The main reasons for slow precision extraction in a vacuum coating machine can be found in the following aspects:
1. The diffusion pump may be insufficient.
Solution: Connect an ionization gauge to the diffusion pump inlet to observe the pump's capacity. Observe the pumping time and its limits, then compare the results.
2. There is a minor leak in the vacuum system.
Solution: This requires careful leak detection to check if the vacuum holding time meets the required standard.
3. The enclosure is too dirty; a dirty enclosure results in a larger air release.
Solution: Clean the enclosure.
4. Insufficient backing vacuum; the ultimate vacuum of the mechanical pump or mechanical pump plus Roots pump is inadequate.
Solution: Use a resistance gauge to check the backing piping separately.
Slow pressure even under no-load: Often due to leaks, pump malfunction, or pipeline blockage.
Normal no-load pressure, but slow pressure after loading: Generally due to workpiece/tool venting or raw material moisture.
Frequent pressure fluctuations: Typical leak point.
Slow pressure decrease but not reaching the standard: Often due to large-area venting or cold trap blockage.
Slow pump-down under no load → Check for leaks, replace vacuum pump oil, clean cold trap and filters.
Slow pump-down with workload → Dry workpieces, extend pre-pumping time, bake fixtures/jigs.
Fluctuating pressure → Locate leakage points, repair vacuum valves.
Slow steady pump-down (no pressure fluctuation) → Clear blockages, perform full chamber bake-out for degassing.
Daily Prevention & Regular Maintenance (To Prevent Recurrence)
Daily: Check pump oil level, cooling water, and air source pressure; clean dust from the surface of the door seals.
Weekly: Clean the primary filter, observe the cold trap for frost, and defrost as needed.
Monthly: Randomly check valve operation and pipeline sealing; perform degassing and baking on the tooling.
Quarterly/Semi-annually: Change the vacuum pump oil for the entire unit; perform deep disassembly and cleaning of the cold trap, baffles, and pipelines.
Standard Operating Procedures: Ensure workpieces are thoroughly dry; minimize the entry of moisture-laden or volatile materials into the chamber; avoid opening the door unless absolutely necessary.
