Seam Construction

Sewing is the most common way of joining fabric together. Before making our screen bags, we researched some alternative methods commonly used for nonwoven fabrics and filters. We tested stitchless (ultrasonic and thermal) seams and compared them with sewing. Here is what we found…

Stitchless (Ultrasonic Seaming): This method employs frictional heat caused by high frequency mechanical oscillations. This creates the heat required for welding and the material is plasticised. This type of seam should eliminate gaps for material to escape through and could be applied to any micron fabric.
Our findings: This seam was by far the weakest of all the seams we tested. It did not hold up even under light pressure. Material easily escaped through the seams.
Stitchless (Thermal Bonding): A process by which materials to be joined are heated causing the thermoplastic materials to melt. They are then compressed by applying pressure, which causes an intermingling of polymers. A seam is formed as the material cools and solidifies. This seam should create an impermeable seam. Disadvantages are seam stiffness and fiber degradation caused by excessive heat.
Our findings: This seam was stronger than ultrasonic seaming. But not as strong as sewing. We saw some promise in this method for hash processing, but due to the high heat used to make the seam, it can’t be used on smaller micron fabrics.
Sewing: The advantage of traditional sewing is strength. The disadvantage is the stitch leaves gaps in the seam that can allow material to pass through the seam.
Our findings: This seam was by far the strongest. The mesh fabric will tear before the seam blows out.
Conclusion: We decided to stick with traditional sewing for our screen bags. We use 100% nylon thread for maximum strength. For flower and trim processing, we found a traditional seam with the bag turned inside out contained the material well. However, for processing finer materials and concentrates, material will escape through a standard seam. To combat this, we designed a special fold in our seam so nothing escapes. Our 25 & 37 micron bags are all made with this seam. It doesn’t hurt anything if processing flowers, if anything it makes the seam stronger. But for fine material, it does the trick! If you still find that pesky fine material is escaping through the seams, apply less pressure and give it a little more time. Another trick is to turn the bag so the long seam is facing up.