DE3135037A1 - Discharge pump - Google Patents

Abstract

The invention relates to the sealing of the shaft journal (9) of a discharge pump, especially a gear pump for molten polymers. Sealing is effected by means of a barrier fluid which according to the invention is a solvent for the polymer and is passed, at a slight positive pressure, into an annular cavity (27) which surrounds the drive-side shaft journal (9) and in an axial direction is bounded on both sides by stuffing-box packings (17, 18) held at a distance by spring elements (20). Owing to this design of the discharge pump, the inevitable leakage of the polymer delivered at high backpressure and high temperature is limited, and solidification, which impairs the sealing effect of the stuffing-box packings (17, 18) and makes them ineffective, is prevented. The barrier fluid can be circulated in a circuit consisting of reservoir (24), down main (32) and rising main (31), and be cooled and monitored at the same time. Further proposals relate to avoiding stagnation of the melt in chambers with reduced melt flow and the pressure relief of the bearing casing (10, 10.1) by a relief duct (16) connected to the suction side (5) of the pump, and by an inverse gap control to reduce friction and wear on the lateral faces of the gear wheels. <IMAGE>

Description

"Discharge pump"

Discharge pump The invention relates to a method for sealing the drive-side shaft journal of a discharge pump for melt liquid polymers, to a method for monitoring the leakage of such discharge pumps and on a discharge pump for molten polymers with a barrier liquid seal claims 1, 3 and 19.

Discharge pumps are feed pumps for highly viscous media that are used in the Production and processing of thermoplastics for conveying the melt at high Counter pressures up to more than 300 bar are used. Such discharge pumps are in particular Can be used for polyamides, polyethylene terephthalate, polypropylene, polystyrene (cf. z. B. Chemical fibers 1980, No. 9, page 670).

Such discharge pumps are preferably gear pumps. A special The problem with these discharge pumps is the sealing of the one connected to the drive motor Shaft journal represents. You have already used barrier fluids for this purpose, which are fed into the stuffing box housing under high pressure. This allows however, only reduce the leakage in the area of the seal, since the pressure of the The sealing liquid must be lower than the pressure of the thermoplastic melt, to allow a pressure gradient to exist from the pump chamber to the outside.

In terms of quantity, this leakage is irrelevant. However, it becomes the Problem when the melt cools and solidifies, or when the leaking The melt cracks and causes increased wear on the bearings and seals.

The solution according to the invention specified in claims 1, ('And 5 this problem provides for a barrier fluidity to seal off the discharge pump which is used, which the polymer to be discharged completely even in the cooled state able to solve. Tetraethylene glycol is known as such a solvent for Polyamide and butanediol or glycol for polyester. It's in the realm of skill one of ordinary skill in the art of chemistry, for other polymers to be dispensed, in particular Polypropylene and polystyrene to find suitable solvents.

The use of a solvent for the polymer as a barrier fluid has the advantage that even the permitted leakage of the polymer melt does not cause any damage the seals can cause more, since the barrier fluid the low leakage flows keeps in solution. On the other hand, it is also harmless if it is low Quantities of the sealing liquid get into the interior of the pump as the solvent mixed with the thermoplastic melt to a homogeneous mass and dissolved will. For this reason it is preferably provided that the sealing area relieves pressure is, preferably in that the sealing area through a channel with the suction side of the pump. When using the discharge pump for discharge the melt from a reactor vessel even result in the sealing area Suppress the external environment, so that there is a pressure gradient from the outside to the outside there is inside if - as further proposed as advantageous - the barrier liquid is under a pressure slightly exceeding the suction pressure of the pump.

The sealing liquid is fed to the seal in such a way that the shaft initially sealed against the stuffing box housing by a mechanical seal is, and that the barrier fluid in the resulting annular space behind the seal is given between the shaft and the housing. The seal was previously designed as a sliding ring. However, it is hereby proposed as preferred that the seal be a robust one well-known stuffing box package is. A special feature of the invention is that that two gland packs are provided at a distance from each other. In between Stuffing box packs result in S, gray becomes the sealing liquid entered. The gland packs are supported against each other in the annular space by springs, so that the two gland packs are axially pretensioned and loaded from the axle end can be. In this case, the stuffing force is interconnected by the Transferring feathers from one package to the other.

