JPH0246795B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a transport pump for transporting polymer melt from a low-pressure suction zone to a high-pressure discharge zone.

Here, the transport pump is used to transport melt during the production and processing of thermoplastics.
Transport pump for high viscosity media used at high back pressures of over 300 bar. Such transport pumps can be used in particular for polyamides, polyethylene terephthalate, polypropylene, polystyrene. (For example, “Chemifasern” 1980 No. 9
edition, p. 670).

BACKGROUND OF THE INVENTION Such transport pumps are preferably gear pumps. In these transport pumps, there are particular problems with sealing the journal that connects the drive motor. For this purpose, sealing fluids are already used which are introduced into the housing of the stuffing box under high pressure. However, this only reduces leakage within the confines of the seal. This is because in order to create a pressure drop from the pump chamber to the outside, the pressure of the sealing liquid must be lower than the pressure of the thermoplastic melt.

This leakage is quantitatively insignificant. However, this becomes a problem if the melt cools and solidifies, or if the flowing melt decomposes and causes high wear on the bearings and packings.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sealing device for a journal on the drive side of a transport pump for molten polymer, especially a gear pump, in which melt for bearing lubrication leaks along the journal and decomposes or solidifies. The object of the present invention is to provide a device that can avoid increased wear on bearings and packings.

Means for Solving the Problems According to the present invention, which solves this problem, a sealing device for sealing the journal of the drive shaft with a sealing liquid under pressure is provided, and the drive shaft of the drive gear is sealed. , between its end face and the mechanical seal of the sealing device, are surrounded by two annular zones adjacent to each other, the first zone facing towards the end face of the drive gear being connected to the pump. A second zone as a pressure relief zone connected to the discharge side and directed towards the mechanical packing is connected to the suction side of the pump via a pressure relief passage, and the pressure relief zone is connected to the suction side of the pump, and is connected to the suction side of the pump. and are connected to each other by an annular leakage gap.

Operation and Advantages According to an arrangement of the invention, the polymer melt under high pressure on the discharge side of the pump is forced into the annular bearing zone of the journal to lubricate the bearing. This polymer melt is divided in the condensation section and moves towards the pressure relief zone as the pressure drops. A small amount of leakage melt that occurs between the gear end wall and the housing wall also moves towards the discharge zone. An annular leakage gap formed between the bearing zone and the discharge zone (e.g. formed on the outer circumference of a stepped journal or between the shoulder of the journal and the nozzle ring) always produces a small amount of leakage. This small amount of leakage is then channeled back to the suction side of the pump. This ensures that the melt discharged from the pump housing is always coupled in the bearing region and does not accumulate in the flow dead zone and break up.

As claimed in claim 3, by limiting the "leakage gap" by means of a nozzle ring inserted between the plain bearing casing and the casing cap, a manufacturing-technically simple measure is achieved. is obtained. This means that the leakage gap is very easily constructed within the desired narrow manufacturing tolerances and
Manufactured. When dispensing a different type of polymer melt, especially a polymer melt with a different viscosity, the leakage gap can be changed by changing the size of the leakage gap by replacing the nozzle ring with one of different dimensions. can be adapted to

As such a sealing liquid, tetraethylene glycol is known for polyamide, and butanediol or glycol is known for polyester. It is within the ability of the average chemist to find suitable solvents for other polymers to be transported, especially polypropylene and polystyrene.

The use of a polymer solution as the sealant also has the advantage that possible leakage flows of the polymer melt can no longer cause damage to the seal, since the sealant constantly dissolves small leakage flows. have On the other hand, even if a small amount of sealing liquid enters the pump chamber, it is harmless because the solvent mixes with the thermoplastic melt and dissolves into a homogeneous substance. If the sealing area is depressurized, in particular by connecting it with the suction side of the pump by a passage, the external environment can be contained within the sealing area when using a transport pump for transporting the melt from the reaction vessel. A negative pressure is created, so that, as is proposed as a further advantage, there is a pressure drop from the outside to the inside, with the sealing fluid being under pressure slightly above the suction pressure of the pump.

