CH402387A

CH402387A - Process for shaping flexible membranes made of plastomeric plastics

Info

Publication number: CH402387A
Application number: CH444363A
Authority: CH
Original assignee: Landis & Gyr Ag
Priority date: 1963-04-08
Filing date: 1963-04-08
Publication date: 1965-11-15
Also published as: BE637840A

Description

  

  
 



  Verfahren zur Formgebung von beweglichen Membranen aus plastomeren Kunststoffen
Die Erfindung bezieht sich auf ein Verfahren zur Formgebung von beweglichen Membranen aus Kunststoffen für den dichten Abschluss von Druckräumen, z. B. für Dampfdruckfühler.



   Für die einwandfreie Funktion solcher Membranen ist die Bedingung zu erfüllen, dass sich die Membrane bei der Ausführung von Bewegungen elastisch verhält und nicht stets weitergehende Deformationen erleidet. Diese Bedingung wäre von den in Frage kommenden Kunststoffen, welche gegenüber den bisher verwendeten Elementen, wie z. B. metallische Federbälge etc., aus Gründen des bedeutend niedrigeren Preises bevorzugt würden, an sich am besten durch die Elastomere erfüllt. Eine zweite Bedingung gestattet indessen die Verwendung von Elastomeren nicht, weil diese gegenüber wichtigen Dampfdruckflüssigkeiten, wie z. B. Freonen, keine genügende   che-    mische Beständigkeit aufweisen.

   Zudem sind die Elastomere in bezug auf die Freone auch hinsichtlich der Permeabilität unzulänglich, d. h. hinsichtlich des Durchtrittes von Freondampf durch die elastomere Folie, so dass dauernd Dampfdruckflüssigkeit verloren gehen würde unter Herabsetzung der Lebensdauer des Dampfdruckfühlers auf unzulässig kurze Zeiten.



   Vorzügliche chemische Beständigkeit und niedrige Permeabilität, insbesondere gegen Freone, weisen hingegen gewisse Plastomere auf, vor allem die Polyester. Das plastische Verhalten dieser Kunststoffe, d. h. ihr Fliessen bei der funktionsmässigen Festigkeitsbeanspruchung hätte deshalb stets weitergehende Deformationen der Membranen zur Folge. Es ist an sich bekannt, dass die Beanspruchung dieser Stoffe über die Streckgrenze hinaus zu ihrer Verfestigung führt, alsdann die plastischen Deformationen weitgehend unterbunden sind. Desgleichen ist es bekannt, dass bei der spanlosen Formung von Werkstücken diese stellenweise über die Streckgrenze beansprucht und verfestigt werden.

   Auf Kunststoffmembranen angewandt, würde ein solches Verfahren nicht zum Ziele führen; denn es würden Flächenelemente ohne Verfestigung zurückbleiben,   die-    später bei der funktionsmässigen Beanspruchung durch - plastisches Fliessen zu Deformationen führen würden.



   Das erfindungsmässige Verfahren, welches die erwähnten Schwierigkeiten behebt, ist dadurch gekennzeichnet, dass zur Herabsetzung des plastomeren Fliessens der Kunststoffe zufolge der Festigkeitsbeanspruchung bei ihrer Funktion, zumindest jedes bei der Funktion beanspruchte Flächenelement bei der Formgebung unter der Wirkung eines in Druck und Temperatur erhöhten   Arbeitsmitbels    durch   Über-    schreiten der Streckgrenze in freiem Fliessen verfestigt wird, und dass die erzielte   Form-bei    der   Ab      kühlung-- ohne    Ausbau der Membrane und durch Aufrechterhaltung des Druckes bewahrt wird.



   Die Erfindung wird nunmehr anhand der Zeichnung näher erläutert.



   Es zeigen:
Fig. 1 eine Vorrichtung zur-Durchführung des erfindungsmässigen Verfahrens für kleine Membranhübe, und
Fig. 2 eine Vorrichtung zur Durchführung des erfindungsmässigen Verfahrens für grosse Ausbuchtungen der Membrane, d. h. für grosse Membranhübe, insbesondere für Rollmembranen.



   In Fig. 1 liegt die zu formende Membrane 1 auf einem tellerförmigen Unterteil 2 einer Vorrichtung zur Durchführung des Verfahrens auf. Eine Bohrung 3 im Unterteil 2   ist - für    die Zuführung des Arbeitsmittels von erhöhtem Druck und erhöhter Temperatur vorgesehen. Ein Oberteil 4 presst die Membrane  zeichnete O-Ringe   bewerkstelligt    wird. Der Durchmesser dieses Kolbens 10 bestimmt die Dimension der zu formenden Rollmembrane. Für die zu erzielende grössere Ausbuchtung der Membrane werden die nicht eingespannten Randpartien derselben herangezogen, indem in einer ersten Arbeitsphase der Arbeitsmitteldruck über die Bohrung 7 unter die Membrane gegeben wird, wobei die Bohrung 9 und damit der Druckraum oberhalb der Membrane an das Arbeitsmittel noch nicht angeschlossen ist.

