I. Dimensional Accuracy
This refers to the degree to which the actual diameter of the chrome-plated rod conforms to the design dimensions after machining, directly affecting the tightness of the fit with components such as bearings and bushings.
Key Parameters:
Diameter Tolerance: Common high-precision grades are g6, g8, and h7.
Example: Φ20h7 indicates a diameter of 20mm, with a tolerance range of 0 to +0.021mm.
Inspection Method: Use a micrometer or multi-point outside diameter measuring instrument to measure multiple segments along the entire length.
Online diameter measuring instruments can achieve real-time full inspection during the production process.
✅ For high-precision guiding systems (such as robot joints), g6 grade is recommended; h7 can be selected for ordinary equipment.
II. Shape Accuracy
This reflects the degree to which the actual geometry of the chrome-plated rod's cross-section and axis matches the ideal state.
1. Roundness (Ovality)
Definition: The difference between the maximum and minimum diameters on the same cross-section.
Acceptable Standard: Generally controlled within ≤0.01mm.
Inspection Tool: Dual-axis or multi-axis online diameter gauge.
2. Straightness (Bending)
Definition: The degree to which the axis deviates from the ideal straight line, especially important for chrome-plated bars with a large length-to-diameter ratio.
Standard Requirements: Bending ≤ 0.05mm per meter length; ≤ 0.01mm/m for high-precision applications.
Inspection Method: Using a laser straightness measuring instrument or a combination of V-blocks and dial indicators.
3. Surface Roughness
Ideal Value: Ra 0.2～0.8μm; mirror polishing can achieve Ra ≤ 0.01μm.
Inspection Instrument: Profilometer or optical interferometer.
Low roughness reduces friction and wear, improving sealing performance.
III. Positional Accuracy
Refers to whether the relative positional relationship between the various machined surfaces of the chrome-plated bar meets the requirements.
1. Concentricity
Definition: The symmetry between the outer cylindrical surface and the central axis.
Requirement: Generally ≤ 0.01mm/m; higher requirements for high-speed rotating parts.
Detection Method: Using a coordinate measuring machine (CMM) or runout tester.
2. Coaxiality
Applicable to stepped shafts with multiple diameter segments, ensuring that the axes of each segment coincide.
Detection: By comparing with a reference axis, runout is often used for indirect evaluation.
IV. Comprehensive Inspection Technology and Trends
Modern chrome plating bar production has widely adopted online dimensional inspection systems, achieving non-contact, high-efficiency, and full inspection coverage:
Outer Diameter and Ovality: Monitored in real time by a multi-axis diameter gauge.
Straightness and Length: Automatically determined by online straightness measuring instruments and length measuring instruments.
Data Management: The LP-SCADA system can collect data from the entire production line for SPC process control and quality traceability.
✅ Tip: Choosing a supplier with full-process online testing capabilities can effectively avoid the risk of missed detections and ensure batch consistency.