Preference is given to using springs with a limited spring deflection, which is particularly important can be achieved in that a pin is located in the springs around a given dimension is shorter than the spring. The use of such springs has the advantage that the seal is still effective when the invention intended pressure relief of the sealing point fails. It can lead to this failure come especially when the pressure relief channel z. B. froze in it Melt is clogged. In this case, the stuffing box packing facing the gear will break under the increased pressure of the high pressure side of the discharge pump and is thereby counteracted pressed the shaft end. However, you can only care about the permitted spring travel move relatively easily against the spring force.

The stuffing box packing is then back between the stuffing flange at the end of the shaft, the following second stuffing box packing and the spring travel limiting pin firmly clamped and thus tight.

The risk of pressure build-up in the relief zone of the shaft seal is reduced by the fact that a scraper is provided there, which Scrapes stagnant and solidifying melt residues and keeps them moving. For the same purpose it can alternatively be provided that in the sealing area the The shaft and the bore of the stuffing box housing are arranged eccentrically to one another, so that - in the installation position of the pump - there is a narrowest gap with an increased one at the bottom dynamic pressure forms, which for a circulation of the melt just in that of Deposits particularly endangered lower area ensures.

With this arrangement, in the upper area of the hole - there, where the eccentricity between the shaft and the bore assumes the greatest value - the relief channel arranged towards the low pressure side.

As the discharge pumps are very heated, it may be necessary to to cool the sealing liquid, on the one hand to protect the packs, on the other hand, to avoid chemical decomposition of the sealing liquid.

The barrier fluid becomes the annulus from one with the annulus communicating reservoir supplied. The storage container can be open If the sealing liquid should be under a slightly higher pressure, can However, the system of storage container and annulus can also be closed.

In order to cool the barrier liquid, it is preferred to use the annular space between the stuffing box packings a downpipe for the supply and a riser pipe for the removal of the barrier fluid connected, in such a way that in the line system natural circulation occurs as a result of a temperature difference.

According to the invention it is finally provided that the tightness of the Discharge pump is monitored by the fact that - if it is an open system is - the level of the storage container or - if it is a closed one System acts - the pressure of the system is monitored. It should be noted that at an increase in the pressure of the melt in the sealing area of the melt in the Exit solvent-containing annular space and will go into solution there. Through this an increase in volume of the solvent-polymer mixture occurs, which can be seen directly or measure via the associated pressure increase and z. B. to generate a Alarm signal ~ usable.

In the following the invention is illustrated by means of an exemplary embodiment described.

1 shows the schematic longitudinal section through a discharge pump designed as a gear pump; 2 shows the sealing area of the drive shaft as a detail in axial section; 3 shows the springs in the area of the stuffing box packings; Fig. 4 8 "and FIG. 4 a shows a detail of the sealing area according to FIG. 2 respectively. Fig. 5 and in each case in axial and cross-section. Fig. 5 a In Fig. 1, the longitudinal section through a gear pump is shown to illustrate its structure. The housing 1 is surrounded by a heating medium chamber 2. The heating means can be a heated liquid or vapors which condense on the walls of the housing 1 and thereby give off their heat of condensation. Of the two intermeshing gears 3 and 4, the gear 3 is driven by the shaft 7. Both gear wheels are rotatably mounted on the shafts 7 and 8, respectively. When the direction of rotation of the gears is shown, the gear pump delivers in the direction of the arrows so that at 5 the suction side of the pump and at 6 the pressure side of the pump. On the pressure side 6 of the pump, a channel 35 is also connected, which is integrated into the bearing bushes and which will be discussed in greater detail later in the description of FIG. 2.

The driven shaft 7 emerges asz the housing and is with a - Not shown - coupled drive motor.

Figures 2, 4 and 5 show in detail the plain bearings and the seal of the drive shaft 7 in the area of the drive journal coupled to the drive motor 9.

In Fig. 2, the gear 3 is shown on the drive shaft 7.

Immediately to the left and right of the gear 3 is the Plain bearing of the shaft 7 in the bearing bush 10 or the bearing cover 10.1. The pinion shafts 7, 8 with the gears 3, 4 are to absorb the axial forces in the bearing cover 10.1 or supported in the bearing housing 10. In the preferred embodiment, between Bearing housing 70 and housing cover 14 a nozzle ring 13 is provided between the Sliding bearing and the shaft seal a gap of a defined width and thus a allows defined leakage flow. The relief zone is attached to the plain bearing 15 at. To explain it should be mentioned that it cannot be avoided so that liquid Melt that under a pressure of z. B.

