Abstract:
To clean a relatively heavy liquid from small amounts of relatively light liquid the liquids are first introduced into a container, in which the light liquid is allowed to collect on the surface of the heavy liquid. A surface layer of the liquid body in the container, constituting a mixture of the two liquids, is caused to flow over an overflow outlet member into a collecting chamber. From the collecting chamber the liquid mixture is pumped further into a centrifugal separator, wherein the relatively light liquid is separated from the relatively heavy liquid. According to the invention the liquid mixture is pumped from the collecting chamber to the centrifugal separator through a pumping member, which is connected with a rotor of the centrifugal separator and, thus, rotates therewith.

Description:
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in PCT/SE00/00551 patent application filed on Mar. 21, 2000 and Swedish Patent Application 9901235-3 filed on Apr. 7, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method and a device for removing from a liquid body a liquid mixture, which forms a surface layer on the liquid body, and separating this liquid mixture into one relatively light liquid and one relatively heavy liquid. 
     BACKGROUND OF THE INVENTION 
       
     In workshops with machine tools for turning and cutting of metal pieces there is a need for a method and a device of the aforementioned kind for cleaning of liquids used for cooling purposes in the machine tools. Coolants of this kind normally are water based and deteriorate during use by, among other things, small amounts of oil being mixed with the coolant, such as hydraulic oil and lubricating oil, used for the operation of the machine tools. Oil of this kind causes an unpleasant smell and makes the coolant unusable in the course of time, if it is not separated from the coolant. It is known to clean coolants from oil by means of a centrifugal separator. In practice, this is performed such that a liquid mixture in the form of coolant and undesired oil is allowed to flow from a surface layer of a liquid body, containing the coolant to be cleaned, over an overflow outlet member into a collecting chamber. The liquid mixture is then pumped from the collecting chamber by means of a pumping device to the centrifugal separator. 
     Even in other connections there is a need for a method and a device for removing from a relatively heavy liquid, small amounts of a relatively light liquid. For example, liquids used for cleaning purposes often must have light floating contaminants removed therefrom, so that the liquid can be used anew. 
     The object of the present invention is to make possible cleaning of a relatively heavy liquid from small amounts of a relatively light liquid in a simple and non-expensive way by means of a simple and inexpensive device. The device should be compact and easily mountable to a container which contains liquid to be cleaned. Furthermore, the device should be operable automatically, and a desired cleaning effect should be obtainable without the need for complicated coordination of the operation of a centrifugal separator and a pumping device required for pumping the liquid to the centrifugal separator. 
     SUMMARY OF THE INVENTION 
     For achievement of this purpose the invention suggests a method of removing from a liquid body a liquid mixture, which forms a surface layer on the liquid body, and separating this liquid mixture into one relatively light liquid and one relatively heavy liquid, the liquid mixture being first caused to flow, as previously known, from the liquid body over an overflow outlet member into a collecting chamber and then pumped therefrom into a centrifugal separator. The method according to the invention is characterized in that the liquid mixture is pumped from the collecting chamber upwardly and into a rotating centrifugal rotor, forming part of the centrifugal separator, by means of a pumping member that is connected with the centrifugal rotor and is rotating therewith and extends down into the liquid mixture in the collecting chamber. Preferably, the overflow outlet member is vertically movable relative to the pumping member, further liquid mixture being caused to flow over from the liquid body to the collecting container in an amount per unit of time corresponding to the capacity of the pumping member and/or the corresponding centrifugal rotor. 
     For achieving a desired function of the vertically movable overflow outlet member a previously known technique may be used. Thus, the overflow outlet member may be kept floating on said liquid body, in accordance with U.S. Pat. No. 3,633,749, or be kept floating on the liquid mixture present in said collecting chamber, as set forth in U.S. Pat. No. 5,693,218. Alternatively, a different technology may be employed for automatic control of the amount of liquid mixture that is to flow over from the surface layer of the liquid body to the collecting chamber. A basic mission for the overflow outlet member is to adapt the flow of new liquid mixture into the collecting chamber to the flow of liquid mixture pumped up from the collecting chamber to the centrifugal rotor by means of the pumping device. 
