Note: Descriptions are shown in the official language in which they were submitted.
~l'hl~{3~7
The present invention concerns a procedure for treating
a fibre web between the forming fabric section and the drying
section of a paper machine, utilizing so-called clo~ed
conduction, such procedure comprisin~ as a combinatlon the
following steps: detaching of the web from the forminy fabric
at the point of detachment and substantially simultaneous
affixing thereof on the surface of a transfer felt; transport
of the web carried by the transfer felt's surface from the point
of detachment to a first press nip; conduction of the lower
felt of the press section into the first press nip defined by
a recessed surface lower roll and a dewatering upper roll con-
nected to a suction system; pressing of the web between the
transfer felt and the lower felt and simultaneous dewatering
of the web in two directions in the first press nip; conduction
of the web on the surface of the transfer felt of the press
section to a second press nip defined by said upper roll and
a solid smooth-surface central roll of the press section;
dewatering of the web in the second press nip with water flow
passing into the transfer felt.
In addition, the present invention concerns a means
applying the procedure of the invention.
It is well known that in paper machines running at high
speeds or used to manufacture low strength paper brands one is
compelled to employ so-called close transfer systems without
any free draws, so that the web will be continuously supported
with the aid of a felt as it passes from the wire over to the
press section. These systems operace in the manner that the
transfer felt of the press section is conducted into contiguity
with the web on the wire. The transfer felt may be urged against
the web on the wire the aid of a rotating roll so that the web
is made adheren-t to the felt and comes ofE the wire and that it
continues its travel affi~ed to the felt surface, this felt
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l~Z1~7
carrying the web subsequently to the Eirst press nip in the
press section.
Generally speaking there are two main t~pes oE clo~d
transfer system. 5implest is the so-called :Lick-up trans~er,
which is based on the ability of a wet so-called lick-up felt
to bind the paper web to its surface. Another type is the
vacuum pick-up system in which suction has been arranged to act
at the point of transfer, and which renders`possible a positive
transfer of the web from the wire to the transfer felt. The
vacuum pick-up system offers greater possibilities, particularly
regarding selection o-f felt, compared with the lick-off system.
In order to affix the web Eirmly to the felt during its
travel between the point of detachment and the Elrst press nip,
it has been a commonly known method to use a comparatively
wet felt to promote the web adhesion. But if the transfer felt
also operates as press felt, the wetness of the felt naturally
detracts form the web dewatering capacity in the Eirst press
nip. It would therefore be desirable, with a view to highest
possible dewatering capacity, to keep the felt as dry as
possible
As a rule, the pick-up system of the paper machine and
- its press section contain a plurality of press felts, which
serve partly as web-supporting means and partly aid the dewater-
ing action in the press nips. There is usually one felt per
web treating point. In some instances one felt may serve the
web treatment at six different points. The pick-up press
section, which has one pick-up nip and three dewatering nips,
may comprise four felts or fabrics. For each of these a great
number of felt guide rolls and tensioning and guiding means
are required for guiding the running of the felt. Also felt
reconditioning means are required for each such felt, for the
continuous washing of the felt during operation.
--2--
? ~ L9~
Owing to the multitude of such e~uipment, the press
section has become unwieldy, space-consuming and expensive.
The numerous, or fre~uently necessary, felt chanyes or replace-
ments are hiyhly inconvenient. Therefc~e, it would be de~ir~
able to provide in the press section the minimurn number of
felts and different felt types which is ~easible.
The most important aim of the present invention is to
provide a simple paper machine press section and procedure which
for its operation implies a minimum of operative components.
By the expression "operative components" are meant: press rolls,
suction rolls in particular, press felts, felt guide rolls, felt
guiding and tensioning means, and felt conditioning means.
Another object of the present invention is to provide a
procedure and means for efficient transfer of the web from the
forming wire onto the transfer felt in the press section,
utilizing the kinetic ener~gy of the web itself while at the
same time making efficient use of centrifugal force towards
detaching the web from the wire and towards it attaching to
the transfer felt of the press section, while at the same time
the consumption of suction energy is minimized, as well as the
noise arising from the operation of suction rolls. The detri-
ments of suction rolls as sources of objectionable noise and
as energy consumers have been discussed e.g. in the same
applicant's Canadian pate~t No. 1,059~356 of July 31, 1979.
