What is the reason why the paper faced gypsum board does not stick to paper and regain moisture

What is the reason why the paper faced gypsum board does not stick to paper and regain moisture

1、 The bonding between the face paper and the gypsum core is poor, resulting in the problem that the board core is exposed or the paper is not stuck locally. This kind of problem is related to the production process of face paper, raw material quality and drying.
First of all, if the air content of the paper is too high or the water absorption is too high or too low, it is easy to cause rapid loss of water and lead to poor binding; Secondly, the grade of gypsum in the raw materials is too low, there are too many impurities or the content of harmful impurities such as K and Na is too high, which affects the bonding between the paper and the gypsum core. Third, the setting time of the building gypsum is too slow, and the building gypsum is not fully solidified or there is a false setting phenomenon before entering the drying area, resulting in the building gypsum is not fully hydrated, thus making the dried board out of paper. Fourth, the molding and drying speed cannot be adjusted in time with the fluctuation of the cover paper or slurry, resulting in the incompatibility between the air permeability and water absorption of the cover paper and the drying speed, and the incompatibility between the setting time of the gypsum slurry and the molding speed, resulting in the non bonding of the paper and the gypsum core or the over burning of the plate. Fifth, too thin slurry, uneven foam, too many or too concentrated macropores in the plate after drying will also cause poor adhesion of paper and core.
2、 Uneven phenomena such as corrugated plate surface and pull groove. This kind of problem is related to paper index and process control.
First, the paper factor. The banner ration, moisture content and air permeability of the face protection paper are not uniform, resulting in different tightness and thickness of the paper, and different water absorption. Where the moisture is large, the moisture expansion is small, and the moisture expansion is large, and the shrinkage is serious in the dry area, while the dry shrinkage is small in the surrounding areas with less moisture, thus causing inconsistent expansion and contraction of the paper and causing ripples or ditches.
Second, the problem of process equipment. If the flatness of the forming platform is not enough or the adjustment is not in place, the uneven plate surface can also be caused. The problems caused by this reason are concentrated and easy to find, but the improvement of the plate surface flatness must be realized through the improvement of the process equipment.
Third, the fluctuation of material properties and slurry is also one of the important reasons for uneven plate surface. Due to the fluctuation of raw materials and additional materials, as well as the fluctuation caused by the pulverizing process, it is inevitable that the coagulation time, weight rise and other indicators of the powder and slurry will change to some extent. However, if the fluctuation is too frequent or large, it will cause the process of the subsequent process to be difficult to adjust and control in time, and may also cause the plate surface groove and other adverse phenomena.
3、 The phenomenon of paper pick-up on the plate surface.
The paper pick-up on the surface of the plate not only affects the appearance quality of the plate, but also adversely affects the internal quality indexes such as the strength of the plate to a certain extent. Therefore, it can not be ignored. The main influence factor of the paper take-up on the surface of the board is the cover paper.
The bonding force between the layers of the protective paper is poor, and the water content of the paper is too high. In the process of forming and absorbing water, the bonding force between the layers of the paper will be further reduced. In the process of relative movement between the plate and the equipment, and between the plates, the phenomenon of paper rubbing will occur. In serious cases, the paper balls produced by paper rubbing will scratch the surface of the plate, and lead to serious quality problems such as easy fracture. Therefore, in the production process of paper faced gypsum board, we should try our best to select the paper with stable water content, water absorption and other indicators.
4、 Low strength, easy to break and crack plate.
