CA2487613C - Vehicle mounted concrete mixing drum and method of manufacture thereof - Google Patents

Abstract

A method of manufacture of a vehicle mounted rotary concrete mixing drum of the type having an opening at one end for receiving and/or discharge of concrete therefrom and at the other end, means for engaging a drive assembly so as to rotate the drum for mixing or discharging concrete. The drum is manufactured from at least one mould using at least plastics material and further includes integrally attached vanes outstand from the internal surface of the drum forming an archimedian spiral disposed such that when the drum is rotated in a first direction, the concrete contents are mixed and when the drum is rotated in a second direction the contents are discharged from the drum; wherein, the method comprises the steps of; a) preparing a first generally helical inner mold part containing a surface extending between first and second helical edges; b) mounting the first helical inner mould part on a support c) enclosing the inner helical mold assembly within an outer mould formed by at least one outer mold part; d) fitting a second mating inner helical mold part to the first inner mould part to form an inner mold assembly; e) injecting a polyurethane elastomer into a cavity defined by said inner mold assembly and the outer mould assembly to form an inner wall element comprising one half of an interior wall of the mixer and one helical blade; f) allowing said polyurethane to cure; g) removing said at least one outer mold parts to expose said inner wall element; h) removing said inner wall element one said inner molds;

Description

TI-IEREOF
BACTCG~aUt~
Th.e present invention relates to concrete mixa~ag apparatuses arid zxtdre particularly relates to a vehicle n;xaunted plastics dtut~ fdx mixing concrete acrd a method manufacture thereof.
PRIOR ART
~o The building industry makes widespread use of concrete mixi:txg flocks for transportatxan of ready mi.~ced concrete to sites ~ox concrete hours, These trucks typically compxi.se a large mixing asserttbiy ixtcluding a mixer dru'ro :mounted to the vehicle atzd which is connected to a. mixer drive for mi~ti~.g aox~erete contents during txaasportation and for discharge of the contents on site. The drive system comprises a gees box which takes is power from the velxioie motor and which appl.i.es s. mixing torque to the dntm im.paxtitz~g axial rotation to the drum with the tax~ue being adjustable depending ttpdn.
the operating xe~uirernents. The above general arrangement is descr. i.bed in United ~tate$
paternk 4,5$5,35 which discloses a concrete mixer truck bcving a mixer drum adapted to be rotated. by the traction motor of the vehicle through an auxiliary transmissiat~ df the 20 txaCtion iriotor transmissiari.
~ccordi.ng to the lc~aowz~ vehicle mounted .rn,ixing assemblies, the mixing drum i.s typi.caliy of heavy duty steel construction and is disposet# at s~sproximately 10 to 15 degrees from horizarital. The drum is fitted with internal vanes or mixing blades dei:ining an a.~rchiznedian spiral sd th~k as the drum rotates in a first direct~.c~z~ the concrete held therein ~5 is mixed and as the dr~a is rotated in the opp~rsite direction, the concrete is di.sclaarged from the drum via an elevated discharge orifice under the reverse actidrc o~
the internal spiral varkes. The drain is disposed such filet the drive end is lowest at~.d the discharge end a highest relative to a generally horizontal plsue of the vehicle.

While steel druaxxs have beetx ia. rose fax' many years, they suffer froze. a nuxalaer o~
attendant disadvantages relating to their ccxst a:f ~ta2~tau~acture arid replacement, working iii"e, wear characteristics, weight and volume.
steel dxu~x~s are e~pe~ive to marxu~.~ctur~ dtxe to their aal~or intensive construction which s involves raping steel sheets into conical pardons snd cylinders which ante Fabricated are then welded to form tk~e ~niskxed tank. The archimedian spirals farmed from flat sheets are then Beaded i.rxta pasiti.ao irxside the drug. ,PAs catxca~t~e is a highly abrasive material, ixxter~.I suxfaces of steel drums are subject to signif~nt weax' abrasion., Tl~.is occurs particularly on the surf'accs which take sI~imp impact, sliding friction and shear load leading to eventual wea~iug out a:~ the dn, Typi.caJJy, .a stetl. tlxuan used. e~x'y day zrxiglat la.~t three to five years, tlteroal~er r~cquirin~
replaoe~nent at significant rJost. The abrasion of internal susfuces is inczeased whex;e 'there axe claazxges of slope in the d~.tr~. walls usuall~r ~xrl~ere tlxe segments of the drum arc joined.
"T'hG nixing blades are welded to the internal surface of the druzx:.
caus.i.xg sharp angled.
recesses in which concrete can gatlxer and eventually build up degrading the intexx'ral surface axxd pra~ritlx;n.g a Gatchment for further unwant~e~d build up of concrete. By its nature, a steel surface is relatively smoo#h and whilst tkruis naay be desixable for the purpose of preventing cozxerete build up an the walls of the drum, the interface between a the concrete and steel wall is an. area of abrasion rather than cancxete nvixaz~g, 2o Ideally, zx~~x;ng of concrete slta~uld take place tlxrauglaout the whole mix, hut an the steel chums, aptimzun mixing does not take place at tlae boundary lgyex and irn crevices in which concrete may collect In fact, due to the nature of the frictional interface betweelt the steel surface and concrete bauadary layer, laminar haw occurs resulting in little or na mixixxg at the baumdary layer. The reason I'or this is that the aggregate in the concrete 2~ slides anal abxades ( with reduced or na mixing) rather rhea rotates fio i'acil.,itate mixing.

