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What are the causes of diffusion pump backstreaming?
High cross-over pressures when transitioning from mechanical pumps to diffusion. Contaminated diffusion pump oil. Poor performance of the holding pump causing high pressures in the diffusion pump. Leaks in the diffusion pump and/or holding pump and associated piping. Poor performance of the backingRead more
High cross-over pressures when transitioning from mechanical pumps to diffusion.
Contaminated diffusion pump oil.
Poor performance of the holding pump causing high pressures in the diffusion pump.
Leaks in the diffusion pump and/or holding pump and associated piping.
Poor performance of the backing pumps causing high pressures
Improper sequencing of the valving
See lessWhat is an acceptable vacuum furnace leak rate?
Typical acceptable vacuum furnace leak rate varies with the application of the furnace or the operations to be performed and/or the materials to be heated. A typical size new furnace would be less than 10 microns per hour for a mechanically pumped furnace. A diffusion pumped pumped furnace mightRead more
Typical acceptable vacuum furnace leak rate varies with the application of the furnace or the operations to be performed and/or the materials to be heated. A typical size new furnace would be less than 10 microns per hour for a mechanically pumped furnace. A diffusion pumped pumped furnace might be less than 5 microns per hour. These rates are for clean, dry and out-gassed conditions.
See lessWhat are the acceptance criteria for a vacuum chamber leak rate test?
The acceptance criteria for a vacuum chamber leak rate test will vary with the application of the vacuum chamber or the operations to be performed in the chamber and/or the materials being placed in the chamber. In the heat treating industry the purpose of vacuum is to reduce the impact of oxygen oRead more
The acceptance criteria for a vacuum chamber leak rate test will vary with the application of the vacuum chamber or the operations to be performed in the chamber and/or the materials being placed in the chamber. In the heat treating industry the purpose of vacuum is to reduce the impact of oxygen on the materials to be heat treated. Typical acceptable leak rate of a new clean, dry cold and out-gassed furnace with mechanical pumps would be less than 10 microns per hour. For a diffusion pumped furnace it would be lower (maybe 5 microns per hour) as the ultimate vacuum capability will be expected to be lower. Pumping becomes more difficult as the pressure is reduced, thus one needs lower leak rates.
See lessWhat is the cause of virtual leaks?
Usually bad design or improper weld procedures.
Usually bad design or improper weld procedures.
See lessWhat is the correct way to perform a leak check on a vacuum furnace?
Pump the cold furnace down as low as possible, close the vacuum valve and time the rise in pressure from that point to another. Calculate the rise in pressure from point A to B to get a millitorr (micron) per hour amount. This will give you what is called the rate of rise. If the rate of rise isRead more
Pump the cold furnace down as low as possible, close the vacuum valve and time the rise in pressure from that point to another. Calculate the rise in pressure from point A to B to get a millitorr (micron) per hour amount. This will give you what is called the rate of rise. If the rate of rise is to high then do the following:
Connect a helium mass spectrometer into the pumping line in front of the vacuum pumps. Reduce the pressure as low as possible and begin to spray helium around all penetrations of the vacuum vessel starting at the top, as helium rises. Care must be given to the maximum operating pressure of the spectrometer relative to the pressure of the furnace.
See lessWhat is the best method to find a vacuum furnace leak?
Typically the best method is to test with a helium mass spectrometer.
Typically the best method is to test with a helium mass spectrometer.
See lessWhat is the difference between a virtual vacuum leak and a vacuum leak?
A real leak would be defined as air or gas leaking through a vessel from the outside of the vessel into the evacuated space. A virtual leak is not a through the vessel situation, it is gas being slowly released into the evacuated space from a place where it is trapped, e.g. a bolt in a blind hole.
A real leak would be defined as air or gas leaking through a vessel from the outside of the vessel into the evacuated space. A virtual leak is not a through the vessel situation, it is gas being slowly released into the evacuated space from a place where it is trapped, e.g. a bolt in a blind hole.
See lessWhat leak detection methods are considered to be the most effective for locating small leaks?
Small leaks in a vacuum system are easily detected with a helium mass spectrometer. Helium leak detection is very effective
Small leaks in a vacuum system are easily detected with a helium mass spectrometer. Helium leak detection is very effective
See lessWhy would a rotary vane pump smoke?
Most likely the pump is operating at a higher pressure than it was design for. Smoke is typically oil vapor carried by the gas (air) leaving the pump.
Most likely the pump is operating at a higher pressure than it was design for. Smoke is typically oil vapor carried by the gas (air) leaving the pump.
See lessCFC, Graphite, or Moly, which is the best choice for vacuum ovens?
Hot zones are the hearth of every vacuum furnace. When purchasing a new furnace, you might face with the Hamletic doubt about hot zones: graphite-based or all-metal design hot zone? That’s the question! The graphite wafer is an excellent material. It allows operation at very high temperatures (up toRead more
Hot zones are the hearth of every vacuum furnace. When purchasing a new furnace, you might face with the Hamletic doubt about hot zones: graphite-based or all-metal design hot zone? That’s the question!
