SE519091C2 - Device and process for pumping liquid gas, pumping system for pumping liquid gas and system and process for cyclic production of polymer products - Google Patents

Abstract

A device for pumping liquefied gas, comprises a pump body (3) having a cylindrical bore (5), a piston (15) arranged in the bore of the pump body and axially movable between a front and a back position; a drive means (19, 21) for movement of the piston between the front and back positions. Liquefied gas is flown into the pump chamber as the piston is moved from the front to the back position and is pumped from the pump chamber as the piston is moved from the back to the front position. The pump includes a control means (23) arranged to control (i) the movement of the piston from the front to the back position to be slow enough to substantially avoid boiling of the liquefied gas flown into the pump chamber; and (ii) the movement of the piston from the back to the front position at a variable velocity.

Description

: ynun 10 15 20 25 30 u »o-u- av con: 519 091 2 The problems with boiling, and thereby impaired accuracy and precision of pumped amount of liquid, can also occur for other reasons such as heat transfer between different gas volumes and sudden pressure drops.

For example, EP 0 501 806 A1 discloses a piston pump for continuous pumping of liquid carbon dioxide bar) (at pressures of up to over 500 having a liner with low thermal conductivity arranged along the inner surfaces of the pump cylinder to prevent heat arising from compression of the liquid the heat is transferred to the pump cylinder.The heat remains in the carbon dioxide, which is pumped out and leaves the pump during compression.When the subsequent pumping cycle is initiated, the newly ingested carbon dioxide is not exposed to any retained heat and thereby remains in liquid form.

If the pressure at the carbon dioxide source is 60-70 bar, it is mentioned that there is still a risk of boiling because the carbon dioxide at this pressure is close to the boiling point. This problem is solved by using a cooler.

Another way to avoid boiling carbon dioxide in the pump cylinder involves circulating a cooling medium, for example liquefied gas, cooling water, see e.g. U.S. Patents 2,439,957 and 2,439,958. or glycol, around the cylinder to cool it, These ways of avoiding boiling of carbon dioxide in the pump cylinder are and / or Furthermore, they do not solve the above-mentioned problems with the pump even for unnecessarily complicated, space-consuming expensive. discontinuous use consumes energy continuously.

OBJECTS OF THE INVENTION It is thus an object of the present invention to provide an apparatus and method for pumping an accurate and precisely controllable amount of liquefied gas which is absent from at least some of the problems associated with the prior art. nn-'u | »,.> 10 15 20 ø n a u; Another object of the invention is to provide an apparatus and method for pumping an accurate and precisely controllable amount of liquefied gas, wherein boiling of the liquefied gas is substantially avoided.

A further object of the invention is to provide an apparatus and method for discontinuous pumping of an accurate and precisely controllable amount of liquefied gas.

A further object of the invention is to provide an apparatus and a method for pumping an accurate and precisely controllable amount of liquefied gas, where the pump speed is variably controllable under a single piston stroke.

A further object of the invention is to provide a system and method for producing polymer products comprising said device and method for pumping liquefied gas, respectively.

These and other objects are achieved according to the invention by an apparatus and a method according to the appended claims.

An advantage of the invention is that the amount of liquid gas pumped during a piston stroke is accurately and precisely controllable, whereby the pump speed can also be changed during the piston stroke itself.

More advantages of the invention, and features thereof, appear in the following description.

DESCRIPTION OF THE FIGURES The invention is described in more detail below with reference to Figures 1-5, which are shown only to illustrate the invention and should therefore not in any way limit it.

Fig. 1 schematically shows, in cross section, a device for pumping liquefied gas according to an embodiment of the present invention. Fig. 2 schematically shows a block diagram of a system for producing polymer products, the system comprising the device for pumping liquefied gas shown in Fig. 1.

Figs. 3a-c are diagrams, sonx showing typical values in arbitrary units for pumped amount of liquefied gas per unit time as a function of the time of the pump device shown in Fig. 2 (solid curves).

Fig. 3c also shows typical values for the amount of plasticized polymer fed per unit time as a function of the time for the polymer product production system shown in Fig. 2 (dashed curve).

