Fiber vs. Scrim Supported Felt

The basic process of making felt consists of orienting layers of short fibers (staple fibers) and forming a layer or layers (called a batt) with a specific weight per square yard. The batt is then gradually compressed, followed by needling thousands of times per inch to mechanically entangle the fibers and form a consistent felt. The felt may then be treated in one or more ways (singeing, calendering, etc.) to achieve the final characteristics required.

The same basic process is followed whether the felt is scrim supported or fiber supported. With fiber supported felt, the equipment is simply configured to form a continuous batt with the weight specified (16 opsy, 14 opsy, etc.) all coming from the staple fiber. With scrim supported fabric, the scrim is set up on a separate unwinder and fed into the process at the same linear speed as the batt. The weight of the batt must be reduced, however, by an amount equal to the weight of the scrim.

The disadvantages of the scrim supported version are that it requires additional raw material (scrim), additional labor in the manufacturing process, and a portion of the fabric weight (the scrim) does not aid in the filtering process.

In terms of physical characteristics, the products compare as follows for a 16 opsy polyester felt:

Advancements in technology have now made possible a fiber supported felt that is equal to and, in most cases, has better performance characteristics than traditional scrim supported felts. Just some of the many advantages are:

1. The absence of a scrim means that all of the fibers in the felt are available for filtration. Scrims are so tightly produced that they cannot contribute to normal filtration.
2. Scrims can blind easily if dust penetrates into the felt. This can lead to premature failure of the bags from the resulting high pressure differential.
3. The absence of a tight scrim means that air can flow more freely, allowing higher velocity or lower pressure drop.
4. Scrims affect the flexing characteristics of the felt, so their removal can improve some aspects of the media's behavior, including allowing easier pulse cleaning.
5. Needling tends to weaken scrims, whereas this process strengthens fibers. In most cases this leads to higher overall media strengths.
6. In general, fiber supported felts are less expensive than those containing scrims, due to the high cost of producing scrims.