Abstract:
Flowable reaction components of a reaction mixture which form solid or foamed material comprising filling material are transported from a storage container to a high-pressure mixing head in pressure stages by the use of gear pumps connected in series without major wear of the gear pumps.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention is directed to a process and device for producing a reaction mixture forming solid material or foamed material from liquid flowable reaction components, wherein at least one of the flowable reaction components comprises filling material. According to the invention, the reaction components are transported from at least one storage container by pumps and metered under high pressure into a mixing head. 
     BACKGROUND OF THE INVENTION 
     Reaction components charged with filling material, such as those used in the manufacture of polyurethane articles, are known to possess high abrasive properties. As a result (and for economic reasons), the processing of such filled reaction components are prohibited in conjunction with particular devices, e.g. high pressure injection mixheads, requiring injection of the components (polyol and isocyanate) into the mixing chamber of the mixhead at pressure of above 100 bar and up to 300 bar. 
     Reaction components without filling material can be delivered using conventional high-speed, high-pressure piston pumps, subjected to high pressure such as 120 to 250 bar, metered, and then injected into the mixing chamber of a high-pressure mixing head. However, delivery of reaction components with filling material through such piston pumps is not possible. Normally, gear pumps may be used up to a pressure of about 100 bar at 1.500 to 3.000 rpm. 
     In producing certain articles, the high-pressure intermixing of reaction components charged with filling materials is indispensable. Even though wear by virtue of the abrasive filling materials can never be entirely eliminated, slow-running piston-type metering instruments or plunger pumps have been employed with success. However, such instruments have the disadvantage of a large overall height, with all the related disadvantages of maintenance. Additionally, the structure of such instruments is very elaborate and, therefore, expensive. 
     For the foregoing reasons, it would be desirable to develop a process and device for pressurizing to high pressure, reaction components charged with filling material by using instruments which are simply constructed and moderately priced and which operate reliably and with less wear. This is achieved by the present invention in that the flowable reaction components charged with filling material are brought to the desired high pressure in several pressure stages with gear pumps having the same rotary speed which are connected in series and via pipelines. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process for transporting flowable reaction components of a reaction mixture, at least one of the flowable reaction components comprising filling material, by bringing the flowable reaction components to a predetermined pressure in several pressure stages through the use of gear pumps operated at low rotational speed. 
     It is another object of the present invention to provide a device for transporting flowable reaction components of a reaction mixture, at least one of the flowable reaction components comprising filling material, the device comprising gear pumps connected in series via pipelines, wherein pressure is provided in stages to the flowable reaction. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the apparatus of the present invention comprising three gear pumps arranged on a common drive shaft and connected to one another via pipeline. 
     FIG. 2 illustrates a preferred embodiment of the apparatus of the present invention comprising throttling elements arranged in pipeline between adjacent gear pumps. 
     FIG. 3 illustrates another preferred embodiment of the apparatus of the present invention comprising pressure-limiting valves arranged in pipeline between adjacent gear pumps. 
     FIG. 4 illustrates yet another preferred embodiment of the apparatus of the present invention comprising a pressure regulator. 
     FIG. 5 illustrates a sectional view of a gear pump taken along line  5  of FIG. 1 comprising gear pumps arranged in series in a common housing. 
     FIG. 6 illustrates a cross sectional view of a gear pump taken along line A-B of FIG.  5 . 
     FIG. 7 illustrates a cross sectional view of a gear pump taken along line C-D of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is directed to a process for transporting and pressurizing flowable reaction components of a reaction mixture from at least one storage container to at least one mixing head, comprising the steps of: 
     (a) providing at least a first gear pump, a second gear pump, and a third gear pump, the first, second and third gear pumps having the same rotary speed of up to about 800 rpm; 
     (b) connecting the first gear pump to the second gear pump by a first pipeline, then connecting the second gear pump to the third gear pump by a second pipeline; 
     (c) transporting the flowable reaction components, at least one of the flowable reaction components comprising filling material, to the first gear pump, then through the first pipeline to the second gear pump, then through the second pipeline to the third gear pump; and 
     (d) providing pressure on the flowable reaction components in stages. 
