Case Study: Solving Flow Line Defects in EPDM Rubber Tubing

The Manufacturing Issue

An industrial client commissioned a hollow profile made from EPDM rubber tubing for a fluid transfer application. While the material chemistry met all specifications for heat and weather resistance, the initial production runs failed visual inspection.

The tubing displayed intermittent horizontal flow lines and "knit marks" along the exterior. In many standard rubber tubing applications, these marks are considered acceptable artifacts of the process. However, this component was destined for high-end equipment where visible flaws were grounds for rejection. The defects suggested instability in the material flow or pressure maintenance.

Root Cause Analysis

Fenlora's engineering team paused production to investigate the custom rubber extrusion line. We identified two factors contributing to the surface turbulence.

First, minor contamination on the screw was creating friction variances. Second, and more critical to the flow lines, was the positioning of the extruder's exhaust port. The standard bottom-positioned vent was failing to fully release gas pockets from the high-viscosity EPDM compound. This trapped gas created micro-voids and striations as the material exited the die.

Engineering Solution

Cleaning the screw was the first step, but the permanent fix required re-configuring the equipment parameters.

We modified the setup by shifting the exhaust port orientation from the bottom to the top position. This adjustment allowed for natural vertical escape of volatile gases, preventing them from being dragged through the die. We also recalibrated the core rod alignment to ensure the hollow profile maintained concentricity under the altered pressure conditions.

Production Results

The adjustment immediately eliminated the horizontal flow lines. Subsequent production runs of the EPDM rubber tubing showed a consistent, smooth surface finish that passed all cosmetic requirements.

This case demonstrates that weather-resistant industrial tubing can be manufactured to high aesthetic standards when the rheological behavior of the material is properly managed during extrusion.