ASTM A367 - Chill Testing of Cast Iron
Understanding ASTM A367: Comprehensive Methods for Evaluating the Chilling Tendency of Materials
ASTM A367 is a standard testing methodology that outlines two distinct procedures for evaluating the chilling tendency of materials. This standard is particularly important for industries that rely on materials with varying levels of strength and hardness, such as manufacturing and construction.
Test Methods in ASTM A367
Method A: The Wedge Test
Designed specifically for higher-strength materials, the Wedge Test consists of a three-step process involving the core, pouring practice, and specimen cooling.
Core Types and Preparation
The test can be conducted using two types of cores: single core and gang cores. These cores are prepared using well-baked and oil-bonded materials. The cores are crafted with an AFS fineness of 70, which has been found to yield satisfactory results.
Pouring Practice
Samples are poured using a ladle line filled with a refractory mixture that does not contain chilled iron or graphite. The ladle is filled immediately before the sample is obtained to maintain consistency.
Specimen Cooling
After pouring, the specimen is quenched as quickly as possible once it has solidified. This avoids cracking at the chill apex of the casting. The specimen can be cooled gradually but should be removed when there is enough residual heat to evaporate the water. Cooling can take place either in the core or in the air.
Method B: The Chill Test
The Chill Test is more appropriate for softer grades of materials and involves a different approach to testing.
Test Specimen Dimensions
ASTM A367 provides specifications for the dimensions of the test specimen, which are crucial for obtaining accurate results. Below are the dimensions for various wedges used in the testing:
W1: 5.1 mm (B), 25.4 mm (H), 11.5 degrees (A), 101.6 mm (Length)
W2: 10.2 mm, 31.8 mm, 18 degrees, 101.6 mm
W3: 19.2 mm, 38.1 mm, 28 degrees, 101.6 mm
W3 ½: 25.4 mm, 44.4 mm, 32 degrees, 127 mm
W4: 31.8 mm, 50.8 mm, 34.5 degrees, 152.4 mm
Data Interpretation
After testing, the specimen is fractured using a striking hammer, ensuring the break is midway and straight along its length. Three key terms are used to describe the measurements:
Clear Chill: The area closest to the apex that is entirely free of any grey spots.
Mottled Zone: This starts where the clear chill ends and continues to the location where the last spot of cementite or white iron is visible.
Total Chill: The measurement taken at the junction of the grey fracture with the first appearance of chilled iron.
Conclusion
ASTM A367 provides industries with two robust test methods for assessing the chilling tendency of grey iron materials. Only one test may be necessary if a test specimen with proper dimensions is selected. The choice between Method A and Method B depends on the material's strength and the specific requirements of the application.
By understanding ASTM A367, professionals can better predict the performance of materials under different conditions, thereby ensuring the quality and durability of their end products.