Vacuum furnace heating elements can fail for several reasons related to material properties and operational conditions. Here are some common modes of failure:

1. Overheating: If the temperature exceeds the design limit of the heating elements, this can lead to rapid degradation and failure.

2. Electrical Overload: If the current exceeds the capacity of the heating elements, it can cause rapid heating and potentially melt or burn out the element.

3. Mechanical Damage: Accidental bumps, drops, and improper handling can cause cracks or breaks in brittle heating elements.

4. Thermal Stress: Repeated heating and cooling cycles can cause expansion and contraction of the heating element, which can lead to material fatigue and cracking over time.

5. Electromigration: At higher temperatures, atoms in the heating elements can move in response to the electric current flowing through them, leading to thinning and eventual breakage of the element.

6. Chemical Degradation: Even in a vacuum, elements can react with residual gases or impurities, which can lead to corrosion or the formation of brittle compounds on the element surfaces.

7. Evaporation: Elements like tungsten can slowly evaporate at high temperatures, which can thin the element and eventually cause it to fail.

8. Creep: At high temperatures, materials can slowly deform under mechanical stress, leading to sagging or distortion of the heating element shape, potentially causing short circuits or mechanical failure.

9. Contamination: The introduction of foreign materials can lead to hot spots, which can cause localized overheating and failure.

10. Design Flaws: If the heating elements are not properly designed for the specific application, including shape, size, or material choice, they can fail prematurely due to inadequate heat distribution or inability to withstand the thermal environment.

To prevent these failures, it’s important to maintain a clean vacuum environment, use materials that are appropriate for the operational temperature and atmosphere, ensure a proper design that accounts for thermal expansion, and avoid rapid temperature changes that can induce thermal stress. Regular maintenance and inspection can also help identify early signs of wear or failure in heating elements.

Sizing a vacuum booster pump for a vacuum chamber involves considering several key parameters and considerations to ensure that the pump can meet the vacuum requirements of the chamber. The size and capacity of the booster pump you need will depend on the specific characteristics of your vacuum system, including the chamber size, desired vacuum level, and the rate at which you need to evacuate the chamber.

Here’s a general guideline to help you size a vacuum booster pump:

1. Volume of the Vacuum Chamber:

• Know the volume of your vacuum chamber. The larger the volume, the larger the pumping speed required to achieve the desired vacuum in a given amount of time.

2. Desired Vacuum Level:

• Define the required vacuum level or pressure you need to achieve inside the vacuum chamber. The vacuum level is typically expressed in Torr, millibar, or Pascal.

3. Pumping Speed:

• The pumping speed of a vacuum booster pump is a critical parameter. It represents the rate at which the pump can remove gas from the chamber and is usually measured in liters per second (L/s) or cubic feet per minute (CFM).

4. Process Throughput:

• Understand the amount of gases or vapors that will be introduced into the chamber during the process. For example, in degassing or drying processes, the material may release gases as the vacuum level increases.

5. Backing (Primary) Pump Capacity:

• Choose a booster with a pumping speed that complements the backing pump. The combination of the two pumps should achieve the desired vacuum level in an efficient time frame. It’s essential to know the pumping speed and ultimate vacuum of the primary pump. The booster’s speed should be matched to the primary pump to prevent overloading or under-utilizing either pump.

6. Account for Gas Load:

• Consider the type and volume of gases that will be present in the chamber. Different gases have different pumping requirements, and you may need to adjust the pumping speed accordingly. You can refer to gas-specific pumping speed charts provided by pump manufacturers.

7. Choose the Right Booster Pump:

• Select a vacuum booster pump that can provide the calculated pumping speed. Booster pumps work in combination with primary pumps (e.g., rotary vane pumps, rotary piston pumps, or oil diffusion pumps). The booster pump enhances the pumping speed of the primary pump.
• Ensure that the booster pump is compatible with the primary pump and the gases you will be handling.

8. Cooling Requirements:

• Some booster pumps may require water cooling, while others may be air-cooled. Ensure you have the necessary facilities for the pump’s cooling and installation requirements.

9. Consider Additional Factors:

• Take into account any additional factors that may affect the performance of the vacuum system, such as tubing size, length, and the presence of valves or other components.
• Make sure the booster pump can handle the maximum pressure differential required for your application.
• A booster pump typically does not start from atmospheric pressure. Determine the pressure at which the booster pump will start. This is usually when the primary pump has brought the chamber to a specific intermediate vacuum level.
• Consider safety devices such as relief valves to prevent over-pressurization. Also, think about accessories like vacuum gauges to monitor the chamber’s pressure.

Remember that sizing a vacuum system accurately is crucial for achieving the desired vacuum level and maintaining the integrity of your vacuum chamber and the processes within it. Consulting with vacuum technology experts and pump manufacturers can help provide guidance based on your specific requirements and can provide detailed specifications, performance curves, and recommendations based on the specific requirements of your application.

Ensuring that a furnace can perform repeatable and accurate cycles is a cornerstone of AMS2750E pyrometry specifications as well as Nadcap and CQI-9 standards. The best way to measure and test any furnace is through a temperature uniformity survey (TUS).

These surveys are critically important, and when working to meet a specification or standard, it’s critical to follow the requirements of that standard.

Source: Conrad Kacsik Instrument Systems Inc.