Observation of Joined Metal and Rubber Parts Using a Microfocus X-Ray CT System

Importance of the Topic

The combination of rubber and metal components is widely used in automotive, industrial machinery, and sealing applications owing to its capacity for high strength, vibration damping, and lightweight construction. However, differential thermal and mechanical stresses at the interface can lead to premature rubber degradation and debonding that are not visible externally. Reliable non-destructive evaluation methods are therefore essential to detect early-stage deterioration before catastrophic failure and to maintain product quality.

Objectives and Study Overview

This study demonstrates the use of a Microfocus X-Ray CT system, the inspeXio SMX-225CT FPD HR Plus, to observe internal defects in rubber-to-metal rollers. Three workpieces were analyzed: Workpiece A (in-service roller), and two test samples, Workpieces B and C, subjected to different loads and travel distances. Each sample exhibited external bulges at the rubber-metal interface, which served as targets for internal defect analysis.

Methodology and Instrumentation

CT scans were conducted under consistent tube settings (225 kV, 300 µA) across overview and magnified views. Voxel sizes ranged from 0.090 mm to 0.034 mm depending on the field of view. The primary instrument was the Shimadzu inspeXio SMX-225CT FPD HR Plus microfocus CT system. Optional imaging software VGStudio Max enabled color-coding of low-density and debonded regions for three-dimensional visualization and volumetric quantification.

Key Results and Discussion

Cross-sectional CT images revealed darker gray regions in the interior of bulges, indicating localized density reduction likely caused by microvoids or sub-voxel air pockets. Surface cracks at bulge sites extended to a consistent depth across samples. Color-coded 3D reconstructions quantified internal deterioration volumes in the order A > C > B, correlating with both the external bulge sizes and cumulative travel distances. Workpieces A and B also exhibited distinct debonded cavities at the rubber-metal interface, visible as black voids in CT slices.

Benefits and Practical Applications

• Non-destructive detection of internal rubber degradation and debonding, even when the exterior appears normal.
• Correlation between CT-derived defect volumes and external wear indicators enables predictive maintenance.
• Quantitative three-dimensional defect mapping supports improved quality control in rubber-metal assemblies.

Future Trends and Applications

Advances in CT resolution and faster scanning protocols will facilitate in-line inspection of rubber-metal components. Integration of CAD comparison tools will allow automated defect quantification against design specifications. Machine learning algorithms applied to CT data sets may provide predictive analytics for service life estimation and optimized material formulations.

Conclusion

The inspeXio SMX-225CT FPD HR Plus microfocus CT system effectively identifies and quantifies internal rubber deterioration and debonding in metal-bonded rollers. This non-destructive approach enhances quality assurance by revealing subsurface defects imperceptible by external examination and supports the development of more robust rubber-metal interfaces.