EP2908010B1 - Piston rod for piston compressors and piston compressor - Google Patents

Description

The present invention relates to a piston rod for reciprocating compressors, which has a base body with a piston-facing end, a piston-remote end and at least one cavity. Furthermore, the invention relates to a piston compressor with such a piston rod.

As standard, compressors and in particular reciprocating compressors are used for the compression of liquids or gases. In order to minimize the friction forces occurring between the moving components of the compressors, compressors with oil lubrication are preferably used. This oil lubrication has the task of producing predominantly hydrodynamic tribological contact between the sliding partners on the piston and guide rings and on the sealing rings of the piston rod seal. By this tribological contact very low rates of wear of these sealing elements can be achieved. Thus, service life of lubricated machines of over 25,000 hours without significant wear can be achieved.

The oil lubrication, however, there is a risk that lubricants are dissolved in the gases or liquids to be compressed. Consequently, the oil-lubricated compressors are unsuitable for sensitive media such as those used in the food industry or in the medical field.

To avoid this problem, reciprocating compressors are increasingly being used with piston rod seals without oil lubrication. This was made possible by the development of plastic-based sealing elements.

Such sealing elements are used for example in the DE 10 2006 015 327 B9 described. As materials for piston rod seals mainly plastics, for example, filled polymers enforced. A commonly used polymer material is, for example, polytetrafluoroethylene. Solids such as amorphous carbon, graphite, glass fibers, metals, ceramics or solid lubricants are incorporated into the PTFE matrix. To increase the service life, usually a plurality of piston rod sealing rings, at least two in the axial direction, arranged one behind the other and form a sealing element set, which is also referred to as a seal pack.

Without the existing oil lubrication, however, there are strong changes in the tribological properties at the contact points of the sliding partners. From the hydrodynamic tribological contact is a tribochemical contact, which only leads to good lubricity and low wear rates when a so-called transfer film is formed. Mechanical / physical forces between the sliding partners lead to structural changes in the surface of the sliding layer. These may be surface enlargement, reduction of particle sizes, formation of fresh surfaces, abrasion of materials and in some cases also phase transformations, which is generally summarized under the terms tribochemical contact or tribochemical process. However, this transfer film has to be permanently renewed by further tribochemical processes. As soon as a stationary renewal process has set in, low coefficients of friction and wear rates are possible, which, however, are still significantly higher than those of the oil-lubricated sliding partners. Usually, only about 8000 operating hours can be guaranteed in dry running today.

Due to the increased friction values of the oil-free sliding partners, the movement of the piston rod leads to an increased development of frictional heat and thus to an increased temperature at the contact points.

Extensive tribological investigations have shown, however, that this increased temperature in turn has a negative effect on the wear rates of the sliding partners. In the worst case, this can lead to premature failure of the compressor. An effective cooling of the sliding partners thus represents a major problem in dry lubrication.

At the piston and guide rings cooling is easy to realize because the cylinder liner and thus the contact point between the piston and cylinder liner can be cooled, but not in a piston rod seal.

The sealing rings of the piston rod seal are in the so-called gasket, which is also referred to as stuffing box arranged. The chambers of the packing are usually cooled with water. However, the cooling is not very effective because a process gas located between the contact surface and the chambers prevents good heat flow.

Much of the frictional heat introduced is transported via the heat pipe along the piston rod from the region of the packing to an area remote from the packing. There, the heat is finally dissipated by the forced convection of the moving piston rod to the environment.

However, conventional piston rods consist for example of steel materials and thus have only low thermal conductivities (steel: 15-58 W / (mxK)). This low thermal conductivity inevitably leads to a large temperature gradient from the gasket area (high temperature) to the area remote from the gasket (low temperature).

However, to enable improved cooling of the piston rod, actively cooled piston rods are known from the prior art.

For example, in the DE-PS 340 086 discloses a piston rod for double-acting internal combustion engines, which has a central bore and a number lying in the vicinity of the surface of the rod bores, so that the surface is cooled by a coolant flowing through the bores.

