Abstract:
A test tube rack ( 1 ) that is suited for storing and transporting test tubes. The test tube rack ( 1 ) according to the invention includes a bottom plate ( 3 ), a cover plate ( 2 ), and a centering plate ( 4 ), which are arranged parallel to one another and spaced apart from one another. The plates have a substantially rectangular shape. At each corner a screw connector ( 8 ) is arranged, through which the plates are joined to each other. The screw connectors ( 8 ) are designed such that, when stacking a plurality of test tube racks ( 1 ), the screw connectors ( 8 ) of one test tube rack ( 1 ) partially engage with the screw connectors ( 8 ) of another test tube rack ( 1 ), and thereby ensure a secure connection, at least with respect to lateral shifting. Additionally, the screw connectors ( 8 ) can be provided with a locking mechanism, which allows a rigid connection between test tube racks ( 1 ).

Description:
BACKGROUND 
     The invention relates to a test tube rack with a plurality of wells for test tubes, with a bottom plate, a cover plate, and a centering plate arranged therebetween, wherein the three plates are arranged parallel to one another and spaced apart from one another, and the cover plate and centering plate in each case have, at each well, a congruent opening for receiving a test tube, and the bottom plate is formed continuously without openings at the wells. 
     A test tube rack of this kind is made, for example, of sheet steel, with two side parts integrally connected to the cover plate. The centering plate and the bottom plate are secured on these side parts by spot weld connections. Alternatively, the side parts can be integral with the bottom plate or can be separate parts. 
     However, the spot welding results in the side parts having cavities in which dirt or liquids can gather. 
     Other known test tube racks use rods or other connecting elements, to which the plates are secured, for example by welding or adhesive bonding. 
     In laboratories, these test tube racks serve both as a storage rack for storing and transporting empty or filled test tubes and also as a work rack for carrying out routine laboratory work. The problem arises that test tube racks having multiple rows are less suitable for working with, since the back rows are difficult to see. At the same time, however, the known test tube racks are also not particularly suitable as a storage rack, since they require a large area to stand on and are difficult to handle. 
     SUMMARY 
     The object of the invention is therefore to make available a test tube rack of the aforementioned type which is especially suitable for storing and transporting test tubes and which by comparison requires a smaller area to stand on. 
     According to the invention, this object is achieved in that the bottom plate, cover plate and centering plate are each connected to one another by at least three screw connectors, and that the screw connectors are designed in such a way that a plurality of test tube racks can be stacked together and, during stacking, the screw connectors of one test tube rack engage partially in the screw connectors of the other test tube rack. 
     The screw connectors are designed such that they each connect all three plates to one another, thus forming a stable and sturdy rack. The screw connectors are preferably designed such that no cavities or edges occur in which dirt can gather. 
     It is important, however, that a plurality of test tube racks according to the invention can be stacked on top of one another, with the screw connectors of one rack each engaging partially in the screw connectors of the other rack. The advantage of the test tube rack according to the invention is that even test tube racks equipped with test tubes can be stacked together. For this purpose, the screw connectors are dimensioned such that the spaces between two stacked test tube racks are large enough. 
     By virtue of the fact that the screw connectors engage partially in one another, at least a lateral shifting of the test tube racks is prevented and good stability is ensured. 
     By stacking a plurality of racks together, it is thus possible for a large number of test tubes in total to be stored on the standing area of one rack. 
     For transporting an individual rack, it is expedient if the test tube rack has lateral carrying handles, which are arranged opposite each other on the cover plate or centering plate. 
     The screw connectors can be configured in various ways. In a preferred embodiment, the screw connectors have a continuous connector rod and an upper connector head and lower connector head. The connector rod passes through all three plates and is fixed from above and below by the connector heads. For this purpose, the connector rod has an external thread, preferably at least at both ends, although a threaded rod with a continuous thread can also be used. The connector heads each have internal threads, with which the connector heads can be screwed onto the connector rod. 
