Patent Publication Number: US-2019184615-A1

Title: Conveying device for conveying a viscous material from a container, and method for operating the conveying device

Description:
TECHNICAL FIELD 
     The invention relates to a conveying device for conveying viscous materials from a container, and to a method for operating the conveying device. 
     The conveying device can be used to reliably convey various medium to high viscosity materials, such as sealants, adhesives or silicone rubber, from containers, for example buckets or barrels, to various processing systems. The conveying device is also referred to as a feed system for transporting viscous materials. 
     Injection moulding machines can be used for the production of injection moulded parts from a viscous one-component or multi-component material, for example liquid silicone, also called Liquid Silicone Rubber (LSR). The viscous material is usually supplied in 20 L to 200 L containers by the supplier of the material. A conveying device is used to convey the material from the container and to feed it to the injection moulding machine. If multi-component materials are used, an additional mixing device may be provided by means of which the individual components can be mixed before feeding them to the injection moulding machine. 
     DISCUSSION OF RELATED ART 
     A conveying and mixing device of this type for the mixing of two liquids is known from printed specification, WO 2014/056011 A2. The conveying and mixing device comprises a pump that is connected to a follower plate. In conveying operation, the follower plate rests on the liquid in the container and is sealed with respect to the container. The pump conveys the liquid through the follower plate from the container. When containers are exchanged, air may ingress between the surface of the liquid and the follower plate. In order to remove the air from this location, a pressure transducer mounted on the pump outlet is used to measure the conveying pressure generated by the pump. Subsequently, the measured conveying pressure is compared to a target value and a ventilation valve integrated into the follower plate is opened so often and for so long that the conveying pressure is identical to the target value, after which the ventilation valve stays closed. It is presumed in this context that an air-free liquid has its specific conveying pressure applied to it, which changes when air is being enclosed. However, this solution is associated with the following disadvantage. If a measurement detects that the measured conveying pressure corresponds to the target value, then it is presumed that only air-free liquid is being conveyed from then on. This is not necessarily the case. It is possible that there is still air present in the liquid, whereas the measuring sample used was free of air by coincidence. In this case, the solution described above conveys air-containing liquid later on without this being detected. If one wishes to circumvent this disadvantage, a number of measuring samples would need to be taken and the liquid would have to be conveyed to the injection moulding machine only once multiple measurements on different measuring samples confirmed that the liquid no longer contains air. This procedure would lead to high losses of material though, because not only the air-containing measuring samples, but also the air-free measuring samples would have to be discarded until it was certain that no air-containing measuring sample follows. Accordingly, the solution described above is either associated with a disadvantage in that it cannot be truly made certain that air-free liquid is being conveyed or in that relatively much liquid—including air-free and therefore usable liquid—needs to be discarded before it is has been ascertained that the liquid is free of air. 
     SUMMARY OF THE INVENTION 
     It is one object of the invention to devise a conveying device for the conveying of a viscous material from a container and an operating procedure, in which it is ascertained that only bubble-free material is being conveyed and in which the fraction of material to be discarded is minimised. 
     The conveying device according to the invention for conveying a viscous material from a container comprises a follower plate that can be inserted into the container, and a pump by means of which the viscous material can be conveyed through the follower plate. Moreover, a measuring chamber for accommodation of a measuring sample of the viscous material is provided. The measuring chamber comprises a closable material inlet opening for this purpose. A closable disposal line leads away from the measuring chamber. Furthermore a closable material return line is provided, which leads from the measurement chamber via the follower plate into the container. The conveying device also comprises a controller that is designed and can be operated appropriately such that the controller determines the compressibility of each of a plurality of measurement samples. The controller opens the disposal line or the material return line to the measuring sample present in the measuring chamber as a function of the compressibility thus determined. 
     Moreover, the invention proposes a method for operating the conveying device described above, comprising the following steps. The material and/or a measuring sample of the material is conveyed into the measuring chamber. Once the material feed line, the disposal line, and the material return line are closed, the compressibility of the material contained in the measuring chamber is determined. A controller is used, as a function of the compressibility thus determined, to dispose the material contained in the measuring chamber via the disposal line or to return said material into the container via the material return line. 
     The conveying device according to the invention can be used for conveying a viscous material. 
     One embodiment of the conveying device according to the invention for conveying a viscous material provides an actuator by means of which a certain pressure can be set in the measuring chamber. Moreover, the invention provides a sensor for determination of the change of the volume of the measuring chamber. Applying a pressure to the measuring sample, the detected volume change can be used to determine the compressibility of the measuring sample. Since air is many times more compressible than the viscous material, the compressibility of the measuring sample can be used as an easy means for determining, at sufficient certainty, whether or not any air is present in the measuring sample. 