Thus th.ex'e axe 'dead' spats in the nxi~z where t~Q mixing takes plsce and ~rhere~ there is an increased potEntial for unwanted collection of concrete. In addition to t'~e dove problems associated with tha use oi" steel mixing drums, that are cast and weigY~t factors which add. to itabez'eni ine~cienoies i~~ use o~ steel drums. l7tte to the dead weight of the steel drum, its value ~nr~.~st be restricted so the combination of the dead weight and concrete v~eight must be maintained within the maximum. 2GlXowable loading limits for the vel;icle to whiclx tlxe drum is attached.
An alternative tt~ the dawn steel drums was proposed in PCT International patent applicafiax~ PCTIIIT~OOJU122G to Rodgcrs and I~~a~. That application teaches the 1o pass~ility of usiatg a Lightweight ztaatexial. such as plastics far c~onstructio~a of a concrete mixing druitt as a. substii.'ute far steel whilst reca~ouzi~s~ that there were numerous structural and mariufaattuin.g difficulties tt~ be Quercamu ixa. malfin~ the trarzsitian to pla,stios nc~~t the least a~f which was tl~.e production of a arum which cau9.d withstand the high static and dyna.txtic landings to wlxich, truck mounted mixing dr. ums are sttbjact to in zs n.4rma1 operation. If the weight of the drug could he reduced without compit~misin.g and possibly increasing drum .'volume, the weight reduction could be taken up with additional ca~xcxete thereby increasing the pay Load.
There axe ~raraety of concrete mixitxg drum arrangements disclosed in the ~~rinx art none of which as far as fhe inventor is sway's anticipate the naWod of ma.uufacture of a plastics dru:tn 'in lie described herein.
iJnitEd States patent 4,491,41.5 discloses a lightweigly:~ pear shaped xotal'y mixing device open at one end and having an. axially elongated sool~at at the large end.
'fhe drum is rotatabIy supported on a unitary base having a tra.nsve~tsely extended forward. entl az~.d an upwardly and angularly ~e~ckend~.~ rear e'ad providing a nearing portion detachably 25 engagable with the socket to rotatably support the dmm at an inclination of abort 35 degrees- The dnuci has a plurality of axially e~tetxding radial fms ~ax li#t~.~; contents in, ro~~tati.on thereof and is pxe~crably fast~ione~l from molded plastics material either as ~.
tmitary body or as a plurality of ir~ter;~tting parts. The dx'cdescribed in this patent is for light duty operation and dries not have the stz'uctural and materixts characteristics s necessary for heavy r~t~ty concrei.e miming operations.
'Clnil~d Mates Patent 5,11.$,198 discloses a c~;mer~t mixing apparatus with a cradle support assembly .anl. .including a polyethelyn.e cement n~ing drum held and supported. by a cradle axxia assembly fanned of cradle base support braces and upright cradle arms which iz~terfit into cradle arxn FeaESSe$ wlZich are lareforrr~d wai~.~ the polyethylene dru3n. A bull 1o gear drives the polyethylene drtrttt.. 'fhs drum disclosed zn, this patient is intended for Iight duty cernextt operations arid does not address floe struotural and.
xx~~nufacturing recluirerz~~ats ~ar heavy duty operations. T,~~ited States patent 5,492,401 discloses 2~
concrete mixer with a mixing druny canszsting of high tle~sity crasslinked polyethylene .aerial. The dt'uzz~. includes ~. btrttom supported buy a conventional rigid metal patz s secured to the external sut'~a.ce thereof' bn ~rigxdify the prlastic drum and extend the life expectancy o~ the plastic dxuxx: by enablx~,g the concrete mzxex to be used tQ
complete a mixing jnb at a jab site even though movament of the concrete trai,~ within.
the d~ruttx during .repetitive xaixing cyc3es xnay ultimately wear a hole tltxaugh the bottano of the plastic drum. Faddle assemblies are positioned ~iuteriorl.~r off' the dram attd ~rriented to 20 rnai~taix~ minir~u.zn splashing during the mixing operation. IQot only is the drum disclaaed in ~tbuis patent unsuitable for heavy duty vehicle ~,t~unted operation the patent in fact teaches a means to accotnmodat-e a. wear faalu~e on site wheretyy a hole c~ruld be worn tiuough, the wall of the drum The prior teaches nse of plastics drug for small cement. m.ixz'vg operations.
However z5 here are inherent diff:ioultics ire ~anufactt~ing plastic dt'un~s tn art acceptable standard o~ .