30u bar, lies in the relief zone 15 through the slide bearing. The function of the relief zone 15 is the pressure relief of the leakage flows through a relief channel 16. The relief channel 16 connects the relief zone 15, i.e. the ring gap between wool 7 and housing cover 14 with suction side 5 the pump and thus leads the leakage flows out of the area of the relief zone 15 back to the inlet side 5 of the pump. The pressure of the in the relief zone 15 located melt corresponds essentially to the pressure on the suction side 5 of the pump plus the pressure loss in the relief channel 16.-The shaft journal 9 of the drive shaft 7 is sealed off from the drive motor by stuffing box packings. For this purpose, the stuffing box housing 12, a tubular body, is on the housing cover 14, set. In it there is a first stuffing box packing 17 with several packing rings, then an annular space 27, which in the axial direction of several - in their details shown in Fig. 3 circumferentially distributed springs 20 bridged and then a second stuffing box packing 18 with further packing rings. By Stuffing flange 19, the gland rings are pressed together from the drive side, the stuffing forces being transferred from pack 18 to pack 17 through springs 20 will. As can be seen from FIG. 3, the springs are clamped between spring heads 22. The spring heads 22 have bolts 21 which limit the free spring travel and if the springs 20 are compressed too much for positive force transmission Take care.

The annular space 27 is connected to a storage container via the line 23 24, which contains the barrier liquid, communicatingly connected, so that the barrier liquid in the annular space 27 only under the pressure of the liquid column, i.e. under the pressure of little more than 1 bar, e.g. B. 1.1 bar. The reservoir 24 has a Measuring scale 25 and also a float 26, which when reaching a certain Liquid level the eiektriech.n contacts 28 closes and thereby a signal generated.

The stuffing box packing 18 serves to seal off the barrier fluid filled annular space 27 opposite the free end of the shaft journal 9.

A natural circulation system is also shown in FIG. 2 with a dashed line indicated for the barrier fluid. It consists of the reservoir 24 to which el ne Falleitung is connected to the annular space 27 between the stop box packs 17 and 18 leads.

Approximately diametrically opposite, a riser 31 is connected to the annular space 27, which leads back to the storage container 24 '. Due to the temperature differences of the Barrier fluid in the rising and falling pipes and the resulting differences in density natural circulation takes place in the system, the barrier fluid being in the annular space 27 heats up and in the storage container 24 - according to its capacity - more or cool down less strongly.

As has already been mentioned in the description of FIG a channel 35 integrated in the bearing bushes connected to the pump back side 6, through the polymer melt under high pressure through the connected pipe system into those arranged in the bearing housing 10 or in the bearing cover 10.1, as throttle sections 36, 37 formed axial grooves is pressed.

From. here the annular surfaces 35 and 34 of the bearing bushes or

alternatively, the end faces of the gear 3 are pressurized, with symmetrical force, the gear 3 between the axial boundary walls "floats" and a tarnish on one of the walls is avoided. This will make the. Friction is reduced and, in connection with this, also the wear and the necessary Drive power. In the described system of gap control, a Equilibrium position of the gear 3 depending on the pressure loss in the Throttle gaps automatically, i.e. when gear 5 is pushed to the right, so the pressure loss increases in the throttle section 37 because of the greater duct length, so that the pressure applied to the annular surface 35 drops and the gear 5 in the Equilibrium position is shifted back.

In addition, it should be noted that the 10.1 mounted shaft journal 11 1 is beveled. Because of this inclination of the face 11.2 in relation to the normal plane a pumping effect arises when the Wt-lle circulates, which in particular prevents stagnation and decomposition of the melt that has reached there and a too: caustic pressure builds up. Corresponding to this pressure increase in the glandular section 57, the annular surface 53 is to be dimensioned smaller than the annular surface 34.

in Figures 4 and 5 measures are shown in detail that prevent that in the relief zone 15 melt collects in dead spaces. Especially as dead space The lower part of the relief zone 15 - in the installation position - is at risk. 4 and Fig. 4 a it is provided that the shaft journal 9 in the area of the relief zone is provided with a scraper 29, which ensures that the melt does not come to a standstill. It can be, for. B. a simple, act as a feather key known as a machine element. In Fig. 5 and Fig. 5a is an alternative Measure provided that the housing cover 14, the shaft journal 9 in the area of Relief zone 15 surrounds eccentrically, so that a narrowest gap 30 is formed below. As a result of the rotation of the shaft journal 9 arises in the area of this narrowest gap 30 an increased dynamic pressure, which contributes to flushing through the narrowest gap 30 and prevents enamel deposits.