However, this device has the disadvantage that connections for the coolant flowing through must be provided on the piston rod. Furthermore, a circulating pump must be operated permanently during operation, which pumps the coolant through the piston rod. Both the connections, as well as the pump increase the cost and maintenance of such cooled piston rods. Furthermore, an unnoticed failure of the circulation pump leads to an immediate increase in the temperature of the piston rod and, consequently, damage to the same. Thus, the functionality of the circulation pump must be constantly monitored during operation, which is also associated with increased costs and time.

From the DE 199 01 868 B4 For example, a piston rod is known which has at least one coolant supply channel and at least one coolant discharge channel. In addition, the piston rod has an axial blind bore and the mindeseine Kühlmittelzuführkanal and the at least one Kühlmittelabführkanal are each arranged laterally to this blind bore.

In addition to cooling through the coolant channels, the blind bore results in a reduction in weight, so that when the piston rod is operated horizontally it is intended to reduce friction and thus reduce wear.

Because the piston rod is the DE 199 01 868 B4 is also actively cooled by means of coolant, however, the same disadvantages occur, as in connection with the DE-PS 340 086 were explained.

Also from the CH 163 967 and the DE-PS 521 491 are each liquid-cooled piston rods known, although cause a reduction in temperature of the piston rod, but also the same disadvantages of DE-PS 340 086 exhibit.

The JP S63215884 A discloses a piston rod having a cavity divided by a flap into two sections. In a portion of this cavity is a small amount of a cooling liquid, which is moved by the piston movement within the cavity back and forth, evaporated and condensed there.

The DE 44 05 091 A1 describes a heat pipe device with a piston rod that is hollow and filled with a certain amount of working fluid. Due to the combustion process occurring in a combustion chamber of a cylinder, a heat flow flows into the head of the piston and into the piston mounting area. From there, part of the heat flow flows into the Piston rod, the wall of which is strongly heated piston head side. The heat is transferred to the working fluid contained in the interior of the piston rod, which thereby evaporates.

The GB 771 247 A discloses a soldering iron whose soldering tip consists of an iron shell with a copper core. The copper material should serve to conduct the heat to the tip.

The US 2,256,479 A describes a rotor blade of a gas turbine whose core consists of a copper material whose end portion in a chamber contacts a hot cooling liquid.

The GB 558 405 A relates to a spark plug with a copper core.

Thus, it is an object of the invention to provide a piston rod for reciprocating compressors that allows a good heat flow from the gasket area and thus reliable cooling of the piston rod seal and compared to the prior art easier to manufacture, is more robust and less maintenance.

This object is achieved with a piston rod according to claim 1 and a reciprocating compressor according to claim 11. Further advantageous embodiments of the invention are claimed in the subclaims.

The piston rod according to the invention for reciprocating compressors has a base body with a piston-facing end, a piston-remote end and at least one cavity. The piston rod is characterized that the cavity is filled with a solid whose specific thermal conductivity is greater than that of the main body.

Under the piston-facing end of the body is understood to be the end of the piston rod, which has the smallest distance to the piston when installed in a compressor. The end remote from the piston represents the opposite end of the piston, which is connectable via a connecting portion in particular with a crosshead.

The piston rod may have exactly one cavity which is filled with solids. It is preferred to provide at least two solid cavities.

Compared to piston rods made of a single material can be dissipated by the filling of the cavity in the body with a solid which has a higher specific thermal conductivity compared to the body, the resulting at the contact point between piston rod seal and piston rod heat energy significantly faster from the seal packing area , The forming within the piston rod temperature gradient between the end facing the piston and the end facing away from the piston is thus significantly reduced compared to the prior art. Consequently, the non-piston end has an elevated temperature so that the heat energy can be dissipated more quickly and effectively by convection to the environment. This allows a much more efficient cooling of the seals of the piston rod seal against piston rods of a single material.

Compared to the liquid-cooled piston rods, the piston rods filled with a solid have a significantly simplified construction. Additional peripherals, such as a pump, are not necessary. Even complex connection constructions for liquid transport are eliminated. Thus, the filled with solid piston rods on a significantly reduced production and maintenance costs and a concomitant cost reduction while good cooling of the piston rod.

