Which figure should be fixed first in a cartridge safety case specification?

Answer: Cell size. Cells set the cavity, the cavity sets the envelope, the envelope sets the walls.

Is a thicker wall always better in a drop?

Answer: No. Extra section brings sink and stress, and corners get brittle; rib spacing does more.

Answer: Decide by exposure. Washdown calls for IP67; rain and splash only, IP65, with lighter latches.

Can the rating be multiplied by stack layers?

Answer: No. The bottom case carries everything above plus itself; uniform and concentrated loads test separately.

Why must the cold drop finish within 30 seconds?

Answer: The surface warms quickly out of the freezer and toughness returns.

Cartridge Safety Case Specifications: Size, Walls and Load

Quick answer: Specify a cartridge safety case backwards. Fix cell size, derive cavity and envelope from it, then set walls and ribs from stack height, and close with sealing class, temperature range and drop height. Get the order wrong and every sample becomes a restart.

Sizing a Cartridge Safety Case from the Cells Up
Wall Thickness and Rib Spacing
Stack Load and How to Rate It
Sealing Class and Temperature Range
Drop Height and Test Conditions
FAQ

1. Sizing a Cartridge Safety Case from the Cells Up

Outer dimensions are an output. A cell must hold an item upright without rattle and leave a fingertip gap of 4 to 6 mm.

Cell count follows. Five columns by eight rows gives 40 cells behind 1.8 mm dividers, near 18 kg loaded, light enough to lift one-handed. A cartridge safety case drawing that starts with the 340 mm envelope usually restarts at the third sample.

Item	Value	Why
Outer	340 x 270 x 120 mm	One-hand carry, fits 400 mm shelf pitch
Cavity	310 x 240 x 95 mm	Leaves wall and rib depth
Cell	30 x 22 mm, 60 mm deep	Upright hold, fingertip access
Layout	5 x 8 cells, 1.8 mm dividers	About 18 kg loaded

Draft angle belongs in that table too: at 1 degree over 120 mm the cavity loses about 2 mm.

2. Wall Thickness and Rib Spacing

Thickness follows load paths: 2.8 mm walls, 3.5 mm base, 2.6 mm lid. The base takes the drop and the stack above it; the lid only resists dishing.

Ribs matter more than thickness. Vertical ribs at 60 mm centres, 4 mm tall, R1.5 at the root, hold the walls against bulge; base ribs sit near 45 mm because span drives deflection. Too dense and the part drags in the mould; too sparse and the rib does nothing.

Shrinkage belongs on the drawing, not just the resin grade. Going from 1.6 to 1.8 percent over 340 mm shifts the envelope about 0.7 mm, cells included, so a cartridge safety case is dimensioned from the centre.

Where thick meets thin, keep sections within 2 to 1, otherwise a sink mark at the seal groove becomes a leak path.

3. Stack Load and How to Rate It

A rating without a bearing area and a duration means nothing. Write three things: 90 kg uniform on the lid, held 72 hours, residual deflection no more than 1.0 mm.

Stack height comes from the store. Shelving at 2.2 m clear suggests 18 layers, yet five is the working figure once picking space and bulge are counted; five layers at 18 kg puts 72 kg on the bottom case.

Test it the same way: 72 hours at room temperature, a 3 mm rubber pad between platen and lid, measured an hour after unloading. Record the mean of four points and the maximum, since a mean hides a collapsed corner.

Read bulge at mid-height with a straight edge and feeler gauge; past 2 mm the case fails. Sample three cavities.

4. Sealing Class and Temperature Range

Never write waterproof; write an IP code with its test. IP67 means 1 m of water for 30 minutes, suiting washdown; IP65 covers rain and spray. Specify too high and gasket compression rises with latch force; too low and one hosepipe ends the argument.

Split temperature into storage and service: minus 30 to 80 Celsius in store, minus 25 to 60 in use. Polypropylene embrittles in cold and cracks at corners; heat hardens the gasket.

Cycling moves dimensions too. After ten cycles between minus 30 and 80 Celsius the envelope should hold within 2.0 mm; more means locked-in stress. Most cartridge safety case specifications omit this line until a winter complaint about lids that will not latch.

5. Drop Height and Test Conditions

Drop height follows handling: 1.2 m for a hand-carried cartridge safety case, roughly chest height, and 0.8 m for vehicle stacking. Higher needs a stated airdrop requirement. At 1.2 m, spell out the sequence: six faces, three edges, 18 drops on one unit.

Cold drop is separate: freeze at minus 25 Celsius for 4 hours, then drop a bottom corner within 30 seconds. Warm the case first and toughness returns, so the test measures nothing.

Check	Condition	Pass
Sealing	IP67, 1 m, 30 minutes	No water or mist inside
Stack	5 layers, 18 kg each, 72 hours	Deflection 1.0 mm or less
Cold drop	Minus 25 Celsius, 4 hours	Corner intact

Drop and stack samples are separate units. A dropped case carries micro-cracks, and loading it afterwards enlarges them until deflection reads high, so say so in the specification.

Conclusion

Specifications translate use into numbers: cells to size, load paths to wall, ribs to deflection, stack and drop to proof, sealing and temperature to limits. Put the table on page one and the cartridge safety case specification is settled.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.