Note: Descriptions are shown in the official language in which they were submitted.
~ :~ 8~2~
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This i~vention relates to the manufacture of
manhole eover frame~.
In thi~ ~3pecification, the term "mamhole cover"
i~ to be understood a~ embracing covers :f`or inspection
i 5 and acce~s openingq, ducts, ser~ice trenche~ and the llke
whether formed as a solid top or a~ a grating and whether
or not si~ed to permit the:passage of ~ person through
the opening spanned by:the co~erO
: The mo9t commonly produced type of ~rame i~
cast in one piece o~ cast iron or cast steel and
separately from the ca~t iron or cast ste~l coYer~ ~ith
which it i~ to be used. Such`frames and cover3 are not
generally gi~ren machined sur:faces, and the manufacturing
proceq~ is such that the cover doe.~ not fit sufficiently
clo~ely a~ain~t the frame with the r~ult that a ga~ and
uid ti~ht s~al i~ not obtained betwe~n them witho~t
the introduction of a sep~rate 1eforrnable gasket or
eal .
Frame~ are also known ~hich are a~se~bl.ed from
; 20 com~onent~ made of cast iron or steel and are generally
constitllted by ~our perimeter barsc namely (and the~e
are term~ of the art) a front ~nd bar, a back end bar,
A left hand sidff bar and a right hand ~ide bar, which
are bolted, fixed or welded tog~ther at the corn~r~ of
the frame so a~ together to forrn a rigid structural unit.
' ~
~ 3 ~35
If one ~i~he~ to eJI.~ure that the joint3 between the four
p~rimeter bar~ a~e ga~ tight, the faces which abut when
th~ bar~ are bolted together are each rec~3~ed and the
mating such rece~ses are filled with a molten ~aterial,
preferably molten lead. Each perimeter bar i~ of
generally L cros~-section~ and the bars are arranged ~o
that the frame e~sentially is con~tituted by a generally
L perim~t~r ~ection which provide~ a well into which a
removable ca~t iron cover may be sunk to ~eat on the
ba.~e of the L cro~s-~ection ~ell and ~eal both on that
ba~q0 and again~t the up~tandin~ side ~ace~ of the w~ll.
To prnmote ~uch a ga~ and liquid tight ~eal, the face~
of each p~rimete~ bar which contact the coYer are
machined a9 by milling, and the corresponding faces of
the cov~r are al~o machined a.~ by grinding~ Frame~q are
matched to covers to en~ure that the re~pecti~e machined
qurface~ fit cloqely a~sain~t one another to make the
requir~d ga~ and li~uid tight seal and Yo that the
cover and frame make ~ub~tantially one ~olid Imit with
the cover being stable ~ithin the frame and not rocking
therein when ~tlbjected to a moving loading as in the
ca~e of fa~t traffic passing thereover.
In accordance with the present invention, a
m~thod of manufacturin~ a manhole oover ~rame comprise~
forming a mould ca~ity having a confi~uration desired
of the frame, u~in~ a manhole cover to define part of
the mould CA~ity, and introducing a hardenable material
when in a flo~able condition into the mould ca~ity ~o
that it wlll constitute the frame when solidified and
30 have a contour conforming to tho~e regions of the man-
hole cover ~hich define said part of th0 mould cavity.
The invention al~o includes a manhole cover
frame manu~Actured in aceordance with the method in
accor~ance ~ith the invention.
The inv~ntion further includes an apparatu~
3 5
for use in manufactllring a manhole co~er frame compri3ingmean~ definin~ a mould cavity ancl formed in part by a
manhole cover ~uch that tho~e region~ of the cover whi¢h
seat in l~.qe again~t the frame con~titute moul~ surface~
of the moul~ ca~ity.
Practi~e of the method in accordance with the
inv~ntion of manuf~¢t~1ring a manhole cover frame reduce3
the nu~ber of oper~tional ~tep~ necass~ry in it~ pro-
duction and results in a fra~e of 3impler ~tructure a~
compared with the aforesaid machined multi-bar con-
~tructio~. PreferablyO the surface~ of a cover which
are to seat again~t a frame in u~e ars machined as by
grinding before the cover i8 u~ed i~ the moulding proce~s,
and when ~uch a co~er is paired to the frame moulded
again~t it we have found, ~urpri~ingly, under te~t, that
the cover and the frame with the latter moulded of
reinforced concrete stand up to a much greater loading
befor~ de~truction than either of the a~ore3aid con-
~entionally ~ado manhole cover and frame a~Yemblie~.
ZO The rea~on for thi~ i~ belie~ed to be the much clo~er
fit obtained between the oover and the frame a9 a
reqult of the mouldin~ technique adopted, and the effect
of the increa~e~ ~trength thus obtained ~hould enable a
thinner cro~-8ection to be u~ed than hitherto ~ith a
con9equent ~aving in co~t ~nd reduction in operating
weight. The frames as manufactured in accordance with
the inven-tion can be prod~lced with relatively un~killed
labour a~ compared wit~ that reqllired to proAl~ce the
0ill0d, multi-bar oon~trllction of frame. Moreover~ ~uch
frame~ ~ay be produced in a fsctory or actllally o~ 8ite
u~ing simple "throw-away" moulding ~igA.
