ASTM B428 - Angle of Twist in Rectangular and Square Copper and Copper Alloy Tube
A Guide to Measuring Twist in Rectangular and Square Copper Tubes
1. Introduction
Copper and copper alloy tubes are commonly used in various industrial applications. To ensure their proper fit in final assemblies and minimize rework, it is essential to measure the angle of twist in these tubes accurately. This article outlines a standardized test method for determining the twist in rectangular and square copper and copper alloy tubes, providing valuable insights into deviation from straightness.
2. Scope
This test method establishes the requirements for accurately determining the angle of twist in rectangular and square copper and copper alloy tubes. The procedure is designed to ensure precise measurements and is suitable for use in different applications where twist control is crucial for tube performance.
3. Significance and Use
The test method outlined herein is of significant importance for several reasons:
Proper Fit and Assembly: In applications where tubes need to fit precisely within assemblies, measuring twist angles helps ensure the tubes are aligned correctly.
Minimizing Rework: By identifying and addressing deviations from straightness early on, manufacturers can minimize costly rework required to bring tubes into compliance.
Standard Technique for Inspection: This method provides a standardized approach for purchasers, suppliers, and manufacturers to inspect copper and copper alloy tubes and verify the twist within acceptable limits.
4. Apparatus
To conduct the twist measurement, the following apparatus is required:
Horizontal Reference Plane: A sturdy reference plane of sufficient length to support the tube specimen, equipped with a clamping device to hold one end of the tube against it.
Transparent Plastic Protractor Segment: An engraved protractor segment with angle lines, enabling accurate angle measurements.
Parallel Face Blocks: These blocks are essential to ensure the protractor segment remains parallel to the reference plane during measurement.
5. Test Procedure
Follow the step-by-step procedure outlined below to accurately measure the angle of twist in the copper and copper alloy tubes:
Place the tube specimen lengthwise on the horizontal reference plane. If the tube exhibits noticeable edgewise curvature, position it in a way that a side with convex curvature comes into contact with the reference plane.
For rectangular tubes, place the major outer dimension side (width side) against the reference plane.
For square tubes with curvature along all edges, position the specimen so that the side with the least convex curvature is against the reference plane.
Clamp one end of the tube specimen firmly against the reference plane while keeping the other end free.
Position the transparent plastic protractor segment flush against the free end of the tube, making sure it is parallel to the reference plane using the parallel face blocks.
Measure the total angle of twist by reading the degrees for the angle line on the protractor segment that most closely aligns with the lower outside edge of the tube end.
Ensure that the lower edge of the protractor segment remains in contact with the reference plane during the measurement.
The angle of twist per unit length can be calculated by dividing the total angle of twist for the specimen by its length, according to the units specified in the material specification.
6. Precision and Bias
The precision for measuring the total angle of twist using this method is 60.5°, and it remains unaffected by any edgewise curvature of the specimen. Furthermore, this test method has no bias since twist values are direct measurements based on the accuracy of the protractor and the operator's observation.
Conclusion
The standardized test procedure outlined in this article provides an effective means of accurately measuring the angle of twist in rectangular and square copper and copper alloy tubes. By adhering to this method, manufacturers can ensure proper fit and alignment, minimize rework, and deliver tubes that meet the required specifications.