Patent Publication Number: US-2021170425-A1

Title: Method by which a lubricant flow rate at a centrifuge is monitored

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention relate to a method by which a lubricant flow rate at a centrifuge is monitored. 
     Centrifuges have a drive device with a motor in order to rotate at least one drum using this motor. This motor is generally an electric motor or—more rarely—a fluidically operated motor. The motor rotates directly or via interconnected further elements such as a transmission and/or a belt on a drive spindle, which is mounted using one or multiple bearings in a housing and/or frame. The drive spindle is in turn coupled in a rotationally-fixed manner to the drum of the centrifuge. 
     If a direct drive is implemented, the drive torque of the electric motor is introduced directly and sometimes even without a clutch into the drive spindle of the centrifuge. The rotor shaft of the electric motor can then even be led out of the electric motor and can even be connected in a rotationally-fixed manner as a drive spindle to the drum of the centrifuge. 
     The drive spindle of the centrifuge is rotatably mounted in a bearing arrangement, which has one or multiple bearings. The bearing arrangement is supplied with lubricant continuously by a lubricant supply in a continuous lubricant flow in many designs, wherein the lubricant supply can be designed according to the principle of a circulating lubrication. The lubricant circulation is generated by one or more pumps. The term “lubricant” is to be understood broadly and comprises free-flowing lubricants of greatly varying types, in particular lubricant oils. 
     Exemplary embodiments of the invention are thus usable at least in all of the above-described variants of centrifuges. 
     For frictionless operation of the centrifuge, a reliable supply of the bearing arrangement with lubricant is to be ensured. It is thus desirable with respect to the highest possible availability of the centrifuge if the lubricant flow is continuously monitored and at least one measured value of an operating state is regularly compared to at least one limiting value, so that it is displayable and/or a warning can be output and/or an action can be started due to deviations from these limiting values. 
     It is therefore desirable to install sensors/measuring devices for direct or indirect flow rate measurement in the lubricant circuit within a centrifuge drive having lubricant circulating lubrication. 
     The use of inductive flowmeters appears less reasonable since the use of this measurement principle is unsuitable due to the electric properties of many lubricants. A mass flow meter is suitable with respect to the measurement principle, but the circulating lubricant quantity is frequently too small for a reasonable use of the often quite costly measuring devices. 
     An oscillating piston meter generates a low counter pressure. Since the measurement takes place on the lubricant return side of the bearing, this lubricant pressure is generally not available in typical centrifuge bearings. The lubricant pressure on the lubricant feed side of the bearing can be used and measured, however, a possible clog in the lubricant circuit cannot be recognized in this way. 
     For this reason, other methods have been developed to measure the lubricant flow rate reliably. 
     In one known method of such a measurement of the lubricant flow rate in the lubricant circuit, the flow rate is determined by means of the weight of the lubricant which flows over a rocker, wherein the location of the rocker is contactlessly detected and evaluated. 
     In another known method of such a measurement of the lubricant flow rate, the lubricant level in a buffer container in the lubricant return line is measured by means of an optical measurement (for example, light refraction or turbidity), wherein the buffer container is provided with a drain and thus runs empty if the lubricant flow rate is disturbed. 
     Proceeding from the prior art, exemplary embodiments of the invention are directed to an improved method, using which a lubricant flow rate at a centrifuge is monitored, in particular of a separator or decanter. 
     A method is provided, using which a lubricant flow rate at a centrifuge is monitored, in particular of a separator or decanter, which has a rotatable drum which is rotatable using a drive device, wherein the drive device has a motor, which directly or indirectly drives a drive spindle that is coupled in a rotationally-fixed manner to the drum, wherein the drive spindle is rotatably mounted in a bearing housing by at least one bearing arrangement having at least one bearing, and wherein the centrifuge has a device for lubricant supply, using which the bearing arrangement is supplied with lubricant, which has at least the following steps:
         a. rotating the drive spindle using the drive device and simultaneously operating the lubricant supply to generate a lubricant flow rate through the bearing arrangement.   b. monitoring the lubricant flow rate through the bearing arrangement on the basis of at least one measurement of a temperature of the lubricant at at least one measurement point on or in the device for lubricant supply.       

     Simple and also inexpensive and nonetheless very reliable monitoring of the lubricant flow rate through the bearing arrangement is possible on the basis of this at least one temperature measurement and monitoring. 
     A measurement point is a point of the lubricant supply, in particular on or in a line, at which a temperature sensor is arranged, the signal of which is evaluated directly at the sensor or at another location by an evaluation unit. This evaluation unit can be, for example, a control computer of the centrifuge. 
