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Asked: October 10, 2023In:
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What is back streaming and back migration in vacuum technology?

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    Back streaming and back migration are two phenomena that can occur in vacuum technology. Back Streaming: Back streaming refers to the movement of gas molecules from the high-pressure side of a vacuum system to the low-pressure side. This can happen when there is a pressure difference between two regRead more

    Back streaming and back migration are two phenomena that can occur in vacuum technology.

    Back Streaming:

    Back streaming refers to the movement of gas molecules from the high-pressure side of a vacuum system to the low-pressure side. This can happen when there is a pressure difference between two regions of the system, causing gas molecules to flow in the opposite direction of the desired vacuum. Back streaming can occur through leaks, permeation through materials, or through the pumping system itself. It can lead to contamination of the vacuum environment and a decrease in the overall vacuum level.

    Back Migration:

    Back migration, also known as back diffusion, is the migration of gas molecules from the pump exhaust back into the vacuum chamber. This can happen when the pressure in the pump exhaust is higher than the pressure in the vacuum chamber. Back migration can occur due to the design of the pumping system, improper sealing, or inadequate pumping speed. It can result in the reintroduction of contaminants or unwanted gases into the vacuum chamber, affecting the quality of the vacuum.

    Both back streaming and back migration are undesirable in vacuum technology as they can compromise the integrity of the vacuum environment and affect the performance of the system. Proper design, sealing, and maintenance of the vacuum system are important to minimize these phenomena and maintain a high-quality vacuum.

    Source: Vacuum Technology and Vacuum Design Handbook” by Karl Jousten

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Asked: October 6, 2023In:
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What are the consequences of back streaming and back migration in vacuum technology?

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    Back streaming and back migration in vacuum technology can have several consequences that can impact the performance and integrity of the vacuum system. Here are some of the consequences: 1. Contamination: Back streaming and back migration can introduce contaminants into the vacuum chamber. When gasRead more

    Back streaming and back migration in vacuum technology can have several consequences that can impact the performance and integrity of the vacuum system. Here are some of the consequences:

    1. Contamination: Back streaming and back migration can introduce contaminants into the vacuum chamber. When gas molecules flow in the opposite direction of the desired vacuum, they can carry particles, dust, or other contaminants from the high-pressure side or pump exhaust back into the vacuum chamber. This contamination can affect the quality and cleanliness of the vacuum environment, which is crucial in many applications such as semiconductor manufacturing or scientific research.

    2. Decreased Vacuum Level: Back streaming and back migration can lead to a decrease in the overall vacuum level. When gas molecules flow from the high-pressure side to the low-pressure side, they increase the pressure in the vacuum system. This increase in pressure can reduce the effectiveness of the vacuum pump and compromise the desired vacuum level. It may require additional pumping or maintenance to restore the desired vacuum conditions.

    3. Reduced Pumping Efficiency: Back streaming and back migration can reduce the efficiency of the vacuum pump. When gas molecules flow in the opposite direction of the pumping direction, they can interfere with the pumping process and reduce the pumping speed. This can result in longer pump-down times, decreased throughput, and overall reduced efficiency of the vacuum system.

    4. Unwanted Gas Introduction: Back migration can result in the reintroduction of unwanted gases into the vacuum chamber. If the pressure in the pump exhaust is higher than the pressure in the vacuum chamber, gases from the pump exhaust can migrate back into the vacuum chamber. These gases may be contaminants or unwanted gases that can affect the process or experiment being conducted in the vacuum environment.

    To mitigate the consequences of back streaming and back migration, proper design, sealing, and maintenance of the vacuum system are essential. This includes using appropriate materials, ensuring proper sealing of components, and selecting suitable pumping systems with adequate pumping speed and efficiency.

    Source: Vacuum Technology and Vacuum Design Handbook” by Karl Jousten.

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Asked: October 4, 2023In:
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How do temperature changes contribute to back migration in vacuum systems?

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    Temperature changes can contribute to back migration in vacuum systems by affecting the behavior of gas molecules. When the temperature inside the vacuum chamber increases, the gas molecules inside gain energy and move more rapidly. This increased energy can cause some of the gas molecules to escapeRead more

    Temperature changes can contribute to back migration in vacuum systems by affecting the behavior of gas molecules. When the temperature inside the vacuum chamber increases, the gas molecules inside gain energy and move more rapidly. This increased energy can cause some of the gas molecules to escape back into the external environment through small leaks or weak seals in the system. Similarly, when the temperature decreases, gas molecules from the external environment can enter the chamber as their energy decreases and they become more easily trapped in the vacuum system.

    The relationship between temperature and gas behavior is described by the ideal gas law, which states that the pressure of a gas is directly proportional to its temperature. As the temperature increases, the pressure inside the vacuum chamber also increases. This increase in pressure can lead to back migration as gas molecules try to equalize the pressure by escaping or entering the chamber.

