Burlington, Ontario, August 17, 2015 - A new column, written by vacuum heat treating expert Dan Herring “The Heat Treat Doctor”® in collaboration with Edwards Vacuum will be published monthly and offer helpful tips and techniques on vacuum pumping systems to a worldwide audience of individuals using all types of vacuum equipment. The first article will appear in the September 15th “What’s Hot!”. This Vac-Aero exclusive publication launched back in September 2007 and contains hundreds of archived articles can now be found in the “Resources” section of the VAC AERO website where anyone can sign up for the monthly newsletter. Keeping pace with the development of new vacuum processing technologies is the reason VAC AERO takes pride in its continued support of the metal treating community by helping to promote, collaborate and assist others in their search for solutions on important issues in the practice and application of vacuum processing.
Vacuum deposition is a generic term used to describe a type of surface engineering treatment used to deposit layers of material onto a substrate. The types of coatings include metals (e.g., cadmium, chromium, copper, nickel, titanium) and nonmetals (e.g., ceramic matrix composites of carbon/carbon, carbon/silicon carbide, etc.), deposited in thin layers (i.e. atom by atom or molecule by molecule) on the surface. Vapor deposition technologies include processes that put materials into a vapor state via condensation, chemical reaction, or conversion. When the vapor phase is produced by condensation from a liquid or solid source, the process is called physical vapor deposition (PVD). When produced from a chemical reaction, the process is known as chemical vapor deposition (CVD).
All brazed joints should be inspected after brazing to verify that the parts being brazed will be acceptable to the end-use customer. If the brazed-assemblies are complex, then 100% of the assemblies should be inspected to verify that the parts have been brazed properly and will meet end-use requirements. This may include visual inspection of the exterior of all surfaces that have been brazed, and it may also involve one or more non-destructive testing (NDT) procedures to verify that each assembly will properly handle the end-use service conditions to which it will be subjected, such as fluid pressure, thermal cycling, or mechanical shock. Sometimes some destructive testing (DT) procedures are mandated, via an appropriate sampling plan, in order to physically examine the internal structure of some of the brazed joints. Is there any danger in using the examination of the cross-sectional microstructure of a brazed joint as an accept/reject criterion for the brazed tubular assembly? Yes, there is! Let’s see why...
The control chart data analysis approach is an ideal method to evaluate the quality of test data using a specific tester, such as a microindentation hardness tester, over a period of usage time. The method described in ASTM E2554 was used for this work. This analysis is done by plotting a means and a standard deviation control chart of the weekly/periodic verification data obtained with certified hardness test blocks at a specific test force and a specific hardness level. The method is illustrated using a Knoop hardness test block certified at a test force of 500 gf and with a long diagonal length of 116.18 µm (527.1 HK). From this data, one can easily calculate the uncertainty of the measurements. The Control Chart method described in ASTM E2554, and discussed by Neil Ullman, is an ideal procedure for evaluating the performance of hardness testers as it will detect any abnormalities that may occur with usage time.
In many vacuum systems, especially those where the chamber is large, has a large internal surface area and the chamber load adds extra surface area, the pump down can be slowed substantially when the chamber pressure drops to the range where the water vapor molecules on the surface desorb and have to be pumped away. Pressure and temperature determine when this vapor desorbs, but at ambient temperature around seventy two degrees Fahrenheit or twenty degrees Centigrade the vapor desorbs from about 50 Torr down to about 0.1 Torr. The vapor pressure of water at ambient temperature is about 18 Torr, so that is where maximum desorption may occur. Oil sealed rotary vane pumps and rotary piston pumps have a fairly constant pump speed from atmospheric pressure down to a pressure of about 10 Torr.
Constructed of the finest materials and craftsmanship, VAC AERO’s high performance vacuum furnaces are operator friendly and designed to minimize maintenance and downtime to deliver outstanding quality and value to commercial and in-house heat treaters alike. VAC AERO’s vacuum furnaces are designed for rapid heating rates to very uniform temperatures at high vacuum levels and can be customized to suit unique applications such as high pressure gas quenching, high temperature heat treating, ultra-clean processing and more. VAC AERO’s high efficiency hot zones are designed for easy maintenance and reduced energy consumption. Our external quench system allows for easy maintenance of the heat exchanger and quench motor. A high efficiency blower and motor combine fast cycle times and quenching speeds to provide uniform gas distribution and superior cooling performance from processing temperatures at pressures of up to 10 bar.