Metal treatment – Process of modifying or maintaining internal physical... – With measuring – testing – or sensing
Reexamination Certificate
2001-05-31
2003-04-29
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With measuring, testing, or sensing
C266S099000, C374S043000
Reexamination Certificate
active
06554922
ABSTRACT:
The invention relates to a method for determining the cooling action of a flowing gas atmosphere on workpieces, especially in the hardening of workpieces of steel, by a measuring body which is provided with at least one temperature sensor and heated to workpiece temperature and is exposed to the gas atmosphere.
It is known through the “Enzyklopädie Naturwissenschaften und Technik,” 1981, Zweiburgen Verlag Weinham, Vol. E-J, key word “Hitzdraht” on page 1851, to determine the velocities of gases by blowing them against an electrically heated resistance with a temperature-related characteristic. This heated resistance has a length of about 1 nm and a thickness of a few &mgr;m and virtually no time lag. In the event of a lowering of temperature by cooling, the original temperature and the original resistance are restored by increasing the current by means of a complex control system. For the determination of quenching curves of workpieces in metallurgical processes such an extremely delicate hot wire anemometer is neither foreseen nor suitable.
For this purpose, the workpieces or workpiece batches are quenched to harden them in a quenching chamber within a given time to temperatures below the perlite, bainite and/or martensite temperatures depending on the particular workpiece. The quenching chamber is designed for pressures up to 50 bar and in some cases higher, and hydrogen, helium, nitrogen or mixtures of at least two of these gases are used preferentially as quenching gases. These gases are fed through the batch(s) and removed again by a circulation blower not represented. On their way the quenching gases are passed through a heat exchanger, not shown, and recooled.
The driving power required for the gas circulation increases with pressure but decreases with the atomic weight of the quenching gases, so that hydrogen and helium gases or mixtures thereof are to be given preference, inasmuch as also the transfer of heat to these gases is especially good and the quenching rate is increased. In this case the transfer of heat to the workpieces but also to the heat exchangers is important.
EP 0 313 888 B2 describes first heating workpieces of steel, especially low-alloy steels that are difficult to harden, and/or workpieces of large or complex shape, and then quenching and hardening them with gases from the group, helium, hydrogen and nitrogen, and by gaseous mixtures of at least two gases of this group, at pressures between 10 and 40 bar. This is intended to eliminate the classical hardening methods using water, oils and salt baths with their adverse effect on the environment. The hardening is performed by means of these gases, which are circulated by means of a blower at a high velocity within the apparatus through a heat exchanger and the workpieces or batches of workpieces. The hardening can be performed in a heated single-chamber furnace or in an attached special quenching chamber belonging to the furnace. In the said disclosure the background for the elimination of the known hardening methods is also given.
In such quenching methods the procedure has formerly been to provide parts of a stationary batch with thermocouples. When this was not possible, so-called passive alpha probes have been added to the batch, i.e., special probes provided with thermocouples without a heating device, which are heated by thermal transfer from the adjacent workpieces. The quenching of the workpieces or components was determined by the measurements obtained (offprint “Ipsen Report” of the Ipsen company, article by B. Edenhofer, “Steuerung der Hochdruckgasabschreckung mittels Wärmestromsensor” [control of high-pressure gas quenching by means of a heat flow sensor] of October 1995). In this case measurements of previously run batches are used as a guide for fresh batches.
Such methods of measurement, however, are not possible in the case of moving batches in continuously operating apparatus with so-called “cold chambers,” since the batches are passed through individual chambers of the apparatus and the individual chambers are separated from one another by pressure-tight slides. Therefore, in such apparatus the control of the quenching action is performed by monitoring “secondary factors” such as gas pressure, gas temperature, cooling water temperature, as well as the power input of the blower motors for circulating the gas. The determination of the quenching rate from these factors, however, is possible only with a great deal of mathematic calculation, and even then it is highly inaccurate due to measurement tolerances. Such indirect measurements and calculations therefore do not satisfy quality assurance requirements in modem manufacturing processes.
The invention is therefore addressed to the problem of providing a method and an apparatus by which the cooling action and quenching effect, and the time and temperature factors can be determined continuously and directly even in the case of large batches, so that possible adjustments can be performed extremely fast, i.e., in fractions of a second. This is to bring it about that the cooling or quenching, and hardening if desired, of all workpieces of a batch can be performed very quickly according to their hardening specifications.
Particularly the heat transfer from the workpieces or batch of workpieces to the cooling gas is to be controlled in order to prevent harmful heat tensions and/or irregular product quality, and furthermore transfer from the cooling gas to the heat exchanger is to be controlled, because the processes occurring at the workpiece surfaces and at the surfaces of the heat exchanger have an effect on one another.
The solution of the stated problem is accomplished in the method cited in the beginning by the fact that the measuring body is disposed outside of the workpieces and heated by a heating device associated with it to a given starting temperature and is then exposed to the flowing gas atmosphere, and that the cooling time curves measured on the measuring body are measured.
The stated problem is solved to the full extent by the solution according to the invention, and especially the cooling action or quench effect and the temperature time curve are continuously and directly determined, even in large batches, so that any necessary adjustments can be performed extremely fast, i.e., in fractions of a second. Thus it is accomplished that all workpieces of a batch are cooled or quenched and in some cases hardened, with great speed, in a measured manner according to their hardening specifications.
At the same time, it is especially the thermal transfer from the workpieces or batch of workpieces to the cooling gas that becomes controllable, and any harmful distortions due to thermal tensions and/or irregular production properties are avoided, and furthermore, also the thermal transfer from the cooling gas to the heat exchangers can be controlled, because the processes at the workpiece surfaces and at the surfaces of the heat exchanger again influence one another. What is involved is to some extent a synergistic effect. The more difficult the workpieces are to harden, for example in the case of low-alloy pieces and hard-to-harden workpieces and workpieces of large dimensions and complex shapes, different wall thicknesses, etc., the more important the employment of the invention becomes.
Pursuant to additional embodiments of the invention it is especially advantageous if-either singly or in combination:
the cooling time curves are compared with set patterns and if the differences between the actual values and the set patterns are used to control at least one factor from the group: gas pressure, gas velocity and cooling performance of a heat exchanger,
if the workpieces are preheated in a heating chamber, the measuring body is heated to the given initial temperature before the workpieces are brought into a quenching chamber equipped with the measuring body, and if after the workpieces are brought into the quenching chamber the heating of the measuring body is interrupted and the measuring body is exposed to the gas atmosphere
Ald Vacuum Technologies AG
Kastler Scott
LandOfFree
Method and apparatus for determining the cooling action of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for determining the cooling action of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for determining the cooling action of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3027201