What are the key production factors that affect the quality of finished fiberglass 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 fibers 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 be carried away through the mat and 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 troughs near the felt factory.

 

Special equipment keeps the storage tank level constant. 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 laid in a horizontal plane, and held together by 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, and the use and formability of the felt.

 

The raw material for chopped strand mat production is the fiber cake from the fiberglass manufacturer, 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 rack

2. Chopped strand process

3. Forming section

4. Adhesive application system

5. Drying oven

6. Cold pressing section

7. Trimming and winding

 

Yarn rack area

 

The rotating yarn rack is placed on the bobbin rack with an appropriate number of frames. These bobbin racks are for framing the fiber cake; the yarn rack area should be in an air-conditioned room with a realistic humidity of 82-90%.

 

Chopping equipment

 

The yarn is drawn from the fiber cake, with several strands passing through each cutter.

 

Forming Section

 

Chopted strand mat is formed by shavings at equal intervals and settling in the forming chamber. Each piece of equipment is equipped with a variable-speed motor. The cutting device is independently controlled to ensure uniform fiber distribution.

 

The section below the conveyor belt simultaneously absorbs the yarn from the conveyor belt. Exhaust air passes through a purifier.

 

Chopted Strand Mat Lay-up Thickness

 

Chopted 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, thin mat, and sponge are generally combined and layered. In this product manufacturing process, a maximum of two layers of mat are used. Even Honda car headliners are made using the same method. Therefore, the amount of chopped strand mat used in fiberglass reinforced plastics (FRP) depends on the manufacturing process; some processes don't require chopped strand mat, while others do.

 

If one ton of FRP is made entirely of chopped strand mat and resin, the chopped strand mat will account 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 also depends on the layup design. The layup design is determined by the product's mechanical requirements, shape, and surface finish requirements.