CA2174199C - Fire door core - Google Patents

Abstract

A core for fire doors comprises hydrated gypsum occupying about 40% to 46% of the core volume and bubbles occupying almost all the core volume which is not gypsum. The larger bubbles preferably comprise about 31% to 38% by volume of bubbles of between 1 and 4 mm and about 17% to 25% of smaller bubbles between .01 mm and .25 mm. The larger bubbles are formed using styrene spheroids.

Description

This invention relates to a core for fire doors A core for fire doors is contained in a door shaped shell, usually, of steel. The core is customarily bonded or glued to both inside surfaces of the door.
Such a shell and core must pass tests before being approved for use in both Canada and the U.S and in other jurisdictions.
A typical test might be: (1) to be subjected to a temperature lU approaching 1000° C on one side of the door and to maintain the temperature on the other side of the door to less than 250° C for at least 60 minutes. (2) Then to maintain its structural integrity as a door for a further 30 minutes.
The parameters or criteria for the door construction differ for tests (1) and (2). During test (1) the heat differential across the door, requires the core to have qualities which inhibit heat transfer which; in turn, causes differential thermal expansion of the steel, and bowing of the panels, on the high temperature side of the door, 20 which threatens the structural integrity of the door.
Because of this threat to the structural integrity of the door, it is desireable after test (1) is completed, in accord with the concepts of this invention, that the temperature differential across the door be reduced so that the core, which in test (1) was asked to reduce heat flow, is in step (2), asked to allow more heat flow, to reduce the differential expansion between hotter and cooler panels to maintain the door shape integrity. In addition, for its ordinary function as a door, the door must be as light 30 as possible, a heavy core would require correspondingly stronger mounting frame, supports, hinges etc. Currently ' the industry requires a core weighing 20-24 lbs./cu.ft.
It is thought by those skilled in the art that a core could be constructed from a gypsum slab which would pass at least test (1) above. However the weight of such a core would be excessive, requiring correspondingly heavy mounting and fitting. Moreover the heat capacity of the gypsum slab might inhibit heat transfer, and interfere with our concept of maintaining door integrity, after an initial period, by allowing heat flow.
(There are many tests, with value and parameters differing from the test set out above. Thus the test above, referred to is not intended to limit the scope of the invention and in fact doors within the scope of the invention may be designed to pass less or more rigorous tests. The test outlined merely serves as an example of a core which during a fire must resist transverse heat transfer for an initial period and transfer heat during a following period.) Other existing fire doors, of which we know, have a core formed principally of mineral fibres with a bonding agent.
Such cores, because of their powdery surfaces have poor bonding characteristics and tend to separate from the door inside surfaces to which they were glued.
They also tend to crumble and disintegrate over time, especially when the core separates from the door skins.
This invention comprises a fire door core comprising a mixture of hydrated gypsum in amounts of about 40% to 46% of the core volume, other solid components, preferably of up to about 1~, and bubbles as hereinafter described

- 2 -occupying substantially the balance of the core volume.
The upper limit for the percentage by volume of hydrated gypsum is primarily set by the risk of excess weight of the core resulting in overstrain of the mountings and fittings, and the risk of excess heat capacity in the core inhibiting heat flow therethrough when such heat flow is desired to maintain the integrity of the core.
The lower limit for the percentage by volume of hydrated gypsum is primarily set by the necessity of a sufficient endothermic value for the hydrated gypsum. The total endothermic value of removing.the combined water in gypsum is 1418 BTU per pound of water.
By "bubbles" herein, we mean spaces in the mix which are frequently spheroidal. Such spaces may be created by any desired method including: (1) inserting in the mix hollow spheres of the desired diameter. This is the preferred method where the diameter of such bubbles is 1-4mm.
Such spaces may also be created by I2) mixing a foaming agent in the mix. This is the preferred method where the diameter of such bubbles is .Olmm to .25mm. The foaming agent is mixed as lately as possible before the mixing because the bubbles in unmixed form tend to deteriorate with time. (3) Large "bubbles" as the term is used herein may be formed by including waterswollen particles, such as tapioca which, when the slab containing said particles is heated to drive off the water, lose their water content to leave a void or "bubble" only slightly less than that of the swollen tapioca. Production of large bubbles in this

