Why are base pad and lid foam graded separately in a Custom EVA foam lined precision instrument case?

A: The 35 mm base pad carries the 12 kg load and isolates, while the 20 mm lid foam only limits lid pressure; one 45 kg/m3 density but split thickness keeps preload even.

How is the +/-0.5 mm milling tolerance checked?

A: A plug gauge reads top, middle and bottom of the slot; the three-depth spread reveals wall squareness, and liners rest before re-measuring.

What condition does the 3% compression set criterion cover?

A: Thickness recovery after a rated 12 kg static hold, using a six-point mean, re-tested after 4000 cycles.

Why is the 4 g figure judged by band envelope?

A: Resonance shifts with base-pad density, so a brief narrow spike still fails; a whole-band envelope avoids averaging the peak away.

Can IP65 replace the cavity re-check?

A: No. It addresses the mouth seal as a background item; cavity tolerance, compression set and transmitted acceleration are re-checked separately after 4000 cycles.

Custom EVA foam lined precision instrument case

Quick answer: A Custom EVA foam lined precision instrument case uses a 45 kg/m3 base pad with +/-0.5 mm slots, holding set to 3% under 12 kg and 4 g over 5-200 Hz.

Density grading inside the Custom EVA foam lined precision instrument case
Milling tolerance and cavity wall squareness
How base-pad compression set is measured
Transmitted acceleration across the sweep band
Cavity re-check after lid-cycle ageing
FAQ

1. Density grading inside the Custom EVA foam lined precision instrument case

The liner is two layers split by load path, not one uniform block. A Custom EVA foam lined precision instrument case has an outer size of 560 x 410 x 260 mm, a cavity of 495 x 345 x 200 mm and a wall of 3.8 mm; an empty 5.4 kg and a rated 12 kg load define the static burden on the base pad. An EVA density of 45 kg/m3 supports that load without passing vibration straight through: the 35 mm base pad carries weight and isolates, while the 20 mm lid foam only limits lid pressure. Shell and lid clearance is set from these two thicknesses so preload stays even across the case.

Liner part	Thickness and density	Function
Base pad	35 mm / 45 kg/m3	Load and isolation
Lid foam	20 mm / 45 kg/m3	Lid pressure limit
Mouth surround	3.8 mm wall	Lateral restraint
Cavity floor	Set by slot depth	Puncture margin

2. Milling tolerance and cavity wall squareness

The cavity is the only locating feature, so the +/-0.5 mm milling tolerance and wall squareness are read together. Cavities in a Custom EVA foam lined precision instrument case are milled to nominal size within a +/-0.5 mm band, keeping the gap around a seated part even; a wall out of square looks fine at the mouth but is skewed at the floor, where the part binds on one side. A plug gauge reads the top, middle and bottom of the slot, and the three-depth spread says more about squareness than any single value.

Custom EVA foam lined precision instrument case workshop engraving machine with several metal spindles over an orange bed, black bellows guards and cable bundles behind

Milling leaves a compacted skin on the cell walls that can shift mouth size as foam rests, so liners are re-measured within +/-0.5 mm before assembly; corners show tool deflection first and are logged apart from straight edges.

Milling specification	Control value	Measuring position
Mouth tolerance	+/-0.5 mm	Top, middle, bottom
Wall squareness	Set by slot depth	Corner and straight edge
Cavity floor	Puncture margin	End of slot depth
Compacted skin	Re-measure after rest	Cell-wall surface

3. How base-pad compression set is measured

Long-term load is judged by compression set, not the springy feel on day one. A Custom EVA foam lined precision instrument case presses a rated 12 kg onto the base pad for a fixed hold, unloads, and measures the share of thickness that does not return; the criterion is 3% or less. At 45 kg/m3, a compound that is too soft lets cell walls buckle and leaves permanent settling, and once set passes 3% the cavity clearance shifts with it.

The reading covers pad thickness alone, excluding shell deflection.

Press-head area, hold time and rest time stay fixed. Six points on one pad give a mean for rejection, and the same head and hold time are reused after 4000 open-close cycles.

4. Transmitted acceleration across the sweep band

Isolation is stated over a band, not at one convenient frequency. A Custom EVA foam lined precision instrument case is swept from 5-200 Hz with input at the case base and response read above the cavity, and transmitted acceleration must stay within 4 g across the run. Base-pad density of 45 kg/m3 and 35 mm thickness place the resonance inside that band: raise density and stiffness climbs, the resonance moves later, and low frequencies are amplified instead.

Custom EVA foam lined precision instrument case grey foam inserts stacked on a factory floor, each milled with square and rectangular cavities, yellow green floor

The sweep runs through 5-200 Hz and logs the peak. A second pass with the lid closed confirms the 20 mm lid-foam preload has not changed the base-pad boundary. The 4 g figure is a whole-band envelope, so a brief spike still fails.

Deformation reading	Condition	Acceptance rule
Compression set <=3%	12 kg static load	Mean of six points
Transmitted acceleration <=4 g	5-200 Hz sweep	Whole-band envelope
Cavity tolerance	After 4000 cycles	+/-0.5 mm not widened
Density check	45 kg/m3	Measured per layer

5. Cavity re-check after lid-cycle ageing

Lid-cycle life ties the earlier items into one timeline. A Custom EVA foam lined precision instrument case runs 4000 open-close cycles, each closing bringing lid foam to its designed position and each opening reaching the stop, and cavities are measured only after the run. The mouth is read first, with top, middle and bottom values compared against the pre-assembly +/-0.5 mm records to see whether fatigue widened the band. The cavity floor comes next, confirming repeated lid pressure has not thinned the puncture margin. Base-pad thickness is re-measured so compression set can be placed beside the earlier 3% figure as a delta. A 5-200 Hz sweep follows to confirm transmitted acceleration still sits inside the 4 g envelope with no resonance drift. Shell-to-lid clearance is checked as well, since wear that lets the lid sit lower changes lid-foam preload. The mouth seal is finally compared against the IP65 method and filed as background, not used for cavity rejection. With this order fixed, a bad reading points to foam fatigue, tool deflection or hardware wear rather than a vague liner-ageing claim.

JUNZHIJIA keeps this re-check as the last outgoing step, with cavity data and sweep curves filed per batch.

Conclusion

Reliability in the Custom EVA foam lined precision instrument case rests on density grading, milling tolerance and long-term load together. Compression set within 3% under 12 kg and transmitted acceleration within 4 g across 5-200 Hz are two measurable lines, and the cavity re-check after 4000 cycles keeps the +/-0.5 mm band from widening with foam fatigue. JUNZHIJIA files density, cavity and sweep records as three separate checks, each judged on its own reading rather than offset against another.