testing & measurement

Testing & Measurement in Sandblasting—Focus on Two Critical Process Parameters

During blasting, two systems with seemingly similar settings can produce different results. On the one hand, the surface is altered by the abrasive media, pressure, distance, and exposure time. On the other hand, a significant pressure drop can occur between the compressor and the blast nozzle. The testing & measurement category therefore deliberately focuses on two practical testing tasks: comparing the resulting surface roughness and checking the actual nozzle pressure.

The product range currently consists of surface comparator discs in grit and shot versions, as well as the Clemco HNG nozzle pressure test gauge. These are not general-purpose measuring instruments, but rather specialized tools for evaluating a blasting process.

Assessing Surface Roughness After Blasting

Abrasive blasting produces a characteristic surface profile. Its characteristics depend, among other factors, on the type of abrasive, grain shape, grain size, impact velocity, blasting angle, and the initial condition of the workpiece. Especially prior to subsequent coating, it can be important not to evaluate the resulting surface roughness solely on the basis of visual appearance as “cleanly blasted.”

Surface comparator discs offer a quick, practical method for this purpose. The blasted surface is compared visually and by touch with defined reference areas on the disc. This allows the surface structure to be assigned to an appropriate comparison grade.

Grit and shot require different references

Angular abrasive media and round abrasive media produce different surface profiles. For this reason, the surface comparator discs are available as SRC-Grit and SRC-Shot. The Grit version is intended for surfaces created with angular abrasive media; the Shot version is designed for surfaces blasted with round abrasive media.

The existing Contracor comparison discs are made of nickel and each feature four defined comparison areas. SRC-Grit covers 20, 60, 100, and 150 µm, while SRC-Shot covers 25, 40, 70, and 100 µm. They are used according to the principle of visual and tactile comparison in accordance with ISO 8503.

Comparison disc instead of precise profilometry

A surface roughness comparator is specifically designed as a comparison tool. It does not provide a continuous digital measurement curve and should not be confused with a tactile or optical profilometer. Its advantage lies in the ability to quickly assess the surface directly after blasting.

For many operational checks, this allows one to verify whether the resulting profile falls within the intended range or whether the process has visibly changed compared to a reference. For requirements that demand precise instrumental measurement, however, a suitably appropriate measurement method is necessary.

Measuring nozzle pressure under actual blasting load

The second test task concerns the actual pressure available at the blast nozzle. The pressure displayed on the compressor or an upstream tank does not automatically indicate the pressure reaching the nozzle during blasting. Losses occur along the way due to compressed-air treatment, piping, fittings, couplings, and blast hoses.

The HNG nozzle pressure test gauge is used to monitor the operating pressure in the blast hose near the nozzle. Measurements are taken under real operating conditions, providing a much more direct indication of the pressure energy actually available to the blasting process.

Systematically identify pressure losses

If the blasting performance is lower than expected, it does not necessarily mean that the compressor is too small. Undersized lines, long hose runs, poorly matched couplings, dirty filters, or other sources of resistance can reduce the pressure at the nozzle. Changes to the system can also be better assessed through repeated measurements.

A documented nozzle pressure can therefore serve as a benchmark: before and after maintenance, with different hose lengths, or following changes to the compressed air supply. This transforms a subjective impression such as “the device is blasting less powerfully” into a verifiable technical parameter.

Evaluate surface condition and operating condition separately

Roughness comparison and nozzle pressure measurement address different issues. The comparison disc shows what profile has been created on the surface. The nozzle pressure test gauge, on the other hand, helps determine whether the system is providing the expected operating conditions at the nozzle.

Both tests complement each other effectively but should not be confused with one another. Correct nozzle pressure alone does not guarantee a specific surface profile, as the abrasive media, grit size, angle, and processing time also affect the result. Conversely, a surface that initially appears to be suitable cannot reliably reveal a gradual loss of pressure in the system.

Test equipment for more reproducible blasting processes

Anyone who regularly performs blasting processes or prepares surfaces for subsequent coatings benefits from verifiable reference values. Surface comparator discs provide a practical reference for the resulting surface roughness, while nozzle pressure measurement allows the actual condition of the system under load to be verified.

The “Testing & Measurement” category is thus intentionally kept concise and technically clear: It contains tools for verifying what matters most at the end of the blasting process—the resulting surface finish and the actual blasting energy available at the nozzle.