     Spacers are preferably arranged between the plates and keep the plates spaced apart from each other. These spacers are expediently sleeve-shaped and are arranged coaxially on the connector rods. However, the spacers can also be arranged separately from the screw connector at another location. 
     To allow the test tube racks to be stacked together in a manner secure against shifting, a preferred embodiment of the invention is one in which the upper connector heads each have a projection, the lower connector heads each have a recess, and, when a plurality of test tube racks are stacked together, the projection engages in the recess. Such a projection can be cylindrical, polygonal or of any desired shape, and the recess is designed with a substantially complementary shape. 
     The connection of two test tube racks that have been stacked together can be secured by an additional locking mechanism. For this purpose, at least two of the screw connectors preferably additionally have a locking mechanism. The test tube racks connected to and locked onto each other in this way form a unit and can be handled jointly. 
     In one embodiment of the locking mechanism, provision is made that the projection has a groove or notch, that the lower connector head has a spring-actuated locking element, which is arranged in the recess, and that, when test tube racks are stacked together, the locking element engages in the groove or notch. 
     The shape of the test tube rack is not essential to the invention. Preferably, the individual plates are substantially rectangular and are connected to one another in each corner by a screw connector. However, the plates can also be square, round or triangular, for example, and, in the latter two cases, three screw connectors are sufficient to obtain good stability. 
     Particularly in the embodiment of the test tube rack with a locking mechanism, it is expedient if a lid with carrying handle can be placed on the test tube rack and can be secured by the locking mechanism. In this way, a test tube rack, or a unit composed of several test tube racks stacked and locked together, can be comfortably transported using the carrying handle of the lid. 
     The height of the test tube rack is preferably dimensioned such that the test tube racks can also be stacked together when fitted with test tubes. The centering plate is preferably arranged substantially in the middle between cover plate and bottom plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below on the basis of illustrative embodiments and with reference to the attached drawings, in which: 
         FIG. 1  shows an oblique view of a test tube rack according to the invention with rectangular plates and four screw connectors, 
         FIG. 2  shows a schematic cross-sectional view of an upper connector head, 
         FIG. 3  shows a schematic cross-sectional view of a lower connector head, 
         FIG. 4  shows a side view of an alternative embodiment of an upper connector head with an additional locking mechanism, 
         FIG. 5  shows a cross-sectional view of an alternative lower connector head with a locking mechanism, 
         FIG. 6  shows a transverse section through the connector head of  FIG. 5 , with the upper connector head locked, and the locking mechanism visible, 
         FIG. 7  shows a partial cross-sectional view of two stacked and locked test tube racks with a lid, and 
         FIG. 8  shows a perspective view of the lid with carrying handle from  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , a test tube rack according to the invention is designated overall by reference number  1 . The test tube rack  1  has a cover plate  2 , a bottom plate  3  and, arranged substantially midway between these, a centering plate  4 , said plates being parallel to one another. The plates  2 ,  3 ,  4  are substantially the same size and have a rectangular shape with rounded corners. The shape of the plates is not essential to the invention, and therefore square, triangular or round plates can also be used. 
     In the exemplary embodiment, the test tube rack has thirty-six wells  5  for test tubes  6  with a diameter of 20 mm or 25 mm. The wells  5  each have a congruent, circular opening  7  in the cover plate  2  and in the centering plate  4 . The bottom plate  3  has no openings at the wells  5 , such that any drips of liquid are caught in the test tube rack  1 . 
     Like the shape of the openings  7 , the number of wells  5  is also not essential to the invention, and therefore the test tube rack  1  can be scaled to any desired degree. For example, a test tube rack  1  with the same standing area can also have fifty-six wells  5  for 16-mm test tubes or forty-one wells  5  for 18-mm test tubes. 
     The individual plates  2 ,  3 ,  4  are connected to one another by four screw connectors  8 , each one arranged in a corner. Each screw connector  8  has a lower connector head  9 , an upper connector head  10 , a connector rod  11  and two sleeve-shaped spacers  12 . The substantially cylindrical connector heads  9 ,  10  each have an internal thread  13 , into which the external thread of the connector rod  11  can be screwed. At their corners, the plates each have a bore for the passage of the connector rod  11 . 
