Decide what is on the cover before anyone mentions a machine
Walk the machine and write down the deposits one by one, because each one pulls the decision in a different direction. A film of straight cutting oil on a painted guard is oil, plain and simple: it responds to heat, and adding water to it mostly spreads it. Dried emulsion baked on near a chip conveyor is a mixed deposit with solids suspended in it; heat alone loosens the binder but the solids still have to be lifted off. Coolant sludge in the tray at the base is a wet, heavy soil that no low-liquid mode will move by itself. Graphite and grinding dust on top of the enclosure is dry and airborne, and water turns it into a paste that ends up in the door channel. A few quick questions settle most of it: does the deposit come off with a dry rag and some elbow grease, does it smear, does it need a solvent to shift at all, and is it on a vertical surface where anything wet will run straight down into a seal line.
What dry steam is actually doing on an enclosure
The reason the low-liquid mode earns its place on machine-tool exteriors is that it puts heat onto the deposit without putting a stream into the shop. Cured oil film and dried emulsion respond far more to temperature than to force; once the film softens, a cloth and a brush finish the job, and there is almost nothing to collect afterwards. On the top face of an enclosure, on the vertical panels beside a control cabinet, and around cable entry points, that low run-off behaviour is the whole point, because the surface being cleaned is covered with penetrations. The cost is time. Dry steam works on contact, so an operator has to stay with the surface and keep the nozzle moving slowly enough for the heat to do the work. A technician used to pressure-washing will find the pace frustrating on the first pass and will try to compensate with force, which is the wrong reflex.
When the wetter mode is the right call
Not every surface on a machine is a risk. The bare cast-iron ways at the base, the underside of the chip conveyor, a steel stand, the outside of the coolant tank, a guard panel that comes off the machine and gets washed on a bench away from the spindle: these can take more water and more push, and the wetter mode gets the sludge off in far less time. The decision is not "dry mode everywhere, always". It is which surfaces in this shop can tolerate run-off and dry inside the window you have. Write that list down and hand it to the operator, because the boundary between the two groups of surfaces is exactly where mistakes happen. Anything with a bearing gap, a seal lip, a glass window for a scale or encoder, a gland plate, or an open vent belongs to the first group. Plain steel and painted sheet away from those features belongs to the second.
The features that set the boundary
Ask the maintenance lead to point out the penetrations on the specific machine you own, because they vary by builder and by enclosure design. Wiper seals at the ends of the axis covers will hold water against the ways. The gaps around telescopic covers and the channels they slide in are traps. Sight glasses, windowed guarding and the small windows on interlocked doors take steam that fogs the inside and leaves residue on the glass. Cable glands, connector hoods, junction-box knockouts and fan vents on the electrical side are the ones to keep completely dry; those you mask or shroud and do not clean at all. Air lines, coolant return ports and the spindle nose taper should be protected or left out of the round entirely. A machinist will point to all of this in ten minutes; an operator handed a machine with no briefing will not.
One machine, both modes, in the same round
In practice a machine-tool exterior gets cleaned in two passes, and the order matters. Take the wetter mode to the base, the tray, the conveyor and the removable guards first, away from the enclosure, so the heavy sludge is gone before anyone works near a seal. Then change the mode and work downward on the enclosure itself, top face first, vertical panels second, and the areas near windows and glands last, with the jet directed away from the gaps and the run-off routed to a floor drain or a tray rather than down the machine. Where the unit switches between modes at the gun rather than at the machine, say so in the written instruction and have the operator confirm the setting before each zone; a mode left over from the previous zone is one of the more common ways an enclosure gets wet unintentionally.
PowerDe's cleaning range includes units listed with both dry and wet steam, and the catalogue pages differ in what else they carry: see the dry and wet steam cleaner page for the fixed unit, and the mobile steam cleaning machine listing for the units usually pushed to a machine bay. Read those pages as descriptions of what the builder publishes, not as a claim that this particular model has been qualified in your shop on your machine. The mode-switching behaviour, the fitting on the water inlet, what the unit tolerates from hard supply water, and where the mains connection has to sit are all things to put to the supplier as a written list.
Reach and downtime decide whether either mode is workable
Ask three questions about the bay before buying anything. Can the unit get to the machine at all, through the aisle and past the fixtures that live on the floor? Does the distance from the mains outlet and the water point let the operator reach the far side of the machine without dragging a cable across a wet floor? And does the hose reach the top face without someone climbing? If the answer to any of them is no, the fix is usually a portable unit and a second socket, not a different cleaning method. Then agree the window with production: the machine has to be stopped, interlocks respected, no bypassing of guarding, and the surface needs time to dry before the next job is loaded. A round that leaves the ways damp at the end of the shift is a round production will cancel.
Prove it on your own machine before the purchase order
Book one bounded trial on a machine you actually own, on the worst-deposit panel and on one panel near a seal line. Before the first pass, tape the boundaries of both test areas, photograph them, and write the acceptance conditions on the same sheet: deposit removed with no residue left in the channel, nothing wet in the seal line or the gland plate, no residue on any window, no flash of surface rust the following morning, and the machine back in service inside the agreed window. Set stop conditions in advance, for water found in a gap, fogging inside a sight glass, or coolant dislodged into the tray in an amount you cannot handle in the window. Run both modes on their own patches so the comparison is real, and have a second person inspect each patch once it is fully dry, one row per patch, the inspector's own name, date.
Where machine tool steam cleaning stops working
Be honest in the record about the limits. Steam does not dissolve thick cured grease skins the way a solvent gel does, and it will not rescue pitting in bare metal or restore a painted surface already lifting. Grease on ways, guideways and ball screws is not an exterior job at all: the lubricant has to be handled by the machine's own maintenance routine, and any attempt to clean inside those features belongs to the builder's instructions, not to a cleaning round. Steam will not lift swarf off a magnetic surface without a separate wipe-down step, and it adds nothing if the deposit is loose dust that a dry pick-up would have taken. Write these limits into the same one-page instruction, because the people who run the routine need to know when to stop.
Turn the choice into one page the operator can follow
Close the decision with a single sheet per machine family, not a manual. It should carry the zone map, meaning clean-wet here and keep-dry there, plus the mode for each zone, the protected features and how they are shrouded, the drain or container the run-off is routed to and who signs off that route, the sequence of passes, the drying time before the machine is released, the re-lubrication points to check afterwards, and the escalation rule for anything the sheet does not cover. Train the operator at the machine rather than in a meeting room, review the sheet on a named date, and change it whenever the shop changes a machine. That sheet is what makes the dry-versus-wet decision repeatable on the next shift; without it the choice gets made again every time by whoever is holding the gun.
