CA1150922A - Mold for injection molding - Google Patents

Abstract

T I T L E
" MOLD FOR INJECTION MOLDING"

ABSTRACT OF THE DISCLOSURE

A mold for injection molding of plastic articles which are automatically numbered or coded without repeating the com-binations. In accordance with the invention one half of the mold comprises concentric ring rotatable about a reference axis perpendicular to the mold surface, the rings forming portions of the mold cavity in equally spaced positions about said reference axis, each ring presenting in the interior of each cavity a marking that is different from those that it presents to the other cavities, means for rotating one of said rings by increments so that its markings are presented, one by one, to said cavities, and for rotating each other ring by an increment each time the previous ring completes a revolution, in a manner similar to a mechanical counter, and actuating means to actuate said rotating means by an increment for each cycle of separation and approximation of said mold halves.

Description

9;2~

The present invention relates to the injection mold-ing of plastic articles numbered or codified in some other way, using a multiple ca-~ity mold, ~ mold is already known in which the cavities are arranged in a row and are traversed by hardened steel bands appropriately engraved with nurnbers or letters so that each band presents a number or a letter to each cavity. The bands are eontinuous, moving around suitable wheels provided at the ends of the mold, whereas the return portions of the bands do not pass through the cavities, but rather behind the mold.
Between each molding operation the bands are moved to present the next number or letter to the cavities. This type of mold has various disadvantages including a compex system for actu-ating the bands, which is partly hydraulic, partly electromag-netic and partly mechanical. Sequential numbering or codifi-eation of the produeed artieles is taken into eonsideration when engraving and controlling the bands.
The objeet of the present invention is to provide a simplified and extremely effieient mold to make multiple mold-ings, producing nurnbered or codified articles and, in a pre-ferred embodiment, without repeating the eornbination - to the highest possible number - but without taking into eonsidera-tion the sequc-~ntial production thcrcof.
~ecording to the prcscnT invcnLion a mold ~or injec-tion molding comprisirlg two halvc?s of a mc)ld scparabLe aTtcr eaeh molding operation arld having mating suria(c~s which definc therebetween a plurcllity of molding cavitics and injection ehannels opening into saicl eavitics, is chaL~actcri~cd by the faet that it eomprisc~s c(~ncel-ltric ~inc3s in a first of said mold halves, rotatable about a rc.~fercrlcc axis pcrper~dieular to said mating surfaccs and forming portions of said eavities in positions equally spaced around the rcference axis, each ring presenting to the interior of eaeh cavity a marking that is different from those it presents to the other cavities, means to rotate one of said rings by increments so that its markings are presented, `~' ~." -1-~5~3~ZZ

onc by one, to silil C.l\,iti.Cs ;ln(l ~or rOt~lti.llg C;lCh Ot~ r ]'ing by ~n increlllent elc]l t:ime the plCViOIls ring complet:es a revo:lll t:ioo, in a manlier simi.]ar ~o c~ mecll~nical count.er, ilnd act~ ting means to .ICt u;lte said rotating meilns by a]l increment for e~c]~
cycle of separation and approxi.mltion of said mold halves.

Preerably, the rings - every one of.whicll may be prov:ide(l lTith markinp, in the for~n of numbers or letters se~uentially dis-tributed around it - are fitted and tightened against e~ch other when the two mold halves are brougllt together to.place their mating sur:~ace in contact with eac}l other.

In order to make sure that there is no re~eti.tion of num~)el or letter combinations bet~een t]lC cavi.ties, eacll C~lVi ty is al-ready l~rovided with an engravel n~lber or lctter ~]l:iC]l does not move Witll the ri.ngs. ]:n this ma]l]ler the mo1d Ca]l nrO(lUCe, I~'i tllout repetition, the higlleit possible n~lml)er Or coml)illltiolls USillg the marking existing on the ri.ngs a]l(l the cavities.

