How to Optimize Trimming Edge Spray Nozzle to Reduce Paper Break?

The smooth operation of a paper machine largely depends on the operation of the trimming edge spray nozzle. The water jet trimming process is crucial, determining the width of the finished paper web and being one of the primary causes of paper breaks. Proper maintenance, parameter adjustment, and selection of trimming edge nozzle can significantly achieve smooth edge trimming and cutting, reducing or eliminating paper breaks caused by improper trimming, thereby improving production efficiency and product quality.

In papermaking, the purpose of spray nozzle trimming is to separate the formed edges, separating the irregular, loose wet and dry edges of the paper after it has been formed, forming a clean and flat edge. This ensures that the paper can be cut according to the production size and reduces the occurrence of paper breaks during subsequent processes.

How to Achieve Ideal Results With Spray Nozzle Trimming?

To ensure ideal results in spray nozzle trimming during papermaking, the following aspects need to be considered and optimized:

• Maintenance of The Trimming Edge Nozzle

  The trimming edge nozzle is the core of the trimming system, and its condition directly determines the quality of the cutting and trimming. First, ensure the spray nozzle is in good condition and check for wear. Wear on the spray nozzle will weaken the water flow, leading to a significant decrease in cutting efficiency. Wear and tear causes the water jet to break and scatter before it even reaches the paper web. When the water jet breaks, it begins to atomize, losing its shape. Small particles detached from the water flow also weaken its impact, leading to irregular cuts, burrs, fiber fraying, and paper breaks. Regularly replacing the spray nozzles helps prevent these problems caused by wear. High-quality materials such as sapphire or ruby spray nozzle can extend the replacement cycle.

• Appropriate Water Pressure Ensures Cleaner Cutting

Water pressure is a key parameter determining cutting quality. Too low a pressure will prevent the water jets from effectively cutting the paper, while too high a pressure will cause splashing, damaging the wire mesh. The water pressure setting needs to take into account factors such as paper weight, production speed, and the orifice diameter of the spray nozzles. Higher water pressure results in a stronger water flow and cleaner cuts. Below, Sun Hong will provide you with suggestions on the diameter and quantity of spray nozzles based on factors such as operating speed, water pressure, and type of paper being produced.

• Use Double Hole or Double Spray Nozzles

In papermaking, spray nozzle trimming is very important for paper quality and operational stability. Using double hole or double spray nozzles is a recommended method. Although the water consumption of trimming edge nozzles is not large compared with other processes, it is still necessary to save costs. Using double hole spray nozzles allows multiple small-diameter water streams to be used at the same time, achieving cleaner cutting and reducing water consumption. The reason for recommending dual spray nozzles is redundancy. When bubbles appear in the water pipe or the main water flow is interrupted, the second set of nozzles provides cutting redundancy, greatly reducing the possibility of paper production interruptions and ensuring a seamless and clean edge finish.

• Spray Nozzle Arrangement and Spray Angle

The spray nozzles are tilted at a 10 to 20° angle to the running direction, facing the dryer section. Adjusting the spray angle prevents water mist from splashing onto the forming fabric and press felt. Even if backsplashing occurs, water droplets will fall back onto the paper instead of accumulating outside the spray nozzle. If the sprayed water splashes back onto the nozzle, impurities may adhere to its outer surface. If too much debris accumulates and falls onto the paper, it can cause paper breakage.

The spray nozzle design is also crucial. Noozle with angled outlet edges can be directionally installed so that debris and water droplets fall onto the damaged area of the paper, preventing contamination of normal paper. In trimming systems employing multiple spray nozzles, air barriers and anti-splash devices can be added to assist in isolating the main water flow, reducing interference, and further preventing fibers from adhering to the nozzle surface.

Tilt the spray nozzle outlet 5° to 15° towards the machine edge to help separate the broken paper edge from the main paper web, thus ensuring that the cut strips do not accidentally re-adhere after trimming; Additionally, pointing the spray nozzle and pipe toward the machine edge directs any droplets or debris towards the cut strip, preventing them from falling onto the paper web.

Position the trimming edge nozzle 50 to 150 mm above the paper machine clothing. The distance of the trimming edge nozzle is also very important. If the spray nozzle is too close to the paper web, a large amount of spray material will splash back onto the nozzle, damaging the fabric. Conversely, if the spray nozzle is too far away, the water jet may break up, reducing impact force and preventing a clean, precise cut. As operating conditions vary across paper machines, Sun Hong recommends a jetting distance of 50 to 150 mm, with the specific setting adjusted based on production conditions, paper grade, nozzle pressure, machine speed, and other factors.

After placing the spray nozzle in the vacuum suction box of a high speed paper machine, the water generated by the trimming edge nozzle or the suction roll on the high speed paper machine may rewet the paper web, causing its edges to close again. This phenomenon leads to sheet breaks and increases energy consumption in the press and dryer sections. Performing the trimming operation at a later stage can reduce the likelihood of the sheet edges re-bonding to the main web.

• Use a Stroboscopic Light to Inspect the Nozzle's Spray Performance

The stroboscopic light is a tool for performance evaluation and adjustment; it allows for clear observation of the spray pattern and water jet shape under ambient lighting. By setting the light frequency to 50–60 Hz, one can accurately assess spray quality.

An ideal jet stream should not produce any droplets or particles from the water stream; it should appear as a transparent glass rod. If the jet stream appears rough, with water droplets splashing, and has an uneven appearance, or even shows signs of water flow distortion. This can cause the spray to break up and reduce impact, so adjustments should be made to avoid such problems and ensure trimming effect and system efficiency.

There are many factors that affect trimming edge nozzle. Following the above scientific recommendations can help reduce the probability of paper breakage in finished products, increase equipment uptime, and promotes sustainability in paper making operations. With 30 years of experience in spray nozzle manufacturing, Sun Hong possesses the professional expertise and technical capabilities to provide tailored advice, helping you achieve efficient and stable production.