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Discussion on measuring method of soft material diameter for cable filling
May 01, 2018

 The roundness of XLPE insulated power cable is often caused by the measurement error of the diameter of the cable filler polypropylene mesh fiber and the Strand soft rope. Because this kind of material is fluffy, soft, no fixed section shape, so the conventional diameter measurement method can not be used. At present, there is no practical and feasible method of measuring the diameter of the soft rope in the industry, and the material specifications are not enough to meet the requirements. Three-core XLPE cable is our leading products, the appearance of quality problems directly affect our factory's products and corporate image, and economic benefits. Therefore, it is necessary to solve the problem of measuring the diameter of the soft rope.

  

     A new method of measuring the diameter of the soft rope is put forward through long-term practice, exploration and summarization. Analysis of the current situation of measuring the diameter of the Strand soft rope three diameter of the same core 22 tangent, and respectively with the outer layer is cut, and the strands of soft cotton occupy the line core and the space of the protective suite, forming a curved edge fan. Obviously, in the cable structure design of this curved edge sector is not difficult to calculate, and how to ensure that the soft cotton in the use of the state of the design requirements of the section is a big problem. And the strands of soft cotton from polypropylene blown film tear into the mesh of fiber, many strands of twisted, its appearance features fluffy soft, irregular cross-section shape, different points of the cross-section size is inconsistent. How do we measure these characteristics and how to define the "diameter" of the soft rope? In this respect, the current industry procurement norms are not stipulated, and the stock of soft rope production plant and cable factory also did not have a clear definition of its "diameter".


The measurement of its "diameter" generally adopts the following methods:

      (1) The soft rope in the natural state, with vernier caliper light card reading, as its "diameter";

      (2) After applying the axial tension to the soft rope, the reading is made by vernier caliper light card;

      (3) The spinning of the outer polypropylene rope along the Strand rope is tightened, and the reading is made by vernier caliper light card; (4) Measuring the weight of a certain length and calculating its "diameter" according to the weight of the unit length provided by the production plant.


Method 1 is obviously inappropriate.


Method 2 is slightly improved than Method 1, but it can not guarantee that the cross section is round and the concept of light truck cannot be mastered, so its "diameter" can not be controlled. Method 3 The spinning of the outer polypropylene rope along the soft rope of the same strand is twisted, its appearance is obviously twist shape, the fluctuation of each point is big and different, it is impossible to determine where to represent its "diameter".


This phenomenon is due to the two adjacent layers of soft cotton rotation to the contrary, along the outer tightening, adjacent to the inner layer will be travel loose, will naturally appear outside the bag, sunken phenomenon. Method 4 with the same material density and open net condition, using this method to calculate the "diameter" is relatively accurate, but because the manufacturers and strands of rope material formulations are not the same, that is, the proportion of the additive, the density of a larger range of changes in another open network situation, and the soft and hard rope has a certain difference, and its "diameter" What exactly is the concept of unclear, therefore, the manufacturer provides the material standard stipulates that the unit length weight to determine the diameter of the strands of soft rope and the allowable deviation is ±25%. And we need and the "diameter" of the soft cotton of each specification difference of 2mm, such a tolerance is unable to distinguish several adjacent specifications.

 

      On the other hand, if the above factors can be eliminated, this method is difficult to be used in the "diameter" control in the production of soft rope. It is difficult to conceive of a section in the production process that is frequently used to weigh its weight; in the use of detection, one is more trouble, the second is too much waste, and can not be the "diameter of the" Wow surface control.


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