DE102010042421A1 - Diaphragm seal and pressure transducer with such a diaphragm seal - Google Patents

Abstract

A diaphragm seal 1b comprises a diaphragm seal body 10; and a separating membrane (20b) which is fastened to the pressure-tight seal on the pressure-tight seal, forming a pressure-release chamber (12) between a surface of the pressure-release body and the separating membrane, a hydraulic path (14) extending from the pressure-release chamber through the pressure-release body (10), wherein the separating membrane (20b) has a metallic material, in particular tantalum or a nickel-based alloy such as Hastelloy, Inconel or Monel, characterized in that: the separating membrane (20b), at least in a deflectable area covering the pressure chamber, has an average material thickness of not more than 30 Micrometers, in particular not more than 25 micrometers and preferably not more than 20 micrometers. The separating membrane can be obtained by electropolishing a thicker separating membrane that was previously joined to the diaphragm seal body.

Description

The present invention relates to a diaphragm seal and a pressure transducer with such a diaphragm seal. For detecting pressures of a process medium diaphragm seals are often used, which have a diaphragm seal to which a separation membrane is pressure-tightly secured to form a pressure chamber between the diaphragm seal and the diaphragm separation, wherein extending from the pressure chamber, a hydraulic path through the diaphragm seal body to the to transfer the pending diaphragm of the pending pressure of a process medium.

Inasmuch as the volume of a transfer fluid of the hydraulic path, which is located in the pressure chamber, in particular subject to temperature-dependent fluctuations, it is known to make separation membranes as soft as possible, so due to the volume-dependent deflection of the separation membrane as low as possible pressure difference between the on the outside of the Separation membrane pending media pressure and the pressure in the pressure chamber occurs. Efforts for this purpose are disclosed, for example, in the published patent applications DE 10 2005 004 942 A1 and DE 10 2005 023 021 A1 and the patents DE 199 462 34 C1 and EP 1 114 987 B1 , Another approach to achieving soft separation membranes is disclosed in the published patent application DE 10 2008 033 337 A1 ,

The cited documents are fundamentally concerned with the macroscopic shape of the separation membrane, insofar as it has an effect on impressed wave or step patterns or vaults. Of course, it is also known that the material thickness of a separating membrane with the third power enters into the rigidity of the separating membrane. Insofar there is the effort possible to use thin separation membrane, which are limited by the common manufacturing processes, such as the welding of the separation membranes on the diaphragm seal body, since too thin separation membrane can no longer be tightly welded, this problem in particular for membranes relevant to a Nickel base alloy such as Hastelloy, Inconel or Monel have.

It is therefore the object of the present invention to provide an improved diaphragm seal with a soft separation membrane.

The object is achieved by the diaphragm seal according to the independent claim 1, the pressure transducer according to the independent patent claim 6 and the method for producing a pressure transmitter according to the independent claim 10th

The pressure transmitter according to the invention, comprises a diaphragm seal body; and a separation membrane which is pressure-tightly secured to the diaphragm seal body to form a diaphragm seal between a surface of the diaphragm seal body and the separation diaphragm, a hydraulic path extending from the diaphragm seal chamber through the diaphragm seal body, the separation diaphragm comprising a metallic material, in particular tantalum or a nickel base alloy Hastelloy, Inconel or Monel, according to the invention, the separation membrane, at least in a pressure chamber covering the deflectable region has an average material thickness of not more than 30 microns, especially not more than 25 microns and preferably not more than 20 microns.

Electropolishing usually serves to reduce the microroughness of surfaces, as the name implies. As a method of material removal for adjusting the rigidity of a mechanical component, it is not known. During electropolishing, the components thus treated are subjected to neither mechanical nor thermal stresses.

This is particularly advantageous for separating membranes which have an impressed contour prior to electropolishing, since the embossed contour influences the mechanical properties of the separating membrane and mechanical or thermal stresses could change the contour.

In one embodiment of the invention, the material of the separation membrane has a mean grain size, wherein the material thickness of the separation membrane is not more than three times, preferably not more than twice and more preferably not more than 1.5 times the average grain size of the material Separating membrane is.

In a further development of the invention, the separation membrane is attached by means of welding, soldering or brazing to the diaphragm seal body.

In a currently preferred embodiment of the invention, the material thickness of the separation membrane is adjusted by means of electropolishing. The separation membrane in the desired thickness is thus available by electropolishing a thicker separation membrane, which was previously joined to the diaphragm seal body.

The diaphragm seal according to the invention can be obtained according to an embodiment of the invention by a method in which the surface of the separating membrane is pickled at least in the region of the joint, in particular before the electropolishing.

