Gear pump having bearings with cooling ducts

The invention relates to a gear pump according to the preamble of claim

1

.

In gear pumps of the generic type, the temperature of the bearing is of decisive importance for the maximally admissible speed and thus for the throughput of the pump. Plain bearings being customarily lubricated by the pumping medium, high energy feed is occasioned in the bearing clearance in the case of highly viscous pumping media. Since the pumping medium has a maximally admissible maximum temperature, the speed and thus the throughput of the gear pump are limited. This is of special importance when the pumping medium is plastic melt, the maximally admissible temperatures of which range from 300 to 350° C.

EP 0 715 078 A2 describes a gear pump of the generic type which has cooling ducts meandering in the plain bearing.

EP 0 607 999 B1 teaches to provide the shaft of the gear rotors with cooling ducts.

The invention is based on the knowledge that the development of heat in the plain bearing varies along the circumference thereof and over the extension thereof in the direction of the central longitudinal axis.

It is an object of the invention to embody a gear pump of the generic type for optimal heat removal in the plain bearing.

Customarily, the highest energy feed is occasioned at the place of most reduced bearing clearance i.e., the clearance between the bearing section of the shaft and the area of the bearing shell called plain bearing; this is the place of maximum shearing of the highly viscous pumping medium. This is where mechanical energy is converted into heat energy to an especially high degree. Very thorough cooling is required in this area.

The sub-claims reflect numerous advantageous and partially inventive embodiments.

Further features, advantages and details of the invention will become apparent from the ensuing description of exemplary embodiments, taken in conjunction with the drawing, in which

FIG. 1

is a cross-sectional view of a gear pump on the line I—I of

FIG. 2

;

FIG. 2

is a cross-sectional view of the gear pump on the line

11

—

11

of

FIG. 1

;

FIG. 3

is a plan view of a first embodiment of plain bearings in accordance with the arrow III of

FIG. 2

;

FIG. 4

is a longitudinal sectional view of the plain bearing on the line IV—IV of

FIG. 3

;

FIG. 5

is an illustration, corresponding to

FIG. 3

, of a plan view of a second embodiment of plain bearings;

FIG. 6

is a plan view, corresponding to

FIG. 3

, of a third embodiment of plain bearings;

FIG. 7

is a plan view, corresponding to

FIG. 3

, of a fourth embodiment of plain bearings;

FIG. 8

is a plan view, corresponding to

FIG. 3

, of a fifth embodiment of plain bearings;

FIG. 9

is a perspective view of a sixth embodiment of plain bearings;

FIG. 10

is a perspective view of a seventh embodiment of plain bearings;

FIG. 11

is a cross-sectional view of the plain bearing on the line XI—XI of

FIG. 10

; and

FIG. 12

is a perspective view of an eighth embodiment of a plain bearing.

The gear pump seen in

FIGS. 1 and 2

comprises a casing

1

with two gear rotors

2

,

3

disposed therein. Each rotor

2

,

3

has a serrated section

4

,

5

; the serrated sections

4

,

5

intermesh. Each rotor

2

,

3

further comprises a shaft

8

,

9

, which is coaxial of the central longitudinal axis

6

,

7

of the rotor

2

and

3

and non-rotatably joined to the gear section

4

and

5

and one end of which is provided with a driving journal

10

.

On both sides of the serrated sections

4

,

5

, plain bearings

11

,

12

,

13

,

14

are disposed and supported in the casing

1

, with the shafts

8

,

9

being rotatably lodged therein by bearing sections

15

,

16

,

17

,

18

. The fronts of the casing

1

are closed by two covers

19

,

20

which are releasably fixed by screws

21

(roughly outlined). The shafts

8

,

9

are extended out of the casing through apertures

22

in the covers

19

,

20

. A seal

23

is provided, sealing between the respective shaft

8

,

9

and the aperture

22

.

The plane seen in

FIG. 2

, which is perpendicular to the plane spanned by the two axes

6

,

7

, includes the suction side

24

of the pump to one side of the rotors

2

,

3

; the delivery side

25

is on the opposite side. In accordance with the arrows

26

,

27

of rotary direction, the rotors

2

,

3

are actuated in opposite senses; their serrations

28

,

29

rotate nearly without play towards the inside wall

30

of the casing

1

. They convey the fluid that is to be pumped from the suction side

24

to the delivery side

25

, corresponding to the arrow of conveying direction

31

.

The casing

1

comprises conduits

33

for a temperature-regulating fluid. The plain bearings

11

to

14

are lubricated by the pumping medium, as a rule a more highly viscous or intrinsically viscous pumping medium such as plastic melt. To this end, pumping-medium branch conduits

34

discharge on the delivery side

25

of the pump, leading to the plain bearing clearance or clearances

35

that are parallel to the respective axis

6

or

7

, where the pumping medium conventionally serves for lubrication between the respective bearing section

15

to

18

of the shaft

8

and

9

and the respective plain bearing

11

to

14

. From the plain bearings

11

to

14

, the pumping medium is returned, via pumping-medium-return conduits

36

, to the suction side

24

; part of the return conduits

36

are formed in the respective cover

19

,

20

and part of them in the casing

1

. Consequently, the pumping medium flows through the plain bearings

11

to

14

in accordance with the arrow of flow direction

37

from the delivery side

25

to the suction side

24

of the pump.

The plain bearings

11

to

14

are cooled. To this end, each cover

19

and

20

comprises a coolant supply conduit

38

which is connected to one or several cooling ducts

39

in the plain bearing

13

and

14

. Formed in each cover

19

,

20

between the shafts

9

,

8

is an overflow duct

40

which is connected to corresponding cooling ducts

39

in the plain bearing

11

,

12

. The coolant flows from the cooling duct

39

of the plain bearings

11

,

12

through a coolant discharge duct

41

. Consequently, the coolant flows in the flow direction

42

through the ducts.

