GLAND PACKING AND METHOD FOR ITS MANUFACTURE

GARNITURE ET SON PROCEDE DE PRODUCTION

English Abstract

The invention relates to a gland packing made of a non-woven fabric, which is
impregnated with
an active substance, particularly PTFE, and which serves as a sealing element
that can be pressed
into annular gaps between a stationary and a moving machine part, whereby the
sealing element
(1) consists of at least two layers, which are radially wrapped around one
another and pressed
together and which are made of a non-woven fabric strip that is impregnated
with the active
substance.

French Abstract

L'invention concerne une garniture à base de non-tissé imprégné d'un substance active, en particulier du PTFE, utilisée comme élément d'étanchéité pouvant être enfoncé dans des fentes annulaires, entre une partie fixe et une partie mobile de machine. L'élément d'étanchéité (1) se compose d'au moins deux couches enroulées et pressées l'une sur/contre l'autre dans le sens radial, d'une bande de non-tissé imprégnée de substance active.

Claims

CLAIMS
1. Process for the manufacture of a gland packing made of a non-woven
impregnated with an active substance for use as a sealing element in annular
gaps
between a stationary and a moving machine part comprising the steps of
obtaining a
mechanically bonded non-woven web of fibers with a fiber length of 3-100 mm,
and a
surface weight of 20 to 200 g/m2, cutting the non-woven web into individual
non-woven
strips of selected length, the width of which is 1.5-5 times a preselected
height of the
sealing element, individually winding the non-woven strips onto a mandrel, and
compressing the wound strips into a sealing element in a press device.
2. Process according to claim 1, wherein the fibers of the mechanically bonded
non-
woven web of fibers have a fiber length of 3-20 mm.
3. Process according to claim 1 or 2, wherein the fibers are aramid fibers.
4. Process according to claim 1 or 2, wherein the non-woven web further
includes
fibers or fiber mixtures of polyamide (PI), polybenzimidazole (PBI), polyester
(PES),
glass (GF) or aramid (AF).
5. Process according to any one of claims 1 to 4, wherein the non-woven web
has a
thickness of .ltoreq.2.5mm.
6. Process according to any one of claims 1 to 5, wherein the active substance
consists of PTFE, an aqueous PTFE dispersion, or an aqueous PTFE dispersion
with
fillers.
7. Process according to any one of claims 1 to 6, wherein the active substance
consists of a grease-graphite-mixture with additional fillers.
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8. Process according to any one of claims 1 to 6, wherein the active substance
includes an elastomeric binder with fillers.
9. Process according to one of claims 1 to 8, wherein a drying of the
impregnated
non-woven web is carried out in a continuous heating oven at a temperature of
30-300°C.
10. Process according to any one of claims 1 to 9, wherein a compression
pressure in
the press device is 5-50 MPa.
11. Process according to any one of claims 1 to 10, wherein the compressed
sealing
element is subjected to a sintering treatment or cross-linking at elevated
temperatures and
elevated pressures.
12. Gland packing made of a non-woven material impregnated with an active
substance for use as a sealing element compressible into annular gaps between
a
stationary and a moving machine part, and made by the process of any one of
claims 1 to
11, comprising at least two layers radially wound about one another and
compressed and
made of a non-woven strip impregnated with the active substance.
13. Gland packing according to claim 12, wherein the non-woven strips have cut
edges and a winding start of a first layer and a winding end of a last layer
of the non-
woven strips are placed with the cut edges one above the other, the cut edges
having
tapered ends.
14. Gland packing according to claims 12 or 13, wherein the non-woven is a
mechanically bound non-woven with a fiber length of 3-100 mm, and a surface
weight of
20-200g/m2, and the mechanical binding was achieved by waterjet consolidation
as
needling.
15. Gland packing according to claim 14, wherein the fiber length is 3-20 mm.
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16. Process according to claim 5, wherein the non-woven web has a thickness of
0.5-
1.25 mm.
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Description