     In an alternative embodiment of the conveying device according to the invention, the pump comprises a pump actuator by means of which a certain volume can be set in the measuring chamber. A sensor for determining the pressure in the measuring chamber is provided as well. This also allows the compressibility of the measuring sample to be determined. Moreover, it is an option for determining whether or not there is any air in the measuring sample. 
     In another embodiment of the conveying device according to the invention, the actuator is a piston or a membrane. The piston can be, for example, the piston of the pump or a separate piston. 
     An additional embodiment of the conveying device according to the invention provides a sensor for detection of the actuator position. Sensors for detection of the actuator position are inexpensive and yield reliable and informative measuring signals. A position sensor can be used to determine the actuator position at any time and rapidly. In addition, a position sensor is versatile in use. It can be used without further ado to detect the stroke of a piston or of a membrane or the angle position or angle change of a rotating shaft and transmit this information to the controller, for example as an analogue or digital signal. Advantageously, the position sensor can be arranged outside of the measuring chamber. As a result, the compression of the measuring sample is not affected by the sensor, which is not necessarily the case during a pressure measurement in the measuring chamber by means of a pressure sensor. Arranged on or in the measuring chamber, the pressure sensor undergoes a deformation and thus affects the volume of the measuring chamber. 
     In a development of the conveying device according to the invention, the controller utilises the signal of the sensor in order to determine the compressibility of the measuring probe contained in the measuring chamber. 
     In another development of the conveying device according to the invention, the travel sensor is provided in the form of a magnetostrictive sensor. 
     In an additional development of the conveying device according to the invention, the pump can supply material to the measuring chamber via the material feed line. 
     Alternatively, the measuring chamber can be part of the pump in the conveying device according to the invention. This allows the number of components that are required to be reduced. 
     In the conveying device according to the invention, the pump can be provided in the form of a piston pump, gear type pump, spindle pump or eccentric screw pump. 
     Moreover, the follower plate can comprise a ventilation valve in the conveying device according to the invention. This can be used ahead of time to discharge part of the air that is contained in the space between the material to be conveyed, the follower plate, and the container wall. 
     Moreover, the conveying device according to the invention can provide the follower plate to be slanted in design in the region, in which its pressure-active area is situated. This allows the pressure acting on the material to be conveyed to be partially increased, and it can be made sure that the material tends to flow in a certain direction, for example towards the conveying opening. 
     In an embodiment of the conveying device according to the invention, the material feed line comprises a valve. Said valve is preferably provided appropriately such that it can be triggered by the controller. 
     If the measuring chamber is part of the pump, the valve in the material feed line can be a non-return valve that opens automatically, when the measuring chamber is being filled, and closes automatically, when material is being conveyed from the measuring chamber and/or in measuring mode. 
     The material feed line can be integrated into the piston of the pump. 
     In another embodiment of the conveying device according to the invention, the material return line comprises a valve. Said valve is preferably provided appropriately such that it can be triggered by the controller. 
     In an additional embodiment of the conveying device according to the invention, the disposal line comprises a valve, which preferably is provided appropriately such that it can be triggered by the controller. 
     Moreover, the invention proposes a conveying system that comprises a first and a second conveying device of the type described above, whereby the first conveying device and the second conveying device are connected, on the output side, to a mixing unit. This can be used to mix different materials, for example a component A and a component B, with each other and to convey them to a processing station, for example an injection moulding machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is illustrated in more detail by multiple exemplary embodiments on the basis of ten figures. 
         FIG. 1  shows a three-dimensional view of a conveying system with a possible embodiment of the powder conveying device according to the invention. 
         FIG. 2  shows a side view of the conveying system with the conveying device according to the invention. 
         FIG. 3  shows a top view of the conveying system with the conveying device according to the invention. 
         FIG. 4  shows a three-dimensional view of a possible embodiment of a mixing device, which is part of the powder conveying device. 
         FIG. 5  shows a longitudinal section of the measuring device. 
         FIG. 6  shows a longitudinal section of a possible embodiment of the pump of the conveying device. 
         FIGS. 7 a  to 7 d    show various operating states of the conveying device based on four block diagrams. 
         FIGS. 8 a  to 8 d    show various operating states of a further possible embodiment of the conveying device based on four block diagrams. 