     If the level of the surface layer of the liquid body is changed, it is desirable that the overflow outlet member automatically adapts itself thereto. This requires, if the collecting chamber is delimited by a collecting container having certain vertically immobile parts, that at least part of one wall of the collecting container is vertically movable together with the overflow outlet member. 
     In a preferred embodiment of the invention a collecting container wall part of this kind includes a bellows but, alternatively, sealing devices of different kinds may be used between the overflow outlet member and vertically immobile parts of the collecting container. 
     For cleaning of a liquid mixture, which has been transferred in the above described manner from the surface layer of a liquid body to a collection container for further transportation to a centrifugal separator, it is suggested according to the invention that the centrifugal separator includes a centrifugal rotor, which is connected with a pumping device adapted to extend from above and downwards into the liquid mixture present in the collecting container. The centrifugal separator further includes a driving device, which is adapted to drive the centrifugal rotor as well as the pumping device connected therewith wherein the pumping device is adapted to pump the liquid mixture to and into the centrifugal rotor. The pumping device may be designed in many different ways. Preferably, it includes a pumping member which is directly connected with the centrifugal rotor so that the common driving device may be adapted for rotation of both, the centrifugal rotor and the pumping member through one and the same transmission device. However, this is not absolutely necessary according to the invention. Alternatively, the driving device may be coupled separately to the pumping member, in which case a gear device of one kind or another may be used between the driving device and one of the centrifugal rotor and the pumping member. Most important is that an increased rotational speed of the pumping member, meaning an increased liquid flow to the centrifugal rotor, brings with it a corresponding increase of the separation capability of the centrifugal rotor as a consequence of an increased rotational speed thereof. 
     In a preferred embodiment of the invention a pumping device includes a tubular pumping member, which is rotatable around a substantially vertical rotational axis, the pumping member defining a central pumping channel for conducting liquid mixture from the collection container to the centrifugal rotor. Preferably, both the centrifugal rotor and the pumping member are rotatable around said vertical rotational axis, and in the preferred embodiment the pumping member, as mentioned, is directly connected with the centrifugal rotor for rotation together therewith. A pumping device of this kind does not subject the liquid to large shear forces. Shear forces of this kind are disadvantageous in this connection, since they cause undesired formation of emulsion of the two liquids to be separated from each other in the centrifugal separator. 
     The method and the device according to the invention may be used for continuous cleaning of a liquid, cleaned liquid being returned directly to said liquid body. The cleaned liquid is preferably returned to a level below the predetermined surface layer of the liquid body, so that the pre-separation having occurred in the liquid body is disturbed as little as possible. In the device according to the invention the returning is made by means of a stationary casing, which surrounds the centrifugal rotor and which has a returning member extending down into the liquid body to said level. 
     As mentioned, the rotatable pumping member extending down into the liquid to be cleaned is preferably tubular. For minimizing the wetted surface of the pumping member and/or for avoiding that liquid is pumped upwardly on the outside of the pumping member, the present invention provides a non-rotatable wall adapted to extend from above and down into the liquid mixture. During operation of the device, a sealing device provided in the collecting container is arranged to seal between the non-rotatable wall and the rotatable pumping member. The sealing device may have any suitable design. For instance, an annular lip gasket of rubber or some other elastic material may be supported by the non-rotatable wall and surround the pumping member and seal radially against the outside thereof. Alternatively, a similar annular lip gasket may be supported by the rotatable pumping member, so that by means of the centrifugal force it may be kept pressed radially outwardly against the surrounding non-rotatable wall. 
     In a preferred embodiment of the invention the sealing device includes an annular axially movable sealing member and means adapted to accomplish an axial sealing force between the non-rotatable wall or non-rotatable members connected therewith and the rotatable pumping member. The sealing member may be rotatable together with the pumping member, but preferably it is non-rotatable and adapted to be pressed axially against a sealing surface, preferably an end surface of the rotatable pumping member. 
     A non-rotatable wall of the aforementioned kind, which surrounds the pumping member, protects against unintentional contacts with the pumping member during rotation thereof. 