The piston rod therefore preferably has no cavities for the passage of cooling liquids or internals, such. Pipes, for the passage of coolant. Also, with the exception of vent holes, the piston rod may not have any e.g. chambers filled with air, in particular between the solid and the base body, since such chambers would impair the thermal conductivity of the entire piston rod.

If the piston rod has no internals and / or no chambers in the cavity, the filled with the solid cavity is limited by the body. This means that the solid rests against the base body, whereby the heat energy to be dissipated can be absorbed and discharged directly by the solid. An exception is e.g. Closure means for the cavity, e.g. are arranged in the filling opening for the solid, and optionally provided vents, which are provided on the cavity.

Due to the good cooling of the piston rod and thus also the contact surface, the formation of the transfer film is favorably influenced by tribochemical processes between the sealing rings and the piston rod. Thus, the wear rate decreases, whereby the life of the sealing rings and thus the entire piston compressor is extended.

In an advantageous embodiment of the piston rod, the specific thermal conductivity of the solid is> 75 W / (m · k), particularly preferably> 100 W / (m · k) and in particular> 200 W / (m · k).

The greater the thermal conductivity of the solid and / or the proportion of solids in the entire piston rod, the more effectively and quickly the heat energy transport will be from the higher temperature piston rod region to the lower temperature region. Thus, the piston rod seals can be cooled much more effectively with high thermal conductivity. It is achieved a significantly improved cooling compared to piston rods, which consist of only a homogeneous body.

An advantageous embodiment provides that the solid consists of at least one material selected from the group copper, copper alloy, aluminum, aluminum alloy, silver and silver alloy. The solid may consist of one of the mentioned materials or else of a mixture of the materials.

Both copper, aluminum, silver, and their alloys are each characterized by high thermal conductivity. For example, copper has a thermal conductivity of 400 W / (m · K), aluminum of 235 W / (m · K) and silver of 430 W / (m · K). Due to the relatively high thermal conductivity and the favorable material price, in particular copper or a copper alloy is preferred as a solid.

In addition to the good thermal conductivity, copper, aluminum or silver and their alloys are also characterized by good processability. Thus, the body can be filled quickly, effectively and inexpensively with the respective solids.

In a likewise advantageous embodiment of the piston rod, the base body has at least one cavity, which is filled with the solid, preferably completely. The main body can be prepared in advance independently of the solid and then filled with the desired solid. The thermal properties can thus be adapted to different requirement profiles of the piston rod.

For the filling of the cavity, the solid is preferably melted and poured in the liquid state into the cavity. Alternatively, the solid can also be pressed directly into the cavity. Furthermore, a cavity is advantageous, which extends from the end facing the piston at least partially up to the piston end remote from the base body.

In a piston rod installed in a reciprocating compressor, the piston-facing end is closer to the piston rod seal than the piston-remote end. It is therefore advantageous if the cavity with the solid also begins at this end of the piston rod and extends from there in the direction of the piston-remote end, wherein the cavity does not have to extend completely to this end. The heat energy can be further dissipated from the gasket area the longer this cavity is, which in turn improves the cooling process. It is therefore advantageous if: L _H ≥ 0.3 · L _G , in particular L _H ≥ 0.5 · L _G , where L _H denotes the length of the cavity and L _G denotes the length of the main body. Preferably, L _H ≥ 0.6 · L _G, and more preferably L _H ≥ 0.75 · L _G.

Preferably, the cavity over the entire length L _H filled with the solid. In this case, L _H = L _F , where L _F denotes the length of the solid-filled cavity section. Preferably, L _F ≥ 0.3 L _G , in particular L _F ≥ 0.5 L _G. Preferably, L _F ≥ 0.6 L _G, and more preferably L _F ≥ 0.75 L _G.

Preferably, the length L _{F of} the solid filled cavity portion extends at least the length of the contact portion of the piston rod contacted by the piston rod seal upon reciprocation of the piston rod.

