CA1115942A

CA1115942A - Hot melt adhesive foam pump system

Info

Publication number: CA1115942A
Application number: CA319,189A
Authority: CA
Inventors: Larry D. Akers; Charles H. Scholl
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 1978-02-01
Filing date: 1979-01-05
Publication date: 1982-01-12
Also published as: FR2416058B1; SE7900843L; GB2013512A; CH629688A5; IT1111968B; DE2902811C2; CH639009A5; GB2013512B; JPS54117544A; FR2416058A1; JPS6145491B2; US4200207A; DE2902811A1; IT7919826A0; SE446827B

Abstract

Abstract of the Disclosure A hot melt adhesive foam pump system having a first stage pump that meters molten hot melt adhesive into a second stage pump, which in turn mixes gas under pressure into the adhesive so that the gas is driven into solution with the adhesive at an adjustably controllable radio. The pump is in-sensitive to changes in adhesive viscosity and pump speed, and provides uniformity of foam density and output flow rate when the adhesive is ejected from a dispenser connected to the pump.

Description

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The invention relates to ilOt melt adhesive Eoam ~systems. More particularly, tllis inven-tion relates to a novel ll hot mel-t ad~es:ive foam p~lmp for use in such a system.
Hot melt aclhesives are widely used throughout industry ~I for adhering subs-trates one with another in many diverse applica-j~ tions. One of -the most common uses of such adhesives is in the packaging and cartoninc~ industries, where -the quick setting time of hot melt aclhesives is particularly advantacJeous. In -this ~¦end use, a col~lon problem is the difF:icult:y of coMpressincJ hot ¦¦ melt adhesive after application so as to ob-tain sufficient 1~ "squeeze out" oE the adhesive be-tween the substra-tes, to achieve a good bond oE adequate surface area. The relative]y hicJh ¦ viscosity, high surface tension, and quick settinq -time of many hot melt adhesives tend to res-train l:i~uid adhesive from spreading over as large a suhstrate surface area as is desirable.
¦l Instead oE spreading, tlle deposited liquid sets up as a thick il bead on the structure. Even when quickly compressed, as for lexample between two flaps of a carton, the adhesive is difficult Il to spread. When -two adhered surfaces are pulled apart, it is jj generally found that i-t is -the substrate wllich Eails, rather than j-the adhesive to substrate in-terface. Consecluently, the greater 'l the area of interface or surace contact between the adhesive ¦l and the substratc, the stroncJer the bond will be.
! It has recelltly beell discoverecl tllat the adhesive strength of a bond achievecl with a givell qualltity oE a selected hot melt aclhesive may be appreciably improved, and in most in- i jstances at lc~ast doubled, iE th~ aclhesive is applied as a cellular Ii f~am rather Inan in the con~en~iollal way ~ non-ro-~mod Rdhesiv~.
The increase(l bondin~3 stren(3~h of t]le :~oalned adhesi.ve l.eSU]. ts at ~least in part from tl~e .Eact that the aclhesii.ve Eoam may he spread over at least twice the area, under thc salllc compressive concliti.onci, as an equal mass o:E adhesive wh:icll llas not been foamed. Ilot melt l¦adhesive foam also has been found to have a loncJer "open" t.ime, ¦laf-ter it has been deposited OlltO a Eirst substrate and during which ¦lit can ef~ectively bond to a second substrate when pressed against !~ it, yet i-t has a shorter "-tack -time", i.e., it will set up and ad-Ihere faster aEter it has been compressed between two substrates.
These charac-teri.stics to~lether are ~articularly desirable in car- I
itoning applications. There is no need to close flaps immediately .
after applying foamed adhesive onto one of the flaps. ~lso,."pop ~opening'` is very substantially redueed, and the adhered surfaces may be released from clamping pressure soon after application of llthat pressure. These cliscoveries are disc].osed in Scholl et a].
¦IU.S. Patent No. 4,059,71~, issued November 22, 1977, entitled "Hot~
Melt Thermoplas-tic Adhesive F`oam System," and in ~Scholl et al l].S.' Patent No. 4,059,466, also issuecl November 22, 1977, entitled "Hot~
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¦'Melt 'rhermoplastic Adllesive Foam System", both of which are as-signed to the c~SSiCJnee of this applicatioll.
I ~S ShOWIl in those patents, in procluclncJ a hot melt jladhesive :Eoam, iE a gas sueh as air or nitroqen at hicJh pressC~ure~
for example 300 pounds per square i.ncll, is thoroucJllLy mi.Yecl with liquid hot mel.t aclhes.ive, tlle cJas can clo intc) solution in the ,adllesive. l~lc~n tlle aclllc~sive/-~as solutiou i.s subsecluellt:Ly dis-.pensed, as from a conventiollal va.lved type of adhesive clispenser or gun, the yas wi.l.l come out o~ ~soluti.on but remains I
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en~rapped in the aclh~sive, to Eorm a closed cell hot melt adhesivc, foam havin(J thc clesirclb:l.e acl~lesive character:istics descri.he{l labove.
il In one preferred emboc1iment oi the techni.que described in paten-t No. 4,059,714, solid thermoplastic aclhesi.ve material `lis heated and melted in a reservoir and the molten adhesive is ¦lintroduced ~ointly with a gas, e.y., air, -to a sinyle stage gear llpump. Within the year pump -the ~as and licluid adhes.ive are mixed, ¦jand the gas is forced into solution Witll thc~ mol-ten liquid ad-llhesive. The liquid/gas adhesive solution, under pUIllp outlet ~pressure, is then supplied to a va.l.v~d type o:E adhesive dispenser from whi.ch the adhesive can selectivc].y be dispensed at atmos-,pheric presswre. Upon emergincJ Erom the out:le-t no,~31e of the !l dispenser, -the gas evolves from the solution in the Eorrn of small ¦¦bubbles causin~3 the adhes:ive to expand volumetrically to form ~la hot melt adhesive foam. The resultant adhesive :Eoam, if leF-t in an uncompressed state, would set up as a homocJeneous :Eoam hav-ing air or gas cells evenly distributed throucJhout, and it has the desired adhesive charac-teristics mentioned above.
1 It is impor~an-t for cert~in applications that the I Elo~l Erom -the valved dispellser or cJun be very smooth ancl of uni-¦lform rate, and that -t}lere he no sicJniE:icant "s~?ittincJ" or 'l"s~utterincJ" Erom the gun noz.,~,].e. Sucll s~itti.nc~ may cc-luse dis-~,crete foarll drop.l.ets ~o splatter orlto tlle sllbstrate OVC~ an un-,contro.l.lecl arca, ~itll recluccd or 110 foa~ pl~licvlt:ioll at tlle in-tended positlon. SE)ittinc3 can be particularly undesirclble a Il ~r in those applications where a gun is rapicdly and repetitively "cycled", or valved on and off, for example as in applying a "stitched" adhesive pattern onto carton flaps.
Moreover, we have found it to be important that the density of the foam as deposited on the subs-trate, should be uniform with time, regardless of whether the dispenser is open for a relatively long period oE time or whether i-t is rapidly cycled on and off. Further; the foam density and deposition rate should remain uniform regardless of melt temperature variations and pump speed varia-tions. There is, of course, a certain amount of tolerance in foam deposi-tion Which is acceptable in co~mercial use, but it is importan-t that the foam density remain within that tolerance regardless of the mode in whlch a particular gun is operated, i.e., regardless of whether it is continuously on or is cycled.
We have also found that under some condi-tions there may be an undesirable delay, or "run-in' period, after the gun is triggered but before the adhesive is delivered from the nozæle. While this may be insignificant in some applications, e.g., where a gun will remain on for relatively long periods, we have found that run-in can be undesirable where a gun is cycled on and off. Particularly in -the latter case, it is an important criteria of operation that, when the gun is cycled on, the adhesive Eoam be emitted immediately (as a practica:l matter), in a uniform state ancl at a steady rate.
Accordingly, it has been the primary objec-tive of this invention to provide an improved hot melt adhesive foam pump jr~!¦