In order to attain the aims stated, and others which
will become evident later on, the procedure of the invention
is mainly characterized in that the transEer felt participates
in the treatment of the fibre web still in the third dewater-
ing nip, in that in association with the aforementioned steps
the transfer felt is detached from the web after the second
press nip and conducted to a first felt conditioning means for
the reconditioning of the felt, that the fibre web is
97
transferred, adherent to the surface o:~ the central roll, ~o a
third press nip defined by the smooth central roll and the second,
recessed surface, roll of the press section, the transEer felt
bei.ng conducted from the first felt conditionil-g means t~ said
third press nip, where the web is pressed between the smoo~h
roll surface and the felt so as to express water from the web
towards the recessed surface roll, whereupon the felt is detached
from the web and conducted throuyh a second felt conditioner
back to be adjacen.t to the return roll within the forming fabric
loop, at which roll detachment of the fibre web from the forming
fabric takes place, and that the fibre web is transferred after
the third press nip on the surface of the smooth roll to the
point where the web is detached from the roll surface to be con-
ducted to the drying section.
The means of the invention, again, is characterized in
that the means comprises in combination the following mutually
associated components:
- a forming fabric;
- a fabric return roll within the forming fabric loop;
- a press suction roll connected to a suction system;
- a first recessed surface press roll, defining with said suc-
tion roll a first dewate~in~ ~ip;
- a smooth-surfaced press roll, defining with said suction roll
a second dewatering nip;
- a second recessed surface press roll, defining with the smooth-
surfaced press roll a third dewatering nip;
- in total ~wo press felt fabrics, whereof the felt fabric
belonging to the top part structure of the press section serves
as transport felt conveying the fibre web from the point of
detachment to the first and second dewatering nips and which
within its loop encloses the suction roll and the second recess-
ed surface press roll, covering of the suction rollsubstantially
,~ ' '
~h'l ~
at least that sector on which the suction oE the s~ction rol1
is active, ancl whereof the ~elt fabric belonging to the bottom
part structure of the press section wi~hin its Lcop enc:Loses ~h~
first recessed surfAce press roll and serves as water-receiviny
lower Eelt in the first press nip;
- a first transfer felt conditioning means on the Eelt run between
the second and first dewatering nips;
- a second transfer felt conditioning means`on the felt run follow-
ing after the third dewatering nip;
- a third felt conditioning means for the lower felt.
Thus, as taught by the invention, the wet fibre web is
conducted with the aid of the Eorming wire onto the return roll at
the point of detachment, to which point the suitably reconditioned
and comparatively dry transfer felt is also conveyed. At thepoint
of detachment the web is detached from the wire and transferred
onto the transfer felt without using any separate pick-up suction
roll. Instead, one may use a detaching suction box or, in an
alternative favourable design, the suction roll of the press
section, which operates as pick-up roll. The transfer felt also
serves as press felt in three nips of the press section. At the
detachment of the web from the wire, and in its transferring onto
the felt, the adhesion forces of the felt and the centrifugal
force acting on the web are utilized, as the web is lapping the
wire return roll on a sector in excess of 90 degrees. After the
web has thus become adherent to the surface of the transfer felt,
the felt proceeds to the ~irst press nip of the press sec~ion,
this first nip being double-felted, the transfer -felt itself
being the upper felt in the double~felted press nip.
~fter the first press nip, the web is acted upon by the
suction of the press suction roll, this serving to make sure
that the web remains adherent to the transfer felt, which
together with the web runs through the first press nip to the
second press nip of the press section, this second press nip
being defined by said suction roll and the smooth-surfaced
roll in the press section.
The present invention is in particular applicable in
press sections o~ the type disclosed in the same applicant's
Canadian pa-tent application No. 971,790 of July 29l 1975~
It is a remarkable feature of the invention that not
more than two press felts are indispensable for the operation
of this press section: the upper felt and the lower felt. The
path of the upper felt has been so arranged that it serves at
one and the same time four purposes or functions, that is:
constituting a pick-up transfer felt and at the same time also
working in three consecutive dewatering press nips. The lower
felt only serves the first nip, which is double-felted. The
minimum number or felts implies that it is possible massively
to reduce the number of felt guide rolls, felt guiding means
and tensioning means, compared with a pick-up part comprising
three dewatering nips in which it may be necessary to use four
felts.
