What impact does the installation of the spray nozzle have on the paper machine mesh section?

Spray nozzle determines whether the paper machine can run well. Paper breaks in the press section, and even paper breaks in the dryer section, sizing press and coating machine can all be attributed to paper edge defects caused by edge trimming water needles. The cutting nozzle's own structure and various production factors will affect its function. To trim neatly, the key factor is to maintain good laminar flow of the jet water (the jet should be thin and smooth, without air, evenly distributed in the lateral direction and have enough pressure to impact the paper web).

Excellent water quality is very important for the spray nozzle to operate well and prevent clogging. The commonly used jet diameter is 0.4mm-0.5mm. The spray nozzle that produces this jet needs to be equipped with a filter element with a maximum mesh of 200um. It is recommended to carry out effective pre-filtration before the trimming water needle pump. The spray nozzle temperature should be fixed at a temperature higher than the ambient air temperature (so that the spray nozzle will not be blocked due to condensation). The water temperature is better at 50°C-60°C. Also note: as the wood pulp content increases, spray nozzles with smaller diameters should be used and the water pressure should be increased.

You can also shorten or increase the distance between the spray nozzle and the paper machine clothing to improve the quality of the cut edge. If the spray nozzle is not working well, this adjustment will only have a short term improvement. Shortening the distance also reduces the fiber mist, but because the spray nozzle is closer to the paper machine clothing, more slurry accumulates on the spray nozzle.

For a paper machine with a speed of 500m/min, a single spray nozzle is sufficient for single or multi layer fabrics. When producing very low basis weight paper grades at medium or higher speeds, good results can be achieved by using a well assembled single spray nozzle on single or multi layer fabrics. However, at high speeds, since the fiber mist produced by the first spray nozzle will inevitably accumulate on the second spray nozzle, it is not recommended to use two single spray nozzles arranged in front and behind, and a double hole nozzle is recommended.

Spray Nozzle Jet Angle

The angle of the water jet cutting nozzle for edge trimming should be optimally adjusted in the longitudinal and transverse directions of the paper machine. As the vehicle speed increases, the angle at which the jet water jet impacts the paper web is particularly critical. The direction of the spray nozzle is slightly inclined to the longitudinal direction of the paper machine (20-40 degrees away from the vertical direction of the fabric). The jet water jet impacts the paper web at the same inclination as deviating from the longitudinal direction to prevent the rebound effect of water and the generation of fiber mist. Neat trimming can be obtained. Considering the speed difference between the jet water stream and the fabric, the vector jet speed should be as close as possible to the speed of the fabric.

How Should The Cutting Spray Nozzle Be Arranged?

On a fourdrinier paper machine, the cutting spray nozzle is usually installed in front of the vacuum couch roll. Since the cut edges of the paper will not be re-pressed, the spray nozzle just needs to make a good cut;

On a clamp net forming machine, if the machine speed is very high and the space structure allows, it is recommended to place the cutting spray nozzle behind the vacuum couch roller. If it is placed in front of the vacuum couch roller and the edge trimming quality is not good, the suction effect of the couch roll can press the trimmed paper web again, causing poor paper web peeling during paper threading.

The cutting spray nozzle must be fixed and vibration free, installed to facilitate adjustment in the transverse direction of the paper machine, with a certain movable angle in the longitudinal direction and the entire spray nozzle device should be easy to remove when changing the fabric.