Product quality is the core issue for customers to consider when they source the product. In addition to the process-controlled measures to enhance the product quality, complete quality inspection measures are also of great importance to guarantee the product quality.
BH International Co. Ltd. (www.abrasivesbh.com) has a fully-functional lab and experienced working stuff to take the quality inspection of every lot of the cargo.
How to take the quality inspection of steel shots? Let us describe each procedure, including sampling, sampling mounting for testing, and testing items in the article.
Sampling
The sampling process must be random sampling. Samples for chemical analysis, hardness, microstructure, density, objectionable defects, and mechanical testing shall be carefully obtained to be representative of each shipment of the production lot.
| Cargo Quantity (tons) | Sampling Frequency |
| 0 < Quantity ≤ 0.5 | 6 |
| 0.5 < Quantity ≤ 1.0 | 8 |
| 1.0 < Quantity ≤ 4.0 | 12 |
| Quantity > 4.0 | And So On |
All the samples drawn will be gathered into one portion of 100g test sample by sample division method.
Sample Mounting for Testing
The 100g test sample shall be mounted one layer deep in bakelite or other suitable strong metallurgical sample mounting media. The test sample is mounted in the mounting media by melting the media.
The mounted sample shall be ground to the center of the particle and polished by acceptable
methods for examination using a microscope. When grinding and polishing the mounted sample, please take care. Avoid overheating the sample, which will affect the microstructure and/or hardness.
Hardness Testing
Hardness measurements shall be taken at the half radius on a minimum of ten (10) randomly selected particles in the mounted sample.
The hardness shall be determined by using ASTM E 384 and using a 500 gf load for sizes S-280 and finer and 500 gf or 1000 gf load for sizes S-330 and larger.
Other microhardness test methods may be used as long as a reliable hardness conversion can be obtained by calibrating various machines against known standards. Approximate conversions to Rockwell C hardness numbers are obtained from ASTM A 370.
Microstructures
The mounted and polished sample shall be etched with 2% Nital and examined at approximately 500X magnification.
Carbide networks, partial decarburization, and grain boundary segregation are undesirable.
No more than 15% of the particles tested shall have these defects.
Objectionable Defects
Objectionable defects shall be measured using a microscope with a 10X magnification. All of the particles contained in the mount shall be evaluated.
Here is the summary of the objectionable defects:
Elongated Particle:
An elongated particle is one whose length is in excess of twice the maximum particle width.
The elongated particles should account for no more than 5% of the total particles in a shot sample shall be elongated.
Voids:
A void is a smooth-surfaced internal hole. If the internal hole is greater than 10% of the particle, it will be considered as harmful and counted as a void.
The particles containing void should be less than 10% of the total particles in the sample.
Shrinkage:
A shrinkage area is an internal cavity with an irregular dendritic surface and must be greater than 40% of the particle area to be considered harmful.
No more than 10% of the particles in a sample shall contain shrinkage.
Cracks:
A crack is a linear discontinuity whose length is greater than three (3) times its width and its length is greater than 20% of the diameter or shortest dimension of the particle and radial in orientation.
No more than 5% of the particles in a steel shot sample should contain cracks.
Density
Density shall be determined by placing 50 ml of ethanol or methanol in a 100 ml graduate, adding 100g of shot, and recording the increase in volume. Dividing 100g by the volume in for more critical density measurements.
No more than 1% of the shot sample, by weight, shall be nonmagnetic material.
Nonmagnetic Material
A hand magnet shall be used to separate the magnetic shot from the nonmagnetic contaminants. The non-magnetic contaminants shall be weighed and the percentage of the original sample weight calculated.
Chemical Analysis
BH takes the chemical analysis according to ASTM A751, Standard Test Methods and Practices for Chemical Analysis of Steel Products.
C- Carbon, Mn- Manganese, Si- Silicon, S- Sulfur and P- Phosphorus compositions are tested for every sample.
Sieve Analysis
Sieve analysis is taken according to SAE J444, Cast Shot And Grit Size Specifications For Peening And Cleaning.
1st The sample shall be placed on the top sieve of a stack of three or four sieves, depending on media and size (please click here to refer to the table about size distribution in this article). Nest the selected sieves and fit a pan to the bottom sieve.
2nd The sample shall be run in the testing machine for 5 min ± 5 s for sizes using sieve designation 35 or coarser and 10 min ± 5 s for sizes using sieve designation finer than 35.
3rd The stack of sieves shall be removed from the testing machine and the percentage of total weight shall be recorded for the media remaining on each sieve.