What Are The Factors That Affect The Stability of Press Felt? How Can We Control It?

What are the factors that affect the stability of press felt? How can we control it?

There are many factors that affect the dimensional stability of BOM press felt , including internal factors such as raw materials and manufacturing processes, as well as external factors such as storage, transportation, maintenance, and use. Below we will analyze from the perspective of usage and maintenance:

There are many factors that can affect the stability of BOM felt size during use. If used and maintained improperly, it will inevitably lead to excessive changes in felts length, width, and thickness, thereby greatly reducing the performance of the felt. Therefore, the correct use and maintenance of paper making felts are not only beneficial for the dimensional stability of the felts themselves, but also for the performance of the felts, in order to achieve the effect of extending the service life of the felts.

1. The influence of tension

The tension used for BOM felts varies depending on the part used on the paper machine. For BOM felts, it is generally required to tighten them all at once after being loaded onto the machine, and the operating tension of BOM felts after being loaded onto the machine is generally required to be between 2.5 and 4.5 kgf/cm. Excessive tension can easily lead to excessive elongation and width shrinkage of the felt, causing the felt and rollers to break and increasing the operating load; Insufficient tension can easily lead to excessive relaxation of the felt, high moisture content, difficulty in dehydrating the paper sheets, unstable operation of the felt, and easy folding.

2. The influence of standard line

In order to facilitate observation and grasp of the changes in the filtration pores of the felt during operation, and effectively control the changes in the width of the felt, each felt is set with a standard line. The standard line is a prominent wide line placed on the front of the felt (on the paper surface) perpendicular to the longitudinal centerline of the felt. During normal production, we require that the standard line be kept as straight as possible to prevent deformation of the standard line, which may cause problems such as reduced water filtration pores, transverse width shrinkage, and decreased water filtration performance of the felt. In severe cases, it may even cause unstable operation and folding of the felt, thereby reducing its service life and affecting product quality and normal production order.

1) There are many types of deformation of felt standard lines, which can be summarized as follows:

(1) The standard line slopes left and right, as shown in Figure 1.

(2) The standard line protrudes forward, as shown in Figure 2.

(3) After the standard line is concave, as shown in Figure 3.

(4) The standard line is S-shaped, as shown in Figure4.

(5) Other irregular deformations.

The deformation of the above standard lines can cause the width of the BOM felt to shrink, and the larger the deformation range, the greater the width shrinkage.

2) The main causes and preventive measures of deformation of felt standard lines:

(1) The tension on both sides of the felt is inconsistent, with one side being larger and the other being smaller. When tensioning the felt after it is installed, it is necessary to ensure that the tension on both sides of the felt is consistent. If any inconsistency is found, it should be adjusted in a timely manner.

(2) The line pressure on both sides of the press roller is inconsistent. During the pressurization process of the press roller, it is necessary to ensure that both sides are pressurized simultaneously, and the magnitude of the line pressure should be consistent. During the process of idle motion of new felt, the line pressure should be adjusted to the normal production line pressure as soon as possible, and long-term low-pressure idle motion should be avoided as much as possible.

(3) The eccentric distances on both sides of the press roll, couch roll and water squeezing roll are not consistent. During the production process, it is important to regularly verify whether the eccentricity of each press roll is appropriate and consistent, especially after replacing the felt.

(4) The setting of the crown of the press roll is unreasonable, with crown being too high or too low, and the line pressure being too high or too low. The crown of the new press roll should be reasonable and accurate. During use, the consistency of the medium to high wear changes of the press roll and the pressure in the pressing zone should be regularly checked to prevent abnormal wear from causing trouble in production. The excessive crown of the press roll or the insufficient pressure caused by the correct crown result in a central protrusion of the standard line of the felt, as shown in Figure 2. Because the line speed in the middle of the roller surface is higher than that on both sides, the line speed of the felt in contact with the middle of the roll surface is faster, resulting in a central protrusion of the standard line of the felt. The standard line of the felt has a concave back in the middle, mainly due to insufficient or excessive pressure caused by the correct crown of the lower press roller. That is to say, if the line speed in the middle of the roller surface is lower than the line speed on both sides, the line speed of the felt in contact with the middle of the roller surface will be slower, resulting in a concave back in the center of the standard line of the felt, as shown in Figure 3.

(5) The coating on the roll surface was not cleaned up in a timely manner. Keeping each roller surface clean at all times is very beneficial for reducing and eliminating the deviation, folding, and standard line deformation of the felt.

(6) The press roll has a displacement phenomenon, and the bearing is damaged and not replaced in time. In normal production, it is necessary to closely monitor the positioning and lubrication status of each roll. If loose screws or damaged bearings are found, measures should be taken in a timely manner to tighten, lubricate, and replace them, especially for the felt roll of the lifting cylinder.

(7) Uneven local wear of rolls such as felt roll and press rolls. Identify the cause of uneven wear on the rolls and replace them promptly.

(8) The local tension of the bottom wire (base wire) of the paper-making felt is uneven. When producing paper making felt, it is necessary to ensure that the tension of the bottom wire (base wire) is uniform and consistent. It is not allowed to use the bottom wire (base wire) with local looseness or elastic bands in the production of felt.

3.The influence of use position

The changes in length, width, and thickness of BOM felts vary depending on their usage areas. For felts of the same variety and weight, when used in the forming section (such as cylinder mould paper machines, super forming paper machines, etc.), the felts have a higher elongation rate due to the larger load; When used in the pressing section, the rate of change in length and width is smaller. As the line pressure increases, the thickness variation of the felt will also increase; When used as a press felt in a yankee dryer cylinder, due to the effects of high temperature and high pressure, the width shrinkage and thickness reduction of the felt will be more prominent, making it easier for the water filtration pores of the felt to become smaller and compacted. These states require us to fully consider them when designing and manufacturing BOM felts.

4. The influence of cleaning system

The quality of BOM felt washing not only affects the water filtration performance of the felt, but also affects the elastic recovery of the felt, that is, the elastic recovery rate of the thickness. If the washing is not done well, it will inevitably lead to the felt being crushed and compacted, the thickness decreasing, the density increasing, and the water filtration permeability decreasing. One of the important functions of high-pressure moveable spray pipes is to increase the thickness of the felt. The requirement for high-pressure water in BOM felt is generally between 10-25kgf/cm2.

5. The influence of abnormal wear and tear

BOM felt should reduce and eliminate abnormal wear during use. Abnormal wear comes from improper settings of roller surfaces and lubricating water such as vacuum box cover, felt support rolls, separating rollers, and press rolls. Abnormal wear and tear will inevitably lead to an abnormal decrease in the thickness of the felt and uneven water filtration.