The following is a description of various embodiments of cooling ducts

39

. Since the design is identical or mirror-symmetrical in the individual plain bearings

11

to

14

, the ensuing description of design and arrangement only deals with a plain bearing

12

.

In the embodiment according to

FIGS. 3 and 4

, the plain bearings

12

a

,

14

a

have continuous cooling ducts

39

a

of identical cross-sectional shape which meander in parallel to the axis

6

and

7

, but which vary in distribution along the periphery of the plain bearing

12

a

,

14

a

. As seen in

FIG. 3

, the plain bearings have an area

43

where the cooling ducts

39

a

are comparatively closely packed. Consequently, heat removal from the plain bearing is considerably greater in this area than in the other areas where neighboring cooling ducts

39

a

have a greater distance from each other. The heat-removing surface of the cooling ducts

39

a

per peripheral unit i.e., per unit angle a, is greater in the area

43

than in the other circumferential areas.

In another embodiment according to

FIG. 5

, the cooling ducts

39

b

also meander as roughly outlined in FIG.

4

. However, they have heat-exchanging surfaces of varying size per peripheral unit i.e., per unit angle a, distributed along the periphery. Consequently, the cooling ducts

39

b

have varying cross-sectional shapes. These may be a cooling duct

39

b

′ of cylindrical cross-sectional shape, or a cooling duct

39

b

″″ of oval or reniform cross-sectional shape, a cooling duct

39

b

′″ having the cross-section of a spline, or a cooling duct

39

b

″″ of square cross-sectional shape. These cooling ducts

39

b

have heat-exchanging surfaces that deviate in shape and/or size.

In the embodiment according to

FIG. 6

, cooling ducts

39

a

are formed in the plain bearings

12

c

,

14

c

, which meander as in the embodiment according to FIG.

4

. In the area of comparatively low energy feed, provision is made for cooling ducts

39

c

with surfaces of varying design by which to influence the heat transmission, per unit area of the cooling duct

39

c

, from the plain bearing

12

c

and

14

c

to the coolant. This may be varying surface roughness affecting the heat transmission coefficients. It is also conceivable to use materials that differ in heat transmission. An insulating bush

44

has been inserted in a cooling duct

39

c

′, which is a solid material bush. An insulating bush

45

has been inserted in a cooling duct

39

c

′, with some clearance

46

formed between the bush

45

and the material of the plain bearing

14

c.

In the embodiment according to

FIG. 7

, cooling ducts

39

a

are formed in the plain bearings

12

d

and

14

d

, which meander as in the embodiment of FIG.

4

. Some of the cooling ducts

39

d

′ have an insulator

47

along part of their circumference on the side turned away from the axis

6

and

7

, so that excellent heat removal takes place from the area of the shaft

8

,

9

, whereas only reduced heat removal or feed will take place from the outer area of the plain bearing i.e., from the casing

1

.

In the exemplary embodiment of

FIG. 8

, provision is made for two meandering cooling ducts

39

e

′ and

39

e

″ in the plain bearing

12

e

,

14

e

. Coolant is separately supplied to these cooling ducts

39

e

′ and

39

e

″; the coolant supplied may differ and have varying thermal capacity. It flows through the cooling ducts

39

e

′,

39

e

″ in the flow direction

42

e

′ and

42

e

″. The coolants, which are supplied through the two cooling ducts

39

e

′ and

39

e

″, can be regulated or controlled individually in temperature and/or in quantity per unit of time.

In keeping with

FIG. 9

, cooling ducts

39

f

may be arranged not only serially i.e., successively—as in the above exemplary embodiments—but coolant flow may take place also in a parallel arrangement. In this case, cooling ducts

39

f

of identical flow direction

42

f

are formed in the plain bearing

12

f

. Junction ducts

48

and

49

are formed in the vicinity of the two ends of a plain bearing

12

f

. A return duct

50

leads back to the junction duct

49

, where the coolant is collected after passage through the cooling ducts

39

f

, for connection to the overflow duct

40

or the discharge duct

41

. In this case too, the cooling ducts

39

f

may of course have the shapes and arrangements as defined in the embodiments of

FIGS. 3

to

8

.

In the embodiment according to

FIGS. 10 and 11

, the plain bearing

12

g

is of two-piece design; it includes an interior bearing bush

51

and an exterior bush

52

, between which is formed an annular cylindrical cooling duct

39

g

, which is divided by a dividing wall

53

that is parallel to the axis

6

so that the cooling is forcibly guided in the flow direction

42

g

through the cooling duct

39

g

and discharged in the flow direction

42

″″. For heat supply i.e., the supply of energy, from the side of the casing

1

to be reduced, the exterior bush

52

is lined with an insulating jacket

54

. Correspondingly, there is disproportionate heat removal from the shaft

8

.

The embodiment of FIG.

12

—as the embodiment of FIGS.

10

and

11

—is a so-called wet bearing bush. The plain bearing

12

h

is configured of an exterior bush

52

′ and an interior bearing bush

51

′. Provided in the exterior bush

52

′ are helical cooling ducts

39

h

′ and

39

h

″ which form separate cooling circuits. Coolants are supplied thereto in the flow direction

42

h

′ and

42

h

″, which vary in temperature and/or quantity per unit of time.

Although the above embodiments predominantly describe designs of plain bearings in which the cooling ducts

39

of the two plain bearings

11

,

13

and

12

,

14

on one side of the rotors

2

,

3

are connected in series, it is of course possible that coolant flow is fed to the individual cooling ducts separately or in parallel. In this case, the overflow duct

40

is for instance replaced by a coolant discharge or supply line.