Ultra-high-vacuum (UHV) system

Product overview

• Most common for special atmospheres and ultra high vacuum are the following options (details below):
• Fully controlled inert gas atmosphere in vacuum chamber furnaces
• Reactive gases (H2, CO, CO2, H2S, H2O, CH4, C2H4 and others on request)
• Vacuum pump options
• Partial pressure option
• Afterburner (thermal, catalytic or with active propane gas flame) option
• Modified atmosphere with metallic retorts in standard chamber furnaces
• SiC tiles for element protection in standard chamber furnaces

1. Fully controlled inert gas atmosphere in vacuum chamber furnaces
The standard GLO, LHT, HTK, HBO, HTBL and V-L vacuum chamber furnaces are fitted with a full inert gas control system as standard. Depending on size and maximum temperature, semi-automated controls with flowmeters or fully automated controls via a PLC with touch screen and mass flowmeters are available. All vacuum chamber furnaces are fitted with one inert gas control as standard. Additional gas controls are available as an option. All vacuum chamber furnaces are available with a full range of optional vacuum pumps (rotary vane, roots, diffusion and turbo). In some cases a vacuum pump is mandatory for safe use of the furnace.

2. Reactive gases option
Vacuum chamber furnaces can be modified to work safely with reactive gases (examples: H2, CO, CO2, H2S, H2O, CH4, C2H4). In principle, a furnace for use with reactive gases is fully automated and includes:

• Control by SIEMENS S7-300 with panel TP1900 or WinCC
• Installation for an inert gas (e.g. nitrogen or argon) controlled by MFC (mass flow controller)
• Installation for a reactive gas controlled by MFC (mass flow controller)
• Reactive gas sensor
• Active afterburner for safe combustion
• Safety purge tank
• SIL 2 standard for safety related parts

For safety reasons the gas supply and operation are designed in accordance with EN 746-3: the furnace must be free of atmospheric oxygen before heating and before introducing combustible gases; safety statuses are monitored and automatic safety measures (e.g. inert gas purge) are applied in hazardous situations.

3. Vacuum pump options
The page describes four vacuum pump technologies with different achievable vacuum levels and operational notes. Key points:

Vacuum pump technologies (summary)
Turbo molecular pump — high rotational speed (>90 000 rpm); used with a pre-vacuum pump; provides high/ultra-high vacuum and removes heavy hydrocarbons and light gases effectively.
Oil diffusion pump — no moving parts; generates high vacuum via oil vapour; very high pumping speed but can leave traces of oil molecules.
Roots pump — suitable for fine vacuum range; requires a pre-vacuum pump; consists of precisely machined rotating lobes with very small internal clearances.
Rotary vane pump — common pre-vacuum pump (single or double stage); greased vacuum chamber; used for direct evacuation from atmospheric pressure; achieves rough vacuum; double stage gives better vacuum.

Notes: ultimate vacuum and pump performance in a furnace system depend on many factors (materials introduced, cleanliness, desorption/outgassing, leakage rate). Carbolite measures and specifies furnace leakage rates and cleans vacuum devices prior to assembly. Special pumps (membrane, cryopumps, ion getter pumps, pumps with special lubrication or without lubrication) can be supplied on request.

4. Partial pressure option
Partial pressure is defined as a controlled gas flow at a defined vacuum pressure inside the furnace. Implementation requires a PLC with mass flow controller and an adjustable gas outlet valve. The incoming gas flow and pressure are set via the PLC; a mass flow controller controls gas flow and a pneumatic valve in front of the double-stage rotary vane pump modulates to maintain the required vacuum pressure (typical range 10 to 1000 mbar). The control software adjusts the pneumatic driven valve opening angle so the vacuum gauge maintains the set pressure during heat treatment.

5. Afterburner options (thermal, catalytic or active propane/methane flame)
Several afterburner solutions are available. For vacuum chamber furnaces the safest exhaust gas treatment is an active afterburner with a methane or propane flame. A heated gas outlet pipe between the furnace and afterburner is recommended to avoid condensation of combustion/pyrolysis gases; this minimizes exhaust system service and is convenient for production.

6. Modified atmosphere with metallic retorts in standard chamber furnaces
For non-gas-tight ovens/chamber furnaces the use of modified atmospheres is limited. By purging inert gas via an optional inlet, oxygen cannot be reduced to very low values in non-gastight chambers. On the HTMA oven range (up to 700°C) oxygen can be reduced to ~50 ppm using a gastight, fully seam-welded inner chamber with needle valves, flowmeters and a non-return gas outlet. Up to 1150°C, gastight metallic retorts for standard CWF and GPC chamber furnaces are available; the retort is sealed with a removable front opening insulated door, with front-mounted gas inlet/outlet connections; oxygen levels down to ~30 ppm are achievable. Retort and furnace must be ordered together as the furnace is modified to accept the retort.

7. SiC tiles for element protection in standard chamber furnaces
Silicon carbide tiles can be fitted to standard furnaces to protect heating elements from outgassing samples.

Special Atmosphere & Ultra High Vacuum - Examples and notes
Several example installations are shown as illustrations, including vacuum chamber furnaces compliant with EN 746-3 and SIL2 provisions for safe operation with hydrogen and other reactive gases, tube furnaces with turbo pump options, custom retort-equipped designs for debinding/sintering, and multi-zone tube furnaces with turbo pump options.

caractéristiques / spécifications techniques

• Brand: Carbolite
• Applications: controlled inert atmospheres, reactive gas processing, partial pressure processes, ultra-high vacuum treatments
• Reactive gases supported (examples): H2, CO, CO2, H2S, H2O, CH4, C2H4 (others on request)
• Control systems: PLC (SIEMENS S7-300) with TP1900 or WinCC panel; touch-screen control and mass flow controllers (MFC)
• Safety standards: EN 746-3 compliance for gas-fired/reactive gas operation; SIL 2 for safety-related parts
• Vacuum pump options: rotary vane (pre-vacuum), roots (fine vacuum), oil diffusion (high vacuum, oil traces), turbo molecular (high/ultra-high vacuum)
• Partial pressure control: PLC + MFC + pneumatic outlet valve; adjustable pressure range typically 10–1000 mbar
• Afterburner options: thermal, catalytic or active flame (propane/methane); recommended heated outlet to avoid condensation
• Metallic retorts: gastight retorts available up to 1150°C for reduced oxygen (down to ~30 ppm); retort and furnace must be ordered together
• HTMA ovens: gastight inner chamber up to 700°C; oxygen reduction to ~50 ppm
• Element protection: silicon carbide (SiC) tiles to protect heating elements from outgassing
• Typical maximum process temperatures referenced on site for ranges: (examples across ranges) up to 2200°C for some vacuum chamber furnaces; system design varies by model and configuration