Method for producing a packing arrangement for a hydraulically operated apparatus and a packing arrangement

The invention relates to a new method for producing a packing arrangement for a hydraulically operated apparatus. The method comprises the following steps: (a) producing a preshaped plastic piece of seal material; (b) compressing said preshaped piece at room temperature into a cylinder; and (c) compressing said preshaped piece at room temperature to its final form in said cylinder between a piston member and a counter press member, at least one of said piston member and counter press member being provided with rounded or tapered head portion facing against said preshaped piece, whereby the cross-section of said final compressed seal member is essentially wedge-shaped. The invention relates also to a packing arrangement produced by the method of the invention.

FIELD OF THE INVENTION 
A method for producing a packing arrangement for a hydraulically operated 
apparatus and a packing arrangement. 
The present invention relates to a new method for producing a packing 
arrangement for a hydraulically operated apparatus and a packing 
arrangement. The invention relates especially to spring energized seals 
for different pressurized apparatuses. 
BACKGROUND OF THE INVENTION 
The new method and packing arrangement is essentially meant for producing a 
packing arrangement, which compensates for the wear and volume changes of 
seal material and of the cylinder, in which the said seal is moving 
axially and/or radially against metal surfaces to be sealed. 
Accordingly an object of this invention is to provide a simple method for 
producing a packing arrangement for purposes, in which an elastic seal 
material, preferably PTFE compound, is compressed to its final shape at 
room temperature by means of press members made of steel, the press 
members being movable against each other by force to compress said seal 
material placed therebetween, thus forming an elastic seal material layer 
for sealing a gap between surfaces to be sealed, and which the packing 
arrangement is capable of compensating the temperature changes and the 
wear of seal material. 
Another object of the invention is to provide an adjustable packing 
arrangement, particularly for a hydraulic fluid operated or mechanically 
operated system, which the arrangement is capable of withstanding 
substantial high pressures, even pressures of several hundred bars in a 
wide temperature range, but being suitable for minor pressures as well. 
Still another object of the present invention is to provide a packing 
arrangement that is displaceable in an axial direction inside a 
cylindrical/tubular space, said packing arrangement being also suitable 
for the axially surrounding sealing of a shaft which is rotatable and/or 
axially displaceable within said space. 
Still another object of the invention is to provide a relatively simple and 
effective packing arrangement for packing or sealing cylindrical/tubular 
spaces or shafts operating in such spaces, especially when applying 
relatively high operating pressures. 
A packing arrangement of the invention finds a plurality of applications in 
mechanical seal components having considerable pressure differences on 
both sides to be sealed, e.g., flap-valves, ball valves, pistons etc. This 
type of seal and packing arrangement also can be used in any geometrical 
form of pistons and cylinders, which are used for seal arrangements on 
various designs in a machine construction. 
To achieve the above and other objects of the invention, there is provided 
a method for producing a packing arrangement for a hydraulically operated 
apparatus, said method being characterized by the following steps: 
(a) producing a preshaped plastic piece of seal material; 
(b) compressing said preshaped piece at room temperature into a cylinder; 
and 
(c) compressing said preshaped piece at room temperature to its final form 
in said cylinder between a piston member and a counterpress member, at 
least one of said piston member and counterpress member being provided 
with rounded or tapered head portion facing against said preshaped piece, 
whereby the cross-section of said final compressed seal member is 
essentially wedge-shaped. 
There is also provided a packing arrangement displaceable in an axial 
direction inside a cylinder/tubular space, characterized in that said 
packing arrangement includes: two metallic compression elements axially 
displaceable relative to each other, whose relative rotation is prevented, 
and a seal member, fitted between compression elements and cold-molded at 
room temperature from a blank and whose material comprises quite easily 
plastically moldable materials with a low friction coefficient, especially 
PTFE plastics in various compounds, or graphite, said cold-molding being 
effected by means of said compression elements in a cylinder/tubular 
space, said space serving as a final operating location for the packing 
arrangement or corresponding in its dimensions to a final operating 
location for the packing arrangement; that a molding surface included in 
at least one of the compression elements and positioned against seal 
member is designed to be conical or convex toward the seal member, whereby 
the seal member has a wedge-shaped cross-section after said molding, and 
that said packing arrangement further includes means for moving said 
compression elements axially toward each other for squeezing a seal member 
fitted therebetween against the wall of space to be sealed with an 
appropriate initial tightness prior to the application of the pressure 
effect of a pressure medium/instrument on said packing arrangement. 
