EP1764422B1 - Method for fabricating housing from austenitic steel. - Google Patents

Description

The invention relates to a method for producing a housing with welded neck, in particular a compressor housing made of austenitic steel.

Hydraulic turbines, steam and gas turbines, wind turbines, centrifugal pumps and centrifugal compressors as well as propellers are summarized under the collective term "turbomachinery". Common to all these machines is that they serve the purpose of depriving one fluid of energy, thereby driving another machine, or conversely, supplying energy to a fluid to increase its pressure.

The housings of compressors must be designed so that they can withstand high internal pressure. Compressor is here understood to mean a working machine for compressing gases, vapors or the like. Compressors are sometimes used at very low operating temperatures. It may happen that the operating temperatures are less than minus 120 ° C. At these low operating temperatures, cold-hard steels having an austenitic crystal structure are used as material for the casings of the compressors. However, such cold-tough steels with austenitic crystal structure have only a low strength. In the case of solid bodies, toughness means the property of being able to plastically deform under macroscopic mechanical strain under mechanical stress. Toughness may also be understood as the strength of the resistance that a body opposes to a plastic deformation, ie, the magnitude of the stress and / or energy that must be applied for deformation. The opposite of toughness can be called brittleness. Under the Strength is the resistance of a component or material to a change in shape or fracture stress, with a distinction between pressure, tensile, bending, shear or shear and torsional or torsional strength.

From the Patent Abstract of Japan Publication No. 07054047 Already stress relieving an austenitic steel after plastic deformation is known. This is preferably used to make seamless tubes of austenitic high alloy nickel chrome Ni-Cr steel alloys. From the Patent Abstract of Japan Publication No. 62286610 It is also known to draw seamless steel tubes with rollers provided outside over a mandrel while reducing the wall thickness and widening of the diameter.

To ensure safe operation of a compressor at low operating temperatures, the casings of the compressors are designed for high temperature, low temperature applications to withstand the internal pressure at low material strengths. Since the austenitic steels also have a low thermal conductivity and a high coefficient of thermal expansion, there is the danger of large temperature transients within the housing and thus the risk of thermal stresses to permanent plastic deformation.

At this point, the invention sets in whose task it is to provide a method for increasing the strength of housings, for which steels can be used, which can be used at low temperatures.

This object is achieved by a method according to claim 1. The dependent claims include advantageous developments.

The invention is based on the recognition that the strength of austenitic steels can be significantly increased by being plastically deformed before stress relief annealing, without the low temperature toughness substantially decreasing.

Experiments have shown that by a plastic pre-deformation the strength can be increased to three times.

In an advantageous development, the plastic deformation is achieved by mechanical stretching in step 1).

As a result, a very simple method step is specified in order to realize a plastic deformation. Other process steps for plastic deformation are conceivable, for. As hydraulic or pneumatic stretching under internal pressure or cold rolling.

According to the invention, the austenitic steel is provided as a cylinder housing or as a ring, and the step 1) is carried out by widening the cylinder housing or the diameter of the cylinder housing or the ring with a deforming device and the thickness of the cylinder housing or of the ring is reduced.

The invention is based on the aspect that if the austenitic steel is present as a cylinder housing or as a ring, there is a very cost-effective way to plastically deform the ring as a whole. In this case, a deformation device is attached to the cylinder housing or the ring in such a way that they are uniformly stretched by a uniform force transmission.

In an advantageous development, the deformation device comprises a conical cylinder.

Thereby, a particularly simple possibility is offered to make the deformation device such that a force is exerted on the inside of the cylinder housing or the ring by a linear movement of the conical cylinder, whereby they are widened as a whole. Other deformation devices are possible. The deforming means may also comprise hydraulic means.

According to the invention, a nozzle on an outer wall of the cylinder housing or the ring arranged and welded in a next step to the cylinder housing or the ring, wherein in a next step, the ring is solution annealed and quenched with the neck and then a plastic deformation, wherein the cylinder housing or the ring are widened, wherein in a next step, the ring is stress-annealed with the neck and then drilled passages through the neck and the ring.

The invention is based on the aspect that it is advantageous if nozzles are to be attached to the cylinder housing or the ring, that they are attached before stress relief annealing.

Thus, a compressor housing made of an austenitic steel, wherein the compressor housing is formed substantially annular, wherein the compressor housing was prepared by a method according to any one of claims 1 to 4.

Embodiments of the invention are described below with reference to the drawings. In this case, provided with the same reference numerals components have the same operation.

Figur 1

eine schematische Darstellung der Herstellung eines Verdichtergehäuses mit Stutzen,

Figur 2

ein Diagramm zur Verdeutlichung eines Einflusses der Kaltverformung auf mechanische Eigenschaften für den Werkstoff X5CrNiTi18-10,

Figur 3

ein Diagramm zur Verdeutlichung des Einflusses der Spannungsarmglühtemperatur auf die mechanischen Eigenschaften auf den Werkstoff X5CrNiTi18-10.

