1.3 Machines:
There are six machines used for insulation: BM 80, BM 100, BM 120, BM 150, BM160 and SAM P BM 160. The number appeared in the name of the machine is related to the diameter of the screw of each machine. Section 3 of this report gives a wide overview of those machines and their specifications. Any machine is able to put insulation, but the BM150 and BM160 is mainly used for bedding and sheathing.
2. PROCESSES
2.1. Introduction
Three different processes are carried out in the insulation section
• insulation,
• bedding,
• Sheathing.
2.2. Insulation process
Two materials are used for the insulation process: Polyvinyl chloride (PVC), and cross-linked polyethylene (XLPE).
The main differences are summarized as follows
• PVC has a maximum operating temperature of 70 C, and for the XLPE is 90 C.
• XLPE, P.V.C are used as insulation for LV cables, while XLPE is used just for MV and HV. However, the incoming material of XLPE used in MV and HV is more pure than in LV, so it is stronger, but at the same time more expensive.
• PCV and XLPE are color less by nature. The color is put according to the customer needs and the Standards; the basic colors are: Red, yellow, blue, and black. The ratio of color is 2 % for PVC and between 0.5 % and 1 % for XLPE. The name of the material used for coloring is "Master batch".
2.3. Bedding process
This process is done right after the assembly process. It is an operation done between stages, before armoring, and before sheathing, if any of those two operations are carried out.
PVC is used as a material, but it is not the same kind of PVC used for insulation. Now, it is recycled PVC of black color. It has not as good electrical characteristics as that one used for insulation, however now there is no need of that, because the objective of the bed layer of the cable is just to be a separator and to protect the insulated cores from the effect of the armoring or screening.
2.4. Sheathing process
The sheath is the outer jacket of a cable used as a cover, just for protection.
This process uses the same extrusion method as that one used for insulation and bedding.
Materials used here are coming in colors, not natural or color less as for insulation.
PVC is used for LV and MV, and its color is according to the Standards (black, red, yellow, etc). The sheathing depends on the customer (depending on its use) and it can be divided as: Flame retardant, flame and termite retardant, acids retardant, ultraviolet retardant, L.S.O.H, underground water resistant.
PE comes in black color, and it is divided into three types, the first two used for MV, LDPE (Low Density PE) and MDPE (Medium Density PE), and the third one used for HV, HDPE (High density PE).
