Oil sealed rotary vane pumps (aka rotary vane pumps) are the primary pumps on most vacuum systems used in the heat treatment industry. They are also referred to as a “backing” pump when used in combination with a booster pump, or with both a booster and secondary (“high vacuum”) pump, typically a diffusion style. A rotary vane pump can also be used alone when high vacuum is not required and slower pumpdown is acceptable.

Two-stage designs are available, which utilize two rotors in series internal to the pump. Single-stage designs can provide a vacuum of 3 x 10^-2 Torr (4 x 10^-2 mbar), while two-stage designs can achieve 3 x 10^-3 Torr (4 x 10^-3 mbar). Due to the prevalence of rotary vane pumps, it is important for designers and users of industrial vacuum equipment to have a good understanding of how these pumps function. This series of articles will cover pump principles of operation, pump designs, pump oils, single-stage versus two-stage pump designs, contamination and gas ballast (manual and automatic), common accessories, applications, troubleshooting and pump maintenance. By Dan Herring

Don’t Blame the Braze because Joint was Poorly Designed, and NO, larger fillets won’t compensate for that!.

Have you ever heard someone tell you something like this: “Well, brazing may be okay, but if you really want a strong joint, you should weld it!” Such comments are often made when someone sees what appears to be a cracked brazed-joint, such as that shown in Figure 1, and they then assume that (1) the crack they are looking at probably extends all the way through the brazed-joint, and that (2) if the joint had been welded it would not have cracked. by Dan Kay

Burlington, Ontario, January 18, 2016 – VAC AERO has recently shipped two complete replacement hot zones for two furnaces to be delivered to a Canadian manufacturer. The hot zones feature unitized construction for easy removal and maintenance. The lightweight design’s low thermal mass enables faster quenching and longer life. The heat shield package consists of three layers of half inch thick graphite felt and an inner reflective layer of graphoil bonded carbon composite that provides added protection and enhanced reflectivity. The graphite felt does not shrink which minimizes heat leakage and contributes to stable uniformity throughout its useful life. The heat shield package is supported by a 14 ga. stainless steel assembly that uniformly distributes the quenching gas to the workload. Some ongoing improvements on VAC AERO’s hot zones include improved durability, thermal efficiency and extended hot zone life.

When problems arise, especially those related to safety, we want to know that we have isolated the root cause and instituted corrective action measures so as to avoid their reoccurrence. 

Worker safety and the safe operation of heat-treat equipment is both MANDATORY and NON-NEGOTIABLE, especially when operating and maintaining vacuum equipment where dangers of asphyxiation, electrocution and explosion are as real as they are with any other type of thermal processing equipment. “It won’t happen to me” is not a phrase that belongs in the heat-treat shop and provides a false sense of security to all involved. There is no substitute for understanding the inherent dangers, taking the necessary steps and placing the right safeguards in place to prevent accidents from happening. Safety and safety issues are a serious matter and should be treated as such by all individuals within the company. By Dan Herring 

A number of companies I’ve visited who conduct vacuum brazing operations have asked for assistance in understanding how to properly use a torch-brazing (flame braze) process to repair some of the assemblies that did not fully braze during their vacuum brazing operations.

The components were such that they did not want to send the entire assembly back through the vacuum brazing furnace, but merely needed to fix a small portion of the assembly where it did not fully braze. So let’s take a brief look at torch-brazing to see what it is, and how it can be used by brazing shops today to meet some of their production-repair needs. by Dan Kay

Steels used for tools and dies differ from most other steels in several aspects. First, they are used in the manufacture of other products by a variety of forming processes. Second, tools and dies are generally used at a higher hardness than most other steel products; 58 to 68 Rockwell C is a typical range. Dies for plastic molding or hot working are usually used a at lower hardness, typically from 30 to 55 Rockwell C.

These high hardness values are required to resist anticipated service stresses and to provide wear resistance. However, the steels must also be tough enough to accommodate service stresses and strains without cracking. Premature failure caused by cracking must be avoided, or at least minimized, to maintain minimum manufacturing costs. Unexpected tool and die failure can shut down a manufacturing line and disrupt production scheduling. Tools and dies must also be produced with the proper size and shape after hardening so that excessive finishing work is not required. Heat-treatment distortion must be controlled, and surface chemistries must not be altered. Because of the careful balance that must be maintained in heat treatment, control of the heat-treatment process is one of the most critical steps in producing successful tools and dies. In addition to controlling the heat-treatment process, tool and die design and steel selection are integral factors in achieving tool and die integrity. By George Vander Voort 

When operating vacuum furnaces, situations may arise in which the hot zone and/or cold walls may become contaminated (Fig. Nos. 1 – 2). This can occur from a variety of sources: air leaks, outgassing from residues left on the parts as a result of the manufacturing or cleaning processes, vaporization of sensitive materials (e.g., chromium bearing materials), process induced contaminations such as carbon in the form of soot or tar, fluxes from brazing pastes, excess braze alloy as well as many other sources. Often times the work being processed is also affected (Fig. 3). The question becomes, how do we attempt to clean up our contaminated vacuum furnaces? By Dan Herring

Medical technology has developed many new devices that can be implanted into humans (in-vivo) to repair, assist or take the place of diseased or defective bones, arteries and even organs. The materials used for these devices have evolved steadily over the past fifty years with titanium and cobalt-based alloys replacing stainless steels. Metallographic examination has become an indispensable tool in the testing, quality control, failure studies and post-mortem analyses of these devices. This paper presents techniques and results for examination of titanium-based acetabular cups and Co-Cr-Mo femoral hip stems and knees. These implants have porous metallic coatings on one side to enhance bone/metal interface adhesion by in-growth of bone into the porous coatings. By George Vander Voort

People sometimes ask me to help them determine if it is better for them to purchase a vacuum furnace or a continuous-belt furnace for their particular brazing needs. This important decision (for any brazing company) should not be a difficult question for them to answer for themselves, and involves understanding primarily three (3) key factors about their production: what is the quantity of brazed components that they need to produce, what is the sensitivity to oxygen of any of those base metals that they are planning to braze, and thirdly, do any of those base metals contain elements that will easily and readily outgas when heated. by Dan Kay