The relationship between the press felt and the wet end of the paper machine and how to solve it?

The press section is the most likely location for impression to appear in the paper production process. Generally speaking, the dryness of the paper exiting section is between 18% and 22%. The wetter the paper is in the press section, the easier it is to change the fiber arrangement, causing fiber displacement and causing impression are produced (in addition, high line pressure can easily cause impression).

Base fabric marks of press felt

During the use of press felt, due to the wear of the surface fluff, the base fabric is exposed and thus printed on the paper. Generally, we can see obvious fine stripes in the longitudinal direction of the paper, and the depth is uniform and dense.

Base fabric marks generally appear in the middle and late stages of press felt. In paper production, it is necessary to pay attention to the newness of the press felt and appropriately reduce the line pressure of the pressing section to reduce the base fabric marks if it is acceptable. If reducing the line pressure still cannot improve the situation, the press felt needs to be replaced at this time.

Sometimes, due to the excessive pressure of high pressure spray water, the wear of the nozzle causes the water column to disperse, or the vacuum box is too high, or the vacuum box panel is too rough, the press felt will be excessively worn during use, so that the press felt base fabric marks appear in advance. At this time, we need to check the high pressure on the paper machine, the nozzle status, the configuration of the vacuum box, and the various pressing rollers in contact with the press felt.

In addition, if regular fine lines can be found on the paper page shortly after the press felt is put on the machine, it may be caused by improper design of the press felt. If the weight of the press felt design is too light, excessive water will pass through the press zone, resulting in the appearance of the paper on the paper. Extrude dehydration marks, which correspond to the density of the base fabric.

Solutions to the initial appearance of base fabric marks on press felt

(1) Increase the weight of the velvet in the press felt to increase the wear resistance of the press felt, thereby reducing the occurrence of base fabric marks. In addition, increasing the weight of the velvet increases the moisture content of the press felt, increases the water flow resistance of the blanket through the pressure zone, reduces the dehydration speed, and reduces the base fabric marks on the paper sheets due to excessive dehydration.

(2) Increase the weight of the base fabric and use the elasticity of the fiber to reduce the pressure of the buffer on the base fabric. Increasing the weight of the base fabric can be achieved by increasing the number of layers of the base fabric and increasing the density of the warp and weft in the base fabric.

(3) Choose base fabrics with different weaving methods according to the different positions on the paper machine and the needs of the paper sheets. Generally speaking, the base fabric marks on plain press felts are more serious.

Traces of press felt pile layer

The press area is the area where the paper sheet bears the greatest linear pressure in the paper machine. When the press felt passes through the press area, improper selection and operation will cause traces to be imprinted on the paper sheet. You can use emitted light to view it from different angles. Or it may show earthworm like dents when viewed against the light, with velvet marks of a single fiber and twisting marks of multiple fibers.

Press felt will have velvet marks at any time. If velvet marks appear in the early stage, it means that the velvet of the press felt is too rough. If they appear in the middle and late stages of the press felt, it means that the fine velvet of the press felt has been worn out, exposing the velvet in the middle layer to the surface.

How to reduce velvet marks?

In the production of Press felt, a finer surface velvet is selected to meet the requirements of paper flatness, increase the amount of surface velvet in the fiber layer of the press felt, and improve the wear resistance of the surface velvet. If necessary, a part of low melting point two component velvet can be added to the surface velvet layer. When the press felt is finished, the temperature is increased to melt the surface layer of the low melting point velvet and condense with the conventional velvet, which can improve the wear resistance of the press felt. Appropriate singeing treatment is used during the production process of the press felt to reduce the floating velvet on the surface of the press felt.

Things to note when putting press felt on the machine

When using the press felt, choose to install it with the arrow indicating the running direction. The press felt forms the reverse direction of the velvet during the velvet

and post finishing. If the running direction of the press felt is opposite to the velvet, it is easy to cause the press felt to wear and cause velvet marks. After the machine is installed, the press felt is fully moistened to reduce the velvet marks caused by dry grinding of the new press felt. When the paper machine is running, pay attention to the configuration of the high pressure water pressure and the vacuum degree of the vacuum box. It is also critical to check the vacuum box panel and vacuum gap and the low pressure fan shaped spray water in front of the vacuum suction box when the machine is stopped. In addition, the water needle of high pressure water should cover the entire width of the felt within one stroke, so that the felt can be washed evenly without omission or repetition.

Pressing dehydration marks on paper sheets

When the paper sheet passes through the pressing area, a large amount of water is squeezed onto the felt, and then transferred to the roller or boot, causing marks.

The characteristics of dehydration marks are also thin, straight and regular marks in the longitudinal direction of the paper sheet, or some regular hole marks.

These marks may be marks of the press felt base cloth, vacuum roller or blind hole roller, groove roller or shoe press belt. When the pressure of the pressing area line is greater, more water passes through the press felt, and the more likely it is to produce dehydration marks, especially in the middle and late stages of the press felt use.

The dehydration marks on the paper sheet caused by the base cloth are easily confused with the groove dehydration marks. (Distinguishing: Whether the number of impressions per centimeter on the paper matches the density of the base fabric or the groove density. Generally speaking, the linear density of the base fabric per centimeter will be higher.) In short, the impressions on the paper formed by the wet end of the paper machine There are many reasons, and different solutions need to be taken according to the actual situation.