-3-CA 02174199 ~ 9i ~ 0~ -f3 w,ry, is not favored because of t.hz~ i_xtra energy required to drive off the contained water, Producing the large (ie. with diameters at 1--4 mm) bubble~> has root keen succesaf-ul. using vermiculite and perlite. Both materials were screened to l.-5 mm size particles. The ,sample core materials core produced with perlite and verrn.iculi.t:e were 1»>t.h too heavy. Moreover the sample produced with vermicul:i.te was too weak, and it is believed that this was due to the "Leafy" nature of the lU expanded vermiculite. An additional problem encountered with both perl:ite and verm:~.culite was fi.heir water absorbancy.
It was necessary t.o add 20~-40(the exact amount varies with the gradation and quality ~~f perlite or vermiculite) more water than would otherwise be required. The additional water was undesireable because its presence increased the cost uf~ dt ying and, for a c~.iven production r~.~te, the capital cost «f the dryer.
Other attempts tc> produce the large air bubbles.
Larg a air bubbles were: produced us:i.ng a commercial foaming 20 agent e.g. Cedepa.l TM arid compressed a:ir-. However, when such agent with larger bubbles is added to the mix the large bukl>los are converted to bubbles of rnuck~ smaller size, e.g. .01-.25mm dia. 't:'his is bel ieve<i tc:o be due to the large shear velocities required to mix gypsum and water. It is noted that such conversion of large to small bubbles occurred even when the mix with large bubbles was added near to the end of the mixing cycle.
Best results in the prov.Lsion of large bubbles in the mix have been achieved when hollow styrene spheroids 30 are used. These are dune uniform and, in typical batches _Q_ 1 l4 ~ 99 have a median diameter of 2.5 mm anc9 about 80% of the spheroids have been found to be between 2.2 anc~ 3 room.
Tests have shown that too tzigh a percentage of small bubbles will sufi:iciently weaken the core to prevent its maintaining its shape during handt.i.ng and use. Tests have further shown that too high as t:~erc:er~ta:~ge of large bubbles will also :reduce the strength of the core and prevent its maintaining its shape during handling and use. The limits indicated for the content range of each size of bubbles indicate ou:r appraisal of where the strength of the core will deteriorate.
Only the relative volume ratio of small and large bubbles discussed below in the text, will allow a core vaeighing 20--24 lbs./cu. ft. tpreferably 223-1 lbs./cu. ft.) to retain sufficient st.renclth fcor handling a~od use, whi.l.e pit the same time retaining tt~e characteri~t:ics which allow the door containing the cure to pass the required tests.
Preferably, in the mixture, large bubbles of between 1 mm and 4 mm are present to displace about 31%-38% of the volume of the core and small bubbly>s ~;yf diameter 80% of wh.lch are between .O1 and .25 mm to displace between about 17% to 25% of the vo7.ume of the core.
Where diameters are glvern it i.s noted that such laxge or small bubblees, for a variE~ty of reasons tend to form spheres. However they will not always form exact spheres. The diameter given is that of a sphere which is equivalent in volume to the space or sphr:~raid.
Tn the preferred core of tt°~e znvezution, the volume occupied by hydrated gypsum is preferably about 43%; by large bubbles of diameter between 1-4 mm, hut 35% of the volume; and by ' s-~rk.-~ll bubbles, about 80~ of whic~~ are of diameter bet-~,reen .O1 and .25mm, about 21% of the valume. Other solids such as additives, the solid residue of bi,~bb) a f-orm:ing members, etc. ; wil_.1 be less than about 2% of the volume.
In accord with the preferred method for making a core for fire doors: dehydrated gypsum is mixed with components adapted to form small and large bubbles in the finished core and with sufCicien~ water to hydrate the gypsum and a sufficient exeess of water to produce a shapeable m a s s , where said bubbles and bubble fax~r~ing com~~onents are sufficient to provide between 54% and X0;6 of the volume displacement of the mixture sa forme:d, when the gypsum is hydrated, forming said shapeab_~E~ mas:~ into a2 least orue slab, having on some of its surfaces a wrapping layer, where said slab with said wrapping layer has the desired core dimensions;
and eliminating the excess of water.
Preferabl y said mc~~thc~ i nm l udes : initial ly mixing, in a first mixture, dehydrated gypsum with water and a large bubble forming camponent; mixing water with a small bubble ?0 forming component in a second mixture; mixing said first and second mixtures in a final mixture where the total water is sufficient to hydrate the gypsum and provide sufficient excess water in the final mixture to render the mixture into a shapeable mass with some coherency; then forming such mass into a 1_ongituc~inally extending :.trip and providing such strip with an outer layer on i.ts sides, where such strip with its outer layer has the width and thickness desired in the finished core; maintaining said strip until hydration of said gypsum has substantially taken place; then 30 cutting said strip into slabs of desired core length; and -b-L~I~I~.~~