strength and reliability. Plastics drums require use of materials which for a drum pxo~'xle 'by ttse c~~ a mould. As the discharge operiirrg tQ a dr, r~u~ ~s ~au.7rc~wcx than the remainder of i;he dr~xm:, it is not possible to remove a mpuld fpm an i.~.r~ex s~tt'~ace uatless the drum is made in. sections which eau be joxtted to fczoa. the drum structure. A, numlyer of methods of manuf~c~.t~re of plastics heavy duty mixing drums have been proposed in PCT
application PGTI~LU0010122b which discloses a h~.vy duty rotary concrete mixing Arum.
for attachment to a vehicle which. is characterized in that the drum is manufactured. l_'rom.
at least ore rioould and from at Least one plastics material and wherein the drum inclzrdes an inner s,CS having a pxopetiy which p~ro~t~otes znixxof, the eoaG~'eto at the boundary xo layer between ttae oot~crete and said inner surface and reduces wear.
~. t~urtaber of di~fezent methods ware proposed in that application. far the manufacture of a dxuncr of the type disclosed.
INVE~1'r'ICxN
'fhe present invention seeks to provide an alternative method of cotastniction of a t s heavy duty vehicle mounted rotating cement or concrete mixing drum fabricated frorn plaatics materials- The drum prtrduced by the method of the invention descn'bed herein rwexco~nes tbe. aforesaid. dasadvanange5 of tlxe prior apt anrl maintains efficient; concrete uxixia~g characteristics. According to the invention there is pxovxded a zoethod of coz~siauctioz~ of a plastics concrete mixing drum wherein the method, includes tl~e use of 2~ inner a~,d outer molds each made up from separate mould parts which are divided along two helical lines mid way t~etween the mi~i.zrg blades thereby ahovu ~or~atio~n of. a druraa interior from t~vQ ~dexxtioal 3onolds.
In orse bxoad i.'x~z'~a tbc paesent invention comprises:
a rr~ethod crf mau~.~e of a vehicle mQUr~ted. .rQ~ary conoz~ete ~.3xang dtu~
oiF the type ~s having an opening at one end i'oz receiving andlar discharge of concrete therefrom and at the t~thex end, mea~as far engaging a drive assembly so as to rotate the drum for mixi ~ ar r discharging concrEte; wherein, the drum i.s manufactured from at least one rnauld using at least one plastics matexial; wbexeiox the dxuxa finer ixacludes ix~tegxadly attached vanes wlxicb, outstand fzom the internal surface of the dnun forming ~an.
archimec~ia.n, spiral s disposed scab that ~vl~e~a the druta is rotated in a ftxst direatia~n. the concrate cantex~ts are mixed and when the drum is rotated in a second direction the contents are discharged firam said drum; wherein, the method comprises the steps of ;
a) preparing a first generally helical inner mold gart containing a surface endi:ag laetween first and second. helidal edges;
t o b) mounting the first helical inner mould Bart on a. support c) enclosing the inner helical mold assembly wltlti.~a aat outer mould formed by at least one outer mold part;
d) fitting a second mating iruuex l~eli.ca.l. maid part to the first inner mould part to form. an inner mold assembly;
15 e) injecting a polyurethane elastomer into a oamity def~xred lay said inner mold assembly and tfxe outer mould asse;nbly to form an innex wwall elent comprising one half of an interior wall of the mixer and o~xe helical blade;
t} allowing said polyurethane to care;
g) removing said at least one outer mold parts to expose said inner wall elex~e~;
20 h) removing said inner wall element one of saaid inner t'nal.ds;
The no.ethad preferably co~xipxi~cs the additional step of placing a rei~xforeang ~.eznbex itx a recess foamed in. said ixuaer ~anold part Steps a) - h) are repeated thexeby pxaviding a.
second helical inter waJ.l exetr~e~ti~ The first and second helical inner wall elements are 25 complimentary and combine to form an inner wall surface of tbmmixi.ng dxum.
The first and second ktelical iz~x~e~r wall eXexnents are then preferably placed into a jzg where opposing edges of said clEments are held adjacent; the wall elements de.ix~.g an. xz~xxex cavity of said drum. C~plaosing edges of the elements are sea3ed to coxtxpXete tha inner v~ra>X
o~ tlxe dxum. . 'The inner wall is removed from the jig and placed the xrmex wall on a so mandrel such that the mandrol is disposal ~. tha inner cavity. The inner waft is placed can the naa~ndrel via an open end of the inner wall whereupon structural laysrs of glass fibre reinforced plastic sxe applied to '~1~~ polyurethane it~.~.e~' layer.
Preferably, the internal.
surfa~x of the dram, includes an elastomex which will aIIQ~.v ;urixing of the contents of the co~cxete at a concrete boundary layer, The rei.~aforcing membex is preferably a rantinuous rope inserted iuQ a recess in a farrxaation which will form helical blades.
The method includos the use of inner arid outer molds each tr~s.de up from separate mould part,, which. are divided ala~ag two helical lxt~es thereby allowing foxxx~stxon of a drum interior wall from t~uvo caznplementary mould part.
1'». another broad fori.~n tlxe present invention corises:
1 o a method of tna.nufacture of a vehicle mounted rotary cox~cxete mixing drum of the type havi~og an oQening at orie ex~.d for receiving at~d discharge of concrete therefrayn and at the other end means fox engaging a. drive assembly so as to rotate the drum fax z~~og or dischaxgi~g concrete; wherein, tlae druua is manufactured frc~~x~ at least one inner mould and at least one oppasiu,g outer mould; wherein the c~u~ ztxcludes inte~aily attached i 5 vanes whic.'h outstand from the inte~al surface of the drum farming an arGhittaed.i~t spiral di~spased such, that when the drum. is xotated in a first directiari the cat~cret~ caz~tezztic are m~i.~ed and when the drum is t'atated in a second direction the contents are discharges from said drum" and wherein the internal surface of the drum is formed ar lined with ao elastc~r,~ex wk~acla causes mincing of the cxr~atents of the concrete at the rancxete batuxdazy 20 layer; whexeita. floe method comprises tl?.e steps of ;
a) preparing a. first per helical mold cantai~ing a surface intErmediate side edges of the mould;
'b) placitt~ a reinforeir~g cad in a recess in sand ir~x~e~' moldy c) enclosing the inner helical mold assembly witlxin at least one outer mold perk;
~5 d) sealing a joint between said index mold part and said at least one outer mold par4 e) injecting a polyurethane elastotner into a cavity deed by said inner txtald stxd said at least. one outer mold part to form ate. iuaner helical wall element comprising gone half of an izrteriar of l~.e mixer and ox~e helical blade;
g) allowing said polyurethane to cure;