Preferably, the volume of the cavity and thus the volume of the solid at full filling of the cavity is at least 25%, more preferably at least 50% of the volume of the entire piston rod. The volume of the solid is preferably at least 10%, preferably at least 25%, in particular at least 50%, of the volume of the entire piston rod. The more solid contained in the body, the faster the heat is dissipated.

The cavity is in a further advantageous embodiment, a cylindrical cavity, for whose radius R _H preferably applies: R _H ≤ 0.5 · R _G , where R _{G is} the radius of the main body of the piston rod. This relationship of the radii applies to basic bodies with a circular cross-section. Preferably, the cylindrical cavity extends or the cylindrical cavities extend parallel to the longitudinal axis of the piston rod. Other cross sections of cavity and body are also possible.

Piston rods for reciprocating compressors generally have a round cross-section. This cross-section allows optimal distribution of force and load within the piston rod. A cylindrical cavity within this piston rod has no significant influence on these load distributions, so that the mechanical stability of the piston rod is only slightly impaired by the cavity. Furthermore, a cylindrical cavity in the piston rod can be easily realized by, for example, a bore. An advantageous embodiment therefore provides that the cavity is a blind hole.

The blind hole is preferably introduced from the piston-facing end into the piston rod. The bore ends before the end facing away from the piston, so that only one inlet opening into the cavity, but no outlet opening is formed. A cavity, which is formed by a blind hole, can be produced quickly and inexpensively, on the other hand, this cavity can also be easily filled with the solid.

The cavity of the piston rod is closed in a likewise advantageous embodiment of the piston-facing end by means of a connecting pin for the piston. For this closability, for example, a thread is cut in or on the end facing the piston, so that the connection pin can be screwed into or screwed into the piston rod. This embodiment allows for quick assembly of the piston rod to the piston. In addition, the closure of the cavity protects the solid from external environmental influences. In particular, a favored by the high temperatures oxidation is prevented. This could possibly have negative effects on, for example, the thermal conductivity of the solid.

If the main body of the piston rod has a cavity, for example in the form of a blind hole, this cavity is preferably provided in the longitudinal axis of the piston rod.

If the main body of the piston rod has two or more cavities which are each filled with a solid, then these cavities can be filled with the same or with different solids. The cavities preferably extend parallel to one another and / or parallel to the longitudinal axis of the piston rod through the base body. The cavities are preferably arranged on a circle about the longitudinal axis of the base body, preferably evenly distributed.

Two or more cavities within the body have the advantage that they can be arranged closer to the surface of the piston rod, without affecting the stability of the piston rod negative. The closer the solid with its high thermal conductivity is arranged on the surface of the piston rod, the more effectively the heat energy can be dissipated from the temperature-stressed regions. The cavities may be cylindrical and arranged side by side. It is also possible to provide annular cavities which are arranged concentrically. Concentric cavities may also be combined with a cylindrical cavity in the longitudinal axis of the piston rod.

In a further advantageous embodiment of the piston rod, the base body has at least one vent opening. This at least one vent opening is preferably formed as a vent hole and preferably extends from the piston end remote from the cavity completely through the main body of the piston rod to the outside. The vent hole may be arranged parallel or perpendicular to the cavity and / or to the longitudinal axis of the piston rod. By means of this at least one vent opening, the cavity communicates with the surroundings of the piston rod, so that the air in the cavity can escape during the filling process of the solid. The filling process is facilitated.

If the piston rod has two or more cavities, a venting opening is preferably arranged on each cavity.

A vent opening offers the further advantage that the risk of air inclusions during the filling process of the at least one cavity with the solid is greatly reduced. Consequently, the filling process of the cavity simplified, which in turn allows a shorter and more cost-effective production of the piston rod.

In addition to a piston rod, the invention relates to a reciprocating compressor having a piston and a piston cylinder having an unlubricated piston rod seal. This piston compressor is characterized in that the piston is connected to a piston rod according to claim 1.

During operation of the piston compressor, the piston rod seal contacts a contact portion on the piston rod due to the reciprocating motion of the piston rod. Preferably, a solid filled cavity portion extends at least over the contact portion.