Pickling removes oxides, especially tarnish in the area of a weld or other discoloration. The resulting clean surface facilitates electropolishing. Pickling baths contain, for example, nitric acid and hydrofluoric acid. The duration of treatment depends on the degree of surface contamination.

The pressure measuring transducer according to the invention comprises a pressure transducer and at least one pressure transmitter according to one of the preceding claims, wherein the pressure transducer can be acted upon by a hydraulic path with a prevailing in the pressure chamber of the pressure transmitter pressure to output a signal dependent on the pressure.

According to one embodiment of the invention, the pressure measuring transducer according to the invention is an absolute pressure transducer or a relative pressure transducer, wherein the pressure transducer outputs a signal which outputs a difference between the pressure and vacuum supplied via the hydraulic path or the difference between the pressure supplied via the hydraulic path and the atmospheric pressure.

According to a further embodiment of the invention, the pressure measuring transducer according to the invention is a differential pressure transducer which also has a second pressure transmitter with a second hydraulic path for supplying a second pressure to the pressure transducer, the pressure transducer outputting a signal which is the difference between the first pressure and second pressure transducer Pressure depends.

According to one embodiment of the invention, the pressure transducer is a capacitive, (piezo) resistive or optical, in particular interferometischer, pressure transducer.

The method according to the invention for producing a pressure transmitter comprises providing a metallic diaphragm seal body and a metallic diaphragm which in particular comprises a nickel-based alloy such as Hastelloy, Inconel or Monel; Joining the separation membrane with the diaphragm seal body to form a pressure chamber between the diaphragm seal body and the measuring diaphragm; characterized in that at least the pressure chamber overlapping, deflectable region of the separation membrane is treated by electropolishing to achieve an average material thickness, which is at least 20 percent, in particular at least 50 percent and preferably at least 75 percent (based on the achieved by the electropolishing medium Material thickness of the deflectable region) is thinner than the average material thickness of the deflectable region before the treatment by means of electropolishing.

In a development of the method according to the invention, the material of the separating membrane has a mean grain size, and wherein by electropolishing an average material thickness is set which is not more than four times, in particular not more than three times preferably not more than twice and more preferably not more than 1.5 times the mean grain size of the material of the separation membrane.

In one development of the invention, the separating membrane has an impressed contour, which is impressed before the joining of the separating membrane to the diaphragm seal body.

In another development of the invention, the separating membrane has an impressed contour, which is impressed on the separating membrane after the joining of the separating membrane with the diaphragm seal body and before the electropolishing.

In the two aforementioned embodiments of the invention is to be considered that the stress distribution in the separation membrane, which is given after embossing, by the

The electropolishing after embossing may, for example, on one side of the separating membrane remove those layers of material which have the greatest distance to a central plane of the separating membrane material, and which have tended to undergo the greatest plastic or elastic deformation during embossing. By electropolishing, therefore, the balance of the stresses in the separation membrane can be changed, which can lead to a change in the rest position or the effective stiffness of the separation membrane.

Therefore, it is advantageous to take into account the subsequent change in shape due to the electropolishing in the design of the embossing die in the cases in which the embossing of the separating membrane is to take place before the electropolishing. This can be done experimentally and / or by simulation by means of finite elements, wherein in particular an iterative combination of experiments and simulations seems to be expedient.

In a further development of the invention, the separating membrane has an impressed contour which is impressed on the separating membrane after the separating membrane has been joined to the diaphragm seal body and after the electropolishing.

The invention will now be explained with reference to an embodiment shown in the drawings. It shows:

1a a longitudinal section through an embodiment of a pressure transmitter according to the invention prior to electropolishing;

1b a longitudinal section through an embodiment of a pressure transmitter according to the invention after the electropolishing;

2 a longitudinal section through an embodiment of a pressure measuring transducer according to the invention;

3 a first embodiment of the method according to the invention;

4 a second embodiment of the method according to the invention; and

5 A third embodiment of the method according to the invention.

The in 1a shown pressure transmitter comprises a diaphragm seal body 10 and a separation membrane 20a which run along a border area 22 is welded pressure-tight with a circumferential weld with an end face of the diaphragm seal body, so that between the end face of the diaphragm seal body 10 and the separation membrane 20a a pressure chamber 12 is formed, which via a channel 14 that separates from the separating membrane 20 facing end face of the diaphragm seal body 10 through the pressure center body to one of the separation membrane 20a remote from the rear end face of the diaphragm seal extends to the in the pressure chamber 12 to transmit prevailing pressure.