then heating said slabs to remove uncambined 'water without substantially dehydrating said gypsum.
Figure 1 schematically demonstrates the operation of the inventive method from the m.i.x:ing of the initial c~c.:mporiE~nts until the iv or ma t: ion uf~ core-.Length slabs from a strip.
Figure 2 demonstrates an oven for removal of excess water from the strip.
In the prefr:rred method iru ac<wrd with the invention l~ and dealing with the per-cecttages as defined in the preceding discussions: dehydrat:ed gypsum, the large bubble forming ingredient and any additives are mix>d with water. In the first mixer 10 we mix 70 leas. cyf calc~iurrr sulphate i.n powdered Forrn, and the large bubble forming agent:, (preferably about 2 lbs, of styrene in the form of hollow spheres with a diameter of between 1 and 4mm) and water.
Other addit:i.ves may be ac9ded to this mix if required, For example, to improve hot strength it may become du:~ir'able to add glass frit, 5ili<=ates or similar material of low melting temperature. To improve toughness or handling characteristics it may become desireabl.e to add mineral i-ibre or other fibrous material in small quantities.
Other components, such as vermiculite, perlite, diatomaceous Earth, and the like, in small quantities, may be desireable to control expansion and further imprcavE; hot strength.
In the second mixer 1~ we mix water arid the selected small bubble foaming agent (here CedepalTM) in the amount of 4.2 lbs. which is adapted to form the .O1 to .25mm srnal.l bubbles. The amount of Cedepal. and the mixing time 30 and temperature are emo?irica:~lly determined.
_~_ ~l ~'4i 99 The first and second m.ixtuz-es are than mixed in mixer 14. The quantity of gypsum :~s selected t:o provide, with any other solids such as addi.t.i.ves or residue from other components, 40~-466 of the :i final ma..x, other solids being less than about 2%. The toi:al. quantity of water in mixers 10 and 12 :is suffic:.Lent tv form the small bubbles, to hydrate the gypsum and to provide suf-.ficient excess water to render the output of mixer 14 shapeable but having limited coherence.
Any other components for fcorm.ing the large or small bubbles may be u~~ed >o long as thk_~y do not interact with t:he gypsum.
The schematic:al_ly shown appar~~tus for performing the method includes the travelling e:onveyor 20. At the upstream end of the conveyor a roll of fibergl.as;5 matte 22 is unwound to providE: strip 23 t<:> l:ie on arid trave:k.. with conveyor 20.
~t'he width of the matte is the sum of t:hc: width of core desired plus the width of the t.wo :tide flanges 24 which side flanges 24 include the width <>f the to-be,~-formed top strips 26.
Forming means of non-stick mai.erial, not shown, but conventionally available in a number of forms, will act to shape the matte to fozm the two side flanges 2.4. Aownstream from the formation of the side flanges, the conveyor frame (not shown) will provide side walls 28 which sl.idably support the flanges 24 as the matte is fi.l.:Led with the final mixture and thereafter will support the (matte) side walls of the core.
Just downstream from the upstream end of walls 28, supply and feeding means 30, not shown i.n detail, provide the final mixture to the matte 20. 'thus, optionally, means 34, 1 ( chown in dotted outline which may be any conventional non stick means? and shown as downwaadly facing edge 35, may be u_~W to level the mix .
Downstream From thu tillirag arid levelling of the mix, the conventional forming means, not shown, forms the top flanges 26 from upper strips can t:he flanges 24 so that the remaining portion 3 7 of the fl:~nge 24 forms the outer layer side walls of the core.
After the formatzon of the top flanges a roller 40 lU supplies a strip of fibreglass matte 42 (matte 22 and matte 42 are available from Schuller International Inc. Toledo Ohio.) 'This matte 42 has the width of the final core and is designed to extend between side walls 37. 'rhe mKatte 42 is, in the vicinity of roll 40, E>rovided with glue, as schematically chown at 44, on what is to be the lower surface of the matte 42, and is laterally located to attach matte 42 U;o top flanges 26 at ~~re~asure roller 4fi.
The matte 4:a is theaefore applied and adhered to t:op flanges 28 and, at the same time the: rcaller 46 finalizes 2U t..lm levelling and shaping of the final rrrix. It is found yrufW gable irr most ca,es to omit levelling means 34 and rely on roller 46 for the levell.i.ncl function. The reason is that gypsum may tend to eollec~t and "c=ake" at the edge 35 interfering with the uniformity of the gypsum in the slabs.
It: will be noted th~rt al:! c:c>nta<~ts of the fibreglass ~r~att.e layer with the foamed mi.x causes some incursions of the glass fibres into the mi.x. Such movement and incursions, in the final core, will cause mutual adherence of these members and improves the integ:rit:y <:~f the c_°ore.

