Paper Machine Clothing Paper Imprints Problem Solve Method

The Impact of Forming Fabric on Printing Marks and its Solution

These marks match the weave pattern of the forming fabric and can sometimes be found at the same angle on the paper. Forming fabric marks are generally caused by improper forming fabric selection or excessively fast dewatering speed (especially in the initial stage). Improper forming fabric selection requires contacting the supplier to improve the design. Inappropriate dewatering speed can be resolved by increasing the pulp beating degree, adjusting the pulp contact point on the wire to reduce initial dewatering, increasing the spacing between dewatering plates, and adjusting the vacuum level of each vacuum suction box. Insufficient wire tension can also cause marks; in this case, the tension can be appropriately increased. Care should also be taken to avoid the suction pick up roller pressing too deeply into the forming section, lead to forming marks.

Seam Marks

Seam marks are relatively easy to identify on the paper. They appear across the entire width of the paper, approximately 10cm in length, and the intervals between them match the length of the forming fabric on the paper machine. This is related to the forming fabric seam process, and most modern forming fabric manufacturers can likely resolve this issue. If this cannot be improved, a more suitable supplier must be selected.

Longitudinal Stripe Marks

These are mostly caused by local blockage of pulp at the headbox lips, improper installation of the baffle plate, local wear or pulp accumulation on the suction box cover, and uneven spraying of high-pressure water. These issues should not be difficult to resolve.

Imprints from The Press Section

The press section is the most prone to imprints during the entire papermaking process. Generally, the dryness of the paper exiting the forming section is between 18% and 22%. The wetter the paper enters the press section, the easier it is to change the fiber arrangement, causing fiber displacement and thus imprints. In addition, high linear pressure during pressing is also a potential cause of imprints.

Imprints Caused By Paper Making Press Felt and Their Solutions

During the use of paper making press felt, the surface layer is worn away, exposing the base mesh, which is then imprinted on the paper. We usually see obvious, very straight, fine stripes along the longitudinal direction of the paper, with evenly alternating light and dark areas, and relatively dense. Base mesh marks generally appear in the middle to late stages of press felt use. During papermaking, it is important to check the condition of the press felt; if acceptable, appropriately reduce the linear pressure of the press section to reduce base mesh marks. If reducing the linear pressure does not improve the situation, the paper making press felt needs to be replaced. Sometimes, excessive pressure from the high-pressure spray water, wear on the nozzles causing water jet dispersion, excessively high vacuum in the vacuum suction box or a rough vacuum suction box cover can all lead to excessive wear on the felt during use, resulting in premature press felt base mesh marks. In such cases, we need to check the high-pressure spray water pressure, nozzle condition, and vacuum suction box configuration on the paper machine, as well as the condition of the press rolls and felt guide rolls that come into contact with the felt.

Additionally, if regular fine lines appear on the paper sheet shortly after the press felt is loaded, it may be related to an inappropriate press felt design. For example, if the felt weight is too light, excessive water passes through the press zone, leaving dewatering marks on the paper sheet. These marks correspond to the linear density of the base mesh.

In the early stage of , if there are base mesh marks, the following solutions are recommended:

Firstly, increasing the weight of the batt fibers in the press felt increases its wear resistance time, thereby reducing the occurrence of base mesh marks. On the other hand, increasing the weight of the batt fiber weight increases the moisture content of the press felt, and appropriately increases the water flow resistance of the press felt passing through the pressure zone, thereby reducing the dehydration speed and minimizing the base mesh marks printed on the paper due to excessive dehydration. Secondly, increase the weight of the base mesh and utilize the elasticity of the fibers to reduce or cushion the pressure on the fabric. Increasing the weight of the base mesh can be achieved by increasing the number of layers and the density of warp and weft threads in the base mesh. Thirdly, choose different weaving methods for the base mesh according to the different positions on the paper machine and the requirements of the paper sheet. Generally speaking, the base mesh of plain weave has more severe scars, with 2/2 broken twill lines being lighter and 1/3 broken twill lines being lighter.

Press Felt Batt Fiber Layer Marks

As is well known, the press section is the area in the paper machine that bears the greatest linear pressure. When the press felt passes through the press section, improper selection of press felt and improper paper machine operation can both cause batt fiber marks imprinted on the paper. These marks are characterized by worm-like indentations on the paper when viewed from different angles or against the light, using reflected light. They can be single-fiber marks or marks resembling twisted fibers. Batt fiber marks can appear at any stage of felt use. If they appear in the early stages of use, it indicates that the felt is too coarse. If they appear in the later stages, it indicates that the fine surface felt has worn away, exposing the middle layer of felt.

How to Reduce Press Felt Batt Fiber Marks?

Paper making press felt manufacturers can consider selecting a finer surface batt fiber to meet the requirements of paper flatness; increasing the amount of surface batt fiber in the batt fiber layer can improve its abrasion resistance. When necessary, consider adding a portion of low-melting-point bicomponent batt to the surface batt layer. During finishing, increase the temperature to melt the low-melting-point batt surface layer and firmly solidify it with the regular batt, thereby improving the batt’s abrasion resistance. Appropriate singeing treatment during press felt production reduces surface batt. Press felt users should ensure that new felt is installed in the indicated running direction (arrow). This is especially important for seam press felt, as the press felt has already developed a reversed batt direction during needling and finishing. If the paper machine’s running direction is opposite to this direction, it can easily cause batt fiber abrasion and batt fiber marks.

After installation, thoroughly wet the press felt to reduce felt marks caused by dry abrasion of new felt. During paper machine operation, pay attention to the configuration of the high-pressure water pressure and suction box vacuum level. For the vacuum suction box, check the vacuum suction box cover and vacuum gaps when the machine is stopped. Simultaneously, the high-pressure water jets should cover the entire width of the press felt within one stroke, ensuring uniform washing without omissions or repetitions. In addition, the low-pressure fan-shaped spray water in front of the vacuum water suction box is also a very important part, and the two adjacent low-pressure lubricating waters are required to cross-cover each other.

Suction Press Roll Marks

When the paper machine press section is in the form of a three roll two press or a four roll three press composite press, the paper often shows suction press roll imprints that are consistent with the pattern of the suction press rolls. This is because during the vacuum pressing and dehydration process, the fine fibers, fillers, etc. in the paper sheet will form a higher proportion in the pore area than in the non pore area under the action of vacuum suction force, resulting in higher opacity. The solutions for paper machines include changing the pressing form (such as changing the four roll three press to five roll three press), reducing the line pressure, and lowering the vacuum degree. In terms of press felt design, multi-layer base mesh can be considered, using larger diameter base mesh warp and weft lines to improve the rigidity of the press felt and achieve bridging effect, thereby increasing the porosity and compression resistance of the press felt.

Spray Water Marks

Uneven high-pressure spray water causes uneven moisture content in the press felt, inconsistent dehydration in the compression zone, and inevitably forms stripe marks on the paper surface. This type of imprint can only be resolved by strengthening on-site management of the paper machine.

There are many reasons that can cause paper imprints in the wet end of a paper machine, and we need to take different solutions based on the actual situation. On site management of paper machines is very important, and paper machine felt manufacturers should also strengthen on-site observation, deeply understand the characteristics of paper machines, and provide press felt products that are suitable for paper machines.