   Die Membrane wird folglich in allen ihren Flächenelementen ungehindert in den Hohlraum des   deckellörmigen    Oberteiles 8 hineingedehnt, wo sie, teilweise an den Deckel 8 anliegend, eine derartige Ausbuchtung erfährt, dass die Höhe der Ausbuchtung an der Stelle des Zylinderkreises des Kolbens 10 der gewünschten Rollmembranhöhe entspricht. Anschliessend wird der Kolben 10 in diese Höhe geschoben, siehe punktierte Lage desselben. Durch Wegnahme des Arbeitsmitteldruckes von der Bohrung 7 und Ansetzen desselben an die Bohrung 9 oder durch Erzeugung eines Vakuums auf der Seite der Bohrung 7 wird nun der Druckraum oberhalb der Membrane 1 beaufschlagt, so dass diese nun in weiterem freiem Fliessen und unter Verfestigung an die freien Kolbenflächen gepresst wird und die Rollmembranenform erhält.



  Durch die vorgesehene Einsenkung am oberen Ende des Kolbens 10 wird eine Einstülpung der Rollmembrane erzielt, in welche bei der späteren funktionsmässigen Verwendung der   Rollmembrane    deren innerer Kolben eingesetzt wird.



   Im Falle, dass mit der Zeit schlauchförmige Polyesterstoffe auf dem Markt erhältlich sind, kann das erfindungsmässige Verfahren in   sinngemässer    Weise zur Erzielung der durchgehenden Verfestigung angewendet werden.



   Bei teilweiser Verfestigung des Kunststoffes schon vor der Formgebung erfährt die Durchführung des erfindungsmässigen Verfahrens keine prinzipielle, sondern nur eine quantitative Modifikation.   



  
 



  Process for shaping flexible membranes made of plastomeric plastics
The invention relates to a method for shaping movable membranes made of plastics for the tight closure of pressure spaces, eg. B. for steam pressure sensors.



   For such membranes to function properly, the condition must be met that the membrane behaves elastically when executing movements and does not always suffer further deformations. This condition would be of the plastics in question, which compared to the elements previously used, such as. B. metallic bellows, etc., would be preferred for reasons of significantly lower price, in itself best met by the elastomers. A second condition, however, does not allow the use of elastomers, because they are resistant to important vapor pressure fluids, such as. B. Freons, do not have sufficient chemical resistance.

   In addition, with respect to the freons, the elastomers are also insufficient in terms of permeability; H. with regard to the passage of freon vapor through the elastomeric film, so that vapor pressure fluid would be constantly lost and the service life of the vapor pressure sensor would be reduced to impermissibly short times.



   On the other hand, certain plastomers, especially the polyesters, have excellent chemical resistance and low permeability, especially against freons. The plastic behavior of these plastics, i.e. H. Their flow under the functional strength stress would therefore always result in further deformations of the membranes. It is known per se that the stress on these substances beyond the yield point leads to their solidification, when the plastic deformations are largely prevented. It is also known that in the non-cutting forming of workpieces, these are stressed and hardened in places beyond the yield point.

   Applied to plastic membranes, such a method would not lead to the goal; because surface elements would remain without solidification, which - later in the event of functional loading by - plastic flow would lead to deformations.



   The method according to the invention, which overcomes the difficulties mentioned, is characterized in that, in order to reduce the plastomeric flow of the plastics due to the strength stress in their function, at least every surface element stressed in the function is carried out during the shaping under the action of a working medium increased in pressure and temperature If the yield point is exceeded, it solidifies in free flow, and that the shape achieved - when cooling down - is preserved without dismantling the membrane and by maintaining the pressure.



   The invention is now explained in more detail with reference to the drawing.



   Show it:
1 shows a device for carrying out the method according to the invention for small membrane strokes, and
2 shows a device for carrying out the method according to the invention for large bulges of the membrane, d. H. for large diaphragm strokes, especially for rolling diaphragms.



   In Fig. 1, the membrane 1 to be shaped rests on a plate-shaped lower part 2 of a device for carrying out the method. A hole 3 in the lower part 2 is provided for the supply of the working medium of increased pressure and temperature. An upper part 4 presses the membrane drawn O-rings is accomplished. The diameter of this piston 10 determines the dimensions of the rolling diaphragm to be formed. For the larger bulge of the diaphragm to be achieved, the non-clamped edge parts of the same are used by applying the working medium pressure via the bore 7 under the diaphragm in a first working phase, whereby the bore 9 and thus the pressure space above the diaphragm are not yet connected to the working medium is.

