Patent Application
20130202473
The invention relates to a twin screw pump of double-flow design with a pump housing, which has a pump portion, two bearing portions and at least one gear portion with at least one gear chamber, the bearing portions and the pump portion being formed separately from one another, with a conveyor housing part as a component of the pump portion, in which feed screws with double-flow flanks arranged on two shafts are provided, the feed screws on the shafts having a root diameter, the shafts being mounted on either side in the bearing portions via bearings (external bearing), a seal for sealing the bearing portion with respect to the conveying portion being provided in the bearing portion, and the shafts extending at least on one side into the gear portion, with gearwheels arranged on the shafts in the gear portion, the shafts being rotatably coupled by means of said gearwheels.
Such a pump is known from DE 43 16 735 A1. For manufacturing reasons, such externally mounted double-flow twin screw pumps are structured such that the root diameter of the feed screw is greater than the seal diameter and that this in turn is greater than the inner diameter of the external bearing. Accordingly, the shaft is graduated such that the diameter beneath the external bearings is much smaller than the diameter in the centre of the shaft. The reason for this is that, for assembly of the feed screws and the axial face seals, these have to be slid over the bearing point and this can only be done easily with this structure.
A disadvantage of this structure is that the shaft has a much lower section modulus in the region of the bearing than in the centre of the shaft. This has a detrimental effect on the deflection of the shaft when under load/in operation and limits the permissible pressure difference during use of the pump since contact between the feed screw and the pump housing has to be avoided.
The object of the invention is therefore to improve the construction of the pump so that this limitation is eliminated.
The object according to the invention is achieved in that on either side the inner diameter of the seal is greater than, or the same size as, the root diameter of the feed screws, and/or in that on either side the inner diameter of the bearing is greater than, or the same size as, the inner diameter of the seal. As a result, the shaft has a greater section modulus in the region of the bearing than in the centre, thus reducing/preventing deflection of the shaft under load/in operation.
In accordance with a further teaching of the invention, a first bushing is provided on at least one shaft side, is arranged in the region of the seal, and has an outer diameter that corresponds to the inner diameter of the seal. In accordance with a further teaching of the invention, a bushing is provided on at least one shaft side, is arranged in the region of the bearing, and has an outer diameter that corresponds to the inner diameter of the bearing. As a result of the provision of a bushing, the inner diameter of the seal and of the bearing can be enlarged particularly easily and simple assembly can be ensured at the same time.
In accordance with a further teaching of the invention, the shaft has an outer diameter in the region of the bushing that is smaller than, or the same size as, the root diameter and/or as the inner diameter of the seal. The shafts can thus be installed particularly easily and the result provided by the solution according to the invention can be achieved.
In accordance with a further teaching of the invention, a hydraulic separation is provided between the pump portion and the bearing portion, preferably via an axial face seal, and/or there is a spatial separation between the bearing portion and the gear portion.
In accordance with a further teaching of the invention, the shaft is operatively connected to this arranged fastening element to produce a retentive connection between the shaft and the gearwheel, wherein the fastening element and the gearwheel have corresponding bores, via which a retentive connection can be produced between the gearwheel and the fastening element via a locking element. In this case the bores in the fastening element are preferably formed so that the gearwheel and the fastening element (and therefore the shaft) are rotatable relative to one another, such that a spacing can be adjusted between the flanks of the feed screws (the flank play of the feed screws). It is also advantageous if the fastening element has a bushing portion for sliding onto the shaft, wherein the bushing portion preferably has a receiving portion for the gearwheel, and/or wherein the shaft and the bushing portion have a groove for receiving a feather key to produce a rotationally operative connection between the shaft and the fastening element.
In this case it is also preferable for the bores in the fastening element to be provided as a radial slot, in which the locking element is radially displaceable in the inserted, yet unlocked state, and for the radial length of the slot to be provided such that the end points thereof coincide at least with the contact points between the flanks of the feed screws.
Maintenance and adjustability of the screw pump are improved in this case since it is possible to adjust the entire flank play of the feed screws by means of the provision of the slot. Previously, it was necessary in this instance for the gearwheel to possibly be removed from the shaft and then refitted in a rotated manner so as to adequately adjust the flank play. This adjustment effort is thus reduced considerably.