adapted to deliver a solution of gas in hot mel-t adhesive on a highl~ reliable and con-tinuous basis, with minimal variation in the volume and density of the foam adhesive ou-tput from a valved dispenser and with minimal spitting or sputtering, thereby to increase the uniformity of the adhesive Eoam. It has been another objective to provide an improved ho-t melt adhesive foam pump capable of providing a molten adhesive/gas solution that permits a reliable and uniform adhesive foam to be ejected from a valved dispenser connected to the pump with no "run-in" time, so that foam delivery, after activation of the dispenser valve is almost instantaneous.
As will become clear in the detalled description of the present invention, there are various different aspects of the invention. Generally, the invention provides a dispensing system for mixing a gas with a li~uid and -Eor pumping the resulting mixture. The system includes a pump having an inlet and an outlet, means for supplying a liquid to the inlet of the pump and means for supplying a gas to the pump for mi~ing therein wi-th the liquid.
In accordance with a particular aspect of the invention, the system further includes a first stage pump and means is provided for delivering the liquid from the outlet of the first stage pump to the inlet of the above mentioned pump, the above mentioned pump being the second stage pump. ~ecycle means is additionall~ provided for a-t ]east par-tially returning the mixture from the second stage pump, through a recycle p~lssage to the inlet of the second s-tage pump when the dispenser i5 not dispensing all of the mixture supplied to it from the second s-tage pump. The mixture recyled to the second s-tage pump bypasses the first stage pump.
In accordance wi-th another aspec-t of -the invention, the first s-tage pump is a me-tering pump and the second stage pump is a mixing gear pump. Both pumps are driven at the same ra-te and the second stage pump has a gxeater displacement than the firs-t stage pump. The gas is supplied -from a gas source to the inlet of the second stage pump at a position which is downstream in the direction of second stage pump gear rotation from the point at which liquid is delivered to the inlet of the second stage pump from the first stage pump.
Other objectives and advantages of this invention will be more apparent from the following detailed description taken in con~unction with the drawing in which:

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~ 1l 11 , ¦,1 L~ J~ c~ ^a~ L-~ :i.].l.~,l,r~ iol~ o~ irs~
embor~irnellt oE an i.nl~rove(l ~ esi.ve :Eoalllcl~ )el-ls.illcJ systeln i.n ,aeeorcl with the l~rineil~les o~ t]lis .invc\llti.on;
ll 1l I;'icJure 2 i.s a eross seetiorl.ll view takell axially of I I'ltne,first eln}~ociiment oE ~llc iml~:rovecl adllesivc foam ~urnp;
Figure 2A is an enlarged fracJmc?ll~ary seetional view, taken Oll line 21~-2A of Figure 2;
I Fic~ure 2B is an enlarqed Eragrrlentary seetional view, ~jtaken on line 213-2B of Figure 2-1l FicJure 3 is a eross s~e-ti.ona]. ViCW taken aloncl llne

3-3 oE Fi~Jure 2;
Fi.cJure 4 is a eross seetional vi.c~ ta]cen along line ,~4-4 oE Figure 2;
!I FicJure 5 is a eross see-tional view taken along li.ne ¦ 115 5 of Figure 2;
1l Fi~Jure 6 is a eross seetional view taken aloncJ line ¦1 6-6 o E Figure 2;
Figure 6A is a eross seetional view taken alon~3 line 6A-6A of Figure 2;
1 Figure 7 :is ~ eross seetional vi.ew takell aloll9 lil~e 7-7 oE Figure 2;
, Figure 8 is a eross seetional. v.iew tal;ell along line 8 8 of Fi~ure 2;
F'igure 9 is a diagramlllatie ill.nstratioll of a seeoncl ernbodimellt oE an ilnprovec-J adllesivc disl)ensi.ncl systelll in aeeord Witil tl~e l~rineil~le~s oE this inVellti.oll;

' 7 , I i Figure 10 is a cross sectional view taken axlally of the second embodiment of the improved adhesive foam pump;
Figure 11 is a cross sectional view taken along line 11-11 of Figure 10;
Figure 12 is a cross sectional view taken along line 12-12 of Figure 10;
Figure 13 is a cross sectiona:L view taken along line 13-13 of Figure 10;
Figure 14 is a cross sectional view taken along line . 14-14 of Figure 1.0; and Figure 15 is a cross sectional view taken along line 15-15 of Figure 10.
The first embodiment of the improved hot melt adhesive foam dispensing system and pump, in accord with the principles of this invention, is illustrated in Figures 1-8. As shown in diagrammatic form in Figure 1, the impro~ed system of this invention includes a two-stage gear pump 10 having a first stage 11 and a second stage 12, each stage comprising oppositely rotating and meshed gear pairs 13a and b, and 14 a and b re-spectively. The driven gears 13a, 14a of each stage are con-nected by a common drive shaft 15, and the idler gears 13b, 14b of each stage are connected by common idler shaft 16. Molten hot melt adhesive is introduced, for example at atmospheric pressure, into low pressure side 17 of the first stage pump 11 from a hot melt source 18. A preferred hot melt adhesive source for use with the improved pu.mp of this invention is illustrated i.n Scholl U.S. Patent No. 4,009,974, entitled "Method and Apparatus for Pumping Viscous jr/.~--9~

