EP0619152B1 - Expansion head for expander for hollow workpieces - Google Patents

Abstract

On an expansion head (1) for expander tools for hollow workpieces, a cup (2) with a guide flange (3) pointing radially inwards and with a set of expansion jaws (4) in the form of sectors, each of which is guided individually so as to be radially moveable on the guide flange (3) by means of an internal-flange sector (5) and of an external-flange sector (6) and of a radial groove (7) formed between these. In order to be able to increase the radial travel of the expansion jaws without loss of the guiding properties, the external-flange sectors (6) have essentially at least the same diameter as the internal-flange sectors (5) and both the internal-flange sectors (5) and the external-flange sectors (6) each have a hole (8 and 9 respectively), in each of which one end of a guide pin (10) is accommodated. Arranged in the guide flange (3) are radial guide grooves for the acceptance and movement of in each case one of the guide pins (10). Annular tension springs (15, 16) for resetting the expansion jaws are furthermore arranged both on the internal-flange sectors (5) and on the external-flange sectors (6). <IMAGE>

Description

The invention relates to an expansion head for expanding tools according to the preamble of claim 1, as is known for example from DE-A-2 459 506.

Such expanding tools are also referred to as expanders. The expanding jaws are moved radially by the axial stroke of a conically tapered end of an expanding mandrel. The expanding mandrel is in turn driven by a cam, toggle lever, control slots or also by hydraulic means, etc. The ratio of the stroke of the expanding mandrel to the radial path of the expanding jaws is determined by the opening angle of the expanding mandrel.

In the expanders of the type described so far on the market, the stroke of the expanding mandrel is limited by the course of the control cams of the cam or slot. This also limits the radial path of the expanding jaws of the exchangeable expansion heads, which are driven by the expanding mandrel under force deflection. (GB-A-866 994; US-A-3 550 424).

From GB-A-866 994 it is known to guide the expanding jaws in radial slots in the coupling cap by means of rivets which are fastened in the flange sectors which are only present in a simple manner. However, the rent can only be fixed by plastic deformation of the rivet shaft, a work step that is difficult to carry out with the required precision. Furthermore, a usable guidance is only guaranteed if the cap and rivet heads overlap. A large radial path of the expanding jaws comes at the expense of the overlap.

From DE-24 59 506 and DE-U-74 41 871 an expansion head with easily interchangeable expanding jaws is known, which requires a slight overlap of the guide flange of the coupling cap and the flange sectors on the expanding jaws. As far as this document describes expansion heads without guide pins, the inner and outer flange sectors have the same but small diameters. As far as this document describes expansion heads of the type described at the beginning with guide pins, only the inner flange sectors of the expanding jaws are enlarged in diameter compared to the outer flange sectors in order to be able to accommodate the guide pins. In addition, only the inner flange sectors have a ring spring. The interchangeability of the expanding jaws would be immediately questioned if the outer flange sectors were also enlarged accordingly in order to achieve a better overlap for a larger radial path of the expanding jaws. Interchangeability is only possible with the use of overhung centering or guide pins if these pins can also be easily removed. For the purpose of removing the first expanding jaw, the jaw set must be displaced eccentrically with respect to the guide flange, which is prevented by the guide pins. The guide pins are therefore accessible from the outside and only held in the overall device when the cap is screwed on.

From EP-A-0 044 795 it is known to hold jaw sets together only with inner flange sectors without guide pins by means of an approximately circular but circumferentially interrupted solid ring spring and to hold them in a cap by means of a polygonal spring as a replacement for outer flange sectors. However, this is only possible via a relatively small radial path of the expanding jaws and with less reliable guiding properties than are made possible by rigid inner and outer flange sectors on both sides of the guiding flange of the coupling cap.

The problem to be found in the prior art of the easy interchangeability of the expanding jaws directly opposes the requirement for a large radial path of the jaws with exact guidance due to a large overlap of the guide elements.