In the preferred embo]i.ment Or t]-e ;.nventioll the mol(l has t:oll eavi.ties traversed by six rings eacll one of thelll engraved l~:ith thenumbers 0, 1, 2, 3, ~, 5, 6, 7, 8 clnl 9 or witll the letters A, ]3, C, D, E, F, C? il, I and J, all the ZCI`OS, a1 I the OIlCS, ete., being positi.o]lecl at the itilrl: Or the ] I'Odl.lCt:iOII i]l a l i]lC' along radii extcn~lirlg rrom sai(l rercrcllcc ;l~i~i ill thc dire(t:iOl) oE the eaviti.es alrel(ly l-ermlllel~tly Cllgl`;lVCd t~itl) tl~c llUllll)Cl''i (), 1, 2, .... 9 respcctively. l`herefore, in ~he ri,~s, mOl(l;lllT ol,cr~, tion, the ~en ;ll`tiClC!i l)l`OdUCCd .IrC nUllll)CI'(`(l nono .... 9999999, the .Ci.lst n~lmber l-e.illg tll(` OllC I~Crl'l.lll(`llt l.y Cllgl;lVCC
in eaeh envi.ty and the o~lleri those Or tho r.ingi.

Preferably, t:he firit ri.ng to rot.lte is the one t:hlt pro(lll~oi the seeond n~lm~er of the seri.es (the f:i.rst beillg the fixe(l OIIC) so that in t.he next moldin~T~ operltion tlle ten articles pro(lllce(l shall be nulllbered 0100000, 1211111, 2322%22 ... 9099999. I~hCII
the first cavity is already producing 0900000 and tlle last 07le 9899999, the next cycle of o~cning and closing thc mold T~ill also move, by one increment, the second ring, so that articles shall ~L~5~9~2 L~e procl~lccd Wit]l thc nlllnbers 00]()000, 1,12]l11 ... 9'.)0~

rl'he rcsult o~ ~iSillg 'I numbcring systelll o:E this tylc is that there are no repetitiolls o~ thc coml)i]lations until ten Illi].liOJl articles have been ~roducecl numberecl ooonooo to 99~9~99.
~:urthermore, tlle articles are being produccd wit]lOIlt a numerical segucncc, but without repetitions, W}liC]I is of great valuc ~hen the articles are to be used in security and it is undesirable for third parties to know beforehancl the numl~ers of the next production in a series. This is of great advantage in the ~roduc tion of securi,ty seals, for instance SUC]I as those describc~l in the US patent nQ 4.106.801.

The invention will now be descr;bed in greater detail Witl reerence to the accon~p~lny;ng ~lrawings, in wll;cll:
igure 1 - is a cross section v;ew of a mo]cl constl~lctccl accold dinll to a prcferre(l cmbodmcl-lt Or the invc]ltion, l~lken a]ong line I'-I of l`igurc ~;
igllre 2 - is a p],an v;cw of t}lC r~,cc O onc halr Or tl-c mol(l S}IOWII i.n F igll re l;
ig~r~ 3 - is cl p~ vic~ Or t.}~c r;~cc Or t.ll~ o~ r ]~.~]r Or tllc~
Inol(l sl~owll .i l~ }~
ig~lrc 4 ~ O~:t)lll Vi.CW ~r tl~ iV(~ ~C~It: or ~)c Oll~.CI' l'illg Or t]~ lol.c~ r ~l~o~ iTl ~ llC -');
ig~lrc 5 - is hOttOIII V:i.C~ O.r OllC Or tllc othcr gcars; an(l igut:e 6 - ;s a si'dc Vi.CW of thc molcl in a scmi-ol)cll positio~

With reference to the drawings W}li.C}I S}IOW a ~rcrcrred embodi-ment of the invention, a circular injection mold comprises two circular mold halves 1 and 2 having mating faces at 3 and defining there betwcen ten cavities 4 (machined in half 1) for molding nullll)ered labels. As better shown in Figure 2, the cavities 4 define blade forming ~arts 5 which are disposed radially round the center of the mold.