The separation membrane 20 has an impressed contour 24a on, for example, on a corresponding contour 16 on the end face of the diaphragm seal after joining the separation membrane 20 with the diaphragm seal body 10 can be stamped, or before the joining of the separation membrane 20 with the diaphragm seal body 10 can be shaped differently. The diaphragm seal body 10 has an at least partially cylindrical shape, wherein the separation membrane 20a is formed circular disk-shaped. The separation membrane comprises a nickel-based alloy, namely Monel, and has a thickness of about 50 μm. By electropolishing the surface of the separation membrane in an electrolytic process in which the surface of the separation membrane 20a As an anode, the separation membrane is thinned at a rate of 2 to 5 microns per minute until it has reached a final thickness of about 20 microns. This condition is in 1b shown.

Details of the electropolishing are, for example, in Volume 11 of the series "Materials and Applications", ISBN 978-2-87997-311-1 shown. In addition to the actual electropolishing step, electropolishing may include a pretreatment and aftertreatment, during which the surfaces are to be cleaned during the pretreatment and, if appropriate, to be freed from surface damage by means of pickling, which may occur, in particular, at weld seams. With the post-treatment, the residues of the electrolyte used in the electropolishing are removed, which can be done in particular with a nitric acid treatment. Controlled drying would avoid staining. Details of the process steps of the electropolishing, as well as the pre- and post-treatment are shown for example in Chapter 3 "process steps" of said reference.

The in 1b Diaphragm seal shown differs from the diaphragm seal in 1a through a considerably thinner membrane 20b , which only has a thickness of 20 microns. Due to the material removal during electropolishing, the separation membrane has the potential to be softer than the original separation membrane with a thickness of 50 μm. Due to the removal of material but can the equilibrium position of the separation membrane 20b , as well as the contour 24b the separation membrane with respect to the initial position in 1a change.

It is expedient to take into account these expected changes in the separating membrane due to the electropolishing in the design of a stamping die against which the contour of the separating membrane is embossed in order to obtain the desired shape of the separating membrane after the electropolishing.

The in 2 shown pressure transducer includes a diaphragm seal 1b that with a separation membrane 20b , which has a nickel-based alloy in a thickness of about 20 microns. It is obtained by electropolishing a separation membrane in a thickness of 50 microns, which previously on an end face of the diaphragm seal body 10 of the diaphragm seal 1b was attached with a circumferential weld. The diaphragm seal 1b communicates via a hydraulic path with a transducer unit 2 , which provides a pressure dependent primary electrical signal from an electronics unit 3 processed and output. The hydraulic path includes a capillary line 18 , which is located between the diaphragm body 10 and a converter chamber 32 extends, in which a piezoresistive pressure transducer 32 is arranged, in the present case, the back of a measuring diaphragm of the piezoresistive pressure transducer 34 is subjected to atmospheric pressure, so that the present pressure transducer is a Relativdruckmessaufnehmer. The electronics unit 3 contains a processing circuit in a housing 36 , which is the primary signal of the piezoresistive pressure transducer 34 prepared and in a suitable for issue Signal converts, which may be, for example, a digital signal or an analog signal, in particular 4 ... 20 mA.

The 3 to 5 now show alternative methods for producing the pressure transmitter according to the invention.

In the first embodiment of the method according to 3 First, the separation membrane is joined in the planar state, ie welded to a diaphragm seal body along a peripheral edge. Subsequently, the embossing of the contour takes place in the separation membrane. The embossing can for example take place against a membrane bed, which serves for example in case of overload to support the separation membrane or against a punch which is to be arranged for embossing on the side facing away from the diaphragm seal body side of the separation membrane. After embossing, the electropolishing takes place, whereby it goes without saying that the electropolishing in all embodiments can include the preparations and subsequent treatments discussed at the outset. If necessary, after the electropolishing, the contour of the separating membrane can be reproduced, wherein the embossing can again take place against the membrane bed or a stamp, which may also be a different stamp than that with which the first embossing. Imprinting is only optional.

In the embodiment of the method, which in 4 is shown, the embossing of the contour takes place before the separation membrane is joined with a diaphragm seal body. In this case, therefore, an already embossed separating membrane is joined to the diaphragm seal body, which can be done in particular by welding or brazing, in particular brazing.

