Abstract:
A plate heat exchanger including adjoining plates disposed adjacent one another and having peripheral grooves and channels alternately for media giving off heat and absorbing heat, seals made of an elastic material each being emplaced between the adjoining plates in the groove of one of the plates, attachment holes in each plate, and nipples on each seal insertable in the holes and with cross-sections different from the penetration cross-sections of the holes such that the nipples when inserted into the holes are not compressed about their entire circumference but only at spaced sites thereon at which the nipples project beyond the margin of the holes. The holes are defined by downturned edges which have radii and point in the insertion direction of the nipples into the holes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to plate heat exchanger and, more particularly, is concerned with a plate thereof having attachment holes and a seal thereof having nipples with cross sections different from the penetration cross section of the holes such that the nipples when inserted into the holes are not pressed about their entire circumference but only at spaced sites thereon at which the nipples project beyond the margin of the holes. 
     2. Description of the Prior Art 
     Before the plates of a plate heat exchanger are suspended in a frame and pressed together to form a packet, seals are fixed in grooves which facilitates handling the plates during the assembly. A known manner of fastening the seals is adhering the seals in grooves by use of an adhesive means which for the sealing effect itself is irrelevant but rather the adhesive means serves for the correct fixing of the position of the seals on the plates. This adhesion technique has some disadvantages. For example, before the application of the adhesive means, the grooves must be cleaned of, for example, oil and fat residues in order for the adhesive effect not to be impaired. Subsequently the adhesive means itself must be applied. All of this is rather time-consuming. Problems are also encountered in the maintenance of plate heat exchangers when a seal needs to be replaced. For this purpose the old seal must be removed and subsequently the groove must be cleaned of the adhesive means. An inspection of the groove bottom and the seal is also only possible, for example after the cleaning work on the dismounted heat exchanger, if the adhesion connection is previously destroyed. 
     Due to these disadvantages and the fact that in some technical fields, such as for example in medicine and food, adhesive means are to be avoided as much as possible, plate heat exchangers have been developed in which the seals are fastened mechanically, thus without adhesive means, on the plates. One feasibility known in the relevant technology for adhesive means-free seal fastening is that elastic nipples or projections, integrally developed with the seals, are brought into press fit with associated holes or openings in the plates. 
     According to patent document Nos. GB 2 071 303 A, GB 2 075 656 A and EP 0 134 155 A1, the nipples should have over-dimensions relative to the holes such that they can readily be pressed into the holes and can be pulled out again. It is therein to ensure that the seal is fixed securely at the intended site. This solution entails problems since the nipples as well as the seal as cast parts are subject to tolerance fluctuations. If the radial over-dimension of the nipples is too large, they can only be pressed into the holes with difficulty or not at all. If this is, nevertheless, successful, the nipples tear off when the seal is removed, for example during inspection or cleaning work, such that the seal must be replaced by a new seal. 
     The problem of tolerances in the radial nipple dimensions is solved through a plate heat exchanger disclosed in patent document No. EP 0 039 229 A2. Here, the nipples are provided on webs disposed laterally to the seal and developed integrally with it, from which the nipples project downwardly. Through the webs extends a pocket hole into the nipples. To fasten the seal, the nipples are positioned above the holes on the plates which are associated with the nipples. Subsequently a pin or like tool is introduced into the pocket hole and the nipples are then stretched by pressure onto the pin such that they become significantly thinner and can be placed into the holes without any problems. After the removal of the pin the nipples contract again to their original dimension whereby the ends of the nipples inserted through the holes expand to form a head covering the hole from below. The seals are consequently fastened securely on the plates. Of disadvantage in this technique is that tools are necessary to press the nipples in the holes. Furthermore, during inspection or maintenance work requiring the removal of the seals, the above-described consequences occur, the tearing off of the nipples. 
     Lastly, patent document No. EP 0 123 379 B1 discloses a plate heat exchanger in which the seal is fastened on the plate by means of elastic projections integrally developed with it, which extend into associated openings in the groove bottom. The openings are developed such that they comprise an insertion and pull-out region into which the projections can freely be moved, and from which they can be moved out again, along the margin of the openings without force. From this region the projections can be moved into a blocking region of the openings, in which the motion of the projections into the openings, respectively out of them again, is counteracted by strong resistance by compression between the projections and the margins of the openings, wherein moving the projections from the insertion and pull-out position into the blocked position, and conversely, is possible due to the elasticity (resiliency) of the seal. 