     If the centrifugal rotor is suspended from a flexible suspension device, said non-rotatable wall is preferably suspended from the same flexible suspension device for avoidance of relative pendulum movements between the rotatable and non-rotatable sealing surfaces of the sealing device during operation of the centrifugal rotor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described following with reference to the accompanying drawings, in which: 
     FIG. 1 is a side elevational view of a separation device according to the present invention shown mounted on a container containing liquid to be treated in the separation device. The container is shown in a section view. 
     FIG. 2 is a partly in section view of the separation device and container of FIG.  1 . 
     FIG. 3 is a partial enlarged view of the separation device of FIG.  2 . 
     FIG. 4 is a sectional view of the separation device of FIG. 3 taken along the line  4 — 4  in FIG.  3 . 
     FIG. 5 is a sectional view of the separation device of FIG. 3 taken along the line  5 — 5  in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show a container  1  containing liquid, which may be intended for use as a coolant in machine tools for turning or cutting of metal pieces. Liquid of this kind may be water based, and deteriorates upon use due to the presence of small amounts of oil. Used coolant enters the container  1  through an inlet  2  and cleaned coolant leaves the container through an outlet  3  to be reused. While the coolant is present in the container  1  it forms a liquid body  4 , in which the oil is collected in a thin surface layer at the top of the liquid body  4 . 
     The container  1  has a horizontal upper limiting wall  5  having an opening  6 , through which a separation device according to the invention extends from above and down into the container. The separation device, which forms a self sustaining unit mounted onto the container  1 , includes a casing  7 , which is suspended from the upper limiting wall  5  of the container through a flexible suspension device  8 . Only one of three alike parts of the suspension device  8  is shown in the drawing. Furthermore, the separation device includes a motor  9 , which is fastened to the upper part of the casing  7 , and a centrifugal rotor  10  (FIG. 2) suspended from the motor and surrounded by the casing  7 . The motor is adapted to drive the centrifugal rotor  10  around a vertical rotational axis R. 
     The separation device further includes a collecting container  11 , which is supported by the casing  7  within the container  1  in a way such that it is surrounded by the liquid body  4 . The collecting container  11  includes a bottom plate  12 , a surrounding wall in the form of a bellows  13  circular in cross section and fastened at its lower part to the bottom plate  12 , and an annular floater  14 , which is fastened to the upper part of the bellows  13 . The floater  14  is adapted to float on the liquid body  4  and to form an overflow outlet member, over which a surface layer of the liquid body  4  may flow into the collecting container  11 . The upper side of the floater has several radial recesses or grooves, through which the liquid may flow into the collecting container evenly distributed around the whole of the floater. The grooves give to the floater a stability, so that it moves the same extent vertically around the whole of its circumference. 
     FIG. 2 shows that the collecting container  11  delimits a collecting chamber  15  for a liquid mixture entering therein through the overflow outlet member (the floater)  14 . The liquid mixture consists mainly of coolant, which is relatively heavy, and a small amount of oil, which is relatively light. Furthermore, FIG. 2 shows that the bottom plate  12  of the collecting container is supported by a casing  7  by means of a sleeve  16 . 
     At its lower part the centrifugal rotor  10  carries a tubular, slightly conical pumping member  17 , which extends down into the collecting chamber  15 . The pumping member  17 , which is fastened to the centrifugal rotor  10  by means of a lock ring  18 , is surrounded by a substantially cylindrical non-rotatable wall  19 , which is supported by the casing  7  and extends from an area above the liquid body  4  down into the collecting chamber  15 . At its lower part the wall  19  carries a sealing device  20  adapted to seal against the lowermost part of the pumping member  17 , so that liquid mixture present the collecting chamber  15  will not get into contact with the outside of the pumping member  17 . The sealing device  20  is described in detail below with reference to FIG.  3 . 
     The centrifugal rotor  10  may be of a conventional kind and is therefore not described in detail. For a closer description of the centrifugal rotor of a suitable kind reference is made to, for instance, EP 312 233 B1, EP 312 279 B1, WO 96/33021 and WO 96/33022. 
