WCA May 2016

Line speed (m/min)

Thickness (mm)

Melt temp (°C)

Type

Press (MPa)

Speed (rpm)

Sample

HB-1 VB-1 VB-2 HB-1 VB-1 VB-2 HB-1 VB-1 VB-2 HB-1 VB-1 VB-2

0.76 0.76 0.76 0.76 0.76 0.76 1.52 1.52 1.52 1.52 1.52 1.52

Solid Solid Solid

10.5 14.1 15.1 10.0 13.9 13.4 10.1 12.5 11.8

50 50 50 55 55 55 80 80 80 85 85 85

2.7 2.7 2.7 2.7 2.7 2.7 2.1 2.1 2.1 2.1 2.1 2.1

159 162 159 161 161 162 160 160 160 160 160 160

Strand Strand Strand

Solid Solid Solid

Strand Strand Strand

9.3

12.9 13.3

The purpose of this paper is to study the effect of conductor type, stranded vs solid copper, on VW-1 burn performance for four moisture-cure compounds of varying degrees of flame retardancy. In addition to conductor type, insulation thickness, which has been shown to be detrimental to flame performance in halogen-free systems [3] , will be studied. The flame performance will be characterised by the samples’ ability to pass the VW-1 test, the average sample burn time and the charred or uncharred length. 2 Experimental 2.1 Materials The samples tested in this paper were various moisture-cure formulations extrusion coated on to 14 AWG (2.08mm 2 ) copper conductors. Both solid and stranded conductors were used. 30 and 60 mil (0.76 and 1.52mm) insulation layers were studied during the course of these experiments. The moisture-cure formulations used were designated horizontal burn formulation 1 (HB-1), enhanced horizontal burn formulation 1 (EHB-1), and vertical burn formulations 1 and 2 (VB-1 and VB-2, respectively). Prior to extrusion all materials, excluding base resins, were dried in a vacuum oven in the presence of desiccant (Dri-Rite: anhydrous calcium sulphate) for 24 hours at 60°C. The dried materials were then weighed and sealed in foil bags to minimise moisture absorption and prevent pre-cure or scorch during extrusion. 2.2Wire Extrusion Insulation coated wires were made using a mini wire line extruder. The unit consisted of a Brabender ¾" extruder with variable speed drive, a 24:1 Maddox mixing head screw, a Brabender cross-head wire die, water cooling trough with air wipe, a laser micrometer and a Con-Air variable speed wire puller. All extrusions were done using a 150°C flat temperature profile across the three heating zones of the barrel as well as the die. ❍ ❍ Table 1 : Extrusion conditions of various moisture-cure constructions

A layered screen pack geometry containing screens of 20/40/60/20 mesh and a die plate were used to filter the molten polymer just prior to reaching the die opening. In addition, the screens provided sufficient back pressure to ensure better melt mixing of the various formulations. A 67 mil (1.7mm) tip and a 124 mil (3.15mm) die were used to produce 14 AWG wires with a 30 mil wall thickness. The same 67 mil tip was used with a 174 mil (4.42mm) die to produce coated wires with 60 mil of insulation. Table 1 shows the head pressure, screw and line speeds and melt temperatures for each sample produced. 2.3 Moisture curing All wires were cured in a 90°C water bath for 18 hours to ensure full crosslinking. Prior to flame testing the wires were allowed to condition in a temperature and humidity controlled room (25°C and 50% RH) for 24 hours. 2.4 Burn Testing Three cured and conditioned specimens from each formulation shown in Table 1 were subjected to FV-2/VW-1 burns in accordance with UL Standard for Safety for Wire and Cable Test Methods, UL25546. Section 9.4 of the standard defines the resistance of a wire to the vertical propagation of flame and dropping of flaming particles [4] . ❍ ❍ Figure 1 : Effect of insulation thickness on burn duration in VW-1 type test for different formulations

30 mil 60 mil

Burn duration (sec)

52

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Wire & Cable ASIA – May/June 2016