In the production, there will be “water wave” and “shun […]
In the production, there will be “water wave” and “shun” in the conveyor belt. This phenomenon is mainly caused by uneven vulcanization of the conveyor belt. The thermal dimensional stability of the EP canvas at high temperature and the vulcanization in the conveyor belt Tension in the process is a key factor. The conveyor belt manufacturers below will take a detailed look at the factors affecting the appearance of the conveyor belt.
Fiber structure and properties
For NN or EP industrial yarns, the fiber state inside the fiber tends to curl. When spinning, it uses high tension at high temperatures and holds it until the fiber cools to allow the molecules to be pulled down at high temperatures and fixed during cooling. However, if heated again, it will again shrink above the glass transition temperature (about 100 degrees) and the amount of shrinkage will depend entirely on the amount of tension the material is subjected to in the original heat treatment. Therefore, the high-tension cooling fiber after stretching has good molecular flatness, which means high strength, low elongation and high heat shrinkage; low tension cooling fiber after stretching has poor flatness and thus low strength. High elongation and low shrinkage. If the same fiber is heat treated at different temperatures and tensions, fibers having different properties are obtained, and then under certain heat treatment conditions, the residual shrinkage of the fibers after free shrinkage of the fibers will be substantially the same.
Another feature of synthetic fibers is that at high temperatures, the material produces shrinkage forces. The greater the pre-tension, the greater the contraction force. Therefore, if vulcanized, excessive stretching will cause a large contraction force of the warp yarn to increase. The greater the tension, the greater the contraction force, which forces the weft yarn to deform further. If the warp yarns are tightly packed, if the EP conveyor belt needs to be widened, there is no room for widening during vulcanization, which can wrinkle the canvas and appear "avoid". After the material shrinks, the absolute strength does not differ much, but the relative intensity varies greatly. If the material shrinks heat, the material becomes thicker and the relative strength is greatly reduced. Other heat shrinkage rates are small, and the material thickness does not change without relative strength, so the fiber strength of low heat shrinkage tends to be low.
However, once the material undergoes the same heat treatment, after shrinkage, if the residual heat shrinkage is uniform, the relative strength is substantially the same. Therefore, when evaluating different matrix materials, the user should heat treat them under normal production process conditions to change the thermal shrinkage of the material and then evaluate its mechanical properties. Otherwise, the assessment is of little significance.
Problems caused by high heat shrinkage
Since the conveyor belt manufacturer usually needs high-strength and lightweight canvas, it can improve the tension during the heat treatment, such as impregnation, so that: 1 the fiber does not shrink and impregnate, the weight of the impregnated canvas increases; 2 the warp yarn is stretched to reduce the warp of the canvas Curl and reduce the weight of the canvas; 3 When the warp is stretched, the inner fibers can also be stretched to keep the molecules straight. The state has also increased its power. All of this maximizes the strength of the canvas before it is subjected to the vulcanization heat treatment, which meets the user's requirements for entering the factory. However, this treatment method does not cause any damage to the finished product performance of the conveyor belt because it severely reduces the curl of the canvas and the thermal dimensional stability is extremely poor, that is, the size of the material is greatly increased. It is heated. Variety. If the heat shrinkage rate is too high, the absolute heat shrinkage unevenness of the impregnated canvas will be improved. For example, the heat shrinkage of the canvas is 5% ± 1%, and the other is 1% ± 0.5%. Obviously, the former has a relative error of only 20%, which is difficult to control during processing; while the latter has a relative error of 50%, which is easy to implement during processing. But the impact on product quality is that the latter is smaller than the former. If there is a large absolute difference between the canvas layers in the conveyor belt, the shrinkage ratio between the fabric layers is inconsistent, and when the tension is insufficient after cooling, canvas wrinkles having a low shrinkage rate may occur. At the same time, the performance of each layer of canvas is inconsistent, affecting the full-layer tensile strength. Therefore, it is not recommended to use high-shrink industrial silk EP canvas warp yarns, but to promote EP canvas produced from low-shrink industrial yarns, as well as low-stretch, impregnated heat shrinkage between canvas warp yarns. More uniform, the vulcanized warp yarns are more uniform. The elongation at break is also relatively uniform and the strength is higher. If high shrinkage industrial yarns are used, the heat shrinkage must be reduced during the impregnation process to ensure the thermal dimensional stability of the canvas.