Why not use standard ABS for a CSSD transfer case?

Answer: ABS deflects at 85–95 ℃ under 1.82 MPa, so the 90 ℃ wash warps it. PP holds 100–110 ℃ at 0.45 MPa and the steam stage lasts 4 min.

Is IP67 enough for wet transfer?

Answer: It handles water from outside. A CSSD transfer case also beats a 30–60 mbar vacuum inside, which is why the 0.2 μm vent and 6 mm drain valve count as part of the seal.

Why do labels blister after sterilisation?

Answer: Moisture in the adhesive flashes at 134 ℃. Load and expiry fields need a polyimide base, while standard polyester starts lifting after 3–5 cycles.

How often is the gasket changed?

Answer: A CSSD transfer case takes 500 cycles or 12 months, whichever comes first. At six loads a day that is roughly three months, with the monthly check watching for set past 30%.

CSSD Transfer Case: Sealing and Labelling

Quick answer: A CSSD transfer case has to survive 90 ℃ wash cycles and 134 ℃ steam without warping, then stay leak-free at IP67 while still wet.

What Steam Cycles Do to the Material
Sealing for Wet Transfer with Two Lips and a Drain
Three Label Fields That Must Stay Legible
Label Life and Stack Load
Gasket Interval and Monthly Checks
FAQ

1. What Steam Cycles Do to the Material

A CSSD transfer case meets temperature before it meets water. A washer-disinfector runs a wet cycle at 90 ℃ for 10 min; the autoclave holds 134 ℃ at 2.1 bar for 4 min. Six to eight loads a day adds up to more than 1500 heat shocks a year on the same shell.

Homopolymer PP deflects at 100–110 ℃ under 0.45 MPa, so the wash is comfortable. The steam stage is survived on dwell time: four minutes will not soften a 3.2 mm wall. The damage shows in the lid, where 500 cycles sag the centre by 0.6–0.9 mm, enough to break the seal line.

Two fixes exist. Four ribs under the lid, wall thickness raised from 2.6 mm to 3.2 mm, hold sag to 0.3 mm; a 316L tray at 0.8 mm carries the load path instead, at 5.4 kg rather than 3.2 kg.

The gasket is judged on two figures, continuous service temperature and compression set. EPDM runs to 120 ℃ continuous and 141 ℃ short-term; silicone to 200 ℃. EPDM is adequate at 134 ℃, provided compression set stays under 25% on ASTM D395 method B at 70 h and 100 ℃.

2. Sealing for Wet Transfer with Two Lips and a Drain

Wet transfer means the CSSD transfer case is pushed away with water still on the shell and drips coming off the tray. IP67, immersion at 1 m for 30 min, covers both the wash-down and the short soaking that follows.

A single lip fails when wet: surface tension carries a water film past the lip and into the groove. The workable layout is two lips, a main lip against the groove floor and a secondary O-ring outside it, with a 1.5 mm drain channel between them that empties through a 6 mm valve at 15° of tilt.

CSSD transfer case in white, close view of an orange latch closed over the rim, seal face along the joint, pale grey background

Pressure is the second problem. After sterilisation the interior sits 30–60 mbar below ambient, so the first moment of opening pulls air back through the seal face, water with it. A PTFE membrane vent in the lid, 0.2 μm pore, equalises without passing water.

Compression has to land between 25% and 30%. Under 20% the joint leaks; over 40% the gasket takes a permanent set and rebound drops to 60% after 200 closures.

3. Three Label Fields That Must Stay Legible

Labels on a CSSD transfer case answer three questions: where it goes, which load it belongs to, when it expires. Fixed format in a fixed location is what makes traceability work.

Position fails more often than content. A label on a raised panel is scraped off by the first case stacked on top, so it belongs in a recess 1.2 mm deep with a 3 mm margin.

Field	Position and size	Format	Durability
Department	Lid recess, 80×50 mm	4 digits + 2 letters	Legible at 3 m, 5 mm type
Steriliser load	Second line of recess	Date + 2-digit load	134 ℃ for 4 min
Expiry	Lower edge, reversed out	Date, 6 digits	50 wipes at 75% ethanol

Type height is the hard number: 5 mm reads at 3 m, the limit for checking a case as the trolley passes; at 4 mm the reader stops and lifts it, and the check stops happening.

The data code goes on the side for a reason. Once four cases are stacked only the side wall is exposed, and a scanner at 20–30 cm reads a 30×30 mm code at 0.5 mm modules.

4. Label Life and Stack Load

Labels face alcohol, humid heat and steam. Fifty wipes with 75% ethanol is the routine figure; 48 h at 60 ℃ and 95% relative humidity stands in for a wet-season store room.

Standard polyester blisters at 134 ℃ as moisture in the adhesive flashes. Steam-durable stock uses a polyimide base at four to six times the unit price, so it goes on the two critical fields only.

CSSD transfer case in white and orange, open, orange insert trays with a grey monitor box and white soft pack, two orange latches

Stack load is a second set of numbers. A single case carries 25 kg on a 3.2 kg shell, and four-high stacking puts 100 kg on the bottom unit for 24 h with no more than 2 mm of deflection. A full CSSD transfer case is rated for a 1.2 m corner drop.

Check	Value	Pass condition
Single case load	25 kg	Handle at 500 N, no set
Stacking	4 high	100 kg for 24 h, ≤2 mm
Full drop	1.2 m on a corner	No crack, latches hold
Gasket life	500 cycles	Set ≤30%

5. Gasket Interval and Monthly Checks

The gasket is replaced on whichever comes first, 500 sterilisation cycles or 12 months. At six loads a day, 500 cycles arrives in about three months, so the cycle count drives the schedule.

Monthly checks cover four items: set beyond 30%, hardness up 10 Shore A, a surface crack longer than 0.5 mm, or a joint that has lifted. Any one of them means replacement.

Fitting takes no tools: the old gasket lifts out of the channel, the new one presses in 30 cm at a time, corners mitred at 45°, and the job runs 2 min with spares at 10% of the fleet.

Conclusion

A CSSD transfer case is specified by the numbers that survive the loop: PP at 100–110 ℃ heat deflection and a ribbed 3.2 mm lid against 134 ℃ for 4 min; 25–30% gasket compression with a 6 mm drain and a 0.2 μm vent at IP67; a 1.2 mm recess and 5 mm type so department, load and expiry read at 3 m. Change the gasket at 500 cycles and stack four high at 25 kg each.

This article covers the case body only: material, sealing, hardware and marking. Nothing here addresses the handling, loading or use of anything carried inside.