• 1. Beim Aufweiten von Kunststoffrohren (z.B. für Fußbodenheizungen) erfolgt nach dem Herausnehmen der Spreizbacken aus dem gerade aufgeweiteten Kunststoffrohr ein rasches Schrumpfen des Rohres, so daß der Aufweitevorgang mit einem Übermaß erfolgen muß.
• 2. Die Wandstärken der aufzuweitenden Rohre aus Metall nehmen zu, insbesondere bei größeren Nenndurchmessern. Die verwendeten Kunststoffrohre haben ohnehin bereits eine größere Wandstärke als vergleichbare Metallrohre.
• 3. Die Spreizbacken müssen in zurückgezogener Stellung kräftefrei in das Rohr einführbar und wieder aus diesem herausnehmbar sein.

It has now been found necessary to increase the radial expansion path of the expanding jaws (diameter increase compared to the starting position), for three main reasons:

• 1. When expanding plastic pipes (eg for underfloor heating), the pipe shrinks rapidly after the expansion jaws are removed from the just expanded plastic pipe, so that the expansion process must be carried out with an excess.
• 2. The wall thicknesses of the metal pipes to be expanded increase, in particular with larger nominal diameters. The plastic pipes used already have a greater wall thickness than comparable metal pipes.
• 3. In the retracted position, the expanding jaws must be able to be inserted into and removed from the tube without force.

It must be taken into account here that the widening of a pipe end usually takes place for the purpose of inserting a non-widened pipe end or - in the case of plastic pipes for water-carrying pipes, in particular for underfloor heating - a force-free connecting nipple into the widened pipe end and sealing the overlap point tightly connect, be it by soldering, gluing, welding or simply by shrink fitting, if necessary with a securing ring. It is obvious that the wall thickness plays a role with regard to the necessary opening of the expanding jaws.

The invention is therefore based on the object of specifying an expansion head of the type described at the outset, which can be used in conjunction with expanders (basic devices) in which the stroke of the expanding mandrel of the basic device is increased with a conventional opening angle and thus the possible opening path of the expanding jaws.

The opening angle is maintained for the purpose of being able to use conventional expansion heads with the same basic device.

In the expansion head described at the outset, the object is achieved according to the invention by the features in the characterizing part of patent claim 1.

This has the following advantages: The use of an outer flange with a large diameter enables sufficient overlap of the bottle sectors on both sides with the guide flange of the coupling cap, despite the fact that the inner circle of the guide flange also had to be enlarged due to the required larger opening travel of the expanding jaws. The two-sided mounting of the guide pins improves their guide properties, especially since the requirement can no longer be met that they too Pins must be easily removable. Rather, the expanding jaws are captively stored in the cap.

The guide pins can no longer loosen even during the usually very rough operation on a construction site. Finally, due to the double arrangement of ring springs on all flange sectors, the stiffness that otherwise occurs due to canting of the expanding jaws within the radial guide elements is avoided when retracting. Since both ring springs are arranged on the maximum possible diameters, i.e. they have long lengths, two strong springs with identical flat characteristics can be used, which is very beneficial for the large radial path of the expanding jaws.

Due to the interference fit in at least one of the two associated bores, the flange sectors are stiffened against one another and despite simple manufacture and little overlap to extremely precise guide elements.

It is particularly advantageous if the bores for the guide pins in the outer flange sectors are designed as blind bores. In this way, the pins can no longer be ejected by laymen, so that the expansion head is protected against being fitted with expanding jaws that do not belong together.

A further advantageous embodiment is given when the guide pins are designed as grooved pins.

An embodiment of the subject matter of the invention is explained in more detail below with reference to FIGS. 1 and 2.

Fig. 1

eine teilweise geschnittene Seitenansicht eines Expansionskopfes mit radialer Blickrichtung und

Fig. 2

eine Frontalansicht des Gegenstandes nach Fig. 1 in Richtung des Pfeils II mit teilweise weggebrochener Überwurfkappe.

Show it:

Fig. 1

a partially sectioned side view of an expansion head with a radial viewing direction and

Fig. 2

a front view of the object of FIG. 1 in the direction of arrow II with a partially broken cap.

In the figures, an expansion head 1 is shown, to which a cap 2 with a radially inwardly directed guide flange 3 and with a set of sector-shaped expansion jaws 4 belongs. Knurls 2a increase the grip of the expansion head to be screwed on by hand. The spreading jaws 4 are each guided individually on the guide flange 3 by means of an inner flange sector 5 and an outer flange sector 6 and a radial groove 7 formed between them. It is understood that the flange sectors 5 and 6 are made in one piece with the expanding jaws.

