Device and method for producing a dyed and an undyed plastic melt

A method for selectively producing a dyed plastic granulate from a dyed plastic melt and an undyed plastic granulate from an undyed plastic melt, the method comprising the following method steps:

• providing a device for selectively producing the dyed plastic granulate from the dyed plastic melt and the undyed plastic granulate from the undyed plastic melt, the device comprising:
• a multi-shaft screw extruder for providing a plastic melt, the multi-shaft screw extruder having a housing, a first infeed opening, a second infeed opening, at least two treatment element shafts and at least two mutually penetrating housing bores configured in the housing, both the first infeed opening and the second infeed opening configured to open into the at least two mutually penetrating housing bores, the at least two treatment element shafts being rotatingly drivable in the at least two mutually penetrating housing bores;
• first metering installation for feeding an undyed plastic material through the first infeed opening into the at least two mutually penetrating housing bores;
• a second metering installation for feeding at least one dyeing agent through the second infeed opening into the at least two mutually penetrating housing bores;
• and
• a control installation for selecting between a first operating mode for producing the dyed plastic melt which is pelletized to generate the dyed plastic granulate and a second operating mode for producing the undyed plastic melt which is pelletized to generate the undyed plastic granulate;
• wherein a first gap is defined between the at least two treatment element shafts, and a width of the first gap in relation to an external diameter of the at least two treatment element shafts is equal to or greater than 0.003 and equal to or less than 0.05 for achieving a self-cleaning of the at least two treatment element shafts:
• and wherein the at least two treatment element shafts and a housing internal wall of the housing define a second gap, and a width of the second gap in relation to the external diameter of the at least two treatment element shafts is equal to or greater than 0.004 and equal to or less than 0.03 for achieving a cleaning of the housing internal wall;
• selecting between the first operating mode for producing the dyed plastic granulate from the dyed plastic melt and the second operating mode for producing the undyed plastic granulate from the undyed plastic melt via the control installation, wherein in the first operating mode at least one dyeing agent is fed through the second infeed opening into the at least two mutually penetrating housing bores via the second metering installation, and an undyed plastic material is fed via at least one of the first metering installation and the second metering installation, wherein in the second operating mode the undyed plastic material is fed through the first infeed opening into the at least two mutually penetrating housing bores via the first metering installation;
• and
• operating the multi-shaft screw extruder, the first metering installation and the second metering installations in a selected operating mode.