Fig. 4 schematically shows, in cross section, a device for pumping liquefied gas according to a further embodiment of the present invention.

Fig. 5 is a diagram showing typical values in arbitrary units for pumped amount of liquefied gas per unit time as a function of the time for the device shown in Fig. 1 (solid curve) and for the device shown in Fig. 4 (dashed curve).

PREFERRED EMBODIMENTS In the following description, for the purpose of explaining and not limiting the invention, specific details are set forth such as particular applications, techniques, etc., to provide a clear understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be embodied in other forms than these.

The invention will now be described in more detail with reference to Fig. 1, which shows in schematic cross-section a first embodiment of a pump 1 according to the present invention. pump body or cylinder 3 with one constitutes The pump comprises a cylindrical hole 5, The pump camshaft is like a pump chamber. which is connected to a source Fig. 1). liquid provided with an inlet 7, liquid CO2 (not The source may be a carbon dioxide for shown in conventional gas cylinder with Vid - uu a .. u. 10 15 20 25 30 uo ø u | o - Q us now 519 091 5 room temperature and at a pressure of about 60 bar, but is preferably a ring line system in which carbon dioxide can be kept in more controlled forms.At the inlet 7 a non-return valve 9 is arranged, which prevents carbon dioxide from flowing out of chamber 5 through the inlet. pressure of about 0.5 bar.

The pump chamber is further provided with an outlet 11, through which the carbon dioxide is pumped out of the chamber. At the outlet 11 a valve 13, preferably opens at a predetermined pressure, for example 80 e.g. a spring-loaded non-return valve arranged, which was carried in the forward direction and is completely closed in the reverse direction.

However, it will be appreciated by those skilled in the art that other valves, e.g. remotely operated valves, can be used to obtain the same functionality. The present invention of course also includes the use of such valves. piston needle 15 hole 5 movable between a front and a rear position, which 1 with a bidirectional arrow 17.

The pump device 1 further comprises one or arranged in the cylindrical of the pump body and is axially indicated in Fig. When the piston is moved backwards, the volume of the pump chamber increases, and when the piston is pushed forward, the volume of the pump chamber decreases. The change in volume is given by the displacement, in Fig. 1 indicated by L, for a given cross-sectional area of the piston 15.

In order for the pump to operate at high pressures, there is a gasket (not shown in Fig. 1> for sealing between piston and cylinder wall. It is of course important that the gasket has good resistance to permeability and / or redemption of carbon dioxide, so that the risk is small that the gasket swells and makes pump functionality impossible.A preferred version of pump device 1 can withstand a pressure of up to 500 bar.

The piston is driven by a motor 19, preferably a linear, electric motor via a transmission medium, in Fig. 1 schematically indicated by 21. The power transmission can be, for example, hydraulic or pneumatic. However, it will be apparent to those skilled in the art that any given power transmission engine capable of effecting a linear displacement of piston 15 is useful with the present invention. For example, a servomotor with rack and pinion can be used to drive piston 15.

Motor 19 is controlled by a control computer 23 with suitable software via signals over a control line 25. In particular, the pump device can be arranged so that movement of piston 15 takes place in dependence on amplitudes or amplitude changes of said signals. Furthermore, motor 19 and / or control computer 23 are, if necessary, equipped (a) with A / D and D / A converters (not shown in Fig. 1).

The computer further has a bidirectional interface 27 outwards for the communication device e.g. with an operator of the pump, or with another control system such as e.g. a control computer for controlling a manufacturing process for necrocellular polymer products. Such an example is described in more detail below with reference to Fig. 4. function comes from the fact that the following general piston 15 is fully called dead volume, is described starting from a position where the forward shot and where the volume of the pump chamber, minimal, and assuming that this dead volume contains liquid carbon dioxide. To fill the chamber with liquid carbon dioxide, the force with which the piston is kept in its advanced position is reduced so that the pressure of the carbon dioxide source becomes sufficient for liquid carbon dioxide to flow into chamber 5 and push the piston backwards.