h) remoYx~g said at least one outer maLd Paris;
i) removing or~.e of said inner "~c~)ds;
3) removing xbe interior polyurethane innEr helical wall element maldi.z~g ~rt~rao. the rema.indcr of the ixuAer mold assembly;
k) r~.ting steps a} -~ j} ra t'oxr~ a second inner wa~.ll eiez~ent.
1-'referably when a first arid. a second inner wall ele;Ctaent are placed in a jig jcrintixag surfaces are held adjacer~f to en~.bie sealing the join fo~aed by the jain.ti~ng sur~.ces.
.~ocord.~irag to a preferred. e~btrdar~aent, a mandrel is ir~sez'ted into an open discharge elxd~
of a dtuzn interior fiollowing which structural. layers nf. glass fibre reinforced plastics are r o wound about an outer sur~aee o~tbe inner wall.
T» another broad farm the present iunvention comprises:
a. method ofconstruotion of a plastics m~x~'~ drum co~.tapx'isi."~g the steps of a) preparing a ~rrst inner mold containing ~. surface extending frc~n~, a joint liz~.e zt~i.dway t5 bet~en two helical blades to a. m.~d line mauid,joint line at an inner edge ol:'said blades;
b) placing a reinforcing xod in ~. recess in said inner mold;
c) fitting a seca~nd boating inner helical mold to form art inner mold assez~iy;
d} enclosing the ~taex heiical.xnold. assembly within at least one outer mold part;
e) sealizn.g a joimt between said inner mold assembly and said at Ieast ot~e cuter ~.ol,d d ~ar~' injecting a polyurerhat~e eia~stomex 7utifia a. cavity dei'med by said inner mold assembly and said at least one cutex gold pa.~'t to fc~r~ one half of the interior of the mixer and onE of the heXica~ blades;
t] allowing said Qalyurethane to cuxe;
25 g) removing said at least one outer r~tc~ld parts;
h) xemoving tine of said inner molds;
i} retxxoviz~.g the interior polyurethane ~oidang from the remainder of the inner rnald assembly;
j) placing said iwo helical blade and ix~ter~or maldarl.gs in. ~. jig where the jointing 3a surfaces are .held adjacenf;
Lt) inserting a mandrel into an open discharge et~d o~tlae dru3m.;
1) appiyizxg structural lagers of glass ~rbre reinforced plastic the pcxymretha~ne layer.
Pref.~rably the reinforcing is fitted using spacers which centrslixe the reitt~areing rod or ropy in ats xecess.

~'rEferal~a~ tire ~~'st and second inner helical maid elements are jointed ~rith, a sealing compound ar gasl~efs along an inner Edge. Accorriing to one ean'bQdiment, the outer mold i~ formed. in three separate tx~ald pants.
preferably, a joi~at between the two inner helical elexne~ts farmiu;~ a helical blade is made with a pol~uretJ~ane elastomer eornpaund.
In another broad ~orrm. the prcscnt invEntion comprises:
a mett~ad of naa.nu~acture of a vehicle ma~xnted canarete x~.i.azuag drcz~a, comprising the z o stegs ot:;
a) tak~in,g a lxelioal iu~xiet- rnauld part and mounting the mould on a suppoa't;
b) placing at least one e~te~a1 zx~.auld. in t~pposing relationship to said inner mould;
~c) in,~ecti~ag a. ;~owable material into a space formed between said i~er mtw7d $nd said outer ~nauld such that the flowabie anatexaal. ~'ox~s a k~elir.~.l element v~ahiob~ twill form at least part of an inner surface o~'said drurr~.;
d) removing the at Least oite attter mould;
e) rexr~avir~g the helical eLe~aent ~raxn said iex rttould;
repeating steps a) - e) so as to ~'ax~ a seeund helical. elemoz~t;
za ' g) Preparing an exleriar st'~'a.ce of the helical elements far bonding to a stntctural IayEr o~ glass ~bxe.
Preferably, the flowable material is polyurethane.
In another broad term of an apparatus aspect the present invention comprises a vehacl.e mow~ted rotary cattcxete rr~~ir~.g dxuaxa ol'the type harri.rxg an opening at one end ~'or receiving andlor, dxsc,aarge ot'ao~.exete tlxerefroxo aztd at t'he atbex ez~.d, znaans ~r engaging a drive assembly so as to .rotate tl~ dxu~na ~'oz ~~raitxg or discbaxging oo~cxete;
wherein, the drum is maaxu~actux d l6roxn at lust one mould usnx~.g at Itast one plastics ao nxaterial; wherein the drum further inpLudes Lntegi:'ally attacked vases whicLa t~ntsta.~d fx~rzz~.
the iz~#ernal surface of the drum forming an archirnedian spiral disposed such that when the dr~tr.~a is rotated in a first direction. the concrete contents are mixed arid when flee drum.
is rotated ~ a second direction the contents sire di~ck~axged ~t'a~. said druxxt; wl~ereztt., the drum is formed b~ a. raethad comprising the steps ot;
~5 a) pxepaxing a first generallx helxaal. i.~~nex z~zold part caxztaaxriza.,~
a surface extending between first arid second helical edges;

