Wire and cable nylon sheath technology

2022-03-04

Because nylon materials have different properties than ordinary plastics, some unique process requirements are presented during the extrusion process.
The main requirements of the production process are discussed below
1. Drying process
Since the nylon material is a polar medium, it is easy to absorb moisture. According to the material manufacturer, when the water content of the nylon material exceeds 0.3%, it cannot be extruded. In the actual production process, it is found that the nylon material is damp, and the extrusion sheath will foam. such as foaming, granulation or breakage. The nylon material itself is packed in a vacuumed vacuum bag, which can be put into use directly if there is no broken bag.
Therefore, damp nylon materials should be pre-dried before use. It is best to use vacuum and rotary bucket heating to remove moisture, and the drying amount each time should not exceed 3/5 of the dryer volume. If the capacity is too large, the material in the dryer is difficult to rotate, resulting in uneven heating, and it is difficult to remove the water in a short time. If the time is long, some materials will oxidize and turn yellow, which cannot meet the requirements of the extrusion surface. The vacuum degree of vacuuming should be above 0.05MPa, otherwise the water will be difficult to remove. If steam heating is used, the heating temperature should be controlled by the amount of steam. The temperature should be 80±50℃. If the heating temperature is too high, the nylon material will oxidize and turn yellow. .
Extruder Requirements
There are two types of extruders, vertical and horizontal. The screw length-diameter ratio is generally 20:1; 25:1, the screw and barrel clearance is 0.14-0.18mm, and the compression ratio is 4:1 or 3.5:1
The ordinary progressive screw can guarantee plasticization at low speed, but the extrusion volume is not large, while the separation screw has more uniform plasticization and larger extrusion volume.
The extrusion temperature of nylon is narrow, and the temperature control requirements are relatively high. If the temperature is too high, nylon will cause scorch, and if the temperature is too low, nylon will condense and solidify, causing blockage of the mold. Nylon has an obvious melting point of 215°C, and the condensation is very fast, so the temperature of each section of the extruder must be slightly higher than 215°C, and the temperature of the extruder is controlled from the feed port to the extrusion die. The allowable deviation is ±7 °C) as follows
Zone 1 Zone 2 Zone 3 Zone 4 Zone 5
230℃ 235℃ 235℃ 235℃ 235℃
The extrusion temperature should be properly adjusted according to the air temperature, the wire speed and the amount of nylon glue, and special attention should be paid to the temperature of the extruder neck, because this is the connection, and there are filter plates, filters, Flange jacket, etc., the heat dissipation area is large, so it is difficult to heat in place. If the heating does not meet the requirements, and the nylon condensation speed is fast, it is easy to form part of the nylon solidification in this area when the machine is just turned on, so that the extruder cannot be glued. , then the screw is in danger of breaking. Therefore, when starting up, the temperature of the neck or the temperature close to the two ends of the machine neck should be 5 °C higher to facilitate heat transfer. After the temperature of each section reaches the specified value, it should be maintained for 5-10 minutes to ensure that the temperature at the machine neck meets the predetermined requirements. , so that condensation and blockage will not occur. In addition, when the screw is just started, you should immediately observe the screw current meter to observe whether the current is abnormally large. If the current is too large, you should stop it in time, and increase the heating temperature or continue to heat.
The role of the filter
1. Filter out particulate impurities and scorched particles
2. Increase the resistance and back pressure of the logistics to make the nylon plasticization more uniform

3. Increase the pressure to make the extrusion flow uniform.