The sealing fluid is introduced into the packing into the annular chamber between the shaft and the casing, where the shaft is first sealed against the casing of the stuffing box by a physical packing, and the sealing fluid forms behind the packing. Supplied as follows. It is therefore suggested that the packing is advantageously a ground packing, which is known to be durable. A particularity according to the invention is that two mechanical seals, for example gland seals, are provided at a distance from one another. A sealing fluid is placed in the annular chamber created between the seals. Since the gaskets are mutually supported by springs in the annular chamber, both gaskets can be subjected to a spring load in the axial direction from the shaft end. In this case, the filling force is transmitted from one seal to the other by means of an intermediately connected spring.

Preferably, springs with limited spring travel are used. Spring travel limitations are especially important during springs.
This is done by the presence of a pin that is a predetermined dimension shorter than the spring. The use of such a spring has the advantage that the seal is still effective even in the absence of relief of the sealing point provided according to the invention. This failure can occur if the pressure relief channel is blocked, for example by melt solidified therein. In this case, the seal facing the gear comes under high pressure on the high-pressure side of the transport pump and is thereby pushed towards the shaft end. However, in this case the seal can be moved relatively easily against the spring force by the permissible spring travel.

Subsequently, the seal is again firmly tightened and sealed between the seal retainer at the shaft end, the following second seal and the pin limiting the spring travel.

The risk of pressure build-up in the pressure relief zone of the shaft seal can be eliminated by providing a scraper, which may enter there, stagnate, and keep it in motion by scraping off the solidified melt residue. can avoid. Also for the same purpose, the shaft and the holes in the stuffing box casing are arranged eccentrically with respect to each other in the sealing area, so that at the pump mounting point a narrowest gap is formed with a high dynamic pressure downwards, which is particularly effective for deposits. It is also possible to consider the rotation of the melt in the lower part where there is danger.

In this structure, the pressure relief path is arranged on the low pressure side in the upper part of the hole (ie, the location where the eccentricity between the shaft and the hole takes a large value).

Since transport pumps are heated to high temperatures, it is necessary to cool the sealing liquid, on the one hand to protect the seals, and on the other hand to prevent chemical decomposition of the sealing liquid.

The sealing liquid is supplied to the annular chamber from a reservoir communicating with the annular chamber. In this case, the storage tank may be open. If the sealing fluid is under slightly higher pressure, the system may be closed by a reservoir and an annular chamber.

For the cooling of the sealing liquid, it is advantageous to provide a downcomer pipe for supplying the sealing liquid and a riser pipe for removing the sealing liquid in the annular chamber between the seals, and also to avoid temperature differences in the conduit system. Connect in such a way that natural circulation occurs.

Finally, according to the invention, the degree of sealing of the transport pump can be monitored by monitoring the fill level of the reservoir, as long as it is an open system, or by monitoring the system pressure, as long as it is a closed system. Suggested.

Furthermore, if the pressure of the melt in the sealing area increases, the melt flows into the annular chamber containing the solvent;
I would like to add that it should be dissolved here. This results in an increase in the volume of the solvent/polymer mixture, which can be measured directly or by the resulting pressure increase and can be used, for example, to issue an alarm.

Next, the present invention will be described in detail with reference to one embodiment.

In FIG. 1, a gear pump is shown in longitudinal section in order to schematically illustrate its structure. The casing 1 is surrounded by a heating medium chamber 2 . The heating medium is a heated liquid or vapor that condenses on the peripheral wall of the casing 1 and releases its heat of condensation in the process. Gear 3 of the two gears 3 and 4 meshing with each other
is driven by shaft 7. Both gear wheels are mounted non-rotatably on shafts 7 and 8. In the illustrated direction of rotation of the gear, the gear pump transports in the direction of the arrow, so that 5 is the suction side of the pump and 6
is the discharge side of the pump. On the delivery side 6 of the pump, a channel 35 is still connected, which channel is integrally formed in the bearing bush, and will be explained in more detail later in the description of FIG.

The drive shaft 7 projects from the casing and is connected to a drive motor (not shown).

FIGS. 2, 4 and 5 show the plain bearing and the seal of the drive shaft 7 in the area of the drive journal in connection with the drive motor.