In one embodiment of the invention, the suction roll of
the press is of a design incorporating an external suction
chamber. In this case the expensive foraminous suction roll
is not absolutely necessary and it may be replaced with a
solid-shell recessed surface roll at which the suction exerts
~-- its effect through passages encircling the roll periphery.
This design contributes to great savings of suction energy.
In the following, the invention shall be described in
detail with reference being made to certain embodiment examples
of the invention.
In Fig. l is shown, schematically, the first embodiment
of the invention.
~ - . _~_
Fig. 2 displays, in equivalent manner, a second
embodim~nt of the invention,
Fig. 3 presents ~n example o~ the surEace st~ucture o~
the press suction roll emplo~ed in ~'ig. 2, in partial axial
section~
The web forming section depicted in Fig. 1 comprises a
pair oE endless wire loops 10 and 20, which have a common
ascending run, thereby constituting a -twin wire former. The
running oE the wire 10 is guided by the aid of the rolls 12 and
also by means of the guiding roll 13 disposed halfway on the
joint run of the wires. Moreover, this wire 10 laps the breast
roll 11 so that it forms a single-wire section, on-to which the
headbox 14 supplies pulp stock. The twin wire former also
comprises a lower forming roll 21 and a wire board 15, which
is disposed to lie on the single-wire run extending from the
breast roll 11 to the lower forming roll 21. The wire board
15 has a solid or perforated cover, or one with slot openings,
adjacent to the wire 10. The ~ower forming roll 21, located
within the wire loop 20, has a suction zone 21a, in the region
2~ of whlch the dewatering takes place. This dewatering is
simultaneous in both directions, namely, away from the roll
21 by effect of centrifugal force and inward in the direction
of the suction zone 21a. The wires 10 and 20 pass along the
point run upward over the lower forming roll 21, the inter-
,. .
mediate roll 13 guiding them onto the upper forming roll orcouch roll 22, which features a suction zone 22a, this zone
ensuring that the web W that has been formed will after the
twin wire forming section continue, carried by the wire 20,
toward the right past the upper forming roll 22, as shown in
Fig. 1 The wire 20 is guided by ~he aid of appropriate guide
rolls 23.
The detachlng of the formed web W from the carrying
--7--
~ire 20 takes place on the wire return roll 25. ~s shown in
Fig. 1, the wlre 20 covers the return roll 25 on an angle
slightly in excess oE 90 degrees, and the transEer felt 30 is
likewise conducted to cover ~his rol~ 2S on a sectc)r thu~ i~a~
been markecl ~. In the region of the sector ~, the web is
detached from the wire 20 and becomes adherent to the ~elt 30.
At the point where the transfer Eelt 30 and the web W residing
thereupn separate from the wire 20 there ha~s been placed a
suction box 24, connected to the suction system of the paper
machine, within the loop of the transfer felt 30, to ensure
the detaching of the web W. The more detailed design of the
suction box 24 is described in the same applicant's U.S. Patent
No. 4,113,557. It should be noted that in actual fact the web
W starts to become detached from the wire 20 already before it
reaches the centre point of the sector ~, this being the
result of the centrifugal force acting on the web W in that
area where the direction of the web-carrying wire 20 first
begins to change. However, the suction box is not indispensable
in every case.
The course of the transfer felt 30, before it comes into
contact with the return roll 25 of the wire 20, is guided with
the aid of the guide rolls 32. As has been schematically shown
in Figs 1 and 2, one special guiding roll 32a is so adjustable
that the transfer felt 30 can be guided into contiguity with
the return roll 25 in such manner that the size of that sector
on which the felt 30 covers the wire 20 and the web W resid-
in~ thereupon can be adjusted. It is possible in this way to
enhance the affixing of the web W to the transfer felt 30 by
increasing the extension of the sector ~ and thereby increasing
the time of contact between the felt 30 and the web W.