         FIGS. 9 a  to 9 d    show various operating states of another possible embodiment of the conveying device based on four block diagrams. 
         FIGS. 10 a  to 10 c    show various operating states of an additional possible embodiment of the conveying device based on three block diagrams. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The structure of a first possible embodiment of a conveying system  1  for conveying viscous material is illustrated in more detail in the following. The conveying system  1  shown in  FIGS. 1, 2, and 3 , comprises a first conveying device  2 , by means of which, for example, a component A can be conveyed, and a second conveying device  102 , by means of which, for example, a component B can be conveyed. As a matter of principle, the two conveying devices  2  and  102  can be identical in design. But this does not have to be the case. The two conveying devices  2  and  102  will be presumed to be identical in design. The reference number of the component of the second conveying device number  102  will be higher by 100 than the reference number of the component of the first conveying device  2  that is identical in design. 
     The conveying device  2  comprises a pump  6  that is driven by means of a drive  4  and a drive rod  5 . If the pump  6  is provided in the form of a scoop piston pump, as shown in  FIG. 6 , the drive  4  is designed appropriately such that it causes the drive rod  5  to perform a stroke motion that is being transferred to the scoop piston pump. The pump  6  can just as well be a piston pump without a scoop piston rather than the scoop piston pump. The scoop piston is advantageous in the case of highly viscous materials in that the viscous material is scooped directly to the pump inlet. This allows the suction behaviour of the pump to be improved. If the pump  6  is provided in the form of a gear type pump, spindle pump or as an eccentric screw pump, the drive is designed appropriately such that it causes the drive rod  5  to perform a rotary motion that is being transferred to the dear type pump, spindle pump and/or eccentric screw pump. 
     The present exemplary embodiment presumes the pump  6  to be a scoop piston pump.  FIG. 6  shows in exemplary manner the possible design of a scoop piston pump of this type based on a longitudinal section. A follower plate  7  is situated below the pump  6  and can have a container with the material to be conveyed inserted into it. The follower plate  7  is preferably configured with a ring-shaped seal  71  to allow the follower played  7  to touch in sealing manner against the container wall. The seal  71  makes sure that no material leaks between the follower plate  7  and the container wall. The follower plate  7  comprises a pressure-active surface  74 , which advantageously is designed to be at least partially slanting. This allows the pressure acting on the material to be conveyed to be partially increased, and it can be made sure that the material tends to flow towards the conveying opening  72  of the follower plate  7 . The pump  6  can convey the viscous material through the conveying opening  72  out of the container. For this purpose, the scoop piston pump comprises a scoop paste  81 , whereby a scoop piston plate  82  is situated at its lower end. In order to convey material from the container, the scoop piston  81  is moved downward such that the scoop piston plate  82  dips into the material and takes up material. During the upward motion of the scoop piston  81 , the scoop piston plate  82  takes along the material through the conveying opening  72  into the inside of the pump. From there, the material gets through a first non-return valve  84  upwards into a lower pump chamber  83 . During the subsequent downward motion of the drive  5  and of the scoop piston  81  connected to it, the material gets through a second non-return valve  86  into an upper pump chamber  85 . The subsequent upward motion of the scoop piston  81  transports the material from the pump  6  into a material feed line  38 . Accordingly, material is being transported into the material feed line  38  with each upward stroke of the scoop piston  81 . The first non-return valve  84  can be provided as a seat valve and the second non-return valve  86  can be provided as a ball valve. 
     The drive  4  is attached to a motor mount  18 . The latter, in turn, is attached to a yoke  10  by means of a first and a second rod  13 ,  15 , respectively. The two rods  13  and  15  can be provided in the form of tubes and also serve as guidances for two lifting rods  14  and  16 , respectively. The follower plate  7  is attached to the two lifting rods  14  and  16 . The pump  6  can be attached to the motor mount  18  by means of further rods  23 . 
     The yoke  10  is supported by two lifting cylinders  11 . The lifting cylinders  11 , the yoke  10 , and the rods  13  to  16  form a pump lifting system, whose purpose is to be able to lift and lower the drive  4  along with the pump  6  and the follower plate  7 . 