     According to one preferred variant, the monitoring can comprise a comparison of the measured temperature or a variable dependent thereon to at least one predetermined condition and the triggering of an action in the event of a deviation from the condition. The action can comprise, for example, the output of a warning signal and/or an emergency mode or a shutdown of the centrifuge. 
     In one preferred embodiment variant of the invention, a temperature of the lubricant is measured in each case at a first measurement point and at a second measurement point in the device for lubricant supply and the temperature difference is calculated in each case from the two measured values and the calculated temperature difference is compared to a condition defined for it—in particular a limiting value. A simply designed and reliable method results therefrom for monitoring the lubricant flow rate through the bearing arrangement of the centrifuge drive, since variations of the ambient temperature or changes of the machine temperature (for example, due to a hot product to be processed) can be eliminated. 
     It is also advantageous if a time curve of the measured temperature of the lubricant is formed, so that a temperature increase or a temperature decrease per unit of time is ascertainable by ascertaining the first derivative function of the measured temperature curve over time. A further simply designed and thus advantageous method for monitoring the lubricant flow rate through the bearing arrangement of the centrifuge drive thus results. 
     It is also advantageous if the device for lubricant supply includes a centripetal pump, to which the lubricant return line is connected. In this case, the device for lubricant supply can advantageously and simply have a ring space in which the lubricant collects in depressurized form. The lubricant circulation can thus be implemented with low design expenditure, since the rotational movement of an oil reservoir provided in any case, which co-rotates on the drive spindle, is used for the pump functionality. 
     A lubricant supply is also conceivable in which a rotating clamshell conveys the lubricant from an idle reservoir through a hole in the spindle to the at least one bearing. 
     In a further preferred embodiment variant of the invention, the temperature of the lubricant is measured continuously or quasi-continuously at the at least one measurement point. An instantaneous temperature can thus be displayed and evaluated, so that the state of the lubricant circulation can also be concluded on the basis of temperature-time curves. 
     The sensor elements used as the temperature sensor can be based on different action principles. The temperature of the lubricant at the at least one measurement point can thus be measured in each case simply, inexpensively, and sufficiently accurately, for example, using one or multiple variable electrical resistances or using one or multiple thermocouples, which preferably use the Seebeck effect, or using one or more thermal sensors having quartz oscillator. 
     In a further preferred embodiment variant of the invention, the position of the first measurement point is at or in the lubricant feed line and the position of the second measurement point is at or in the lubricant return line. In another or optional embodiment variant of the invention, the position of the first measurement point is at or in the lubricant return line and the position of the second measurement point is in the lubricant reservoir. The position of the first measurement point can also be in the lubricant reservoir and the position of the second measurement point can be located on the machine frame, however. Variants of these combinations are also conceivable. The measurement points are thus advantageously at locations each having clearly pronounced and well measurable temperature level, so that inferences about the instantaneous state of the lubricant circulation can be derived with high reliability and thus advantageously from a measured temperature difference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The invention is described in greater detail hereinafter on the basis of exemplary embodiments with reference to the figure. However, the invention is not restricted to these exemplary embodiments. In the figures: 
         FIG. 1 : shows a front view of a separator in section; and 
         FIG. 2 : shows a detail of the front view of the separator from  FIG. 1  in section. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is described hereinafter on the basis of a separator having vertical axis of rotation. This is a preferred but not required embodiment. The invention is also to be applied in centrifuges of other designs and also different alignment of the axis of rotation in space, thus in solid-wall scroll-type centrifuges or decanters. 
       FIG. 1  shows a separator  1  having a drum  2  having vertical axis of rotation D here, which is enclosed by a hood arrangement  3 . Terms such as “top” and “bottom” refer hereinafter to the vertical arrangement of the drum  2 . The drum  2  is placed on a drive spindle  4 . This spindle is mounted rotatably in a bearing housing  7  using a bearing arrangement, which comprises a top bearing  5  and a bottom bearing  6  here. For example, this bearing arrangement has two roller bearings. Other designs are conceivable (not shown here). 
     A separator drive having an (electric) motor  8  as a drive device is used to drive the drum  2 . This motor  8  has a motor housing  9  having a stator  10  or a stator winding and a rotor  11 . 
     The motor  8  advantageously does not have a separate mounting here, which enables an inexpensive design. The bearing arrangement is arranged here between the motor  8  and the drum  2 . 
     The drive spindle  4  is furthermore directly—i.e., preferably without interconnected elements, for example, a clutch—connected to the rotor  11  here by way of example. The motor housing  9  having the stator  10  is, in contrast, arranged rigidly and unsprung on the machine frame  12  of the separator  1  or supported thereon. 