In FIG. 2 the gear 3 on the drive shaft 7 is shown. Immediately to the left and right of the gear wheel 3 are plain bearings of the shaft 7 in bearing bushes 10 or bearing caps 10.1. The shafts 7, 8 with the gear wheels 3, 4 are mounted in a bearing cap 10.1 or a bearing bush 10 for receiving axial forces. According to an advantageous embodiment, the bearing bush 10
A nozzle ring 13 is provided between the housing cap 14 and the housing cap 14, which allows a defined and thus defined leakage flow between the plain bearing and the shaft seal. Adjacent to the plain bearing, a pressure relief zone 15 is provided. For illustration, for example
It is stated that the melt under a pressure of 300 bar enters the pressure relief zone 15 (second zone) through a plain bearing. The function of the pressure relief zone 15 is that the pressure relief path 16
The purpose is to relieve the pressure of the leakage flow through the Pressure relief path 1
6 connects the pressure relief zone 15, i.e. the annular gap between the shaft 7 and the casing cap 14, with the suction side 5 of the pump and thus returns the leakage flow from the area of the pressure relief zone 15 to the suction side 5 of the pump. . The pressure of the melt present in the pressure relief zone 15 therefore approximately corresponds to the pressure on the suction side 5 of the pump plus the pressure loss in the pressure relief channel 16. The polymer melt is forced from the pressure side, ie suction side 5, of the pump through a channel 35 into a condensation section 36 of the bearing area.
Nozzle ring 13 and stepped journal 9
A "leakage gap" is formed between the outer peripheral surface of the journal 9 and the shoulder of the journal 9, and the polymer melt flows through this "leakage gap".
The pressure is released into a pressure release path 16 connected to the suction side 5.

The journal 9 of the drive shaft 7 is sealed to the drive motor by a mechanical seal, for example a gland seal. For this reason, the stuffing box casing 12 is placed on the casing cover 14.
(cylindrical body) is placed. In the cylindrical body,
A first mechanical packing 17 (e.g. gland packing) with several packing rings, then an annular shape which is axially pressed by several circumferentially distributed springs 20, the details of which are shown in FIG. There is a chamber 27 and then a second mechanical seal 18 (for example a gland seal) with another seal ring. The packing ring is compressed from the drive side by the packing holder 19, and the filling force is transmitted from the packing 18 to the packing 17 by the spring 20. As is clear from Figure 3,
The spring is mounted between spring ends 22. The spring end 22 has a pin 21 which limits the free travel of the spring and provides a form-locking force transmission if the spring 20 is compressed too strongly.

The annular chamber 27 is connected by a conduit 23 in communication with a reservoir 24 containing sealing liquid, so that the sealing liquid in the annular chamber 27 is only under the pressure of the liquid column, i.e. slightly less than 1 bar. under high pressure, e.g. 1.1 bar. The reservoir 24 has a scale 25 and also a float 26 which closes an electrical contact when a certain liquid level is reached, thereby emitting a signal.

The seal 18 serves to seal the annular chamber 27 filled with sealing liquid against the free end of the journal 9.

Furthermore, in FIG. 2, the natural circulation system of the sealing liquid is shown by broken lines. The circulatory system consists of Patsukin 17 and 1
It consists of a reservoir 24 to which is connected a downcomer pipe 32 leading to an annular chamber 27 between 8 and 8. Annular chamber 27
A riser pipe 31, which again leads to the storage tank 24, is connected almost diametrically opposite to the riser pipe 31. Due to the temperature difference and resulting density difference of the sealing liquid in the riser and downcomer pipes, a natural circulation takes place in the system, the sealing liquid being heated in the annular chamber 27 and containing it in the reservoir 24. Depending on the capacity, it can be cooled to a certain extent.

As already mentioned for the explanation of FIG. 1, the discharge side 6 of the pump is connected to a channel 35 integrated in the bearing bushing, which allows the polymerization melt to be connected under high pressure. It is introduced into the bearing bush 10 or the bearing cap 10.1 through a conduit system and is forced out into an axial groove configured as a contraction section 36, 37. From here, pressure is applied to the annular surfaces 33, 34 of the bearing bush or to the end surfaces of the gear wheel 3. If a symmetrical force is applied at this time, the gear 3 will move between the partition walls in the axial direction,
Avoid getting close to any of the walls. This reduces friction and, with it, the wear and the required driving forces as well. In the gap control system described, an equilibrium state of the gear wheel 3 occurs in the contraction gap due to the pressure loss. That is, when the gear 3 moves from side to side, the pressure loss increases due to the large passage length in the contraction section 37, so that the pressure generated on the annular surface 33 decreases and the gear 3 moves to the equilibrium position again.

