1.Reasons for black bars:
1-1 Thermal decomposition of materials
1-2 Damage to the screw of the injection molding machine
1-3 The material is carbonized due to friction and air compression
2.Related knowledge
2-1 The most common black stripes are caused by the residues of material decomposition remaining in the barrel of the injection molding machine.
2-2 In plunger-type injection molding machines, residues tend to remain in various parts.
2-3 Injection molding machines with valve-controlled nozzles are also prone to residues remaining in the valve-controlled part.
2-4 The air in the barrel is compressed to a high temperature. This high-temperature gas, combined with the shear heat at the gate, easily forms black stripes.
3.Solution
3-1 Immediately: When replacing materials, reduce the injection pressure and the temperature of the heating barrel.
3-2 Short term: Clean the heating barrel (using a copper wire brush).
3-3 Long term: Repair of barrel.
4.Due to the difference in materials
4-1 The pigment, paint, lubricant, UV absorber, antistatic agent, etc. in the mixed resin are overheated in the barrel. The thermal decomposition of these materials when they are retained for a long time is also the cause of black stripes. This tendency will be more obvious when some types of additives have poor heat resistance.
4-2 When using polycarbonate (PC) for molding, black stripes are also easily produced with valve-controlled nozzles.
4-3 Screws with backflow prevention washers are also prone to having burnt residues.
5.References:
5-1 When replacing materials, if no special cleaning materials are used, ordinary soft polystyrene (GPPS) should be used.