Waterjet-cut pressboard needs an edge-to-interior moisture comparison through the subsequent processing route. Register the wetted region and verify the finished material state for the ordered geometry. [1]
Calculation basis. Project-specific values and gates in the illustrative screens below are assumptions; cited catalogue values retain their source test conditions.
Do not presume a particular penetration depth. It depends on the material, geometry, exposure and delay before sampling. The sampling plan should be capable of finding a gradient, rather than starting with an assumed wet-band width.
Preserve distance from the cut
Take representative witnesses from the same sheet and conditioning history. Compare the proposed waterjet route with a qualified dry-cut reference where practical. Include an uncut reference to separate the cutting exposure from ambient moisture pickup during transport and sampling.
- Identify each cut edge and its time of exposure; distinguish the jet-cut face from surfaces reached by spray or handling.
- Define successive sampling bands by distance from that face, with an interior reference region.
- Record how each band is separated, transferred and protected before measurement.
- Use a validated moisture method and a consistent reporting basis for all bands.
- Repeat the map after the proposed drying and storage sequence, alongside dimensional and edge checks.
Sectioning itself can alter a moisture profile. Slow preparation in uncontrolled air, warm cutting or contact with a wet support may change the result being measured. Include preparation controls and enough sample mass for the method without combining all distances into one specimen.
Why the overall average can conceal the edge
Consider a purely illustrative part in which an edge region accounts for 5% of its dry mass. If that region has 3.0% moisture and the interior has 0.5%, both reported on the same dry-mass basis, the mass-average result is 0.05 × 3.0 + 0.95 × 0.5 = 0.625%.
The average is much closer to the interior value than to the edge value. These fictional values demonstrate dilution; they are not a measured waterjet penetration profile or acceptable moisture levels. Reporting the average alone would remove the information needed to judge the newly exposed surface.
Moisture history must be retained when comparing conditioned pressboard parts. Consequently, a route comparison should inspect dimensional change and local damage as well as moisture. A part can dry to a selected condition and retain a changed profile or damaged edge.
The post-drying check must cover the relevant thick sections, internal corners and holes, not only a thin straight coupon. Maintain the time between drying, protected storage and measurement so that a handling difference does not masquerade as cutting-route performance.
Define the qualified material and geometry range from the edge-to-interior map. Add witnesses for large sections and deep slots before releasing those parts to assembly.
Use the wettest qualified region in the drying decision
Drying evidence depends on material mass, temperature and moisture history [2]; it does not supply a waterjet wet-band width.
For the assumed 5% dry-mass edge region at 3.0% moisture and 95% interior at 0.5%, average moisture is 0.625%. The edge remains 4.8 times the average. Assume a project requires every sampled region to remain at or below 1.0% dry-basis moisture. The 0.625% average passes that value, but the 3.0% edge fails by 2.0 percentage points. Hold the route for local drying verification and inspect edge damage; the bulk average cannot release the wetter boundary.
References
- IEC, IEC 60641-2:2004, Pressboard and presspaper for electrical purposes — Part 2: Methods of tests.
- Y. Brahami, A. Betie, F. Meghnefi, I. Fofana and Z. Yeo, Development of a Comprehensive Model for Drying Optimization and Moisture Management in Power Transformer Manufacturing, Energies 18, 789, 2025. DOI: 10.3390/en18040789.