Fixturing decides more than the machine setting
Housings arrive with cored cavities, drilled cross-holes and machined bearing seats. If a cavity faces upward during spraying, liquid and swarf pool in it instead of draining. If a bore is plugged by a fixture finger, that bore never sees the wash medium at all. Two practical checks come before any parameter change:
- Every cavity faces down or sideways so that medium and debris drain out during the cycle.
- Long blind holes and oil galleries are either lanced from the inside or blown through with air at the end of the cycle.
- The seating points sit on the flange face, not on a machined bearing bore, so the housing does not rock and shield one side.
If the same housing passes or fails depending on how it was loaded, the problem is fixturing and basket layout rather than chemistry or temperature.
Reach: nozzles, pressure, and line-of-sight shadows
Spray cleaning works where the medium physically hits. Housing inner ribs, boss clusters and the inside of the bearing bores sit in shadow behind the outer wall, and a single fixed spray bar cannot cover them. Rotating the part, moving lances in and out of the openings, or combining spray with an immersion and agitation stage are the usual answers. Higher pressure is not automatically better: on a machined aluminium housing an aggressive jet aimed at a thin wall drives oil and swarf deeper into the pore structure instead of off the surface.
Where heat and vapor do the work, the equipment choice matters. A fixed steam cleaning machine such as the PowerDe HW02 delivers steam at a stated 160 °C and 0.8 MPa from an 80 L SUS304 tank with 6 kW heating power, and switches between dry and wet steam. Dry steam carries the heat that softens hardened grease on an external housing face, while wet steam supplies the condensate volume that flushes the loosened soil away. The same reasoning explains why a wet-only cycle leaves grease on the mating face and a dry-only cycle leaves the residue sitting on the part.
Soil type sets the chemistry and the dwell
Three soils dominate on gearbox housings, and they do not respond to the same treatment:
- Cutting and grinding oil plus swarf — needs an alkaline detergent and enough bath temperature to keep the oil mobile; the swarf must be flushed, not smeared.
- Press-fit and running-in grease — needs heat plus dwell; a short cold spray leaves the film intact at the seal seats.
- Weld flux and drawing compound — usually water-soluble but hardens if it dries, so the interval between machining and washing matters as much as the wash itself.
Where the residue is mixed, run a staged sequence — soften, then flush — rather than one long aggressive spray. If a housing carries heavy carbonised oil, that points to heavy-duty cleaning equipment with heated medium and a dwell stage, not to a longer cold rinse. Where the part also has to stay dimensionally stable, a manufacturer that develops its own intelligent cleaning equipment can match the cleaning medium to the housing material instead of asking the buyer to accept one fixed recipe.
The last rinse and the drying stage cause most late failures
Parts that pass the wash and fail the inspection an hour later usually fail at the rinse. Detergent left on the surface becomes a stain or a residue film once it dries, and a rinse tank loaded with dissolved oil redeposits that oil onto the next housing. Two controls are worth more than any extra spray minute: a clean or flowing final rinse, and a rinse bath kept below its contamination limit by skimming or replacement on a fixed schedule rather than when an operator notices the water.
Drying has the same hidden effect. Trapped water in a cored cavity drips out after the part has been inspected and carries dissolved salt or detergent to the outside face. Blow-off air that is not filtered, or a cavity that is not angled for drainage, will put back exactly what the rinse removed.
Verify the result the way the next process will judge it
A visual check of the outer face cannot see the inside of an oil gallery. Before changing parameters, fix the acceptance method first: a white-glove wipe over the accessible seats, a residue-weight check on a sample lot, or a water-break test on the machined face, with the sample points written down so the same place is checked each time. Ask the parts supplier to confirm the required cleanliness level for the assembly they feed — seal seats, bearing bores and mating flanges each tolerate different residue, and an over-cleaned part is extra cycle time that buys nothing.
Where the cleaning step sits outside an established line — a small machining cell, a remanufacturing bay, a service workshop cleaning returned housings — equipment and process can be specified together. Customised cleaning solutions cover exactly this case: the housing geometry, the soil, the throughput and the available utilities define the machine, rather than the buyer adapting to a catalogue model.
Where to look first
When results on gearbox housings drift, work through the list in order: loading and drainage, then nozzle reach and lance movement, then dwell and temperature against the actual soil, then the rinse bath condition, then drying and air quality, and only then the machine rating. Changing heat or pressure first, without checking whether the medium reaches the cavity and whether the final rinse is still clean, is how a stable process becomes one that passes intermittently.