Both in the inner flange sector 5 and in the outer flange sector 6, a bore 8 or 9 is arranged, both of which are aligned with one another and in which the respective ends of a guide pin 10 parallel to the axis "A" are accommodated, which in this way have the groove 7 , stored on both ends, bridged. The outer flange sectors 6 have essentially at least the same diameter as the inner flange sectors 5 and have groove sectors 11 and 12 on their outer sides, which complement each other on the entire circumference to form an annular groove, interrupted by gaps 13.

Radial guide grooves 14 for receiving and moving the guide pins 10 are arranged in the guide flange 3. Both in the inner flange sectors 5 and on the outer flange sectors 6 are in said groove sectors 11 or 12 annular tension springs 15 and 16 for the provision of the expanding jaws 4.

As can be seen from FIG. 1, the bores 9 in the outer flange sectors 6 are designed as blind bores. The guide pins 10 are held with a press fit in at least one of the two associated bores 8 and 9. In particular, the guide pins 10 are designed as grooved pins.

For a better understanding it should be mentioned that the expanding jaws 4 have been produced from a rotating body with the axis "A", which has been broken down into six sectors by the column 13 (sawing column), as can be seen from FIG. 2. The gap width was chosen in accordance with the radial stroke, in such a way that the working surfaces 4a and 4b, in the most widely spread position, complement each other to cylindrical surfaces which are only separated by the said gaps and correspond to the maximum expansion diameter if one considers the resetting or springback of the workpiece once.

Inside, the sectors are delimited by conical surfaces 16, which interact with the expanding mandrel, not shown here, which is subjected to pressure and consequently have its opening angle. These conical surfaces do not lie, at least not at the beginning of the expansion movement, over their entire axial length on the conical surface of the expanding mandrel, and they only lie flat on the expanding mandrel in a single axial intermediate position, so that they can perform rocking movements outside of this position, e.g. then, when the pipe material flows differently when expanded over the circumference, which is by no means rare.

It is important here that the largest cross-sectional area of the cone, the so-called base area, is in the Area of the flange sectors. This distinguishes such an expansion head from devices with the cone surfaces in the opposite position. In such devices, the expanding mandrel is subjected to tension, but must then be removed to change an expansion head. In the subject matter of the invention, it is sufficient to separate the expansion head 1 from the basic device by means of the internal thread 2b of the cap 2.

In addition, in the last-mentioned prior art, the greatest spreading forces occur at a point which is the furthest away from the flange sectors, as a result of which clampings are favored.

The flow behavior of the materials during expansion additionally illuminates the value of the radial guide elements in the area of the guide flange 3: The expansion jaws, which are particularly slim for smaller pipe diameters, are subjected to very high bending stresses, which in turn results in tilting moments in the area of the radial guide elements. Tilting leads to additional stiffness, which requires higher actuation forces and thus puts additional strain on the expanding jaws. It should be noted that the complete device is a hand tool, which is usually operated like a pair of pliers and has two hand levers for driving the expanding mandrel. By increasing the stroke of the expanding mandrel, the situation is becoming increasingly critical.

Claims (3)

1. Expansion head (1) for expander tools for hollow workpieces, in particular pipe ends, comprising a cap (2) with radially inward oriented guide flange (3) and a set of sectorially formed expanding jaws (4) which are respectively individually guided on a guide flange (3) by means of an internal flange sector (5) and an external flange sector (6), and a thereinbetween established radial groove (7), and on the interior flange sectors (5) are arranged circular tension springs (16) for returning the expanding jaws (4), and in the interior flange sectors (5) are arranged bores (8) in which the one end of guide pins (10) are received, and in the guide flange (3) are arranged radial guide grooves (14) to receive and move the guide pins (10), characterised in that

   a) the external flange sectors (6) have at least the same diameter as the internal flange sectors (5) and bores (9) which receive the other ends of the guide pins (10);

   b) the guide pins (10) are pressure-seated in at least one of the two associated bores (8, 9);

   c) annular tension springs (15) for returning the expansion jaws (4) are also arranged on the external flange sectors (6).
2. Expansion head according to Claim 1, characterised in that the bores (9) for the guide pins (10) in the external flange sectors (6) are pocket bores.
3. Expansion head according to Claim 1, characterised in that the guide pins (10) are notch pins.

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