Background art More particularly, the invention relates to an exchanger particularly suitable to be associated with air heaters for dryers of granulated plastics for molding.

It is known that granulated plastics must be dried appropriately before being placed in the mold.

Plastics can in fact contain a certain amount of moisture which, during molding, can compromise the successful outcome of the process because of the formation of steam bubbles, which prevent the correct filling of the mold and interrupt the continuity of the outer surface of the component.

Air heaters for dryers have long been used for this purpose aiming at eliminating any moisture that is present in granulated plastics for molding processes.

Such air heaters are conveniently provided with air/air exchangers which substantially comprise, in a thermally insulated box-like containment body, a tube bundle or nest constituted by groups of parallel straight tube portions whose heads are welded to box-like manifolds so as to define a winding path, in which each group of tube segments is arranged between two manifolds and such manifolds define the direction changes for the internal exchange fluid, which is generally constituted by air to be heated.

Moreover, partitions are fixed inside the box-like body in order to divert the exchange fluid, generally constituted by combustion gases, that flows on the outside of the bundle.

This type of exchanger, which is usually in countercurrent, achieves the intended aim but is not free from drawbacks.

In particular, the main drawback is connected to the fact that all stresses

due to thermal expansions induced by the high temperature of the combustion gases are discharged substantially onto the welds, thus compromising the overall durability of the exchanger.

Welds have long been identified as an overall critical spot of the internal structure in tensioned states induced by expansions.

Other problems are caused by the very shape of the connection between the tube segments and the box-like manifold, which allows limited adaptation to the expansions and contractions of the material determined by the thermal conditions of operation.

As a whole, the structure of currently commercially available exchangers has low adaptability to thermal gradients and is accordingly subject to a rather rapid functional wear.

Moreover, the manifolds concur to provide, as a whole, a high level of resistance to flow, which accordingly requires adequate means for generating the pressure of the exchange fluids.

Disclosure of the invention The aim of the present invention is to provide an air/air exchanger whose structure solves the drawbacks mentioned above, particularly ensuring high structural adaptability to deformations induced by thermal variations and allowing a long operating life in optimum conditions.

Within this aim, an object of the present invention is to provide an exchanger whose structure greatly limits the use of welds and allows to discharge any deformations onto regions where none of such welds are present, ensuring that the welds are not subjected to stresses which would damage them.

Another object of the present invention is to provide an exchanger whose structure is flexible as regards the use for which it is designed.

A further object of the present invention is to provide an exchanger whose structure can also optionally be easily adapted to air heaters that are already in production.

Still an object of the present invention is to provide an exchanger whose structure allows a considerable reduction in maintenance operations and in operating costs.

Another object is to provide an exchanger which can be manufactured with known equipment and systems.

This aim and these and other objects which will become better apparent hereinafter are achieved by an air/air exchanger, characterized in that it comprises, in a box-like containment body, a tube bundle or nest constituted by a plurality of tubes, each whereof is shaped so as to define a winding path and is fixed, at its ends, to corresponding box-like inlet and outlet manifolds.

Brief description of the drawings Further characteristics and advantages of the present invention will become better apparent from the description of an embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein: Figure 1 is a partially sectional view of an air/air exchanger having the structure according to the invention; Figure 2 is another sectional view, taken along the line 1-1, of the exchanger of Figure 1; Figure 3 is another sectional view, taken along the line 11-11, of the exchanger of Figure 1.

Ways of carrying out the invention With reference to Figures 1 to 3, an air/air exchanger for air heaters of dryers of granulated plastics intended for molding processes, having the structure according to the invention, is generally designated by the reference numeral 10.

The exchanger 10 comprises, in a thermally insulated box-like containment body 11 shown schematically in the figures and designated by the reference numeral 12, a tube bundle or nest, generally designated by the reference numeral 13, constituted by a plurality of tubes 14 which in this

case trace a winding path along their length, each tube being continuous along the entire length of the exchange path, which is substantially formed by straight portions alternated with elbows, and being fixed at its ends, respectively a first end 15 and a second end 16, to corresponding box-like manifolds, respectively a first manifold 17 and a second manifold 18.

The exchanger 10 also comprises, within the body 11, multiple partitions 19 and walls 20 so as to form, as a whole, a first exchange duct 21 in which the tube nest 13 is placed and in which one of the exchange fluids (typically combustion gases) flows on the outside of the nest.

A second feeder duct 22, connected to the first duct 21, is formed in the body 11.

Moreover, the first manifold 17 is connected to the outside, while the second manifold 18 continues so as to expand and form a chamber 23, which also is connected to the outside.

The tubes 14 that constitute the tube nest 13 are fixed to the ends of said first and second manifolds 17 and 18 by welding.

The first duct 21 is connected to the outside by way of a corresponding sleeve 24.

Likewise, the second duct 22 is connected to the outside by way of a corresponding sleeve 25.

In practice it has been observed that the present invention has achieved the intended aim and objects.

In particular, attention is called to the extreme limitation of welded connections because of the presence of only two manifolds and to the particular shape of the tubes that constitute the tube nest, in which the elbows absorb the expansions caused by thermal gradients.

It should also be noted that the structure as a whole is substantially simple from the constructive point of view thereby ensuring a good economy of processes during production.

It should also be noted that thanks to the particular shape of the tubes that

constitute the tube nest, the only welds that are possibly provided at the end of said tubes are in practice relieved of most the stresses, since any deformations are absorbed substantially in the regions where the tubes proper form bends.

It should also be noted that the continuity of the tubes that constitute the tube bundle or nest ensures limited resistance to the flow of the fluids since there are substantially no interruptions.

The present invention is susceptible of modifications and variations, all of which are within the scope of the appended claims.

Technical details may be replaced with other technically equivalent elements.

The materials and the dimensions may be any according to requirements.

The disclosures in Italian Utility Model Application No. PD2000U000059 from which this application claims priority are incorporated herein by reference.