Messung schneller Druckänderungen im Grobvakuumbereich

Measurement of fast pressure changes in the rough vacuum range Using commercially available vacuum gauges, pressure jumps executed in the millisecond range between 1000 and just below 1 mbar were measured in a specially developed system. Of the investigated vacuum gauges, the piezoresistive devices had the shortest response times. They reacted within 1 – 5 ms and achieved a valid measured value after approximately 20 ms. The capacitive manometers responded after 5 – 20 ms and reached a valid measured value after 50 – 100 ms. Lower‐priced Pirani gauges reacted with a response time of 50 – 100 ms and a valid measured value after 200 – 500 ms, which is based on the measuring principle. Besides, a pressure measurement opposed to the actual pressure tendency can be problematic with Piranis.     

Das Saugvermögen von Pumpen: Untersuchung verschiedener Meßverfahren im Grobvakuumbereich

The term pumping speed of a vacuum pump denotes the volume flow rate of gas removed by the pump. In a measurement of the pumping speed it has to be taken into account that the volume of a quantity of gas depends on pressure and temperature. The present article presents a critical investigation of two different procedures for measuring the pumping speed in the rough vacuum regime: In the first procedure, gas flows continuously through the test dome and the pump under investigation. The pumping speed is obtained from the stationary values of throughput and pressure in the test dome. This procedure is well established, technical details are described in various standards. In the second procedure, a large vessel with known volume is evacuated by the pump, and the pumping speed is derived from the pressure decrease with time. In order to avoid disturbances by thermal effects, the vessel may be pumped only during short time intervals with intermediate waiting for thermal equilibrium. The second procedure offers instrumental advantages and its practices are described in a new DIN standard. The physical basis and technical aspects of both procedures including disturbing thermal and other effects are investigated. If applied correctly at inlet pressures in the rough vacuum range, both procedures are expected to yield the same values of the pumping speed. Comparative measurements at a diaphragm pump confirm this expected behaviour within the experimental uncertainty of about 3% (2σ).     

Zeitstanduntersuchungen an Titan im Hinblick auf die Verwendung im Chemie-Apparatebau

Investigations on creep behaviour of titanium for chemical engineering applications . Long term creep tests with titanium No. 3.7055 (DIN 17 850) made as a team work by Dechema Specialists Committee ?Materials and Structure in Chemical Engineering”? (see this journal 5 (1974), pp. 262–273) were continued and evaluated. Creep strengths and 1% creep limits are presented for 1000 hrs, 10000 hrs and 100000 hrs at temperatures between 20 and 400°C. As the results fill the lower half of the tolerance range for the tested material they may be taken as minimum and average creep values, respectively. The characteristical behaviour, already observed with titanium, showing decreasing creep rates when temperature is increasing (up to 300°C) is confirmed by these investigations. Creep values for welded titanium were found in the same range as for the basic material.     

Stahl im Apparatebau

Steel for use in fabrication of boilers and vessels . This summary of steel grades describes steel qualities for the use in the chemical and petrochemical industry. The different steel grades have been arranged following their various applications and their chemical properties have been explained accordingly. This presentation covers steel grades ranging from DIN 17 100 standard to Ni. based alloys. It is also dealing with their workability with regard to cold-and hot forming and their weldability.     

Plasma im Beutel

Plasma in a bag — Internal coating of bags using atmospheric pressure plasmas for cell culturing. “Plasma in a bag” stands for a new low‐cost technique for coating the inside of closed plastic bags by means of atmospheric pressure plasma. The technique allows the deposition of homogeneous, long‐term stable functional layers on the inner surfaces of cell culture bags. The area density of functional amino groups was determined by chemical derivatization in combination with ATR‐FTIR spectroscopy. A prototype of an equipment was built for the automated and reproducible deposition of coatings under standard laboratory conditions maintaining the sterility of the bag. High yields of adherent grown human mesenchymal stem cells can be achieved even after long periods of storage of the bag before use. With suitable variation of the film‐forming agent different functionalities can be obtained on the surface. Future goals are the deposition of migration barriers as well as the coating of bottles with hydrophobic surfaces.     