   The membrane is consequently stretched unhindered in all of its surface elements into the cavity of the cover-shaped upper part 8, where it, partially resting on the cover 8, experiences such a bulge that the height of the bulge at the point of the cylinder circle of the piston 10 corresponds to the desired rolling membrane height . The piston 10 is then pushed to this height, see the dotted position of the same. By removing the working medium pressure from the bore 7 and applying it to the bore 9 or by creating a vacuum on the side of the bore 7, the pressure space above the membrane 1 is now acted upon, so that it now continues to flow freely and with solidification to the free Piston surfaces is pressed and the rolling diaphragm shape is retained.



  The indentation provided at the upper end of the piston 10 results in an indentation of the rolling diaphragm into which the inner piston is inserted during the later functional use of the rolling diaphragm.



   In the event that tubular polyester fabrics become available on the market over time, the method according to the invention can be applied in a corresponding manner to achieve continuous consolidation.



   In the case of partial solidification of the plastic even before shaping, the implementation of the method according to the invention does not undergo any modification in principle, but only a quantitative modification.

Claims

PATENT CLAIM A method for shaping movable membranes made of plastomeric plastics for the tight closure of pressure areas, in particular for the production of rolling membranes from such materials, characterized in that in order to reduce the plastomeric flow of the plastics due to the strength stress in their function, at least every surface element stressed in the function is solidified in free flow during the shaping under the action of a working medium with increased pressure and temperature by exceeding the yield point, and that the shape obtained is retained during cooling without dismantling the membrane and by maintaining the pressure.

SUBCLAIMS 1. The method according to claim, characterized in that, to achieve a larger membrane 1 along its edge to the lower part 2, whereby the pressure space below the membrane is sealed off. The upper part 4 has an annular recess 5 in which the membrane can rotate. The recess 5 is dimensioned in such a way that the bulge of the membrane that arises under the action of the working medium includes those of its surface elements which are exposed during later functional use, i.e. H. without load-bearing walls, are exposed to the pressure medium and allow the lifting movement through the most elastic possible deformation. These bulging membrane surfaces are therefore those whose plastic flow should be prevented as far as possible through solidification.

In accordance with the method according to the invention, the membrane in its bulging areas is now stressed beyond the yield point under the action of the working medium, which is increased in pressure and temperature, and undergoes shaping and solidification as it flows. Since the membrane is not hindered in its flow thanks to the recess 5 by any solid walls in the areas in question and the working medium acts on all surface elements of these membrane portions, the flow and thus the solidification extends to all these surface elements, which as above executed - represent those surface elements which should have the least possible plastic deformation when exposed to the pressure medium later for functional use.

In order to prevent the bulges from receding during cooling, the pressure of the working medium is maintained until the cooling has taken place.

When the requirements for flexibility are high, plastic in the form of thin foils is chosen as the starting material for the membrane. The resulting limitation of the permissible pressure can be remedied by using several thin foils, which are shaped in a joint operation, whereby they fit into one another in terms of shape.

Fig. 2 shows the device for performing the method according to the invention for those cases in which larger bulges of the membrane are to be achieved in order to enable correspondingly larger membrane strokes. The membrane 1 rests on an annular lower part 6 of the device. A hole 7 in the lower part 6 allows the supply of working medium with increased pressure and temperature under the membrane 1. A lid-shaped upper part 8 presses the membrane 1 along its edge against the lower part 6, thereby sealing the pressure spaces below and above the membrane 1 becomes. The upper part 8 also has a bore 9 for the supply of working medium.

In the cylindrical cavity of the annular lower part 6 there is a movably arranged piston 10, the sealing of which against the lower part 6, for example, by bulges not gb here, especially in the case of rolling diaphragms, in addition to the functionally stressed surface elements, further surface elements of the membrane up to their entirety during the shaping by flowing are solidified, the bulges being obtained not only from the first-mentioned surface elements, but also from the last-mentioned surface elements.

2. The method according to claim and dependent claim 1, characterized in that the exceeding of the elastic limit of the plastic is brought about by increased pressure and increased temperature of a gas or vapor or a liquid as a working medium, such that the surface elements of the plastic membrane to be solidified by flowing are not hindered in their expansion by any solid walls during the manufacturing process or certain partial phases thereof.

3. The method according to claim, characterized in that polyester is used as the plastomeric plastic for the purpose of chemical resistance and low permeability, in particular against freons.

4. The method according to claim, characterized in that thin foils are used as the plastic starting material for the purpose of good flexibility of the membrane.

5. The method according to claim and dependent claim 4, characterized in that for the production of the membrane, for the purpose of good flexibility and sufficient strength against high pressures, several thin foils are used, which are formed in the same operation.

6. The method according to claim, characterized in that a tubular shape is used as the starting form of the plastic.

7. The method according to claim, characterized in that the solidification of the plastic material is partially accomplished before the membrane is shaped.