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::: Applications ::: Stationary Showers ::: Oscillators ::: Shower Nozzles

Products >> Paper >> Cleaning & Conditioning

The objective of the felt/Fourdriniers fabric conditioning system is to improve the overall press/Fourdriniers fabric efficiency. The system can use either mechanical or chemical cleaning or a combination of both depending upon the conditions. All of the raw materials and additions used in the papermaking are potential fillers of a press felt/Fourdriniers fabric. This problem is even more severe where the majority of stock is waste and secondary fibers.

In addition, most mills are operating with a closed system, which is adding more contaminates which can cause problems in felt/fabric operation. The frequent use of wet-end starch, wet-strength resins, and various synthetic retention-aid polymers has increased the felt/Fourdriniers fabric filing problems.

With all these potential problem areas, the paper maker may need more than just showers and suction boxes. Frequently it is necessary to use chemicals, either on a continuous or a shutdown program.

Mechanical cleaning and conditioning of the felts/Fourdriniers fabric is attained through three methods:

High Pressure Showers (essential)
Lower Pressure flooding Showers (recommended)
Full width suction boxes (essential)

The function of the low-pressure flooding shower is to provide the flushing media for removing the fillers from the felt/Fourdriniers fabric. It is usually located on the inside of the felt/Fourdriniers fabric An effective position is into the nip formed by the felt/Fourdriniers fabric and the felt/Fourdriniers fabric roll. This creates a hydraulic wedge action that forces the water through the felt/Fourdriniers fabric, flushing out the filling materials.

The jet leaving the nozzle is homogeneous in the beginning and with mainly a laminar flow. After about 1500-150 mm, it begins to get irregular and after 150-200 mm, it starts to form into small drops with high energy its diameter has also increased to 2-3 times that of the nozzle. The distance to the interval where the jet disintegrates depends on water pressure, the design of the nozzle and water temperature. With the jet changing in character from a homogeneous flow to a particle one, its ability to open and clean the felt also changes. A jet is at its best when consisting of a particle flow.

Oscillating high-pressure showers with needle nozzles are probably the most efficient means of keeping press felts/Fourdriniers fabric clean and open. When such showers do not operate efficiently, it is usually due to poor positioning of the shower and the use of oscillating mechanisms which are not designed to give 100% coverage, such as air and water cylinder and the crank arm oscillator. Using them in the press/fabric section is today a routine matter. The need for cleaning felts / Fourdriniers fabric has Increased because of the rising use of secondary fabrics, the increase in felt/Fourdriniers fabric life, and a greater degree of closed system in the paper machine. For the same reasons, the need for opening the structure of the felt/Fourdriniers fabric has also increased.

An optimum use of oscillating high-pressure showers should provide the following benefits:

Maximum cleaning and increase in bulk width
Minimum of water consumption.
Minimum damage to the felt/Fourdriniers fabric
Minimum shower maintenance
Minimum power requirements.

For optimum operation, the high-pressure shower with a needle nozzle should be placed 250-400 mm from the felt/Fourdriniers fabric, normally against the paper side. Depending on requirements and limitations, showering can be continuous or intermittent. The mist suitable water pressure is often in the range of 0.7-2.0 MPa. The most suitable nozzle diameter is 1.0 mm.

The water temperature should be equal to the temperature of the felts/Fourdriniers fabric being cleaned and the jet angle should be adjusted to suit individual application (start at 90 degree then experiment with or against the run by a few degrees).

Oscillating speed of the high-pressure shower is in most cases not matched to the length of the felt or machine speed. This leads to uneven conditioning, with some parts of the felt/Fourdriniers fabric being treated many times and others one or not at all. It is of the utmost importance that the speed of the shower is matched to the speed of the felt/Fourdriniers fabric. This means that the shower moves, for instance 1.9 mm after 250 mm distance) and thus cleans the whole felt/Fourdriniers fabric once and possibly twice per oscillation.