A specific concern to a vacuum furnace user is processing critical work during summer months with high temperatures and high humidity. This same concern could also be a problem on rainy winter months. Under these difficult conditions, it is most important to understand the impact that humid conditions can have on the final surface condition and appearance of the processed parts. Work discolored or oxidized by residual water vapor is unacceptable and must be controlled for many critical components like aerospace parts or medical implants and instruments. This paper will try to explain factors relating to humidity, air temperature, and methods to improve final product appearance and minimize possibility of contamination.
Proportional-Integral-Derivative (PID) control is the most common control type algorithm used and accepted in the furnace industry. These popular controllers are used because of their robust performance in a wide range of operating conditions and because of their simplicity of function once understood by the processing operator. The purpose of this paper is to further define and thoroughly explain the basics of the PID controller. It should be noted that many current instruments incorporate what is called an “Autotune” feature which can automatically set the PID variables for a given temperature setting allowing the operator to bypass much of the initial manual requirements. However, Autotuning was not introduced until the late 1980’s and there still exists many instruments in use which do not have this tuning feature and must still be manually set-up. Also, Autotuning often requires additional tuning or tweaking to reach final acceptable results. By understanding fully the basics of the PID functions as described below, it is hoped that any final adjustments or tuning will be simplified. Further discussion of the Autotune feature follows below. As the name suggests, the PID algorithm consists of three basic components: proportional, integral and derivative which are varied to get optimal response. If we were to observe the temperature of the furnace during a heating cycle it would be rare to find the temperature reading to be exactly at set point temperature. The temperature would vary above and below the set point most of the time. What we are concerned about is the rate and amount of variation. This is where PID is applied.
Since the early development of the vacuum furnace, engineers and thermal experts have continually tried to improve the insulating characteristics of the furnace hot zone. Several materials have been used for different applications with varying success. However, all designs must still deal with the heat losses penetrating through the insulation materials and the need to minimize these losses. This is especially important today with the continual escalation of electrical power cost. This paper will review the different types of hot zone insulation materials used, the projected losses of the different designs, the impact relating to furnace cycle heating rates and cycle times, and the projected cost advantages of one design over another.
A Temperature Uniformity Survey ( TUS ) for a vacuum furnace to satisfy AMS 2750D must be performed using established procedures and methods that fully meet the requirements of the specification and allows for consistent and more accurate results of actual furnace capabilities. Solar Atmospheres and Solar Manufacturing, with their extensive vacuum furnace experience and processing knowledge, have combined to create a standard procedure for TUS for all newly manufactured and current in-production vacuum furnaces. This procedure considers the many critical aspects of AMS 2750D that must be fully satisfied to produce acceptable processing results and the following outline could be applied to any vacuum furnace user to satisfy their TUS requirements.
This work is an update of the original reference compilation by Charles F. Burns, Jr., Copyright 1997. The current booklet contains revisions to the original work as well as numerous additions. This booklet should serve as a handy reference for people that work in the metals industry.
Electrochemical capacitors, also called supercapacitors, store energy in two closely spaced layers with opposing charges, and are used to power hybrid electric vehicles, portable electronic equipment and other devices. By offering fast charging and discharging rates, and the ability to sustain millions of cycles2–5, electrochemical capacitors bridge the gap between batteries, which offer high energy densities but are slow, and conventional electrolytic capacitors, which are fast but have low energy densities. Here, we demonstrate microsupercapacitors with powers per volume that are comparable to electrolytic capacitors, capacitances that are four orders of magnitude higher, and energies per volume that are an order of magnitude higher. We also measured discharge rates of up to 200 V s21, which is three orders of magnitude higher than conventional supercapacitors. The microsupercapacitors are produced by the electrophoretic deposition of a several-micrometre-thick layer of nanostructured carbon onions6,7 with diameters of 6–7 nm. Integration of these nanoparticles in a microdevice with a high surface-to-volume ratio, without the use of organic binders and polymer separators, improves performance because of the ease with which ions can access the active material. Increasing the energy density and discharge rates of supercapacitors will enable them to compete with batteries and conventional electrolytic capacitors in a number of applications.
Aeronautical engineers are consistently searching for new and optimal materials to achieve specific applications throughout an airframe. There are a multitude of considerations affecting the structural design of an aircraft such as the complexity of the load distribution through a redundant structure, the large number of intricate systems required in an airplane and the operating environment of that airframe. All of the above criteria is governed primarily by weight savings. Thus, the optimal materials selected today and for the future of airframes are composite material and titanium.
Solar Atmospheres has established a method of controlling the amount and depth of White layer resulting from Gas Nitriding. This procedure was accomplished following extensive testing using AISI 4140 Steel in a Solar Atmospheres Gas Nitriding Vacuum furnace. Various applications requiring Nitriding often require specific White layer limits which can now be provided by this process. Following an initial rapid pump down to produce an Oxygen free, vacuum environment, the Nitriding cycle consisted of a pre-heat at a partial pressure of Nitrogen followed by Nitriding at a slightly positive pressure using an Ammonia/Nitrogen mixture. Many cycles were performed varying the time and gas flow parameters at temperature and the resulting White layer composition and thickness determined. The key to controlling the White layer formation was the introduction of a Boost-Diffusion technique during the Nitriding phase. Surface hardness and depth of nitride zone were then recorded from microhardness measurements and metallography. All this data was compiled to establish Nitriding procedures that provide the final desired structure in the minimum cycle time. This includes processes that produce the minimum depth or complete absence of White layer as dictated by the final application of the parts.
Results of study of steel carburized at low pressure using a vacuum furnace show no evidence of hydrogen embrittlement, which should relieve any concern of the possibility of such an occurrence in low pressure gas carburizing.