In order that the invention may be well
under~tood there will now be de~cribed one embodiment
thereof, given by way of e~ample, reference being had to
the accompanying drawing, in which:
2~3 5
Figure 1 is a sectioned elevation of a Jig
ill~trating the use thereof in the manufacture of a
frame; and
Figure 2 i~ a plan ~iew, partly broken a~ay,
of the sa~e ~ig when in u~e.
Briefly~ in thi~ embodiment of the invention
a frame i~ moulded in one piece of a hardenable or
~etable material. The setable material i~ poured into
a jig and i~ actually moulded again~t tho~e ~urfaces of
a fini~hed co~er ~ith which it i~ to intsrfit in u~e.
Tharefor~ the frame is matched automatically to th*
cover ~hen being made.
More particularly9 a jig 1 include~ a ba~e 2
which is rectangular in plan and which has up~tanding
marginal ~tepped 3ection~ 3 around it~ periphery which
provide a ledge 4 and, inwardly thereof, a generally
; vertical locating surface 5 ~hich is .qlightly inclined
in a direction a~ay ~rom the ledge.
Th~ marginal stepped section~ 3 a~ formed
above are de~i~ned to accept and :Locate a ca~t iron
cover C which ha~ been machined at it~ ~urface~ which
will seat against the frame in us~. In this instance,
the inverted cover C i~ of the open top type formed by
: a honeycomb rib ~tructure r up~ta~ding from a bottom
25 plate ~ with lt~3 perimet~r bend defined by side and end
fla~ge~ ~ also integral with the bottom plate. Accord-
ingly, it i3 the external ~urfac~s 3 and ~1 of the
flanges f and the marginal region of the bottom plate
p, re~pectively, which are machined. It is to be
understood that the frame cou}d be moulded to other
configlJratio~s of cover C ~ith the jig base 2 being
~uitably conflgurad to locate po~itively the co~er in
po~ition.
Suitably afflxed, a~ for example by hinging
3S at 6 to the bottom edge~ of the base 2, are four 3ide
~ 3 ~g~S
~hutters 7 ~ith mitred ends. ~hen hinged fully upwardly
a~ shown the shutters form a continuous frame around
the ba~e and slope outwardly away from the ba~e at an
angle determin~d by the correspon~ingly inclined side~
8 of the ba~e. Any sllitable mean~ may be ~rovided for
hDlding the ~hutters in that moulding attitude, such as
a ~uick release mechanisrn taking the form of spring
clip~ (not ~hown). On the inner side, each qhutter 7
is provided with an inwardly extending protub~rance 9.
Additi~nally, each shutter 7 has its protuberance 9
provided with transver~e rece~qe~ 10 ~see Fi~ure 2).
The jig 1 i9 completed by a top shutter 11
which locat~s on vertical pins 12 carried by the base
2 to ~eat on the plate p of the cover C and which i~
held again~t t~e cover by any ~uitable means such as
taper wedge~ l3 a~ shown. A packing 14, ~hich may be
of neoprene, is provi~ed bet~een the top shutter 11
an~ the cover plate ~ to take up any irregularities
there ~ight be in the plate ~lrface. The packin3 14
wollld be bonded to the top ~hntter 11.
When the ~ is 30 completed, there i~
provided a continuous cavity 15 defined between the top
~h~ttsr 11 an~ the four ~ide ~hutter~ 7 do-~n to -the
le~ge 4 of the ~ig ba~e 2 and adjacent the machined
snrfaces ~ an~ sl of the flange f and the margin of the
p~ats ~ ~f the cover C. A ~etable material m i~
intro~ ced into that cavity 15 to fill it, and when that
material i9 sufficiently ~olidified, the top ~hutter
11 is removed and the side shutter~ 7 hinged downwardly,
therehy to permit the frame F moulded from the setable
material m in the cavity to be removed to~ether ~ith the
_
cover C. Since the frame F ha~ been moulded to the
Yurfaces of the cover C ~hich are to qeat against it,
a perfect match is made and no fllrther finishing
operation~ ~re neces~ary.
3 5
-~ will be seen, the moulded one-piece frame
~ com~rises four perimeter bars b each of which has a
U-section base s ~ormed by the correspondin~ protuberance
9 which mould~ a rece3~ into the bar and ~ro~ which is
upstanding a mar~gi.nal flange 1. Trans~erse stren~then-
ing ribs (not shol~) ~ould be moulded into each frame
bar b ~y the rece~s~s 10 in the ~hutter protuberances 9.
In use, the fram~ F wollld, of course, be inverted from
the orientation shown, and the base g would be suitably
permanently secllred around the mouth of a pit opening
in a floor or the like~ The matching cover C would be
laid into t~e frame F so that it~ machined surface~ g
and sl seated ~g~inst the correspon~ingly moulded
sllrfaces of the frame base s and flange 1 to mak~ a
closely mated interface th~rewith to pre~ent the ingress
of extraneous matter therebetween.