Show

FIG. 1

a schematic representation of the production of a compressor housing with nozzle,

FIG. 2

a diagram to illustrate an influence of cold working on mechanical properties for the material X5CrNiTi18-10,

FIG. 3

a diagram illustrating the influence of stress relief annealing temperature on the mechanical properties on the material X5CrNiTi18-10.

In the FIG. 1 6 sub-steps for the production of the compressor housing 1 are shown.
In the FIG. 1 is a sectional view of the housing 1 can be seen. The length of the housing 1 is therefore from the FIG. 1 not to be taken.
In FIG. 1 is in step 1) a compressor housing 1 as an embodiment of a cylinder housing or ring at least comprising a housing 2 and two nozzles 4a and 4b shown. The housing 2 is made of an austenitic steel and is formed substantially annular. The housing 2 is formed annularly about a rotation axis 3.
In a step 1) two stubs 4a and 4b are provided with a bore 5a and 5b.

In a step 2), the nozzles 4a and 4b are welded to an outer wall 6 of the housing 2.

In step 3), the housing 2 is solution annealed and quenched with the nozzles 4a and 4b. The solution heat treatment takes place at temperatures and over periods of time that depend on the choice of material of the housing. The quenching of the housing and the nozzle is done by conventional methods.

In step 4), the housing 2 is plastically deformed by a deformation device, not shown, whereby the thickness 7 of the housing 2 is reduced.

The deforming means may comprise a conical cylinder. In alternative embodiments, the deformation device may comprise hydraulic power drives. However, other deformation devices are conceivable as well.

In step 5), the housing 2 and the nozzles 4a and 4b are stress relieved. The temperature and duration of the stress relief annealing is done according to conventional process values, which depend on the choice of austenitic steel.

In step 6), passages 8a and 8b are bored through the housing 2. Subsequently, a mechanical processing takes place.

In the FIG. 2 the influence of cold deformation on the mechanical properties of the material X5CrNiTi18-10, 1.4541 is shown. On the left Y-axis 9 is the 0.2% proof stress and on the X-axis 11, the strain is plotted in percent. On the right Y-axis 10, the consumed impact energy 18 is plotted in the Charpy impact test at minus 196 ° C. Curve 12 shows a clear increase in the 0.2% proof stress as a function of the elongation. At 5% elongation, the 0.2% proof stress has a value of 300 MPa. At an elongation of approximately 50%, the 0.2% proof stress has a threefold value which is approximately 900 MPa. The consumed impact energy 18, however, decreases at 5% elongation from 100 joules to 60 joules at an elongation of almost 50%.

Tests have shown that the 0.2% proof strength of the standard steel X6CrNiTi18-10 increases from 200 MPa to 600 MPa by a 25% pre-deformation.

In the FIG. 3 is the influence of temperature during stress relieving on mechanical properties of the material X5CrNiTi18-10 at a cold working degree of 25% dargstellt.

In the FIG. 3 On the left Y-axis 9 is the 0.2% proof stress and on the right Y-axis 10 the consumed impact work is plotted. On the X-axis 15, the stress relief annealing temperature is given in degrees Celsius. The curve 16 shows the course of the consumed impact work from 250 ° C to 550 ° C. The curve 17 shows the course of the 0.2% proof stress of 250 ° C to 550 ° C. In this diagram, it can be seen that the properties of the steel are hardly changed by a stress relief annealing.

Through the in FIG. 1 shown method wall thicknesses for compressor housing 1 can be reduced. This would require significantly less material. Another advantage would be that temperature transients and thermal stresses decrease. In addition, the risk of plastic deformation would be reduced by thermal stresses.

Claims (4)

1. Method for producing a casing with a welded-on connection piece, in particular a compressor casing, from austenitic steel,
   characterized by the following steps:

   1) a connection piece (4a, 4b) is arranged on an outer wall (6) of a casing (2), and, in a

   2) next step, is welded to the casing (2),

   3) in a next step the casing (2), together with the connection piece (4a, 4b), being solution-annealed and quenched, and subsequently

   4) plastic deformation of the austenitic steel taking place, the casing (2) being expanded,

   5) in a next step, the casing (2), together with the connection piece (4a, 4b), being stress-relief-annealed, and,

   6) subsequently, passages being drilled through the connection piece (4a, 4b) and the casing (2).
2. Method according to Claim 1, in which, in step 1), the plastic deformation takes place by means of mechanical stretching.
3. Method according to Claim 1 or 2, in which the austenitic steel is essentially in the form of a cylinder casing (1) or ring (1), and step 1) takes place in that, by means of a deformation device, the diameter of the cylinder casing (1) or of the ring (1) is expanded and the thickness of the cylinder casing (1) or of the ring (1) is reduced.
4. Method according to Claim 3, in which a conical cylinder is used in the deformation device and the cylinder casing (1) or the ring (1) is expanded by the conical cylinder being moved.

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