Note: Descriptions are shown in the official language in which they were submitted.
~J ~ 3
6~
-1- llT~04609
CURRENT-LIMITING FUSE WIT~ I~R0~713D
Thi~ in~ention relates ~o an electric fuse oiE
the current-limiting type andO moxe particulArly,
ts~ a fllSe of thi~ type which can interrllpt a wide
rar~ge o:f abnormal currents but is especi~lly adapted
5 to interxupt relatively low overcurr2n~s..
It is well recognized that a type oiE ~no~mal
current that is diificult for a s~urxent~limitirlg
fusP to interrupt is a relatively low overcurr r~t
thalt persists for a long period of time be:~o:r33
10 mel~ing the fusible element or elemen~s of ~he
f use O For example, in a typical curr rlt ~limitting
use, an overload current of 1,, 5 to 3 ~imes ithe
s t:eady~state ral:ing o the fuse may p~rsist :Eor an
hour ox even more before it melts the fll~iible
3.5 elem~n s of the fuse.
To assist in extirlguishing the arc or ar6::s
fo~med lapon ~uch melting, i has be~n common to
provide, in each regio~ where an arc is .~llticipa~ed
structure of gas-evolving material whic:h evolves
2(3 ~n arc-~xtinguishing ga~ when ~xposed tc3 the arc.
Example~ of such fuses ~re di~;clos~d in U~, S .
Pa~ents 3,76~509-Cameron, 37238,333~ozacka~
09
--2--
4,167,723-Wilk~ 3,4~7,971~Mikulecky~ and
3; 562 ,162~Pitha.
1~ s'cudying typlcal sEu~es of ~i~; general
type ~ we have o~ served ~hat during a prolollged
5 period ~:~ low s: vercurrent æ uc~h as xeferred to
above ~d prif:~r to arc init.iation, the gas
etrolvi~ag struc:ture evolves ~substan~ial amo~ts
0:~ ga5i~5 iA response to heating of the fllse
lements~ Such ga.~ evolutioll i5 undesirable for
10 at leas t the following reason~:
1. Ths~ total available amount of easily-
evolvad gas is limited, and any anLourlt lc1st befor~
a:~c-initiation is not a~ailable for arc-extinction.
Insufficient gas flow at the time of arc~initiatio
ï5 could in~rfere with arc-extinction.
2. ~:as evolved be~ore araing may caus~ ex
s~essive pressure to dev~lop in th~ fuse.
3O The gas release proc~ss is endothe~:mic so
~hat the desired temperatur@ rise of the fusible
20 elemerlt or elements can be retarded by such gas
evolution. This may distort the ~ime-to-melt v.
current curve of the fuse by lncreasing ~he me~Lting
time alt low ovPrcurr~3nts.
~ecordingly, an obj~ct of our inventiorl is to
pxovide, :Eor a current limiting ~use ~ gas~evolving
stxucture which: ~1) is capable of evol~riny he
requires~ quantities c~f ga~es for readily extinguish-
ing the arc:s produced by fus~-element m~lting after
prolonged period~ of low overcurrent~ and ~2) evolves
le o.r no signific:ant $~uantities of gas prior to
arc~initiakion under such low overcurren~ co~diti~ns.
6~
llT~04609
~3~-
~o~her ob; ect i~ to provid~ yas~evolvirlg
s tructure capable of performing as i~ ~e i~s~edi-
. a~ely precedialg paragraph ~Eclr prt)tracted ~svercurr~rlts
o~ approxilllate~y one hour in durationO
~other objs~c~ i ~o provide gas~d~volving
strllcture capable of p~rfo~ing as ~3tate~d in the
. first object and alss~ having good electrical ~ SII-
lating properties which are maintairl~3d d~spite pro-
longed healtins and despite the arcing which ac::com~
panies illterruption.
Ill carryirlg out our invention in one fo:cm J W!e
pro~,ride a high-voltage current-limitirly :Eu~e compris-
ing a ~usible element and mealls at a predetermined
location on the fusible element- for causillg the
element to melt at said predetermilled location i~
response to prolonged overcurrents of relatively
low value, thereby initiating an arc: at said locatim
; when s~id prolong~d overcurrents have pers.i~ed for
a predetermined duratioll. For in~reasing the arc
voltage developed by the axc, there i~ provîded gas-
evolving means comprising an electric~l insulatillg
membex dispc~sed about the f-l~ible e~ ~men~ i~ the
region of said location and at a point ~u~ficierlltly
close to said locatiorl that at lea~t a p~:rtie3n of
the arc burns wit~in said irlsulat:ing me~3ex and
causes vapor~ to be evolved from ~e material of
the inslllating memberO The insulatirlg member i~ of
a mate:rial t~at ~volves substantially no vapors ox
gas al: the tlemperatures rE3aGhed by ~a~d in~ulating
member pri~r to arc-initiation durirlg proIongesl
ov rcurrents of up to s:~ne houx in duration.
