Process Control of Surfacing Repair Quality for Roller Press Squeezing Rolls

Literature Overview

This paper, authored by Wang Zizhou from Jurong Taini Cement Co., Ltd., was published in New Century Cement Herald in 2011 (Vol. 17, No. 6, pp. 40–43). The study focuses on the process control of surfacing repair quality for the squeezing rolls of roller presses used in cement production. The paper emphasizes three key quality control aspects: proper wire selection, thorough understanding of the base material condition, and strict adherence to the welding process design. The practical results from the RP-Z170/180 roller press at Jurong Taini Cement confirm the importance of systematic quality control.

Technical Background

Roller presses are used in cement production to crush clinker and other materials. The squeezing rolls are subjected to extreme operating conditions:

High compressive stress: The rolls exert forces of several thousand tons to crush material.
Abrasive wear: The material being crushed (clinker, limestone, etc.) is highly abrasive.
Thermal effects: Friction and the temperature of the material being processed can raise the roll surface temperature significantly.
Impact loading: Irregular materials and tramp metal can cause impact damage.

The surfacing repair of these rolls is a critical maintenance activity that directly impacts production efficiency and cost.

Quality Control Process Framework

The paper outlines a three-pillar quality control framework:

Pillar 1: Wire Selection

The selection of the surfacing wire is the first and most critical decision. The wire must be chosen based on:

Wear mechanism: Abrasive wear, adhesive wear, or a combination.
Operating temperature: The wire must maintain hardness and strength at the operating temperature.
Base material compatibility: The wire must be compatible with the roll material to prevent cracking and ensure good adhesion.
Service life requirement: The wire must provide adequate life between maintenance intervals.

Common wire types for roller press surfacing include:

Wire Type	Composition	Application
High-carbon steel wire	C > 2%, Cr, Mo	Abrasive wear; moderate temperature
Nickel-based wire	Ni-Cr-Mo-C	High temperature; thermal fatigue
Tungsten carbide-filled wire	Ni or Co matrix with WC	Severe abrasive wear
Ceramic-filled wire	Ni or Co matrix with B₄C, SiC	Extreme abrasive wear

Pillar 2: Base Material Condition Assessment

Before surfacing, the base material must be thoroughly assessed:

Chemical composition: Verify the carbon, alloy, and impurity content. High carbon content or high sulfur/phosphorus content can increase cracking susceptibility.
Hardness distribution: Map the hardness profile to identify hardened zones, soft zones, and transition zones.
Defect inspection: Use magnetic particle testing (MT) or ultrasonic testing (UT) to detect existing cracks, inclusions, or other defects.
Geometry assessment: Measure the roll diameter, taper, and surface profile to determine the required overlay thickness.

Pillar 3: Welding Process Execution

The welding process must be executed according to the designed parameters:

Preheat temperature: Typically 200–400 °C, depending on the base material and wire type.
Interpass temperature: Controlled to prevent excessive grain growth and cracking.
Welding sequence: A systematic sequence should be used to minimize distortion. For cylindrical rolls, a helical or circumferential pattern is typical.
Layer thickness: Each layer should be deposited to a controlled thickness (typically 1–3 mm per pass).
Cooling rate: Controlled by preheat and interpass temperature to prevent cracking and maintain microstructure.

Process Parameters for RP-Z170/180 Roller Press

The RP-Z170/180 roller press at Jurong Taini Cement uses the following surfacing parameters:

Parameter	Value	Notes
Welding process	FCAW	Flux-cored wire arc welding
Wire type	High-carbon or Ni-based	Selected based on wear mechanism
Wire diameter	1.6 mm	Standard for FCAW
Welding current	300–400 A	Adjusted for wire type
Arc voltage	30–38 V	Maintained for stable arc
Travel speed	150–300 mm/min	Controlled for layer thickness
Shielding gas	CO₂ or Ar/CO₂	For flux-cored wire
Preheat temperature	300 °C	For high-carbon base material
Interpass temperature	≤ 350 °C	To prevent cracking
Number of layers	2–3	Total thickness 4–6 mm

Defect Analysis and Countermeasures

Defect	Cause	Countermeasure
Cracking	High cooling rate; high carbon base	Increase preheat; use Ni-based wire
Porosity	Inadequate gas shielding; wire contamination	Ensure clean wire; use proper shielding gas
Excessive dilution	Too high current; too fast travel speed	Reduce current; slow travel speed
Poor adhesion	Inadequate surface preparation; contamination	Grind to bare metal; clean thoroughly
Distortion	Thermal input too high; constrained geometry	Control preheat; use back-up plate

Quality Control Inspection Plan

A comprehensive inspection plan should include:

Pre-weld inspection: Visual inspection, MT/UT for defects, hardness mapping, chemical analysis.
In-process inspection: Monitor welding parameters, check interpass temperature, inspect each layer for defects.
Post-weld inspection: Visual inspection, PT for surface cracks, hardness testing, dimensional measurement.
Final acceptance: Verify overlay thickness, hardness, and surface finish according to specifications.

Study Reflections

This paper, while focused on a specific application (cement roller press), presents a universal quality control framework that can be applied to any surfacing repair operation. The three pillars—wire selection, base material assessment, and process execution—are fundamental to any surfacing project. The emphasis on systematic quality control is particularly valuable in industrial settings where maintenance is often performed under time pressure and with limited resources. The practical results from the Jurong Taini Cement case study confirm that investing in quality control pays dividends in terms of service life and cost savings.