b) ~mot~~utit~.g tlxe first helical inner mould part oz~ a. support c) enclosing the r~z~~r helical mold assembly within an outer rxtetrld ~'arnzed by at least one ov.~ier r~ar~Id part;
d) fitting a second mating inner helical mold part to the first ix~.t~~x mould paxk to ~axltx an rJ ~r~ rX~.4~d ~,$S~l~lys e) i~xjectir.~, a polyurethane elastomer into a cavity de~.t~ed by said iz~xaez mold assembly and the outer mould assem$ly to fonh att iur~.er wall element coxnpzising one half of an itxtsxiar 'wall t~f the mixer and one helical bladed allowing said polyurethane tp cure;
o ,g) removing said at least one ~ouier r.~r~ld parts to ease said x~x~e~' wal3 ele~e~tw h) removing said inner wall element cane af'said inner molds;
l:n another broad form Qf4;he apparatus aspect, the pxesent in~rentian comprises:
a.vehicle mounted concrete mixing drum formed by a method of manufacture comprising i s the steps af;
a) taking ~, helical inner mould part and mounting the awuld on a support;
b) placing at leas one external iuoul~l in ogpasixig relatxo~sl~xp tea said iranex ~noould;
c) injecting a ~torval~le noatexial into a space formed between said inner mould. and said zo c~~tex m4uld such that tide ~,ovuabl.e tna.'kexial. fi~rrns a helical element which will form at least paxt of atr inxxer surface of said drum.;
d) rem~ovang the at Ieast axe outer mould;
e) :removing ~tkae lxelical ele~~e~.t frtrixt said iranex mould;
repeating steps a) - e) so as to farm a second helical element 2s g)preparing an exteriox surface of the helical elements for bonding to a structural layer of glass fibre.
1.'xefexably the flowable material is polyurethane.
According to one em>~odit,~ez~t, xhe helical blades projec'4~g f'c~tza an anger surface wf said so drum have a pztcl~ diznez~sion of between 1- ~ meters and are formed by elastomeric ~atexial. Preferably the wall strength of said drum. is around G001~~f'a at a wall thickness of Emar~. Preferably the polyurethane form an inner layer which is approximately 3~nm thick.
to I'xeforahly the structural layer coz~;l~xises fila.t~ent windings formxt~g ~
layer of ~p.Pro~mately ~mm tia.ickrless.

In another broad farm the present invention rarnprises;
a heavy duty rotary concrete drum capable of attachment to a vehicle; the drum cr~zx~.prAS:i~.g a ~xrst end whzcl~ ~u~gages a dxi~e asscz~obly w~xch ~Qtates said drum fir mixing of said conoretc and a s~ecand end from which wed, crrxtcrete is dxsal~arged;
wherein said drum is manufactured from at least one layer of plastics material wherein the drum includes a wall having intc~ral interna.I formations which promote mixing of said 2Q concrete and an irerier surface v~rhjch pro~oteS llh~itrg of the Concrete at '~7outadaty Iayer betwcezr. tlxe concrete and said izrnez s~uxfar~; wherein the drum is fornred aocazci.iuag to the vrxcthod steps o.~
a) 't~.ki,~g a. helical inner mould a.nd mounting tire .mould on a support;
2s b) placing at f east a;~e ex~xnal mould in opposing relationship to said inner z~auld;
a) injecting ~rolyurethane ~iz~tv a~ space formed between said inner mould and said outer rxtauld;
d) re~,vving the at least one outer mould;