CA 02446268 2006-12-12
GLAND PACKING AND METHOD FOR ITS MANUFACTURE
DESCRIPTION
The invention relates to a gland packing made of a non-woven fabric
impregnated
with an active substance, especially PTFE, which serves as a sealing element
that can be
compressed into annular gaps between a stationary and a moving machine part as
well as
a process for the manufacture of such a gland packing.
Gland packings often consist of special cord or braided rings, extruded rings
or
compressed rings. The packing materials used are generally graphite, PTFE,
fiber
materials, carbon, metal, or corresponding combinations thereof. The fiber
materials can
also be provided with special impregnations. For gland packings, which are
required to
have a high chemical resistance in combination with good sealing and abrasion
properties
at high temperatures, PTFE has been established as the active substance. The
manufacture of the PTFE gland packings is however relatively costly,
especially when
PTFE yarns are braided into a packing strand.
PRIOR ART
It is known from German Application DE 44 23 043, published January 11, 1996
to make gland packings of annular disks which are cut from compressible
textile webs
and are impregnated with an active substance of, for example, PTFE particles.
After
impregnation, the annular disks are dried at a temperature of about 105 C
and then
compressed into a sealing body in a press device. A gland packing is achieved
in this
manner which has a high thermal load capacity at low friction moments and low
leakage.
A non-woven fabric impregnated with PTFE can also
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be used as the textile sheet in this gland packing. The manufacturing process
is especially
uneconomical in that significant waste is created during the stamping of the
annular
disks. Furthermore, the horizontal layering planes generated by the stacking
of the
individual annular disks lead to an uneven sealing surface between the gland
packing and
the associated shaft.
SUMMARY OF THE INVENTION
It is an object of the invention to create a gland packing which has a high
sealing
capacity at very good friction properties.
This object is achieved in accordance with the invention in a gland packing of
the
generic type mentioned above in that the seal element is made of at least two
layers
radially wound around one another and compressed which layers are made of a
non-
woven strip impregnated with an active substance. Thus, instead of the axially
stacked
and compressed annular disks, a non-woven strip is used in accordance with the
invention
which in radial direction is wound into several layers and then compressed. By
this
arrangement of the non-woven strip into radial layers a very good internal
compression of
the packing material is achieved during the compression process with a
simultaneous
very good hooking together of the impregnated non-woven strips with one
another. It was
also discovered that the active substance impregnation incorporated into the
non-woven
band is partially pressed during the compression towards the surfaces of the
sealing
element so that the accumulation of the active substance impregnation there
leads to an
especially smooth surface. An especially planar and unstructured sealing
surface with
best sealing and friction properties results therefrom.
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It is especially advantageous for the realization of the invention when the
wound
beginning of the first layer and a wound end of the second layer of the non-
woven band
are placed with their cut edges one on top of the other so that no thickening
or the like
occurs in the finished compressed sealing element. It is thereby especially
advantageous
when the cut edges are provided with taperings so that in this manner an even
thickness is
present even during the winding process over the whole circumference of the
sealing
element. The number of layers can vary between at least 2 and a maximum of
200.
In order to achieve the highest possible uptake of the added active substance,
it is
advantageous when the non-woven material has a high openness and porosity.
This is
achieved in that the non-woven material is a mechanically bonded non-woven of
aramid
fibers with a fiber length of 3-20mm and a surface weight of 20-200g/m2. The
short fiber
length hereby leads to a high porosity. The aramid fibers are especially
suitable for use at
high temperatures. However, it is also possible to use different fibers or
fiber mixtures in
place of the aramid fibers, for example those which are highly strong and
suitable for
high temperature applications. For example, the non-woven web can include
fibers or
fiber mixtures of polyamide (PI), polybenzimidazole (PBI), polyester (PES),
glass (GF)
or aramid (AF). The bonding of the non-woven is achieved mechanically, for
example
by water jet solidification or needling. The mechanical solidification is of
special
importance since it has, in contrary to a chemical bonding, a high stability
even at high
temperatures.
A process is used for the manufacture of the gland packing from a non-woven
material impregnated with an active substance, such as a grease-graphite
mixture with
additional fillers, or PTFE, for use as a sealing element in annular gaps
between a
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stationary and moving machine parts, in which process a mechanically bonded
non-
woven web of fibers with a fiber length of 3-100 mm is impregnated with an
active
substance and subsequently dried and then cut into
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individual non-woven strips of selected length, the width of which is 1.5-5
times the
preselected height of the sealing element and in which the non-woven bands are
individually wound onto a mandrel and compressed in a press device to the
sealing
element. The width of the non-woven strips depends on later parameters,
especially on
which hardness the sealing element of the gland packing is supposed to have.
The
compression pressure in the press device is also dependent hereon. The higher
the desired
hardness of the sealing element, the layer the selected compression pressure
and the
larger the width of the non-woven strips.
The non-woven strip itself has a thickness of s 2.5mm, preferably between 0.5-
1.25 mm. The residence time in the impregnation bath is dependent on the
desired degree
of impregnation and the active substance used. Preferably, the active
substance consists
of an aqueous PTFE dispersion or an aqueous PTFE dispersion with fillers.
In order to avoid a dripping of the impregnation, a drying of the impregnated
non-
woven band is preferably carried out in a continuous heating oven at a
temperature of
about 30-300 C.
Normally, the non-woven web is saturated up to a maximum degree of saturation,
which means up to a portion of about 95-98% active substance. However, it is
also
possible, for example for reasons of durability of the sealing property, that
a higher fiber
portion in the sealing element is desired. To achieve this and to achieve an
especially
good distribution of the active substance in the non-woven web, the
impregnation can be
partially squeezed from the non-woven web in a subsequent stripping stretch
between
two rollers.
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The axial pressure in the compression device is between 5 and 50 MPa. It was
found through experiments that this pressure leads to a good internal
compression of the
packing material and at the same time to a good linking of the material of the
impregnated nonwoven strips with one another. The compression duration is from
several
seconds up to two minutes, depending on the desired degree of compression.
Higher
pressures generally lead to very hard sealing elements which during subsequent
use in the
gland packing space require very high gland packing compression forces for the
sealing.
It has been found advantageous in special applications to subject the
compressed
sealing element to a sintering treatment at elevated temperatures and elevated
pressures.
It is furthermore possible to impregnate the sealing element with a lubricant,
if desired, in
order to achieve a better friction behavior.
BRIEF DESCRIPTION OF THE DRAWINGS
The sealing element as well as the press device for its manufacture are shown
in
the attached drawing.
Figure 1 is a plan view of a sealing element in accordance with the invention;
Figure 2 is a cross-section of the sealing element shown in Figure 1; and
Figure 3 is a section through a press device with inserted sealing element.
DESCRIPTION OF THE INVENTION
The sealing element 1 in accordance with the invention for use as a gland
packing
is shown in plan view in Figure 1. The sealing element 1 consists of three
layers 2, 3 and
4 radially wound onto one another and each made of a non-woven fabric strip