     The centrifugal rotor  10  has an inlet chamber  21 , which through a channel  22  communicates with a separation chamber  23 . Furthermore, the centrifugal rotor  10  has a first outlet  24  for a separated relatively light liquid, in this case oil, and a second outlet  25  for a separated relatively heavy liquid, in this case water based coolant. The casing  7  has a first outlet  26  adapted to receive separated oil leaving the centrifugal rotor through its outlet  24  and a second outlet  27  adapted to receive separated coolant leaving the centrifugal rotor through its outlet  25 . 
     Separated oil is conducted through the outlet  26  to some suitable recipient therefor, whereas separated coolant is conducted through spaces in the casing  7  back to the liquid body  4 . Thus, the casing  7  is formed so that separated coolant is conducted on the outside of the stationary wall  19 , which surrounds the pumping member  17 , down to and through the aforementioned sleeve  16 . As can be seen in FIG. 2, there is delimited within the casing  7  a return chamber  28 , in which returned cleaned coolant forms a liquid body, the free liquid surface of which during operation of the separation device will be present somewhat above the liquid surface of the liquid body  4 . 
     FIG. 3 shows in a larger scale than FIG. 2 the collecting container  11  and the sealing device  20 . As shown in FIG. 3, the sealing device  20  includes an axially movable sealing member  29 . The sealing member  29  is adapted by means of a sleeve formed upper portion to seal against the inside of the stationary cylindrical wall  19  and by means of an annular lower portion to seal against the rotatable pumping member  17 . A screw spring  30  resting on wings  31  is adapted to press the sealing member  29  upwards, with reference to FIG. 3, into sealing engagement with the pumping member  17 . For this purpose, the pumping member  17  carries at its lowermost part a sealing member  32  rotatable therewith. The sealing members  29  and  32  abut against each other through axially facing sealing surfaces. 
     The wings  31  are connected with the bottom plate  12  and are intended, apart from supporting the spring  30 , for counteracting rotation of liquid in the collecting container  15  in the area of the lower part of the pumping member  17 . As shown in FIG. 3, at least one of the wings  31  extends all the way up to the inlet opening of the pumping member  17  in the area of the sealing member  32 . 
     FIG. 4 shows a section through the pumping member  17  along the line  4 — 4  of FIG. 3 illustrating the pumping member  17  having three internal axially and radially extending wings  33  intended for entrainment of liquid in the rotation of the pumping member. 
     FIG. 5 shows a section through the casing  7  along the line  5 — 5  of FIG.  3 . As shown, the outside of the casing  7  has three wings  34  extending both radially and axially therefrom. The wings  34  have, like the wings  31 , a function of counteracting rotation of liquid in the collecting chamber  15 . 
     The separation device according to the invention operates in the following manner: 
     The floater  14  is formed such that, as long as no liquid is present in the collecting container  11 , it may float on the liquid body  4  but only at a level such that a surface layer of the liquid body  4  flows over the floater  14  and into the collecting container  11 . When the liquid surface in the collecting container  11  approaches the floater  14 , the floater is actuated also by the liquid in the collecting container  11 . Then, the floater  14  is lifted up to a level such that it blocks further inflow of liquid into the collecting container  11 . This occurs before the liquid surface in the collecting container  11  has reached up to the same level as the liquid surface in the surrounding container  1 . 
     When the motor  9  is started for driving the centrifugal rotor  10  and the pumping member  17  connected therewith around the rotational axis R, liquid is pumped from the collecting container  11  upwardly through the pumping member  17  and into the centrifugal rotor  10 . The liquid surface will then sink in the collecting container  11 , whereby also the floater  14  will sink somewhat, and new liquid will flow into the collecting container  11  from the surface layer of the liquid body  4 . If an even flow of liquid is pumped out of the collecting container  11 , the liquid surface therein will be adjusted to a certain level, as can be seen in FIGS. 2 and 3, and the same amount of liquid will flow in via the floater  14  out through the pumping member  17 . 
