A screw jack is two machines in one housing: a worm gearbox and a lifting screw with bronze (or ball) nut. Most premature failures are lubrication or contamination failures, not mysterious “bad metal.” This guide is for intermittent industrial duty on catalogue-class jacks (Anand Gears range 5 kN–350 kN). Always follow the specific unit’s lubrication notes when they differ.
Two lubrication zones
1. Worm gear compartment
Grease-filled worm housings are common on intermittent jacks. Check for grease at the recommended points; do not over-pack to the point that seals blow. Some continuous or high-duty designs use oil bath lubrication in a sealed chamber — keep oil level at the sight mark if fitted, and change oil on a plant schedule after break-in contamination is flushed.
Listen for new noise or heat at the worm input after long runs; worm mesh heat is the thermal limit that defines intermittent duty.
2. Lifting screw and nut
Trapezoidal (Tr) screws: wipe the screw clean, then apply a thin, even film of suitable extreme-pressure grease on the active thread before and after major cycles in dirty environments. Dry screws cut bronze nuts quickly. Ball screws: use the grease grade recommended for the ball nut; grit is the enemy — bellows matter more here.
Never mix incompatible greases without purging; when unsure, clean and re-grease fully.
Grease intervals (practical, not absolute)
Exact hours depend on dust, temperature, and cycles. As a plant baseline for intermittent Tr jacks in normal indoor duty:
- Weekly visual — bellows intact? Screw film present? Leaks at seals?
- Monthly light service — wipe and re-film exposed screw; check limit-switch cams still trip cleanly.
- Quarterly deeper check — axial backlash measurement; safety-nut indicator; worm housing grease/oil; coupling set screws.
- After dusty outages or washdowns — re-grease immediately; inspect bellows for tears.
High-cycle ball screws need denser re-lubrication — set the interval from duty, not from the Tr calendar.
Wear checks — nut backlash and safety nuts
Bronze load nuts wear as a planned consumable. Measure axial free play under light load at a fixed height and log it. When play exceeds your acceptance limit (or the manufacturer wear mark on a dual-nut arrangement), plan replacement.
A safety nut (dual-nut wear monitoring) is designed so that as the load nut wears, the gap to the safety nut closes or an indicator becomes visible. That is the early warning before catastrophic drop. Do not defeat or shim the safety nut to “make it quiet.”
Bellows / boot care
Protective bellows keep dust and scale off the screw. Torn boots are how foundry grit destroys a nut in weeks. Keep boots free to compress without pinching; replace cracked neoprene or silicone sections rather than running open. Clean outside surfaces; do not flood the accordion folds with high-pressure water that drives grit inward.
When to re-screw vs replace the jack
- Nut worn, screw still good — replace load nut (and safety nut if fitted); inspect screw flanks for polishing or gouges.
- Screw and nut both worn — replace as a pair; mixing a new nut on a tapered worn screw shortens life.
- Worm mesh noisy, housing sound — rebuild worm shaft / worm wheel as a matched set; see related gearbox spares practice on worm gear sets.
- Housing cracked, mounting distorted, or imported obsolete unit with long spares chain — full drop-in replacement from sample; see replacement & spares and the imported jack case study.
Limit switches and multi-jack trains
Verify end-of-travel switches still stop before hard metal stops. On multi-jack systems, a jammed corner can overload one jack if the motor still pushes the train — investigate binding early (alignment, dry screw, bent platform). Re-grease miter bevel nodes on the same quarterly walkaround as the jacks.
Quick maintenance card
- Film on screw · grease/oil in worm · seals dry outside
- Bellows whole · limit switches trip
- Log backlash · read safety-nut indicator
- Couplings tight · shafts free to turn by hand when unloaded (if safe)
- Plan nut/screw spares before the wear limit, not after
Related: Machine Screw Jacks · Tr vs Ball · Sizing · Contact