CA 02446268 2006-12-12
impregnated with an active material. The wound beginning 10 of the first layer
2 and the
wound end 11 of the last layer 4 of the non-woven band are laid one on top of
the other
with their cut edges 12 and 13. The cut edges 12 and 13 are provided with
tapered ends.
A cross-sectional surface through the sealing element 1 is referenced by 14.
At that
location, the sealing element 1 is split in axial direction in order to
facilitate its lateral
mounting onto the shaft to be sealed whereby the sealing element 1 can be bent
open
there.
Figure 2 shows a cross-section through the sealing element I along line A-A
shown in Figure 1. The radial orientation of the individual layers 2-4 is
apparent.
Figure 3 shows the press device 20 in which the impregnated, prepared sealing
element I is compressed. The press device 20 consists of a die 21 with the
core 22 and
the mantle 23 as well a stamp 24. As shown on the left side of the Figure, the
sealing
element 1, consisting in the present case of the layers 2-8, is inserted into
the space 25
between the core 22 and the mantle 23. The stamp 24 is subsequently pressed as
indicated
by the arrows 26 and 27 axially into the opening 25. This results in a
compression of the
sealing element I as shown on the right side of the Figure. Preferably, the
compressed
sealing element is subjected to a sintering treatment or cross-linking at
elevated
temperatures and elevated pressures. The axial compression results in that the
inner layer
2 and the outer layer 8 of the sealing element 1 are provided on their inner
or outer
surfaces with an especially smooth structure. This is important for the later
sealing
process as a gland packing. At the same time, a good interlinking of the
layers with one
another is achieved as illustrated in the Figure by the zigzag shaped
formation of the
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layers 3-7. After the pressing process, the sealing element I is removed from
the press
device and can be guided to its use as gland packing.
6a

Representative Drawing