     The measuring device  30  shown in  FIGS. 4 and 5  is one possible embodiment and can be part of the conveying device  2 .  FIG. 4  shows a three-dimensional view and  FIG. 5  shows a side view, sectioned, of the measuring device  30 . The measuring device  30  comprises a measuring chamber  31  in a measuring chamber housing  41 , whereby the volume of the measuring chamber  31  can be changed by means of a piston  40 . The position of the piston  40  can be set by means of a pneumatic cylinder  32 . The farther the piston  40  projects from the cylinder  32 , and thus projects into the measuring chamber  31 , the smaller is the volume inside the measuring chamber  31 . A piston seal  42  is situated on the upper end of the piston  40  in order to seal the measuring chamber  31  in downward direction towards the cylinder  32 . In order to be able to apply compressed air DL to the cylinder  32 , a corresponding control port  48  is provided on the cylinder  32 . The control port  48  can be used to apply compressed air DL to the piston  40  in the cylinder  32 , and to move the piston. As shown in  FIGS. 4 and 5 , the measuring chamber housing  41  can be provided to be tube shaped. An opening is situated on the upper end of the measuring chamber housing  41 , by means of which the material to be tested, i.e. the measuring sample, can get into the measuring chamber  31  and by means of which the measuring sample can also be conveyed out of the measuring chamber  31  again. 
     By means of an inlet valve  33 , which can be provided, for example, as a needle valve, the material to be tested can be conveyed via a material feed line  38  (see  FIGS. 1 to 3 ) into the measuring chamber  31 . The material feed line  38  shall be referred to as feed line, in short, hereinafter. It can be connected to the inlet valve  33  through a T-piece  43 . When the measuring unit  30  is not in use, the conveyed material can be directed someplace else by means of the T-piece  43 . The inlet valve  33  can be provided in the form of a pneumatically driven valve having two control ports  44 . 1  and  44 . 2 . Applying compressed air to the control port  44 . 1 , the piston in the valve  33  causes the material inlet of the valve to be opened such that the measuring sample gets into the measuring chamber  31 . 
     Applying compressed air to control port  44 . 2  instead, the piston in the inlet valve  33  causes the material inlet of the valve to be closed. 
     Using an outlet valve  34 , which is also called a return valve, the material to be tested/measuring sample can be conveyed via a material return line  37  (see  FIGS. 1 to 3 ) out of the measuring chamber  31  and back into the container with the material to be conveyed. The material return line  37  shall be referred to as a return line, in short, hereinafter. The outlet valve  34  can be provided in the form of a pneumatically driven valve with two control ports  45 . 1  and  45 . 2 . Applying compressed air to control port  45 . 1 , the piston in the outlet valve  34  causes the material outlet of the valve to be opened. Applying compressed air to control port  45 . 2  instead, the piston in the outlet valve  34  causes the material outlet of the valve to be closed such that the return line  37  is closed. 
     Using another outlet valve  35 , the material to be tested can be conveyed via a material disposal line  36  (see  FIGS. 1 to 3 ) out of the measuring chamber  31  and, for example, into a waste container that is not shown here. The material disposal line  37  shall be referred to as disposal line, in short, hereinafter. The outlet valve  35  can be provided in the form of a pneumatically driven valve having two control ports  46 . 1  and  46 . 2 . Applying compressed air to control port  46 . 1 , the piston in the outlet valve  35  causes the material outlet of the valve to be opened. Applying compressed air to control port  46 . 2 , the piston in the valve  35  causes the material outlet of the valve to be closed such that no material gets into the disposal line  36 . 
       FIGS. 7 a  to 7 d    show four different operating states of the conveying device  2  based on four block diagrams. The operating states shown apply analogously to the conveying device number  102  as well, if one is present. 
     The conveying device  2  can be operated in conveying mode or in ventilating mode. 
     In conveying mode, the conveying device  2  uses the pump  4  to convey the viscous material from the container  8 . 
     In the embodiment shown in  FIGS. 1 and 2 , the conveying device  2  conveys component A to the outlet  51 , and the conveying device  102  conveys component B to the outlet  151 . From there, the two components A and B can be guided to a mixing unit  200  and/or a processing station. Pressure transducers  50  and  150  can be provided on the outlets  51  and  151 , respectively. 
     When the container in the conveying device  2  is empty, the conveying mode is interrupted. The pump lifting system is then used to lift the pump  4  along with the follower plate  7  appropriately until the follower plate  7  is situated above the container. Then the empty container is pulled out of the conveying device  2  and a full container is pushed into the conveying device  2  and is positioned below the follower plate  7 , whereby transport castors  21  ease the processes of pulling out and pushing in the container. 
     Subsequently, the pump lifting system is used to lower the pump drive  4  and the pump  6  along with the follower plate  7  appropriately until the follower plate  7  in the container rests on the material  9  to be conveyed. In the course of this process, air may get trapped between the surface of the material  9  to be conveyed, the container wall, and the follower plate  7 . 