     In the pumping member  17  a substantially cylindrical liquid surface will be formed, as is illustrated in FIG. 2, which extends all the way from the lower part of the pumping member to the inlet chamber  21  of the centrifugal rotor. In the liquid body, which is thus formed in the pumping member  17  and which is entrained in its rotation by the wings  33  (see FIG.  4 ), liquid flows axially upwardly as illustrated by means of arrows in the FIGS. 2 and 3. Centrally in the pumping member  17  there is left an air filled space which, if desired, may communicate with air surrounding the pumping member  17 . For this purpose the pumping member  17  may carry a small pipe, which extends from the centre of the pumping member radially outwardly to the outside of the pumping member. A pipe of this kind is indicated by dotted lines in FIG. 2 at the upper part of the pumping member  17 . 
     Liquid entering the inlet chamber  21  of the centrifugal rotor  10  through the pumping member  17  is conducted therefrom through the inlet channel  22  into the separation chamber  23 . In this chamber there is arranged a set of conical separation discs, which between themselves form thin separation spaces. In the separation spaces the small drops of oil suspended in the coolant are separated by being forced by the centrifugal force to move towards the rotational axis of the centrifugal rotor and out through the outlet  24 . The coolant freed from oil first flows in a direction from the rotational axis of the centrifugal rotor out of said separation spaces and then through one or more collecting channels back towards the rotational axis to the centrifugal rotor outlet  25  for cleaned coolant. 
     Whereas separated oil is conducted through the outlet  26  in the casing  7  to a particular recipient therefore, the cleaned coolant is conducted through the outlet  27  back to the liquid body  4  in the container  1 . Thus, the coolant is conducted from the outlet  27  to the return chamber  28  and from there through the pipe  16  out into the liquid body  4 . 
     Since the amount of oil separated from the coolant is extremely small, there is returned to the liquid body  4  a flow of liquid which is substantially of the same magnitude as that passing via the floater  14  into the collecting container  11 . A certain difference as to levels comes up between the liquid surfaces in the return chamber  28  and in the surrounding container  1 , respectively, as illustrated in the FIGS. 2 and 3. 
     As also illustrated in the FIGS. 2 and 3, there are formed in the area of the floater  14  two particular liquid surfaces immediately inside and outside, respectively, the bellows  13 . These liquid surfaces are formed because air has been enclosed on the underside of the floater both inside and outside the collecting container  11 . It should be mentioned, that the overpressure coming up in the air thus trapped contributes to the floating ability of the floater  14 . 
     As can be understood, the floater  14  adapts its position to the amount of liquid present in the container  1 , whereas the bottom plate  12  is maintained at an unchanged level. Furthermore it can be understood, that the pumping capacity of the pumping member  17  is automatically increased, if the separation capacity of the centrifugal rotor is increased by increasing of its rotational speed. Upon such an increase of the pumping capacity the inflow of liquid into the collecting container  11  from the liquid body  4  automatically increases. 
     The collecting container  11  need not necessarily be carried by the casing  7 , which surrounds the centrifugal rotor  10  and the pumping member  17 . Alternatively, it may be supported by the container  1 , e.g. stand on its bottom. Also, the stationary wall  19 , which surrounds the pumping member  17  and supports part of the sealing device  20 , need not be carried by the casing  7 . Even the wall  19  may alternatively be carried by the container  1 . However, the arrangement shown in the drawing is advantageous for several reasons. Thus, for the function of the sealing device  20  it is advantageous that both of the co-operating sealing members  29  and  32  are carried by one and the same suspension device. Since a suspension device for the rotatable centrifugal rotor  10  should be flexible and thus, the rotatable part of the sealing device  20  becomes flexibly suspended, also the non-rotatable part of the sealing device should be flexibly suspended. Furthermore, since the non-rotatable wall  19  around the pumping member  17  is preferably flexibly suspended, it is also advantageous that the collecting container  11  is flexibly suspended from the same suspension advice. Thereby, for instance the wall  19  or other members connected therewith may be used for guiding the vertical movements of the floater  14 . In the shown arrangement the wings  34  (see FIG. 5) are used for such guiding.