Figur 1

eine schematische Darstellung eines Kolbenkompressors im Schnitt mit einem Hohlraum im Grundkörper der Kolbenstange,

Figur 2a

eine schematische Darstellung der Kolbenstange mit einem Hohlraum im Schnitt,

Figur 2b

eine schematische Darstellung der Kolbenstange im Schnitt mit einem Hohlraum und Entlüftungslöchern

Figur 3

eine Querschnittsdarstellung der Kolbenstange mit einem Hohlraum,

Figur 4

eine schematische Darstellung eines Kolbenkompressors im Schnitt mit zwei Hohlräumen im Grundkörper der Kolbenstange und

Figur 5

eine schematische Darstellung der Kolbenstange mit zwei Hohlräumen im Schnitt.

Figur 6

eine Querschnittsdarstellung der Kolbenstange mit zwei Hohlräumen

Exemplary embodiments of the invention are explained below with reference to the drawings. Show it:

FIG. 1

a schematic representation of a piston compressor in section with a cavity in the main body of the piston rod,

FIG. 2a

a schematic representation of the piston rod with a cavity in section,

FIG. 2b

a schematic representation of the piston rod in section with a cavity and vent holes

FIG. 3

a cross-sectional view of the piston rod with a cavity,

FIG. 4

a schematic representation of a piston compressor in section with two cavities in the main body of the piston rod and

FIG. 5

a schematic representation of the piston rod with two cavities in section.

FIG. 6

a cross-sectional view of the piston rod with two cavities

The FIG. 1 shows a sectional view of a reciprocating compressor 10. The reciprocating compressor 10 has a cylinder 11 which is closed at a first end 11a and at a second end 11b has an opening 18 for the passage of a piston rod 20.

In the interior of the cylinder 11, a piston 12 is arranged to be movable in the direction of the longitudinal axis L of the compressor 10. The piston 12 has piston seals 17 and a connection pin 15, which connects the piston 12 with the piston rod 20. The connecting pin 15 extends through the piston 12 and is connected to the piston 12 with a first end 15a. With a second end 15 b of the connecting pin 15 is fixed to the piston rod 20.

The piston rod 20 has a piston-facing end 20a and a piston-remote end 20b, wherein the piston-facing end 20a is connected to the connecting pin 15. The piston rod 20 has a base body 21 made of a steel material with a connecting portion 22 to which a crosshead (not shown) can be attached. The main body 21 is partially filled with a solid 26, which has a higher thermal conductivity than the material of the main body 21. For this purpose, the piston rod 20 a cavity 24 which is formed as a blind hole 23 and which is filled with the solid 26.

The main body 21 of the piston rod 20 extends through a piston rod seal 13 which is arranged at the second end 11b of the cylinder 11 and which has a plurality of sealing chambers 13a-f with sealing rings 14 which, for example, consist of PTFE. It is an unlubricated piston rod seal 13, which forms in operation between the sealing rings 14 and the base 21 of the piston rod 20 of the above-explained transfer film.

In the in FIG. 1 As shown, the solid filling extends from the piston-facing end 20a to the connecting portion 22, so that not only the contact portion 28 of the piston rod 20, which is contacted during the reciprocation of the piston rod of the piston rod seal 13, but also the exposed portion of the piston rod 20th between the contact portion 28 and the connecting portion 22 is filled with solid such as copper or a copper alloy. The heat frictionally generated in the contact portion 28 is easily dissipated from the contact portion 28 into the exposed area by means of the solid, where the heat is released to the environment.

In the FIG. 2a is the one in the FIG. 1 contained piston rod 20, which has a length L _G , shown enlarged with the connecting pin 15 in section.

In the main body of the piston rod 20 is the blind hole 23 which is located in the longitudinal axis L of the piston rod 20 and has been introduced from the end 20a facing the piston in the main body 21 of the piston rod 20. The blind bore 23 has the length L _H and extends to the front of the connecting portion 22. With L _F , the length of the cavity 26 filled with solids cavity portion 24 'is designated. Both L _H and L _F are ≥ 0.5 · L _G. The Length L _{F of} the solid-filled cavity portion 24 'extends on both sides of the in FIG. 1 drawn contact portion 28 addition. L _F thus extends at least over the length of the contact portion 28. It is also possible that the blind hole 23 extends into the connecting portion 22.