For further explanation it should be mentioned that the reference numerals in the figures 4 and 5 relate to the elements of the discharge pump shown in FIG.

Before the function of the discharge pump is described, it is important to note to point out that the sealing liquid used according to the invention is a solvent represents for the polymer to be carried out.

The person skilled in the art can find suitable solvents for each one to be discharged Specify polymers. Since the discharge pump is generally only is used for a single product, only a single blocking agent is used to use. It has a particularly positive effect that according to the invention Locking means under no significant pressure compared to the pump output and therefore no leakage of blocking agent is to be feared.

Regarding the expansion tank 24, it should also be mentioned that this is also closed can be. In this case the float would be replaced by a pressure transducer, which emits a signal when a specified permissible pressure is exceeded.

The use of packing packs ensures that a good, adjustable seal that is insensitive to dirt and has a long seal Service life is guaranteed. Because of the pressure relief of the melt in the area of the Relief zone 15 there is no pressure gradient in the direction of the melt of the annular channel 27. On the other hand, there is an -if also for the Spe.rrriquid only slight - pressure gradient from the annular channel 27 in the direction of the relief zone 15, so that at most small amounts of the barrier liquid get into the melt there can.

These small amounts of the barrier fluid cause that eventually Melt residues that got into the stuffing box packing 17 are loosened and constantly removed wsrden. This ensures that the stuffing box packings are constantly cleaned and kept in function. In particular, it can be avoided that melt residues Crack and harden in the area of the stuffing box packing and thereby the stuffing box packing to make something useless.

If now by melt deposits in the area of the relief zone 15 and in particular the melt pressure due to clogging of the relief channel 16 increases in the area of the relief zone 15, a small amount of melt residue could through the stuffing box packing 17 enter the annular space 27 and / or the stuffing box packing 17 is displaced to the right against the force of the springs 20 (in FIG. 2). In both In cases, the filling level in the storage container 24 changes. This filling level change can be read on the scale 25 and is controlled via float 26 and contacts 28 resp. - If the storage container is closed - detected by a pressure transducer.

The signal generated can give rise to shutdown or repair the pump. Even in this case, however, the pump does not leak. Much more is guaranteed by the fact that the spring travel of the springs? 0 is limited by the bolts 21, that due to the increased pressure in the relief zone 15 also an increased tamping force is exerted on the gland packings 17 and 18. This increases the sealing effect the stuffing box packings adapted to the increased pressure. The pump can remain in operation bit the entire system for plastics production or plastics processing on a regular basis or is taken out of service for other reasons.

REFERENCE SIGNS 1 housing 2 heating medium compartment 3 driven Gear 4 revolving gear 5 inlet side, suction side of the pump 6 outlet side, Pressure side of the pump 7 Drive shaft 8 Output shaft 9 Shaft journal 10 Plain bearing housing, Plain bearing area of shaft 7, bearing bush 10.1 Bearing cover with bearing bush 11 bearing area of the shaft 11.1 shaft journal 11.2 beveled end face of the shaft journal 12 stuffing box housing 13 Nozzle ring 14 Housing cover, housing 15 Relief zone, pressure relief 16 Relief channel, Channel 17 first stuffing box packing 18 second stuffing box packing 19 stuffing flange 20 Spring 21 Bolt, pin 22 Spring head 23 Supply line 24 Storage container 25 Scale 26 swimmer 27 Annular space, annular channel 28 Contact 29 Scraper 30 narrowest Gap 31 Riser in the case of a circulating system for barrier fluid 32 Downpipe 33 Annular area, Annular gap 34 Annular area, annular gap 35 channel 36 channel section, throttle section 37 Canal section, throttle section

Claims (19)