e) removing ~ helical blade part from said inner mould;
~ repeating steps a.) - e) so as to farm a second helical blade part;
g) mating tk~e fist and second helical blade parts with an interiox s11.e11;
g) preparing an ~~terior of the drum for boz~d.i~ag to a structural layer o~
glass fibre;
~h h) winding tlxe structural layex about said exterior.
b~T.AIL~D ~l~~~l~Tl.'T'ION
The pt'esent invcntivn will nonv 1?e described according ~ a. px'efexxed but con limiting ernbadixnent az~.d. with reference to tire accompanying illustrations whcrei~n:
7 o Figttxe 1 shows a side elerratiou. of an inner helical mould part;
figure 2 shows a side ~leva#.oz~ of the mould Bart of figure 1 iz~caudi.~ag exploded external moulds;
I~igure 3 shows a side view of the innex x~auld part of figures 2 and 2 fully enclosed by e~al rnvuld sections z 5 laigita'e 3a shows an enlarged view afi external. xx~.oulds exploded ~t'otxx a. lxelioal blade part;
Figure 3b shows an enlarged view of the ~ssem~bly of figure 3a. with outer mould parts x~naulds assembled.
Tigure ~ shows outer mold sections exploded firom the ir~nex rnr~uld assexcxbhy tepox~
completion of injection of an elastomer.
2o Figure 5 shows a heli.caJ blade paxt p~'oduoed by and removed from the inner mould assembly of.' ~guxe ~;
>~igure 6 shows a cvugl.irxg of separa#e and complementary helical blade parts formed by the axzsngements of figures 1-5 avd wl~ioh foz~nn an inner wall of the drum;
Figure 7 shows a housing for assembly aiz~ which the inner wail of the drum i~
placed 2s afker mouldit'rg, lxelical blade parts for preparatxo~a. of. the blade parts to receive an autex structural layer;
figure 8 shows an assembly including a mandrel for mour~tirtg squid inner payer for applying an outer siruetural layer of glass i;~bre;
J;'igure 9 shows a caxnpJeted. drrxt~. with traok xing fitted.;
The concenirai~d '~ea,~' pbints ity, the priox art steel drums reduces the working life of the dnttx~s necessitating costly repair or replacement. Steel drums are fabricated ~roxn. xolled flat sheets which form cones and a cylinder wlxich. are then joined together by weJ.duug.
Archimedian spirals are tJ~ez~. welded to the ~uu~ner surface of the drum resulting ~ a higb specific gravity vessel whose self weight reduces the amount of concrete which can. be .
carried by the vehicle tar which it is attached. The steel dnlms suffer from a numJaer c~f to dzsaduantages i~GJudi~g susceptibJli~r to abrasiar~ at the junctions of the cylindrical and conical sections and the tendency for unwanted concrete build up at xhe sharp ooxners and ,crevices formed Jay the mixing hlades, fn addition, the smooth internal surface of the steel drum promotes sliding abrasion and inhibits mixing at the bc~~.ztc'iary l.~,yer due to tlxe low cae~cient of friction at the cancrcte/metal interface, ~5 'fhe xnethrrd to be desoxibed Jaelow is axA aiterz~at3ve to both steel drums and the plastics dnuns formed by the methods of manufaetute desc~'.bed in Internatiaaa,l Patent . application No. fCTl~r'U001~1226 to ~.odgers and. hhouri. ,.A~.ccbxding to the ~rtethod, a plastics heavy duly concrete mixing drum is formed using both an:~t'na3. az~d exter~raal moulds. 'fhe dram. xno~udes ate xxtterttaX arclaxxt~edaan spira,~ ~orruEd by helical blades or zo vanes wvbich x»ix conc~'ets during xotataon of the dxutta itr one d~.reCtion and dt,SChar~
concrete when the drum. is xofated ixat an apptrsite diurebtit~r~. ~'.t~e drum is get~exail~y peas shaped axed inel.udes an opening at one end for entry and discharge of concrete.
2s The first step ix~. the thod according to one embodiment, ixtvolves the use of arx interbal mould. A. polyurethane drum interior complete with ini:ernal helical blades is forn~.ed between. an. iritez~ior and an exterior mould set. ~'he exterior tno~tlds are easily removed after the polyurethane i~~ farmed, however i~ecause the mixer is a closed vessel with the discharge apenit~~ strral.ler than the ~axincm~. dia~r~ter, and due tc~ the complexity c~f the blade mau.lds, it is not possible to form: the interior as one caxnplete piece ~i then xezz~.ove tlxe mould. ~hecord.in~ly, the elastonrcric drum interior is moulded in sections which can be removed from the znou9ds, and then joi~aed to ii'o;nm tlxe complete ~ntexxor.
This ~tet'iar is then reinforced with. structural layers to co;rrplete the mixer. The joining tt~gether of two aaxz~plem~eai~.ry inner wall sections which arc each forzaed by the same 1 a zne'daod steps sequentially is a new approach to forming a drum interior not known in the prior art_ l~efex~r~z~g to ~,~u~re ~ there is ;~awa az~ ass~ably 1, wl~.ich cosxrprises a suppo~: ~ ~vhxclr receives apd retains thereon a helical mould part 3. Mould. 3 is shown. ~
pxd~le 'by lxz~.e 4.
~ s .Mould 3 is initially prepared in a sEparate mould having a helical interior so that mould, ~
con~fozxns to the shape u~ tk~at interior. ~aee mould 3 is formed, it may be transferred xnazaually ox otherwise for n~aunting an support 2 iun. prepaTati.on. fog' receiving external ~a~xlds. Figure 2 slxows a side elevation of the mould ~ c~f ~gu~re 1. with expJvded opposing external mould parts 5 and 6, Mould parts 5 and 6 enrapture mould 3 but leave 2o a generally helical, carrity tberel~etcueen. (7n~ce ex~xn~al ;tnouJ.d parks 5 arad. t have ~ez~.
secured and sealed, polyuretl~a~ae is injected. into the aforesaid cavity. It will be appreciated by pe~'sc~as skilled in the art that more tl3an two external moulds msy be used to ~l~ll tlae same t~bjectives of encapsulating inner mould 3. k'igure 3 shows a side viier~
af, the inner xnt~uld 3 eaalosEd by external rnauld sections 5 and ~.
zs ~ .figure 3a, shores an enlarged view of external moulds S, 6 and 7 e~tploded fro~ao, izuQ.er znauld 3 revealing a suction view of a part helical blade 8 retrieved frame the cavity defined by cuter moulds 5 arid ~ aid ina~ex mould 3 following injection of ~olyurethaype.
!Figure 3b sb.aws an. enlarged section view of the asse~biy aF i:i.gure 3a witla moulds assembled. lWlaulds 5, 5 ~d 7 are sbawn. in figure 3b in abutting relation$hip with. paxt helical blade S, which is formed by injection of a polynretriane ela.~tomer into a cavity farmed between moulds 5, 6 and 7.
~tefcrring to figure 4 thexe ifi SlaOwn. outer oaold sectivx~ .5 anal G
exploded from inner mould assembly 1 upon completion of injection of an elastomer. Upon removal ~f inner mould section 3 part helical blade ( or blade elermez~t) S whiclx leas beer frrrm~ed from tl7e elastdznexio xxxaterial injected irztd t'he cavity d.ef'zued by assezrrbled external 1a ~r~ulds 5 and 6 and inner mould 3 as shown an. fi~mee 3 may be relessecl.
>~igure 5 shows a first helical blade p~at~ 8 farmed in a first belieal ( ar~chi~dian) spiral, The above descn'bed process is repeated once again to form. a seco~ud lteliaal ( axclxi~xaedian) spx~'a.l 9.
Helical blade part 8 forms one hal~ of a ~napleted helical blade which is integrally dzspased o~. ate. i~nex surl;'ace of, tlxa d'xt~m forrx~ed by tllc processes described herein, A
5 repeat of steps described. with xefexence to ~guxes 1-5 t~sult ixa. a second helical. inner blade element 9 which ca operates with and is camltlementaxy 'tc~ lielxcaJ.
>alade elexnez~t .&
to form a complEted inner wall including integral helical blade figuxe 6 sb~ows a. pafr of helical blades 8 and 9 farmed by the assembly and process as descn'bed with reference to figures 1-~ . Blades 8 aad 9 axe ar the ~oxx~ of two ~a~rallel helical spirals spaced at 1,80 dagx'ee exia.l phase difference each with a reinforcing rod 10 ( see figures 3a. and 3b~ in the interior edge, wbaclx znay be e. continuous flament and resin rope. As these blades are i~.t~gral with the interiox surface of xlae xoi~e~ra xt is convexdu~t to ~olx~
these two stxuu~es along two helical !tunes znid way between the blades. In this way the interior is formed as two idEntacai mouldings wbuich. can he removed from the interior mould 3 and e~.ter~ior z~ mould sections 5, 6 and 7 anal which al$o co~.taia. tlxe corraplete reittfc~rcixxg rods 10.
is The exterior moulds contain a layer c~f' glass rei.nfor'ced ISLa,.Stic which.
hoztds tc~ the polyurethane which is formed, against it. 1n this way the two zxaouldtin~s are fonnaed with two hElireal jaintang~ lines tnid. way between the blades and a stiff inner sized ready tar s receive the structural layers is farmed.
Acecrding to cane embt~di.~ttent a. prefei~x'ed method of manufacturing the mixer is as faltaws.
1o The inner hclicai mould 3 which incl,~tdes tlae st~u.'face which. o~,teuds ~rozn. ~. joint line mid way between two formed helical bladES ~ 8 and 9) to a mid-line mould joint tine at an.