By means of the cavity opening 27 located at the end facing the piston 20a, the solid 26 is introduced into the cavity 24 formed by the blind bore 23. After filling with solid 26, the cavity opening 27 is closed by means of the connecting pin 15. The cavity 24 is completely filled with the solid 26 except for the area where the connecting pin 15 is arranged. For fastening the connecting pin 15, an internal thread 25 is provided on the inside of the main body 21 of the piston rod 20 at the end 20a facing the piston, and an external thread 16 corresponding to the internal thread 25 is provided on the outside of the second end 15b of the connecting pin 15. By means of this screw connection, the piston rod 20 and the connection pin 15 can be releasably connected to one another.

In the FIG. 2b a piston rod 20 is shown, in addition to the already in FIG. 2a described cavity 24 of the piston rod 20 has a vent opening 29a. This vent opening 29a is formed as a vent hole and facilitates the filling of the cavity 24 with the solid 26, since the excess air can escape from the cavity 24 through this vent hole. Preferably, the vent bore extends parallel to the longitudinal axis L and in particular on the longitudinal axis L from the end of the cavity 24 to the piston end facing away from the piston rod 20. In the illustration shown here is also in the vent bore of the solid 26th

In the FIG. 3 is a section along the line AA through the in FIG. 2a shown piston rod 20 which has a cylindrical base body 21. With R _H1 , the radius of the blind hole 23 and thus the radius of the cavity 24 is referred to. R _G is the radius of the cylindrical body 21, where R _H1 > 0.5 · R _G.

The main body 21 may also other cross-sections such. B. rectangular or oval. Also, a plurality of blind holes 23 can be introduced into the main body 21, which are filled with solid 26.

In the FIG. 4 is like in the FIG. 1 a piston compressor 10 is shown. Unlike the FIG. 1 has the piston rod 20 of the FIG. 4 two cavities 24, which are each filled with a solid 26. Furthermore, a vent 29b is arranged in each case at the piston end remote from the cavities 24. These vent openings 29b preferably extend perpendicular to the longitudinal axis L through the main body 21 of the piston rod 20th

All other features are identical to FIG. 1 , so at this point to the description of the FIG. 1 should be referenced.

In the FIG. 5 is the piston rod 20, which has a length L _G , with the connecting pin 15 in section, similar to FIG. 2 represented.

In contrast to the piston rod 20 off FIG. 2 are in the main body of the piston rod 20 of the FIG. 5 two cavities 24 in the form of blind holes 23, which have been introduced from the piston-facing end 20a in the main body 21 of the piston rod 20. The blind holes 23 each have the length L _H and extend parallel to each other to the front of the connecting portion 22. The solid-filled cavity portion 24 ' of the cavity 24 has a length L _F. It is also possible for the blind bores 23 to extend into the connecting section 22. In addition, the lengths of the two blind holes 23 may be the same or different. At the ends of the cavities 24 facing away from the piston, in each case at least one ventilation opening 29b is arranged in the form of a ventilation bore. These extend, as already in connection with the FIG. 4 has been explained, preferably from the cavity 24 perpendicular to the longitudinal axis L completely through the main body 21 of the piston rod 20. The vent holes contain no solids 26th

By means of the cavity opening 27 located at the end facing the piston 20a, the solid 26 is introduced into the cavities 24 formed by the blind bores 23. Through the vent openings 29 b, the excess air can escape from the cavities 24. In this case, each cavity 24 can be filled with the same but also with different solids 26. After filling with solid 26, the cavity opening 27 is closed by means of the connecting pin 15. For this purpose, on the inside of the main body 21 of the piston rod 20 at its piston-facing end 20a also an internal thread 25 and on the outside of the second end 15b of the connecting pin 15 to the internal thread 25 corresponding external thread 16 is provided. By means of this screw connection, the piston rod 20 and the connection pin 15 can be releasably connected to one another.

