Manufacturing Process Flow for Rubber Fabric-Reinforced Diaphragms
The production of a high-quality rubber-fabric diaphragm requires precise control over material preparation, layering, and vulcanization to prevent defects like wrinkling, fabric breakage, or surface unevenness .
A. Preparation of Fabric-Containing Sheet
1. Fabric Preparation and Adhesive Treatment
A substrate fabric (commonly woven from nylon, polyester, cotton, or rayon) is selected .
The fabric is pre-treated with an adhesive agent, typically via dipping or spreading, to ensure a strong bond with the rubber layer .
If the fabric strip contains defects, they are marked (e.g., with yarn or tape) on the edge for later identification and removal, preventing them from entering the final product .
2. Rubber Coating
The adhesive-treated fabric is combined with an uncured rubber compound. The specific rubber formula (e.g., NBR, EPDM, CR) depends on the application requirements like oil resistance or temperature range .
Calendering (Traditional Method): The fabric is passed through a calender machine, which applies rubber layers onto one or both surfaces. However, this method can lead to thickness variations .
Extrusion Method (Advanced Method): The fabric is passed through an extrusion molding machine with a die that produces a fabric-containing sheet of uniform thickness. This method is preferred as it reduces waste and allows for continuous, automated processing .
B. Molding and Vulcanization
3. Blank Cutting
The rubber-coated fabric sheet is fed into a press. Using a punching die, individual circular blanks (or other required shapes) are cut from the continuous strip. This step can be automated to handle multiple diaphragms at once .
4. Pre-forming and Vulcanization
A blank is placed into a vulcanization mold. The mold typically consists of upper, middle, and lower parts designed to shape the diaphragm's specific geometry (e.g., a bowl shape, a flat flange, and a central hole) .
Fabric Tensioning: A critical step is the initial pressing of the fabric blank by the middle mold. This "tightens" the fabric to prevent it from wrinkling or breaking during the subsequent forming process .
Pressing and Curing: The mold is closed under heat and pressure. The heat activates the vulcanization (curing) process, which cross-links the rubber molecules. Typical parameters for NBR might be a temperature of 150-170°C for 20-40 minutes, though this varies by compound . This step bonds the rubber to the fabric, giving the diaphragm its final strength and elasticity .
5. Secondary Vulcanization (Optional)
In some automated processes, the diaphragm may undergo a secondary vulcanization step in an oven or tank. This reduces the time the diaphragm must spend in the press, thereby increasing overall production speed .
6. Trimming and Finishing
After vulcanization, the formed diaphragm is trimmed to remove excess material ("flash") from the edges .
Post-Curing Machining: For precision applications (e.g., in aerospace), the diaphragm may be coated with grease, stacked, and clamped for high-precision grinding of the inner and outer diameters to exact specifications .
Finally, the finished diaphragms are visually inspected for defects (like mottling or bubbles) and checked for dimensional accuracy (diameter and wall thickness) before packaging .