NNEWS CENTER

Summary: The rectifier roll is a hollow thin-walled roll with regularly distributed round holes on its surface. It uses the efficacy of these holes and the micro-eddies produced when the pulp flows through the holes to rectify and disperse the fibers. When the pulp passes through the rotating rectifier roll, a wave effect inevitably occurs, leading to fiber orientation stripes, compromising the rectifying effect and causing a series of paper defects. This problem becomes more pronounced at higher speeds, so the rectifier roll is suitable only for medium and low-speed paper machines. This article discusses the principles of the rectifier roll and its existing problems, as well as solutions.

Uniforming Principle and Existing Problems in the Pulp Chest of the Toilet Paper Papermaking Machine

1. The rectifier roll, a traditional uniforming component, is widely used in open and air-cushion headbox as a device to produce flow resistance, rectify, and disperse fibers. The rectifier roll is a hollow thin-walled roll with regularly arranged holes. The holes on the roll’s surface play a role in energy dissipation. Its efficacy can adjust the uneven flow rate in the width direction after passing the headbox and generate certain vortex turbulence to rectify and disperse the fibers. If designed properly, the turbulence created by the rectifier roll can meet the requirements for uniform pulp flow. Early studies by J. Mardon and R.E. Monahan provided some basis for the design of the rectifier roll, such as the open rate and nozzle length.

2. The waveform generated by the pulp passing through the rectifier roll, known as the wave effect, is a critical aspect of rectifier roll design. The fiber orientation issue in the rectifier roll’s pulp chest is related to its wave effect. As paper quality requirements increase, the issue of paper orientation distribution is receiving more attention. Orientation stripes often lead to a series of paper defects in subsequent coating and super-calendering. These are different from quantitative stripes and stem from design issues in the headbox.

3. It’s evident that the design of the rectifier roll is crucial for a paper machine.

4. Fluid dynamics effects of the rectifier roll.

5. The flow through the rectifier roll can be approximated as passing through two perforated plates. First, it flows towards the roll’s center and then radially outwards. After passing through the roll, intense mini vortices form between the holes, making the pulp in a micro-turbulent state, thereby dispersing the fibers and preventing fiber floc formation. The holes help adjust the uneven flow rate in width direction, while the mini vortices provide moderate dispersion

1. The flow speed decreases due to head loss when passing through the rectifier roll. The faster the flow in the channel, the more significant the head loss, leading to a substantial decrease in speed after passing through the rectifier roll. The rectifier roll relies on intense mini vortices and head loss to control pulp flow. If the turbulence is too strong, it can adversely affect forming. Ensuring the pulp is in a micro-turbulent state after passing through the rectifier roll is key to design.

2. Determining the distance from the gate roll to the lip front edge.

**Uniforming Principle and Existing Problems in the Pulp Chest of the Toilet Paper Papermaking Machine**

3. The rectifier roll near the lip – the gate roll is crucial, primarily serving as a final rectifier. A relatively uniform pulp flow has minimal disturbances after passing through it, with shorter waves that easily dissipate, preventing wave crests or troughs from forming on the wire mesh’s suspension surface. This position needs full attention. Generally, it is believed that when the wave just disappears after the rectifier roll and before the fibers floc again, the pulp reaches the wire at the right time, resulting in optimal rectification. This determines the distance from the rectifier roll to the lip opening. Many factors affect the wave effect of the rectifier roll, best represented by Mardon’s “wave-free” formula.

5. The main factors affecting the rectifier roll’s efficiency are the flow rate (pulp flow speed through the roll’s holes) and the roll’s diameter and hole rate. Simply put, the rectifier roll relies on the “wave effect” generated by rotating holes. In rectifier roll pulp chest design, the wave-free calculation length is key, used to calculate the distance L from the lip rectifier roll outlet to the spray point (this distance is called nozzle length). The nozzle length should be just right; if too long, the wave effect disappears, causing large pulp clusters at the lip and poor forming; if too short, the pulp will still be turbulent when hitting the wire, leading to streaks on the forming wire. The actual nozzle length is determined by paper machine speed, flow rate range, and other factors. Typically, the distance from the gate roll to the convergent lip spray is 20-25 times the hole diameter. If the speed is >370m/min, it is 20 times the hole diameter. Too large a distance can cause fiber floc.