~5$9ZZ

The mold half 1 is the movable part when mounted on the injection machine and the half 2 is stationary and has a nozzle for central injection 6. The half 1 is formed with an internal cavity 7 provided with a sliding plate 8 from which a main ejector pin 9 and ten pairs of secondary ejector pins 10 project which pass with precision though corresponding holes in half 1 as far as its face. The main ejector pin 9 is aligned with the injector nozzle 6 in the other half 2 of the mold whereas the two ejectors 10 of each pair of secondary ejectors enter a corresponding cavity 4.
The ejector carrier plate 8 is itself mounted on a metal part 11 which passes through a hole in the rear plate 12 of the mold half 1 where it is provided with a head 12a whose diameter is bigger than that of said hole and is held away from plate 12 hy a spring.
The faee of mold half 1 is formed with ten channels or grooves 13 starting from the end of the hole traversed by the main ejector pin 9, eaeh channel 13 ending at a restriction 14 where it enters the blade forming parts of the corresponding cavity 4.
Reverting to the second half 2 of the mold, it has a sandwieh structure, comprising a front portior, which defines the face, an intermediatc? portion wherc? the numberinc3 mechanism is mountc?d and a rear OL bas~ port.i.on which iS cc~)nrlcctcd w:ith the injection systc=?lrl of the inie?ction machin(? (not shown). The front portion compriscs an outer :ri.n(~ 1.5 prov:i.clecl with an outer flange 16 for an e~act posit:ioninc~ of the othc?r half 1 of the mold, and a srnooth flat face mat:ing witl-l the faCC? of h<~llf 1.
Around the inner border of this smooth face the ring 15 is formed with ten srnall cavities whcrc? part 5 of ~?ach cavity 4 machined in the other half 1 begins. Elerrlents 17 individually engraved with the numbers of the cavities ( O, 1, 2, 3, 4, ... 9), are firmly placed in such small cavities.

~5~!~ZZ

Inside tl~e r:i]lg :l5 tJlerc~ clre si.x t-)liJI Cy] in(lrie.ll r:incgs ]8 1' 21 22 c1n(l 23 r~dially sp];t (It 60 as S]lOWIl i.n ]~Igure 3.
T]le inllerlllost ring 23 is ~orme(l wj.th an internll eonie.l]. ].i.p 2~
whicll eooperatc~s w;.th a frusto-conieal member 25 whie]l eomp]etes the ront port:ion o~ hcllf 2. All of ri.ngs 18 to 23 are engr(lved at equal angular intervals with tlle ten numbers 0 1 2 3 4 5 6 7 8 an(l 9 so that when correetly al.eglled the rings toget]ler with tl-e engraved elements 17 make up eombinations eomposed Or seven numbers along the radial lines eorresponding to parts 5 of the eavities ~ (see ~ig~re 2).

Frusto-eonical member 25 has a eentral bore havillg eylindrie<l]
and eoni.cal parts separ(lted by l step 26. I`he eonie~ll part ancl the step 26 eorreetly pOs:it;.oll tlle ;nller encl of tlle injeetor nozzle 6 wllen thc~ mo].d is closecl the step 26 serving also to support one end Or a eomT)ression spr;.ng 27. The intermed;.ate plrt of the mold hal.f 2 ine~.udes fixecl to thc~ h.lsc plate 28 by tllree serews 29 (only one bcing visih].e in ligure 1) a su~l)ort member 30 having a two di.allleter bore tllat is a lowc?r l)oltioll witl smal].er cliameter and an upper port:i.on wit}l a bigger d:ianlet:er separated by all intcrllal fl<lllge 31.

The otl~er (lower) end s<l:i(l eompresxion spr.ing 27 Iresses ag<l-ins-t the upper surfle.e o:C rl<ll~ge 31 wllere<ls t.l~e he<l(l Or t]lC ;njeetol nozzlc 6 is helcl :in s.~i~l gl`C<ItCI cliamc!t:er l)ortion Or t:ho bole :in support Illel111)el` ~'i;O. '~ C Col~.iC<lJ. IIICIIII)CI` 25 - b~ l';ed Ollt~ lrdy l)y spring 27 - h.ls its movelllel)t linlitecl l~y ll~ree S('l`CI~'; 32 ( Ollly one l)eillg visi.ble in l:ig~lre 1) whose llC(l(lS :rl`CCly (`llt.(`r thc CclVi.ti.C)S 33 in sul~port mellll)er 30.

