Method of Manufacturing Fin-Tube Heat Exchangers

1. Field of the Invention

The present invention relates to a method of manufacturing a fin-tube heat exchanger which is suitably used as an evaporator of a refrigerator, show case or the like.

2. Description of the Prior Art

Heat exchangers of so-called fin-tube type are used in refrigerators, show cases and so forth. Generally, in such type of heat exchangers, plate fins are arranged at a predetermined pitch in the direction of air flow, i.e. in the direction of a row of the fins, while refrigerant pipes are arranged in an alternating or staggered manner in the direction of rows of the plate fins, so as to attain a boundary layer front edge effect and turbulence promotion effect thereby to improve the capability of the heat exchanger. This type of heat exchanger is shown, for example, in U.S. Pat. No. 3,381,494.

In the manufacture of such fin-tube heat exchangers in which plate fins in a row are arranged in non-alignment with plate fins in adjacent rows and straight portions of refrigerant pipe are arranged in a staggered manner as viewed in a direction of air flow, the plate fins and straight portions of refrigerant pipe are assembled together and then U-bends or return bends are connected by brazing to the ends of lengths of straight pipe so as to permit a refrigerant to flow in a zigzag manner. Thus, in terms of manufacture, such heat exchangers are not favorable due to the necessity of brazing work and inspection after the brazing and yet the fraction defective is considerably high.

On the other hand, such a heat exchanger having a continuous length of refrigerant pipe bent in a zigzag manner without the use of lengths of pipe having U-bends is known. The method of manufacturing this type of heat exchanger is disclosed in U.S. Pat. No. 2,156,538 or Japanese Patent Publication No. 29606/1981. By way of example, the manufacturing method as shown in Japanese Patent Publication No. 29606/1981 will be explained hereinunder with reference to FIGS. 1 to 4. A plate fin 1 is formed provided, at positions spaced equidistantly away from its upper and lower edges, with two pipe-receiving holes 3 for passing therethrough a length of refrigerant pipe 2. These plate fins are placed in fin-receiving grooves 4 which are formed at a predetermined pitch in a fin positioning fixture 5. More specifically, the plate fins 1 are of the same shape and are placed in the fin positioning fixture 5 in a manner shown in FIG. 1. Namely, a predetermined number of plate fins 1 (five fins in this case) are placed into every other groove 4 at a pitch designated at 6 and then, leaving out a predetermined number of grooves 4 (four grooves in this case) to provide that portion of the pipe which is bent to form U-bends, a predetermined number of plate fins 1 (nine fins in this case) are placed in the grooves 4 at the pitch 7 of the grooves 4. Then, leaving out a predetermined number of the grooves 4 to provide that portion of the pipe which is to be bent, the plate fins 1 are placed in respective grooves 4. Thus, the plate fins 1 are arrayed on a straight line. Subsequently, the refrigerant pipe 2 is inserted into the pipe receiving holes 3 of the plate fins 1 and is then expanded by inserting a tube expander, so that it is in close contact with the plate fins 1. Subsequently, the assembly of the refrigerant pipe 2 and the plate fins 1 is removed from the fixture 5 and is arcuately bent as at portions 8 (see FIG. 3) to make the refrigerant pipe 2 zigzag-shaped. Consequently, the plate fins 1 are arranged in parallel rows with gaps 9 between the adjacent rows. In the manufacture described above, the refrigerant pipe 2 is necessarily arranged to form squares in section transverse to the axial direction of the pipe since the plate fins 1 are lined up in the fin positioning fixture 5. Namely this manufacturing method is disadvantageous in that a staggered pipe arrangement which offers a high performance of the heat exchanger cannot be realized.

The invention aims at obviating these problems of the prior art.

Accordingly, it is a primary objectof the invention to provide a method of manufacturing a novel heat exchanger, in which a continuous length of refrigerant pipe is formed to provide a staggered arrangement, thereby obtaining a higher performance than that of heat exchangers produced by the conventional method.

Another object of the invention is to eliminate defects such as deformation, cracking and so forth in the refrigerant pipe which may be caused in realizing a staggered arrangement of the refrigerant pipe and which would impair the performance of a finished heat exchanger.

FIG. 1 is a side elevational view of a part of a fin-tube heat exchanger during the course of manufacture;

FIG. 2 is a top plan view of the part of the heat exchanger shown in FIG. 1;

FIG. 3 is a perspective view of the finished part of the heat exchanger;

FIG. 4 is a side elevational view of the finished part of shown in FIG. 3;

FIG. 5 is a perspective view of a fin-tube heat exchanger constructed according to the method of the invention;

FIG. 6 is a plan view of a plate fin as used in the heat exchanger shown in FIG. 5;

FIG. 7 is a perspective view showing the econd step of the method of the invention;

FIG. 8 is a plan view showing the third step of the present method;

FIG. 9 is a perspective view showing the fourth step of the present method;

FIG. 10 is a side elevational view showing the fourth step of the present method;

FIG. 11 is a plan view showing the fifth step of the present method prior to setting;

FIG. 12 is a partial perspective view showing the fifth step of the present method prior to twisting;

FIG. 13 is a side elevational view showing the fifth step of the present method prior to twisitng;

FIG. 14 is a side elevational view showing the fifth step of the present method after twisting; and

FIG. 15 is a side elevational view of the finished heat exchanger.