     Preferably the gear pumps are operated at up to 600 rpm, particularly preferred is a maximum of 400 rpm. 
     The pressure provided in each stage is preferably between about 30 to 70 bar. 
     The invention is also directed to a device for transporting flowable reaction components of a reaction mixture, at least one of the flowable reaction components comprising filling material, from at least one storage container to at least one mixing head, comprising: at least a first gear pump, a second gear pump, and a third gear pump, all having the same rotary speed, the first gear pump being connected to the second gear pump by a first pipeline, the second gear pump being connected to the third gear pump by a second pipeline, and providing pressure on the flowable reaction components in stages. 
     A key feature of the present invention is that several consecutive pressure stages comprising gear pumps are operated at the same rotary speed, connected via pipelines and arranged in series. Another key feature of the present invention is that the pressure level is increased by each gear pump until the desired high pressure is attained. The present invention is illustrated generally in FIG.  1 . 
     Referring now to FIG. 1, gear pumps  3 ,  4 , and  5  are the so-called low-speed engines which are used in polyurethane application technology but which operate under low pressure, i.e. approximately up to about 60 bar. Gear pump  3  is preferably connected to gear pump  4  via pipeline  6 . Gear pump  4  is preferably connected to gear pump  5  via pipeline  7 . Line  8  emanating from a storage container (not represented) leads to gear pump  3 . Line  9  leads from gear pump  5  to a high-pressure mixing head (not represented). 
     In a preferred embodiment of the present invention, gear pumps  3 ,  4 , and  5  have a drive  1  with a common drive shaft  2 . As a result, only a single drive motor is required, thus the rotary speeds of all the gear pumps are the same. 
     Gear pumps  3 ,  4  and  5 , operating under low pressure, are subject to less wear in the delivery and metering of filled reaction components. Surprisingly, it has been discovered that the wear arising in the individual gear pumps remains within justifiable limits. Additionally, the wear arising in the series connection of gear pumps  3 ,  4  and  5  for the purpose of achieving high pressure, i.e., from 120 to 250 bar, remains within justifiable limits. Additionally, with such series connection, internal leakage of reaction components is kept within justifiable limits. “Internal leakage” is defined as that leakage which occurs internally between the suction side and the pressure side of a pump, which, as a result, generates loss in delivery and therefore affects the efficiency of the gear pump. This can, in principle, be calculated or preferably ascertained empirically by experiments and compensated in the stated manner. 
     Less wear of gear pumps  3 ,  4 , and  5  is achieved due to a smaller pressure gradient per pressure stage. Thus, only a normal overall height of the device is necessary, and as such makes the system cost effective and manageable. Additionally, since gear pumps  3 ,  4  and  5  are of a simple construction, they can be exchanged more easily in the event of wear, which also makes the system cost effective and manageable. 
     An almost equally large increase in pressure is generated in each pressure stage. The term “pressure stage” refers to the pressure present between the entrance (suction side) of one gear pump and the entrance of the subsequent gear pump, such as that pressure present between gear pumps  3  and  4  and/or that pressure present between gear pumps  4  and  5 . Since the increase in pressure generated in each pressure stage is roughly equal, the sequence of operations of the process becomes easily grasped. Additionally, the equality between pressure stages makes for a more reliable process. 
     The reaction components used in the present invention are those reaction components which have a compressibility of about 3% at 100 bar. This can, in principle, be calculated or preferably ascertained empirically by experiments and compensated in the stated manner. The gases (e.g. up to about volume percent (at normal pressure) of nitrogen or air as seed gases for subsequent foaming of the reaction mixture) that frequently have to be introduced into the reaction components during processing amplify this effect, according to their proportion. 