. In on,e fDrlll s~ the inverltiorl ~ the ~ sulatilag
member is of a baked material, a major por1:ion ~sf
which is hydrated aluminum silicate iLncludi~g water
.. ~
o
,j l
. ~ llTRO4609
- -4
of hydratisrl that is released only at ~nperatures
. in excess o f those attained by said insulating
member during prolonged ovex~urren . ~ a5 lorlg a~s
one ho~ar~ The material i.~; balced for sevexal hour~
5 at emperatures up to at lea~t the value reachl3d
by the irlsulatirlg member duri~g prolonged over
s~larrents as long as one hour~
I
i Bri f Desc~on of Drawi ~
For a better understarldi~çl of lthe inventioI,
r~fer~nce may be had to the fo11Owing description
. tak~n in connection with the drawings J wherein:
Fig~ 1 is a sectional view through a high
vo1tage ~urrent-1imiting fuse embodying one form
of our invention.
Fig. 2 is ~n enlarged perspective ~iew in
simp1ified form of the certain compone~ts contain~d
in the fu~e of Fig. 1.
Fig. 3 is a schematic ~howing of a pai.r of
fus1b1e elements with gas-evo1vi~g beads located
thereon in accordance with one foxm of our inventionO
Detai1ed Descrip ion of
~8~
~ eferxing now to Fig. 1, thare is shown a high-
vo1tage current-1imiting fuse comprising a tubu1ar
casing 2 of e1ectrica1 insu1ating material elosed
at it~ opposite ends by meta1 end cap~ 3 and 4.
Within the casing 2 is an insu1ating coxe 5 on whach
ar spira1:Ly wound two fusible e1ements 6 ~nd 6a of
ribbon fon~ extending a1Ong the leng~h of th2 core.
Axranged at opposite end~ o~ core 5 in e1ectrica1
contact with the ends of fusible e1~ments 6 a~d 6a
ar~ c3nductiv~ t~xmina1 c1amp members 7 and 8 which
llTR~4609
5_
electrically connect fusible elenents 6 and 6a to
the corlductive end caps 3 anld 4, respectively~ by
means of ou~wardly xtending finser~ 11. Filling
~she Gasirlg 2 i~ a pulverulent filler 12 ~ l?referably
5 of quar~z sand~ in whi~h ~he core 5 and ~he fusible
elements 6 and ~a are embedded. The depicted coxe,
fi.ller 9 and casing stru~tur~ are similar ~o those
disclos d in U.S. Pa~ent 3/5627162~Pi~ha issued
February 9, 1971 and assi~ned -to the as-si~nee
of the present invention.
