Plate heat exchanger

A plate heat exchanger has a frame plate, a pressure plate and heat exchange plates clamped therebetween, all suspended from a carrying bar passing through a hole in the pressure plate and extending at least some distance into a corresponding hole in the frame plate. The pressure plate is slidable on the carrying bar. The frame plate and the pressure plate are identical so that the hole for the carrying bar in the frame plate is identical to the hole for the carrying bar in the pressure plate. The carrying bar is fastened in the frame plate by means of a locking device.

The present invention relates to a plate heat exchanger comprising a frame 
plate and a pressure plate and heat exchange plates clamped therebetween, 
which heat exchange plates are suspended from a carrying bar passing 
through a hole in the pressure plate and extending at least a distance 
into a corresponding hole in the frame plate. 
A plate heat exchanger comprises, as mentioned, a frame plate and a 
pressure plate, which usually are termed end plates, and heat exchange 
plates arranged between these. Further, the plate heat exchanger comprises 
an upper carrying bar, in which the heat exchange plates are suspended, 
and usually a lower guiding bar, which also is intended to cooperate with 
the heat exchange plates for determining their positions. The frame plate 
and the pressure plate differ as a rule from each other referring to their 
design. Thus, the frame plate may as an example be provided with four 
ports, two for each heat exchange medium, while the pressure plate thus 
would not need to have any single port. Another essential difference 
between the frame plate and the pressure plate is that the sizes of the 
holes for the carrying bar and the guiding bar are unequal. The reason 
hereto is that the carrying bar and the guiding bar are intended to be 
fastened to the frame plate, while the pressure plate should be slidable 
towards and backwards along these bars, depending on the amount of heat 
exchange plates mounted between the frame plate and the pressure plate. 
Thus, it has been usual that the pressure plate has been provided with a 
hole for the carrying bar and the guiding bar having a diameter somewhat 
larger than the diameter of the carrying bar and the guiding bar, while 
the frame plate, however, has had a smaller hole which has been threaded 
and lain in engagement with a threaded outer part of the carrying bar to 
fasten the same to the frame plate. Another known method to fix the 
carrying bar and the guiding bar to the frame plate has been to fasten 
these by means of a bolt. The carrying bar and the guiding bar have thus 
with their one end surface been borne against the inner side surface of 
the frame plate and been fixed in this position by means of a bolt which 
has gone through a hole in the frame plate, which hole corresponds to the 
thickness of the bolt, and has engaged into the carrying bar and the 
guiding bar. 
The consequences of these differences between the frame plate and the 
pressure plate has lead to that the manufacturer of plate heat exchangers 
has been forced to have a stock of both frame plates and pressure plates, 
which is both expensive and taking up a great deal of storage space. 
The problem with an equal number of ports in the frame plate and the 
pressure plate can be solved in the way that all of the frame plates and 
the pressure plates being provided with four ports, whereafter the ports, 
which will not be used, are provided with caps. This technique to provide 
the ports with caps is previously known, but despite that, nobody has 
previously suggested a plate heat exchanger being provided with a frame 
plate and a pressure plate identically manufactured. The reason hereto 
obviously has been that one has had such a fixation on the thought that it 
requires conventional fastening according to the above of the carrying bar 
and the guiding bar, that one has not thought of the possibility to make 
the holes for the carrying bar and the guiding bar identical in the frame 
plate and the pressure plate. That one has not thought of the possibility 
of making the frame plate and the pressure plate identical is shown by the 
fact that despite that plate heat exchangers have existed on the market in 
at least 60 years nobody has previously suggested this solution. The 
present invention is thus characterized in that the frame plate and the 
pressure plate are identical so that the hole for the carrying bar in the 
frame plate is identical to the hole for the carrying bar in the pressure 
plate and that the carrying bar is fastened in the frame plate by means of 
a locking device. 
This implies that for each type of plate heat exchangers only one kind of a 
plate need to be manufactured, which thus could be used both as a frame 
plate and as a pressure plate. The great advantage with this invention is 
that the storage of end plates becomes inexpensive and requires relatively 
small storage space.

