A gearbox housing is a bad object to clean and a necessary one. It has cored passages that hold swarf, machined faces that must be flat and oil-free before a seal is fitted, bearing bores whose fit depends on nothing being left on the circumference, and cavities that were full of cutting fluid until an hour ago. A checklist for housings therefore has to be written backwards, starting from what the housing has to do next, because "clean" has a different meaning before a seal is fitted than it does before paint.
Write the checklist around the four places that fail inspection
Core drill holes and the passages between them. These are where swarf and cutting-fluid residue hide, and they are the reason housing cleaning exists as a task at all: the debris is trapped inside geometry that a brush cannot reach and a rinse cannot flush unless the flow is directed. Note the diameter, length and number of each passage on the checklist and state how each is verified.
Mating faces and the sealing grooves. Any residue here shows up later as a leak, and the damage that matters is scratch, not soil. The checklist should require visual and tactile inspection of the face, and should prohibit scraping with anything that leaves a mark on the machined surface.
Bearing and shaft bores. The cleanliness that matters here is particle cleanliness, because a retained particle changes an interference fit. Record the measurement after cleaning, not only before assembly.
External surfaces. Oil film on the outside decides whether paint or adhesive will wet the housing, and it is the one item most crews do properly by accident, which is why it fails when the fluid changes.
Add the columns that make the list enforceable
Each line needs the method, the acceptance check, and the disposition of what is removed. Cleaning chemistry without a rinse specification is a defect waiting to happen. Swarf without a collection route ends up back in the next housing. A checklist that does not say how the operator proves the passages are clear is a checklist that assumes it.
Heat is the input that shortens this job on oily housings. Cutting fluid and gear oil release from cast surfaces when heated, and a method that supplies heat with little water leaves the housing dry enough to move on to assembly rather than waiting in a drying area — the reason machine tool steam cleaning and similar low-volume hot methods are considered where a wash bay is not available or the rinse water cannot be handled. Where a machine's published figures are used to frame a supplier question, read the stated application first: the 6 kW, 220 V unit in PowerDe's cleaning range, the Fixed Steam Cleaning Machine PowerDe HW02, is described on its product page around vehicle cleaning at fuelling and parking sites, not around component degreasing, and its model naming is inconsistent on the customer's own site. Its numbers — an 80 L SUS304 tank, 0.8 MPa vapour pressure, dry and wet steam modes — are a specification reference, not a qualification for cast housings. Ask the manufacturer whether the pressure and temperature are acceptable on your material and your machined faces before specifying it.
Define cleanliness as a number someone can measure
Adhesive and seal suppliers publish the cleanliness they require; use their test rather than inventing one. Common verifications are a water-break test on a degreased surface, a wipe sample weighed for residue, or a flush-and-filter method that captures and weighs the debris from the passages. Choose one, write it on the checklist, and record the result against the housing serial or batch.
Then set a frequency for the checks nobody likes: the cleanliness of the cleaning equipment itself. A bath, a tank, a spray lance or a steam wand that has not been cleaned will re-deposit what it removed. Add it as a line with a named owner and a date.
Test the list on a housing straight off the machine
Take a housing at the point it actually enters cleaning, run the checklist, and inspect the passages afterwards with a borescope or against a light. Whatever the inspection finds is the missing line. Rebuild the list around that finding, then repeat — a housing-cleaning checklist is only finished once it has caught a defect you would otherwise have shipped.