     The test tube rack  1  is now easily constructed as follows. The lower connector heads  9  serve as support feet for the test tube rack  1 . The connector rods  11  are screwed into the lower connector heads  9 . The bottom plate  3  is placed on the lower connector heads  9 , a respective connector rod  11  passing through each of the bores in the corners of the bottom plate  3 . Spacers  12  are now each pushed coaxially onto the connector rods  11  and bear on the bottom plate  3 . The centering plate  4  lies on the spacers  12 . Further spacers  12  define the distance between centering plate  4  and cover plate  2 . The upper connector heads  10  are now screwed over the cover plate  2  onto the connector rods  11 , as a result of which all the structural parts are pressed against each other and fixed. On the circumference, the connector heads  9 , each have two mutually opposite flats  14 , to which a fork wrench can be applied for tightening the screw connectors  8 . However, the connector heads can also have other means to permit tightening. 
     Instead of a continuous connector rod  11  with spacers  12 , a two-part connector rod can also be used which at the same time serves as a spacer and is screwed via an additional pair of threads, with the centering plate  4  being clamped in this screw connection. 
     As is shown in an exaggerated form in  FIGS. 2 and 3 , the connector heads  9 ,  10 , on the side resting on a plate, have a tapering peripheral edge  15 , which is flush with the outer circumference. When the screw connectors  8  are tightened, this edge  15  is pressed into the respective plate surface and forms an annular groove there. By virtue of the plastic deformation, the connection between connector head and plate is substantially sealed off, such that no liquid and no dirt can get into the gap between connector head and plate. 
     Analogously, the spacers  12  also have tapered edges of this kind on their end faces, such that the connections between the spacers and the plates are also sealed off in this way. However, this is not shown in the drawings. 
     A carrying handle  16 , by which the test tube rack  1  can be easily transported, is arranged on each of the narrow sides of the cover plate  2 . The carrying handle  16  is formed by a U-shaped bracket  17  which is secured, for example by screw connections, on two tabs  18  formed integrally with the cover plate  2 . However, the carrying handle can also be designed in another way, for example entirely in one piece with the cover plate. Alternatively, the carrying handles can also be arranged on the centering plate  4 . An individual rack  1  can be transported easily and comfortably using this carrying handle. 
     The upper connector heads  10  each have a central, cylindrical projection  19 , as can be seen more clearly in  FIG. 2 . The lower connector heads  9  each have a recess  20  matching the projection  19  ( FIG. 3 ). 
     With this design of the screw connectors, it is possible for a plurality of test tube racks  1  according to the invention to be stacked on top of one another. 
     If a plurality of such test tube racks  1  are now stacked on top of one another, the projections  19  of the upper connector heads  10  of one test tube rack  1  engage in each case in the recesses  20  of the lower connector heads  9  of the other test tube rack  1 . This creates a connection between the test tube racks  1  that at least prevents a lateral shifting. 
     The distances between the individual plates  2 ,  3 ,  4  and the heights of the connector heads  9 ,  10  are preferably dimensioned such that there is enough free space for test tubes  6 , such that test tube racks  1  fitted with test tubes can also be stacked. 
     The fact that the test tube racks  1  can be stacked means that, compared to the prior art, a large number of test tubes  6  can be stored or transported on the same standing area. 
     To make transport even safer, the screw connectors  8  can additionally have a locking mechanism, which permits a releasable, secure connection between two test tube racks  1 . These screw connectors with locking mechanism have an upper connector head  21  as shown in  FIG. 4  and a lower connector head  22  as shown in  FIG. 5 . 
     Compared to the connector head  10  in  FIG. 2 , the upper connector head  21  has a higher, narrower and substantially cylindrical projection  19  which, at its free end  23 , tapers in the shape of a truncated cone. Approximately half way along its length, the projection  23  has a circumferential groove  24 . 
