EVEN FEED OF MATERIAL TO THE CARD
- THE NEED FOR TRANSPORT
Blow room installations consist of a combination of a number of individual machines arranged in sequence. In processing, the material must be forwarded from one machine to the next. Previously, this was performed manually, but now it is done mechanically or pneumatically, i.e. using air as a transport medium. Mechanical transport is limited exclusively to forwarding within the machine; outside the machine, material is now transported only pneumatically.
- BASIC PRINCIPLE
Air is not inherently a very efficient transport medium. Very large quantities must be moved at high speeds in order to keep the tufts that are being transported floating. The current of air itself is a further disadvantage, since the air flows in a turbulent fashion through the ducting, i.e. vortexes are created. Since the tufts are subjected to these vortexes, entangling of tufts can arise in long ducts and finally neps can be formed. A closed duct (generally a pipe) and a source of partial vacuum (a fan) at one end of the duct are needed to move the air. The air speed should be at least 10 m/sec, and 12 - 15 m/sec is better; it should never exceed 20 - 24 m/sec. At a given air speed, the required quantity of air can be calculated as:
where L is the quantity of air; A is the cross section of the duct in m2; v is the air speed in m/s. The duct must terminate in a device that separates the air from the material.
- SEPARATION OF AIR AND MATERIAL
By far the most widely used assembly for this purpose is the perforated drum (Fig. 69). It is used in various machines and parts, often in so-called suction boxes (condensers).
A partial vacuum is created in the drum, and thus in the duct, by a fan at one end of the drum. Air and material flow toward the drum. However, while the air can pass through the perforations in the drum, and is then passed to filters for cleaning, the fiber tufts remain on the surface of the rotating drum and are carried along with it. In the lower region, the drum surface is screened off from the partial vacuum in its interior. The tufts are no longer retained by suction and fall into a chute. Another assembly for separating air and material is the slotted chute of the Rieter UNIflex (Fig. 57), where the transport air is extracted through the slot, while the material slides down on the aluminum ribs of the rear wall of the chute. |
- Control of material flow
Since, as already discussed, the blowroom line is a sequence of individual machines, each machine must always receive an exact quantity of material per unit of time from the preceding machine, and must pass on the same quantity per unit of time to the next. To ensure an adequate flow of material, the machines are adapted to each other so that each machine can produce a little more than the succeeding machine requires. Since each machine has excess capacity, a control system must be provided to ensure the correct delivery quantities. Two basic principles are used: batch operation and continuous operation.
- CONTINUOUS OPERATION
Fig. – Trützschler CONTIFEED
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As a concept, this is not new in the blowroom; it has been used for a long time in the scutcher as pedal regulation of the feed to the beater. What is new is that now the whole blowroom line operates continuously and regulation is performed electronically. This installation, developed by Trützschler, will be presented briefly (see Fig. 71).
The central regulating unit, to which all the individual machines are connected, is the “CONTIFEED”. This receives an analog signal from the tacho-generators of the cards; the instantaneous demand for material is continuously calculated from this signal. Using this demand, the microcomputer can establish the basic speeds of all drives that determine the throughput and the drives can be correspondingly controlled. A second signal is superimposed on this basic speed signal, derived from the contents of the storage unit of the succeeding machine. In this way, the successive machines are linked via individual control loops. The programs for speeds, production quantities and allocation are first established manually, which represents a fairly substantial initial outlay. When balanced operation is achieved, they can be transferred to the “CONTIFEED” and stored there. |