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Патент USA US3099714

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July 30, 1963
Filed April 19, 1957
3K lr-lIrF/g
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Patented July 30, 1963
6 in 'order rto ensure suthciently «long electrical creep paths.
Because the danger residing »in the formation of creep
paths can never be entirely precluded it is `often neces
sary to arrange the bolts in such a manner that they can
Hubert Naimer, Schumanngasse 35,
Vienna XVIII, Austria
Filed Apr. 19, 1957, Ser. No. 653,794
Claims priority, application Austria Apr. 23, 1956
be earthed. In many cases only the fultilling of these
requirements necessitates the electrical apparatus to be
1 Claim. (Cl. 174-138)
sons or in View of the electrical power to be handled. In
that case a certain «alleviation can be provided by sur
made larger than would be required tor mechanical rea
In the construction of electrical apparatus it is often 10 rounding the bolts with lan insulating tube but that meas
ure renders also the construction yof the device more
gether and to hold them together by tie rods. The lami
nated core of an electromagnetic device or a switch as is
In order to avoid said disadvantages it is proposed ac
diagrammatically shown in FIGS. 1 and 2 of the drawing
cording to the invention that the tension element con
may be referred to as` examples. In that drawing FIG. l
sists exclusive-ly of -a thermoplastically deformable, elec
is a side View, partly in section, ot a switch composed of
trically-insulating plastic, which is of high tensile strength
four identical units, and FIG. 2 is a top plan view of
and is moderately ilexible and tough `at normal temper
a switch unit. The problem with which the invention is
atures, and is equal to or better than polyamide-base plas
concerned may be set forth iirst with reference to the
tic in all said propenties. Superpolyamides have proved
necessary to force a plurality of structural elements to
latter iigure.
The switch apparent from FIGS. l and 2, which is
20 particularly satisfactory in that connection.
Superpolyamides have a melting point of about 200°
shown in the left-hand part of FIG. l in a sectional view
C. and a strength which is suiiìcient for the present pur
taken on line l--l of FIG. 2 and in the right-hand pant
poses in a temperature range of _20° to at least +l30°
of FIG. l in a sectional View taken on line Ia-Ia of
C. In that temperature range their tensile strength is
FIG. 2, whereas the latter is a sectional view taken on 25
50G-600 lig/sq. cm., which is less than that of iron.
line II-~II of FIG. l. The switch which is apparent trom
can easily be compensated by the fact that owing
said iigures has an operating shaft 1 provided with cams
to the excellent insulating properties of said plastics no
2, which coact with rollers 3 acting by means of forks
consideration has to be given Iany longer to creep paths.
4 on plungers `5, with which the jumper bridges 6 are
Thus the diameter of the plastic tie bolt can be increased
connected, which can be lifted against the action of the 30
and yet the bolt can be disposed more closely to the live
«closing springs 7 from the countercontacts t5 having
parts. It must also be considered that tension members
terminals 9‘. The shaft 1 extends through the bottoms
of iron are generally overdimensioned in a high degree.
of casing parts 10, lila, ltlb, 10c and a cover 11 and may
Because such plastics are thermoplastic they can be
be rotatably supported in known manner. The shafts 12
of the rollers 3 extend through the prongs of the forks 35 made by injection moulding in multiple moulds, with head
and screw thread, so that the separate forming of the
4 and are guided in slots 13l formed in the casing part
screw thread is eliminated as well as any surface iinish
lû-liic and in the cover 11. The casing parts 1ti~1ilc
ing treatment. Owing to the elastic properties of such
and the cover 11 are held together by four tie bolts 15.
plastics, split locking rings and the like are eliminated and
Such a switch construction is known. The number of
it is easily possible to connect the nut and bolt by local
casings 10 may vary within wide limits.
40 welding with the aid of a soldering iron or the like to
The invention is concerned more particularly with a
special construction of tie rods of substantial length,
illustrated by the bolts 15, which are found wherever
several or many structural parts must lbe held together
by tie rods, the length of which is a multiple of their 45
These tie rods consist in practice generally of metal
and owing to their considerable length are not designed
permanently and perfectly secure them against undesired
opening, particularly if the nut consists also of thermo
plastic material. It is thus «apparent that the Substitution
of the usual tie rods of metal by tie rods of thermoplas
tically shaped suitable plastics ensures important advan
tages not only from manufacturing but also from the
design aspect.
`Electrically non-conductive screws have already been
as headed screws but represent bolts having screw threads
at both ends for threaded engagement with a nut with 50 proposed which consist of a metal core «and a plastic cover
ing which forms the screw thread and the screw head.
locking ring or with a double nut. S-uch a -bolt is ap~
parent from FIG. 3.
The construction and arrangement of such metal t-ie
rods in electrical devices must meet several requirements.