The broken plate is mainly shown as transverse fracture, and the bad operation phenomenon during lifting is excluded. The main influence factor of the broken plate should consider the longitudinal strength of the cover paper. The strength of cover paper has an important relationship with its quantitative and other indicators. At present, with the development and competition of gypsum board and cover paper industry, the quantitative of cover paper is reduced from 230g / ㎡ - 250G / ㎡ to 180g / ㎡ - 210g / ㎡. The reduction of quantitative will inevitably lead to the reduction of strength and changes of other indicators. Gypsum is the main raw material of gypsum board. Its grade and physical properties are another important factor affecting the strength of gypsum board. For natural gypsum, it is generally required that its grade is not less than 75%, and the 2H bending strength of building gypsum is not less than 1.8MPa, which is the most basic requirement to ensure the strength of gypsum board In addition, the impurities and acidity and alkalinity of gypsum also have adverse effects on the strength of gypsum. In the production of gypsum board, glass fiber is often used as the reinforcing material to improve the strength of the board. Therefore, if the reinforcing fiber is not added enough in the production, the strength of the board will be reduced and the board will be easily broken. At the same time, if the material of the reinforcing fiber fails to meet the requirements, its reinforcing effect will be greatly reduced For example, if glass fiber is used as reinforcement material, alkali free fiber is generally used, which has certain flexibility and high strength. If alkali containing fiber is used, even high alkali containing fiber will not play the role of reinforcement due to its brittle material and low strength, resulting in brittle fracture of plate. It is also an important reason that the plate is easy to break due to the scratch on the plate surface In the production process, if there are hard particles such as rust and sand left on the plate surface, it is very easy to scratch the surface of the cover paper of the plate during the relative movement of the plate, and the plate is easily broken along the scratch Such problems generally do not occur in large quantities. Careful observation is easy to find and clear. The crack mainly occurs along the longitudinal direction of the plate In addition to the low transverse strength of the protective paper and gypsum strength, another important reason is the edge warping of the plate, which causes cracks in the plate at the stress concentration when the plate is pressed during storage and transportation. There are many reasons for the edge warping of the plate If the expansion rate of the cover paper is large or the shrinkage rate of the upper and lower paper is inconsistent; If the slurry is too thin or the material property is unstable, the process control is unstable and the operability is poor, which will lead to the edge warping of the plate. Therefore, in order to improve the strength of the plate and reduce the problems of fracture and crack, we should try our best to select the protective paper and high-grade gypsum with strength, air permeability and water content suitable for the production requirements; Strictly control the processing and molding process of powder.
5、 The surface of the plate is bubbling and bubbling.
The blistering and bulging on the surface of gypsum board are mainly caused by too thin slurry or improper use of foaming agent in production, poor air feeding performance of face paper, etc. Sometimes, the foaming diameter is less than 1cm, but it is almost all over the whole board surface. This is mainly because the gypsum slurry is too thin or the foaming agent has poor foam stability, and there are many large bubbles, so that a large number of bubbles are concentrated on the surface to form large bubbles. Especially after the board is placed for a period of time, the bubbles are more obvious. Some bubbles are larger and sometimes more regular, such as a straight line along the edge; In some cases, the number of bubbles is small, and it is difficult to determine their regularity, which is related to the low and uneven air feeding property of the cover paper and the low bonding force between layers. The air permeability of the paper is low, which makes the moisture in the paper difficult to evaporate and the bonding force between the layers of the face paper is low. During the production or storage process, local poor adhesion or paper delamination occurs, which leads to the bulging of the plate surface, and the serious performance is large-area non adhesion.
6、 The plate is easy to deform.
With the development and competition of the gypsum board industry and related industries, the unit quality of face paper and gypsum board has been reduced to a certain extent. First of all, the paper shrinkage rate is too large due to the reduction of the quantitative value of the cover paper, which leads to the insufficient tightness of the cover paper, resulting in the insufficient stiffness of the gypsum board, and the machine is easy to deform after moisture absorption; Secondly, if the air permeability of the cover paper is low, the air permeability is slow, and the drying is slow, the deflection of the dried sheet after moisture absorption is large; In addition, during the forming process, if the slurry consistency is adjusted depending on the water consumption, the water consumption will be large, and large voids will be generated in the plate after drying and evaporation, the plate will be too light or soft, and the deformation deflection will be increased.
7、 Paper interruption in the production process.