Furthermore, the journal 11.1 mounted on the bearing cap 10.1 is beveled.
This slope of the end face 11.2 relative to the reference plane prevents, in particular, stagnation and disintegration of the melt reaching it and creates an additional pressure when the shaft rotates. A pumping action occurs. In response to this pressure increase in the contraction section 37, the annular surface 3
3 must be dimensioned smaller than the annular surface 34.

4 and 5 show in detail the means for preventing the melt in the pressure relief zone 15 (second zone) from collecting in the dead space. A particularly dangerous dead space is the installation location below the pressure relief zone 15. According to FIGS. 4 and 4a, a scraper 29 is provided in the journal 9 within the pressure relief zone to ensure that the melt does not stand still. This may, for example, be a simple mounting spring known as a mechanical element. In FIGS. 5 and 5a, alternatively, the casing cap 14 is connected to the journal 9.
eccentrically surrounded within the pressure relief zone 15,
It is shown that the narrowest gap 30 is formed below. Due to the rotation of the journal 9, a high dynamic pressure is generated in the area of this narrowest gap 30, which contributes to cleaning the narrowest gap 30 and prevents melt settling.

The reference signals in FIGS. 4 and 5 refer to the portion of the transport pump shown in FIG.

Before explaining the operation of the transport pump, it must be pointed out that the sealing liquid used according to the invention is a solvent for the polymer to be transported. A person skilled in the art will be able to describe suitable solvents for each polymer to be transported. Since a transport pump is generally used with only one type of polymer during its lifetime, only one type of sealant is used. In this case, it is particularly advantageous that according to the invention the sealant is not under pressure and therefore leakage of the sealant need not be a concern.

Regarding the compensator 24, it is mentioned that it can also be closed. In this case, the float is converted into a pressure signal generator that emits a signal when a certain permissible pressure is exceeded.

By using a mechanical seal, that is to say a gland seal, a good, adjustable and dirt-proof seal with a long service life is guaranteed. Since the pressure of the melt is relieved in the area of the pressure relief zone 15, no pressure drop of the melt in the direction of the annular chamber 27 occurs. On the other hand, there is a (albeit small) pressure drop in the sealing liquid from the annular chamber 27 in the direction of the pressure relief zone 15, as a result of which
In any event, a small amount of sealing liquid can enter the melt here. This small amount of sealing liquid dissolves and constantly removes any melt residue that may enter the seal 17. This ensures that the gasket is always clean and performs its functions. In particular, it is possible to avoid melt residues decomposing and hardening within the packing, thereby rendering the packing unusable.

Due to melt deposition within the pressure relief zone 15,
If the melt pressure increases in the area of the pressure relief zone 15, in particular due to the blockage of the pressure relief channel 16, small melt residues will enter the annular chamber 27 through the seal 17 and/or the seal 17 will be forced into the spring 20 (the Move to the right against the force shown in Figure 2). In either case, the filling height within the reservoir 24 changes. This change in filling height is
It can be read on the scale 25 and, if the float 26 and the contact 28 or reservoir are closed, it is detected by the pressure signal generator. The emitted signal can give the pump a chance to be deactivated or repaired. However, the pump does not become non-liquid tight in this case either. Rather, the spring stroke of the spring 20 is limited by the pin 21, which ensures that a high filling force is exerted on the seals 17, 18 due to the increased pressure in the relief zone 15. . The sealing action of the seal is thereby adapted to the increased pressure. The pump is operated until the entire plastics manufacturing or processing plant is shut down cyclically or for other reasons.