In the case of a composite switch of the type shown in 55
FIGS. 1 and 2 these requirements are as follows:
>For cost reasons the tie rod consists in most cases of
iron but in that case it must be given a surface protection,
In that known screws the metal core has a ribbed sur
face with which it is embedded in the plastic to ensure a
torsion-resistant and tension~resistant connection there
That prior proposal relates to a countersunk screw
rather than to a tie rod; whereas a countersunk screw
cooperates with the nut thread, as a rule, over a length
which is a multiple of the diameter of the pin, this is not
the case with tie bolts acting in the manner of a screw or
in most cases by Ielectro-cadn‘iiumplating, electro-galvaniz
ing, electro-nickelplating or the like. This is necessary 60 rivet. It was not recognized that tension-stressed struc
tural elements of the present type can be made entirely of
because the switch (or another electrical apparatus) is
thermoplastics and the use of metal cores can be entirely
often used in aggressive atmospheres or in moist rooms.
eliminated and that it is also possible to provide tension
The screw thread is either produced by machining or in
elements which combine the advantages of perfect insu
a thread rolling machine. This requires in the iirst case
tools subject to a particularly high wear and in the second 65 lation with suiiicient strength «and moderate plasticity, and
which are formed with force-transmitting surfaces .which
case also an expensive machine. Similar requirements
are subjected to shearing stress and are not larger or not
exist regarding the nuts, the screw thread of which must
substantially larger than in the case of a pure metal con
in any case be cuit. Thus the making of such bolts takes
struction. -It is also not new to use rivets of thermoplas
considerable time.
As to the arrangement of these bolts in the switch there 70 tics; this applies also to electrical apparatus. This has
is the requirement «that the bolts must be sufficiently spaced
always concerned only short rivet pins, the length of -which
from live parts, e.g. the terminals 9 or the jumper bridges
was only a small multiple of their diameter so that a good
heat soaking of the entire rivet shank and thus a good lill
ing of the rivet hole was achieved when the rivet pin was
aligned parts of an electrical apparatus, said rod having
heated in order to form thel second rivet head. Highly
stressed tie rods of large length (i.e., of a length which
entirely precludes a continuous engagement of the rod
of a thermoplastic resin at least equivalent to polyamide
periphery with the hole periphery and which is practically
unlimited) and which consist of plastics are an entirely
new structural element in electrical apparatus.
As is shown in FIG. 4 the present tie rod 20 may sub
stantially take the form of a headed screw of metal.
Contrary to metal tie rods the head 21 may now be pro
vided because its formation in an injection mould involves
no diñìculties and the mould may easily be adapted to the
manufacture of ties of dilîerent length by means of inter
mediate mould sections.
The screw thread 22 is also pro
duced in the mould and is used 'without any subsequent
machining. The (exaggeratedly shown) burr 23, which
is due to the mould is not removed, for reasons which Will
be described hereinafter.
Another advantage of the plastic tie rods according to
the invention consists in that when constructed as
threaded bolts they can easily be made self-locking. 'lf
the spontaneously formed burr 23, which is due to the
split injection mould, is left on the bolt 20, as is apparent
from FIG. 4, the burr will be deformed by the nut 24
when the latter is subsequently applied to the bolt. This
has proved an excellent lock for the nut even if the same
does not consist of plastics (the invention being not re
stricted to the use of plastic nuts). r'That burr need not
be thicker than the one which is formed where good 30
moulds are used.
-It is obvious that such -a burr may also
be provided in the nut itself.
I claim:
A tension-stressed tie rod interconnecting a plurality of
a length which is a multiple of its diameter and consisting
plastics in thermoplastic deformability, tensile strength,
electrical insulating power, ilexibility and toughness at
normal temperatures), said rod being injection molded in
a mold having two mold parts with meeting faces and
having at least one threaded end portion, and further com
prising an axially extending ridge-like burr formed as an
integral portion of said threaded end portion at the meet
ing faces of the mold and extending radially beyond the
threaded crest.
References Cited in the ñle of this patent
Hahn _______________ __ May 20,
Weldon _____________ __ Aug. 30,
Warren et al __________ __ lune 11,
Martin et al ___________ __ lune 1,
Podell ______________ __ Dec. 12,
Ferguson _____________ __ May 8,
Kindelberger _________ __ Sept. 18,
Borkland ____________ __ Oct. 14,
Persak ______________ __ Tan. 13, 1953
Mugford ____________ __ Dec. 29, 1953
Mason et al. _________ __ July 17, 1956
Thompson ____________ -_ Nov. 6, 1956
Kiekhaefer __________ __ lune 16, 1959
Product Engineering (published by the lPolychemicals
Department, E. I. du Pont de Nemours and Co. Inc.)
April 1954, pages 1, 2 and 3. Copy in Division 57.
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