Views: 0 Author: Site Editor Publish Time: 2022-07-15 Origin: Site
Dehydration element selection principle?
The wear properties of a material determine how long it can maintain the correct shape, such as the leading edge of the ceramic strip and the angle of inclination. The stable operation of the paper machine can only be provided with the performance that can be used for a long time, and the initial high cost investment is not in vain. There is no standard classification method for wear-resistant grades, and different suppliers have their own classification and testing methods for wear-resistant grades. In-machine performance is instructive in order to evaluate the wear properties of used materials. In any case, the expected material life is always a machine- and application-dependent selection basis.
If the surface of the paper machine is often worn, indicating that the slurry is very abrasive, ceramics with high wear resistance must be selected; if the slurry is poor in abrasiveness, any qualified ceramic can be used, and the choice of material mainly depends on other characteristics. Require.
In some cases, wear resistance needs to be sacrificed in consideration of other principles such as thermal shock resistance or toughness. For heavily worn paper machines, the ceramic surface needs to be checked regularly. Very rough dewatering elements should be checked every time the forming wire is changed.
Forming wire wear:
Ceramics are so wear-resistant materials that they often wear away other relatively soft materials, like a grindstone. Therefore, special planning is required when selecting ceramic surface materials for the wet end of the paper machine to reduce the wear of the forming wire. It is very important to avoid contact with sharp leading edges and rough surfaces of ceramic components, in addition to providing adequate lubrication. Likewise, there is no standard method for classifying the wear level of the forming wire. It is important to refer to the performance of the ceramic material, which can also be checked against the performance of similar or higher loads, vehicle speeds, and filled paper machine ceramic components.
Ceramic surface roughness and edge sharpness are very important, but their effect on forming wire life is a combination of the grade of ceramic used and the specific application of the paper machine. There is no standard for how sharp the edges of ceramic components are. Most suppliers specify an edge chamfer radius of 0.25~0.64mm for new ceramic components to avoid sharp edges. The chamfer radius should increase as the vacuum level increases. When applied under high vacuum conditions, the edge chamfering radius of the ceramic dewatering panel can be as high as 1.52mm. When the application position is larger than the conventional wrapping angle, the edge chamfering radius of the ceramic dewatering element also needs to be correspondingly increased. Some ceramic dewatering elements in the wire forming area require different chamfering radii due to sheet making. Old dewatering elements can be ground to their original chamfer radius to avoid safety hazards caused by sharp edges and the resulting shortened forming wire life.
It is strongly recommended to test the surface roughness and edge sharpness of the ceramic dewatering elements in conjunction with the acceptable level of forming wire wear for each paper machine operation. The detection of surface roughness requires careful interpretation. At or near the edge of the ceramic, the ceramic surface is often highly polished due to high wear, and rougher in relatively large, flat areas due to relatively low wear; therefore, both Perform surface roughness inspection. Any material selected should be smooth, crack-free, and free of internal voids to avoid sharp edges that can wear out the forming wire when voids are exposed, and also deposit or slow down rough particles running on its surface.
Some factories offer regrinding services to refurbish or grind worn or rough ceramic surfaces and sharp edges to their original surface finish values.
Mechanical stress due to impact or roughing can limit some applications that could benefit from choosing a higher strength material. Ceramics are known to be sensitive to cracks, and the cracks in the ceramic microstructure can propagate under sufficient mechanical stress. There are two ways to assess the ultimate strength of ceramic materials in order to draw conclusions about the load/shock resistance of ceramic dewatering elements. The "Toughness" K1c or "Notched Beam Test" method refers to measuring the energy required to cause crack propagation in a notched test specimen. The "Flexural Strength Test" (ASTM F417-78) is a four-point bending test method to determine the modulus at break of a notched test specimen. If ceramic elements are frequently handled or broken, another tougher material may need to be considered. All ceramic components should be handled horizontally and should not be bent. Due to the loading and tension of the paper machine, some parts of the paper machine require tougher materials. While tougher materials are better at resisting damage, no ceramic is completely resistant to damage due to its inherent brittleness. In some cases, ceramic toughness needs to be sacrificed, considering wear or thermal shock resistance.
Thermal shock resistance:
Under the premise of no visible cracks, the high-speed cooling that ceramic materials can tolerate is called thermal shock resistance. For materials with simple shapes, the value is usually given in degrees Celsius (or Kelvin). Materials with complex shapes will be relatively less impact-resistant because thermal stress will be higher. Some phenomena such as sudden temperature changes: flushing cold water or lubricating water to the hot parts of the paper machine, or low temperature slurry to the dry hot parts, if these phenomena cannot be avoided, you need to consider the selection of ceramics with high thermal shock resistance. Other factors that influence the need for thermal shock resistance are paper machine speed, vacuum level, drying capacity and ceramic geometry. Even if the ceramic material has high thermal shock resistance, losses cannot be avoided, so the solution is to change the operating procedures to eliminate the thermal shock hazard and/or provide adequate lubrication.