- As shown in Fig. 1, the press section comprises four
.
press rolls and which define three press nips. the Eirs-t nip N1
is defined between press rolls 31 and 4:L, whereof the upper
roll 31 is a conventional suction roll, whi:Le the lower ro~l
41 is a water-receiviny roll having a recessed surface, for
instance a grooved or blind drilled surEace. The upper roll
31 is provlded with a suction sector having two compartmen-ts
34a and 34b, The first suction compartment 34a extends ahead
of the press nlp Nl to such extent that the~detachment of the
web W from the ~elt 30 ~by centrifugal effect for instance) is
prevented. The purpose of the suction compartment 34b is on
one hand to keep the web attached to the felt 30 while travelling
between the nips Nl and N2 and, on the other hand, to prevent
rewetting of the web, by maintaining the water in the mesh of
the felt. The suction roll may as well be of the type describ-
ed later on in connection with Fig. 2.
The press section furthermore comprises a smooth-surfaced
central roll 61, for instance a stone roll, which together with
the upper suction roll 31 deEines the second press nip N2.
This roll 61 cooperates also with the press roll 71, defining
the third press nip N3. The roll 71 has a water-receiving
recessed surface. On the free sector on the underside of the
smooth-surface press roll 61 a doctor blade 62 has been provid-
ed to keep its surface clean, The web is detached from the
roll 61 in a well-known manner and it is conducted by -the aid
of the roll 74 to the drying section of the machine.
As shown in Fig. 1, in the press section only two
press felts 30 and ~0 are used to aid the dewatering in the
press nips and the transport of the web through the press
section, these being the transfer felt 30, which transports
the web from the forming wire 20 to the first nip Nl and which
at the same time serves as upper felt of the whole press section,
participating in the pressing process also in the second nip N2
and in the third nip N3; and the press felt 40 of the lower
press roll ~1, this Eelt operating in the pressing event in
one nip only: in the Eirst nip Nl as the lower ~elt thereof,
under guidance by the ~lide rolls ~2. qlhe Eel~ ~0 has been
provided with reconditioning means ~3, whi~h ma~ be of any
conventional and expedient design,
As already mentioned, the course of the upper felt 30
has been arranged with the aid of the guide~rolls 32. It is
necessary in order to gaarantee a successful pressing event,
to clean, wash and press the felt 30 in all nips during opera-
tion. To this end, after the nip N2, the felt 30 is conducted
into the felt reconditioner 33, whereafter the felt 30 is
further conducted to the third press nip N3, whereafter the
felt 30 is once again conducted to another felt reconditioner,
this being a washing press and comprising two press rolls 34a
and 34b. Such felt reconditioning means and their connection
with the water supply and vacuum systems are well understood
by persons skilled in the art and need therefore no detailed
explanation. After passing the washing press, the felt 30 is
conducted back to the wire section and to the point of
detachment of the web W on the roll 25.
The main part of the guide rolls 32 of felt 30, and the
felt drying means, have been accommodated on a supporting beam
structure 35, shown by a schematic dotted line above the press
roll part.
In Fig. 2, another embodiment of the invention is depic~-
ed, comprising a wire section and a press section, both of
which are in the main similar as shown in Fig. 1. However, in
the design shown in Fig. 2, the wire return roll 25 has been
disposed substantially on the same horizontal level as the press
roll 31' of the press section so that the wire return roll 25
and the roll 31' of the press section are side by side and
--10--
9~7
define a transfer nip NO, in which the web W is detached from
the forming wire 20 and becomes adherent to the felt 30.
The transfer oE the web W Erom wire 20 ko Eel~ 30 i~
facilitated, in part at least, b~ effect of centrifuc~al force,
this Eorce being created on the wire return roll 25' owing to
the change of direction of the wire 20, similarly as in the
embodiment example of Fig. 1. However, in the design shown in
Fig. 2, the transfer of the web W to the felt 30 is greatly
promoted by the aid of suction from the suction roll 31' of the
press. The wire return roll 25' may simply comprise a solid
shell (either smooth or grooved), but a foraminous shell may
also be employed, as has been disclosed in the same applicant's
Canadian patent No. l~0~?/~l7r o~ rch 10r 1981, accor*in~ to which
within the shell of the corresponding roll particular blowing
means have been provided. Moreover, the detaching of the web
W and its trans~er from the wire 20 to the felt 30 may be
facilitated by an appropriate selection of the line pressure
in the transfer nip NO.
The suction roll 31' is of such type wherein the suction
chamber 36 is located on the outside of the roll and has been
provided with seal'ing strips abutting on the outer surface of
the rol~ shell and/or acting against the felt 3~. A design of
this kind, and is advantages, have been extensively covered in
~ the same applicant's Finnish patent application No. 7.721.129.