According to another aspect of the present invention there is also provided 
a packing arrangement for sealing or packing a shaft rotatable and/or 
axially displaceable in a cylinder/tubular space, characterized in that 
said packing arrangement includes: two metallic compression elements, 
axially displaceable relative to each other and surrounding a shaft to be 
sealed, whose relative rotation is prevented, and a seal member, fitted 
between compression elements, set against said shaft and cold-molded at 
room temperature from a blank, whose material comprises quite easily 
plastically moldable, low friction coefficient materials, especially PTFE 
plastics in various compounds or graphite, said molding being effected by 
means of said compression elements; that a molding surface included in at 
least one of the compression elements and abutting against the seal member 
is designed to be conical or convex toward the seal member, whereby said 
seal member has a wedge-shaped cross-section after said cold-molding; and 
that said packing arrangement further includes means for moving 
compression elements axially toward each other for pressing said seal 
member fitted therebetween against said shaft to be sealed with an 
appropriate initial tightness prior to the application of the pressure 
effect of a pressure medium/pressure instrument on the packing 
arrangement. 
One advantage gained by a packing arrangement of the invention is its 
relatively simple installation as the packing arrangement can be set up 
with relatively wide tolerances. 
Thus, the packing can be installed in position by allowing first some 
pressure medium therethrough for the easy removal of any possible air 
entrapped in the pressure medium prior to the initial tightening of the 
packing, during which the seal member is brought into a sealing contact 
against a surface to be sealed. Following the initial tightening and by 
virtue of the structure of a packing arrangement, the pressure effect 
applied to the packing arrangement by a pressure medium subjects the seal 
member to a pressure exceeding that of the pressure medium, whereby the 
seal member presses more tightly against a surface to be sealed for 
preventing leaks through the packing arrangement. The selection of a 
coning angle can be used to provide a desired pressure reinforcement in 
the seal member. 
THE PRIOR ART 
The molding of granular polytetrafluoroethylene (PTFE) powders require 
techniques different from those commonly used with other thermoplastics. 
The PTFE-compound is molded with processes similar to those used for 
ceramics or powdered metals. Finished articles may then be obtained by 
machining or, sometimes directly from the molding process without other 
treatment. In the most common PTFE molding process the PTFE-compound 
powder is compacted in a suitable mold; the compact is then removed from 
the mold, heated to a temperature above the crystalline melting point 
(360.degree. C.) to effect fusion of the individual particles, and cooled 
in a controlled manner to give the molded article a finished form. The 
compaction process is generally known as preforming and the heat treatment 
as sintering. During sintering the dimensions of the PTFE molded articles 
change significantly with a reduction in the dimensions perpendicular to 
the direction of preforming pressure application, and an increase in said 
direction. When making a mold for an item of any given diameter, the 
allowance must be made for any given PTFE-compound measurement, because of 
diametrical shrinkage of the PTFE-compound, which occurs during sintering. 
Thus the mold should be made slightly oversize, by using the data given by 
the manufacturer of PTFE-powder. Filled compounds consist of granular 
PTFE-resin with various inorganic fillers. The PTFE-compounds are used in 
low friction, high temperature mechanical products requiring less 
deformation under load and better wear-resistance than offered by unfilled 
PTFE-compounds. The fillers that may be used are glass-fibre, graphite and 
various types of carbon, as well as bronze, and molybdenum disulfide in 
compositions ranging up to 60% by weight of filler. The recommended filler 
types and contents, depend on the applications, e.g., on load, speed, 
temperature, mating surfaces, wet or dry conditions, chemical or 
electrical stresses, etc. Also available are free-flow filled compound 
grades that have been developed especially for automatic molding and ram 
extrusion. 
PTFE compounds are attractive because of their temperature properties and 
thermal stability. PTFE-compounds have an excellent resistance to heat. It 
is capable of continuous service at 260.degree. C. and can withstand 
temperatures up to 360.degree. C., for limited periods. Thermal expansion 
of PTFE-compounds is shown in FIG. 7 showing that the thermal expansion is 
not linear. Thus, the final operating temperature of a precision part must 
be accurately determined according to the manufacturers' recommendations. 
Filled PTFE seals have been used in conditions where normal elastomer 
seals often fail. The usual designs are shown in FIGS. 8-10 in which also 
steel and rubber springs are used to support the PTFE-seal against the 
wall. FIGS. 11-12 depict the pressure to temperature relationship of these 
designs respectively. Said constructions fulfill requirements for low 
friction, nonstick properties and resistance to chemicals, their drawbacks 
are, however, deformation which tend to creep under high load especially 
in high temperature range. The great thermal expansion of PTFE-compounds 
and elastomers may cause seal failure if not taken into account during 
seal design. In general, it is recommended that standard groove design be 
used as a starting point in the evaluation of a seal of PTFE-compounds 
elastomer. If the groove volume is inadequate, thermal expansion will 
result in either extrusion splitting of the seal (usually along the 
parting line of the seal) through the clearance gap or circumferential if 
it cannot extrude. In either case, it is recommended that the groove width 
is normally so great that the thermal expansion is possible and to 
accommodate the volume-increase in the elastomer O-ring and 
PTFE-compounds. 