The illustrated fuse is a circuit pxotecti~e
device which acts in a known manner to interrupt
~he curxent therethrough in the event the current
should rise to an abnormally high value. If ~he
~bnoxmal current is a fault current, it w.ill rapidly
rise t~ward a value tens of times higher -~han normal
steady-state current, quickly melting portions of the
fusihle el~ments ~ and 6a and produci~g arcs which
vaporize the mol en metal and additional metal of
~0 the fusible element~ 6 and 6a. The hot metal vapors
resulting from such vapori~ation rapidly ~xpa~d into
~he spaces between the granules of filler material
12~ where they condense and are ~o longex available
for ~urrent conduction. This condensing and ~ooling
25 action builds up in the cllrrent pa~h a high arc
~ol age which limits the current ~hrough *he fuse
to a small raction of that available in the circuit
and also forces the curxent to ~ero bef~re the next
natural current zero. Under fault current conditions,
aroing i5 initiated at region~ o~ reduced cross-
sectio~ i~ the fusible elements 6 and 6a fo~ned by
perforatîons 13 in the fusible elements~
If the abnormal current is an overcurrentO rather
than a fault: current~ the fusible el~ments do not melk
11~6~
609
~ -
~mmediately but melt only ai.ter the overcurEent
has persisted for a predetel~mined period D the
dlJratis~n of whic:h is inver~ely relat~d tcl the
curlrent magnitu~le. ~or lo~- ïevel o~rercurre~t:s ~
5 ~uch as 1. 5 ta 3 time~ steacly-~tate c:urrent~ the
:f usibli3 elemerlts may conduct for an hour or even
more bef ore melting . Ts limit this p~riod p :It i~
conventional t:3 provide each Pusi~ble s31ement with
one or mc)re overlays capable of producing the
10 so-6al~ed "~q-effe~-t~. In thi~ regard, eas~h over~
lay is of a matf~rial ~ ~uch as tin, which has ~
much lower melting p~int than the silver of the
xibbon typ~ fuse elemer~ts. When the ov~rl~
~emperature reaches the melting point o:f the
15 overlay material, the overlay material :~acts
me~allurgically with the silver to orm an alloy~
This ;~ y has a relatively high resis i:anc~ ar d a
much lower melting point tha~ the silver ~d causes
a relativaly :capid meltir~g of the fuslble elem~nt
20 03lce khe overla~ s~arts to melt. Sucll melting pro-
dlacl3s a gap in the fusibl~ element across which an
arc is initiated. Th~ arc bllrns thP fusi1ble element
back to ïengthen the gap and al80 causes gases to
be eYolved ~ in a m~nner soon to be described~ These
25 gases play ar~ important role in extinguishing th~
low current arc, a~ will soon be descri~d~
The aboveodescribed overlays ar~ ~how~ on fuse
elements ~ and 6a at 15. Each overlay :15 is po~i-
tic)ned at ~ region of the f usible elelTle~at which i~
30 of reduced cross~sectio~ as a re~lt o a~ 0ngatsd
perforatis~n 16 provided in the fusil:~le el~renl; i~
this regio~O On protracted overcurrerlts 0 ~he ~usible
element melts at the overlay g as de~cribed above " and
the resulting arc burns back the fusible elemerlt,
llTR 04609
forming the above-described gap. Each fusible
element is preferably pro~ided with a plurality of
regions of restricted cross-section which are provided
with overlays of this type where arcs are formed
in the above-described manner when the fusible
element melts in response to protracted low
level overcurrents.
For evolving gases to increase the arc
voltage and thus aid in extinguishing such arcs, each
of the fusible elements is provided with a
plurality of beads 20, respectively located adjacent
the regions ~here the above-described arcs are
established. Each of these beads is of an electrical
insulating material capable of reacting with -the
arc to generate the desired gases. A preferred
configuration of such a bead is shown and claimed
in United States Patent Number ~,339,743, Leach et al
issued July 13, 1982 and assigned to the assignee of
the present invention.
Referring to our Fi~. 2, each bead
comprises a block 20 of electrical insulating
material which has a slit 26 in it. The block 20 is
preferably assembled onto the ribbon-type fusible
element after the fusible element has been wound on the
core 5. This is done by slipping the block 20 onto
the fusible element from the side of the fusible
element, the fusible element entering the slit 26
through the open mouth of the slit at one side of the
block.
When the above-described arc burns back along
the fusible element, one of its terminals enters the
ad~acent bead 20 through the slit 25. As this occurs,
the arc ~uickly heats to a h~gh temperature the region
; ~ 60~
of ~h~ bead that is i~ proximity to tlle arc ~ calasing
the bead rapidly to evolve the d~!8irl~t9 ~c:~to~tiaguish-
ing gas~s, or vapors~ ~hese gases a~d ~e constrict-
ing actioll of the walls of l~he sli~ 26 ac~ i:o effect-
5 ively extlnguish the arc.
During the protr~cted perioà when ~e ~usible
elemPnt~ 6 and 6a ar~3 carrying low l~vel oveEc::urreAts,
the temperatur~ of the fusible element~ in the r2gions
of the beads can rise to relatively high 1~l3vel~ rh~
extent of t:his ternperature rise is 1 ed by the
presence of the "M-effect" overlays and d~pend$ upon
the material of these overlays. ~ith an overlay o~
tin, we estimate that the fusible element in the
region of a bead 20 rises to about 35DC before
m~lting of the fusible element at the ovexlay occ~s.
