Colour coding gives automotive tubing a visual identification layer that can simplify assembly, routing, inspection, and service work across complex vehicle systems. Yet producing many standardized colours on the same high-volume line creates a less visible manufacturing challenge: every transition can leave residual material, consume setup time, and generate off-specification tubing.
Nylon tube extrusion must consequently balance colour accuracy with rapid changeover and stable dimensional control. DEKUMA develops multilayer nylon tube extrusion technology for automotive applications, providing an equipment framework in which material feeding, die conditions, and process adjustments can be coordinated during repeated colour changes.
Why Colour Changeovers Create Production Losses
Multi-colour automotive tubing rarely involves one pigment change repeated throughout an entire production run. A single manufacturing schedule may contain numerous identification colours, with some colours requiring especially careful transition management because residual pigment from the previous material can remain inside the screw, adapter, or die flow channel. The first meters after a change may show streaks, mixed shades, or inconsistent opacity.
The amount of transition scrap depends on more than the quantity of material inside the extrusion system. Screw geometry, melt residence time, flow-path design, pigment concentration, temperature, and the colour sequence itself can all influence how quickly the previous shade disappears. A dark pigment followed by a light colour, for instance, may require a different transition strategy from two visually similar shades.
Production planning can reduce unnecessary disruption before the machine even stops. Grouping compatible colours, selecting an appropriate sequence, and reserving shorter runs for colours with difficult transitions can reduce the number of full changeovers. Nylon extrusion becomes more efficient when colour scheduling is treated as part of process planning rather than as an operator adjustment made only after the previous batch ends.
Controlling Material Flow During Colour Transitions
Stable feeding is fundamental because colour concentration depends on the ratio between base polymer and masterbatch. Small changes in feed rate can alter shade intensity, particularly with highly concentrated pigments. Servo-controlled feeding can help maintain a more consistent material ratio while the line moves between production conditions.
Temperature deserves careful attention during a transition as well. Excessive heat can change melt viscosity and affect colour appearance, while insufficient thermal stability may interfere with flow through the die. The objective is not simply to increase temperature until the previous colour disappears; process conditions need to remain within the acceptable window for the polymer and pigment system.
DEKUMA’s Multi-layer Nylon Composite Tube Extrusion Line uses three extruders for separate outer, middle, and inner layers, with servo motors and a listed maximum combined extrusion output of 50 kg/h. Its spiral multilayer die head uses mould steel with a treated flow-channel surface, ceramic heating up to a listed 300°C maximum, and an adjustable die-to-core gap. Although the system is designed around multilayer composite tubing, its controlled feeding and die-management principles illustrate the type of process stability required when production schedules involve frequent material or colour changes.
Designing Changeover Strategies for Low Scrap
Not every colour sequence creates the same amount of waste. A practical production schedule can use colour families to reduce severe transitions, such as moving progressively from lighter to darker shades where the formulation permits. This approach does not remove the need for purging, but it can reduce the amount of material required before the next acceptable colour is established.
Purge material also has to be evaluated economically. Excessive purging may shorten transition time while generating unnecessary waste, whereas insufficient purging can leave mixed-colour tubing that cannot enter the saleable stream. Operators can define acceptance criteria using colour measurements, visual standards, or both, depending on the identification requirements.
Inline monitoring can further shorten the decision interval. Diameter, wall thickness, melt pressure, and other process signals can indicate whether the line has stabilized mechanically, while colour measurement can determine when the visual output has reached the specified range. Nylon tube extrusion benefits from this combined approach because colour acceptance and dimensional acceptance can be assessed as related but separate conditions.
Linking Colour Coding With High-Volume Quality Control
Identification colours serve a functional purpose, so consistency matters beyond appearance. If adjacent batches show noticeable shade variation, technicians may have difficulty distinguishing tubing during assembly or maintenance. The acceptable colour range should be defined according to the identification system, material formulation, lighting conditions, and inspection method rather than relying solely on subjective visual judgment.
High-volume production also requires traceability. Batch information for polymer, pigment or masterbatch, production time, machine settings, and inspection results can help connect a finished tube to its manufacturing conditions. Such records become particularly useful when a colour deviation appears after several transitions and the source cannot be identified through appearance alone.
Changeover performance should be measured using more than scrap weight. Useful indicators include transition length, time until colour acceptance, number of adjustments, rejected tubing, and frequency of repeated changeovers. DEKUMA’s automotive extrusion technology incorporates controlled material feeding and multilayer die management, while broader line configurations can integrate automated process monitoring. These capabilities can provide production data that helps manufacturers evaluate whether a revised colour sequence or setup procedure actually reduces disruption.
Conclusion
Automotive colour coding may appear straightforward on the finished tube, yet producing numerous identification colours efficiently requires coordination between material formulation, production sequencing, melt behaviour, and inspection criteria. Nylon extrusion can support high-volume tubing production when feeding and thermal conditions remain sufficiently stable during repeated transitions.
Scrap reduction depends not on one adjustment but on the interaction of colour sequencing, purge strategy, process monitoring, and acceptance standards. DEKUMA‘s multilayer extrusion configuration, servo-driven material handling, and controlled die system offer a relevant equipment foundation for this type of production environment, while the final colour-change strategy must be adapted to the specific polymer, pigment system, tubing structure, and production schedule.