As shown in Figs 2 and 3, theshell of the roll 31' has
a recessed surface structure, comprising for instance grooves
37 or passages extending peripherally around the surface of the
roll 31'. The suction chamber 36, extending over the whole
breadth of the machine, is connected to the vacuum system of
the paper machine, which is in itself known in the art. The
suction chamber 36 covers the surface of the roll,31' on a
sector ~. The subatmospheric pressure which is caused in the
~ -11
grooves 37 of the sur~clce of the roll 31 on the sector ~ becomes
effective also in the grooves 37 of the roll 31' on the sector
~which is opposite to the sector ~ The sec-tor ~is substantial-
ly equivalent to the sector NO-N1-N2. rrhereby, thc suba~ osphe~ic
pressure prevailing in -the groovecl surface conigura~ion of the
sec~or ~ has the same effect and task as has the suctlon in the
compartments 3~a and 34b in Fig. ]..
The roll 31' may, although it is pro~ided with an
external suction chamber 36, alternatively have a foraminous
shell of the kind employed in conventional suction rolls. Such
a design presents the advantage that it is possible to place
an additional suction box within the shell in the region of the
transfer nip NO. This suction box (not depicted) may have a
narrow suction area in order to create a comparatively high
vacuum in the nip NO to ensure the detachment of the web from
the forming wire 20. The subatmospheric pres~sure produced by
the suction chamber 36 in the foraminous shell and therein
acts on the web W through the felt 30 and this suffices to
keep the web adherent to the felt between the nips NO and Nl
and the nips Nl and N2.
The apparatus depicted in Figs 1 and 2 operates as
follows The headboxl4 supplies pulp stock onto the wire 10 of
- - the twin wire former so that water escapes ~o some extent at
the foraminous wire board 15 before the forming roll 21,
although the dewatering mainly takes place on the forming roll
21. Dewatering continues in a lesser degree at the guide roll
13, and some dewatering is also effected at the couch roll 22.
~he suction sector 22a of the roll 22 effects the adherence of
the web W to the wire 20, which transports the web to the wire
return roll 25 (or 25' in Fig. 2). In the latter area the
transfer felt 30, which also constitutes the upper felt of the
-12-
press section, is conducted into contiguity with the web W so
that the web is detached Erom ~he wire 20 and become~ a~herent
to the felt 30 as has been presented beEore.
The web W, which is attached to the felt 30, goes along
with the felt 30 to the first dewateriny press nip Nl. The first
press nip Nl is defined between the upper suction roll 31 (or
31' in Fig. 2) within the upper felt loop and the lower press
roll 41, this latter being a water-receiving roll and having a
recessed surface, e.g. onethat has been sui~ably grooved.
This roll 41 naturally has its own felt 40. After the first
press nip, the web W remains adherent to the felt 30 thanks
to the subatmospheric pressure present on the suction roll 31,
and the web is thus transferred with the aid of the felt 30
to the second press nip N2.
In the second press nip N2, defined between the roll 31
(or 31' in Fig. 2) and the smooth-surfaced roll 61, which is
the central roll of the press section, additional pressing of
the web W takes place for water removal, but in this nip the
web W is detached from the felt 30 and becomes adherent to the
smooth surface of the roll 61 and goes together with the roll
61 into the third press nip N3. The felt 30 is now conducted
into a felt reconditioner 33, where the felt 30 is washed and
water is remove~ therefrom. This is an important step because
in the nips Nl and N2 the felt takes up from the weh ~ a large
quantity of water and, along therewith also a considerable
amount of fines and fillers. After being reconditioned, the
felt 30 proceeds to the third nip N3.
The third press nip N3 has been accomplished by placing
in cooperation with the roll ~I, a water-receiving roll 71,
which also operates within the felt loop 30 as hasbeen shown
in the foregoing~ This roll 71, too, is a foraminous surface
roll, for instance a water-receiving grooved roll, and in the
-13-
third press nip N3 the web is Eurther dewatered so that lts dry
matter content lncreases. After the third press nip M3r the
web has been shown to be de~achecl ~rorn t~e ro~ 1 in aonven~
tional manner, and it then goes to the drying section o~ the
paper machine, which is known in itsel-f in the a~t. After the
press, the felt 30 is conducted back again to the wire return
roll at the point of detachment.