As pointed out in the i.ntroductory port:io~ of
this ~pecification, temperatures i~ thi~ ranse
maintained for substantial durations are capable
of causing typically used gas-evolving ma~erial~ to
~volve substantial quantities of gases. ~his is
undesirable for at least ~h8 thr~e re~ons set ~orth
in th~ introductory portion t and e~pecially becau~e
it can materlally reduce the quantity o ga~e~ that
are available for arc-extinction when the arc i~
25 i~itiated~
An ob~ec~ of our invention i~ to limit to
insigniflca~t qua~tities the volume o~ ga~ evolved
prior to arc-initiation by protracted low level~ of
overcurrent requiring up to approximately one hour
for fuse me.Ltins. In one e~bodiment of our invention,
we are ~ble .~ achi~ve this object by fonming our
~eads 20 fr~m a completely inorganic material that
~11 is primarily o hydrated aluminum ~ilicate in the
~L8~i~16 ~3
so~
~g
:Eorm of kaolirl clay and (2) i~ cured by 1ba:ki:n~T it
(a~ for a substantial periodl 21t a ternperature
lev 1 ~xceeding the teloperatur~s that it w.ill ~be
2XpC)Sed to prior . o ~:c initiation durillg ~uch
S protracted overcurrents, bult. tb) at a tem;peratur~
lev~l sufficien~ly low for the kaolin clay ~o r~tain
most of its water of hydratiorl. In one ~nhodiment,
where protracted overcurrents of a~ lc~ng as ~pproxi-
~akely on~ hour are exp~cted b~for~ arc-ini~ia~ioxl,
1 n we rely upsn a ba~sing operatio~ that corltirlues for
at least: approximately one hour at the above-d~?scribed
temp~rat;are level. In addition, the temperature
during the ~aking operation is raised to ~his level
progressively over the course of seve.ral hours.
In on~ specific embodiment of ~he inven~ion,
we form ~he bead 20 by starting wi~h a d~y powder
comprising the following components by weight p~rcent
~loxida kaolin clay ~12Si207 2 ~2)~ 66.7
Mill~d Zircon (Zr2SiO4) ~ 22.3
Boxon Phosphate (BPO4~ 11.0
These components are thoroughly blended in a
mixer to form the powder. T~ ~his powdex i$ added
a liquid binder in a ratio of 4 parts by weight
liquid binder to 15 parts by weight p~wdarD The
li~uid binder is made from the following components
by weight percent:
A 50~ solution of monoaluminum phosphate ~A1~2PO4)3)---40%
Watex ~ $0%
The liquid binder and the dry powder are ~horoughly
mixed usi~g a morta~ and pestle. The mixed material is
then screened through a 12 mesh screen.
llT~Q4609
The resul~ rag material i~ then a~olded in steel
dies Df a sui~able shape to :~orm ~e bloc:ks 20,
Glycerine is pr~ferably used a a mold xF~leaseD
The mcalding pxe~suxe is about 6~01D psio
The molded bl~clcs are then removed from he
dies and ~ub jec~ed to the fs:llowing cure~e ~cleO
; a. Air dry at ~m ambient :for 1 hour
bo Raise t~nperature to 60~C a~ 40~C per hour~
c. Hold a-t 60C for 1 hour"
d. Raise temperature to 360~C a~ 90~C pPr hourD
e~ ~lold at 360$:: for 1 hour~,
f~ Cool to room temperature iLn î 1/2 t:o 2 hours.
The resulting compo~ition is a pximarily lcaolin
clay material that is converlted by the b~k.ing operating
15 into a hard, rigid solid! but, significani;ly, a ~olid
which i~ st.ill not vitrified.
Despite the lbalcirlg operatio~ ~ the kaol:Ln ~lay
~omponent oiE i:his material has retained over 90 percent
by weight of its water of hydratiorl. I t is ollly wh~n
~0 $emperatures in the ran~e of 4SS - 600C are reached
~hat a :Large portion of thi~ wat~r of ~dration of the
kaolin clay is released, more ~pecifically abc)llt 77%.
A9 pe~in~e~l out above, we texminat~ the balcirlg operation
when the temperature is well below this range and there--
25 fQre do not r~lease lthi~ major portion of t~e water o:Ehydra~io~ The ~aked material cDntains a very low
pe.rcenta~g~ of ~he liquid bi~der th~lt was u~;~d in[ com-
polmding it ~ince thi~ liquid, ~rhich is pr:imar:Lly wa er~
haL~ been 3mostly ~vaporated by the baking operation,
30 ~OyO ~ the se~ral houx~ in progressivel~ buildi2lg up
to 360Ge ancl i::he one hour at 360C. Although sc~me of
thi~ water O b~fvre the bakin~ operaltion ~ apE~ea:rs as
water of hydration ~Eor the boron phosphate ~ almost all
of this wa~!r of hydration is released by the l:~ak:Lng
lïT~4609
op@ratiorl~ More specifically ~ ~out 90P~ oP bsron
phosphate I s water of hydlration is released at temp
~rakures below 260~C.
