Vacuum Applications and Processes

Product Testing and Lab Applications -
Vacuum chambers and components are specialized vessels that can maintain a high vacuum process environment. Depending upon their configuration and optional components or features, they can be used for a wide variety of product testing and lab applications in which a product or material is stressed and analyzed under specific atmospheric or environmental conditions.

Vacuum chambers, when combined with a variety or optional accessories, can be used for a wide variety of product tests in which atmospheric or environmental conditions must be simulated.

The following is a listing of examples of the variables that can be controlled and measured using Abbess Vacuum Chambers.

What can you control in a Vacuum Chamber?

- Pressure
- Temperature
- Humidity
- Atmosphere/ Altitude or pressure
- Electromagnetic Radiation
- Microwave Radiation

What Product features can you measure in a Vacuum Chamber?

• Leakage
  - Rigid Packaging
  - Flexible Packaging
  - Packages with threaded or lug-style closures
  - Packages with mechanical dispensing systems
  - Filtration membranes/Reverse Osmosis devices
  
  
• Product integrity
  - Flexible material seams
  - Effects of altitude on packaging
  - Gaskets
  - Bond Strength
  - Corrosion
  - Contamination
  
  
• Hermeticity
  
  
• Porosity
  
  
• Permeability.
  - Liquid permeability
  - Gas permeability
  - Difusion permeability
  - Water vapor permeability
  - Liquid permeability
  
  
• Absorption/Saturation Capacity
  
  
• Gettering Rates.
  
  
• Specific Gravity
  
  
• Vapor Pressure
  
  
• Density
  
  
• Deposition Rate/Film Thickness
  
  
• Specific Gravity
  
  
• Vapor Pressure
  
  
• Density
  
  
• Deposition Rate/Film Thickness
  
  
• Instrument Calibration
  - Helium Leak detectors
  - Thermocouples
  
  
• Volatility
  - Total Mass Loss
  - Collected Volatile Condensable Materials
  - Total Mass Flux
  
  
• Emissions
  - Acoustic
  - Gaseous
  - Electromagnetic EMI
  
  

Altitude vs. Pressure, Temperature and Density see datasheet

see ABBESS chambers Acrylic, Round, Cube, Systems, Cart mounted

see ABBESS chambers Acrylic, round, cube, systems, cart mounted

Introduction

When material like those listed above are mixed, air bubbles become trapped within the mixture. If allowed to cure without removing these bubbles, defects such as hollows, cavities or nodules will be present in the finished casting. These defects may degrade the integrity of the end application immediately or may emerge after a period of use such as with electrical encapsulation whose components may fail over time.

The components of a mixture may be mixed by any appropriate means before degassing. However, for effective vacuum degassing to be performed, the mixture must be fluid i.e. able to be poured. The mixture can then be placed into the vacuum chamber, which will reduce the air pressure such that gas bubbles (i.e. air) which were initially formed at atmospheric pressure will expand and escape from the liquid’s surface. This released gas will then be pumped out of the vacuum chamber.

Deaeration of RTV Silicone Rubber Curing Agents

Air entrapped during mixing should be removed to eliminate voids in the cured product. Expose the mixed material to a vacuum of at least 22mm (29 in.) of mercury. The material will expand, crest and recede to about the original level as the bubbles break. Degassing is usually complete about two minutes after frothing ceases. When using RTV silicone rubber for potting, a step ( vacuum filling using a fill under vacuum option) may be necessary after pouring to avoid capturing air in complex assemblies. For vacuum chamber options call Abbess Instruments.
Automatic equipment designed to meter, mix, deaerate and dispense two-component RTV silicone rubber compounds will add convenience to continuous or large operations.

Vacuum Distillation

Vacuum Fumigation - Used to eliminate insects, rodents, funguses and molds from various materials such as food, books, art work, etc. Objects are placed into a vacuum chamber. Then, toxic gazes are injected inside the chamber to eliminate any king of life at the surface as well as inside the objects. That gas is then drawn up and neutralized. After that, the objects are ventilated in order to remove any residual gas particles. This chamber should also be equipped with fans or recirculating systems, to ensure even distribution of the fumigant.

