Plastic vented screws are often used in vacuum systems. They either have a hole drilled through their axis or along the side of the screw. This hole allows the evacuation of trapped pockets of air and surface contaminates from blind-tapped holes. A bind-tapped hole is one that is drilled to a specified depth without breaking through the other side of the work piece.
Vacuum Systems in HV, and UHV
Vented screws allow for faster and more efficient pump-down of High Vacuum (HV), and Ultra High Vacuum (UHV). Many vented screws used in the construction of a vacuum system are made of metals. Plastics are usually avoided because they out gas and may have a tendency to absorb water. A plastic may out gas unpolymerized monomers, plasticizers, stabilizers and other additives while a metal will not. But plastic vented screws may be desirable for a variety of reasons. For example where thermal insulation is required. High performance plastic versions such as PEEK, and Vespel® may be options as they are not hydroscopic and are low out gasing. However, they are relatively expensive.
Vented screws are used in the assembly of a vacuum chamber. A virtual leak refers to a trapped volume of a gas within a vacuum chamber. This trapped gas can be found in the tiny voids between the screw threads and between the screw end and the bottom of a blind-hole. These voids occur during assembly at atmosphere and include air, particulate and other forms of contaminates. Therefore, the volume of these will become significant during the pump down process in the vacuum chamber. Over time these contaminants will work their way around the screw threads causing a virtual leak. Vented screws are used to allow them to escape.
A vacuum chamber is a rigid enclosure from which all gases and contaminates are pumped out resulting in a vacuum. Vacuum chambers are used in:
Scientific research such as surface science experiments that require a chemically clean sample surface. Analytic techniques such as x-ray spectroscopy, secondary ion mass spectrometry, thermal desorption spectroscopy and many others require vacuum systems to reduce surface contamination.
Space exploration to simulate the conditions of outer space to test devices that must perform in that environment. A thermal vacuum chamber is used for recreating the conditions spacecraft and instruments will experience in space. The largest largest vacuum chamber is NASA’s Space Power Facility.
Particle accelerators. The Large Hadron Collider in under the France-Swiss border. It has three Ultra High Vacuum systems and is the largest machine in the world.
Gravitation wave detectors use vacuum systems to eliminate temperature fluctuations and sound waves that might jostle a device too much to sense gravitational waves.
Vacuum chambers can also be used to test for leaks in packaging and also to remove gases from compounds entrapped when the compounds were mixed.
Vacuum drying is a method by which water and other liquids that may have accumulated on a product during manufacturing is used with heat to dry it.