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Material" and assicJned to ~he assignee oE this application. The I adhesive is delivered at the outlet side 19 of first pump 11 at ¦ a metered rate, and from there is introduced into inlet side 20 ¦ of the secolid stac]e pump. ~ clas, e.CJ.-, air, nitrogen or carbon ¦I dioxide, is also introduced into inlet 20 of second stage pump ¦l 12, through a c3as line 21 from a qas source 22 which may for example be at a pressure in the range of about 1-45 psi. Gas inlet line 21 includes a check valve 23 that prevents back flow llof molten adhesive from the first stage pump's outlet side 19 1I throuc3h that line 21 toward the cJas source 22.
The cJas and molten adhesive are intimately admixed in , secolld staye pump 12, which places them uncler such pressure that i the cJas goes into solukion with the molten adhesive, thereby I, providincJ the molten ~dhesive/gas solution previously discussed.
¦¦ This solutlon is ejected from the outlet side 24 of second stage pump 12 -throuc~h a line 25 to a valved adhesive dispenser 26, e.cl., ~ a gun or the like. One valved dispellser structure which may l~
,1 used wi-th the pump of this inventioll is illustrated in U.S. Patent , No. 4,059,714, previously referred -to. ~ recycle line 27 is pro-~!
I vided between the outlet side 24 of second stac3e pump 12 and the inlet side 17 of first stac3e pump 11. This recycle line in-ll cludes a relief valve 9 therein, for recycling a part or all of i! -the adhesive/cJas solution if the system pressure exceeds the relief settincJ of valve 9. A variable restl~ictor 2'3 in the return hose or line 26a from dispellser 26 restricts t}le recycle flow durin(J cycling of a Jun.
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,. i In eE:Eec-t, first stage pump 11 meters and delivers mo~ ten hot mel-t adhesive to the inlet side 20 of second stage pump 12. It stabilizes the second s-tage against viscosi-ty changes and motor speed changes. The second stage pump 12 functions as a mixing device for intima-tely admixing and pressurizing into solution the metered molten hot melt adhesive from first stage pump 11 with the gas infeed from source 22.
It has been found tha-t the combination of a first stage metering pump 11 with the second stage mixing pump 12 provides a more uniform adhesive/gas solution output, and that this in turn enhances the reliability and continuity of the adhes:ive foam output from the valved dispenser 26. In other words, this pump 10 structure improves the mixing o:E the adhesive and gas and insures that the foam dispensed will be very uniform and virt-ually free from spitting and spu-ttering~
More particularly, and with specific reference to Figures 2-8, the first embodiment of the improved adhesive foam pump 10 of this invention includes a series of special~y con-figured plates stacked on top of, and connected to, a manifold block 30. As shown in Figure 2, the pump 10 includes an inlet end plate 31, a first stage pump plate 32, a center port plate 33, a second stage pump plate 3~L, and an outle-t end plate 35, all of generally the same peripheral configuration and size, and all stacked one on top of the other.
Firs t stage pump plate 32 defines a pair of partiall~
overlapping circular gear cavities 36a, 36b, which receive a first pair of meshed gears 13a, 13b, as shown in F`igure S. The second stage or mixing pump plate 3~ defines a second pair of partially overlapping gear cavities 37a, 37b, which receive a second pair of meshed gears 14a, l~b, as illustrated in Figure 7. Note that in this embodirnent the gears of bo~-h pairs have ~ .
i r ~ i the same number of tee-th, but the gears 14 of second stage pump 12 are thic~er than those of the first s-tage pump. Since the gears of hoth s-tages rotate at the same rate, the second stage pump 12 has a displacemen-t greater than that of the firs-t stage. This ratio controls the maximum densi-ty oE the foam that is ultimately produced; lesser densities are produced as gas pressure is increased, because a greater mass of gas will then be compressed in the intertooth cavities of the second stage in relation to a given.mass of liquid adhesive from the first stage. Preferably the displacement ratio of the second stage to the first stage should be in the range of about 1.25-2; a 1.5 ratio is preferred. By way of specific example, the gears of both pairs may be 1.25" in pitch diameter, have 20 teeth, and be rotated at a speed of about 200 to 800 rpm. The gears of the first stage may be .200" thick and the gears of the - second stage .300" thick, which establishes a difference in displacement of 1.5 to 1. .The volume of gas delivered to the second stage from source 22 fills the additional displacemen-t volume of the second stage, i.e., the volume which :is in excess of the volume of hot melt received therein.
One gear 13a, 14a of each stage is a drive gear, and the other gear 13b, 14b is an idler gear~ The drive gears are connected by shaft 15, which as a connec-tor end 39 for coupling to a drive ~not shown). The first and second sta~e drive gears are connected to shaft 15 hy ~eys 40 received in ~ey-ways 41, see Fig. 3. Shaft 15 extends through bearing bores 42-44 in plates 31, 33 and 35. The two idler gears 13b, 14b are connected by a jr/~
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Il l l cornmon idler sllaft 16 ~llich icller shaEt e~ctends throuyh bearing bores 45-'17 in the inlet end plate 31 center por-t pla-te 33 and I outlet end plate 35 respectively. The icl:l.r r rlears 13b, l ~Lh ¦' may be connec ted to thc idler shaf t 16 in t.l-le sc~Lme fc~sh:ion as the drivr gear 13a, lla arr.-~ collnectccl to thc drive shaft 15, lnamely, by ~1 ball L0 allcl slot 41 key-~vay st:ructurr. NotL~ the I¦ drive 1.5 and icller 16 sha:Ets are parallel. In assembly therefore, - ~' rotation of the drivc shaEt 15 causes simul talleous ancl equal ¦ rotation of thr :Eirs t 13 and second 1~ stac~ ear pai.rs, the 1I rotation direction 2~ o~ tlle clrivc ~Jcars l.3 a 1.4a oE tlle pairs beincJ the same, and the rotational dir~ct:ioll 33 of the i.dler cJears 13b, l lb of th~ pairs heing the salne an(l opE~oslte to that ¦ ro-tational direction of the drive cJears, al] as illustr(lted in Figure 1.
~¦ The pump' s plates 32-35 are retained in alirJnecd stacked relatioll by four bolts 52-55 (see FicJs. 3-~) rec_ived therethrOUCJ~ llld illtO threadect hores 56 i.n the inlet ~nd plate ~l 31, -t'he heads 57 of those bolts beincJ receiv~d in scats 58 pro-vi.d~d in the C`lld pl.cl tc 35. Ihrou~lllL~o:Ll:-; 59 p~lss throuc~ll posi t.ionc~r )l sl~eve 48 .i.n p].ate boxes ~i'3, allc~ are tllrea(lcld illtO tc~pped bores Il :Ln tlle mani.~olcl blocl~ 30, sec~ PiCJ. 2, to Inol.lnt the preassemblecl ¦I plates 31-35 to the mc~rlifold bloc}; .
Tll~ l~orti.rlc~ of tlle :c:i.rs~ [)ulllp 1.0 e nlbodinlent: is illus-t-ratcd ~ rticu:Lc~rLy in Fic3ul-c~s 2 and 1~ sl~ l i.n Ficlur~s 2 cllld L~, the i llct p()rt platc 31 pr(!vicles ~I Eirst sta~Je llot melt inl.et port 60 thl-retllrou;Jll, that inlet porl cooper~tiJlcJ witll an allcJlc(1 .in.Eec(l thLc)al. G.L d( L:i.nccl .i.ll tlle l:ol) s~1:rEacc ol. tllat l~ort plate. i~ hood 62 i.s dispos::~d Oll top th~ inlL~t port vlate 31. to ¦ ! ' 1 ~
. i aid in directing the molten hot melt adhesive inflow into the first stage inlet port 60, as shown in U.SO Pa-tent ~,009,974 previously identified. Inlet port 60 opens into first stage hot melt inlet zone 63, where the gears come ou-t of mesh, as illustrated in Figure 2 and in phantom lines in Figure S. The first stage pump plate 32 also includes a first stage outlet zone ~4, ~rom which the metered molten hot melt adhesive is directed into intermediate transport port structure 66 defined in the center port plate 33, see Figures 2, 6 and 6A. The 1~ intermediate transfer port structure directs metered molten adhesive from outlet side 19 of first stage pump 11 to inlet side 20 of second stage pump 12. This intermediate transfer port structure includes first stage hot melt out port 65~ first to second stage transfer bore 66, and second stage hot melt in port 67, all defined in center port plate 33. The metered molten adhesive from first stage pump 11 is thereb~ introduced into second stage pump 12 from the top side thereof, as shown part-icularly in ~igure 2. The second stage pump plate 34 ~Fig. 7) further defines a second stage hot melt "in" zone 68 and a second stage "out" zone 69. The molten adhesive/gas solution outlet 76 of the second stage pump 12 is illustrated at Figures 2 and ~. The outlet port 76 cooperates with an outlet throu~hbore 77 in outlet end plate 35, and that outlet throughbore 77 connects the second stage outlet port 76 with discharge bores 78a-78c in .
the manifold block 30. The dischar~e bore secti.on 78b in the manifold block is connected with the valved adhesive dispenser 26.

