On the delivery end of a used offset press, the powder spray unit is both the guardian against set-off and a regular on the fault list: moisture-caked powder blocks the hoses, the pump overheats under load until it seizes and the blower motor burns out, while airborne powder mixed with oil forms sludge that can lock the suction decelerator shaft. On a second-hand press, the state of the powder system reveals the previous plant's maintenance discipline better than the impression counter does.
- Nozzles: remove them whole, clear the orifices with a pin and compressed air, and watch the spray pattern after refitting.
- Hoses: blow first and dismantle only when caked; before extended shutdown, vacuum the powder out of the tubes.
- Filters and belts: vacuum the air intake and filter cartridge regularly; check belt tension every three months.
- Spray test: every two or three months depending on the model, together with cleaning nozzles, hoses and ionizing rods.
- Delivery end: clean guide plates and powder deflectors with the blower on; remove dust from the sheet-brake shaft with a vacuum.
Nozzles, hoses and fluidization
A blocked nozzle shows up as uneven lateral powder distribution: set-off in the middle of the sheet, clean edges. Take the nozzle assembly off, clear each orifice with a pin, blow it through and refit. Clean the metering nip with a paint brush before re-checking its function, and verify fluidization with a 19 mm spanner. Stick to blow-first for hoses; empty the container, then purge the residue with the test key so old and fresh powder do not cake together.
Filters, belts and spray-test intervals
The air path is the heart of the unit. Powder build-up on the pump filter and blower intake cuts the air volume: too little air slows the powder feed, too much scatters dust onto bearings and guide rails. Treat air filter cartridges in two steps, clean then replace; check belt tension and condition every three months and re-tension or replace immediately if it slips. Run the spray test every two months on some models and every three on others; if it fails, inspect nozzles and ionizing rods first, then hose integrity.
Delivery-end cleaning and chain lubrication
The secondary damage lands on the delivery: sheet guide plates and powder deflectors must be cleaned with the blower switched on and valves open, or blocked air holes leave sheets floating unstable and piling up in disorder. Remove powder from the sheet-brake shaft with a soft cloth and a vacuum, and clean its air filter at the same time. Count the chain lubrication points: 8 gripper systems on a standard delivery, 14 on an extended one, each with one grease nipple on the shaft lever, two on the bearings and one open hole on the centre bearing; lubricate grippers with spray grease. Mind one exception: never lubricate the format-adjustment chains after cleaning, as oil and powder only accelerate fouling.
Bottom line: powder maintenance comes down to dry, clean and open. Keep the powder dry, the hoses clear and the air path unobstructed; service nozzles, filters and belts on schedule, clean the delivery with the air on and grease the chain points exactly. That alone removes about half of all delivery faults on a used press.