In the FIG. 6 is a section along the line BB through the in FIG. 5 shown piston rod 20 which has a cylindrical base body 21. The two cavities 24 are arranged off-center and close to the surface of the main body 21. With R _{H2 in} each case the radius of the cavities 24 and thus the radius of the blind holes 23 is designated. This radius may be identical or different for each blind hole 23. R _G is the radius of the cylindrical basic body 21, wherein in the case where the radii R _{H2 of} the blind bores 23 are equal: 2 · R _H2 > 0.5 · R _G.

However, if the blind-hole bores 23 have different radii R _H2 , the following applies preferably: the sum of the radii R _H2 > 0.5 R _G.

The main body 21 may also other cross-sections such. B. rectangular or oval.

LIST OF REFERENCE NUMBERS

10

piston compressor

11a

first cylinder end

11b

second cylinder end

11

Cylinder of the reciprocating compressor

12

piston

13

Piston rod seal

13a-13f

seal chamber

14

sealing ring

15

connection thread

15a

first connection spigot end

15b

second connection spigot end

16

External thread of the connecting pin

17

piston seal

18

opening

20

piston rod

20a

piston-facing end

20b

butt-end

21

Basic body of the piston rod

22

connecting portion

23

Blind hole

24

cavity

24 '

filled with solids cavity section

25

inner thread

26

solid fuel

27

cavity opening

28

Contact section

29a

vent hole

29b

vent hole

L

longitudinal axis

A-A

Cutting plane through the piston rod

B-B

Cutting plane through the piston rod

L _G

Length of the main body

L _H

Length of the cavity

L _F

Length of solid-filled cavity section

R _G

Radius of the body

R _H1

Radius of the cavity

R _H2

Radius of the cavity

Claims (12)

1. Piston rod (20) for piston compressors, wherein the piston rod (20) has a base member (21) having an end (20a) facing the piston and an end (20b) facing away from the piston, wherein the base member (21) has at least one hollow space (24),
   characterised in that
   the hollow space (24) is filled with a solid material (26) whose specific thermal conductivity is greater than that of the material of the base member (21).
2. Piston rod (20) according to claim 1, characterised in that the specific thermal conductivity of the solid material (26) is > 75 W/(m-k).
3. Piston rod (20) according to either claim 1 or claim 2, characterised in that the solid material (26) comprises at least one material selected from the group consisting of copper, copper alloy, aluminium, aluminium alloy, silver and silver alloy.
4. Piston rod (20) according to any one of claims 1 to 3, characterised in that the hollow space (24) which is filled with solid material (26) extends from the end (20a) facing the piston at least partially as far as the end (20b) of the base member (21) facing away from the piston.
5. Piston rod (20) according to any one of claims 1 to 4, characterised in that the hollow space (24) filled with solid material extends from the end (20a) facing the piston with a length L_H in the direction of the end (E20b) facing away from the piston, wherein there applies: L_H ≥ 0.5 L_G, wherein L_G is the length of the base member (21).
6. Piston rod (20) according to any one of claims 1 to 5, characterised in that the volume of the hollow space (24) is at least 25% of the entire volume of the piston rod (20).
7. Piston rod (20) according to any one of claims 1 to 6, characterised in that the volume of the solid material (26) is at least 10% of the entire volume of the piston rod (20).
8. Piston rod (20) according to any one of claims 1 to 7, characterised in that the hollow space (24) is a blind hole (23).
9. Piston rod (20) according to any one of claims 1 to 8, characterised in that the hollow space (24) can be closed at the end (20a) facing the piston by means of a connection pin (15) for a piston (12).
10. Piston rod (20) according to any one of claims 1 to 9, characterised in that the base member (21) has at least one ventilation opening (29a, b).
11. Piston compressor (10) having a piston (12) and a piston cylinder (11) which has a non-lubricated piston rod seal (13),
    characterised in that
    the piston (12) is connected to a piston rod (20) according to claim 1.
12. Piston compressor according to claim 11 having a piston rod seal (13) which during operation of the piston compressor contacts a contact portion (28) on the piston rod (20),
    characterised in that
    a hollow space portion (24') of the hollow space (24) which is filled with solid material extends at least over the contact portion (28).

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