The prior art seals in FIGS. 9-10 are spring energized sealing elements for 
pressure applied from one side, they are used primarily for sealing 
reciprocating pistons and rods but also for rotary and swiveling motions 
and for static applications. The seal consists of two-components: an outer 
housing of a high strength plastic (e.g. PTFE) and integrated 
stainless-steel spring. As the seal is installed in the groove the spring 
forms a pretension to the seal. Since the seal is installed with the open 
side facing the higher system pressure, the sealing effect is increased as 
the pressure rises. The steel spring also has the additional function of 
compensating for wear at the seal lips. 
The seal structure described above has one serious drawback, namely that it 
does not resist high-pressure and heat alterations simultaneously, as 
shown in FIGS. 11-12. For example, the seal does not resist 150 bar 
pressure in temperature of 150.degree. C. The reason for this is due to 
the creep effect of the PTFE-compounds, especially in higher temperatures. 
Nominal dimensions and tolerances are defined in standards ISO 
6194/1-1982(E) and DIN 7160 or 7161 for the lip seals, which define strict 
nominal dimensions for the machined seal materials and metal parts, which 
means expensive machining, careful storage and the installation 
procedures. 
The present invention is designed to avoid said drawbacks, particulary of 
PTFE-compound creep properties under high pressure and temperature to 
obtain the seal structures that do not leak in a widely changing 
temperature range, and to use said creep property as an advantage by means 
of the invention. 
SUMMARY OF THE INVENTION 
In view of the operation of the method for producing a seal arrangement of 
the invention, it is essential that the seal member is compressed into its 
final form between press members of metal, and wherein at least one of 
said press members can be left on its place to form actuating and/or 
adjusting means for said seal member which is forming the wedge-shaped 
seal layer between surfaces to be sealed. Said seal material is first 
machined or stamped from the PTFE-compound plate at room temperature near 
its final form and then said piece is compressed into its final place, 
wherein the said pressing means molds the seal material into its final 
wedge-shaped form. 
The essential idea is tighten the seal material all the time during usage 
and cause high pressure to the plastic seal material by said press member 
so that the pressure of the seal is higher than the process pressure 
whereby the seal does not leak. Preliminary tests have indicated that the 
PTFE matrix reinforced with carbon/graphite fibers being compressed 
between said press members provide a packing arrangement which can 
compensate volume alterations of the seal material resulting from 
alterations due to thermal expansion and wear of the PTFE-composite and a 
metal body. 
The most significant advantage gained by the seal arrangement of the 
invention is a considerable pressure and heat resistance with low friction 
properties. 
BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION 
According to FIGS. 1 and 2, a packing arrangement of the invention includes 
compression elements 3 and 4 with a seal member 5 fitted therebetween. In 
the embodiment of FIG. 1, the compression element 4 is provided with a rod 
portion 6 for facilitating relative tightening of the compression elements 
with the compression elements properly positioned in a space to be sealed. 
