Nitrided Screw Head

Updated: 2026-08-12

Overview

The nitrided barrel screw head is a critical component in plastic processing machinery, serving as the front-end part of the injection screw or extruder screw. These components undergo gas nitriding or ion nitriding surface treatment, creating a hard nitride layer (typically 0.2-0.5mm thick) that significantly improves surface hardness up to 1000-1200 HV. Common base materials include alloy steels like 38CrMoAlA, chosen for their excellent nitriding response and core toughness. The nitriding process forms a compound layer of iron nitrides (Fe2-3N) that provides exceptional sliding wear resistance against plastic materials and additives.

Structure and Working Principle

Structurally, the screw head consists of multiple functional zones: the feeding section, compression section, and metering section. The nitrided surface treatment is primarily applied to the flight crests and mixing elements where wear is most severe. During operation, the screw head rotates within the barrel, conveying plastic pellets forward while generating shear heat through friction. The nitrided surface maintains dimensional stability under high pressure (commonly 100-200MPa) and temperatures reaching 300-400°C in demanding applications like engineering plastics processing.

Key Features

The nitrided surface provides 3-5 times greater wear resistance compared to untreated steel, particularly against abrasive fillers like glass fibers or minerals. This treatment also improves corrosion resistance against acidic or corrosive plastic additives. Modern designs incorporate advanced features like barrier flights, mixing pins, or special tip geometries to enhance melting efficiency. The nitride layer maintains its properties up to approximately 500°C, beyond which tempering effects may reduce hardness.

Application Areas

These components are essential in injection molding machines for producing precision plastic parts (automotive components, electronic housings) and extruders for pipes, profiles, and sheet production. They're particularly valuable when processing filled polymers (30-50% glass fiber), flame-retardant compounds, or engineering resins like PEEK or PPS. Specialized versions serve niche applications: three-zone screws for general-purpose plastics, barrier screws for improved melting, and vented screws for volatile removal. The choice depends on material characteristics and production requirements.

Maintenance and Precautions

Proper maintenance includes regular inspection of wear patterns using bore gauges or optical measurement. The nitride layer typically lasts 1-3 years depending on usage, after which re-nitriding may be possible if base material dimensions permit. Critical precautions include avoiding metal-to-metal contact (maintain proper barrel clearance), preventing thermal shock during startup/shutdown, and using appropriate purge compounds when changing materials. Cooling channel maintenance is essential to prevent overheating that could compromise the nitride layer.

B2B Procurement Guide

Industrial buyers should specify: material grade (e.g., 38CrMoAlA), nitriding method (gas vs. ion), surface hardness (typically ≥900 HV), and dimensional tolerances (commonly ±0.05mm). Lead times range from 4-12 weeks for custom designs. Quality verification should include hardness testing (microhardness indentation), metallographic examination of the nitride layer, and dimensional inspection. Some manufacturers offer performance warranties (e.g., 1 million shots for injection molding applications). Consider total cost of ownership rather than initial price, as premium-grade nitrided screws can reduce downtime costs.