[Brief explanation of the drawing]

The accompanying drawings show an embodiment of the invention, in which FIG. 1 is a schematic cross-sectional view of a transport pump configured as a gear pump, and FIG. 2 is an axial sectional view showing details of the sealing portion of the drive shaft. , FIG. 3 is a sectional view showing the spring in the mechanical packing part, FIGS. 4 and 4a or 5 and 5a show details of the seal part according to FIG. 2, and FIG. 4a is a cross-sectional view, and FIG. 5 shows a case in which the casing cap encloses the journal eccentrically within the pressure relief zone. FIG. 5a is a cross-sectional view of the axial cross-sectional view. 1... Casing, 2... Heating medium chamber, 3...
Drive gear, 4... Driven gear, 5... Pump suction side, 6... Pump discharge side, 7... Drive shaft, 8
... Driven shaft, 9 ... Journal, 10 ... Bearing bush, 10.1 ... Bearing cap having bearing bush, 11 ... Bearing portion of shaft, 11.1 ... Journal, 11.2 ... Journal Diagonally cut end face, 12... Stuffing box casing, 13... Nozzle ring, 14... Casing cap, 15... Pressure relief zone, 16... Pressure relief path, 17... First mechanical Patsukin, 18...
Second mechanical seal, 19... Seal holder, 20... Spring, 21... Pin, 22... Spring end, 23... Supply pipe, 24... Storage tank, 25... Scale, 26... Float , 27... annular chamber, 28...
... Contact point, 29 ... Cray pass, 30 ... Narrowest gap,
31... Ascending pipe, 32... Descending pipe, 33... Annular surface, 34... Annular surface, 35... Passage, 36... Contraction section, 37... Contraction section.

Claims (1)

[Scope of Claims] 1. A transport pump for transporting a polymer melt from a low pressure suction zone to a high pressure discharge zone, for sealing the journal 9 of the drive shaft 7 with a sealing liquid under pressure. A sealing device is provided, in which the drive shaft 7 of the drive gear 3 is surrounded by two annular zones adjacent to each other between its end face and a mechanical seal 17 of the sealing device, A first zone directed toward the end side of the drive gear 3 is connected to the discharge side 6 of the pump, and a second zone as a pressure relief zone 15 directed toward the mechanical seal 17 is connected to the discharge side 6 of the pump. A transport pump, characterized in that it is connected to the suction side 5 of the pump via a channel 16, and that the discharge side 6 and the suction side 5 are connected to each other by an annular leakage gap. 2. The first zone is configured as a bearing part 11 for the drive shaft 7 and has a constriction section 36 between the end face of the gearwheel and the annular leakage gap; Transport pump according to claim 1, characterized in that the pump is connected to the discharge side (6) via a channel (35). 3. Transport pump according to claim 1, wherein the leakage gap is limited by a nozzle ring 13 inserted between the plain bearing casing 10 and the casing cap 14. 4. The transport pump according to any one of claims 1 to 3, wherein the mechanical packing 17 is configured as a gland packing. 5 An annular chamber 27 for the sealing fluid is arranged in front of the mechanical seal 17 on the drive side; These mechanical seals 17,
5. Transport pump according to claim 4, in which the journal 9 is compressed from the free end thereof and a spring 20 with a limited spring stroke bridges the annular chamber 27. 6. Transport pump according to claim 5, wherein the sealing liquid is under a slightly elevated pressure of at most 0.5 bar above the pressure in the suction zone 5 of the pump. 7. The journal 9 has a scraper 29 in the pressure relief zone 15 that does not touch the casing wall, or the journal 9 is eccentrically surrounded in the pressure relief zone 15 by the casing cap 14 and Also, any one of claims 1 to 6 is surrounded such that the narrowest gap 30 is arranged downward at the mounting position of the transport pump and the pressure relief passage 16 is arranged upward. Transport pumps as described in section. 8. The bearing zone for the journal 11.1 of the drive gear 3 opposite to the journal 9 also has an axis-parallel constriction section 37 in which:
The molten polymer under pressure in the discharge side 6 of the pump reaches through the passage 35, and the two end sides of the drive gear 3 have annular surfaces 33, 34, which annular surfaces The transport pump according to any one of claims 1 to 7, wherein the melt polymer under melt pressure is supplied to the pumps 33 and 34. 9 The annular surface 34 on the drive side end surface of the drive gear 3 loaded with the melted polymer is the drive gear 3
An annular surface 33 on the end surface opposite to the drive side of
9. The transport pump of claim 8, which is larger than the transport pump of claim 8.