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.` I ~ cJas in irltrocXueed into i~l.et side 20 of seeond , stacJe~ purnl~ 12 .L~rom tlle bottolll side thereof tllrou~3ll c3as inlet j''port 70, see .~ic~ures 2 and 8. The cJ(Is i.s clireeted to this gas inlet port 70 throu~JIl a eheek valve 23 and ~!as feed throuc~ll bores !1 21a-21e, the feed 1~OI^eS bei.n~J eonneet?d witll a gas souree 22 .land the eheek valve preventillcJ ba(kEI.ow oE molterl adllesive from jthe seeolld staqe L~um~ into c3as feed bores 21b, 21e upstream of , ¦jthat eheek valve. Chc?ek valve ~3 ineludes a ball 73 ur~3ed by a spriny 72 onto a sea-t, alld is reeeived in fittinc3 74 eaptured ¦.be-tween outlet end plate 35 and mani.Eolcl hloek 30, as shown in ¦IFic3ure 2~ ~n O-rinc~ sea]. 75 is l~rov.iclecl a.roullcl ~:ittin~3 7~1 between ou-tlet end ylate 35 ancl maniEold b.loek 30.
~3 ¦1 It is to be noted, in Figure.s 7 arld ~3, thclt the molten adhesive Erom the firs-L stacJe is fed by port 68 into the seeond stage gear inter-tootll sl?aees or eavities be~ore those spaees ~pass the gas inlet ~ort 21a, 70. Tlle sequellee of Eirs-t admittin~T
,l-the mol-ten adhesive into -the re.speetivc? too-th eavi-ties, and then ! eompleti.ng the fillincJ o:E the rernainill~J volume of the eavity with l~the gas, has been found to i.nsure thaL- the eavitie~s will reeeive ¦'the adhesive and qas at the intellcled rat.io. Fi.ll.in~l Eirst (or simultalleousl.y) ~i.th (las, beeause oE iL.s eomp:ress:i~ility, rnc-ly result in a clas "bll~ble" ~hiell ~-esist.s e~ ry of the llquicl into the ~arl:ieu:Lar clear tooth poe~et, allcl th-?rel~y may leacl to :Eoam in-homo(Jellei.ty~
;l rL'Il(~ I)r.i.m.l.~y F~o~ ~J.Itlll tllrc~ Ll~ L~ Llen hot ¦Imelt adhesive a11d o.E moltell adllesive/(3as solutioll onee that solu-.Itioll is c-l(lrlli~o(l ill t l l o s o c o l l cl S t a (J ~ , i .s illu,tlat(ld by phantolll arro~ ~() and l.eads to bore 7~3b ial the maniEold bloek ~hieh~
,in use is eonlle~eLe(l t:o a cJun. Ilo~ever, a reeyele .Llo~ atll is also~

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provided by which a portion of all ol' the moltell adhcsive/gas solution can be recycled back throuc~ the nump 10 from the gun, into the fi.rst StaCJe pump's inlet s.ide 17, as illustrated by dottecl arrow 81 in FicJure 2. (This dotted pa-th 81 eorresponds to the recyele path 25, 26, 26a, 28 ancl 27 in ~lgure 1.) For this purpose, reeyele passages are provided in :Eirst stage pump plate 32, center port pla,te 33, second stac~e pump plate 34, outlet end plate 35 and manifolcl block 30. ~s shown in Figures 2 and 5-8, this reeyele porting ineludes a reeycl.e l~ore 82 in the manifold bloek 30 tha-t eonneets bore 78c with a reeyele throughbore 83 in outlet elld plate 35. Recyele througllbore 83 ,l in outlet plate 35 eonneets with a reeycle t~lrougllbore 8~ in seeond staqe pUMp plate 3~1. Reeyele througilboLe 8~ in seeond stage pump plate 34 eonneets ~itl~ a reeye],e bore 85 defined in eenter port pla-te 33, ancl thi.s bore 85 in center port plate 33 I, opens i.nto a lateral passaqe 36 defined betweell f.irst stacJe pump plate 32 and eellter port plate 33, see Ficrures 2, 6 and 6~. The reeyele borinc3 82-86 eonneets with inlet si.cle 17 oE fi.rst stac~e pump 11, from the bottom surface oE first stage pump pla-te 32 a-t a reeyele in:Let port 87, see Ficlures 2 and 6, for introclueirlcJ reeyel.e ,Elow of mo.l.ten adl-leslve/gas solu:tlon Erom outlet 24 oE second stage pum~ inlto llot melt inl.et zone G3 whlle Eeed mo].ten adhesive (not in solutioll) is added to the reeireulatecl materia1. in Zolle G3.
The pressure relieE valve lnclleatecl at ~ ln T.'icJure 1 m~y l~ col~or~t~ q ~ t o~ c~ c~ v.~lv~ el~ e - r .
desigllatecl cJenerally at 130 in Fi~. 2 which i.s r.eeeived in bore 78c of maniLolcl 3(). rrl~:L~; circulation VLI1Ve structure inclucles an outer s:Leeve 182 whieh is threaded into bore 78e at 181. A
relief valve seat 1û3 is secure~l at ttle inner end oE sleeve .1.82, i.e., at its leftmost end in bore 78e as sceell in I;icJure 2. Seat 183 has an a~ial port 184 on whieh is seated a bal:l. 185. Ball 185 is bi.ased ayains~ port 184 by a c3uic1e 186 haVillC~ a erueiform shape, see Fic3. 2l~, whiell is in turn aeted upon by a spring 187.
Ball 185 is thereby biased toward its seat 184 to form the check valve 29~ ¦
Sleeve 182 is sealed with respeet to bore 78e l~y O-rincJs ¦178 and 179 around it. l~n internal ehamber 1.91 inside sleeve 182 ¦opens -throuqh the sleeve wall via radi.al ports 192 in-to eorrununie~-~tion wi-th recycle l~ore 82 o:E the mani.~olcl. In the event of e~-eessi.ve pressure builclup within the hoses or the clispenser, a high pressure eondition will exist a-t bore 7~J~. rl'his eondition will :~ be relieved by openilly oE the ball eheek va`Lve 18~1, 185 so that fluicl can flow throuclh bore 18~1, the interior 191 o:l~ sleeve 18~, ¦ and radial ~)orl:s 192 to reeyele bore û2.
¦ ils i.ndieated diacJrammatieal].y in F:i.g. 1, return line 26al .Erom valvecl d:ispenser 26 inellldes a vari.al)l.e restr;ieto:r 2~3. Pre-:Eerably, as shown in I~icJ. 2, this variab:Le restrietor 28 .is also ineluded as part of the ei.reulation valve slrueture 180. More speciEically, an adjustable val.ve rnember :1.93 i.5 a~ial:Ly position-able in the i.nterior of sleeve 182 to the r.i~)ht o.F ports 192.
~ Valve member 1')3 presellts a notell o.r (Iroove l94 at: its intler end, ¦ this groove h~lvinc3 a V-shape as seell in seetic>n, see Fi.clure 2b, ¦whieh forms a valve with a shou.lder 195 in sl.eeve 182. Noteh 194 z il , i,l i i can be positioned axially with respect to shoulder 195 by thread-ing valve member 193 into or out of the sleeve, to control the ~ area of the valve opellincJ. ~ lock nut now sho~n, is provided -to '¦secure the member 193 with respec-t to sleeve 182.
Manifold bloc~ 30 inclucles a yun returll passaye 197, ! which corresponds to line 26a sho~n diacJrammatically in Fig. 1.
!~ This passacJe 197 communicates with shoulder 195 through radial ¦por-ts 198 in sleevc 182. TocJether, tlOtCh 194 and shoulder 195 I form the variable rcstrictor 28 in the hose returll line 26a ~Iwhicl~ comMunicates throuyh ports 192 witli rcc~rcle bore 82. I`he axial position of valve member 193 with res~ect to shoulder 195 thus controls the proportion o Elow that ~ill be recycled.
use oE -the first ertlbo(1imellt 10 of the improved ¦ladhesive foam pump, when pump 10 is operating molten hot melt ¦ adhesive is introduced through port 60 in inlet port plate 31 into E:irst stclcJe purmp 11, via flow pa-th 80. The hot meli ad-hesive enterincJ the first staye pump may be at ambien-t pressure.