     Consequently, a need exists for an innovation in a plate heat exchanger of the type described above which will overcome the aforementioned problems without introducing new problems in place thereof. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned problems in a plate heat exchanger by providing a simple solution for the mechanical fastening of the seals on the plates, which solution nevertheless permits a secure hold of the seals on the plates and also a problem-free removal of the seals from the plates. Specifically, each plate has attachment holes and each seal on a given plate has nipples projecting therefrom with cross-sections different from the penetration cross section of the holes such that the nipples when inserted into the holes are not pressed about their entire circumference but only at spaced sites thereon at which the nipples project beyond the margin of the holes. Since the cross-sections of the nipples are smaller than the penetration area of the holes, at other sites there is still clearance between the circumference of the nipples and the margin of the holes. Due to the elasticity of the nipples, their compressed material can expand into these free volumes, which leads to a decrease of the compression and consequently facilitates pressing the nipples into the holes. Through this displacement mechanism overtolerance in the radial dimensions of the nipples is extremely well compensated or, expressed differently, it is possible to work with relatively greater radial over-dimensions than is possible with the prior art. 
     Accordingly, the present invention is directed to a plate heat exchanger which comprises: (a) a plurality of adjoining plates disposed adjacent one another so as to form a packet, the plates having peripheral grooves and a plurality of channels alternately for media giving off heat and absorbing heat, and inlet and outlet openings for passage of the media through the channels between the adjoining plates; (b) a plurality of seals made of elastic material, each of the seals being emplaced between the adjoining plates in the groove of one of the adjoining plates; and (c) means for mechanically fastening each of the seals on one of the plates. The fastening means includes a plurality of attachment holes defined in each of the plates and a plurality of nipples made of elastic material and being insertable in the holes, the nipples being integrally formed on each of the seals at intervals spaced longitudinally along the seal, the nipples having cross sections different from penetration cross sections of the holes such that the nipples when inserted into the holes are not compressed about the entire circumference of the nipples but only at spaced sites thereon at which the nipples project beyond margins of the holes such that due to the elastic material the nipples can compress radially and axially so as to permit the pressing-in and pulling-out of the nipples into or out of the holes. 
     More particularly, the nipples have one of a polygonal and circular cross section and the holes have the other of the polygonal and circular cross section. The margins of the holes are provided as annular downturned edges pointing in the direction of insertion of the nipples into the holes. This forming of the holes has various advantages. Thus, for one, the contact area between nipple and hole is increased. Thereby, the radial over-dimension of the nipples required according to the prior art can be decreased while maintaining a secure hold of the seal. This permits the nipples to be pressed into and pulled out of the holes more readily. For another, the immersion of the nipples into the holes is facilitated since the ends of the nipples when they are inserted into the holes run against an encompassing radius on the margin of the holes. This radius also permits providing a radius at the transition from nipple to seal. This, for one, has advantages with respect to fabrication engineering during the production of the seal and, for another, it reduces the danger of the nipples being sheared off at this site during movements of the plates. 
     The tips of the nipples have truncated conical shapes which facilitates inserting the nipples into the holes. Preferably, each of the nipples has a trigonal cross-sectional configuration and each of the holes has a circular configuration. Further, each of the nipples has three edges circumferentially spaced apart and rounded off. 
     These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following detailed description, reference will be made to the attached drawings in which: 
     FIG. 1 is a schematic top plan view of a plate heat exchanger showing a plate according to the invention. 
     FIG. 2 is an enlarged fragmentary perspective view of a margin region of the plate with an emplaced seal. 
     FIG. 3 is an enlarged sectional view taken along line A—A of FIG. 2 showing a second plate with the first plate and the inserted seals thereon. 
     FIG. 4 is another enlarged sectional view taken along line B—B of FIG. 2 showing the first and second plate and inserted seals. 
     FIG. 5 is still another enlarged sectional view taken along line C—C of FIG. 2, extending substantially perpendicular to the sectional views of FIGS. 3 and 4, showing the first and second plates and inserted seals. 
     FIG. 6 is an enlarged cross-sectional view taken along line D—D of FIG.  5 . 