     The ventilating mode shall be described in more detail in the following. 
     To remove the trapped air from this location, the follower plate  7  can first be made to rest on the material  9  to be conveyed for a certain period of time during a first ventilating phase in order to give the material time to distribute. The period of time (resting time) can, for example, be adapted to the viscosity of the material. Subsequently, the ventilating valve  17  on the follower plate  7  is opened such that the air under the follower plate  7  can escape. Then the ventilating valve  17  is closed again. This procedure is advantageous, but not obligatory. 
     In a second ventilating phase, the remaining air is removed from the container. In this context, the controller  22  can be used to distinguish between usable (air-free) and non-usable (air-containing) material. For this purpose, the inlet valve  33  is opened, the outlet valve  34  and the discharge valve  35  are closed. It is of advantage to the ventilating mode to have the material transport line  92  be closed. The material  9  and/or the measuring sample  19  is transported out of the container  8  and into the measuring chamber  31  via the material feed line  38  ( FIG. 7 a   ). This takes place by the cylinder  32  pulling the piston  40  out of the measuring chamber  31 . As a result, the volume in the measuring chamber  31  is increased and a negative pressure is generated in the measuring chamber  31  that aspirates the material into the measuring chamber  31 . Alternatively or complementary, the material can also be pumped into the measuring chamber  31  by means of the pump  6 . 
     Subsequently, the material feed line  38  is closed by closing the inlet valve  33  ( FIG. 7 b   ). The two outlet valves  34  and  35  stay closed. Then, a defined pressure is applied to the cylinder  32  such that a defined pressure p is also being applied in the measuring chamber  31  by means of the piston  40 . The path x travelled by the piston  40  is measured in a next step. In this context, the travelled path x is a measure of the compressibility of the material that is present in the measuring chamber  31 , i.e. the measuring sample  19 . If there is air in the measuring chamber, and therefore in the material, the piston  40  travels farther than when the material is free of bubbles. This is the case because the material itself is hardly compressible, whereas air is strongly compressible as compared to the material. The controller  22  compares the measured travelled path x of the piston  40  to a reference value xref. 
     If the controller  22  detects the measured travelled path x to be larger than the reference value xref, the material is classified to be not free of bubbles ( FIG. 7 c   ). In this case, the outlet valve  35  is being opened, whereas the two other valves  33  and  34  stay closed. The measuring sample  19  (material and air) is pushed out of the measuring chamber  31  by means of the piston  40  and is disposed, for example, into a waste container via the disposal line  36 . 
     If the control and  22  classifies the material that is present in the measuring chamber  31  to be free of bubbles and therefore usable ( FIG. 7 d   ), the outlet valve  34  is being opened, whereas the two other valves  33  and  35  stay closed. The material (measuring sample  19 ) is pushed out of the measuring chamber  31  by means of the piston  40  and is returned into the container  8  via the material return line  37 . 
     In order to make sure that no residual air is still present in the container  8 , the process described above can be repeated once or multiply. For this purpose, the outlet valve  34  is closed again and the inlet valve  33  is opened. The discharge valve  35  stays closed ( FIG. 7 a   ). Subsequently, another measuring sample (new material) is transported out of the container  8  and into the measuring chamber  31 . The aforementioned steps can now be repeated. If the controller  22  no longer classifies material as bubble-containing after repeated performance of the afore-mentioned steps during any compression measurement, i.e. none of the measuring samples, it can be presumed that there is no longer any air contained between the follower plate  7 , the surface of the material  9  to be conveyed, and the container wall. To make sure of this, for example the following can be provided. Only when the controller  22  classifies the tested material to be free of bubbles in six subsequent measurements and therefore in six subsequent measuring samples  19 , the material  9  that is present in the container  8  is considered to be free of bubbles. 
     In order to further reduce the probability of erroneous release of the material  9  for conveyance, the following can be provided just as well. Only when the controller  22  classifies the tested material to be free of bubbles in eight subsequent measurements and therefore in eight subsequent measuring samples  19 , the entire material is considered to be free of bubbles. 
     Accordingly, the larger the number of measuring samples  19  detected to be free of bubbles, the lower is the probability of erroneous release of the conveyance of the material  9 . 
     If the controller  22  declared the material  9  in the container  8  to be useful after a series of tested measuring samples  19 , the controller can cause the conveying device  2  to switch from ventilating mode back into conveying mode. 