     This compressibility therefore becomes noticeable in a disadvantageous manner in the course of the new type of delivery using gear pumps in several pressure stages. Thus, preferably, at least as much delivery-volume surplus is offered from the pressure stage arranged upstream to the following pressure stage as is lost in the pressure stage arranged upstream as a result of internal leakage and compressibility of the reaction components. 
     The delivery-volume surplus may be provided by adjusting the supply capacity of the upstream pump to a respective higher capacity as compared to the subsequent pump. In a preferred embodiment of the present invention, the supply capacity of the upstream pump is adjusted with the gear wheels having about 3 to 10% larger extension in axial dimension as compared to those of the subsequent pump. 
     One advantage of the present invention is that the quantity of reaction components delivered in excess from the pressure stage upstream is drained off downstream of the pressure stage and is either recycled back into the system or is recycled back into the storage container. As a result, the subsequent pressure stage always receives more flowable reaction components than it requires for the further pressure increase of the pressurized reaction components. As a result, an undesirable suction effect of the subsequent pressure stage is avoided. 
     However, in order to keep the amount of pressurized reaction components conveyed back as small as possible, after each pressure stage the pressure of the reaction components that is generated therein is preferably measured and the increase in pressure of the pressure stage is adjusted accordingly. For the same reason, after at least one pressure stage the pressure of the reaction components that is generated therein is preferably measured and the increase in pressure of the pressure stage is regulated as a function of the measured value. This regulation is particularly appropriate when the compressibility of the reaction components is dependent on temperature. These measures are particularly advantageous when the charged reaction components, viewed over time, exhibit fluctuating gas content and/or fluctuating processing temperatures. 
     It is preferred that filling material be already fed into the reaction components prior to the processing thereof. However, filling material can also be fed into the line system upstream of the gear pumps. 
     Referring now to FIG. 2, gear pump  13  is connected to gear pump  14  via outgoing line  16 . Gear pump  14  is connected to gear pump  15  via outgoing line  17 . Line  18  emanating from a storage container (not represented) leads to gear pump  13 . Line  19  leads from gear pump  15  to a high-pressure mixing head (not represented). Return line  20 , bypassing gear pump  13 , connects outgoing line  16  to line  18 . Return line  21 , bypassing gear pump  14 , connects outgoing line  17  to outgoing line  16 . A first throttling element  22  is arranged in return line  20 . A second throttling element  23  is arranged in return line  21 . 
     Outgoing line  16  of gear pump  13  is preferably connected via return line  20  to either line  18  or to a storage container (not represented). Outgoing line  17  of gear pump  14  is preferably connected via return line  21  to either outgoing line  16  or to a storage container (not represented). Return lines  20  and  21  allow for excess reaction components to be recycled back into the system, preferably to the suction side of the gear pump generating the excess reaction components or to the storage container. 
     In a preferred embodiment of the present invention, gear pumps  13 ,  14 , and  15  have a drive  11  with a common drive shaft  12 . As a result, only a single drive motor is required, thus the rotary speeds of all the gear pumps are the same. 
     Referring now to FIG. 3, gear pump  33  is connected to gear pump  34  via outgoing line  36 . Gear pump  34  is connected to gear pump  35  via outgoing line  37 . Line  38  emanating from a storage container (not represented) leads to gear pump  33 . Line  39  leads from gear pump  35  to a high-pressure mixing head (not represented). Return line  40 , bypassing gear pump  33 , connects outgoing line  36  to line  38 . Return line  41 , bypassing gear pump  34 , connects outgoing line  37  to outgoing line  36 . A first pressure-limiting valve  42  is arranged in return line  40 . A second pressure-limiting valve  43  is arranged in return line  41 . 
     Pressure-limiting valve  42  opens automatically into return line  40 , at a set pressure, thereby protecting gear pump  34  against any excessively high pressure that is generated in gear pump  33 . Pressure-limiting valve  43  opens automatically into return line  41 , at a set pressure, thereby protecting gear pump  35  against any excessively high pressure that is generated in gear pump  34 . 