~he molten adhesive infeed is metered by the Eirst s-tage pump i ;and transferrecl throuyh portill~ 65-67 in center port plate 33 1~ i I to in:Let 20 of second stacJe pump 12. The yas is introduced in ' second stac1e pumL~ 12 ~ust af-ter introduct:io)l oE the metered lnolte !jl adllcsive Erom Eirsl stlge pump 11. rllhe pressure at which the cJas ¦lis introduced ~ill control the derlsity oE the Eoam; pressures in ,the rcnllcJe oE approximately 1-45 psiclllrlve a]~Aeacly been used. The secolld stacJe L~wllp 12 mixes the adhesive alld yas to provicle, under prcssure, a nlolten adll(sive/yas solutio~ hicll is c~haus~cd from I

~ I .

-l7-, the outlet side 24 of the second stage pump, into the dis-charge bore 78a of manifold block 30. When valved dispenser 26 is full open i.e., when it is discharging adhesive, relief valve 9 restricts recycle flow of the solution along recycle flow path 81. When the valved dispenser is closed~ i.e., when no adhesive foam is being dispensed, the pressurized adhesive/
gas solution recycles through valve 28, sleeve interior 191, recycle bore 82 in the manifold block 30, through rec~cle bores ~3-85 of outlet end plate 35, second stage pump plate 34, and center port plate 33, through passage 86 back -to inlet side 17 of ~irst stage pump 11. As can be seen from Fig. 5, when re-cycling occurs, the recycled solu-tion is introduced immediately at the point where gears 13a and b begin to come out of mesh.
The spaces between the teeth are filled with rec~cle material;
the feed material flowing from the molten adhesive source ma~es up the additional re~uirement to fill the spaces between the gear teethO Thus, in this first embodiment, the recycled solution flows through both the first and second pump s-tages 11 and 12.
A second embodiment of the improved adhesive foam pump and system, also in accord with the principles of this inVention, is illustrated in Figures 9-15. The pump 90 of the second embodiment includes a first stage 91 and a second stage 92. The first 91 and second 92 stage pump drive gears 93a, 94a are mounted on a common shaft 95, and are driven by a power unit (not shown). The irst 91 and second 92 stage pump idler gears 93b, 94b are mounted on a common idler shaft 96 and mesh with the respective drive gears 93a, 94a. The pumpls drive gears 93a, 9~a turn in j r ~
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the same rotatLc nal clirec ~ion, as in~icate~1 by arrows 10~, 105 ~l and thc-? id:l,er clears 93b, 9~1b rotat:e i.tl tllc oE)posite rota-tional !' direct:ion a~ indi,c:ated by arrows 1()~" 107.
Moltell llot melt tldllesivc~ is sur~l~Ji,cd to the ink?t side ', 97 oE Eirst stacle pllml) 9:L Erom 1110l tCII a~ e~-; i,ve c o~lrce 89 througl a variable rcs tric tor or valve 171. When tlle valved cli,spenser ¦ 109 is fully OpC?Il, t he Eirst sta~3e's metered output is delivered Erom first stacJe outlet side 98 throl,lcJh a variable restrictor 1' valve 173 to the inlc?t sicle 99 of second ~sta~e punlp 92. Gas 1l is introduced -to inlet side 9'~ of the secon(~ stac3e pump throuqh gcas line~ 101, a checlc valve 102 beirlcJ ~Jrovidecl in lille 101 to , prevent ad~sive 1O\" back throu~,~h the line ~owa~cl c~c~s so~rce 103.
,, , , The second s tac,le pun~)? admixes the mol ~en adhesive outL~ut Erom the I first stage pump' s outlet side 9c'3 with the cJas to provi (~e c~ pres-!I surized aclllesive/gas solution at the outlet side 10.3 for transEer I
!1 -to one or more valved dispensc?rs 109 . ( :rhis pllmp 90 is j~ar-¦l ticularly acla~ted for servincJ mult iple valvcd disc)en~sc?r outlets, , e.g., multipl~ cJ~Ins. ) I\ first stac~e recycLe path 111 connects , the outlet 98 oE l:lle Eirst st;ac~c~ ~:O t~le inleL 97 ~,-ia a variable I restrictor or valve 172. ~imilarly, a secolld stacJe recycle ua-th I¦ 112 COIlllC!CtS tll-? o-ltl~t sicl~ L0c'3 oE tllclt st~ to tllC? :inlc?t 99 ¦l of that stacJe, via a variable restricl:ol- or valve 17~.
Tlle seconcl embodimellt pllmp 90 di FEers Erom tlle First enlbodllllenl: p~llllL~ alllo~ other res~)c?cts~ ill t~le proviC;ion of pro-~, portionincJ valve mealls Eor l?ro~ort:ionately relcltil-lcJ the recyclt?
! Elows in patlls 111 an(l 112 to tlle first a~ S~COlld .Citc-l~lC?S
' respectively. '~ e ;~roport:iollin~l val.ve mc~ licll :is dc~.C;i.c~llcltecl, . I .

,, , 5~%

generally at 110 in Fig. 10, inc]udes a spool which forms a part of each of the valves 171-174. When all the dispensers of a multi-dispenser system are open, the proportioning valve 110 operates to block all recycle flow. When at least one but less than all the multiple dispensers is closed, proportion-ing valve 110 splits the first stage's outpu-t (prior to dis-solving the gas ? between -the recycle path 111 and the second stage. In doing this, valve 171 is partially closed and valve 172 is partially opened to establish the recycle path 111 -through the first stage pump. At the same time, valve 110 also ~perates to permit a similar proportion of the output of the aclhesive/
gas solution from the second stage to recycle within the second sta~e pump 92. It throttles or partially closes valve 173 and partially opens valve 174, thus establishing the second recycle path 112 through the second stage pump only. In opening recycle valves 172 and 174, spool 110 simultaneously ;~ tends to close valves 171 and 173. Thus, valves 171-174 are operated by the proportioning valve 110 to establish a separate recycle path 111 or 11~ for each pump sta~e, and to establish the same proportion of recycle flow to total flow in each stage.
In the situation where all valved dispensers 109 are closed, all of the molten adhesive delivered from the transfer port, first stage pump 91 is recycled back to the inlet side 97 of the first stage pump, and all of the adhesive/gas solution delivered from second stage pump 92 is recycled back to the inlet side 99 of that second stage pump. In this full recycle attitude, the valve 110 simultaneously blocks the molten adhesive inlet port from the source to the first stage pump 91~ and simultaneously blocks the transfer of molten adhesive from the first stage pump 91 to second stage pump 92.

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The pump 90 of the second embodiment fur-ther differs from the first embodiment pump 10 in that -the gears of the second stage have the same thickness as those of the first stage, ~ut the gears of the second stage have a larger dis-placement area by reason of a greater diame-tral pitch and fewer teeth~
By way of specific example, in the second embodiment the gears of both stages may be .250" thick and 75~l pitch diameter, with the gears of the first stage having 24 teeth and those of the second stage having 16 teeth. It will be noted t~at the ~ tooth rati.o establishes a 1.5 displacement differential or ratio; the same preferred ratio as was esta-blished in the first embodiment by thic~ness ratio. Tooth number ratio and gear thickness ratio are thus alternative ways of controlling maximum foam density.
The second embodiment pump 90 includes an inlet end ; plate 120, a ~irst stage pump plate 121, a center port plate 122 a second sta~e pump plate 123, and an outlet end plate 124r all secured together, assembled with first 93 and second 94 stage gear pairs therein, and connected with drive 95 and idler 96 shafts in the same manner as previously described in respect to the first embodiment pump 10. However, because of the proport-.
ioning valve 110, the porting of the various plates 120-124 of the se.cond embodiment pump 90 is significantly different from the porting of the first embodiment pump plates, as will jr/~