In accordance with a further teaching of the invention, the fastening element with the slots is only provided on one shaft. This takes into account the fact that it has been found that it is sufficient to adjust merely one shaft, whilst the other shaft remains assembled.
In accordance with a further teaching of the invention, the radial length of the slots is longer than the radial spacing of the contact points of the flanks of the feed screws. It is thus possible to compensate for any one-sided wear of the flanks by corresponding movement beyond the original end points.
In accordance with a further teaching of the invention, an opening is provided in the gear portion of the pump housing, the opening is provided with a removable cover, the opening is arranged such that the cover is removable when the screw pump is assembled, and the gear chamber can be reached in order to adjust the flank play of the feed screws using the tool necessary for this purpose.
Due to the provision of the opening in the housing, it is possible to considerably reduce the time required to readjust the screw because it is no longer necessary to disassemble the gear housing to expose the gear chamber, and it is also not necessary to disassemble the drive module.
The invention will be explained in greater detail hereinafter on the basis of an exemplary embodiment in conjunction with a drawing, in which:
Furthermore, the screw pump 10 has a driven shaft 15 and a driven shaft 16. A feed screw 17 is arranged on the driven shaft 15, and a feed screw 18 is arranged on the driven shaft 16. The feed screws 17, 18 each have a first screw portion 52 and a second screw portion 53, which are interconnected via a central part 54. The screw portions 52 and the screw portion 53 are each engaged for conveyance. The root diameter 61 is illustrated in the central part. A needle bearing 19 and a roller bearing 20 are provided in the bearing portion 13 so that the shafts are mounted outside the pump portion 12 in an external bearing. The needle bearing has an inner diameter 63.
In the embodiment according to
Likewise, a seal portion 57 and a bearing portion 58 are provided on the shafts 15, 16 to the left of the first screw portion 52. These are arranged on the respective shaft 15, 16 as a sealing bushing 59 and as a bearing bushing 60.
The root diameter 61 is smaller than the inner diameter 62 of the axial face seal 141. The inner diameter 63 of the needle bearing 19 is greater than the inner diameter 62 of the axial face seal 141. The outer diameter of the sealing bushing 57 and of the sealing portion 55 in this case correspond substantially to the inner diameter 62 of the axial face seal 141. The outer diameter of the bearing bushing 58 and of the bearing portion 56 in this case correspond substantially to the inner diameter 63 of the needle bearing 19. The shaft is tapered (not illustrated) to receive the bushings 57, 58.
The shaft ends 22, 23 are located in the gear chamber 21 (see
A fastening element 27 is arranged on the driven shaft 16 on the shaft end 23 (see
A plan view of the gear portion 14 without an assembled cover (not illustrated) over the opening 42 is illustrated in
If it is necessary to readjust the flank play, as a result of maintenance works on the axial face seals for example, due to wear, or because the feed screws 17, 18 are being replaced, it is possible to access the gear chamber 21 through the opening 42 with a tool (not illustrated) by removing the cover (not illustrated). For example, it is possible to loosen the hexagon screws 38 so as to rotate the driven shaft 16 relative to the gearwheel 26 and therefore readjust the flank play. Once the flank play has been adjusted, the hexagon screws 38 are then tightened again and the cover 43 is made operational again on the planar portion 50 with the fastening screws by introducing the fastening screws into the bore 51.
It is therefore no longer necessary to remove the drive units 49 and/or the gear portion 14 of the housing 11. As a result of the slots 41, it is also no longer necessary to remove the gearwheel 26 from the shaft 16, which is a complex process, in order to then adjust the flank play in a complex manner by turning the gearwheel 26 accordingly over a segment of a circle until the next bore 36 is aligned, and then fitting the gearwheel 26 back onto the shaft 16.
| Number | Date | Country | Kind |
|---|---|---|---|
| DE 202012000893.5 | Jan 2012 | DE | national |
| DE 202012000894.3 | Jan 2012 | DE | national |
| DE 102012005949.3 | Mar 2012 | DE | national |