The said intc?rllledilte p<ll~t o~ tlle mol.cl ll;llr 2 ineln(les as wel.l an outer ring 34 fixed between t:lle base pl.lte 28 all(l the ouler ring 15 of the front part. Saicl r;.ng 34 is spaeed from sup~ort member 30 to.define an anllular spaee eontailling six geclrs 35 36 37 38 39 and 40 provided witll centr~l slecves projecting upwardly and having diameters ;.dentical to thosc of the co-rresponding rings 18 19 20 21 22 and 23. Sleeves 35 to 40are coupled Wit}l the corresponding rings 18 to 23 by means of pins projecting downwards from each ring which penetrate small .. . .

~56~92~

ra(lia1 sl:its in t}le eorresl)oncl:i.ng slecves W}liC`I~ l~c~'mil-s a limit(?cl C'Xp~lnSiOll or eontrJet:i.on oL tlle ring W]l:iCi~ is sl)1i.t-at 24 ( I:igure 3 ). I`hc ~ears 35 to 4n wllic~. arc s~lsce~t~ c to rotation in re]citi.on to eaeh otller round the su~lort mc ber 30 eool~er~te i.n a manner that ~i1]. ~c deseribed 1ater wit]l ~ group of fi.ve identiea] toothed sproekets 41 42 43 44 and ~5 moun~ed onc on tol~ of the ot]ler on a bearing l~in ~6 fixed to base p1ate 28 by a serew 47. The set of sproekets is housed in a eavity in ring 34 outsicle the spaee where tl~e gears are housed.

The upper gear 35 W]liC]I drives the outer split ring 1~ is S]lOWil from bel.ow in ~igure 4 whcrc it ea~l be seen thlt it is prov:icled wi.th ten ratehet tCCt]l 48 so th.lt the rotation O.r tlle geal th~ 0ll~]-an ang]e eorrespondi.ng to the p:itch Or t]~c,~ tec?t}l will move tlle numbers engraved on the ring 18 from OllC eavity 5 to anotller.
Ilowever the ratehet tceth 48 are formed on1y in thc u~pcr llal.r of the gelr 35 the lower ~art l>einr frec? of tCCt]l Wit]l thc? cxee~
tion of six gëar teeth ~9 throu~}l all ang1e 1imitec} by thc I)iteh of the ratehct teeth 48.

The ratcllet teetll ~8 eoopcr.lte Wit}l two di;llnetr:iea11y o~osecl ~aw~.s 50 alld 51 Or wh:iell l)al~l 51 fixes t:he gcar in eaeh l)osi-tion a~ awl 50 (}I':iVCS ~}IC gC~II` by IIIC~I~IS of a S ~ c 52 il~ i ts turn drivell ly I lever 53 intcgtl1 t.}lercwit}l. I`l~e two ~tlwl.s 50 and 51 allcl the s1i(1e 52 .II`C dllly IIIOUIltCd ill a~ rOI)ricltC
eavities in the outer rin~ 3~ Or t}le i.llterllle(li.lte l)ortion Or 1110ld }l;ll.r 2, the lever 53 I)rojeeti.ng r.l(lillly outwar(lly thercl`rom .
.
rhe si:x tec~th ~9 o:f the gelr 35 COOI)Cr~ltC onc'c for every rota-tiOIl thcreo Wi.t}l thc~ u~l)er half of tllc toothed wheel 41.
Eaeh on of the toothed wlleels has 40 teet}l so th.lt at the encl o eacll rcvolution of thc gear 35 thc teeth 49 rotate the whccl 41 a ~raction of a revolution.