     In this way, the drum  2  having the drive spindle  4 , the rotor  11 , and the bearing housing  7  form an oscillating unit, which is elastically supported on the machine frame  12 , but with which the stator  10  is not associated, so that relative movements occur between the rotor  11  and the stator  10 . 
     The drive spindle  4  is arranged by means of the bearing  5  and the bearing  6  in a hole-type opening  13  of the one-part or multipart bearing housing  7 . 
     The bearing housing  7  has an upper flange  14  and a lower sleeve-like section  15 , which extends through an opening  16  in the machine frame  12 . 
     The upper flange  14  is supported via a circumferentially-distributed elastic damper elements  17  on the machine frame  12 , which are distributed between the bottom side of the flange  14  and the top side of the machine frame  12 , wherein the flange  14  and the machine frame  12  are provided with ring-like steps  18 ,  19  in the region of the damper elements  17 . 
     The separator  1  furthermore has a device for lubricant supply  100 , which supplies the bearing arrangement or the bearing  5  and the bearing  6  here with lubricant. The device for lubricant supply  100  operates here according to the principle of circulating lubrication. 
     The device for lubricant supply  100  is illustrated in  FIG. 2 . The device for lubricant supply  100  has a lubricant reservoir  101 , in which a lubricant stock is stored. A lubricant feed line  102  plunges into the lubricant reservoir  101 . A lubricant pump  103 , which conveys the lubricant through the lubricant feed line  102  to the top bearing  5 , is arranged in the lubricant feed line  102 . The lubricant then flows through the bearing  5  and supplies the bearing  5  with lubricant at the same time. After the lubricant has left the bearing  5 , it flows through the hole-type opening  13  of the bearing housing  7  to the bearing  6 . The lubricant then flows through the bearing  6  and supplies the bearing  6  with lubricant at the same time. 
     The lubricant then exits from a bottom open end of the hole-type opening  13  on the lower sleeve-type section  15  of the bearing housing  7  and collects in unpressurized form in a housing-type ring space  104 . The housing-type ring space  104  is formed by a housing  105  and the bearing housing  7 , wherein the housing  105  encloses the bearing housing  7  on its lower sleeve-type section  15 . Due to the rotation of the drive spindle  4 , the lubricant collects in operation of the separator  1  on the outside  106  of the housing-type ring space  104 . 
     A tubular attachment or projection  107  extending radially outward from the lower sleeve-type section  15  of the bearing housing  7  into the ring space  104  extends into this housing-type ring space  104  and merges like a non-corotating centripetal pump into a lubricant return line  108  for the lubricant, which firstly extends radially inward and then upward in the bearing housing  7  and exits therefrom on top and opens into the lubricant reservoir  101 . 
     By means of this attachment  107  like a centripetal pump having the downstream lubricant return line  108 , it is possible during rotations of the drum  2  and/or the ring space  104  to discharge the lubricant under pressure from the ring space  104  like a pump and conduct it back into the lubricant reservoir  101 , without mist or sprays resulting. A centripetal pump is formed in this way, to which the lubricant return line  108  is connected. 
     Within the separator drive having such a device for lubricant supply  100 , which operates according to the principle of the described lubricant circulation lubrication, a part of the resulting waste heat of the bearing arrangement, which arises due to bearing friction here in the top bearing  5  and the bottom bearing  6 , is discharged to the lubricant. 
     This results in heating of the lubricant. This heating is measurable on or in the lubricant return line  108 . If lubricant circulation no longer takes place (for example, because of a clog, a leak, or the failure of the lubricant pump  103 ) or if the lubricant circulation is reduced (partial clog), the value of the heating of the lubricant in the lubricant return line  108  changes. 
     In the event of a clog or interruption of the lubricant flow rate, the heating in the lubricant return line  108  is reduced starting from a previously reached operating temperature, since the power loss from the bearing can no longer be absorbed by the lubricant flow. In the event of a partial clog and a reduced volume flow in the lubricant return line  108  of the lubricant circuit, the lubricant temperature will increase, since the reduced oil quantity has to absorb the entire power loss from the bearing. The deviation of the lubricant temperature in the lubricant return line  108  from a defined normal state can thus be used to monitor the volume flow and therefore the lubricant flow rate. 
     It is now proposed that the lubricant temperature in the lubricant circuit be measured and the present state of the lubricant flow rate be concluded depending on the measured temperature. 
     The temperature can be measured at a single measurement point M 1  in the lubricant circuit. The measurement can take place continually or quasi-continuously at short intervals. 
     By way of an evaluation of the results of such a continuous or quasi-continuous temperature measurement at this at least one measurement point Ml, it is possible with the aid of a control unit and a suitable monitoring computer program to draw inferences about the state of the lubricant supply. 
