Abstract A tubing unit useful, for example, as part of a heat exchanger includes a first tube containing a second helically corrugated tube having on its outer surface helical ridges which engage the inner wall of the first tube to mechanically lock the two tubes in assembly and to form one or more helical passageways between the first and second tubes. The first tube may be of a substantially straight cylindrical shape or may include helical grooves on its inner surface for receiving and mating with the radial outer end portions of the helical ridges on the outer surface of the second tube. A third tube may surround the first tube and include helical corrugations with inwardly extending ridges engaging the outer surface of the first tube to form another set of helical passageways between the first tube and the third tube. In the making of the tubing unit, the second tube is assembled over a mandrel and within the first tube and then twisted to form the helical corrugations therein, the mandrel limiting the inward growth of the inwardly extending ridges and the first tube limiting the outward growth of the outwardly extending ridges. In cases where a third tube is used, such third tube is placed over the second tube and twisted to form helical corrugations therein, the outer surface of the first tube limiting the radial inward growth of the inwardly extending ridges thereof.
The method of making a tubing unit which method comprises the steps of: providing a first tube, providing a second tube having an outside diameter substantially less than the inside diameter of said first tube, providing a mandrel having an outside diameter substantially smaller than the inside diameter of said second tube, assembling said first and second tubes and said mandrel with said mandrel inside of said second tube and with said second tube inside of said first tube, thereafter twisting said second tube by applying a twisting torque at two separate points along its length to form helical corrugations therein defining a first set of ridges on the outer surface of said second tube and a second set of ridges on the inner surface of said second tube, the radial outward growth of said first set of ridges during said twisting step being limited by engagement thereof with the inner surface of said first tube, and the radial inward growth of said second set of ridges during said twisting step being limited by engagement thereof with the outer surface of said mandrel, and subsequently removing said mandrel from said second tube.
Claim 2
Independent Claim
192 words
The method of making a tubing unit which method comprises the steps of: providing a first tube, providing a second tube having an outside diameter substantially less than the inside diameter of said first tube, providing a mandrel having an outside diameter substantially smaller than the inside diameter of said second tube, assembling said first and second tubes and said mandrel with said mandrel inside of said second tube and with said second tube inside of said first tube, thereafter twisting said second tube by applying a twisting torque at two separate points along its length to form helical corrugations therein defining a first set of ridges on the outer surface of said second tube and a second set of ridges on the inner surface of said second tube, the radial outward growth of said first set of ridges during said twisting step being limited by engagement thereof with the inner surface of said first tube, and the radial inward growth of said second set of ridges during said twisting step being limited by engagement thereof with the outer surface of said mandrel, and subsequently removing said mandrel from said second tube.
Claim 3
Dependent Claim
85 words
The method defined in claim 1 further characterized by forming a plurality of circumferentially spaced indentations in said second tube in a zone spaced from one end of said second tube with all of said indentations having substantially the same spacing from said tube end, said step of forming said indentations being performed prior to the twisting of said second tube so that said indentations serve as starting points for helical grooves formed in the outer surface of said second tube during said twisting operation.
Claim 4
Dependent Claim
29 words
The method defined in claim 1 further characterized by reverse twisting said second tube following said twisting operation to relieve said second tube from tight engagement with said mandrel.
Claim 5
Dependent Claim
93 words
The method defined in claim 1 further characterized by providing a third tube having an inside diameter longer than the outside diameter of said first tube, placing said first tube within said third tube, and twisting said third tube by applying a twisting torque at two points along its length to form helical corrugations therein defining a set of helical ridges on its inner surface, the radial inward growth of said latter set of ridges during said latter twisting step being limited by engagement thereof with the outer surface of said first tube.