accordance with GB/T 17470-2007 "Chopted Straight Filament Matte and Continuous Filament Matte of Glass Fiber". Simultaneously, it must be supported by ISO and GB/T series standards to ensure the accuracy of product testing results.
1. Key Product Testing Items
Unit area mass is tested according to GB/T 9914.3-2001 standard to check if the weight deviation is normal.
Tensile strength is tested according to GB/T 6006.2-2001 standard to check if the longitudinal and transverse tensile strength meets the standards.
Combustible content is tested according to GB/T 9914.2-2001 standard to check if the impregnating agent is compatible.
Moisture content is tested according to GB/T 9914.1-2001 standard to check if the product and raw materials are damp.
Appearance quality is checked by the quality inspector according to GB/T 17470-2007 standard for defects.
2. Product Appearance Quality Inspection
- Whether the product is damaged, has holes, or stains.
- Uneven yarn dispersion, poor adhesive felt dispersion.
- The product should be free of creases, wrinkles, and impurities.
- Straight edges, tight roll diameter, no looseness.
3. Key Points of Product Testing
1. Sampling Requirements: Randomly select 3-5 rolls of the same weight from each batch. Cut a 100mm × 100mm sample from each roll, weigh it, and calculate the average weight and deviation.
2. Environmental Requirements: Testing temperature approximately 23±2℃, humidity between 50% and 70%, to avoid affecting data accuracy.
3. Equipment Accuracy: The balance accuracy must be ≥0.1g, and the tensile testing equipment loading rate must be 100mm/min to ensure accurate data.
III. Application Areas of Chopped Strand Mat: New Energy Vehicles, Fiberglass Products, etc.
Choped strand mat is mainly introduced for its applications in the automotive and fiberglass fields due to its ease of molding, high strength, and cost-effectiveness. Precise selection is required for different scenarios to avoid failing to meet quality and performance requirements.
1. New Energy Vehicle Sector: The Core Choice for Lightweighting and Safety
- Main Application Scenarios:
- Structural Components: Battery pack lower guard plate, upper cover, protective plate, etc., mainly for lightweighting, good insulation, and high temperature resistance.
- Covering Components: Bumper frame, fender, spoiler, etc., mainly for safety, impact resistance, and corrosion resistance.
- Material Selection Points:
- Material: Alkali-free fiberglass, high strength, good insulation; suitable for battery packs, corrosion resistant.
- Specifications: 225~300g emulsion chopped strand mat, suitable for molding and SMC processes, meeting rapid prototyping requirements.
- Performance: Tensile strength ≥100N/150mm, moldability ≤5mm, ensuring excellent fit for irregularly shaped parts.
2. Fiberglass Products Sector: A Suitable Reinforcing Material for Various Products
- Main Application Areas:
- Bathroom Fixtures: Bathtubs, shower trays, panel washbasins
- Chemical Corrosion Protection: Chemical storage tanks, pipelines, cooling tower linings
- Ships and Amusement Facilities: Hulls, Deck, Slides, Chairs
- Building Materials: Skylights, Waterproof Membranes, Fireproof Decorative Panels
- Application Selection
- Hand Lay-up Molding: 300~450g chopped strand mat, suitable for complex curved surface products
- Corrosion Protection: 600~900g chopped strand mat, used with vinyl ester resin to improve corrosion resistance
- Surface Layer: Paired with 30~50g surface mat to create a smooth surface, concealing textures and providing a good finish
IV. Chopped Strand Mat Application Process: Three Common Problems + Solutions
Due to inadequate operational control during construction, unsatisfactory results can occur. I will now list three common problems and their solutions.
Problem 1: Bubbling and Delamination After Product Manufacturing
- Main Causes:
1. The chopped strand mat is damp, with excessive moisture content, or the construction environment is humid, allowing moisture to seep into the resin.
2. Insufficient resin dosage; the glass fiber is not fully impregnated, resulting in dry spots.
3. Fiberboard is laid too quickly; the next layer of glass fiber is laid before the previous layer has solidified.
- Solutions:
1. Storage Method: Store chopped strand mat on a dedicated wooden frame, raised off the ground to prevent moisture absorption; use it as soon as possible after opening the packaging to prevent the glass fiber from getting damp.
2. Construction Requirements: Ensure each layer of mat is completely clear, without white spots or dry spots; single layers should not be too thick. Lay the next layer only after each layer has gelled. Laying two layers of mat simultaneously is strictly prohibited.
3. Important Operation: Use a dedicated defoaming roller to repeatedly press and expel air. Use a brush to repeatedly apply defoaming material to corners and curved surfaces to ensure complete resin and glass fiber penetration and prevent air accumulation.
Problem
2: Causing Wrinkling and Dimensional Deviations in New Energy Vehicle Parts
- Core Reasons:
1. Chopped strand mat cannot fit irregularly shaped components such as battery packs.
2. Excessive weight deviation leads to uneven stress during molding, causing product deformation.
3. Incorrect resin ratio results in incomplete curing, leading to poor dimensional stability.
- Solutions:
1. Selection: Chopped strand mat with moderate softness and a molding thickness ≤5mm is suitable for irregularly shaped molds.
2. Inspection: Check each batch for weight deviation ≤±5% and tensile strength ≥100N/150mm.
3. Process: Strictly follow the resin ratio (1%~2% curing agent), control molding temperature at 120~150℃, and holding time ≥15min.
Problem 3: Exposed texture and insufficient strength on the surface of FRP products
- Core Reasons:
1. No surface mat was laid, resulting in insufficient surface resin content (<60%).
2. Poor dispersion of chopped strand mat leads to clumps of fibers, affecting surface smoothness.
3. Incompatible styrene solubility results in insufficient resin wetting and localized low strength. Solution:
1. Process: Lay a surface layer of 30~50g/㎡ surface mat to ensure a surface resin content ≥60%.
2. Selection: Chopped strand mat with good dispersibility (no lumps, no fibrous strands), suitable for hand lay-up process.
3. Testing: Select H/M type for styrene solubility to ensure rapid resin wetting and improve overall strength.
V. Selection of Fiberglass Chopped Strand Mat
The main function of chopped strand mat is to balance molding efficiency and mechanical properties, making it suitable for applications in various fields such as lightweighting of new energy vehicles, fiberglass products, and tanks. When selecting materials, three main principles should be followed: process matching, performance requirements, and scenario suitability.
1. For molding and SMC components in new energy vehicles: Select 225g~300g alkali-free chopped strand mat, with a molding coverage of ≤5mm and tensile strength ≥100N/150mm.
2. For hand lay-up FRP bathroom fixtures and corrosion protection: Select 300g~450g powder or emulsion chopped strand mat, combined with surface mat, to improve surface quality.
3. For critical corrosion protection products: Select 450g~600g alkali-free chopped strand mat, which is corrosion-resistant and extends service life.
