Where does the stock splashing originate?

High-speed paper machines equipped with multi-layer forming and top-wire dewatering systems are all fitted with vacuum transfer boxes. Along with shifts in paper market demand and strategic adjustments by paper manufacturers, many paper machines have undergone technical retrofits and equipment upgrades. Consequently, their production basis weight and operating speed far exceed the original design parameters. This inevitably triggers a prevalent malfunction: stock splashing on the wire section. The splashing occurs under two conditions: excessive wire running speed, and converting low basis weight production to high basis weight production. In such cases, the pulp flow fails to adhere to the bottom wire and flies out directly from the outlet of the vacuum transfer box or composite roll. This forces an unplanned machine shutdown and may even damage wire fabrics and spare parts in severe cases.

Apart from visually observable causes such as a long dry line and low dryness of the web, stock splashing on the wire section is mostly attributed to abnormal conditions at the peeling point of the vacuum transfer box.

Main causes of stock splashing induced by faulty peeling points of transfer boxes

1. The panel of the vacuum transfer box has been in service for an extended period and suffers severe abrasion. When the worn surface is more than 2 mm lower than the standard surface, stock splashing easily occurs due to variations in basis weight, machine speed and dry line position. The solution is simply to replace the transfer box panel, while ensuring the new dewatering panel has identical thickness to the removed one. If the replacement panel is refurbished, the correct peeling point must be relocated via a wire tensioning method and calibrated after installation.

2. Stock splashing persists even when the peeling point of the transfer box is positioned correctly per installation drawings. In this scenario, check whether the actual production basis weight is far lower and the operating speed much higher than original design values. If so, reposition the peeling point by moving it backward to realize early peeling. For conventional paper machines, the peeling point is generally 110~140 mm away from the inlet of the transfer box; for slotted transfer boxes, it lies between the 3rd and 4th slots. During normal production, the boundary on the transfer box panel where vacuum suction pulls down the wire (visible side) and the non-suction zone (invisible side) is exactly the peeling point, which can be identified by naked eyes.

3. The vacuum transfer box is installed non-parallel to the machine frame, adopting an inclined layout with a higher inlet and lower outlet.

4. Vacuum setting for transfer boxes: based on field operational experience, vacuum pressure of the transfer box shall be maintained within -25 ~ -40 kPa.

5. Calibration method for transfer boxes. To prevent stock splashing and other unexpected faults, all adjustments shall be carried out under machine shutdown status using the wire tensioning method:First, align the inlet of the transfer box horizontally with the panel of the preceding vacuum box; then adjust the elevation of the transfer box outlet to locate the accurate peeling point.