I

be describe~:l. rlle malliEold b].ock 125 oE tlle 5c?colld pump embodi- ;
ment 10 may be simi.lar to mani:Eold block 30 of the first pump embodiment, and i.ncludes similar ci.rcu].ati.orl valve s tructure 180 with a check valve 9 and a restrictor 28.
The check valve assembly 1.02 Eor cJas inlet line 101 is somewhat di.Eeren~ .in this second embod.:imellt l)uml~ 90, althouclh i t serves the same purl?ose . ~lere the chcck valve asscmbly in-cludes a sprinc3 :1.26 biasing a valve ball 127 in a charnber 128 defined by an inlet 129 :rr ceived in a fittillcr 130. Fitting 130 is captured between a recess 131 in outlet end plate 124 and a recess 132 in manifold block 125. Check Vcl].Ve assembly 102 opens at .its upstream encl into yas feecl bore 133 (which i.s inter-connected with cJas source 103) in mallifo:l.d bloc3c .L2.5, and opens a-t its downstream end into gas discharqe l)ore 132 in outlet end pla-te 12~1. The gas discharge bore 13~ leads to the c3as inle-t port 135 tha-t opens in-to the second s taye pump, see Figures 10, 14 and 15 . The chec}; valve ' s fit-tin~3 130 is provided witll O-rinc3s 137, 138 which seal with outl.et encd plate 124 and manifold block 125.
ll The portinc3 oE the pump's l~lates 120-12~-1 in th:is second embocliment, ~s previousl~ mentiollecl, is c1i.:Efcrent .Erom thc pOXtillC3 ill the :Eirst ernbodllnent. Inlet encl plate 120, as lllustrated in Fiyures 10 and 11, includes a feed throat 14û
for directing moltell adhesi.ve from adhesive source ~9 illtO first stacJe ho-t melt in:let port 1~ lo:ltell adllesivc l~lo~ hroucJh port 141 .Elows lnto a first hot mc Lt inle~ 9 7 ial l~irst .;l-a~le p~lmp plate 121 as s hown in l;`i(luxc~s 10 and 12. L)orl: :L~I:I. cll~crs whcrc the - gears are j us-t comin~ out o F mesl~ , i . e ., at wlla t is the ~ I
i ~ -22- 1 inle-t side of the first stage pump 91 by reason of the rotat-ional direction 104, 106 of ~he pump gears 93, as shown in Figure 12. The outlet side 98 of firs-t stage p~mp 91 feeds a port 143 defined in port plate 122 below -the first stage pump plate 121, as illustrated in Figures 10 and 13. The molten hot melt adhesive at port 143 is directed -through a first-to-second stage transfer bore 144 in center port plate 122, and passes from that transfer bore 144 through second s-tage melt entrance port 145 (see Fig. 10) into the second stage hot melt inlet 99 in : 10 second stage pump plate 123, see Figures 10 and 14.
The adhesive/gas solution formed in second stage pump 92 is delivered to .its outlet side 108 as defined by second ; stage hot melt out chamber or zone 147 in second stage pump plate 123, see Figures 10 and 14. E~rom there, -the mo~.ten adhesive/
gas solution passes through a second stage hot melt outlet port 148 into an outlet bore 14~ defined in outlet end plate 124 as shown in Figure 15. Outlet port 148 and outlet bore 149 connect with discharge bores 150a-150c in the manifold block, the mani-fol~d block being retained in sealed relation with outlet end plate 124 by O-ring 151, see Figure 10. The manifold block's discharge bore section 150 is interconnected with one or more valved dispensers 109 through hosing or the like, as described in relation to the Figure 1 system.
Valve 110 of the second embodiment pump ~0 and its associated porting are illustrated in Figures 10 lS. In effect, two recycle flow paths are defined in the second embodiment pump, the first recycle path circliny only first stage pump 91, as j r/~

illustrated by phantom loop 155 in FicJure 10 (analoclous to the reeyele loop 111 of FicJure 9), and the secollcl reeycl.e path eirelin(7 the second stacJe pulnp only, as i].1 ust.ratecl by phan-tom loop 156 (analoqous -to the reeyele loop 112 of Fic3ure 9). The first reeyele p~th 155 is -through first staqe hot melt outlet port 143, first-to-seeolld stage tral-sfer bore l~l4, and a first stac3e reeyele port 157 in center port plate 122. The second reeyele path 156 is through bores 149 ancd 150a and b -to -the dispenser 109, haek Erom the cdispenser via passage 197, through restrietor 28 to reeyele bore 158 in manifolcl bloek 125, and seeond stage reeye3.e bore 159 arld port 160 i.n plat:e 12~1. I'he first stacJe reeyele port 157 opens :into inlet ~.one 97 o ~irst stac3e pump 91, and second stage reeycle port 160 opens into inlet zone 99 of seeoncl stac3e pump 92.
Proportioning valve 110 ineludes four individual valve mealls. A spool designated generall~ hy lG5 forms tl)e rnovable valve member for eaeh val.ve, havi.ncJ lancls 161-163 and a stop lr"1 formed on it. The lands funetion in valving rel.ation with ports or passages 1~1, 157, 145 ancl 160 respec-tively. More speeifieally, shift:iny spool 165 moves land lGl between a Eirst position shown in FicJure 10, whereat the :Lancl eloses :Eirst st~ e ree~el.e port 157, and a seeond pOSitiOII (not shown) whereat the land eloses first stac3e ilOt melt inlet por-t 1~11. I,arld :lG2;s move~d 1~etween an open pOSiti.OIl StlOWIl in Fi~J. 10 and a seeoncl pOsit:ioll (llOt shown~ ¦
wllereat it: eloses seeond sta(le hot rnelt .irllet port l45. Third 'I
land lG3 i-: mc)ve~d l)c~ /oell a i~:i rst l)osi.tioll sl~o~ J. 10 wl~ereal;
it eloses seeoncl stac3e recyele port 160 ancl an open position (not shown). Stop lG4 .is moved be~w~een a Eirst position, shown in Fic3.

l~ -24-11 !

5~4~2 !

10 which locates tl~e spool l.65 in thc no recycle attitude ancl a second posi~ion (no-t sho~-~rl) W}liCh loc~es tllt spool in the ful.l recycle attitu(le. In the first pOSitiOIl stop lancl 164 is seatec:l against the top surface of outle- t end por~ plate 124 and in the second pOSltiOIl tllc sto~ land is seated acJclillsct the unclerside of the center port plate 122.
ovc ment oE spool 165 :is .I.oncJituclillal alonc3 its axis 166. ~ sc ries of tapered or collical st cti.on lG7-170 arc formed on -the spool adjacellt larlds 161 163 rcspcctively. Thus land 161 adjacent tapcred secti.on l.G7 Eo.rm~s valvc 171. witll port 191 and ad jacent section 16~ Corlll( valvt :L72 l~c tWCCII t:ralls~er l~ore 144 and inlet ~7. Land 162 adjacent taperccl section 169 forms valve 173 Ji.th por~ 145 below bore ].44, see ~ic~. 10. Lancl 163 adjacent -tape~recl section 170 forms valve 174 wi-th bore 159.
The lands 161-163 are all of the same diarlleter to seal with the~
bores in which they nlove; stop 164 is larc~er in diameter.
Bias means in the f~orm ol~ a sprintJ loaded plunger 175 is mounted to the pumU housincJ to bias spool 165 toward the no-recyclc pc)sition shown in Fi~J. 10 . P].un~lt. r 175 i.s sliclal~ly re-ceived in casincJ 176 arlcl is continuously hias.ed (lown~/arclly by a sprincJ. rhc p.Lullc3c-~r' s casincJ 17G i a(l justcll)J.y threadecl into an arm 177 projectinc3 :Erom inlet encl platc 120. Note thc? plunger 175 is movable lonc3i tudina].ly and i.s coa~ially a].icJned ~ith a~is 166 oE spool ].10 . PreEerab:Ly the sprincl ~i thin thc sprillcJ
loade d plullc~ o.. tal.~li.slles a l)ia ;in(T Eorcc col~res~ollclillc~ to a relativcly lo~ rec~cle ~res ;ure c.(l. 200-25n psi(~.