The initial form of seal member 5 can be, e.g., a blank lathed close to a 
final form or simply a blank made of a sealing compound. The molding of 
seal member 5 to a desired final form is effected by pressing at room 
temperature said blank 5 between mutually opposing molding surfaces 17 and 
18 included in compression elements 3 and 4. The compression elements 3 
and 4 are attached to each other with a screw, including a head portion 
12, a stem portion 11, and a threaded portion 13 at the end of the stem 
portion. The screw extends through a through-going centre hole formed in 
first compression element 4 and its rod portion 6 and through a centre 
hole formed in seal member 5 into a threaded fastening hole 21 formed in 
second compression element 3. Tightening the screw causes the axial 
displacement of compression elements 3 and 4 toward each other, whereby 
said seal member 5 set therebetween moves radially toward the wall of a 
space 2 to be sealed. Simultaneously, the seal member is subjected to yet 
a little further deformation between molding surfaces 17, 18. The molding 
of seal member 5 is preferably effected, e.g., with a separate hydraulic 
press between said molding surfaces with the compression elements 
positioned in space 2, the compression elements not being joined together 
with the above-mentioned screw until after this molding action. During the 
course of tightening the screw, said compression elements 3, 4 must be 
locked or clamped against the relative rotation. This can be effected, 
e.g., by means of locking pin 7 fitting in a locking hole included in 
compression elements 3 and 4 whereby, upon turning the screw, said rod 
portion 6 is grabbed with an appropriate tool to prevent the compression 
elements from rotating in unison. When the space to be sealed has a 
cross-section other than circular, rotation of the compression elements is 
eliminated without a separate locking means. The object of a fastening 
screw is to join compression elements 3 and 4 together and to adjust the 
initial tightness of a seal member set therebetween. This possibility of 
adjusting the initial tightness makes it possible to dimension the outer 
diameter of seal member 5 to be smaller than the inner diameter of a space 
to be sealed for an easier installation of the packing arrangement. By 
adjusting the initial tightness the seal member can be brought against the 
wall of a space to be sealed for preventing the pressure medium leaks 
prior to the application of full pressure on the packing arrangement. In 
the embodiment shown in FIG. 1, a pressure medium acts from the direction 
of compression element 3 whereby, as the pressure effect created by the 
pressure medium is applied on compression element 3, the latter shifts 
toward the opposite compression element 4, thus resulting in a further 
displacement of the seal member toward the wall of a space to be sealed 
for even more effective operation of the packing. This axial displacement 
of the compression elements is facilitated by providing between 
compression elements 3 and 4 an axial clearance 15 within the central area 
thereof not provided with an intermediate seal member 5. This arrangement 
serves also as a limiter to said axial displacement. In order to reduce 
friction between compression element 4 and cylinder walls the outer 
surface of the element 4 has only a small area 4a close to said walls the 
remaining portion of said outer surface having a reduced diameter. Said 
small area is placed adjacent the outer edge of the melding surface 18. 
Correspondingly, the compression element 3 has a small outer surface area 
3a adjacent the outer edge of its molding surface 17. By means of these 
areas 3a and 4a the seal member 5 is placed in an essentially closed 
space. 
As shown in FIG. 1, the packing arrangement further includes spring members 
9, 10 between the fastening screwhead portion 12 and the outer end of rod 
portion 6 included in first compression element 4, said spring members 
serving to compensate for the wear of seal member 5 and/or to adjust its 
initial tightness. In addition and according to the embodiment of FIG. 1, 
the packing arrangement includes a spring member 14, surrounding said rod 
portion 6 and positioned between a locking nut 19 and the outer surface of 
compression element 4. The object of spring member 14 is to return 
compression elements 3 and 4 back to their original position upon ceasing 
the pressure effect and to operate with locking nut 22 as a blocking means 
for preventing the displacement of packing arrangement 1 out of a space to 
be sealed as a result of the pressure effect applied on the outer surface 
of compression element 3. 
The embodiment of FIG. 3 differs from that of FIG. 1 in that the former is 
intended to seal or pack a shaft 16 operating in a cylinder space, the 
packing arrangement surrounding said shaft 16 and the seal member 5 being 
located in the packing arrangement centre hole and setting against shaft 
16 upon pressing said compression elements 3 and 4 toward each other. This 
embodiment preferably includes more than one fastening screws, e.g., 4 
screws, for squeezing a seal member 5 as uniformly as possible against 
said shaft 16 to be sealed. 
The sealing material used in a packing arrangement of the present invention 
comprises preferably various types of graphite- or carbon-fiber 
compounded/reinforced plastics, such as PTFE plastics, graphite or carbon 
fibers, or similar materials having a low friction coefficient and being 
plastically quite easily moldable at room temperature. 
A second embodiment for a cylindrical/tubular packing arrangement of the 
invention is described in FIG. 4. A seal 22 is formed by pressing seal 
material, e.g., PTFE-compound, within cylinder 21 between a ball bearing 
23 and counterpress member (not shown) having a conical head portion the 
diameter of said head portion being less than that of ball bearing 23. In 
this embodiment ball bearing 23 with shaft means 24 are left in their 
place to be used as a piston means, in order to transmit pressure to the 
pressure medium 26 while said counterpress member is replaced with a 
rubber ball 25 press fit into the seal material 22. Said rubber ball 
serves as a spring means for said seal 22. Said seal forms a lip portion 
32 which enhances the effect of the seal. 
A third embodiment for a cylindrical/tubular packing arrangement of the 
invention is described in FIG. 5. A seal 22 is formed between ball bearing 
27. One end of the seal 22 is facing toward pressure medium which is 
pressurized, e.g., by means of hydraulic apparatus (not shown). At the 
other end of the seal 22 there is arranged a piston rod 31 extending 
outwardly from the ball 27, said rod 31 being provided with a pressure 
plate 28 at the end facing against the ball 27. Around the piston rod 31 
is assembled a spring element, e.g., compression spring 29. Said spring is 
arranged to stay in a cylinder space around rod 31 by means of threaded 
cylinder 30 provided with a hole for the piston rod 31. The use of the 
compression spring 29 helps return the seal 22 backward as the pressure 
effect ends and piston rod 31 returns to its original place. 
