METHODE ET DISPOSITIF DE RACCORDEMENT PAR SOUDAGE ABOUTE A L'OUTIL CHAUFFE, DU CORPS EXTRUDE D'UN CONTENANT ET DE SON COUVERCLE

PROCESS AND DEVICE FOR CONNECTING TOGETHER BY HEATED- TOOL BUTT-WELDING A VESSEL BODY OBTAINED BY EXTRUSION AND A VESSEL LID

Abrégé anglais

ABSTRACT
Process and device for connecting together an extruded plastic
cylindrical vessel body (2) with a plastic lid (1) by means of butt-
welding of edges (4.5) heated with a heated plate (12) the said lid
being deformed elastically to a larger diameter prior to butt-welding,
the device for expanding the lid (1) having a conical expansion element
(9), a supporting ring (10) and locking elements (11) holding the
expanded lid at a diameter corresponding to the edge diameter of the
body (2).

Revendications

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A process for connecting together by heated tool butt-
welding a vessel body obtained by extrusion and a vessel lid
which has a circular rim, comprising:
elastically deforming the edge of the lid by mechanical
means to a dimension which corresponds to the dimension of the
edge of the vessel body,
welding the vessel body and lid together in this state,
cooling the weld, and
removing said deformation of the lid after cooling.
2. A device for the application of the process according
to claim 1 comprising
a vessel body obtained by extrusion having a first
attachment surface,
a vessel lid to be connected by heated-tool butt-
welding to said vessel body having a circular rim and a second
attachment surface,
a supporting ring for gripping an outside edge of the
lid in such a manner that it can hold the edge of the lid in an
expanded state,
a conical expansion element which is movable in the
open side of the lid away from said supporting ring and in the
edge towards said supporting ring,
locking elements for keeping the lid in contact with
the supporting ring and which engage with the periphery of the
lid at an edge of the lid near the welding point,
heating means for heating said first and second
attachment surfaces for heated-tool butt-welding, and
means for pressing and holding together said first and
second attachment surfaces after said surfaces have been
sufficiently treated by said heating means.

Description

~Z64~
BO 33165
Process and device for connecting together by heated-tool butt-
welding a vessel body obta ned by extrusion and a vessel lid.
The invention relates to a process for connecting together by
heated-tool butt-welding a vessel body obtained by extrusion and
a vessel lid which has a circular rim.
Such a process is known from British Patent 1,535,287.
The vessel body used therein is cylindrical in shape. The
finished vessel can, according to British Patent 1,535,287, be
subjected to internal excess pressure in order to give the vessel
body a barrel shape, i~e. preferably a shape in which a large
centre section of the body is a cylinder of greater diameter with
adjoining barrel-shaped end parts.
This shape is advantageous for stability in respect of axial
forces acting eccentrically upon the edge parts as a result of
stacking of pallets, and in particular it prevents the vessel
wall from being permanently or otherwise dented in the vicinity
of the welded seam.
A disadvantage of this process is that the vessel body is not
inherently stable before it is connected to a lid. This
instability arises from the cylindrical shape and the thin wall
of the vessel body. The result of this is that special measures
have to be taken to preserve the cylindrical shape of the vessel
body during production of the barrel.
Another disadvantage is that a separate treatment and expensive

~2~
equipment are needed to shape the vessel body to a barrel form.
It has also been found that, despite precautionary measures,
stresses may remain in the region round the weld seams of the
finished product.
The object of the invention i.s therefore to produce a process
which does not have these disadvantages.
This object is achieved according to the invention in that the
edge of the lid is deformed elastically by mechanical means to a
dimension which corresponds to the dimension of the edge of the
vessel body, body and lid are welded together in this state and,
after cooling of the weld, the deformation of the lid is removed.
With this process, it is possible to use a vessel body which has
outward curled edges. Such a vessel body is stable even when not
connected, because the curled edges act as flanges. With a
circular lid or body wall end the dimension is determined by the
diameter. The edges are then bent outwards in the radial
direction.
Such a form of the vessel body can be obtained by starting from
an extruded tubular object whose inside is subjected to greater
cooling than the outside. In such an object compression stresses
prevail on the inside and tensile stresses on the outside of the
wall. After cutting through perpendicular to the axis of the
object, the axial components of these stresses make the cut edge
curl outwards.
To the vessel body thus obtained, whose ends curl outwards, a lid
is now connected by means of heated-tool butt-welding, The edge
of this lid is stretched in axially symmetrical fashion to such
an extent that when the lid has sprung back the vessel body has a
barrel shape. During the elastic springing back of the lid the
plastic material of the adjoining part of the vessel is still

~i42~6
warm, as a result of which the geometrical change in the vicinity
of the weld poi~t can take place without internal stresses being
built up.
In the process according to the invention, as can be seen from
the above, no special measures need be taken t~ preserve the
shape of the vessel body during the manufacture of the vessel.
Nor is it necessary to subject the finished vessel to a separate
treatment in order to make it a barrel shape.
The device for carrying out the process can be designed in such a
way that it consists of a supporting ring gripping the outside
edge of the lid in such a way that it can hold the edge of ~he
lid in the expanded state, for example radially, a conical
expansion element which is movable in the open side of the lid
away from and in the edge towards the supporting ring, and
locking elements which can engage all round the periphery of the
lid with an edge of the lid situated near the welding point, and
which keep the lid in contact with the supporting ring.
The supporting ring rests here against the inside edge of a ring
disposed on the side facing away from the open side, and it
retains the lid in the expanded position when the conical element
has been removed in order to make ~he lid accessible for the
butt-welding, The lid is held in place here by a locking element
which presses the lid in the axial direction against the
supporting ring. For this, provision is made for a supporting
surface which springs back relative to the weld surface, so that
it remains accessible for the heated-tool butt-welding.
The invention will be explained in greater detail with reference
to the drawing.
Fig. 1 shows a lid and the vessel body with outward curled edge.

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Fig. 2 shows the lid with the conical expansion element.
Fig. 3 shows the heating of the edge of the vessel body to be
attached and of the expanded vessel lid.
Fig. 4 shows the finished barrel.
Fig. 1 shows a vessel lid 1 and a vessel body 2. The vess~l iid 1
has a circular edge 3 with an attachment surface 4 which must be
attached to the at~achment surface 5 of the outward curled edge 6
of the vessel 2. The vessel lid 1 also has a ring 7 and an edge 8
situated next to the attachment surface 4.
Fig. 2 shows a conical expansion element 9, which rests against
the inside of the circular edge 3. When this element is pressed
into the cir~ular edge 3, the lid obtains the desired diameter.
Fig. 3 shows the device with which the lid 1 is held in the
expanded state after the expansion element 9 has been removed.
Against the ring 7 presses a supporting ring 10; the lid 1 is
held against the supporting ring 10 by means of a locking element
11 .
Also illustrated is a heated plate 12, which heats the attachment
surfaces 4 and 5 for the heated-tool butt-welding. Once these
surfaces are sufficiently heated, the plate 12 is removed and the
surfaces 4 and S pressed against each other. After cooling of the
~eld, the supporting ring 10 and the locking element 11 are
removed, as a result of which the lid can spring back and the
vessel becomes a barrel shape, as shown in Fig. 4.
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