     FIG. 7 is another enlarged cross-sectional view taken along line E—E of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings and particularly to FIG. 1, there is schematically illustrated a plate heat exchanger of the present invention having a plate  1  with a heat exchange area  2  which is framed by a seal  4  placed into a peripheral groove  3  and comprised of a synthetic rubber or another elastic sealing material. The plate  1  can be in the form of a sheet metal slab. At the corners of the plate  1  are provided inlet and outlet openings  5 ,  6 ,  7 ,  8  for the heat exchange media. While in the depicted plate  1  the inlet and outlet openings  5 ,  6  are encompassed by the seal  4 , the seals and plates disposed in front and behind plate  1  which encompass the inlet and outlet openings  7 , 8  are now shown in FIG.  1 . In such manner, the plates and seals are bundled into a packet such that alternately flow channels are formed for a medium giving off heat and a medium absorbing heat. The plate heat exchanger described thus far corresponds to the structure known from the prior art and therefore does not require further explanations. 
     Referring to the margin section of the plate  1  shown in FIG. 2, the seal  4  is shown fixed in the groove  3  without using any adhesive means. A second plate  1 ′, depicted in FIGS. 3-5, has been omitted in FIG. 2 for reasons of clarity. For this purpose, on the side of the plate  1  facing away from the heat exchange area  2 , there is provided a plurality of retaining parts  9  (only one shown) associated with the groove  3  and integrally formed with the seal  4 . The retaining parts  9  are disposed at suitable intervals from one another on the circumference of the seal  4  and project laterally therefrom. 
     As is evident in FIGS. 2-4, the groove  3  is formed by an inner side wall  10  extending downwardly from the level of the heat exchange area  2 , an outer side wall  12  extending upwardly again to the level of the heat exchange area  2  and a groove bottom  11  extending between and interconnecting the inner and outer side walls  10 ,  12 . The outer side wall  12  is adjoined by a plate margin  13 . This plate margin  13  is not at one level but rather is formed by channels  14  and  15  alternately opening upwardly and downwardly as well as outwardly and having the form of a trapezoid in cross section. Channels  14  have bottoms  16  at the level of the groove bottom  11  and channels  15  have bottoms  17  at the level of the heat exchange area  2  so as to form the plate margin  13  with a “corrugation” configuration. The channels  14  define troughs which are closed by front walls  18  adjacent to the groove  3 . Bridges  19  are provided between the front walls  18  of channels  14  and the outer side wall  12  of the groove  3 . The spaces  20  formed underneath these bridges  19  connect the channels  15  which extend up to the outer side wall  12  of groove  3  on the underside of plate  1 . 
     Each retaining part  9  takes the form of a generally U-shaped web  21  which extends into two adjacent channels  14  and a channel  15  disposed inbetween. The web  21  is integrally connected with seal  4  along the entire width of the web  21  extending along the groove  3 . As seen in FIGS. 3 and 4, the thickness of the web  21  is less in an intermediate portion  24  of the web  21  which overlies a region of bottom  17  of channel  15  adjacent to the channel  3  than in a bight portion  23  of the web  21  which overlies the bridges  19  between the two channels  14  and the outer side wall  12  of the groove  3  such that the web  21  is thereby reinforced at the end portion  23 . In order to receive this reinforced bight portion  23  of the web  21 , bridge  19 . 1  of channels  14  into which each retaining part  9  extends is provided, in comparison to the remaining bridges  19 , are indented downwardly by the magnitude of the reinforcement provided by bight portion  23  such that the bridges  19 . 1  formed thereby have a lesser height above bottoms  16  of channels  14  than do the bridges  19 . 
     Also, adjoining opposite ends of and extending transversely to the bight portion  23  of web  21  of each retaining part  9  is a pair of end extension portions  22  which extending away from the seal  4  and groove  3  with the channels  14  of the plate margin  13 . The intermediate portion  24 , adjacent to and connected with the bight portion  23 , also extends between and interconnects the extension portions  22 . 
     As seen in FIGS. 3-5, when installed the end extension portions  22  lie within the associated channels  14 , while the intermediate portion  24  rests on the bottom  17  of the channel  15  disposed inbetween. As is evident in particular in FIG. 5, the cross sections of the extension portions  22  are selected such that they fill completely the hexagonal cross section formed by the channels  14  of plate  1  and the channels  15  of plate  1 ′ being superimposed on the plate  1 . In other words, the extension portions  22  are in contact formfittingly in the associated channels  14  and  15  of respective plates  1 ,  1 ′ facing one another. Since the channels  14 ,  15  are open toward the outside, and thus toward the environment, the retaining parts  9  can expand in this direction, whereby thermal and mechanical stresses are reduced and thus deformations of the plate margin  18  are avoided. 