     The temperature can thus be ascertained directly and can be used directly or indirectly as an indicator for the state of the lubricant supply. 
     Thus, for example, the temperature curve over time can also be ascertained and an item of status information about the trend of the temperature curve can be obtained from the first derivative of this function, which enables a prediction of the temperature development. At least one property of this derivative function (for example, slope) can also be compared to a defined limiting value to trigger an action in dependence thereon. 
     The temperature in the lubricant circuit can alternatively also be measured at multiple, in particular two different (each suitable) measurement points M 1 , M 2  in the lubricant circuit and then, for example, the differential temperature ΔT between the temperatures respectively measured at the two measurement points M 1 , M 2  can be used as a status criterion or monitoring criterion for a correct lubricant flow rate in the lubricant circuit. Using this method, variations of the ambient temperature or changes of the machine temperature (for example, due to a hot product to be processed) are eliminated, which results in significantly more stable operating behavior of the monitoring system. 
     A preferred suitable position for the first measurement point M 1  is, for example, on or in the lubricant feed line  102 . A preferred suitable position for the second measurement point M 2  is on or in the lubricant return line  108  (see  FIG. 2 ). Further suitable positions of the measurement points M 1 , M 2  are the lubricant return line  108  (M 1 ) and the lubricant reservoir  101  (M 2 ) or the lubricant reservoir  101  (M 1 ) and the machine frame  12  (M 2 ). 
     The following example explains these relationships in greater detail: 
     With a volume flow or a lubricant circulation quantity (having an oil as a lubricant) of 1 L/minute and a thermal power emitted due to friction of the bearing arrangement of the drive spindle  4  of 400 W, a heating ΔT of 15° C. thus results between the measurement point M 1  on or in the lubricant feed line  102  and the measurement point M 2  on or in the lubricant return line  108 . This heating is thus stored as the “normal value” in the controller of the centrifuge. 
     A defined deviation from this normal value to be reliably monitored could thus be T Deviation &gt;=5° C. This means that with a deviation of greater than 5° C. from a temperature differential previously ascertained as the normal value between the measurement points M 1  and M 2 , a malfunction in the lubricant circuit has to be concluded and therefore a warning message or an action is triggered. 
     The temperature measurement is advantageously carried out in a continuous or quasi-continuous manner by commercially available temperature sensors or measurement principles. 
     With respect to the preferred measurement principles, for example, variable electrical resistors (for example, platinum measuring resistors such as Pt 100  or silicon measuring resistors) can be used. The use of thermocouples, which utilize the Seebeck effect, is also conceivable. The use of a thermal sensor having quartz oscillator is also conceivable. 
     The signal of these temperature sensors is detected and evaluated, for example, by an electrical controller (not shown here) and can be continuously displayed. 
     As described, the time curve of the temperature of the lubricant in the lubricant circuit at a measurement point M 1  or the temperature differential ΔT of the lubricant flowing to the bearing arrangement and the lubricant flowing back from the bearing arrangement can be calculated from the respective measured values which are ascertained at the measurement point M 1  or M 2 , respectively, to then compare the result to a defined threshold value or limiting value. 
     In addition, the controller can be used during the startup of the centrifuge or the separator  1 , thus when a temperature time curve which can be evaluated is not yet present or stable temperature differential ΔT has not yet resulted between lubricant flowing in and flowing back, to suppress a comparison to the defined limiting value. 
     This suppression can take into consideration both the startup time of the centrifuge or the separator  1  and also the run-down time. In addition, such a controller can adapt the defined limiting value to be monitored to the present operating conditions of the centrifuge. For example, if the speed of the centrifuge or the separator  1  is lowered due to method requirements, the power loss of the bearings  5 ,  6  also changes, which in turn requires a different defined limiting value which has to be monitored. 
     Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description. 
     LIST OF REFERENCE SIGNS 
     
         
           1  separator 
           2  drum 
           3  hood arrangement 
           4  drive spindle 
           5  top bearing 
           6  bottom bearing 
           7  bearing housing 
           8  motor 
           9  motor housing 
           10  stator 
           11  rotor 
           12  machine frame 
           13  opening 
           14  flange 
           15  section 
           16  opening 
           17  damper element 
           18  step 
           19  step 
           100  device for lubricant supply 
           101  lubricant reservoir 
           102  lubricant feed line 
           103  lubricant pump 
           104  ring space 
           105  housing 
           106  outside 
           107  projection 
           108  lubricant return line 
         M 1  measurement point 
         M 2  measurement point 
         D axis of rotation
       cm.  1 - 16 . (canceled)