The performance of a single-screw extruder for the processing of cross-linkable low-density polyethylene in cable coating applications is examined. In particular, the aim is to demonstrate that the melt quality is markedly dependent on the melting efficiency. An instrumented 120 mm, 24: 1 LID extruder is used to perform the study. So-called pull-out tests are carried out for investigating the melting behavior inside an extruder At the beginning of the melting zone, a typical Maddock melting mechanism is observed. Thereafter as melting proceeds, the solid polymer becomes totally surrounded by melt according to the Lindt-Decker melting mechanism, and finally a solid-bed break-up occurs in many circumstances. This undesirable phenomenon can be avoided by screw cooling which, however has its own drawbacks. In addition to the experimental work, numerical simulations of the melting behavior are conducted. The results provided by the simulation are in accord with the experimental findings.