     FIGS. 3 and 5 together show that the bottom  16  of channel  14  of plate  1 ′ which is disposed above the intermediate portion  24  of web  21 , is raised in its rear region by the thickness of the intermediate portion  24  such that it conforms from above to the presence of the intermediate portion  24  of the web  21 . It can also be seen in FIG. 3 that the transverse bight portion  23 , after assembly, substantially fills the space  20  under bridge  19  of overlying plate  1 ′. 
     The above-described form-fit development of the retaining parts  9  with the plates  1 ,  1 ′ covering the parts  9 , stabilizes the orientation of the plates  1 ,  1 ′ in the plate packet of the plate heat exchanger and prevents, or reduces, in cooperation with conventional metal guidance elements developed on the plates, movements of the plates  1 ,  1 ′ in the plate plane, during operation of the plate heat exchanger, due to the internal pressure of the heat exchange media. 
     Since the retaining parts  9  and thus also seal  4  in the embodiment described so far rest only loosely on plate  1 , measures for fastening must be taken in order for the seal  4  to be reliably fixed in the groove  3  to enable handling the plates during the assembly of the plate heat exchanger. For this purpose, a nipple  24 , integrally formed with each retaining part  9 , is provided, which projects downwardly and, with the seal  4  mounted in the groove  3 , projects through a circular attachment hole  26  formed in plate  1 . The margin of the hole  26  is developed as a draw-through feature having an annular downturned edge  27  pointing in the direction of insertion of the nipple  25 . The radius of the annular downturned edge  27  facilitates inserting the nipple  25  into the hole  26 . The transition of the nipple  25  to the intermediate portion  24  of the web  21  can simultaneously also be implemented with this radius. This provision of a radius on the downturned edge  27  about the margin of the hole  26  prevents, for one, the shearing forces acting on the nipple  25  by the margin of the hole  26  and facilitates, for another, the production of the nipple  25  since radii can be realized more readily in a casting mold. To further facilitate the insertion into the hole  26 , the tip of the nipple  25  is provided in the configuration of a truncated cone. 
     Referring to FIGS. 6 and 7, furthermore in contrast to the circular cross-sectional configuration of the hole  26 , the nipple  25  has a trigonal cross-sectional configuration. The three edges  29  of the trigonal cross-sectional configuration of the nipple  25  are rounded off, as most clearly seen in FIG.  6 . In FIG. 6, a circle  28  enveloping the cross-section of the nipple  25  is drawn in. Diameter D 1  of the circle  28  shown in FIG. 6 is greater than the inner diameter D 1  of the hole  26  shown in FIG.  7 . But simultaneously the cross-sectional area of nipple  25  is smaller than the penetration cross section of the hole  26 . 
     If, during the mounting of seal  4 , the nipple  25  is pressed into hole  26 , the nipple  25  becomes centered due to its conical tip and the radius of the downturned edge  27  of the hole margin itself. Simultaneously, the penetration of the nipple  25  into hole  26  is facilitated. When the nipple  25  is pressed in further, its material is compressed at the positions projecting over the inner diameter of the hole  26 , which, in this case, are the rounded-off edges  29  of the nipple  25 . But, due to its elasticity it can expand into the free volumes between the cross-section of nipple  25  and the downturned edge  27  of the hole  26 . In FIG. 7, these free volumes are identified with the reference numeral  30 . Since the material of nipple  25  thus has radial and axial freedom of flow, the pressing-in and pulling-out of nipple  25  into or out of the hole  26  is facilitated. Simultaneously the required clamp-fit of nipple  25  in hole  26  is ensured, which is even further improved due to the greater inner wall area of hole  26  provided by the downturned edge  27 . 
     In implementing the invention, either the holes  26  can have a circular or polygonal penetration cross-sectional shape and the nipples  25  vice versa. 
     It is thought that the present invention and its advantages will be understood from the foregoing description and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form(s) hereinbefore described being merely preferred or exemplary embodiment(s) thereof.