     The lower screw connector  22  ( FIG. 5 ) has a recess  20  into which the projection  19  of the upper screw connector  21  can engage. In addition, the lower connector head  22  has a spring element  25  ( FIG. 6 ), which is arranged in the lower third transversely with respect to the recess  20 . In the example, the spring element  25  has approximately the shape of a question mark, although a straight or a differently shaped spring element  25  would also be suitable. The spring element  25  is connected to a push rod  26 , which is guided movably and tangentially in the connector head  22  and via which the spring element  25  can be tensioned. In the untensioned state, the spring element  25  protrudes partially into the recess  20 , while in the tensioned state the recess  20  is free. The spring element  25  can also be operated by another actuator element. 
     When the lower connector head  22  is placed onto an upper connector head  21  as per  FIG. 4 , the spring element  25  is initially tensioned by the frustoconical projection  23 , such that the recess  20  is free and the projection  19  can be completely inserted. As soon as the circumferential groove  24  reaches the height of the spring element  25 , the spring element  25  relaxes and engages at least partially in the groove  24 . The projection  19  is thereby fixed in the recess  20 . 
     To release this locked connection, the spring element  25  has to be tensioned by pressing the push rod  26 , until the recess  20  is free, and has to be held until the projection  19  is removed from the recess  20 . 
     Generally, other known forms of locking are also conceivable. The design shown here is given only by way of example and is not in any way limiting. 
       FIG. 7  shows two test tube racks  1  according to the invention stacked one on top of the other. In the example, each test tube rack has, at two diagonally opposite corners, connector heads with a locking mechanism  21 ,  22 , whereas the two other corners have connector heads without a locking mechanism  9 ,  10 . It is of course also possible for all the screw connectors to have locking mechanisms, but this makes the release of the locking mechanism difficult, since all four push rods  26  have to be operated at more or less the same time. Similarly, in the example, spacers  12  are shown only on one screw connector  8 , and the connector rod  11  concealed in the spacer  12  is indicated by broken lines. However, the other screw connectors  8  have the same features. 
     The test tube rack  1  additionally has a lid  27 . At each of two diagonally opposite corners, the lid  27  has a lower connector head with locking mechanism  22 . The lid  27  can thus be connected securely to a test tube rack  1  that has upper connector heads with locking mechanism  21 . The two other corners merely have stubs  30 , which have the same height as the connector heads  22  and thus bear on the connector heads  21  of a test tube rack  1 . 
     The lid  27  has a continuous lid plate  28 , which completely covers the test tube rack  1  and prevents test tubes  6  from falling out at the top and prevents dirt from getting into the test tubes  6 . The lid  27  also has a U-shaped handle  29 , by which one or more test tube racks  1  locked underneath it can be comfortably carried with one hand. The handle  29  is preferably screwed onto the lid plate  28 . 
     By means of the locking mechanism and the lid  27 , it is also possible for a plurality of fully stocked test tube racks to be stacked and safely transported. 
     The test tube rack  1  according to the invention can also be part of a system that includes test tube racks  1  for different test tube diameters. All the racks  1  of the system have the same standing area and can be stacked on top of one another in any desired manner. 
     In another expedient embodiment, the lower connector heads without locking mechanism as per 3 can have an additional recess into which the projection of the upper connector head as per  FIG. 4  can be inserted. At the same time, the lower connector heads as per  FIG. 5  must have an additional recess for the projection of the upper connector head as per  FIG. 2 . In this way, test tube racks with locking mechanism and test tube racks without locking mechanism can be stacked on top of one another in any desired combination, with no locking being carried out in some circumstances. 
     In addition, the test tube rack  1  can have an inscription plate or similar inscription possibility, such that the rack and/or also individual wells can be clearly identified. The inscription plate can be connected fixedly to the rack, for example screwed onto it. 
     Moreover, shelves or other transportation means present in trucks or in automobiles, for example, can have connector heads which have a locking mechanism and which are compatible with the test tube rack, such that the racks can be securely locked in the shelf. This permits safe transportation of the racks in the shelves without additional holding means.