Why layer the base pad by density in a Shockproof Military Equipment Case?

Answer: One slab serves only one part of the travel. The lower ply carries 14 kg static, the upper ply takes small bumps and the 20 mm lid foam holds the top, keeping compression set within 3.0%.

Is the 68 mm rib pitch arbitrary?

Answer: No. With a 4.4 mm wall it moves the short-span natural frequency clear of the 40-120 Hz window; too few or too many ribs both worsen the transmitted acceleration reading.

Is ≤3.8 g an average across the band?

Answer: No, it is the resonance peak ceiling over a 5-200 Hz sweep.

How is the ≤1.0 mm shift measured reliably?

Answer: Mark pairs at the four corners and inner wall, drop 1.2 m on six faces, read with a depth gauge and take the largest. Eyeballing the lid gap does not count.

Shockproof Military Equipment Case

Quick answer: A Shockproof Military Equipment Case keeps transmitted acceleration under 3.8 g at 14 kg over 5-200 Hz, with liner shift within 1.0 mm after a 1.2 m drop.

Base Pad Density Layering for a Shockproof Military Equipment Case
Wall Rib Spacing and Stiffness Allocation
Transmitted Acceleration Readings Across the Sweep Band
Measuring Liner Shift After a Drop
Pad Rebound Recheck After Lid Cycling
FAQ

1. Base Pad Density Layering for a Shockproof Military Equipment Case

A Shockproof Military Equipment Case measures 610×440×270 mm outside and 545×375×205 mm inside, with a 4.4 mm wall, a 6.8 kg empty shell and a 14 kg rated load. Those figures set the cushioning budget: the 205 mm internal height loses clearance to the lid pad, so the base cannot be one uniform slab.

Each density takes a different part of the travel. The bottom ply against the shell uses 45 kg/m³ EVA for the static load, the upper ply a softer blend for small bumps, and the 20 mm lid foam only holds the top face. The main pad is 42 mm thick with compression set capped at 3.0%, which decides whether the pad still returns the mass to position after thousands of lid cycles.

Liner zone	Density and thickness	Compression set	Role
Base lower ply	45 kg/m³, lower half of 42 mm	≤3.0%	carry 14 kg static
Base upper ply	softer blend, upper half of 42 mm	≤3.0%	absorb small bumps
Lid foam	20 mm	≤3.0%	hold top face
Wall root strip	follows the ribs	≤3.0%	block sideways creep

A ply cut with recycled content shows up first on the scale, then on the sweep curve, which is why a Shockproof Military Equipment Case is weighed before it is shaken.

2. Wall Rib Spacing and Stiffness Allocation

The wall of a Shockproof Military Equipment Case is not a flat panel. Longitudinal ribs divide the shell into short spans at 68 mm pitch; with the 4.4 mm wall they move the natural frequency away from the busiest part of the 5-200 Hz band. Too few ribs and the wall follows the table like a drum head, too many and weld lines multiply.

Shockproof Military Equipment Case red and black closed shells stacked on a workshop bench, wrapped black shells at left and an assembly sign behind

Four latches ring the mouth at 430 N each, so the lid seats on the shell step and cannot bounce during a sweep. The assembled Shockproof Military Equipment Case reaches IP66, with the gasket pressed to a fixed squeeze that seals without lifting the lid.

3. Transmitted Acceleration Readings Across the Sweep Band

To read transmitted acceleration, a 14 kg mass goes into a Shockproof Military Equipment Case clamped to a shaker, and a 5-200 Hz sweep runs with one accelerometer on the table and another above the liner. The ratio shows whether isolation works. The ≤3.8 g limit is the peak reaching the liner at resonance, not a band average.

Sweep segment	Drive level	Transmissibility	Peak reading
5-40 Hz	low frequency, large displacement	near 1	≤2.6 g
40-120 Hz	resonance dense	highest	≤3.8 g
120-200 Hz	high frequency, small displacement	falling fast	≤1.9 g

Readings are split by segment. At low frequency the shell tracks the table, transmissibility sits near 1, and acceleration stays within 2.6 g because the pad is barely working. In the 40-120 Hz window the pad-and-mass system hits resonance and the peak presses hardest against the 3.8 g line; this is where density layering proves itself. Above 120 Hz inertia shrinks relative motion and the reading falls to about 1.9 g. Cut the load from 14 kg to 8 kg and resonance shifts upward, so every Shockproof Military Equipment Case report states its measured load. One forward-and-back pass is a single set; an up-sweep versus down-sweep peak gap beyond 0.3 g means the pad is loose and must be refitted.

4. Measuring Liner Shift After a Drop

Drop testing on a Shockproof Military Equipment Case runs at 1.2 m, one drop per face across six faces. With the lid still shut, liner shift against the shell datum is measured to a ≤1.0 mm limit: mark pairs at the four pad corners and inner wall, read the difference with a depth gauge, report the largest.

Shockproof Military Equipment Case assembly floor with wrapped black shells on pallets, rows of closed shells, blue totes, ceiling fans and yellow aisle markings

Acceleration reading	Load	Recheck segment	Drop height	Liner shift
3.8 g	14 kg	40-120 Hz	1.2 m	≤1.0 mm
3.2 g	14 kg	40-120 Hz	1.2 m	≤0.8 mm
2.6 g	14 kg	5-40 Hz	1.2 m	≤0.6 mm

A higher resonance peak means more liner shear on impact, so the two columns are read together. A Shockproof Military Equipment Case fails the liner once shift passes 1.0 mm; checking the lid gap by eye is not a measurement.

5. Pad Rebound Recheck After Lid Cycling

A cycling rig opens and closes the lid at a fixed rate, then the pad is measured again. The 3.0% compression set limit is only truly tested after that run: lay the pad flat, read recovered thickness against a new part. A loss beyond 3.0% means the foam has packed down and the sweep peak will climb.

Rebound and layering pull against each other. A dense lower ply recovers slowly, a soft upper ply quickly; a wide gap points to mixed batches, and even passing single readings then call for re-sorting by density. JUNZHIJIA ships the new, post-sweep and post-cycling thickness sets with each Shockproof Military Equipment Case, so a buyer can recheck the trend with the same gauge.

Conclusion

Two limits define a Shockproof Military Equipment Case: ≤3.8 g under 14 kg and ≤1.0 mm after a 1.2 m drop. Density layering, rib pitch and gasket fit carry them together, and relaxing any one lifts the sweep curve. Ask for the sweep and drop-shift records before pad thickness and rebound; those say more than wall thickness alone. JUNZHIJIA attaches the three thickness sets to each shell, so a buyer remeasures with the same gauge and settles the spec on data.