Referring to FIG. 1 there is shown a frame plate 1 and a pressure plate 2 
and a carrying bar 3 connecting the two plates with each other. The frame 
plate 1 and the pressure plate 2 has been manufactured identical, whereby 
the hole 4 in the frame plate and the hole 5 in the pressure plate are 
essentially equal. 
As shown from the figure, the hole 5 in the pressure plate 2 is so big that 
the pressure plate can freely be displaced along the carrying bar 3. Since 
the hole 4 in the frame plate 1 is as big as the hole 5 in the pressure 
plate this implies that the frame plate would be displaceable relatively 
the carrying bar. As mentioned earlier the carrying bar must however be 
fastened into the frame plate. This fastening of the carrying bar into the 
frame plate is effected by means of a special locking device. The locking 
device is composed of a tightening means 6, a washer 7 and an expander 8. 
As evident from the figure a thin portion 9 of the part of the carrying bar 
3, which extends into the hole 4 of the frame plate 1, has essentially 
less thickness than the rest of the carrying bar. The reason hereto is 
that there should be space for an expander of a certain size, which is 
intended to surround the portion 9 of the carrying bar and thus be placed 
between this portion and the wall of the hole 4 in the frame plate. 
Further, the expander 8 bears against a shoulder 10 of the carrying bar, 
which is formed at the transitional area between the thin portion 9 of the 
carrying bar and the portion 11 of normal thickness. This transitional 
area is in this case arranged in the part of the carrying bar, which is 
located in the hole of the frame plate. Naturally, it can be arranged in 
another part of the carrying bar, as an example, close outside of the hole 
in the frame plate. This latter location, however, has the disadvantage 
that on one hand the expander 8 must have a larger axial extent and on the 
other hand the natural support between the portion 11 of the carrying bar 
and the frame plate becomes lost. 
The washer 7 has a hollow cylindrical part 12 which surrounds the thin 
portion 9 of the carrying bar and whose one end bears against one side 
surface of the expander 8. The cylindrical part 12 of the washer 7 is thus 
placed between the portion 9 of the carrying bar 3 and the wall of the 
hole 4 in the frame plate. The other end of the cylindrical part 12 has a 
flange 13 which is intended to bear against the outer side surface of the 
frame plate. 
The tightening means 6 is in this case constituted of a bolt, which is 
intended to engage into a threaded hole in the carrying bar. Thereby the 
head of the bolt is intended to bear against the flange 13 of the washer. 
The tightening means 6 can, instead of a bolt, consist of a nut which is 
provided with threads for engagement with the portion 9 of the carrying 
bar, whose at least outer part is also provided with threads. 
The carrying bar 3 and its thin portion 9 usually have circular 
cross-section, whereby the hole 4, the part 12 of the washer 7 and the 
expander 8 at rest have circular-cylindrical shape. The carrying bar 3 and 
its thin portion 9 may however have another shape, as an example a form 
having rectangular or square cross-section. However, the outer part of the 
portion 9, which is provided with threads for cooperation with the nut, 
must be circular-cylindrical. Hereby, also the hole 4, the part 12 of the 
washer 7 and the expander 8 ought to have a rectangular or square 
cross-section. 
Upon locking of the carrying bar in the frame plate the bolt or the nut 6 
is tightened on the bar 9, whereby the cylindrical part 12 of the washer 7 
is pressed against the expander 8. Hereby the expander is axially 
compressed, but radially expanded, so that its inner radial part is 
pressed against the portion 9 of the carrying bar, while its outer radial 
part is pressed against the wall of the hole 4 of the frame plate. Hereby 
the carrying bar is fastened in the frame plate. 
It is not necessary that the carrying bar 3 is provided with a thin portion 
9, but the tightening means 6 may consist of a bolt which directly engages 
into a threaded hole in the carrying bar 3 extending into the hole 4 of 
the frame plate. Upon tightening of the bolt 6 the expander 8 will expand 
radially so that it is pressed on one hand against the shaft of the bolt 
and on the other hand against the wall of the hole in the frame plate 1 
and it will be compressed axially between the cylindrical part 12 of the 
washer 7 and one end surface of the carrying bar 3. 
Even if the guiding bar of the heat exchanger is not shown on the drawing, 
it is lying within the scope of the invention to apply the same locking 
devices for the guiding bar as for the carrying bar. 
According to the described embodiments in connection to FIG. 1 the devices 
for fastening of the carrying bar in the frame plate comprise a washer 
between the tightening means and the expander. It is, however, possible 
within the scope of this invention to modify the tightening means, i.e. 
the bolt or the nut, in such way that on one hand it will bear direct 
against the expander, and on the other hand against the side surface of 
the frame plate, whereby the expander upon the tightening of the bolt or 
the nut will be axially compressed and radially expand with a fastening of 
the carrying bar in the frame plate as a result. 
In FIG. 1 a number of heat exchange plates have schematically been shown, 
which are held clamped between the frame plate 1 and the pressure plate 2 
by means of a screw joint comprising two or several clamping bolts 15. 
Referring to FIG. 2 there are also shown a frame plate 20, a pressure plate 
21 and a carrying bar 22, which preferably are cylindrical. Thereby, like 
the device according to FIG. 2 the frame plate and the pressure plate are 
made identical, implying that the holes in the frame plate and the 
pressure plate are of equal size. The locking of the carrying bar into the 
frame plate is however effected in a different way in this case. Thus, the 
cylindrical end 23 of the carrying bar, which is intended to cooperate 
with the hole in the frame plate, has been plastically deformed by means 
of knurling, whereby the diameter of the end of the carrying bar has been 
enlarged. In this case, knurling implies that the end of the carrying bar 
has been deformed by means of a tool whereby longitudinal grooves 24 are 
formed around the envelope surface of the cylinder. Thereby the distance 
between the tops of the two diametrical opposite grooves 24 becomes larger 
than the diameter of the end 23 of the carrying bar before the 
deformation. Upon locking of the end 23 of the carrying bar in the frame 
plate 20, the end of the carrying bar is pressed into the hole of the 
frame plate, whose diameter is somewhat less than the distance between the 
tops of the two diametrical opposite grooves in the end of the carrying 
bar. Hereby the end of the carrying bar is locked by press force. 
The carrying bars of th embodiment according to FIG. 1 and 2 can either be 
solid or tubular. 
Also in the embodiment according to FIG. 3 the frame plate and the pressure 
plate are made identical, whereby the holes in these plates are of equal 
size. According to this embodiment the carrying bar 30 must be tubular. 
The locking of the end 31 of the carrying bar into the hole of the frame 
plate 32 is in this case also effected by press force by means of the 
outer diameter of the end 31 of the carrying bar having been made somewhat 
larger than the outer diameter of the carrying bar 30. This enlargement of 
the outer diameter of the end 31 of the carrying bar 30 has been effected 
by means of plastic deformation of the carrying bar. The plastic 
deformation can be made by rolling for example or by means of a mandrel 
which is punched into the end of the hollow carrying bar. For this reason, 
the carrying bar should not have a too big wall thickness.