The graphite wafer is an excellent material. It allows operation at very high temperatures (up to 3000°C based on the vacuum level), has low density, reduced weight and modest thermal capacity. It creates the ideal black body conditions (emissivity about 1) inside the heating chamber for obtaining high uniformity.
All-metal hot zones are used in high demand industries where sensitive materials are processed, such as aerospace, electronics and medical. There are heat treatments that require a particularly clean environment or extreme vacuum levels. There may be different reasons: in some cases the chamber’s graphite could interfere with the process, resulting in unwanted carburation of the pieces treated. In other cases, the load could be particularly sensitive to the presence of residues in the oxygen or hydrogen atmosphere (which could lead to embrittlement of the pieces), and so graphite wafer degassing during the cycle could be damaging. In these circumstances, the user should opt for all-metal heating chambers (shields and resistor).
If you want more information on this topic and a detailed analysis of the differences, take a look at the following 2 articles:
See lessVacuum furnace hot zone: graphite vs all-metal design [1/2]
Vacuum furnace hot zone: graphite vs all-metal design [2/2]
Why use partial pressure in a vacuum furnace?
Partial pressure can be used to assist in removing impurities and heat distribution during the heating process.
Partial pressure can be used to assist in removing impurities and heat distribution during the heating process.
See lessWhere is it required to do hydrogen bakeout?
Hydrogen bakeout is commonly used for materials or processes when hydrogen induced cracking is a concern. Heating the material to a temperature high enough and long enough to allow the trapped hydrogen to escape from the areas where it is trapped in the material. This is a common process for post weRead more
Hydrogen bakeout is commonly used for materials or processes when hydrogen induced cracking is a concern. Heating the material to a temperature high enough and long enough to allow the trapped hydrogen to escape from the areas where it is trapped in the material.
This is a common process for post welding of chrome moly steels that do not use low hydrogen welding processes or electrodes and heavy weldments.
See lessWhat temperature is vacuum brazing performed at?
Technically brazing is performed above 840F. Vacuum furnace brazing temperatures are determined by the braze filler metal being used and the base metals involved. You should refer to the appropriate material specification for your industry for the applicable variables.
Technically brazing is performed above 840F. Vacuum furnace brazing temperatures are determined by the braze filler metal being used and the base metals involved. You should refer to the appropriate material specification for your industry for the applicable variables.
See lessWhat is the difference between freeze protection and burst protection in a water cooling system?
Freeze Protection requires a glycol concentration level sufficient to prevent the formation of ice crystals at the lowest temperature experienced by the fluid. Freeze protection is imperative when the system requires pumping. Slush is formed when you get colder than its freeze protection rating. BurRead more
Freeze Protection requires a glycol concentration level sufficient to prevent the formation of ice crystals at the lowest temperature experienced by the fluid. Freeze protection is imperative when the system requires pumping. Slush is formed when you get colder than its freeze protection rating.
Burst Protection only requires a glycol concentration high enough (generally 30% by volume or more) to prevent bursting and other mechanical damage from freezing, but not necessarily high enough to keep the fluid pumpable. Burst protection requires less glycol than freeze protection and is suitable for chilled water systems that are dormant in the winter. As the temperature drops below the freezing point of the fluid in a system with burst protection, ice crystals begin to form, and the solution becomes a slush. The fluid expands as ice is formed. This mixture may or may not be pumpable, but it is fluid enough so that the excess volume flows into an expansion tank without damage to the system. As the temperature drops further and all the water freezes, the glycol will begin to freeze and contract.
Source: Dry Coolers
See lessWhat type of water treatment do you recommend for an open-loop water cooling system?
Because evaporative towers scrub the air that passes through them, they are prone to collecting debris from the air. This debris can accumulate and cause flow restrictions as well as aggravate corrosion. After the water evaporates, dissolved minerals are left behind and accumulate rapidly until theRead more
Because evaporative towers scrub the air that passes through them, they are prone to collecting debris from the air. This debris can accumulate and cause flow restrictions as well as aggravate corrosion. After the water evaporates, dissolved minerals are left behind and accumulate rapidly until the mineral come out of solution (known as scale).
For these reasons, a properly engineered and administered water treatment program must be employed continuously with the cooling tower. In an open tower cooling system, the water quality must be regularly monitored and treated to control the following conditions:
• Limescale and other water mineral deposits
• Corrosion of all types
• Micro-biological growth, such as algae, bacteria, fungus, and molds
• Suspended solids accumulations, such as airborne dirt and debris that is washed into the cooling tower water
Dry Coolers recommends consulting a local water treatment supplier (Calgon, Nalco, Culligan, etc.) that is familiar with your local water quality to monitor your treatment program.
Source: Dry Coolers
See less