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'. ~
, ;9~2 . .
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In use, plunc~er ]75 urcJes spool l.65 downwardly so that stop :I.64 abuts tlle top face o~ the oul:].et elld plate 124. Tllis llopens flow patll :l54- and :fully closes recyc] e flow paths 155, 156.
¦IWhen mul-tiple dispensers are used ancl al.~. ~`lre open, the p~lmp will thus be .in the .~ttilude illust:rate(l in li~ure 10, wi~h the :Elow beincJ along patll ]5fil. In this full oper) attitude, fresh molten hot melt adhesive is introduced into the first stage gear pump ~1 throuc3h ~fi.rst stage hot melt in]et port 141, and . I' from the first stage pump t:llrougll transfer bore 144 through I second stacJe hot melt inlet port 1~5 into tl~e second stage 92 , at in3e-t slde 99 tlleLeo~. Ga~ i.ntrocl~lceEI i.nto secc>ncl stage throuc~h gas inlet. port 135. 'I`he secoll~l s~clge ~umL) 92 aclmi~es the molten hot melt adhesive ancl CJaS .into solution form, and Il discharges same throucJIl port 148 into bore 150a of manifold block 125 . Wi th all adhesive dispensers Op~?n and cllspensing I adhesive foam, no ~ack pressure builc'lup is ~xpcc-tecl to occur, and there is ordinarlly no recycliny.
; When one or more but less than all valved dispensers 1~ 109 are closed, -the pressure in Manifold block 125 rises and , acts a3ainst the end area o.~ spoo]. 1~5, agairlst the bias of spring loaded plunger 175, and slli.fts Ll-ie spool uL~warcl.ly. Lalld ; 163 moves away ~rom c:LosincJ relation witll sec(~l~cl sta(Je recycle ort 160, pclrtia:Lly openincl that port to recycle E:Low. By the same movement o:~ spooll6~, tl~e :Eirst sta(le llo~ me:Lt rccycle port i 157 is cllso l~art:ial:Ly OpellC`CI alld e';tal~Li'~ eC'ICle El0~7 o:E
I molten hot mc?lt adl)esive witl~in the Ei.rst st,~(le pump 91.

, lj .
l l ' Simultancously sceollcl Sta~C? hot mc~l.t :i.nlc~l E)orl l~i5 is partially elosed -to flow ~rom the :Eirst St.?(~C pump 91 -to the seeond stage pum~) 92. ~lso, the hot melt inl.et port 141 to first stage pump 91 i.s partially elosed to :Elow from molten ad~lesive sourcc b9 to tllc f i L-'i t slac~e L~llrllr) 91. Th~? v~lvc?s 172 and 174 open i.Fl proportion to the amount valves 171 ancl 173 elose. The po.si.L.ioll o.E spool L65 is eo]ltrol.lecl by thc? pressure in reeyele ~ores 158, 159 OnCC:? that ires7;urc cYeec?(ls the pre-established sl?rln~l bias on plunclc?r 175. rrhe spool 165 ean thus shift be-Lween the fu:ll ol~cn ~.-oC;.tioll ;hown in ~.ic~.l:rc? 10 alld a full elosed pOXitiOIl ext~blisllc?d whc?ll stol~ :LGl ~?~ul ec?lltc?r port plate 122 in rcsponse to the reeyelc flo~ or baek pressure of ..
tne adhesive/gas solution whiell i.n turn is res~onsive to -the proportion of adhesi.ve dispense.rs elosecl.
When al]. dispensers are elosed pressure of the adllesivc?/yas solution out~ut from the seeon(l 7 tacJe pump forees spool 165 up~ardly ac~ainst the bias oE sprinq loaded plunger 175 until stop l.G~ abuts eellter port plate 122. In tlli.s at-titude valves 174 anci 172 are full OpC?Il. ~t thc? saFllc time, valves 171 alld L73 .~r~? e~osed tllerc?by eomlllc?tc?l.y SC?~l i i.lly :Eirst st~c~e ~ump 'il from '7eCOn~ stacJc? puml~ 92. :LII:is pc?rrl~itC; moltc?~ ot me].t adhesive withill the first stacJe pump to l~c? reeyeled the.rein along r~?eyele ~low ?i~a Lll 155, illdc?p~llcl~ tly of L llc? ~clllc?sivl?/c~as solution :
incJ L-eeyel~?cl till.c)llcJIl t~-e SCCC)II~I X t~ C ~ ')2 .-llollc~ l.eeyel~?
.Elow p:ltll 15~.

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. 1.
~ I I

Tllrougl-lout this specificatiorl al-lcl cl.a:ims, the tcrm "solution" has been used to clescribc the molten liquicd adhesive/
gas dispersion supplied under hicJh pressure whi.cll, when dispensed from a dispenser at atmospheric pressurc, will provide a foamed adheslve. It is believed thls mi:~ture is a true solution in which the yas is molecularly clispersecl in the li.quid aclllesive. llowcve~., as used in the s~eci.fication arld the~ clai.mr; hereof, tlle term is intended to encompass the broader concept o.E a gas homogeneously I mixed with moltell liquid adhesive, whether or not the gas is in , ~act moleculcl]:ly dis~)cr-ecl. I~ rt:her, thro-lcJIIollt this sl~eciEica-- 1, tion and claims the phrase "hot melt ad}lcsive" has been used as ~ meaning a solvent~Eree material which is apE)lied in a mol-ten ¦ state.
ElavincJ described in detail thc r)rc:Eerred embodimen-t of j! the invention, what is dc-si.red to be claimed and pro-tected by Letttrs Patent i~:

.1 ~

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1, .1 .
I _ ~ Q _

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH IN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED IS FOLLOWS:

1. A dispensing system for mixing a gas with a liquid and for pumping the resulting mixture to a dispenser comprising, first and second stage gear pumps each having an inlet and outlet, a passage for supplying said liquid to the inlet of said first stage pump, means for delivering said liquid from the outlet of said first stage pump to the inlet of said second stage pump, means for supplying said gas to said second stage pump for mixing therein with said liquid, means for delivering said mixture of gas and liquid from said second stage pump to a dispenser, and recycle means for at least partially returning said mix-ture from said second stage pump, through a recycle passage to the inlet of said second stage pump when said dispenser is not dispensing all said mixture supplied to it from said second stage pump, the mixture recycled to said second stage pump bypassing the first stage pump.

2. The dispensing system of claim 1 in which said liquid is a molten hot melt adhesive and in which said gas is selected from the group consisting of nitrogen, carbon dioxide and air.

3. The dispensing system of claim 1 including valve means interposed in said recycle means, said valve means functioning to restrict recycle flow through said recycle means when said dispen-ser is dispensing all of the mixture supplied to it by said second pump.

4. The dispensing system of claim 3 wherein said recycle means includes a return line from said dispenser, said return line including a circulation valve.

5. The system of claim 1 wherein said recycle means includes a pressure operated valve responsive to the pressure of said mixture, for opening said recycle passage when said pressure exceeds a predetermined value.

6. The system of claim 1 wherein said recycle passage delivers the recycled mixture to the inlet of the first stage pump, at a position which is upstream in the direction of gear rotation, of the position at which said liquid is delivered to said inlet.