     Alternatively, the controller  22  can be provided appropriately such that it can do the following. In a first testing cycle, a first measuring sample is drawn and analysed for the presence of air in it. If the material of the measuring sample is classified to be free of bubbles, it is returned into the container  8  via the material return line  37 . If the tested material is classified to be not free of bubbles, it is disposed via the material disposal line  36 . Subsequently, a second measuring sample is drawn in a second testing cycle and handled in the same manner as the first measuring sample. In total, n consecutive testing cycles with n measuring samples can be conducted, whereby each of the n testing cycles proceeds analogous to the first testing cycle. After a switch of barrels, for example n=8 testing cycles can be run and therefore n=8 measuring samples can be drawn; after the eighth testing cycle, the controller  22  switches from ventilating mode to conveying mode. The number n of consecutive testing cycles can just as well be, for example, n=5, 6, 9 or 10. The more testing cycles are run, the lower is the probability of the controller  22  erroneously releasing the material  9  for conveyance, i.e. of erroneously switching from the ventilating mode to the conveying mode. 
     A mixed form of the two procedures described above is feasible just as well. Accordingly, the controller  22  can be provided and is operable as follows. At least seven testing cycles are run, whereby the switch from ventilating mode to conveying mode is made only if the tested material of the last three testing cycles, in time, each was classified to be free of bubbles. Otherwise, the controller  22  effects one or more additional testing cycles to be conducted. 
     The amount of material to be tested by the controller  22  in the ventilating mode can depend on the type of the material  9  and on the requirements considering an error-free decision whether or not and when the switch from ventilating mode to the conveying mode is to be done. If the controller is to test, for example, between 2 and 4 L of material, approximately 40 to 80 testing cycles are run. The machine operator can set the number of testing cycles. The machine operator can also determine, for example, that the controller  22  is to switch from ventilating mode to conveying mode, if no air bubbles are detected any longer in the measuring samples  19 , for example after ten testing cycles. 
       FIGS. 8 a  to 8 d    show four different operating states of another possible embodiment of the conveying device  2  based on four block diagrams. The second embodiment of the conveying device  2  differs from the embodiments of the conveying device described above in that the measuring chamber  31  is not accommodated in a separate measuring chamber housing  41 , but rather is part of the pump  6 . Here, the pump chamber  85  simultaneously serves as measuring chamber by means of which the compressibility of the material to be conveyed and/or of the measuring sample  19  is determined. 
     The piston pump according to  FIG. 8  has a double effect meaning that the piston pump conveys at the pump outlet both during the upward stroke and the downward stroke. 
     During the downward stroke, the measuring chamber for determining the compressibility of the measuring sample  19  is provided by the lower chamber  83  and the upper chamber  85  ( FIG. 8 a   ). During the upward stroke, the measuring chamber is provided by the upper chamber  85  ( FIG. 8 b   ). 
     The embodiment of the conveying device  2  described in  FIGS. 8 a  to 8 d    works basically in the same way and manner as the embodiment described in  FIGS. 7 a  to 7 d   . Likewise, the conveying device  2  can be operated in conveying mode or in ventilating mode. In conveying mode, the conveying device  2  uses the pump  6  to convey the viscous material from the container  8 . 
     As has already been described above, the ventilating mode can comprise a first and a second ventilating phase. In order to avoid repetitions, reference shall be made to the description above for illustration of the first ventilating phase. 
     In the second ventilating phase, the remaining air is removed from the container  8 . 
     For this purpose, the controller  22  can be provided to close the return valve  34 , the discharge valve  35 , and the conveying valve  87  at the start of the second ventilating phase. Subsequently, the piston  96  is moved upwards with the aid of the drive rod  5  such that a defined pressure is applied in the pump chamber/measuring chamber  85 . The position sensor  39  is used to measure the path travelled by the piston  95  during this process. The pump chamber simultaneously serves as measuring chamber  85 , and the measured path is a measure of the volume change in the measuring chamber  85 . If the result of the measurement is that there still is useful material present in the measuring chamber  85  (usually, this will be material from the previous batch), the controller  22  causes the return valve  34  to be opened. If this is not the case, it causes the discharge valve  35  to be opened and the return valve  34  to stay closed. Then the piston  96  is moved all the way up by means of the drive rod  5  such that the material that is present in the measuring chamber  85  is transported out of the measuring chamber via the valve  34  or  35  that was opened by the controller  22 . 
     Simultaneously, the scoop piston  81  is moved upwards along with the upwards motion of the drive rod  5 . In this context, the scoop piston  81  conveys material  9  out of the container  8  and through the chamber  88  via the return valve  84  into the lower pump chamber  83 . 
