Principles and applications of chopped strand mat
Working Principle
The formation of chopped strand mat (CSM) involves cutting glass fiber filaments (or untwisted roving) into 50mm long filaments using a cutter, which are then randomly deposited onto a stainless steel mesh belt to form a mat. The chopped filaments are bonded together by spraying an adhesive and/or spraying water and applying a powdered adhesive, followed by high-temperature drying and cooling to form emulsion-based or powdered CSM.
Raw Materials
The glass commonly used in fiberglass products is a calcium alumina borosilicate with an alkali content of less than one percent. It is often referred to as "E" type glass because it was originally developed for electrical insulation systems.
The production of glass fiber involves drawing molten glass from a furnace through a platinum sleeve containing numerous small holes to form glass filaments. The filaments used for commercial applications are typically between 9 and 15 micrometers in diameter. Before being aggregated into fibers, the filaments are coated with an emulsion. The fibers are very strong-the tensile strength is particularly high. They also exhibit good chemical and moisture resistance, excellent electrical properties, are resistant to biological attack, and are non-flammable, with a melting point of 1500°C-excellent performance among plastic reinforcement materials. Glass fibers can be used in various ways: chopped into short lengths ("chopped strands"); aggregated into loosely bound ropes ("rovings"); woven into various fabrics; and produced by twisting and doubling the yarn to obtain continuous strands. In the UK, the most widely used glass fiber material is chopped strand mat, which is made by cutting glass fiber strands into approximately 50mm lengths and holding them together in mat form using polyvinyl acetate or polyester binders. The weight range of chopped strand mat is from 100gsm to 1200gsm, and it is useful for general reinforcement.
Sizing Section
The glass fibers are bonded from the settling section to the conveyor belt. The settling section needs to be kept clean and dry. The bonding of the powder is done by two powder binder applicators and a series of demineralized (distilled water) sprays.
On the chopped strand mat, the top and bottom sides are lightly sprayed with distilled water; this step is necessary for better adhesion of the adhesive. A special powder applicator ensures optimal powder distribution. A vibrator between the two applicators allows the powder to be transferred to the underside of the mat.
Combining with Emulsion
The curtain system used ensures sufficient diffusion of the adhesive. Excess adhesive is recovered via a special suction system. This system allows air to pass through the mat and remove the adhesive. The adhesive is evenly distributed, and excess adhesive is eliminated. Obviously, the adhesive can be reused after filtering out contaminants. The adhesive is stored in containers in the mixing chamber and transported via low-pressure pipelines from a small trough near the felt factory.
Special equipment keeps the storage tank at a constant level. Recovered adhesive is also transported back to the tank. Pumps transport the adhesive from the storage tank to the sizing section.
Production
Glass fiber chopped strand mat is a nonwoven fabric made by cutting filaments into 25-50 mm lengths, randomly laying them on a horizontal surface, and holding them together with a suitable adhesive. There are two types of adhesives: powder and emulsion. The physical properties of the composite material are mainly determined by the fiber diameter composition, the choice and amount of adhesive, the use of the felt, and its formability. The raw material for chopped strand mat production is fiberglass cake from fiberglass manufacturers, but roving is also frequently used, partly to save space. Good fiber cutting characteristics, low static electrical load, and low adhesive usage are very important for the quality of the mat.
The factory production consists of the following sections:
1. Fiber Yarn Ladder
2. Chopped Strand Process
3. Forming Section
4. Adhesive Application System
5. Drying Chamber
6. Cold Press Section
7. Trimming and Rewinding
Yarn Ladder Area: Rotating cake yarn ladles are placed on bobbin frames of an appropriate number. These bobbin frames are for framing the fiber cake; the yarn ladle area should be in an air-conditioned room with a realistic humidity of 82-90%.
Chopped Strand Equipment: Yarn is drawn from the fiber cake, with several strands passing through each cutter.
Forming Section: Chopped strand mat is formed by shavings at equal intervals, settling in the forming chamber. Each piece of equipment is equipped with a variable speed motor. The cutting device is independently controlled, ensuring even fiber distribution.
The section below the mesh belt simultaneously absorbs the yarn from the mesh belt. Exhaust air passes through a purifier.
Fiberglass Chopped Strand Mat Lay-up Thickness
Fiberglass chopped strand mat is involved in most fiberglass products. The quantity and method of using chopped strand mat vary depending on the product and process, and the lay-up thickness also varies according to the required process.
For example, in fiberglass cooling towers, the first layer is gel coat, followed by a thin layer of mat or 02 fabric, with 6-8 layers of 04 fabric in between, and a final thin layer of mat to cover the seams of the inner fabric layers. This product uses only two layers of mat in total. Similarly, in automotive headliner manufacturing, woven fabric, non-woven fabric, PP plastic, chopped strand mat, and sponge are typically layered together. In this process, a maximum of only two layers of mat are used. Honda automotive headliner manufacturing follows the same principle. Therefore, the amount of chopped strand mat used in fiberglass is determined by the process; some processes do not require chopped strand mat, while others do.
If 1 ton of fiberglass is made entirely of chopped strand mat and resin, the chopped strand mat accounts for approximately 30% of the total weight, or 300 kg. In other words, the resin content is 70%.
The amount of chopped strand mat used in the same process is determined by the layup design. The layup design is based on the mechanical requirements, shape, and surface requirements of the product.
Application Standards
The application fields of alkali-free fiberglass chopped strand mat are becoming increasingly widespread, involving high-tech fields such as automobiles, ships, aircraft, wind power generation, and military production. However, you may not be familiar with the relevant standards for fiberglass chopped strand mat. Below, we introduce the requirements of an international standard from five aspects: alkali metal oxide content, unit area mass difference, combustible content, moisture content, and tensile breaking strength.
1. Alkali Metal Content: The alkali metal oxide content of alkali-free fiberglass chopped strand mat should not exceed 0.8%.
2. Unit Area Mass
3. Combustible Content: In the absence of an agreement, the combustible content should be 1.8%-8.5%, with a range not exceeding 2.0%. 4. Moisture Content: The moisture content of felt using powder binders should not exceed 2.0%. The moisture content of felt using emulsion binders should not exceed 5.0%.
5. Tensile Breaking Strength:
Generally, alkali-free chopped strand mat meeting the above requirements is considered fully qualified. However, depending on the product's intended use and manufacturing process, higher requirements may be placed on tensile strength and unit area mass deviation. This necessitates that our purchasing personnel be familiar with their product's manufacturing process and determine the required type of fiberglass mat so that the supplier can produce accordingly.
