Cut wire shot: as cut, G1, G2 or G3

A cylindrical particle strikes with its edges. In cleaning that is an advantage —the sharp edge cuts and releases contaminant— but in shot peening it is a serious problem: the edge can nick the surface and create a local concentration of tensile stress at that point, exactly the opposite of the compressive stress the process is meant to introduce. A part treated with cylindrical media can end up with crack initiation points instead of fatigue resistance. That is why peening specifications call for conditioned media.

Conditioning is carried out in a blast machine purpose-built to process the abrasive itself: instead of projecting the media against parts, it projects it against wear plates housed in a chamber designed to take that impact continuously. The material is recirculated for a set number of cycles, and with each pass the sharp edges lose their bite until the target grade is reached.
The grades are not different processes: they are increasing numbers of cycles through the same machine. That is why the progression from as-cut to G3 is continuous, and why the most rounded grade costs more: more process hours and more material lost to wear during conditioning itself.

As cut: the particle straight from the cut, with sharp edges and flat faces.
G1 (normal conditioned): the edges are broken but the particle keeps its recognisable cylindrical shape.
G2 (double conditioned): rounded but irregular shape, with no sharp edges and not yet spherical.
G3 (special conditioned): practically spherical, with no trace of the original cut geometry.
Grade assessment is visual and comparative, not dimensional: the sample is checked against reference standards.

As-cut is used in cleaning and desanding, where the sharp edge works in your favour and the part has no fatigue requirements. G1 and G2 cover the middle ground: demanding cleaning, deburring and surface preparation where some roughness is wanted without aggressiveness. G3 is the grade for precision shot peening —aerospace, automotive, springs and gears— where impact uniformity defines the homogeneity of residual stresses and the repeatability between batches.

Cast shot, as it wears, fractures and generates angular fragments that change process behaviour and force more frequent classification. Cut wire does not fracture: it delaminates, wearing away in layers and keeping its spherical shape to the end of its service life. That is the technical reason behind its greater durability and the stability of the operating mix.

The reference standard is SAE J441, specific to cut wire shot, complemented by AMS 2431 for aerospace applications. Within AMS 2431 two hardness specifications coexist: AMS 2431/3D (AWCR), regular hardness, and AMS 2431/8A (AWCH), high hardness. Choosing between them is not a matter of «harder is better»: the higher the hardness, the lower the durability of the media, so the criterion depends on the required Almen intensity and on the material of the part.