Force to hold piston 15 during the intake phase is required to ensure that the carbon dioxide intake is slow. As a result, the pump l is non-self-priming.

The slower the carbon dioxide is allowed to flow into the pump chamber the smaller the amount. gas is obtained in the chamber and the better the accuracy and precision regarding the amount. carbon dioxide intake l0 15 20 25 30 n u s - u n I 0 ° 'I' un 519 091 šïï; 7 is achieved. In practice, the intake phase should last for a period of from a few to a few tens of seconds and up to minutes, but it obviously depends on the particular application. In order to be able to perform pumping, if applicable, ie. piston propulsion more often a multi-piston pump can be used, which will be described in more detail with reference to Fig. 4 below.

When the pump has sucked in a predetermined amount of liquid carbon dioxide (ie the piston has been pulled back a corresponding length), the pump is ready for pumping out the carbon dioxide.

Pumping out the amount of liquid carbon dioxide is software controlled in any suitable manner. The rate at which the amount of carbon dioxide is pumped out in a controlled liquid manner can be controlled at a predetermined rate so that an accurate and precise amount can be delivered at exactly the right time.

The pump according to the present embodiment thus operates with a single piston stroke which can be repeated after the slow piston movement backwards.

In this case, a discontinuous pumping function is obtained. special version of the pump is able to pump up to 2 g / s during the piston projection with a back pressure of up to 500 bar (this back pressure must therefore be overcome to pump the carbon dioxide out through the outlet).

The maximum amount that can be pumped (during a piston stroke) is given by how much the volume of the chamber increases when the piston is retracted, which for a given cross-sectional area of the piston is given by the retracted length L. In this case it is very important that the piston is retracted longer than 10 s. preferably for a period of time which is 30 s, (ie slowly, a 20 s, the carbon dioxide does not boil or longer to ensure that so-called cavitation does not occur).

There will always be a two-phase flow in the chamber, but very small amounts of gas do not give a major problem because on the one hand the amount of carbon dioxide absorbed is only slightly lower (given by .faxa lO 15 20 25 IIIOII.. '. L' 519 091 p. W 8 the gas density compared to the density of the liquid), partly this amount of gas condenses immediately when the pressure increases as the piston is pushed forward.

The pump may further comprise a position sensor 29 which suitably sends the piston 15 one to 23.

The present invention provides very accurate and precise measurement of the exact position and position signal via a signal line 31 control computer control of, during a piston stroke, pumped amount of liquid carbon dioxide and this control can be improved by providing the control computer with this feedback, whereby the position signal can, if measured the position of the piston does not correspond to the real-time compensation calculated in the control computer for controlling the movement of the piston.

Furthermore, the carbon dioxide source, whether a bottle or a ring line system, is advantageously located above, particularly high above, the pump itself. In this case, the hydrostatic pressure which occurs in the obtained liquid column can prevent boiling of the carbon dioxide or at least reduce the amount of carbon dioxide boiling.

In an alternative embodiment, a cooling medium, in particular liquid carbon dioxide, is conducted, Fig. 1) the same and further minimizes the risk of boiling. cooling water or glycol, through passages (not shown along the outside of the pump body for cooling) Fig. 2 shows a system 41 for injection molding or blow molding of microcellular plastic parts in a mold space 43 of a mold tool 45. The system comprises a smooth device 47 for plasticizing and feeding polymer including an inlet for supplying polymer raw material (indicated by arrow 49) and a screw for feeding and plasticizing (schematically indicated by an arrow 51), the screw being driven by a motor 53 controlled by a computer 55 or other control equipment provided with suitable software. The plasticized polymer is further fed to a mixing chamber or mixer 57, in which liquid carbon dioxide is added in a controlled manner, which is described in more detail below: The polymer and the carbon dioxide are mixed, the mixture being passed to a piston system 59 for pressure increase. When the part itself is sprayed, a valve 61 is opened and the mixture is allowed to be sprayed (foamed) into the mold. the mold space 43 of the tool 45 for the production of microcellular plastic parts, i.e. plastic parts with very small gas-filled microcells, which are typically on the order of a micrometer or less.