7. A dispensing system for mixing a gas with a liquid and for pumping the resulting mixture to a dispenser comprising, first and second stage gear pumps each having an inlet and outlet, a passage for supplying said liquid to the inlet of said first stage pump, means for delivering said liquid from the outlet of said first stage pump to the inlet of said second stage pump, means for supplying said gas to said second stage pump for mixing therein with said liquid, means for delivering said mixture of gas and liquid from said second stage pump to a dispenser, and recycle means for at least partially returning said mixture from said second stage pump, through a recycle passage to said second stage pump when said dispenser is not dispensing all said mixture supplied to it from said second stage pump, said recycle means connecting the outlet of said first stage pump with the inlet of said first stage pump, and connecting the outlet of said second stage pump with the inlet of said second stage pump, said liquid being recycled through said first pump and said mixture being recycled through said second pump.

8. The dispensing system of claim 7 including restrictor means interposed in said recycle means, said restrictor means functioning to restrict recycle flow to both said first and second pumps when said dispenser is dispensing all of the mixture supplied to it from said second pump.

9. The dispensing system of claim 8 wherein said restrictor means is variable, the variable restrictor means permitting an increased amount of recycle flow through said first and second pumps in response to decreased draw through said dispenser, and permitting a decreased amount of recycle flow through said first and second pumps in response to an increased draw through said dispenser.

10. The dispensing system of claim 9, said restrictor means comprising valve means adapted to close the inlet of said first pump to liquid supplied thereto, and adapted to close the inlet of said second pump from the outlet of said first pump, when none of said mixture is being discharged through said dispenser.

11. The dispensing system of claim 9, said restrictor means comprising a spool valve structure to cooperate with porting structure formed in part by pumping chambers of said first and second pumps, and bias means adapted to bias said spool valve to a full open position when the entire output from said second stage pump is being discharged through said dispenser, thereby closing said recycle means to recycle flow.

12. An improved hot melt adhesive foam pump system comprising a pump having an inlet and outlet, means for supplying molten hot melt adhesive to the inlet of said pump, means for supplying gas from a gas source to said pump, said pump being operable to mix said gas and said molten adhesive and to force said gas into solution with said molten adhesive, means adapted to supply said solution of gas and molten adhesive from the outlet of said pump to the inlet of a selectively operable dispenser, recycle means for connecting the outlet of said pump with the inlet of said pump, said recycle means providing a path for recirculating said solution through said pump when said dispenser is not dispensing all of the solution supplied to it by said pump, and valve means interposed in said recycle means, said valve means functioning to restrict recycle flow through said pump when said dispenser is dispensing all of the solution supplied to it by said pump, said valve means increasing the rate of recycle flow through said pump as the rate of solution discharge through said dispenser decreases, and decreasing the rate of recycle flow through said pump as the rate of solution discharge through said dispenser increases, said valve means including a valve which closes the inlet of said pump to incoming molten hot melt adhesive when none of said solution is being discharge through said dispenser.

13. An improved hot melt adhesive foam pump system comprising a pump having an inlet and an outlet, means for supplying molten hot melt adhesive to the inlet of said pump, means for supplying gas from a gas source to said pump, said pump being operable to mix said gas and said molten adhesive and to force said gas into solution with said molten adhesive, means adapted to supply said solution of gas and molten adhesive from the outlet of said pump to the inlet of a selectively operable dispenser, recycle means for connecting the outlet of said pump with the inlet of said pump, said recycle means providing a path for recirculating said solution through said pump when said dispenser is not dispensing all of the solution supplied to it by said pump, and valve means interposed in said recycle means, said valve means functioning to restrict recycle flow through said pump when said dispenser is dispensing all of the solution supplied to it by said pump, said valve means increasing the rate of recycle flow through said pump as the rate of solution discharge through said dispenser decreases, and descreasing the rate of recycle flow through said pump as the rate of solution discharge through said dispenser increases, said valve means comprising a spool valve cooperable with porting in said pump and bias means urging said spool valve to a closed position restricting all recycle slow when all solution delivered by said pump is being discharged through said dispenser.

14. An improved hot melt adhesive foam dispensing system comprising a first stage metering pump and a second stage mixing gear pump, each said pump having an inlet and an outlet, means for driving both pumps at the same rate, means for supplying melted hot melt adhesive to the inlet of said first stage pump, a passage for delivering molten hot melt from the outlet of said first stage pump to the inlet of the second stage pump, means connectable to a gas source to supply gas from said gas source to the inlet of said second stage pump, said second stage pump being operable to mix said gas and said molten adhesive and to force said gas into solution in said molten adhesive, said second stage pump having a greater displacement than said first stage pump, said gas being suppled from said gas source to the inlet of said second stage pump at a position which is down-stream in the direction of second stage pump gear rotation from the point at which molten hot melt adhesive is delivered to the inlet of the second stage pump from the first stage pump.

15. The improved system of claim 14 wherein the displacement of said second stage pump is in the range of about 1.25 to 2 times greater than that of the first stage pump.

16. The improved system of claim 14 wherein said second stage pump has gears which are at least 1.5 times thicker than the gears of the first stage pump, thereby to provide said greater displacement.

17. An improved hot melt adhesive foam dispensing system comprising a first stage metering pump and a second stage mixing pump, each said pump having an inlet and an outlet, means for driving hot pumps at the same rate, means for supplying melted hot melt adhesive to the inlet of said first stage pump, a passage for delivering molten hot melt from the outlet of said first stage pump to the inlet of the second stage pump, means connectable to a gas source to supply gas from said gas source to the inlet of said second stage pump, said second stage pump being operable to mix said gas and said molten adhesive and to force said gas into solution in said molten adhesive, said second stage pump having a greater displacement than said first stage pump, and recycle means for recycling the output of said second stage pump back to inlet of said second stage pump and bypassing said first stage pump, and for recycling the output of said first stage pump back to the inlet of said first stage pump and bypassing said second stage pump.

18. An improved hot melt adhesive foam dispensing system comprising a first stage metering pump and a second stage mixing pump, each said pump having an inlet and an outlet, means for driving both pumps at the same rate, means for supplying melted hot melt adhesive to the inlet of said first stage pump, a passage for delivering molten hot melt from the outlet of said first stage pump to the inlet of the second stage pump, means connectable to a gas source to supply gas from said gas source to the inlet of said second stage pump, said second stage pump being operable to mix said gas and said molten adhesive and to force said gas into solution in said molten adhesive, said second stage pump having a greater displacement than said first stage pump, recycle means for recycling the output of said second stage pump back to the inlet of said second stage pump and bypassing said first stage pump, and for recycling the output of said first stage pump back to the inlet of said first stage pump and bypassing said second stage pump, said recycle means includ-ing a proportioning valve for maintaining the same proportion between the rate of recycle through the respective pumps to total flow therethrough.

19. A system for mixing a gas with a liquid and for pumping the resulting mixture to a dispenser, comprising a first stage metering pump and a second stage mixing pump each having an inlet and outlet, a passage for supplying said liquid to the inlet of said first stage pump, means for delivering said liquid from the outlet of said first stage pump to the inlet of said second stage pump, means for supplying said gas to said second stage pump for mixing therein with said liquid.
means for delivering said mixture of gas and liquid from said second stage pump to a dispenser, and recycle means for returning said mixture to said second stage pump when said dispenser is not dispensing all said mixture supplied to it from said second stage pump, said recycle means including a pressure operated spool valve responsive to the pressure of said mixture at the outlet of said second stage pump, for opening a path to at least partially recycle said mixture to said second stage pump when said pressure exceeds a predetermined value.

20. The system of claim 19 wherein said first and second stage pumps are gear pumps which are in axial alignment with one another, said pumps being housed in a series of stacked plates with said first stage pump disposed above the second stage pump, and said valve is disposed in a bore in said plates which is parallel to but offset from the axis of said pumps.