     In a preferred embodiment of the present invention, gear pumps  33 ,  34 , and  35  have a drive  31  with a common drive shaft  32 . As a result, only a single drive motor is required, thus the rotary speeds of all the gear pumps are the same. 
     Referring now to FIG. 4, gear pump  53  is connected to gear pump  54  via outgoing line  56 . Gear pump  54  is connected to gear pump  55  via outgoing line  57 . Line  58  emanating from a storage container (not represented) leads to gear pump  53 . Line  59  leads from gear pump  55  to a high-pressure mixing head (not represented). Return line  60 , bypassing gear pump  53 , connects outgoing line  56  to line  58 . Return line  61 , bypassing gear pump  54 , connects outgoing line  57  to outgoing line  56 . A first throttling element  62  is arranged in return line  60 . A second throttling element  63  is arranged in return line  61 . In a preferred embodiment of the present invention, throttling element  62  can exert an influence on the return quantity in return line  60 . In another preferred embodiment of the present invention, throttling element  63  can exert an influence on the return quantity in return line  61 . 
     Preferred throttling elements are orifice plates. Most preferred throttling elements are adjustable orifice plates. In a preferred embodiment of the present invention, the throttling elements set the pressure for the respective return quantity in the return line and hence the increase in pressure, or, to be more exact, the pressure upstream of the subsequent pressure stage. 
     The throttling element exerts an influence on the quantity of recycled reaction components. It is preferred that throttling element  62  have control instrument  65  connected thereto. It is also preferred that throttling element  63  have control instrument  67  connected thereto. Pressure gauge  64  is connected to both outgoing line  56  and to control instrument  65 . Pressure gauge  66  is connected to both outgoing line  57  and to control instrument  67 . The control instrument is assigned to the throttling element to which it is attached. 
     In a preferred embodiment of the present invention, gear pumps  53 ,  54 , and  55  comprise drive  51  with a common drive shaft  52 . As a result, only a single drive motor is required, thus the rotary speeds of all the gear pumps are the same. 
     In a preferred embodiment of the present invention, the throttling element can be ventilated, thereby allowing agglomerates of filling material, which are possibly dammed up in front of the throttling element, to pass through the throttling element. 
     Referring now to FIGS. 5,  6  and  7 , drive  71  drives common drive shaft  72 . On drive shaft  72 , three gear pumps  73 ,  74  and  75 , are arranged in common housing  76 . Gear pump  73  comprises toothed gear  77 . Gear pump  74  comprises toothed gear  78 . Gear pump  75  comprises toothed gear  79 . Toothed gears  77 ,  78  and  79  are arranged around drive shaft  72 . The toothed gears are preferably arranged in a stepped manner. Shaft  80  comprises mating toothed gears  81 ,  82 , and  83 . In a preferred embodiment of the present invention, toothed gear  77  mates with mating toothed gear  81 , thereby forming a first pressure stage, while toothed gear  78  mates with mating toothed gear  82 , thereby forming a second pressure stage, and toothed gear  79  mates with mating toothed gear  83  thereby forming a third pressure stage. Mating toothed gear  81  is separated from mating toothed gear  82  by partition  84 . Mating toothed gear  82  is separated from mating toothed gear  83  by partition  85 . Mating toothed gear  81  has a width B 1 , while mating toothed gear  82  has a width B 2 , and mating toothed gear  83  has a width B 3 . In a preferred embodiment of the present invention, B 1 &gt;B 2 &gt;B 3 . 
     Gear pump  73  is connected to gear pump  74  via pipeline  86 . Gear pump  74  is connected to gear pump  75  via pipeline  87 . Line  88  emanating from a storage container (not represented) leads to pump  73 . Line  89  leads from pump  75  to a high-pressure mixing head (not represented). In order to avoid internal leakage, toothed gears  77 ,  78  and  79  closely fit with mating toothed gears  81 ,  82  and  83 . Additionally, in order to avoid internal leakage, partitions  84  and  85  closely fit with housing  76 . 
     Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.