     Once the piston  96  has reached its top end position and, thus, the material has been conveyed out of the pump chamber  85 , the previously opened valve  34  or  35  is closed again. Now, another compression measurement can take place. For this purpose, the drive rod  5  and the piston  96  are pushed downwards. Since all outlet-side valves  34 ,  35 , and  87  on the outlet of the pump  6  are closed, the downward motion of the drive rod  5  reduces the total volume (volume of chamber  83  plus the volume of chamber  85 ) and compresses the measuring sample  19 . The compressibility of the measuring sample  19  can now be determined in the way and manner already described above. Once the compression measurement is completed, the return valve  34  or the discharge valve  35  can be opened as a function of the result of the compression measurement and the classification of the material (as described above). The subsequent downward stroke of the piston  96  empties the lower chamber  83 . One portion of the material is conveyed out of the lower pump chamber  83  via the return valve  86  into the upper pump chamber  85  and from there out of the pump  6 . The other portion of the material is also conveyed out of the lower chamber  83 , but remains in the upper chamber  85 . 
     Subsequently, the valve  34  or  35  opened earlier is closed again.  FIG. 8 a    shows the operating state of the conveying device, in which the piston  96  is situated in its lower end position and the valve  34  or  35  is closed again. 
     After the piston  96  has reached its lower end position, the drive rod  5  with the piston  96  is pulled upwards again in a next step, in which the non-return valve  86  is closed ( FIG. 8 b   ). In the process, a defined pressure p is applied to the measuring sample  19  in the upper pump chamber/measuring chamber  85  now. 
     The path x travelled by the drive rod  5  is measured with the position sensor  39  in a further step. The position sensor  39  can detect, for example, the stroke of the piston  95  that is connected to the drive rod  5 . The travelled path x is a measure of the volume change and/or compressibility of the measuring sample  19  that is present in the pump chamber/measuring chamber  85 . If there is air in the pump chamber/measuring chamber  85 , and therefore in the material, the drive rod  5  travels farther than when the material is free of bubbles. The controller  22  now compares the measured travelled path x of the drive rod  5  to a reference value xref. The analysis of the measuring results and the classification of the measuring samples  19  takes place analogous to the description provided above. 
     If the air motor  4  is operated at a defined air pressure, the friction arising in the air motor  4  can lead to an error in the determination of the compressibility. In order to compensate for this effect and to be able to determine the compressibility of the measuring sample  19  even more accurately, the conveying device can, in addition, as is shown in  FIG. 8 , also comprise a pressure sensor  91 . The pressure sensor  91  can be used to measure the effective pressure in the measuring chamber  85 . 
       FIGS. 9 a  to 9 d    show four different operating states of another possible embodiment of the conveying device  2  based on four block diagrams. The further embodiment of the conveying device  2  differs from the embodiment according to  FIG. 8  described above in that the pump drive  4  is not provided as an air motor, but as an electric motor and preferably as a servo motor. 
     The servo motor  4  uses an integrated incremental encoder to deliver a position signal by means of which the rotational position of the drive shaft of the servo motor, the position of the rod  5  and/or the position of the piston  96  can be determined. The position signal is transmitted to the controller  22 . 
     The embodiment of the conveying device  2  described in  FIGS. 9 a  to 9 d    works basically in the same way and manner as the embodiment described in  FIGS. 8 a  to 8 d   . Likewise, the conveying device  2  can be operated in conveying mode or in ventilating mode. In conveying mode, the conveying device  2  uses the pump  6  to convey the viscous material from the container  8 . 
     As has already been described above, the ventilating mode can comprise a first and a second ventilating phase. In order to avoid repetitions, reference shall be made to the description provided above with regard to the illustration of the ventilating phases and in particular with regard to the embodiment according to  FIG. 8 . Rather than detecting the travelled path x of the drive rod  5 , the rotational position of the drive shaft of the servo motor can also be detected in the embodiment according to  FIG. 9 . 
     The calibration can take place in that the servo motor drives into one end position once, while the chambers  83  and  85  are empty, and the controller  22  then saves the position signal it receives. Subsequently, the servo motor drives into the other end position and the controller  22  then saves the position signal it now receives. 