inner edge of the blade. This surface faces towards the drive end of the txxi~ter atad contains a recess far the reinforcing rod or filament rape 3Ø The next step is fitting reinforcing mc110 with polyurethane spacers, which centralize the rod in a zecess in inner is ~.ou~ld 3.
A mating inner helical ~mauld is prepared and fitted and is joined with sealing' gaskets alan~ its inner edge. 'The helical inner mould 3 is enclosed within the three external moulds ~, 6 and 7, the 5urfacc5 of which are pre coated with glass fibre reinforced plastics to provide an interior moulding to the polyurethane elastomer. SIs are zo incorporated into a joint formed between the inner and outer moulds.
Following this floe polyurethane elastomer is moulded into the cavity farmed between the inner and outer moulds- 'flze elastomer palynner~es tc~ farm blade 8 which comprises half the interior layer of the mixing drum. The polyurethane is allowed. to cure whexeupo:u t~txter ;moulds 5, 6 and 7 are removed t0 expose an inner shell and outer surface of the paly~.'ethsine as blade part 8. This allows removal of the ltelzcal blade .part: 8 and iziterior polyux'etbaue moulding. The above process is repeated to provide a second helical blade part 9 and intera~ax z~~ul.di~ng. The twc~ helical blades 8 axzd 9 axe the:a assembled ~.
a jig 11 as shown in i;agyxre 7 wl~ereupoa they ase joined tagethez~ usi~og a polyurethane elastomer compound.
At this stage ofthe processing a drive rang is applied. to tk~e polyurethane layer which. will 3o farm the inner layer of the rni~ei~g dt'~xara.. '1~ite jig is ~~.oved and the now formed inner Dyer of the churn is transferred to a ~wixtdix'~g stati.du as shown in figure 8.
A steel mandrel. 1~ is inserted into the ogez~ ( discharge ) end 13 of the mixer so that ;it reaches the drive ring which is common to heavy ditty drums of this type. "fhe drive ring which imparts rotation to the mixer i.s spigotted and drilled to suit a gear hex flange. The ss glass fibre reinforced plastic exterior t~.f 'khe polyurethane interior is bonded to the drive ring and allowed to cure. The glass fibre xer.~,fot'ced plastic exterior is Extended over ~,~e discharge end suppr~rt flange which then i'oraas azt ez~clxrsc~l vessel against the mandrel.
An inflation pressure is applied ~ the ir~tcxir~z of the mixer to ensure at cat~fn~rt»s tv the interior u~ the jointing jig. 'fhe top half of the jig is removed and the exte~t~~l surface xrf the pvlyetl~ylerre joints is covered r~.th glass fibre reinforced plastics.
Follo'vvzr~g tlaat, tlae external s~t~ace of the moulded polyuretl~a.ne iotexiox of the mixer is prepared for bc~nc~xttg to the structural layer .
flr'ttctut'al layers of glass fibre reinfbrced pla..Sticare applied by one of the knr~wn rnethod,9 standard to the industry such as 1 U ~.) ~oxttact moulding of random ar~dlox d~ixeotions.l glass fibzes and resin_ b) F~ilaz~.exrt winding.
c) Surface ~r~ishing by filling and grindi~t~g oz/ Moulding a ,gel coat finish using vacuum or pressure.
'l.'lxe windixrg step is oonductcd after dt~m it~u~ex layer' 11 xs r.~otxnted d~ ~at~drel 1~. ( see is figure 8). As represented by ~gaxe 9, the filial step ~n the construction of the drum 1~
involves the installation of the track ~cit~,g These are known in conventional heavy dray dxtt~s and camiprise ~.
cylt~~.dxical. t'a.il.
attaohed to the miner adJacent to the discharge end and which. is supparfed by two rollers to allow the imi~er tv be xatated by the ,geaxbox at the dxxve end. The ring is held ua 2o position with rubber gaskets which seal to the ,tx~z~er a.~.~I this space bettwee~z the rang and the mixer is filled with a liquid polyurethane which bonds to both as it gels and cures.
In opexatac~n this elastomer transmits the lt~ads from the mixer shell to the steel track ring aa~d hence to the steel support rollers, In this way the coxacenlrated l.vads one spread and only low stresses era transmitted via the elastomer to the mixer shell 2s According to carte e~vdxz~necx'ts a computer may bs employed to program and control the delivery afthe pvlytxter to the maid surface and the application oi;'the structural. layer.
'flue windhxg of a. fibre rea~i~r~xced structuxal layer may involve computer controlled u;awiaading of resin wetted. fibre rovings from around a .rvtati~g ~vt't~.er.
The tensile 3o sfTer~gth of the windings tray be in the order of d00 Mf~a. To ob~.izz tbte Qptimuia~. physical properl:ies of tlxe filament wound structure the fibres are aligned t~o the loads it~nn~sed in use of the ~.~i~hcd drum. Typical Ioadirxgs a;n the datum aze axial bending under weight of vvet concrete, an applxecl dyx~anaic Load at the drive end of the dt'um, driving torrlue and sappor# Loads at dischazge End trunicr~ rolls. ~'.be wuxdin~g patteza of the filaa3ents aligns the ~~bres to withstand bending stresses, increasing in angle and in wall thicl~t~ess towards s the discharge end td accozaaytaodate applied roller loads. ' 'Floe rvv~o.gs which line the drum may altexinatively be drown through the resin. iyath and applied to the s~xfaof the dzum as a wide riblavn comprising ~vusar~ds of tensioned ~6res_ Ttye windaz~.gs overlap until the required thickness is reached. 'ft~c sar~ace of the drum may be covered with wet z~esin arad stz~a..l1 ~itxegulazities wl~i~h need to be addressed tp to prc~ride the ex~z~l finish. A.s a result of this construction, the spiral mixing blades inside the drum. are capable of wiihs~tanding high bending and shear resistance during mix_in,~ operatiQ~ns. The inz~ex el~stobvexic surface is hx~b.Iy resistant fo ~abzasiozt by concrete yet it is softer and. Lighter than the steel equival.e~ot. Tl~.e higher resistance to abrasion is facilitated by the natural elastic deformation of the elastomer which absorbs the lcixretic enexgy of the ootaoxetc particles witb~out gcugirig of the sturface xnatexial_ Zxt addition, due to 'gibe pxopexky of the ixa~nez surface wbicla will preferably be polyuzet'batae, floe cnriczete will be mixed, rather than slide at the boundary layer ensuring e~cieidt mixing of the concrete thrQU~lzotri the rai.~t ~d xeduc~.on ol:' abrasion dx~e to tl~e Szt~ootb.
curves throughout the iztterivr af. the drum.
2o F'urthcrmore, the blades are strez~,thened by their molding iutegr~t,lly with the wall of the drum and have a stit~'~ss factor which will sustain all applied normal operatixxg Loads.
A fur<~h.er adva~ta.~ in the use of plastics for the mixaz~ dt'nrlies in the thezmal properties ~f the plastics material,_ l~;ot coztditxons sre unxlesirable for concrete mixing as they accelerate hydration reduci».g eonczete workability which is an.
essential property required immediately following a cQncrefe pour. In very ht~t climates, the conventional steel vehicle mounted, ~uixa~xg drugs conduct high heat loads which increase heat at the conGxete boundary layer due to contact with the super heated drum wall causing utruvanted acceler~tad hydration, This phenomenon is dif.~cuIt to avoid with steel dress as the coztductivxty of steel leads to high conductive heat irar~sfer fxatn tlxe otter skin of tire s drum to the ixax~ex wall which is :narmahy in contact with the concrete. Irt saxrre lrat climates, ice is placed in the steel drums in aaa. attezxapt to arrest temperature increase inside the drotta, ,A,s concrete hydration is an exothermic reaction, it is sensitive to external temperatures. Accordingly it is desiraf~Ie that the concrete temperature ren~.i~
acceptably low to ensure a satisfactory level af. woxkabi,lity and to retard hydration. Steel drums heat up significantly and conduct heat through their thicl~ess x~ds~in~g tlxe co~;ct'ete vulr~exrable tn the vagaries of'ternperature variation. Overheating of the concrete mix i~ ~.
pxablem to be avoided and has xc accorcia~ce 4vitlr one aspect provided a meth4d of manufacture of a plastics drum to take the place of the catywentlo~lal steel dry thereby xeduc.ing t;he tutwanted e~ec~ o f high thErtnal conductivity typical of the steel dxurns.
~s The plastics druul allows the ct~ztcxete to ~tx~ai~x ~u'ort'lrahle inside the drum far longer periods compared tt~ concrete itz steel iztg drcttns under tire same external teml?erature conditions and transporting concrete.
'T~e xt~etltod of canst~uc~iaz~ t~~ a plastics cQ»crete mixing drum as descrrl~d herein provides an alterkiative yet efficient method c~f production of plastics drums. The methods 2o descrz'bed herein allaur for mass .production with reduction i:a the zrumber of production steps ca~nparred to the known methods.
It will be recognized by persons ski~lcd in floe art that xwumerotts varzatic~r~s and modifications may 'he made to the xn~enti.az~ as broadly desczr'bed herein.
without departing from the overall spirit Grad scope of the invention.