The vacuum denies the insect oxygen and facilitates rapid penetration of the commodity by the fumigant. As a result, a vacuum fumigation treatment time may be reduced by as much as 75% as compared to fumigations at atmospheric pressure. Vacuum fumigation is used largely in plant quarantine work and for fumigating materials that are difficult to penetrate at atmospheric pressure. It is also used in some food manufacturing industries for the fumigation of packaged cereals and prepared foods. The procedure cannot be used with tender plants or produce, such as fresh fruits and vegetables, that are unable to withstand reduced pressures. Advantages of vacuum fumigation include not only reduced exposure period and increased penetration by the fumigant, but also many of the previously mentioned advantages associated with the use of a fumigation chamber.

Methods
The two main methods of vacuum fumigation are sustained-vacuum and restored-pressure. The method used is determined by the commodity. The sustained-vacuum method is used for seeds, grains, tobacco, and dry plant products, whereas commodities that cannot withstand prolonged exposure to reduced pressures are treated using the restored-pressure method.

With the sustained-vacuum method, the pressure in the loaded chamber is reduced and the fumigant introduced. The reduced pressure is maintained until the fumigation period ends, at which time atmospheric pressure is restored by allowing air to enter the chamber. The fumigant-air mixture is pumped out, and the cycle of air introduction and evacuation repeated (a process known as "air-washing") until it is safe to open the chamber door.
The actual pressure used, the length of the fumigation period, and the fumigant dose can be adjusted to fit specific needs. For example, some commodities can withstand lower pressures than others.

The restored-pressure method differs from the sustained-vacuum method in that the reduced pressure is not maintained throughout the fumigation period. Instead, the inside of the chamber is returned to or near atmospheric pressure in one of the following ways:

• Gradual restoration of atmospheric pressure. The required dosage of fumigant is discharged and air is then slowly introduced until a pressure just below atmospheric is reached after 2 hours in a 3-hour exposure period.
• Delayed restoration of atmospheric pressure. Following discharge of the fumigant, the vacuum is sustained for about 45 minutes before air is introduced rapidly into the chamber.
• Immediate restoration of atmospheric pressure. After the fumigant is discharged, atmospheric pressure is rapidly restored in the system by opening one or more valves leading into the chamber. This "released-" or "dissipated-vacuum" method has been used extensively for the fumigation of baled cotton
• Simultaneous introduction of air and fumigant. In this technique, special metering equipment is provided whereby the fumigant is introduced simultaneously with air so that a constant proportion of fumigant to air is maintained until the entire dosage has been introduced.
  

Once a restored-pressure fumigation is ended, the chamber is aerated by air-washing as described under the sustained-vacuum method.

See ABBESS chambers Acrylic, round, cube, systems, cart mounted

- Rigid Packaging
- Flexible Packaging
- Packages with threaded or lug-style closures
- Packages with mechanical dispensing systems
- Filtration membranes/Reverse Osmosis devices

Altitude vs. Pressure, Temperature and Density see datasheet

See ABBESS chambers Acrylic, round, cube, systems, cart mounted

- Flexible material seams
- Effects of altitude on packaging
- Gaskets
- Bond Strength
- Corrosion
- Contamination

MEASURING
Hermeticity is commonly measured by dye-penetrant, bubble-emission, pressure-decay, microbial-ingress, radioactive, and mass spectrometer systems. All of these techniques are commercially available and can be used to detect leaks. Some—like the bubble and dye methods—can pinpoint the exact location of a leak. Others only detect the summation of all the leaks present and are used in go/no-go inspections.
Regardless of the measurement system, the basic approach is the same. A pressure difference is developed between the internal volume of the package and the external environment. This pressure gradient causes gas or liquid to diffuse or leak through the bulk material or seal area. The material "leaking" through to the external environment is then sensed. In the case of radioactive, microbial, and mass spectrometer methods, the test can be both qualitative (what is leaking) and quantitative (how much is leaked). For the purpose of this article, all leak rates refer to helium rates measured at 1 atm pressure differential and 20°C and are defined as helium atoms per cubic centimeter per second (for example, 10-5 He/cm3/sec (STP)).

More thorough discussions of leak-rate measurement are provided in a number of sources and will not be covered here. However, a few key points should be highlighted. The permeation of materials through the barrier is a function of the concentration of the diffusing material, its affinity for the matrix (chemical adsorption), and the physical size of the molecules. The major point is that just because a joint leaks helium at a rapid rate, the same joint may not leak water vapor because of pore size or chemical binding of the moisture in the base material. This is also true for direct leak paths, for which the path may be so tortuous and small in diameter that the leaking molecule may not physically fit. In another case, the pressure drop across the leak path may be so minimal that the leak becomes diffusion limited, with the added effects of absorption of the material to the walls of the leak channel. In these cases, the package may actually be "hermetic" according to the needs of the client, even though a leakage path exists.