Vakuumtechnik im Chemielabor

New ways are shown of generating vacuum in chemical laboratories. Top priority is given to environmental protection and, at the same time, to maintaining the operating costs for vacuum generators at a low level. Moreover, information is given on the correct application and on constructive details of modern vacuum generators, such as rotary vane pumps and diaphragm pumps. Operation of these vacuum generators can be optimized by means of suitable vacuum control systems. Also explained are details of vacuum control systems for use in chemical laboratories.     

Vorreaktionen im Otto-Motor

Zusammenfassung In dem von einem Otto-Motor verdichteten Kraftstoffdampf-Luftgemisch treten schon vor der Entzündung durch die von der Zündkerze ausgehende Flammenfront chemische Umsetzungen auf, die sog. Vorreaktionen. Ihre Untersuchung, die wegen ihrer Bedeutung für das Klopfen des Motors wichtig ist, kann am mit eigener Kraft laufenden Motor geschehen oder in Verbrennungsbomben. W?hrend ersteres Verfahren versuchstechnisch sehr schwierig ist, hat das letztere den Nachteil, da? es von den Verh?ltnissen im Motor erheblich, abweicht. Es wird deswegen zu neuen Versuchen ein frend angetriebener, gemischverdichtender Motor ohne Zündung benutzt, in dem die auftretenden Vorreaktionen durch ihre W?rmewirkung der Messung zug?nglich sind. VDI     

Der Verbrennungsvorgang im Vergasermotor

Zusammenfassung Es ist m?glich, den Ablauf des Verbrennungsvorganges in einem homogenen, an einer Stelle gezündeten brennbaren Gemisch ungef?hr vorherzusagen, wenn man für dieses Gemisch die Verbrennungsgeschwindigkeit bei irgendeinem Verbrennungsraum und irgendeiner Anfangstemperatur und einem Anfangsdruck empirisch kennt. Eine gro?e Rolle spielt dabei die Verschiebebewegung, die alle Teilchen infolge des Ausdehnungsbestrebens des zuerst verbrannten Ladungsteils ausführen. Die Geschwindigkeit dieser Bewegung ist stark abh?ngig von der Form des Verbrennungsraumes und kann durch eine Kurve, die sog.γ-Kurve, quantitativ dargestellt werden. An einigen Beispielen wird gezeigt, da? der berechnete Verbrennungsablauf ziemlich gut durch Versuche best?tigt wird. M?glicherweise sind mechanische Bewegungen der Ladungsteilchen im Gemisch die ausl?sende Ursache der Detonation.     

Verschnittoptimierung im praktischen Einsatz

Zusammenfassung In einem Unternehmen der metallverarbeitenden Industrie sind rechteckige Blechtafeln in kleinere rechteckige Teilstücke mit geforderten Abmessungen zu zerteilen. Zum Erreichen des gesetzten Ziels, Minimierung des Verschnitts, wurde ein Standard Software Paket eingesetzt. Diese computergestützte Planung führte zwar zu der gewünschten Reduktion des Verschnitts, bewirkte jedoch deutlich erhöhte Fertigungszeiten und als Folge davon Einkommensverluste bei den Mitarbeitern. Eine detaillierte Analyse ergab, daß durch die Wahl einer entsprechenden Reihenfolge bei der Abarbeitung der optimalen Schnittpläne dieser Nachteil behoben werden konnte. Deshalb wurde eine Computer Routine zur Lösung des Reihenfolgeproblems entwickelt und wegen der günstigen Ergebnisse in das Standard Software Paket integriert.

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Summary A company of the metal working industry that has to cut rectangular metal sheets into smaller pieces of given size intended to diminish occuring waste. For this reason a standard software package for planning waste was in use. However, this procedure resulted in a further problem, namely in greater production times and hence in lower wages for the workers. A detailed analysis of the situation revealed that this new problem could be solved by rearranging the schedule of the cutting patterns. A solution procedure for this sequencing problem was developed and coded as a computer routine. Because of the favourable results this routine is now part of the standard software package.

     

Thermodynamische Aufgaben im Flugmotorenbau

Ohne Zusammenfassung VDI