       FIGS. 10 a  to 10 c    show three different operating states of another possible embodiment of the conveying device  2  based on three block diagrams. The further embodiment of the conveying device  2  differs from the embodiment according to  FIG. 9  described above in that the pump  6  is not provided as a scoop piston pump, but as an eccentric screw pump, screw spindle pump, spindle pump or gear type pump. The pump  6  can be operated appropriately such that it permanently attempts to convey material  9  into the chamber  85 . For this purpose, the pump  6  can be permanently driven by an electric motor, for example by a servo motor. By this means, a defined volume is set in the chamber  85  and a pressure p is established that is being detected by a pressure sensor  91 . The pump  6  comprises a pump actuator  90  that sets the material volume in the measuring chamber  85  and thus establishes the pressure p in the measuring chamber  85 . The pump actuator  90  can be the eccentric screw in the case of an eccentric screw pump, the screw spindle in the case of a screw spindle pump, the spindle in the case of a spindle pump, and those cogs in the case of a gear type pump, which establish the pressure p in the measuring chamber  85  and/or set the material volume in the measuring chamber  85 . 
     Comparing a bubble free measuring sample  19  to an air-containing measuring sample, a lower pressure p is established at a defined angle change of the drive shaft of the servo motor  4  in the chamber  85  in the air-containing measures sample  19  than in the bubble-free measuring sample Accordingly, the controller can use the rotational angle signal SPos reflecting the rotational angle of the drive shaft of the servo motor  4 , and the pressure P in the chamber  85  to deduce the compressibility of the measuring sample  19 . The rotational angle of the drive shaft of the servo motor  4  can be detected using the position sensor  39 . If any air is present in the measuring sample  19 , a predetermined reference pressure Pref, which is equivalent to a threshold value, is not reached. In contrast, if no air is present in the measuring sample  19 , the reference pressure Pref is reached or exceeded. This allows the controller  22  to run the ventilation according to the procedures described above (see, for example, the section on the embodiment according to  FIG. 8 ). 
     As has already been described above, the ventilating mode can comprise a first and a second ventilating phase. In order to avoid repetitions, reference to the description provided above and, in particular, to the description of the embodiment according to  FIGS. 7 and 8  shall be made with regard to the illustration of the ventilating phases. 
     If the controller  22  determining the compressibility of the measuring sample  19  detects that air-containing material is present in the measuring chamber  85  ( FIG. 10 b   ), it opens the discharge valve  35  to dispose the material like in the other embodiments described above, In contrast, if the controller  22  determining the compressibility of the measuring sample  19  detects that useful material is present in the measuring chamber  85  ( FIG. 10 c   ), it opens the return valve  34  to return the material into the container  8  like in the other embodiments described above. 
     The conveying device  2  and/or  102  can be used to convey various viscous materials, for example low-viscosity silicone. 
     If the conveying system  1  is equipped with two conveying devices  2  and  102 , it is also feasible to feed two-component materials, such as two-component silicone under pressure to a downstream mixing unit  200 . The materials conveyed separately to the mixer  200  can be mixed in the mixer  200 , for example at a ratio of 1:1. If needed, additives can be admixed to the conveyed materials in the mixer  200 . This allows to influence the colour or the properties of the material. 
     Preferably, the follower plate  7  of the conveying device  2  comprises a passage  73  for the return line  37 . 
     Moreover, it is advantageous to provide the valves  33 ,  34 ,  35  of the conveying device  2  in the form of needle valves. But this does not have to be the case. One or more of the valves  33 ,  34 ,  35  can just as well be provided as ball valves. 
     Advantageously, the volume of the measuring chamber  31  is less than 50 ccm. But the measuring chamber  31  can just as well comprise a volume of 60 ccm. A smaller measuring chamber volume is advantageous because it allows smaller measuring samples to be drawn. This allows the fraction of losses, i.e. the material classified not to be free of bubbles, to be reduced even further. 
     The preceding description of the exemplary embodiments according to the present invention is for illustrative purposes only and shall not limit the invention in any way or manner. Various changes and modifications are feasible within the scope of the invention. Accordingly, for example, the different components of the conveying device shown in  FIGS. 1 to 8  and/or the conveying devices  2  and  102 , can just as well be combined with each other in a way different from the one shown in the Figures. 
     Moreover, the conveying device  2  according to the invention can be provided to have a quick release device by means of which the measuring device  30  can be connected to and taken off the conveying device  2  and/or  102 . This is advantageous, in particular, when multiple conveying devices are present. A single measuring device  30 , which can be connected rapidly and easily to the corresponding conveying device, is sufficient for conducting the measurement and, if applicable, the subsequent ventilation. The quick release device is preferably provided appropriately such that the measuring device  30  can be connected to it without any need for tools.