Archives for July 2017

The demands on space simulation chambers from the extremes of temperature and vacuum were discussed in Part One along with the development of space simulation chambers (aka space simulators) for testing of components used on vehicles for space travel such as sensors, landers and ion thrusters (Fig. 1) under the same conditions they will encounter during deployment in space. We continue this discussion by exploring the vacuum systems used to make these chambers function properly.

There is a wide range of commercially available space chambers, from small 460 mm diameter x 610 mm long (18” diameter x 24” long) units, to field-erected systems large enough to enclose a satellite, rocket section or space telescope. These large units can be 15.2 m (50 ft.) or more in diameter.

Finding leaks in vacuum furnaces is a task that few of us cherish but all of us know is important and necessary. Leaks are a problem experienced by almost every vacuum user. Leaks can occur suddenly or develop slowly over time but in either case, they are damaging both to product quality and to furnace internal components. In extreme cases, the problem is obvious: the furnace will not pump down and/or the hot zone (or heating elements) shows obvious signs of attack. Tiny leaks, however, are more common often going undetected because of the pumping systems ability to overcome them. However, even small leaks can cause continuous and sometimes catastrophic damage. Thus, routine leak checking and leak repair should be a part of any good vacuum furnace maintenance program.

Like any job, leak detection can be made easier by having the right tools, looking in the right places, having patience and using a great deal of common sense. Leaks can be inherent in the materials of construction, created during the manufacturing process, be introduced during maintenance or repair, or occur over time due to corrosion, wear, fatigue or stress. The question is: “Can the system tolerate the leak?” In other words, can the process and equipment survive the consequences of the leak? The answer is almost always, “No.”

The most obvious place to look for a leak is in and around the last place that was repaired or serviced. Begin by asking the question, “What was the last area worked on or modified? ” (e.g. thermocouples, power feedthroughs, door “O” rings, etc.). It is incredible how many leaks are found and corrected by simply asking questions before one begins leak detection in earnest.