The embodiment illustrated in FIG. 5 can be used on the opposite direction 
by means of changing the compression spring to an extension spring, 
whereby when the pressure effect is directed to the piston rod 31, e.g., 
mechanically, the seal 22 moves in its cylinder space away from the part 
30 causing pressure on the pressurizing medium 34, which in turn can use 
apparatus suitable for the application. Thus, when the pressure effect to 
the piston rod 31 ends, the extension spring withdraws the pressure plate 
28 backwards, whereby the pressure of the pressurizing medium drops and 
the apparatus returns to its initial state. 
FIG. 6 shows one embodiment of producing phases. In phase I a preshaped 
seal piece 35, which has been produced by stamping or cutting from a plate 
or rod of PTFE-compound, and a cylinder 21 are placed into an assembly 
cylinder 36. In phase II the seal piece 35 is pressed at room temperature 
against cylinder 21 so that seal material enters into cylinder space 33 of 
the cylinder 21 and into a gap 38 between the outer wall of said cylinder 
21 and inner wall of the assembly cylinder 36. This pressing of the seal 
piece 35 is effected by a push rod 43 having a conical head 40, whereby 
the conical head 40 cuts the preformed seal piece 35 as the head 40 is 
pressed against the cylinder 21. At this stage the seal material in the 
space 38 outside the cylinder 21 forms an exterior seal having a lip 
portion 41. The tapering angle of the head 40 and the lip portion 41 
depends on the material to be sealed and the pressure used. Preliminary 
tests have proved that the advantageous angle against the PTFE compound is 
about 60.degree., while the fluid generally requires a smaller angle. 
Preliminary tests are required to find the right angle for each material 
combination. 
The exterior surface of cylinder 21 forming said gap 38 is preferably 
provided with a chamfer 37. Said cylinder body 21 provided with the 
exterior seal is advantageous when the cylinder 21 is used for the initial 
setting of pressure in a cylinder where the cylinder 21 is assembled, 
whereby fine adjustment of the pressure happens in cylinder space 33 by 
seal 22 and its pressure means, like steel balls 27. 
In phase III the seal material is compressed at room temperature to its 
final form, which compression is being made by means of steel ball 
bearings 27 and pressurizing means, or with dies (not shown) so that the 
steel balls are forming the seal material to its final form, while the 
balls (pistons) are moving toward each other under the compression. 
The lip portion 32 adds the seal effect on seal 22, which is caused by 
means of a pressure medium and the pressure means, which are compressing 
the lip portion 32 against the inner wall of cylinder 21. Said lip portion 
32 creeps in use and tightens against said wall. 
This kind of seal arrangement can be constructed as a separate cylinder 
part, which can be assembled into the body part of the machine or 
apparatus. Naturally the seal 22 can be assembled into the cylinder hole 
made in the body part, wherein many different sizes of cylinders are 
connected to each other by means of a common pressure medium channel, to 
form a closed pressurizing system. 
On one aspect of the invention the seal material is carbon or graphite 
reinforced PTFE-plastic, which has a very low friction factor. 
The seal material according to the invention is preferably carbon/graphite 
reinforced PTFE-compound. The advantage of the PTFE-compound is that it 
has good friction properties and wide temperature range. 
The disadvantage of the PTFE-compound is its creep property, especially at 
a higher temperature range and that property is used as an advantage 
according to the invention, wherein the said PTFE-compound is always kept 
in closed space. 
According to the invention, piston end and/or counterpress member is 
forming the seal material all the time when pressure (either from the 
piston means or from the pressure medium) is affecting said seal member, 
thus forming effective seal structure that is compensating wearing of the 
seal material. In addition by choosing a suitable gap between the cylinder 
space and the piston means and/or counterpress members, wearing of the 
cylinder space is smaller as the PTFE-compound is the only material 
affecting the wearing. 
In the embodiments shown it is naturally possible to use also ball end, 
conical end piston, or pressing means instead of a ball bearings. 
In addition an application of a similar seal profile and construction can 
be applied to any geometrical form of piston elements, e.g., square, 
triangular, etc., which can move in the equivalent cylinder. 
Although the seal construction and a method of the invention have been 
described above, further modifications can be made without departing from 
the inventive concept, the invention is not to be limited to the 
embodiments, except by the scope of the appended claims.