    It is important to note that temperature changes alone may not cause significant back migration in a well-designed and properly sealed vacuum system. However, if there are existing leaks or weak points in the system, temperature changes can exacerbate the problem and contribute to back migration.

    To mitigate the effects of temperature changes on back migration, vacuum systems should be designed with robust seals, gaskets, and valves that can withstand temperature fluctuations. Regular maintenance and monitoring of the system are also essential to identify and address any potential sources of leaks or weak points. Additionally, techniques such as bake-out and degassing can be used to remove trapped gases from the system and minimize the potential for back migration.

    Source: https://www.lesker.com/newweb/vacuum_technology/vacuum_technology_handbook/vacuum_system_design.asp

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Asked: February 24, 2021In:
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diffusion pump oil
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    In the context of oil diffusion pumps, backstreaming is generally considered undesirable, as it can lead to contamination of the vacuum chamber and the parts within it. However, there are some inherent aspects of oil diffusion pumps that provide advantages, particularly when certain steps are takenRead more

    In the context of oil diffusion pumps, backstreaming is generally considered undesirable, as it can lead to contamination of the vacuum chamber and the parts within it. However, there are some inherent aspects of oil diffusion pumps that provide advantages, particularly when certain steps are taken to control backstreaming. Here are some benefits related to controlled or minimized backstreaming in the use of oil diffusion pumps:

    1. High Vacuum Capabilities: Oil diffusion pumps are capable of achieving very low pressures (high vacuum), often down to the 10^-7 to 10^-9 Torr range. This performance makes them ideal for applications like heat treating, thin film deposition, and coating, where ultra-high vacuum is critical for process quality. Proper backstreaming control allows for these benefits without contaminating the chamber.

    2. Low Cost and High Throughput: Compared to other high-vacuum pumps (like turbomolecular pumps), oil diffusion pumps are often more economical, both in terms of initial cost and maintenance. With backstreaming control (using baffles or cold traps), oil diffusion pumps can operate for long periods, supporting high-throughput applications without requiring frequent oil changes.

    3. Compatibility with Heavy Gas Loads: Diffusion pumps can handle higher gas loads and are relatively robust when processing residual gases. Effective backstreaming management (such as using foreline traps or cold traps) ensures that the oil stays contained, allowing the pump to work with larger loads without contaminating the chamber.

    4. Thermal and Mechanical Stability: Oil diffusion pumps have no moving parts, making them reliable with low mechanical wear. By minimizing backstreaming, you can maintain this stable, low-vibration vacuum environment, which is beneficial for sensitive applications like high-precision coating or crystal growth.

    5. Enhanced Pump Longevity with Proper Backstreaming Control: When measures like baffles, cold traps, and routine maintenance are in place, oil diffusion pumps can operate with minimal contamination and reduced backstreaming. This prolongs oil life, reduces downtime, and helps maintain the vacuum level and quality required for heat treatment and other high-vacuum processes.

    In summary, while backstreaming itself is usually a drawback, the advantages of oil diffusion pumps—such as cost-effectiveness, high vacuum levels, and stable operation—can be fully realized when backstreaming is effectively managed. By controlling it with traps, baffles, and proper maintenance, oil diffusion pumps offer a strong balance of performance and economy for high-vacuum applications.

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Asked: February 24, 2021In:
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back purgingironnitrogen
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    Back purging in a vacuum furnace with nitrogen is often done to remove any residual gases or contaminants that may have entered the furnace chamber during processing, especially after vacuum cycles or before opening the chamber to the atmosphere. In vacuum furnaces processing tool steel or high-speeRead more

    Back purging in a vacuum furnace with nitrogen is often done to remove any residual gases or contaminants that may have entered the furnace chamber during processing, especially after vacuum cycles or before opening the chamber to the atmosphere. In vacuum furnaces processing tool steel or high-speed steel, nitrogen back purging serves as a way to flush out reactive gases like oxygen that can cause oxidation, which is critical for ensuring a clean environment for subsequent loads.

    However, when iron is present, especially at high temperatures, there’s a risk of iron reacting with nitrogen to form iron nitrides. Iron nitrides can alter the properties of steel, potentially affecting hardness, brittleness, or machinability. Here’s how back purging works in this context:

    1. Cool-Down Phase: Nitrogen is often introduced after the furnace has cooled to a point where the risk of forming nitrides is minimized (usually below 400–500 °C). At lower temperatures, nitrogen is inert and will not react with iron.

    2. Controlled Purge Cycles: Multiple cycles of nitrogen purging may be used to ensure all oxygen is removed from the chamber. Since nitrogen is relatively inexpensive, purging until reaching a safe oxygen level is feasible.

    3. Inert Gas Usage Consideration: For higher-temperature applications or highly sensitive materials, an inert gas like argon is sometimes preferred, as it does not react with iron even at high temperatures, though it is more costly than nitrogen.

    In your case, where tool steels and high-speed steels are processed, nitrogen is typically safe for back purging as long as the temperature and timing are managed properly to avoid nitride formation.

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