~he xircon additive is an es~ntially inert
5 filler and does not chemically combirle with the water
that i~ ~ased for hondi~g; and thus there :Ls no signif-
icallt water vapc)r evolved ~Erom the zircon duri3lg the
period when the fusible el~merlt is beirlg heated by
overcurrerlts O
lD The monoalumimam phosphate ~hat is u5ed in ithe
binder acts as a ceramic cement ~or holding the
kaolin clay together and gives it increased mechan~cal
s~ab.ili~yO Most of the water contained in the mono-
alum.inlIm phosphate is raleased by ~he bak.ing operation
lS and is thus not present to create wat~r Yapor during
the overcurrent heating period.
~ uses using beads of the above describ2d material
h~e shown exceptional ability to interrupt low valu~s
of ovexsurrent. Extensive tests have shown that,
despite the persistence of low overcurren for one
hour or even lon~er before an axc is ini~iaked, ~u~f i-
cient quantities of water vapor are retained by the
bead material until it is exposed to ~he c~rc to en~ble
the fuse to ~ffectively achie~e such interruptio~.
~5 The presence of the boron phosphate component appear~
to aid in ~uch i.nterruption ~i~ce its dec~mposition
products have a high electron af~inity~ thereby eon-
~ributing to ~n increas~d rate of dielectric recove~y
a~ter a curr~nt zero. Alth~ugh our inv2ntion in it8
preexr~d form use~ boro~ pho~phate a~ a ccmponent of
~.he bead mal~erial, the invention in its b~oade.r aspects
con~emplates using for the ~ead a material primarily
o~ ~aolin clay compounded substa~tially as above de~-
cribed but without the ~oro}l phosphate.
~ 6û9
f' -12-
: It has heretofore be~n proposed to make the
. core portioal c>f th~ fuse c~f a material which evolves
arc-extin~uishing gase~ when ~ os~d to an are: 80 as
to ~ssis t i~ low overcurrent int:srruption~ ,. A cora
mad of our gas-~volvi~g material ~, if o ~e rather
intric:ate cros~-sectional ciDnfiguratie:~n s~own~ ha~
a tende~ y ~o develop cracks during the baking oper~
atiorl or during its assembly or u~e in ~e fusa~ D an~
such crarks constitute di~les::tricall3! w~ah; rQ~ions
10 that can detract from tl e insulating properties of
the c:ore. We are able to utilize our gas~evolvirlg
mat:erial without encounterirlg dielectric probl~ms
associated with such cracks by employing such material,
not in the core, but rather in beads (20~ that are
: 15 relatively small arld o~ low mass compared to the core.
Because of their size and low mass the i:)eads c:an
readily be formed and balced as above descril;ed
without developillg any detrimental c:raoks~
3~ecaus~ we do ns:~t rely upon the core ~5~ for
20 ~as evolutiorl~ it can be made Ol' an inexperlsive, low-
mass s::onstrUC~iQn. For example, it c:an be made of
twc~ plat~s oiE mica ~ disposed at right angles to each
other. Ea h of the~e plal:es i~ provided with a
. entrally located slot ~not ~hown~ extending along
25 ha:Lf i~s length and permittixlg the plates to b mated
ts:)gether at ri~ht angles to each s:~therO The det2~
of l;his ~use coxe form no part s:~f the pre~ent invesltion
and are therefore not ~pecifically illustxated or
described.
