Vacuum chamber

01

Set material, surface finish and bakeout

Leybold, a vacuum pump maker, explains that chamber walls release gas that limits pressure, and that cleaning removes gross and fine contaminants and adsorbed water, followed by bakeout; Leybold notes that a set of fingerprints can take more than a day to desorb. Surface treatments reduce the effective area: for stainless steel it cites outgassing reductions of about 30 times for electropolishing, about 50 times for mechanical polishing and over 70,000 times for a 30-hour bakeout at 250 °C. [1]

Coatings can also help: Leybold describes passive barrier coatings and active NEG coatings that pump gases and need periodic heat activation. [1]

Super Q, a supplier listed here, offers 304 and 316 stainless chambers in spherical, cylindrical, box, bell-jar and D shapes with sandblasted, electropolished or hand-polished finishes, NW or CF ports, helium leak testing, and states vacuum down to 1 × 10⁻⁶ Torr with suitable pumps. [3] Editorial calculation: 1 Torr = 133.3 Pa, so 1 × 10⁻⁶ Torr ≈ 1.3 × 10⁻⁴ Pa.

Give the supplier the pressure to reach and pump-down time, process and temperature, internal size and shape, material and finish, bakeout temperature, port and flange list, viewports and feedthroughs, door type, leak-test method and acceptance limit.

02

Specify leak testing and acceptance

In the rate-of-rise method, the chamber is isolated from its pumps and the pressure rise in the closed volume measures the gas load from leaks and outgassing. A NASA study of the method measured known leaks of nitrogen and methane to within about ±20% and helium to about ±25%, but found errors up to a factor of 10 caused by pumping in the ionization gauge, reduced by limiting gauge pumping. [2]

Editorial calculation: the gas load is volume × pressure rise ÷ time. For a 500 L (0.5 m³) chamber whose pressure rises by 0.1 Pa in 1,000 s, Q = 0.5 × 0.1 ÷ 1,000 = 5 × 10⁻⁵ Pa·m³/s, which includes both leaks and outgassing. [2] Agree the method, gauge, temperature and acceptance limit in the order.

Super Q states that its chambers are helium leak tested. [3] Ask for the test method, the sensitivity and the result for each chamber.

03

Compare steel outgassing and set a helium leak limit

A 2016 protocol paper from the Pohang Accelerator Laboratory (POSTECH) and the Korea Research Institute of Standards and Science built test chambers by TIG-welding a steel cylinder to two CF35 end flanges, about 2,400 cm² of inner surface and about 7 L of volume, with argon back-purge at 5 L/min and torch argon at 8–9 L/min. Each welded seam was bagged in helium and had to show a helium leak rate below 1 × 10⁻¹¹ Pa·m³/s (1 × 10⁻¹⁰ mbar·L/s). Outgassing was then measured by rate of pressure rise with a spinning rotor gauge after an in-situ bakeout at 150 °C for 48 h. [4]

The authors report that untreated 304 stainless steel outgassed 5.1 × 10⁻⁹ Pa·m³·s⁻¹·m⁻², and that a 36 h vacuum-furnace pretreatment at 450 °C cut this about 22-fold to 2.3 × 10⁻¹⁰. Untreated S20C mild steel measured 2.6 × 10⁻¹⁰ and 4.0 × 10⁻¹⁰, and a 12 h treatment at 850 °C lowered one sample by 66% to 8.8 × 10⁻¹¹. They attribute the low hydrogen outgassing of untreated mild steel to vacuum degassing during steelmaking. [4]

Editorial calculation: for the paper's 0.24 m² chamber, untreated 304 at 5.1 × 10⁻⁹ Pa·m³·s⁻¹·m⁻² gives a gas load of about 1.2 × 10⁻⁹ Pa·m³/s; in 7 L (0.007 m³) that is a closed-volume pressure rise of about 1.7 × 10⁻⁷ Pa/s. The same chamber after the 450 °C treatment gives about 5.5 × 10⁻¹¹ Pa·m³/s. [4]

Editorial note: state in the order the steel grade, any vacuum-furnace pretreatment (temperature and hours), the bakeout the chamber must survive, and the helium leak limit per seam and flange.

04

Compare what suppliers offer

Suppliers linked to this page list process vacuum chambers, thermal vacuum test chambers or degassing chambers. [3]

Super Q and HTC list customised stainless vacuum chambers with valves and components; Ruijia lists vacuum chambers with flanges and fittings; Grande, Hardy and Linpin list thermal vacuum test chambers among environmental test chambers; MEST lists customised vacuum chambers alongside dispensing equipment, and Troy lists vacuum degassing chambers. [3]

05

Trace the chamber components

This is a functional reference built from the sources cited; it is not one maker's parts list.

06

Fill the specification fields with values for your process

A vacuum chamber quotation needs values for your process. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the process, pressure and acceptance data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Process: [coating, test, degassing, research; temperature]
Pressure: [target; pump-down time; pump set]
Chamber: [shape; internal size; material; finish]
Ports: [list with NW, ISO or CF flanges; viewports; feedthroughs]
Bakeout: [temperature; heaters]
Testing: [helium leak test; rate of rise; acceptance limit]
Documents: [drawing; material certificates; leak test report]

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