Such plastic parts are substantially lighter than the corresponding homogeneous details, at the same time as the strength can be obtained as well or even in some respects slightly better.

The carbon dioxide is added by means of the pump shown in Fig. 1. In Fig. 2 the pump 1 is shown only in overview comprising pump body 3, pump piston 15, wwtor 19 and control computer 23. The inlet of the pump is connected to a source of carbon dioxide 63 and its outlet is connected to the mixing chamber 57 via a non-return valve 65. This non-return valve 65 ensures that no polymer can flow in the reverse direction, ie. towards the pump outlet.

Furthermore, there is a bidirectional communication interface 67 between the pump control computer 23 and the system control computer 55 for controlling device 47 for plasticizing and feeding raw polymer.

In an alternative embodiment, control computers 23 and 55 are constituted by a single control computer, and in a further alternative embodiment, motors 19, 53 are also constituted by a single motor.

Pumping of carbon dioxide takes place during a limited part of a cycle for plastic spraying, where a cycle typically takes about 60 - 150 s.

Preferably, pumping (propulsion of the pump piston) typically takes about 20 s, the pumping speed being typically in the order of 2 g / s of liquid carbon dioxide. In this case, there are about 40 - 130 s for suction (piston extraction) of liquid carbon dioxide in the pump. This time may be fully sufficient for some processes (so that the carbon dioxide does not boil), while in other contexts it is insufficient. In such a case, a multi-piston pump can be used.

It will be further appreciated by those skilled in the art that the pump of the present invention may be used in a variety of cyclic manufacturing techniques for the production of polymer products.

By means of the software-controlled motor, the pump speed of the pump according to the present invention can be varied during the piston stroke. Figs. 3a-c are thus diagrams showing typical values in arbitrary units of pumped amount of liquefied gas per unit time as a function of the time of the pump device shown in Fig. 2 (solid curves in Fig. 3a). the result of fig. 3b the pump speed is varied according to a step function and fig. shows pumping with constant pump speed, i shows the result of pumping where 3c shows the result of pumping where the pump speed is varied continuously - first increasing and then decreasing - during a piston stroke.

Fig. 3c also shows typical values for fed amount of plasticized polymer per unit time in any scale as a function of time for the polymer product manufacturing system shown in Fig. 2 (dashed curve). Thus, through the communication interface 67, supply of liquid carbon dioxide can take place between polymer and synchronization.

Note that the pump according to the present invention not only allows the pump speed to be accurately and precisely controlled but also provides a flexible and variable projection of the piston according to, for example, the functions shown in Fig. 3.

Referring now to Fig. 4, which shows in schematic cross-section a device for pumping liquefied gas, a further embodiment of the present invention will be described. 81-87 next to Each of the pumps 81-87 consists in principle of a The device comprises four pumps arranged each other. 10 15 20 25 30 S19 091 ll pump as shown in However, the four-pump system \ en. common motor with power transmission and a fig. 1. uses this common control computer (not shown in fig. 4).

Furthermore, the four-pump system comprises a supply system 89 which in parallel connects a source of liquid carbon dioxide (not shown in Fig. 4) to 81-87, a drainage system 91 which connects the inlet of each pump and pump, respectively, and 81-87 outlets to a common drain.

The motor with the control computer is arranged to perform pump cycles with the respective pump 81-87 in accordance with the method according to the invention described with reference to Fig. 1. Preferably, the pump system is arranged with the same phase shift between each pump (as illustrated in Fig. 4), so that the system appears as a single pump of the type shown in Fig. 1, but which is four times as fast.

This embodiment of pump system is particularly useful in a system for injection molding or blow molding a microcellular plastic part where the cycle times are short.

In another version, the pistons are completely in phase so that the system appears as a single pump of the type shown in Fig. 1, but which has four times higher pump capacity per stroke. The present invention does not set phase shifts between the pistons included in the system. limitations with respect to Fig. 5, finally, is a diagram showing typical values in arbitrary units for pumped amount of liquefied gas per unit time as a function of the time for the device shown in Fig. 1 (solid curve) and for the device shown in Fig. 4. (dashed curve). It is seen that the frequency of the piston strokes increases in proportion to the number of pistons.