Leak Site Identification
Helium spray sniff testing is a technique that can be utilized to isolate hermetic leaks on open cavity packages as well as packages subjected. Typically, a helium spray creates a small envelope of helium in the proximity of a leak site region would be measured and recorded.

Fluorescent Dye Impregnation
Fluorescent dye impregnation is utilized to identify leak site regions and characterize the physical attributes of the ingress pathways to improve package sealing processes. This technique also eliminates the problem of misinterpretation when cross-sectioning fragile materials.

Fine Leak
Devices are typically preconditioned in a helium pressurized chamber and, after the required conditions are met, the helium leak rate is measured and recorded, applying pass/fail criteria. Devices sealed with helium need not be pressurized if requested.

Expanded Fine Leak for Other Gases and Compounds
Specialized leak testing is available for determining leak rates for gases other than helium. Leak rates of various gases (i.e. Argon, CO2, Acetic Acid, Ethylene Glycol, etc.) may be measured at low leak rates utilizing a specialized mass spectrometer tuned for the particular substance of interest. Applicable standards are normally available in a wide range of leak rates.

Gross Leak
A device with a gross leak could theoretically pass the fine leak test. Therefore, this test is typically performed after fine leak. Depending on the requirement of the specification being followed, gross leak may be performed by two different methods.

1. The device is submerged in an indicator fluid tank at a specified high temperature of 125° C, and observed for evidence of bubble stream emanating from a gross leak site. A lower temperature may be used depending on device material constraints.

2. The test may require preconditioning in a pressurized chamber filled with an inert detector fluid that characteristically has a low boiling point. After preconditioning, the devices are submerged in an inert indicator fluid with a higher boiling point. In theory, any detector fluid located within the internal cavity of the package would boil when exposed to the high temperature of the indicator fluid, thus creating a bubble stream from the gross leak site.

Definition: Porosity - The ratio of the volume of all the pores in a material to the volume of the whole.

There are several ways to estimate the porosity of a given material or mixture of materials, which is called your material matrix.

- The Volume/Density method is fast and surprisingly accurate (normally within 2% of the actual porosity). To do this method you pour your material into a beaker, cylinder or some other container of a known volume. Weigh your container so you know its empty weight, then pour your material into the container. Tap the side of the container until it has finished settling and measure the volume in the container. Then weigh your container full of this material, so you can subtract the weight of the container to know just the weight of just your material. So now you have both the volume and the weight of the material. The weight of your material divided by the density of your material gives you the volume that your material takes up, minus the pore volume. (The assumed density of most rocks, sand, glass, etc. is assumed to be 2.65g/cc. If you have a different material, you may look up its density) So, the pore volume is simply equal to the total volume minus the mateial volume, or more directly (pore volume) = (total volume) - (material volume).

- Water Saturation Method is slightly harder to do, but it more accurate and more direct. Again, take a known volume of your material and also a known volume of water. (Make sure the beaker or container is large enough to hold your material as well.) Slowly dump your material into the water and let it saturate as you pour it in. Then seal the beaker (with a piece of parafilm tape or if you don't have parafilm tape a plastic bag tied around the beaker will do.) and let it sit for a few hours to insure the material is fully saturated. Then remove the unsaturated water from the top of the beaker and measure its volume. The total volume of the water originally in the beaker minus the amount of water not saturated is the volume of the pore space, or again more directly (pore volume) = (total volume of water) - (unsaturated water).

- Water Evaporation Method is the hardest to do, but is also the most accurate. Take a fully saturated, known volume of your material with no excess water on top. Weigh your container with the material and water and then place your container into a heater and/or vacuum chamber to dry it out. Once dry, weigh your sample. Since the density of water is 1 g/cc, the difference of the weights of the saturated versus the dried sample is equal to the volume of the water removed from the sample (assuming you are measuring in grams), which is exactly the pore volume. So once again, (pore volume in cubic centemeters) = (weight of saturated sample in grams) - (weight of dried sample in grams).

- Liquid permeability
- Gas permeability
- Difusion permeability
- Water vapor permeability
- Liquid permeability

Definition: Absorprtion - absorption of particles of gas or liquid into liquid or solid materials.

- Helium Leak detectors
- Thermocouples

- Acoustic
- Gaseous
- Electromagnetic EM