PROCESS FOR LINING A TUBE

PROCEDE DE REVETEMENT D'UN TUBE

English Abstract

A measuring tube for a flowmeter and a process for
making the measuring tube. The measuring tube is lined with
a tubular lining of thermoplastic material, particularly
PTFE or PFA, which comes into contact with the measured
substance which flows through the tube. The ends of the
tubular lining are flanged around end flanges of the
measuring tube after the ends of the tubular lining have
been plasticised by heating. The plasticised ends of the
tubular lining are turned outward by more than 90° and then
forced into undercuts in the end faces of the end flanges.
Upon cooling, the ends of the lining are in intimate contact
with the end faces of the end flanges and the undercuts in
the end faces.

Claims

CLAIMS:
1. 1. A process for lining a flowmeter measuring tube
comprising the steps of:
supplying a flowmeter measuring tube having a
longitudinal axis and an end face with an opening
therein, a first surface extending radially outwardly
from said opening, and a second surface spaced
longitudinally from and connected to said first surface
by a surface forming a circumferential undercut in said
end face, said second surface extending radially
outwardly from said undercut;
then placing a tubular lining of thermoplastic
material, of lesser thickness than said flowmeter
measuring tube, within said flowmeter measuring tube
with a selected length of said tubular lining extending
beyond said end face of said flowmeter measuring tube;
plasticising at least said selected length of said
tubular lining;
opening out said plasticised length of said
tubular lining over said end face of said flowmeter
measuring tube by more than 90° from said longitudinal
axis of said flowmeter measuring tube and pushing a
free edge of said plasticised length of said tubular
lining into said circumferential undercut in said end
face;
and permitting:
(a) said opened out plasticised length of said tubular
lining to solidify, and
(b) the free edge of said opened out plasticised length
of said tubular lining to be drawn by shrinkage radially
inward into intimate contact with said circumferential
undercut in said end face of said flowmeter measuring tube,
thereby lining said flowmeter measuring tube with
a securely held lining, which will not detach itself
from said flowmeter measuring tube.
2. A process according to claim 1 wherein said
plasticising is by heating and said solidifying is by
cooling.
3. A process according to claim 2 wherein said tubular
lining material is PTFE.
4. A process according to claim 2 wherein said tubular
lining material is PFA.

Description

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FAP-060
PROCESS FOR LINING A TUBE AND ARTICLE MADE BY THE PROCESS
TECHNICAL FIELD
The present invention relates, in general, to
lining fluid-carrying tubes and, in particular, to a
process for lining the measuring tube of a flowmeter and
the article made by this process.
BACKGROUND OF THE INVENTION
In a known process of this kind, the ends of
l0 the tubular lining are heated and flanged onto sealing
strips which are located on the end faces of the end
flanges and 'which encircle the measuring tube. After the
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flanging, the flanged ends of the lining have a tendency
to return to their original tubular shape, with the
result that they detach themselves from the sealing
strips. This frequently leads to damage when the
measuring tube is installed.
SUMMARY OF THE INVENTION
The airn of the present invention is to provide
a process and an article made by the process by which the
flanged ends of the tubular lining do not detach
themselves from the end flanges after the flanging
process.
As a result of the fact that the ends of the
tubular lining are opened out by more than 90° by heating
after the plasticisation, annular forces are produced in
the ends which cause the ends to shrink, as they cool,
around the non-widened portions of the tubular lining.
If the flanging is carried out in undercuts on
the end faces of the end flanges, the ends of the tubular
lining can no longer detach themselves from the end
flanges.

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BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is hereinafter described
with reference to embodiments by way of example, referring
to the accompanying drawings.
Fig. 1 explains the process of widening by more
than 90 in accordance with the present invention.
Fig. 2 shows a first embodiment of a flanging in
accordance with the present invention.
Fig. 3 shows a second embodiment of the present
invention with an additional securing of the flange
connection.
Figs 4, 5 and 6 show different undercuts made in
the end faces of the end flanges of a flowmeter tube in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 shows an end portion of a tubular
thermoplastic lining 2 (i.e. PTFE or PFA) with an end 4a
which has not yet been everted (i.e. opened out) and an end
4b which has been opened out by more than 90° after
plasticising, for example, by heating. When the opened out
end 4b cools,

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forces are produced in the direction of the arrow F which
ensure a secure hold for a flanged connection.
Fig. 2 shows an end portion of a measuring tube
6 with an end flange 8 which has an acute-angled undercut
10. The outer edge 12 or contact surface of the undercut
is rounded. The end 4b according to Fig. 1 is flanged
into the undercut 10.
In the embodiment according to Fig. 3, the end
flange 8 radially adjoins the undercut 10, so that
10 precisely the flanged and 4b of the tubular lining 2 has
room in the undercut 10. In order to secure the end 4b
even more, the end flange 8 is enclosed by an annular
mounting 14 which forces the end 4b of the tubular lining
2 into the undercut 10.
Fig. 4 shows a right-angled undercut 16 in the
end flange 8.
Fig. 5 shows an inwardly directed annular
groove 18 in which an undercut 20 ends.
Fig. 6 shows a substantially acute angled
undercut 22, the outer edge 24 and inner edge 26 of which
are rounded.

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' CA 02039300 1998-10-16
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The process for lining the flowmeter measuring
tube includes supplying the flowmeter measuring tube having
a longitudinal axis and end face with an opening therein, a
first surface extending radially outward from the opening,
and a second surface spaced longitudinally from and
connected to the first surface by a surface forming a
circumferential undercut in the end face, the second surface
extending radially outward from the undercut; placing the
tubular lining of thermoplastic material within the
flowmeter measuring tube with a selected length of the
tubular lining extending beyond the end face of the
flowmeter measuring tube; plasticising at least the selected
length of the tubular lining; opening out the plasticised
length of the tubular lining over the end face of the
flowmeter measuring tube by more than 90° from the
longitudinal axis of the flowmeter measuring tube and
pushing a free edge of the plasticised length of the tubular
lining into the circumferential undercut; and permitting the
opened out plasticised length of tubular lining to solidify
and the free edge of the opened out plasticised length of
the tubular lining to be drawn by shrinkage radially inward
into intimate contact with the circumferential undercut in
the end face of the flowmeter measuring tube, so that the
lining is securely held and will not detach itself from the
flowmeter measuring tube.

Representative Drawing