Method for sealing the drive-side shaft journal a discharge pump for molten polymers - such as polyamides, polyester, polypropylene, Polystyrene using a barrier medium, characterized in that as Barrier medium a barrier liquid is used, which is a solvent for the is to be discharged polymers. 2. Use of a solvent which dissolves a certain type of polymer as a barrier liquid for sealing a discharge pump for the polymer, in particular of tetraethylene glycol (TEG) for polyamide and butanediol or glycol for polyester (Polyethylene terephthalate = PETP). 3. Discharge pump for molten polymers, designed as Gear pump, the shaft journal of which, in particular the shaft journal on the drive side, through a sealing liquid which is under slight excess pressure to the outside is, characterized in that in the sealing housing surrounding the shaft journal (9) (12) an annular space (27) is present on which a feed line (2S) for a barrier liquid is connected, through which a solvent for the polymer to be discharged the annular space (27) can be fed under slightly reduced pressure. 4. Discharge pump according to claim 3, characterized in that the annular sealing point - viewed from the gear (3) - one pressure relief zone one after the other (15), a mechanical seal (17) and an annular space (27) with barrier fluid having. 5. Discharge pump according to claim 4, characterized in that one Pressure relief takes place through a channel (16) which forms the pressure relief zone (15) connects to the suction side (5) of the pump. 6. Discharge pump according to claim j and 4, characterized in that the annular space (27) containing the barrier fluid both on the pump side and to the free end of the shaft journal (9) through a mechanical seal (17, 18) is sealed. 7. Discharge pump according to claim 4 or 6, characterized in that the mechanical seal is designed as a stuffing box packing (17, 18). 8. Discharge pump according to claim 7, characterized in that both sides of the annular space (27) containing the sealing liquid, stuffing box packings (17, 18) are arranged, which are pressed together from the free end of the shaft journal (9), springs (20 ') bridging the annular space (27) which receives the barrier fluid. 9. Discharge pump according to claim 8, characterized by springs (20) with limited spring travel in the annular space (27) that receives the barrier fluid (Fig. 3). 10. Discharge pump according to one or more of the preceding claims 5 to 9, characterized in that the pressure of the barrier liquid is slightly preferably a maximum of 0.5 bar above the pressure on the suction side (5) of the discharge pump lies. 11. Discharge pump according to one or more of the preceding claims 4 to 10, characterized in that the shaft journal (9) is in the pressure relief zone (15) has a scraper (29) which does not touch the housing walls (Fig. 4, Fig. 4a). 12. Discharge pump according to one or more of the preceding claims 4 to 10, characterized in that the shaft journal (9) is in the pressure relief zone (15) is eccentrically surrounded by the pump housing (14), preferably in such a way that that the narrowest gap (3o) in the installation position of the discharge pump is below and the relief channel (16) is arranged at the top (Fig. 5, Fig. 5a). 13. Discharge pump, in particular according to one or more of the preceding Claims 5 to 12, characterized in that the shaft end (11.1) opposite the housing axially delimiting the bearing housing (leakage (10.1)) (11.2). 1k. Discharge pump according to one or more of the preceding claims, characterized in that the barrier fluid is connected to the annular space (27) communicating storage container (24) with level monitoring (26, 28) can be supplied is. 15. Discharge pump according to one or more of the preceding claims 4 to 14, characterized in that the barrier liquid can be circulated for cooling is. 16. Discharge pump according to claim 15, characterized in that the Annular space (27) and the storage container (24) through a riser (31) and a Downpipe (32) for generating a gravity cycle caused by a temperature difference (Natural circulation) are interconnected. 17. Discharge pump, in particular according to one or more of the preceding Claims, characterized in that in at least one of the gears (3, 4) from the high pressure side of the pump (channel 35) into an annular gap (35, 54), which in the circumferential area of the two end faces between the housing (1) and the gear (3) 'is gebil det, each via a throttle channel (36, 37) polymer melt under Melt pressure can be supplied. 18. Discharge pump according to claim t7 in conjunction with claim 5, characterized characterized in that the applied with polymer melt annular gap (34) on the the drive-side face of the driven gear (5) is larger than the annular gap (33) on the opposite face of the gear (3). 19. Method for monitoring leakage from discharge pumps for molten liquids Polymers in which the area of the drive-side shaft journal is behind a mechanical Seal is acted upon with a barrier medium via an annular channel, characterized in that that a certain amount of a polymer dissolving barrier liquid under one lower than the pump pressure in the annular channel (27) and the amount of Barrier liquid - with an open system - or the pressure of the barrier liquid - in a closed system - is monitored.