~igure S is a bottom view of the second gear 36. It has eighty teeth 54 of W}liC}I only six indicated by reference 54' have thc ~5~92Z

eomplete heig]lt of tllc~ ~e.lr. 'I'he tee~h 5~ h.lve the sanle piteh as teet]l 49 a3~(l n~ecill perm.ll-lent]y Wit]l the :lower hcl~.r Or thc~
teet]-l of toothe(] wlleel ~1 so th.lt or eaeh inerement Or the revoiutio]l Or w]lee] 41 gear 3G and ;ts eorl-esl~o]lding r;ng l~
are rotatccl one te]lt]l o~ a revolutioll. 'rhe ]ower hal~ Or tlle six teeth 54' mesh w;th the up~er ]~1f of the next toothe(l whee1 42 whose lower half meshes perm~ne]ltly with the uI?per p~rt of the next gear 37. This gear ancl also gears 38 ancl 39 ale identi-eal to gear 37 exeept for their internal sleeves W]liC]I have ~rogressive]y .smallcr (liameters where.ls gc~r 40 being t]le ]ast and not being re~luire(] lo eoopelate with two w]leels is only provided with teeth of maxi.mum ]ICi g]lt.

Eaeh one of ~]le geals ~S 36 ~7 38 39 and 40 is also assoe:iated with a eorrespor~d;n~ sprin~ hi~lsecl pawl. 55 wh;eh eooperateci Wi.t]l tlle tCCt]l 54 to a]:i.rle anc?J ste.lcl~ t]lC corrc~s~onclill~T gc~lr ancl numberc?cl r;ng aft:er eaeh il~eremenlnll advallee. These four paw]s 55 are alinecl vertieally l)e:low pawl 51 of the ratehet ~r}leel 35 all hei.ng moulltc?(l on the SalllC pin .

Fina]ly to eomp] c~te t]lC desCl':il)t i on of l-lle mo]d strueture tl~e upper h~llf ]. ici provi.(lc(l ~ at: i t'i out:er wlll I ~ wi t]l a two~ ongecl.
fork 56 extend:i]l~ in l:hc'~ gellel;ll dilect.:i~)ll of mo]d ~ r 2 I)ut inel.ined w;l-h recipe(.Z: to t:l~e axix cr tlle nl(llcl. As sl~ow~
I'igure 6 fork Sfi Sel~eS ;Is ;In ;Ietu/~ g n~enll~er rnr leve~ 5:i IllOVing it to l-]~c? ]c?rt il~ a slo~ 57 ~ r.il~g 34 Or t:lle il~ternlc~diilte pOrtiOII of ~:hc mo]cl ~ % Wl~ C 11101(l .is CIO'iil~g~ (i l:n tlle rigllt ~ c~l t]~e 1110~ o~ ; tl~;lt fol~ cil.cl~
OpCllill~ CI CIOSi.~ 'y('lC ~.f t]l~ Illol~l t:l~e l~lte]~el wl~e] :~S ~is rotate~l by the piteh o r one ;ts teeth ~

Considerin~ now the oper.ltiol~ Or the mo]d in the l~osition sl~own in ~i~ures l to fi th;lt is to say witll the mold elosecl and tilC
various eavities 4 witl~ tlleir parts 5 associated Witll numl~cIs idcntical to those of the vari.ous rings 17-21 ( 0000000 1111111 ...... 9999999 ) the injection of the ~lastic is made through the nozzlc G. The meltcd pl~stic inje~ted through nozzle 6 is distributed along the ten radial channels 13 and through the ~L~5~2Z
restrictiolls 11 to r; ~ c ten C~IVi~i.Cs 4 In(l l]~us to mol(l tC'J\
e1s ]ulnll!crccl witl~ s.l;d con~ i.nations 0()0000(), l:l]1.].11, 2222222, ...... 99~ )9'~).'Wl~cn t]lC injection is over, thc injcctioll m~lc]lillc ~not shown) se~lral:cs mo].d hal~ 1 from Tnold ha1f 2, pcrmil-~ing the conical. elcment 25 (see Figlire 6) to projec-~ beyond t]-c ~ace o~ mo1d h~1f 2 cll~e to the force Or comprecsion spring 27.
This move]nent is only 1imited by the heacls o the thrce scr~s 32 which abut against t]le bottom of the cavities 33. Un~ler thcse conclitions, the rings 18 to 23 - s~lit at fi0 (ligure 3) - bccome re].atively ]oose ancl, anyway, s~scepti~le to rotation with respect to the other.

