Analysis of Common Causes for the Quality of Paper faced Gypsum Board

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Analysis of Common Causes for the Quality of Paper faced Gypsum Board
1 Impact of face protection paper
1.1 The air permeability of paper is too low. Air permeability actually refers to the air permeability resistance of the paperboard. The air permeability of paper mainly affects the forming speed of gypsum plasterboard. At the same production speed, the greater the air permeability of paper (s/100ml), the wetter the plate from the dryer, and the greater the plate deflection. In order to ensure the production quality, it is necessary to reduce the production speed and output. However, if the air permeability is too low, the moisture in the gypsum board evaporates too fast during the drying process. The moisture in the starch in the gypsum core evaporates through the junction of the paper core and migrates to the paper, which affects the dry bonding performance of the paper and the core, and makes the board brittle.
1.2 The water absorption of paper is too high or too low. The water absorption of paper is related to the sizing degree of face paper. In the process of gypsum hydration, the growing needle like crystals will grow into the face paper, thus forming a good combination with the face paper. If the sizing is too heavy, the paper surface is relatively hard, which is not conducive to crystal penetration; If the size is too small and the water absorption is too large, the water in the gypsum slurry will be largely absorbed and evaporated quickly, which is not conducive to the growth of gypsum crystals, and will also affect the good adhesion of the paper core. The proper air permeability of paper depends on the actual situation of the production line and cannot be generalized. In general, the production line with large water solid ratio should choose the face paper with large quantitative and slightly high water absorption. Generally, the production line with water solid ratio of 60~70 uses 220 g/m2 of face paper, and its water absorption is generally 15~20 g/m2. The determination of the quantity and water absorption of paperboard must be combined with the production process and industrial and mining conditions of gypsum board. Such as production speed, drying process, etc.
2. Influencing factors of gypsum and other raw materials
Gypsum is the main raw material for the production of gypsum plasterboard, and the performance of gypsum is an important factor affecting the performance of gypsum plasterboard. The grade and impurity content of gypsum, the setting time of building gypsum and the use of various additives will have a certain impact on the bonding performance of face paper and gypsum core.
2.1 The grade of gypsum is too low
Generally, the grade of natural gypsum is required to be no less than 75%. If the content of calcium sulfate dihydrate in gypsum is too low, too few gypsum crystals will be formed during the forming process of gypsum board, which will affect the bonding between face paper and gypsum core.
2.2 Content of K, Na and other impurities in gypsum
Generally, the content of K, Na and other impurities is not too high, but it has a great impact on the bonding performance of gypsum plaster. Therefore, it is generally required that the content of K, Na in gypsum plaster board is not higher than 0.02%. If the content of K, Na and other impurities in gypsum is high, a layer of salt mold will be formed at the junction of paper core during the molding and drying process of paper faced gypsum board. When the board is in a low temperature and high humidity environment, the board is very easy to absorb water, making the paper core detached.
2.3 Effect of additives such as foaming agent
In order to improve the physical properties of building gypsum and gypsum plasterboard, additives such as water reducing agent, foaming agent and setting regulator are often added in the production of gypsum plasterboard. The use of these additives will also have a certain negative impact on the plate. Firstly, some additives contain a certain amount of Na inorganic salt, which will increase the accumulation of Na in gypsum slurry and affect the bonding of paper core to a certain extent; Secondly, if the PH value of the additive is not controlled during selection and procurement, the PH value of gypsum slurry will fluctuate due to its influence, which will affect the setting time of the slurry and the bonding performance of the paper core; In addition, the foam stability of foaming agent has always been an important index affecting its performance and use effect, and this index of domestic foaming agent is mostly in the critical state required. For example, the foam diameter of foaming agent is too large or the stability is low, and there are many large bubbles formed after mixing with slurry, even more concentrated, which will cause poor local bonding of gypsum board.
3. Influence of process control factors of gypsum plasterboard
3.1 The gypsum slurry is too thin and contains a large number of large bubbles or moisture, resulting in a large number of large voids or boards in the board core after drying