Xn the foregoing the most important ~feature of the
present invention has been described: that the transfer felt
30 operates as press felt throughout the press section, and
expressly it serves as the upper felt thereof. This upper
felt contributes to the treatment of the web W and to the
pressing process in four steps: to begin with, in the detach-
ing of the web W form the forming wire - or in the pick-up
process - and later at the pressing of the web W in the three
subsequent press nips.
The system of the present invention numerous advantages
over a conventional paper machine having separate felts at
least for the pick-up nip and with it Eor the first press nip,
for the second nip and for the third nip. The system here
. . .
presented implies in structural respect that the course of the
felt may be arranged in a very simple manner so that it com-
prises virtually all felt guide rolls and felt reconditioning
means disposed to be carried by one single supporting beam
construction. This design implies that felt change is easy
to carry out, because the number of felt tensioning and guiding
members has been minimized.
Another conse~uence of the ~urnishing of the press
section with one single upper felt and one lower felt is that
shut-downs necessitated by the changing of a worn-out felt
will occur considerably less than in the case in which the
press section has four felts with different changing intervals.
97
One advantages oE the system presented here is: that the
web W may be ~etachecl Erom the forming wire withou~ any separate
pick-up roll. As has been described, -the detachment is effected
by utili~in~ th~ centrieu~al ~rce ac~inc~ on the w~h and ~hl~
combined with the adhesive force of the transEer felt, and
furthermore applying suction if required. In the alterna~ive
design, the pick-up roll has been replaced with the suction
press roll of the press section, said press~roll defining,
simultaneously, three operative nips.
The felt 30 is required to meet certain conditions so
that it might operate as intended in this system. The most
modern felt manufacturing technology, which uses new
materials and new weaving techniques, affords new, improved felt
brands and structures, which are appropriate in the application
of the present invention.
The design outlined in Fig. 2, in particular, implies
no exceptional felt adhesion properties with regard to the
web W. No water film is necessary on the surface of -the felt
in transport of the web from the transfer nip NO to the first
nip Nl, and the structure of the felt 30 may be wholly selected
considering its water absorption properties. The felt 30 may
be as dry as possible when it is being conducted into the nip
NO. Sufficient dryness of the felt can be achieved by the
aid of appropriate felt conditioners and a felt press 34a/34b.
Therefore, the principles of operation of the present
invention and the consequential advantages may be briefly
stated as follows. The number of press felts needed in the
- press section is only two, with the result of a simple and
comparatively inexpensive design featuring rather few guide
rolls. The changing of felts is easy owing to the simple
design. The felt change intervals and the need to change felts
is reduced, particularly in comparison with the four-felt
system. In the whole system only one suction roll is needed,
and this roll may operate with an external suction chamber, a
solution which economizes the suckion power and lessens' the
noise detriment.
It is undes-tood that the speci~ic desiyn of the p~ess
section and oE the components participating in the web trans-
fer which precede it may be modified from the design shown
in the figure. In the case of the embodiment presented in Fig.
2, for instance, it is possible within the scope of the present
invention to furnish the suction roll 31' with a foraminous shell
and with a conventional suction compartment therewithin, to
further facilitate the transfer of the web to the felt and to
enhance the dewatering in the nips Nl and N2. The seals of
the suction box 36 may be designed in numerous different ways.
As regards the design of the suction roll 31' and its external
suction box 36, reference is made to the same applicant's
Canadian patent No. ik05913'56 of July 31,-1979.
It is also obvious that the invention is not confined
to the twin wire former apparatus types depicted in ~igs 1
and 2. It may be applied e.g. in connection with a conven-tion-
al Fourdrinier wire machine. In the a~ea between nips Nl and
.. ~ . . ~
N2 a steam supply may be provided in order to enhance the
dewatèring action, so as to achieve sufficient dryness of the
web in and after the nip N2. At this point, reference is made
to the same applicant's Canadian patent ~o. 1,076,861.
As regards the felt reconditioning apparatus, many alternatives
' and combinations are passible by which the desired result is
attained.
Theinvention is in no way confined to the designs
disclosed in the foregoing and which have been described in
detail above and illustrated in the drawings: instead, the
details in the carrying out of the invention may vary within
-16-
the scope of the inventive idea defined by the set of claims
following below.
-17-