At thc samc t;.m~, duri.ng thc o~ening o:f' the mo1(1, the ].evcl- 5~
i.s moved to thc lc~t l~y the fork 56 (see ~igurc ~)), wllicll a(lvances paw]. 50 (~igure 4) .]ncl rotatcs ratchet 35 one tcnth Or a rcvolu-tion or the pitch o~ one tooth ~8. At t:hc sclmc t;mc ]~cll~]. 5] al.so meshes Wit'.]l the ncxt t:ooth ~8 on thc ot]~cr s:idc o~ tl~e gcar, holding it ag~linst unclcrsirahlc movcmcllt~s. Tll;.s l~otati.on Or onc tentll of a revolutioll Or the ge~ll 3~ ~I]So rcsultc. in an iclcl~t;.cal.
revolution of the outer ring 1~, so t`h.~t its ll~lnll)CI` n aclva]lccs i.nto cavity nQ 1, its nulTIher 1 ~lclvallccs ;ntO cav.ity nQ 2 ~lncl so rortll. l'}le next co~)i.llatioll.~ w;.ll t:]~crcrol~c l)c n]0n0()(), 12111.11., 2322222, 3~ i3~3, ~5~ , r,(ir~'i55r~, (i7~ 6, 7877777, 8988888 and 9()999~'.).

Just beorc t:lle mokl l~c~lchs :i.ts r~lly o~c!l ~os:it ion~ lhe l~c;l(l ].2a o ~art 1.1 slrilics .1 ~i.xed ]~art o.r t11e injeclio~ c, whicll imllc?11s thc cjcctor car-li.cr ~ c ~ rol~ ;llclly .in tl~c direction of thc molcl .I`.~cc, I)rojcct::il)g ~lIC C~l(ls ol t:}lC cjcc~.or ~ins 9 ancl 10 beyolld thc~ facc o.f t]~c lull.-r 2 t.o cjcct tl~c nlol(led articles alld tllc? i.njc~ction tr:imrll:ings ~'rom C~IV:it:i.Cs ~ an(l cl~;lr~ncls 13.

At the end of thc? closing movement Or the mo]cl, the facc Or thc mold halr 1 strikes the coni.cal meml-er 25 forcing it back ~Ig~inst the elastic force of spring 27 and to ~ISSUIIIC the configuration shown in Figure 1. Tllis expands ri.ngs 18 to 23., ensuring-that they are tightly fitted to cach othc?r, with no s~aces or interva].s ~s~9~z causing the formation of burrs during the next injection.
Up to the tenth injection, when the number combina-tions produced go as high as 0900000, 1011111, 2122222, ..... 9899999, the operation of the mold is simply repeated.
However, when the mold is opened after the tenth injection, the rotation (one tenth of a revolution) of the gear 35 causes the teeth 48 to cooperate with the toothed upper wheel 41 which transmits the rotation of one tenth of a revolution to the second gear 36. As a result, the numbered ring 18 returns to its initial position and the next ring 19 is simultaneously moved to pass its numbers from one cavity to another. This means that the eleventh injection will produce the following combinations: 0010000, 1121111, 2232222, 3343333 . . 99o9999 Consequently the contlnuation of the injection cycles will perrnit one to produce ten millions combinations (0000000 to 9999999) without repetition and without having the appearance of a serial production.
Although the above mentioned mold uses numbers in its marking rings 18 to 23, it shall be understood that letters or other type of identification would also be possible. Further-more, Figure 3 shows an alternative in which thc ten nurnbcrs are used intermittently with the letters A, B, C, D, E, F, G, H, I and J. Therefore, a small relativc rotation o~ rings 18 to 23 in relation to their gc~ars 35 to 40 an(l th~ sllbst:itution Z5 of the elemenl:s 17 I~or others c~nc3ravcd with letters, is suf-ficient to corlvert the n~nbcr combirlatiorls into letter combina-tions.
It will also be ullder:sloo(l th~lt the n~[lber oE cavities 4 was limited to ten only bcc.lus~ oE the decirllal systcrn. In a mold of, say, eiglltecn caviLics, it is possible to use rings with eighteen lettcrs (A to R) in which case the gear of the ratchet 35 would have to have eightecrl teeth 48, whereas the teeth 49 and the gears 39 to 40 would have to be properly as-sociated for the purpose of transmitting among themselves fractions of one eighteenth of a revolution.