A preferred embodiment of the invention will be described hereinunder with reference to the accompanying drawings. A fin-tube heat exchanger constructed in accordance with the method of the invention is shown FIG. 5. The heat exchanger shown in FIG. 5 is used as an evaporator for refrigerators. The heat exchanger comprises a multiplicity of plate fins 10 arranged at a constant pitch and a jointless refrigerant pipe 17 extending through plate fins 10 at a right angle to the latter. The plate fins 10 are grouped into independent rows a, b, c and d. The pitch of the plate fins 10 in the row a disposed upstream in the direction of air fow is selected to be greater than the pitch of the plate fins in the downstream-side rows b, c and d. That is, the upstream-side row a has a smaller number of plate fins 10 than that of other rows b, c and d. The refrigerant pipe 17 passes through the plate fins 10 of the rows a and c at higher positions than it does through the plate fins 10 of the rows b and c. That is, the refrigerant pipe 17 is arranged in a staggered manner in section transverse to the lengthwise direction.

A description will be made hereinunder as to the method of the invention for manufacturing the heat exchanger of the type shown in FIG. 5.

In the first step of the method, two pipe-receiving holes 11 are formed in each of a plurality of plate fins 10, as shown in FIG. 6. The holes 11 are spaced from each other in the longitudinal direction of the plate fins 10 and are offset to one longitudinal end of the same. The end 13 spaced from the adjacent end by a greater distance will be referred to as "longer end" while the end 12 spaced by a smaller distance from the adjacent end will be referred to as "shorter end", hereinunder. As shown in FIG. 7, there is provided a fin positioning fixture 14 which comprises fin-receiving grooves 15 for receiving the plate fins 10 and pipe receiving grooves 16 for receiving the refrigerant pipe 17. In the second step of the method, plate fins 10 are placed in the fin-receiving grooves 15 such that the longer ends 13 and the shorter ends 12 of the fins appear on opposite sides in every adjacent row and such that the pipe-receiving holes 11 are aligned with the pipe-receiving grooves 16. More specifically, the fins in the rows a and c are disposed on the fin positioning fixture 14 such that the longer ends 13 thereof appear on this side in FIG. 7 while, in the rows b and d, the longer ends 13 of the plate fins 10 appear on the other side in FIG. 7. Subsequently, in a third step of the method, a jointless refrigerant pipe bent in U-shaped configuration is inserted through the aligned pipe-receiving holes 11 in the plate fins 10. Then, a tube expander such as a mandrel (not shown) is inserted into the refrigerant pipe 17 to expand and secure same in tight contact with the plate fins 10.

The assembly thus formed is taken out of the fin positioning fixture 14, as shown in FIG. 8. Then, in the fourth step of the method, the refrigerant pipe 17 is bent substantially in arcuate shape as at 18 as shown in FIG. 9 such that the bent bent refrigerant pipe 17 in transverse cross-section occupies respective corners of squares. In this state, the rows of the plate fins 10 are arranged in parallel with one another with gaps P therebetween such that the longer ends 12 in one row and the shorter ends 13 in the next row are offset relative to one another, as shown in FIG. 10.

Namely, when the plate fins 10 are placed on the fin positioning fixture 14 as described above in connection with the second step, a large row pitch L is provided between the respective rows a to d of the plate fins 10 to accommodate bending of the refrigerant pipe 17 so that, after the bending of the refrigerant pipe 17 in the fourth step, the refrigerant pipe 17 in transverse cross-section occupies corners of squares at a row pitch L as shown in FIG. 10. The row pitch L is selected to meet the equation L=.sqroot.l.sup.2 +s.sup.2 where l represents the row pitch in the final product and s represents the distance of twisting of the refrigerant pipe 17, as shown in FIG. 15. By selecting the row pitch L to meet the above equation, it is possible to eliminate any deformation such as flattening, collapsing and so forth of the bent portions 18 of the refrigerant pipe 17 as well as cracks in the same.

Subsequently, in a fifth step of the process, as shown in FIGS. 11 to 14, spacers 19 having a thickness Po, corresponding to the distance between the opposing edges of the plate fins 10 in adjacent rows in the finished product, are placed in the gaps P between the opposing edges of the plate fins 10 in adjacent rows, and the bent portions 18 of the refrigerant pipe 17 are held by means of holders 21 of a twisting apparatus 20. Thereafter, torque is imparted to all the holders 21 by means of a motor 22 mounted on the twisting apparatus 20. Thus, a couple of forces are applied to the straight portions of the refrigerant pipe 17, so that portions of the refrigerant pipe 17 are twisted together with the plate fins 10 in the plane of the fins. The twisting of the plate fins 10, however, is prevented by the spacers 19. Consequently, only the refrigerant pipe 17 is twisted, by a twisting distance s, such that the upper or lower ends of the plate fins in the rows a to d are flush with one another. The relative twisting movement between the inner surfaces of the pipe-receiving holes 3 in the plate fins 10 and the outer peripheral surfaces of the straight portions of the refrigerant pipe 17 is conveniently accommodated by a slight slip produced therebetween. After this twisting operation, the assembly is taken out of the twisting apparatus 20 and the spacers 19 are withdrawn from respective spaces between adjacent rows of the plate fins 10, so that the evaporator is completed to have a staggered arrangement of the refrigerant pipe 17 as shown in FIG. 15.

As will be understood from the foregoing description, the present invention offers the following advantages.

(1) The heat exchanger having a staggered arrangement of the refrigerant pipe can be provided by the present method which involves substantially the same steps as those of the conventional method. The staggered arrangement of the refrigerant pipes causes turbulence in the air flow and can diminish the formation of the dead water zones behind each refrigerant pipe.

(2) It is possible to provide a staggered arrangement of the refrigerant pipe which ensures a high heat exchanging performance merely by adding a simple step of twisting without causing any dislocation of the fins.

(3) The slip between the inner peripheral surfaces of the pipe-receiving holes in the plate fins and the outer peripheral surfaces of the refrigerant pipe is so small that it does not matter substantially.

(4) Defects such as flattening, cracking and so forth in the bent portions of the refrigerant pipe which tend to be cuased in the conventional method can be eliminated and the manufacture itself is facilitated remarkably.