Finally, electropolishing and optional optional stamping of the contour takes place as in the exemplary embodiment according to FIG 3 ,

5 shows an embodiment of the method in which first the separation membrane is joined in the planar state with the diaphragm seal body by welding or brazing. Subsequently, the electropolishing of the still unembossed, flat separation membrane. Finally, the thinned separating membrane, which after the electropolishing, for example, still has a thickness of 20 microns, impressed a contour, the contour can either be formative against a membrane bed or against a, the membrane bed facing away punch.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005004942 A1 [0002]
• DE 102005023021 A1 [0002]
• DE 19946234 C1 [0002]
• EP 1114987 B1 [0002]
• DE 102008033337 A1 [0002]

Cited non-patent literature

• Volume 11 of the series "Material and Applications", ISBN 978-2-87997-311-1 [0035]

Claims (14)

Diaphragm seal ( 1b ) comprising: a diaphragm seal body ( 10 ); and a separation membrane ( 20b ), which under formation of a pressure mediator chamber ( 12 ) is fastened in a pressure-tight manner to the diaphragm seal body between a surface of the diaphragm seal body and the separating diaphragm, wherein a hydraulic path (of the pressure diaphragm chamber) ( 14 ) through the diaphragm seal body ( 10 ), wherein the separation membrane ( 20b ) comprises a metallic material, in particular tantalum or a nickel-based alloy such as Hastelloy, Inconel or Monel, characterized in that: the separating membrane ( 20b ), at least in a deflectable region covering the pressure chamber has an average material thickness of not more than 30 micrometers, in particular not more than 25 micrometers and preferably not more than 20 micrometers. A pressure transmitter according to claim 1, wherein the material of the separation membrane has a mean grain size, and wherein the material thickness of the separation membrane not more than four times, in particular not more than three times preferably not more than twice and more preferably not more than 1.5 times the mean grain size of the material of the separation membrane corresponds. A pressure transmitter according to claim 1 or 2, wherein the separation membrane is fixed by means of welding, soldering or brazing to the diaphragm seal body. Diaphragm seal according to one of the preceding claims, wherein the material thickness of the separation membrane is adjusted by means of electropolishing. Diaphragm seal according to the preceding claims, obtainable by a method in which the surface of the separating membrane is pickled at least in the region of the joint, in particular before the electropolishing. Pressure transducer, comprising a pressure transducer ( 34 ) and at least one pressure transmitter ( 1b ) according to one of the preceding claims, wherein the pressure transducer via a hydraulic path ( 14 . 18 ) is acted upon by a pressure prevailing in the pressure chamber of the pressure mediator to output a signal dependent on the pressure. A pressure transducer according to claim 6, wherein the pressure transducer is an absolute pressure transducer or a relative pressure transducer, wherein the pressure transducer outputs a signal which outputs a difference between the pressure and vacuum supplied across the hydraulic path and the difference between pressure supplied through the hydraulic path and atmospheric pressure. The pressure transducer of claim 6, wherein the pressure transducer is a differential pressure transducer further comprising a second secondary seal having a second hydraulic path according to any one of claims 1 to 5 for supplying a second pressure to the pressure transducer, the pressure transducer outputting a signal representative of the difference between the first pressure and second pressure. Pressure measuring transducer according to one of claims 6 to 8, wherein the pressure transducer is a capacitive, (piezo) resistive or optical, in particular interferometischer, pressure transducer. Method for producing a pressure transmitter, comprising: Providing a metallic diaphragm seal body and a metallic separation membrane, which in particular has a nickel-based alloy such as Hastelloy, Inconel or Monel; Joining the separation membrane with the diaphragm seal body to form a pressure chamber between the diaphragm seal body and the measuring diaphragm; characterized, in that at least the deflectable region of the separating membrane covering the pressure chamber is treated by electropolishing in order to achieve an average material thickness which is at least 20 percent, in particular at least 50 percent and preferably at least 75 percent (based on the achieved average material thickness of the deflectable region) thinner is the average material thickness of the deflectable region before the treatment by electropolishing. The method of claim 10, wherein the material of the separation membrane has a mean grain size, and wherein by means of electropolishing an average material thickness is set which is not more than three times, in particular not more than two times and preferably not more than 1.5 times the average Grain size of the material of the separation membrane is. The method of claim 10 or 11, wherein the separation membrane has an embossed contour which is impressed prior to joining the separation membrane with the diaphragm seal body. The method of claim 10 or 11, wherein the separation membrane has an impressed contour which is impressed on the separation membrane after joining the separation membrane with the diaphragm seal body and before the electropolishing. The method of claim 10 or 11, wherein the separation membrane has an impressed contour which is impressed on the separation membrane after joining the separation membrane with the diaphragm seal and after the electropolishing.

Images