FR2493735A1 - Cold forming press for corrugated metal tube for heat exchanger - has two indented rollers with circular mandrel reducing work ovality - Google Patents

Abstract

The press uses serrated rollers (1,2) to obtain thin-walled metal pipes (7) with annular or spiral pattern wall grooving (6), the products being used as turbulence pipes for heat exchangers. It uses cold-forming with two rollers, the tendency for the work to become oval being counteracted by a circular guide rigidly connected to the substructure. The guide may comprise a barrel with a cylindrical inlet (8) and outlet (9) and an indented intermediate zone (11,12). The latter zone supports the work whilst permitting roller penetration and the rollers may have undulating surfaces, the work being executed in a single pass.

Description

 The present invention relates to the shaping of thin single or double wall tubes, made of ferrous and non-ferrous metals intended for the manufacture of heat exchangers and other fluid transfer systems with helical or turbulent stirring.

 As a rule, this helical shaping must be carried out using special and expensive tools.

 The invention aims to indicate a method of. shaping which can be carried out under economic conditions and which also guarantees the accuracy of the profiles sought.

 According to the invention, this object is achieved by the fact that standard machines known as cold roll forming machines are used, by adding to these machines a simple tool, and by giving the wheels some details of particular shapes.

Without the provisions of the present invention, the shaping in a helix or in parallel turns of thin single or double wall tubes proves to be impossible to achieve on this type of machine.

 The present invention also makes it possible to effect a geometric helical deformation by limiting the rolling of the metal and the alteration of its primitive physical qualities.

 The description which follows, with reference to the drawings annexed by way of example and without limitation, will make me understand.

The invention can be put into practice.

 Figure (1) is a top view in partial section of the tool as it is mounted on a cold roll forming machine.

The two motorized forming wheels (i) and (2) traditionally mounted on two parallel axes (x, y) in a vertical plane, comprise
- a conical zone of progressive deformation (3)
- a cylindrical calibration zone (4)
- a conical clearance zone (5)
- a machined profile (6) corresponding exactly to the profile
desired on the tube to be shaped (7). The tilt in
degrees of the helix performed on each wheel is little
different from the helix angle alpha <) desired on the
shaping tube (7)
Reminder
The above descriptions illustrate the method used for cold forming of full or thick-walled cylinders.

The originality of this invention is described below
- The guidance of the tube to be shaped is effectively ensured at the inlet (8) and at the outlet (9) by a very rigid monobloc "barrel" (sections AA and BB fig.2). This "barrel", located between the two rollers in a horizontal plane, is hollowed out in its central part (10) (section CC fig.3) this so as to allow the rollers to plunge into the tube 7 to be deformed.

The two parts of the guIdage "barrel" (11) and (12) remaining in the central working area ensure energetic maintenance of the shaped tube (7), limiting as much as possible the ovalization of the latter under the action of further ornaments concentric5 which are balanced: Fig 3
- F1 and F2 = wheel actions
- F3 and FZ = actions of the guide "gun".

 The barrel has at its lower part a rigid support (13) making it integral with the frame (14) of the machine (Fig 2 and 3).

The rotational drive of the tube (7} is improved, compared to conventional methods, by two details of shapes described in Figure No. 4 which represents a detailed enlargement of the profile (6) of the wheel
The entire working surface (15) of each wheel will be treated by the process known as shot peening in order to obtain micro cavities and giving the wheel a rough appearance. In addition, the projecting parts of the working area of each wheel are striated by knurling operation (16).

These two details of shapes made on the working areas of the wheels ensure
- A perfect rotation drive of the tube (7) to be shaped, avoiding slippage which causes an overlap of the shaped propellers and a "stuffing" of the tube (7), blocking the latter in rotation.

The present invention therefore makes it possible to shape helical or parallel impressions in a single pass on single or double wall tubes without length limitation.
In addition, the shape details (15) and (16) Fig. 4 made on the knobs (1) and (2) Fig.1 reproduce in shallow depth on the external surface of the shaped tubes. The streaks and the micro cavities thus reproduced during the deformation of the tube (7) give the latter a surface condition suitable for improving heat exchanges (heat exchangers), thus the exchange surface obtained with this system is greater than . that of a smooth tube with the same dimensional characteristics.

 In addition, these roughnesses cause mini turbulence at the level of the flow of the fluid in contact with this surface thus bringing a higher coefficient of heat exchange.

Claims (5)

 1. Method of helical or annular knurling of thin-walled tubes on cold forming machines with two knurls, characterized in that a circular guide is used limiting the deformation of ovalizations due to this knurling.  2. circular and integral guide system integral with the frame of the machine according to claim 1, characterized in that it is in the form of a "barrel" or mandrel composed of three elements - (8), cylindrical with the entry of the tube, - (10), notched in the working zone allowing the plunging of the rolls while ensuring a lower (11) and upper (12) holding of the tube, - (9) again cylindrical in the zone of tube outlet  3. knurling method according to claim 1, characterized by the use of two knurls having a rough surface according to details (15) and (16) in the contact zone (6) with the tube.  4. A method of manufacturing a tube with a rough helical surface, characterized in that the helical deformation and the rough surface state are obtained in a single pass in the apparatus according to one of the preceding claims.  5. Exchanger tube obtained from the process according to the preceding claims.