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How to configure trim pick-up lines for inline cutter systems

We're doing a series of blog posts about how inline cutter systems (cutter/fan trim removal systems) efficiently convey, process and remove continuous edge trim and waste filament. Part 1 explored inline cutting systems vs. conventional venturi systems. Part 2 discusses trim and filament pick-up lines.

Trim and filament pick-up lines start close to the edge trim or filaments point of origin and continue to the junction point of the lines just before the inline cutter.

Each leg of the pick-up line system should be the same length and be placed as symmetrically as possible to insure an equal, balanced airflow in each line.

Most conveying systems require that the trim or filaments are taken away under tension to effectively release the trim from the trimming knives and parent web or the filaments from the thread line.

The conveying air passing by the trim or filaments in the pick-up lines creates this tension in accordance with the following formula:

Tension = XLV2


X = a factor associated with the surface shape, velocity and other characteristics of the trim or filaments and with the density of the conveying air.

L = length of the trim or filaments subject to the conveying air.

V = the velocity of the conveying air.

X is usually fixed for any given situation. L and V are the controllable design factors. Therefore, for any given situation, the tension generated in the trim or filaments is proportional to the length of the pick-up lines and the square of the velocity of the conveying air.

The recommended minimum velocity of the conveying air in the pick-up lines is 4,500 feet/minute, though a velocity of 5,000 feet/minute or higher is preferred. The velocity of the conveying air must always be substantially higher than the velocity of the trim or filaments.

Pick-up Line Length

The length from the pick-up lines to the cutter fan must not be too long. Trims or filaments cut or broken off close to the source rapidly accelerate and bunch up in the line due to the difference in the velocity of the material and the conveying air. This bunching up action in an overly long pick-up line will result in the formation of a large, undesirable bundle that can jam the cutter fan.

In most situations, a pick-up line of 6 to 12 feet, in conjunction with a 4,500 to 5,500 feet/minute conveying air speed will provide adequate tension. The bunching action will have virtually no effect in pick-up lines of 6 to 12 feet.

Smaller Lines Are Better

The pick-up lines should be as small as possible while still being compatible with air flow and the size and characteristics of the trim or filaments to be conveyed.

For instance, a very stiff 6-inch wide edge trim will require a relatively straight pick-up line with a width somewhat greater than 6 inches, but a 6-inch wide thin, flexible trim can easily be conveyed in a 4-inch curved or bent pick-up line.

Part 3 of our series discusses inline cutters.

Contact us to learn more about how a cutter/fan system can save your company money.


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