VAC Burlington, Ontario, November 18, 2014 - VAC AERO has recently shipped four complete replacement hot zones for various sized furnaces to be delivered to a North American 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.
We continue our discussion on the maintenance of vacuum furnaces. Part One talked about establishing a sound maintenance strategy and once this has been determined, the real maintenance work can begin. Let’s talk about the specifics on what, when, how and why we maintain certain critical components on our vacuum furnaces. Vacuum furnaces come in all shapes and sizes and have many common features and operational/maintenance needs. However, it is important to understand the particular needs of the vacuum furnaces in your shop to have an effective maintenance program. When performing maintenance it is important to have a written plan defining the specific task to be performed, and the reason why a particular task is necessary. A work order should be issued and the work signed off upon completion (which includes testing to ensure that the repair was successful).
There are many vacuum-brazing shops out there that still believe it is necessary to try to use the strongest vacuum possible for brazing if they expect to get good results. Such thinking is erroneous, and has led many shops to actually see “worse” results (increased void content of joints, increased discoloration on furnace walls, etc.) than they would have seen if they had merely used a “weaker” (less strong) vacuum. Many people today still like to use some of the older vacuum terminology, such as "soft vacuum", "rough vacuum", "hard vacuum", etc., and some of those same people still believe that a “very hard vacuum” is always necessary for effective brazing.
Grain size can be measured after detecting the grains, and removing twin boundaries in face-centered cubic (FCC) metals, using electron backscattered diffraction (EBSD) with the SEM. For metals with annealing twins, or where it is difficult to reveal by etching a high percentage of the grain boundaries, EBSD provides advantages over the traditional light optical microscopy (LOM) approach described in ASTM E 112. Specimen preparation for EBSD must remove all damage from the preparation process and leave the surface very flat. Specimens are studied as-polished, not etched. One or more representative fields are scanned, pixel by pixel, developing a diffraction pattern at each pixel position.
This article is written for vacuum pumps such as the oil sealed rotary piston pumps used on many heat treating and vacuum furnace applications. The same information would also apply to the oil diffusion holding pump if it is used. This pump may be either a vee belt driven pump or a direct drive pump. The holding pump is used to keep the oil diffusion pump evacuated below the critical backing pressure when the main pump is in roughing mode. All mechanical vacuum pumps need maintenance and the pump manufacturer usually lists the basic checks needed in the pump operation manual. This will vary with the application that the pump is used on but, at a minimum, will include the following: check oil level daily or weekly, depending on the application and use, change oil and check the shaft seal area for leaks every 6 months and inspect the exhaust valves and gas ballast valve seals every 12 months.
VAC AERO offers complete turnkey services, including planning, designing, building and installation of vacuum furnace systems and controls. VAC AERO’s experience, proven through decades of service in commercial heat treating, has provided us with valuable insight into the changing needs and rigorous demands of our furnace customers. As a result, VAC AERO has developed a keen understanding of the design and performance of vacuum furnace systems built to meet the most stringent requirements for reliability. VAC AERO’s vacuum furnace design innovations are thoroughly tested in our own heat treating facilities before being offered to our customers. That means better quality, reliability and efficiency to maximize uptime and productivity. Horizontal vacuum models provide great flexibility for general heat treating and brazing applications and Vertical bottom-loading models are ideal for processing large circular and/or long parts.