~l f41~~'~
'fhe resultant slab 4~i wa.th its fibreglass skin travels slowly down the conveyor, while 'the travelling ~lat~ sets, and then before arud after setting the formerly dehydrated gypsurn in these slak:~ ~.~camt:oe~k:es the hydration of thu gypsum from water in the slab. ~~omo of the excess water in the slab evaporates but moat is lest.
Downstream krom the location where the hydration is complete the slab is cut into lengths 54 corresponding to the desired length for the core. It wi:il be noted that there lU i.:~, in this example, rro layer cover':i.rog for the core ends where the cut has taken place. However it is found that the slab 54 has acquired, du.rirug setting and hydration, enough coherence and integrity to allow tuan<llirrg between this stage and the next. 'fhe coherence and integrity is provided try a number of factor~a: ttxe evaporation of water from, and the setting of thr:a mix in, the slab, and the hydration of the gypsum therein, which supply sufficient integrity for handling the cut ~elab, and do neat: require any "skin"
or retaining means for the uncovered ends of i:he cut slab.
20 The cut slab portions are there placed in a heated oven or enclosure ~6 ::~s ~~hown. 't:'Lre trer~v:ing is carried on at about 150°F and is not allowed to rise materially higher to avoid t: he risk of "calcin:ing" c>r "detaydrating" gypsum in :Locations of higher neat, during the heating process.
'fhe heating is continued until the excess water is driven of f and only the "comkv~ined" water in t:hc~ hydrated gypsum remains. The heating must be then stopped to avoid a risk of calcini.ng or dehydrating the gypsum. The point at which the excess water is drivE:n off may be reasonably accurately 30 determined since with a heating environment of 150°F the C~ 7~l ~t9 temperature of the care will remain below 150°F until the excess water is removed. As the excess water is removed, the temperature of the ccare will start to increase toward that of the heater environrnent.
4Jhatever method of' head ng is used it wall be necessary to provide for air or gris flaw into and out of the heating area to avoid the efiect5 on the process of an excess of humidity, caused by the excr~~s w<3t.er driven of:E from the cores.
The core, with substanti a~.l.y a.3 l the uncombined water removed, may th~4n be combined with the door shell to farm a complete door.
Although thw above is the presently preferred method, other methods, within the a~°.ope of the invention may be used.
The resultant core wi_Ll nave a preferred composition of about: 43% hydrated gypsum, 1% at.her solids, 35% large bubbles (1-4 mm) and 21% small buk:>blE>s (80% of which) (.O1-.2.5 mm). Such a core in dimensions of about 34 1/2" x 81 1/2" (nominally 3' x 7') and a tt-rickness of about 1 5/8", in a steel door will, (if heated tc> L000°C an one side), maintain the temperature: on t:he cc~c>7 side. of the door to less than 250°C for at least: 60 mi.nute:> (test (1D above). A door W th such core wil.:1 preserve i t:s .=-xtructur-al i:nt.egrity ( of the shell since the core will. Ire dehydrated or calcined) for a further 30 minutes.
The invention may be used for fire door cores which pass other tests either more or less stringent than the test used as an example. 'Chey rnay a:lsa bc> designed to pass a test analogous to (although more ar Lass stringent -:11-s~ ~' . C~.~.~
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than) step (1) without passing the step (2) test or equivalent.
(Such as in a wooden door.) for these broader aspects the proportions and quantities of the ingredients will be limited only by the +eaching herein, as defined in the claims.
Additives for better fire resistance or any other purpose may be added within the limits set out.

-12- '

Claims (4)

WHAT IS CLAIMED IS:

1. A core for fire doors, comprising the mixture of:
hydrated gypsum occupying 40%-46% of the core volume, the remainder of the core volume being large bubbles which are between 1 and 4mm small bubbles of about 80% of which are between .01 and .25mm, and other components where the large bubbles occupy about 31%-38% of the core volume, and the small bubbles occupy about 17% and 25% of the core volume.

2. A core as claimed in claim 1 wherein 80% of said large bubbles are between 2.2mm and 3mm.

3. A core as claimed in claim 1 or claim 2 wherein said hydrated gypsum occupies about 43% of the core volume, said large bubbles occupy about 35% of the core volume, and said small bubbles occupy about 21% of the core volume.

4. A core as claimed in any one of claims 1 to 3 where said large bubbles are formed of styrene spheroids.