Claims (10)

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A concrete mixing drum comprising: a first molded polymeric helical wall element; and a second molded polymeric helical wall element joined to the first molded polymeric helical wall element, wherein the first molded polymeric helical wall element and the second molded polymeric helical wall element form a substantially continuous common wall circumferentially extending about a longitudinal axis to form an interior of the drum, and wherein the first helical wall element and the second helical wall element are joined along a helical seam

2. The drum of claim 1 wherein the first molded polymeric helical element includes an integrally formed blade disposed proximate a mid-line of the first molded polymeric helical element.

3. The drum of claim 2 wherein the second molded polymeric helical element includes an integrally formed blade disposed proximate a mid-line of the second helical element.

4. The drum of claim 3 wherein the blades are helical, and the helical seam is disposed mid way between the blades.

5. The drum of claim 2 including a reinforcing member within a tip of the blade.

6. The drum of claim 1 including a second substantially continuous layer extending across a junction of the first molded polymeric helical wall element and the second molded polymeric helical wall element.

7. The drum of claim 6 wherein the second continuous layer is a fibre reinforced elastomer.

8. The drum of claim 1 wherein the first molded polymeric helical wall is an integrally molded one-piece member that forms one half of a shell of the mixing drum.

9. The drum of claim 8 wherein the second molded polymeric helical wall is an integrally molded one-piece member that forms a second half of the shell of the mixing drum.

10. The drum of claim 5 wherein the reinforcing member comprises a continuous filament and resin rope.