Fins are formed monolithically from the material of a tube body. The fins extend from the tube body outer surface, and include a fin base and a fin top. Wings extending from a fin side surface between the fin base and fin top can produce upper and lower channels between adjacent fins. Depressions can be formed in the fin top with platforms below the depressions. The tube can also include helical ridges on an inner surface of the tube. The tubes are used for heat transfer, and can be included in shell and tube heat exchangers.

A process for manufacturing a bellows, made of austenitic high-grade steel with high compressive strength and fatigue strength, forms a single-layer or multilayer sleeve into a bellows with hydraulic forming. The pressure resistance and fatigue strength are improved by the bellows being cleaned after the forming and by the bellows being exposed to a surrounding area containing carbon and/or nitrogen atoms at temperatures between 100° C. and 400° C., preferably 200° C. to 320° C. With this a hardening of the bellows takes place by means of the diffusing in of carbon and/or nitrogen atoms. A bellows made of austenitic high-grade steel with one or more layers created in this manner has the edge layer hardened by the incorporation of carbon and/or nitrogen atoms up to a hardening depth of at least 5% of the wall thickness.

A process for manufacturing a bellows, made of austenitic high-grade steel with high compressive strength and fatigue strength, forms a single-layer or multilayer sleeve into a bellows with hydraulic forming. The pressure resistance and fatigue strength are improved by the bellows being cleaned after the forming and by the bellows being exposed to a surrounding area containing carbon and/or nitrogen atoms at temperatures between 100° C. and 400° C., preferably 200° C. to 320° C. With this a hardening of the bellows takes place by means of the diffusing in of carbon and/or nitrogen atoms. A bellows made of austenitic high-grade steel with one or more layers created in this manner has the edge layer hardened by the incorporation of carbon and/or nitrogen atoms up to a hardening depth of at least 5% of the wall thickness.

A method of manufacturing a rectangular tube having a stepped portion includes: forming V-shaped grooves on a rectangular tube at surfaces of an end thereof in a direction parallel to a longitudinal direction thereof; and pressing each of the surfaces having the V-shaped grooves formed thereon with a rotating roll from outside to inside, whereby the end of the rectangular tube is radially reduced.

The production method for producing a rifled tube, which includes a plurality of first helical ribs on its inner surface, includes: a steps of: preparing a steel tube; and producing a rifled tube by performing cold drawing on a steel tube by using a plug which includes a plurality of second helical ribs, the plug satisfying Formulae and:

0.08 <W×(A−B)×N/(2π×A)<0.26  (1)

0.83<S×(A−B)×N/(2×M)<2.0  (2) where, W is a width of a groove bottom surface of the helical groove; A is a maximum diameter of the plug; B is a minimum diameter of the plug; N is a number of the second helical ribs; S is the width of the groove bottom surface; and M is a pitch of adjacent second helical ribs.

The production method for producing a rifled tube, which includes a plurality of first helical ribs on its inner surface, includes: a steps of: preparing a steel tube; and producing a rifled tube by performing cold drawing on a steel tube by using a plug which includes a plurality of second helical ribs, the plug satisfying Formulae and:

0.08 <W×(A−B)×N/(2π×A)<0.26  (1)

0.83<S×(A−B)×N/(2×M)<2.0  (2) where, W is a width of a groove bottom surface of the helical groove; A is a maximum diameter of the plug; B is a minimum diameter of the plug; N is a number of the second helical ribs; S is the width of the groove bottom surface; and M is a pitch of adjacent second helical ribs.

A stator for a downhole motor configured for use in a downhole environment. includes an inner tubular member formed from a first metallic material having an outer surface and a helically lobed inner surface, and an outer tubular member comprising a second metallic material that is different from the first metallic material. The inner tubular member is connected to the outer tubular member by compressive force passing from the outer tubular member through the inner tubular member to a rigid mandrel removably disposed within the inner tubular member. The inner tubular member and the outer tubular member form the stator of the downhole motor.

A method for forming features in an exterior surface of a heat transfer tube includes forming a plurality of channels into the surface, where the channels are substantially parallel to one another and extend at a first angle to a longitudinal axis to the tube. A plurality of cuts are then made into the surface substantially parallel to one another and extend at a second angle to a longitudinal axis to the tube different from the first angle. Individual fin segments extend from the surface and are separated from one another by the channels and the cuts. The fin segments have a first channel-adjacent edge adjacent substantially parallel to the channel, a first cut-adjacent edge substantially parallel to the cut, and a corner formed by a second channel-adjacent edge and a second cut-adjacent edge. A tube formed using this method can be used as a condenser tube.

An electric power steering assembly includes a rotor assembly that is rotatable about a longitudinal axis. The rotor assembly has an outer surface and an inner surface. The rotor assembly defines a plurality of magnet pockets that are disposed proximate the outer surface. The inner surface defines a plurality of rotor teeth.

A heat transfer tube is made of aluminum and includes a streak-shaped Zn diffusion layer (6, 106) which is spirally formed on a circular outer peripheral surface in a length direction. According to this heat transfer tube, even in a case where rainwater or dew concentration water is intensively accumulated in a portion of the outer peripheral surface in a circumferential direction, it is possible to obtain a sufficient corrosion resistance.