KraussMaffei MC45: Screw Speed Overload — Plasticizing Unit Diagnostics

KraussMaffei Alarm MC45 indicates the screw drive motor (electric servo or hydraulic motor, depending on machine series) has exceeded its maximum torque/current limit during screw rotation (plasticizing phase). This is fundamentally different...

KraussMaffei Alarm MC45 indicates the screw drive motor (electric servo or hydraulic motor, depending on machine series) has exceeded its maximum torque/current limit during screw rotation (plasticizing phase). This is fundamentally different from an injection pressure alarm — MC45 indicates the screw cannot rotate under load, which points to either a mechanical binding condition in the plasticizing unit or an overload condition from processing material at incorrect temperature.

Diagnostic Protocol

Electric Drive (CX, GX, PX series with BluePower servo drive): The MC4 controller records peak torque, RMS torque, and duration of the overload event. Pull up the screw drive torque trace for the last 10 cycles — it will show whether the overload occurs at the start of rotation (cold polymer in the barrel), during the entire rotation period (excessive backpressure), or intermittently (mechanical binding at a specific angular position of the screw — indicates bent screw or uneven barrel wear). Hydraulic Drive (MX, older CX series): Measure hydraulic pressure at the screw motor inlet during rotation — compare to specification. High pressure with slow screw rotation indicates either: (a) excessive backpressure setting (check Setup > Plasticizing > Backpressure — typical 5-20 bar for standard materials, up to 50 bar for engineering resins requiring homogenization); (b) hydraulic motor internal leakage (worn rotating group in a piston motor — case drain flow >10% of nominal motor flow); or (c) pressure compensator on the pump stuck at low displacement — pump cannot deliver required flow at the pressure needed for screw rotation.

Mechanical Binding: If the screw rotates freely by hand when the drive is decoupled (electric: remove belt and rotate screw shank with a strap wrench; hydraulic: disconnect drive coupling and rotate with a bar), the problem is in the drive system. If the screw cannot be rotated by hand, the screw is bound in the barrel — NEVER force rotation with a cheater bar (this will gall the screw flight lands to the barrel wall, requiring barrel replacement). If bound, remove the screw and inspect for: bent screw (check runout on V-blocks — >0.5 mm TIR at the screw tip is unacceptable), galled flight lands (embedded aluminum or other metal transferred from the barrel ID — indicates the screw contacted the barrel wall, typically from operating the screw at high RPM without polymer in the barrel during purging), or a solidified plug of degraded polymer in the compression zone (requires barrel removal and burn-out oven cleaning).

Alarm Details

Troubleshooting Protocol

Equivalents & Cross-References

Related Diagnostics & Materials

References & Industry Standards

• ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
• UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
• MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
• ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org