In one embodiment, the fuse o~E this application
is ~o const:xucted that the beads on a given ~usible
eïement not only assist in l2xt:inguishis~g the ars:s
initi~ted along lthat particular fusible elemellt during
low overcurxent intexruptions I ~ut al50 assis t în
~ .
llTR04609
~: ~13-
extinguishins the arcs init.iated alollg ~ ~ad~ acent
: el~Qent during such interruptic)n. More speci:~c:ally d
re:Eerri~ o the ~;chematic ~showing oP ~ 3, ~th;E~
beads 20 on ~he first fusib:Le element 6 ~:re loc~ated
5 ~ot only adjac:ent its OWll a'Lloy-forming overlay~ 15
but ~lso adjace3lt the alloy~ forr~in5~ ov~rïay~ on the
ad; acenlt fu~ible element 6a, As a r~sult ~ when ar
a~rc i~ :Lrlitiat~d at the overlay on the adjac:ent
element 6a in response to melting under low over;
10 current c:onditions, an external surface of ~e b ad
2û on element 6 is located i~ proximi~ to this arc,
and the arc is able to react with the mat:2ri2l1 of
the external surf ace to evolve the des.ired aro~
extinguishing gases ts~ aid i.n arc ext~nctiorl.
The material o: bead 2a, beirlg c~npletely
inorganic, is not susceptible to tracki~g a~; a
re~ult of arcing or other forms of electrical dis-
charge. As a result, i~s surfaces ma:intain their
diel~c~ric strength and do not ~orm dielectrically
~0 wealc paths between the usible elements or acxos~
~y gaps forrned in the fusible ~lemer~ts ~s a xesult
of :u~ operation.
As poi:nted out above ~, the monoalumirlum phosphate
bindex and the zircon ~Eiller ~npart mechanical
strength and stability ~co the bead matexial, This
help~ l~e bead 20 withs~and without disinteg.rat:Lng
or breaking up the c:ombinatioll Df pre~sures and high
temperatures that it is exposed . o ~d r high current
interrupti ng Col dltis:~ns .
~l~hough, ideally ,, we bake the beads at a temper-
ature in exc:ess of that which will be reached by ~e
beads ,during any lnw overcurrent conilitions that the
:use will 'be exposed to, our invention in its ~roader
______
7~
llTP~04609
aspects cs:)ntemplates bakirlg at temperatllres at least
a~ high as that reached by t:he bead~ du.ria~g pxolonged
ovexcurrents as long as one ~hour. Th2 m~im~ b~king
~emperature i~ kep~ ~3uffic:iently low that th~ hydrated
5 aluminum silicate, or kaolirl c:lay~ will re~ain mv~t
o:~ its water of hydration de~spite the baking operatio
Although we prefer ~hat each bead 20 be slightly
spaced from the locatîon whe:re the as~ociated low
overGurrent arc will be initiated, a~ Llu~trated
in khe drawiIlgs ~ our invention in its broader aspects
con~emplates locati~g the bead around ~he arc=initiation
location so tha~ the arc is initiated within th~ bead.
In ~his arrangement, as well as khat illustratedJ ~he
alloy-forming overlay 15 limits the temperature rise
o~ ~he bead pxior to arc-initiation under low over-
eurrent conditions to a level sufficienkly low to
:Limit to insignificant quantiti~s the vol~me o gases
evolved prior to such arc-initiation.
Although we prefer to use alloy-forming means
20 such as ~hown at 15 iEor initiating ars:~ing ~u~der low
overc:urrent conditions ~ our invention ira it:5 br~ader
aspects contemplates the use of other converltiorlal
means, such as an overlay of explosive material ~ for
initiating arcing at the elongated perfc~ratis~n 16 in
25 response ~c the persistence of a low overcurxent ~or
a predetermined prolonged perivdO
While we have shown only two locations OII each
ribbon where ~rci~g i~ initia~ed in xe~p~nse ~o low
o~excuErent~, it i~ to be understood that few~r or
more ~uch lDcations ~an b~ pro~ided, as is xe~uired
for sa~isfactory interruption. A gas evolvincJ bead,
such a~ ~0 D i~ preferably provided at each ~uch
location.
~ ~8~
11~E~0~6û~
-~5
I~ is nolted that in the above descrlptioIl,
, the terms ~gase~" and ~'vaps~r~ re used inte;rcharlge-
}` ~ly is~ referrin~ to thç~ product~; eYolved fr~m the
bead mate~eial.
~ 5 While we have ~hown and de~cribed pa:rtlcular
r embc)dilllent5 of our inven~ion, it wiL31 b¢ e:bviou~ to
those skiïled in ~he art that various c~anges ~d
modificatiorls may be made without d~paxSing frsm our
inventioFI in its bro2lder aspeelts; and we ~ there~ore,
10 intend her~in to c:over all suc:h changes and mosli~Eications
as ~all within lthe t:rue spirilt and ~cope of s:jur in-
Sren1:ion ~
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