Thus, a multi-piston system according to the present invention could be made to pump almost continuously if a sufficient number of pistons are used. Such a system would in 5 19 091 šïï = - -; Particularly suitable for use in a continuous production system, e.g. extrusion, of polymer products such as pipes and profiles.

The present invention as described herein solves the problems associated with the prior art. It is, of course, not limited to the embodiments described above and shown in the drawings, but may be modified within the scope of the appended claims.

Claims (27)

10 15 20 25 u. u ø nu c 519 091 13 n uu nav PATENTKRAV Device for pumping an accurate and precisely controllable amount of liquefied gas, comprising - a pump body (3) with a cylindrical hole (5), which constitutes a pump chamber, - a piston (15) arranged in holes movable between a front and a rear position, of the pump body and axially - a drive means (19, 21) for moving said piston between the front and the rear position, - an inlet (7) to said pump chamber, which inlet is connectable to a source of liquefied gas, and - an outlet (II) from said chamber, wherein - liquefied gas from said source can be caused to flow into the pump chamber through said inlet as the drive means moves said piston from the front to the rear position and liquefied gas can be made to flow out of the pump chamber through said outlet when the drive means moves said piston from the rear to the marked front position, by - a guide means (23) arranged to guide the drive means to - move said piston from the front to the rear position sufficiently to substantially avoid boiling of the liquefied gas flowing into the pump chamber, and - moving said piston from the rear to the front position at a variable controllable speed, whereby the amount of liquefied gas which can be made to flow out through the outlet is accurately and precisely controllable. 10 15 20 25 519 091 14 Device according to claim 1, wherein the control means is arranged to control the drive means to move said piston from the rear to the front position at a speed which is varied according to a step function. The device according to claim 1, wherein the control means is arranged to control the drive means to move said piston from the rear to the front position at a speed which is varied continuously, first increasing and then decreasing. Device according to any one of claims 1-3, wherein the device is arranged for discontinuous pumping of said liquefied gas. Device according to any one of claims 1-4, wherein the control means is arranged to control the drive means to move said piston from the front to the rear position so that pumping of up to 2 g / s is obtained at a pressure of up to 500 bar. Device according to any one of claims 1-4, wherein the control means is arranged to control the drive means to move said piston from the front to the rear position at such a speed that said movement takes at least 10 seconds. The device according to any one of claims 1-6, further comprising a position sensor (29) connected to said control means by means of a signal line (31), said position sensor being arranged to measure the position of the piston and signal this to the control means. Device according to any one of claims 1-7, further comprising a passage along the outside of the pump body arranged for transporting a cooling medium, in particular a liquefied gas, and thus for cooling said pump body. Device according to any one of claims 1-8, wherein the drive means comprises a linear motor. 10 15 20 25 5 19 091 _ fr '15 Device according to any one of claims 1-9, wherein the liquid gas is carbon dioxide. 11. ll. Pump system comprising at least two pieces (81, 87) 83, 85, of the device according to any one of claims 1-10. Pump system according to claim 11, wherein the inlets of all devices are connected by means of a supply system (89) and the outlets of all devices are connected by means of a discharge system (91). Method for pumping an accurate and precisely controllable amount of liquefied gas, by means of a pump comprising a pump body (3) with a cylindrical hole (5), which constitutes a pump chamber, a piston (15) arranged in the hole of the pump body and axially displaceable between a front and a rear position, an inlet (7) to said pump chamber, which inlet is connectable to a source of liquefied gas, and an outlet (11) of said chamber, said method comprising: - obtaining liquefied gas from said source flowing into the pump chamber through said inlet as said piston is moved from the front to the rear position, and - liquefied gas is caused to flow out of the pump chamber through said outlet as said piston is moved from the rear to the front position, characterized in that - piston is moved from the front to the rear position slowly enough to substantially avoid boiling of the liquefied gas flowing into the pump chamber, and - said piston is moved from n the rear to the front position at a variable controllable speed. lO lS 20 25 30 5 19 091 -2 11222221 'nu oro 16 