The ~etable material would conveniently be
concrete pre~erably reinforced as by glass fibre, steel
fibre or epoxy resin. Instead of the reinforcement being
incorporated in the liqu.id concrete, reinforcement such
as a steel grid could be laid in the cavity to reinforce
the concrete in situ.
The top and hinscd shutters and jig base could
conveniently be of woo~ or any ot~er material, for
example melamine, suitable for forming a mould wall with
respect to concrete. To a.ssi~t r¢moYal of the ~hutters
from the ~oulded frame and to ensure that the moulded
external surface of the frame has a clean9 unbroken
profiLe 9 any sui.tahle parting agent may be ap~lied to
th~ moulding ~ur~aces.
~ rames may be moulded one at a time or in
mnltiplea usin$ a number of ji~s positioned adjaccnt one
another. It is contemplated that a single jig could b~
~ub-divided to mould a mlmber of frames simultaneou31y
or to mould a multi-~pan frame ~eating a plurality of
cover~, sach of which woul-3 be uqed in the moulding
proces~. Whilst the ~ide shutters are shown hing~d
to the jig base, other mean~ cf ~ecural may be equally
appropriate. It i~ to be empha.sised that the illustrated
frame having a U-~ection ba~e i~ but one configuration
amongst many which may be moulded u3:Lng th~ technique
describ~d~ That technique enab1es a frame to be made
from but a single operatibn, nam~ly b~ ~oulding, and
matched during the moulcling proces~ with the cover tD
be u~ed with the frameO Although ~uch opti~m matching
is preferred to ensure a clo~ely ~ated interface, a
set of cover~ may be maintained for mouldin~g purpo~e~,
and framcs ~oulded from tho~e cover~ matched 3ub-
sequently to other cover~.
Whil~t reinforced concrete i~ preferred a~
the mouldi~g material, other mAterials which can be cast
or moulded ~uch as metal alloy~ or ~ynthetic plastic~
may be utilized, and the proce~ and moulding apparatu~
ada~ted a~ may be nece~sary.
The moulding proce~s may be performed away
from site in a factory or frame~ could actually be
moulded in position on ~ite by ms2~ns, if wished, of
"throw-away7' .simple shutter jig~.
Provi~ion may be made within the reinforced
25 concrete frame for metal or plastic in~ert~ designed
to r~cei~e fastenerc that will ~ecurely locate the
manhole cover to the frame.
Frame~ ~oulded in reinforced concr~te h~ve
been put under te~t. Unexpectedly, the resulting
matched cover and frame ~howed a much greater reqistance
to loa~ing than a multi-bar constrllction of frame. It
is thought that this i3 becaus~ of the closer fit
between the cover and the frame which can be achieved
with the de~cribed ~oulding technique which enables gaps
between tho~e components of no ~ore than 1~ thou to be
1 ~ &~ 5
obtained wherea~ with the convention~l machined multi-
bar fram~ and cast iron co~er the manufacturing
tolerance~q are of the order of 10 thou. As a r03ult,
whereas ~ith the latter construc~-ion a co~er failed
under a loading of around 30 tons, w~th the cover and
frame of the present embodimsnt, the cover and fra~e
still held good at 60 ton~. The inference is that
th~nner cro~s-~ections of coYer and frame can be
utili~ed than hitherto wlth att0ndant cost sa~ings
addin$ to those obtain.ed by the ~impler manufacturing
techniqua to~ether ~ith reductions in the operating
weight of the oover.
We have also found that it iq not nece~ary
to machins those ~urface~ of the cover ~hich are to
~eat against the frame ~i~ce the moulding techniqus
en3ures that a frame will make an excellent ma*ching
fit with an un~achined cover used to mould it~ givin~
~ub3tantially the same seal and s*rength as ~hen the
co~er haY machi~ed Yurface~.
To ensure ease of ~liding removal of an un-
~achined cover from its moulded frame, the unmachined
mating surfaces of the cover are preferably coated ~ith
a low friction material Yuch a3 a polyurethane varnish
or a silicone or te~lon coating.
An alternative moulding jig could co~pr~e
a flexible ~heet as, for example, of thin PVC or a
~ilicone or polyurethane rubber ~h1ch i9 pre~ed into
~hape YO a~ to have a base and integral up~tandin~ Yide
walls~ the latter being backed externally by a rigld
former~ After moulding, with the rigid former removed,
the ~heet would be peeled a~ay from the moulded frame.
Such a flexible Yheet mould would not need to be coated
with a parting agent and would constitute an ine~penYive
"throw-away" jig suitable for u~e on Yite or in a
factory. The base wall of the peelable jig, like that
~ ~ ~g~35
of the hinged ~ide jig, would be ~tood orl a suitable
moulding table ~hich would be vibrated by co~venltional
means to ensure even filling of th~ mould caLvi ty. It
i9 ~nYi~Saged that a top shutter would ~3till be used
5 with the peulable ji,g.
