INFLUENCE OF THE AIR LAYER BETWEEN THE CONDUCTOR AND THE LAYER OFINSULATING MATERIAL IN CABLE PRODUCTS

There are developed mathematical model of physical and chemical processes of polymerization adhesive coating stranded cable. There are shown difference in the temperature distribution along the radius of the finished product in the presence of an air gap between the conductor and the rubber sheath. Also, due to the need to change process parameters with possible loose contacts inside the cable. Such as the temperature of the heating surface, feeding speed and dwell time in the oven.


Introduction
Production of cables is a long and energy-intensive process. The result is a whole product length of 100 meters. In this case, even a small marriage invalid. It is believed that contact between the conductor and the layer of insulating material of the finished cable product is ideal, in shell tightly to the copper conductor. Acceptable dimensions of gaps, as a rule, does not exceed 0.01 mm [1].
The aim of this study was to determine the possible impact of the presence of the air layer between the copper wire and the rubber shell, exceeds the limit, the polymerization on the final products of the cable sheath.

Problem statement
Numerical simulation was carried out in the system shown in Fig. 1. It was assumed that the cable consists of a copper conductor, an air layer and a rubber sheath. Considered axial symmetric system. In the numerical simulation used the following assumptions do not impose significant restrictions on the common statement of the problem: 1. The cable has a right cylindrical shape. 2. We consider a fragment of a perfectly insulated cable end. 3. The thermal characteristics of the material strands, the cable sheath and the air in the heating chamber does not depend on temperature.
4. The activation energy of the polymerization process is constant with temperature. 5. The cable is stationary relative to the camera. A mathematical model of heat and mass transfer system "hot aircable" in a cylindrical coordinate system (Fig. 1) for 0 <t <t p can be formulated in the form of a typical stationary differential equations of mathematical physics [2,3]. The heat equation for the core (0 <r <R 1 , 0 <z <Z 1 ): The heat equation for the air layer (R 1 <r <R 2 , 0 <z <Z 1 ): The energy equation for the insulating sheath ( R2 <r < R3 , 0 <z <Z 1 ): The initial (t = 0) conditions: T=T 0 at 0<r<R 3 , 0<z<Z 1 ; φ=φ 0 at R 2 <r<R 3 , 0<z<Z 1 .
The system of non-stationary differential equations with appropriate boundary conditions is solved by finite difference method [4]. Difference analogs of differential equations solved locale-no-one-dimensional method and variable direction [4]. To solve the two-dimensional difference equations applied sweep method using a four-point implicit scheme [4].

Results and discussion
It can be seen that the presence of the air layer, exceeding the limit value considerably influences the temperature distribution along the radius of the finished product (Fig.2). The surface of the cable is heated to considerably higher temperatures, which can lead to burnout of the shell. Also, due to gapping may be incorrectly selected process parameters (time, speed of pulling, the temperature of the heating surface), which in turn may affect the polymerization of the shell.
It is necessary to control the fit sheath to core in the manufacture of cable products to improve the quality of the finished product (the degree of polymerization of the rubber should be close to 1).