The method of claim 13, wherein said piston is moved from the rear to the front position at a speed that is varied according to a step function. The method of claim 13, wherein said piston is moved from the rear to the front position at a rate that varies continuously, first increasing and then decreasing. A method according to any one of claims 13-15, wherein said method comprises discontinuous pumping of said liquefied gas. A method according to any one of claims 13-16, wherein said piston is moved from the front to the rear position so that pumping of up to 2 g / s is obtained at a pressure of up to 500 bar. A system for cyclic production of polymer products comprising a device (47) for plasticizing and feeding a polymer, one (1), (57) connected to a source (63) of liquefied gas, with a mold space piston pump (45) a mixing chamber and a molding tool (43), wherein, for each manufacturing cycle, the plasticizing and feeding device is arranged to receive a polymer, to plasticize the polymer and to feed it, the pump is arranged to pump liquefied gas, the mixing chamber is arranged to receive the plasticized polymer and the liquefied gas, as well as for mixing them, as well as the mold with the mold space are arranged for receiving the mixture and for forming the polymer product, the core of which the pump consists of a device for pumping an accurate and precisely controllable amount of liquefied gas, comprising a pump body (3) with a cylindrical hole the hole of the pump body and axially displaceable between a front (5), which a pump chamber, a piston (15) arranged in and a rear position, a drive means (19, 21) for moving said piston between the front and the rear position, an inlet (7) to said pump chamber, which inlet is connectable. 15 20 25 30 519 091 '' '' "unoonnucgo,; ~ cv: nu q vv en »17 to a source of liquefied gas, and an outlet (ll) from said chamber, whereby liquefied gas from said source can be caused to flow into the pump chamber through. said inlet as the drive means moves said piston from the front to the rear position and liquefied gas can be made to flow out of the pump chamber through said outlet as the drive means moves said piston from the rear to (23) the drive means to move said piston from the front to the rear position. front position, and a control means is arranged to control the rear position slowly enough to substantially avoid liquid whereby the amount of liquid gas which can be caused to flow out by boiling the gas flowing into the pump chamber, the outlet is accurately and precisely controllable; wherein the device for pumping is arranged to strike only one stroke per production cycle. A system according to claim 18, wherein the control means (23) is arranged to control the drive means to move said piston from the rear to the front position at a variable controllable speed, whereby the amount of liquefied gas which can be made to flow out through the outlet is accurate and precise controllable. A system according to claim 19, wherein the control means is arranged to control the drive means to move said piston from the rear to the front position with a speed which is varied according to a step function. The system of claim 19, wherein the control means is arranged to control the drive means to move said piston from the rear to the front position at a speed which is varied continuously, first increasing and then decreasing. A system according to any one of claims 18-21, wherein the control means is arranged to control the drive means to move said piston from the front to the rear position so that pumping of up to 2 g / s is obtained at a pressure of up to 500 bar. 10 15 20 25 519 091 18 A system according to any one of claims 18-21, wherein the control means is arranged to control the drive means to move said piston from the front to the rear position at such a speed that said movement takes at least 10 seconds. The system of claim 23, wherein the pump is arranged to take in liquefied gas during a first time period of each cycle, and to blow out liquefied gas during a second time period of each cycle, the first time period being longer than the second time period. A process for the cyclic production of polymer products comprising the steps of: - a polymer being provided, - said polymer being plasticized, - an amount of liquefied gas being added to the polymer, - said amount of liquefied gas and said polymer being mixed, and - the mixture being injected into a mold mold space (43) and read mehm, characterized by said amount of liquefied gas is supplied to the polymer by pumping by a process according to any one of claims 13-17. The method of claim 25, wherein said amount of liquefied gas is supplied to the polymer by pumping by a single piston stroke of said pump. A method according to claim 25 or 26, wherein. liquefied gas is taken up in the piston pump during a first time period of each cycle, and liquefied gas is pumped out during a second time period of each cycle, where the first time period is longer than the second time period.