_g_ It woulcl .ll.so bc possil:)lc to m.l]ic t]~e prcscnt].y describe(l mo].d with tWC]l~.y CclVi.tiCS, the ri.~ s ]nlVin~ thc a]:fa-llul]lcric Cllgl-lV-ings S]IOWII i]l l:igllrc 3, so th~t a]l comb~ t:iolls Or l:he tcn letters or numbers coulcl bc used withou-t repetition.

These and other modifications of the presently described prc~cl-red embodimellt will: be obvious to a l~erson versed in the art as also will other ~ari.atioJIs within the spirit of t]lC in~cilt-ion which is liinited only by the following claims.

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Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A mold for injection molding comprising two mold halves separable after each molding operation and having mating surfaces which define therebetween a plurality of molding cavities and injection channels opening into said cavities, concentric rings in a first of said mold halves, rotatable about a reference axis perpendicular to said mating surfaces and forming portions of said cavities in positions equally spaced about the reference axis, each ring presenting to the interior of each cavity a marking that is different from those that it presents to the other cavities, means to rotate one of said rings by increments so that its markings are presented, one by one, to said cavities and to rotate each other ring by an increment each time the previous ring completes a revolu-tion, in a manner similar to a mechanical counter, and actual-ing means to actuate said rotating means by an increment for each cycle of separation and approximation of said mold halves.

2. A mold according to claim 1, in which said concentric rings are fitted and tightened against each other when the two halves of the mold are approximated with their mating surfaces in contact with each other.

3. A mold according to claim 2, in which said rings are expandable, being in an expanded state when the mating surfaces of the two halves of the mold are in contact with each other.

4. A mold according to claim 3, in which said rings are in an unexpanded state when the two halves of the mold are separated from each other so as to facilitate their relative rotation.

5. A mold according to claim 4, in which it comprises means to expand said rings when the two halves of the mold are approximated.

6. A mold according to claim 5, in which said means for expanding the rings comprise an element in the form of a cone or a truncated cone, coaxial with said axis, forming the central portion of said first mold half, the base or the major base of said element comprising a portion of said mating surface of said first half, an internal conical surface associated with the inner-most ring of said rings and mating with the conical surface of said element, and resi-lient means impelling said element into a projected position in relation to the other portion of said mating surface of the first half of the mold.

7. A mold according to one of claims 3 to 5, in which each of said rings is split so as to be expandable.

8. A mold according to claim 1, in which there are ten said cavities and each ring has ten markings.

9. A mold according to claim 8, in which the ten markings are represented by the numbers 0, 2, ...... 9.

10. A mold according to one of claims 1 to 3, in which said markings are represented by letters in a number equal to that of the cavities.

11. A mold according to claim 9, in which the rings have ten other additional markings in the intervals between the numbers, said other markings comprising letters so that the mold may be used with the letters or the numbers pre-sented to the cavities.

12. A mold according to one of claims 1 to 3, in which each cavity has a fixed marking which differs from the fixed marking of each of the other said cavities.

13. A mold for injection molding, comprising two mold halves separable after each molding operation and having mating surfaces which define therebetween a plurality of molding cavities and injection channels opening into said cavities, a plurality of concentric split rings in a first of said mold halves rotat-able about a reference axis perpendicular to said mating sur-faces and forming portions of said cavities in positions equally spaced about said reference axis, each ring presenting to the interior of each cavity a marking that is different from those that it presents to the other cavities, means to rotate one of said rings by increments so that its markings are presented, one by one, to said cavities, and to rotate each other ring by an increment each time the previous ring completes a revolu-tion, actuating means to actuate said rotating means by an in-crement for each cycle of separation and approximation of said mold halves and means to expand said rings to be tightly pressed against each other when said two mold halves are approximated with their said mating surfaces in contact with each other.

14. A mold according to claim 13, in which said means for expanding said split rings comprise a conical element coaxial with said axis, forming the central portion of said first mold half, the base of said element comprising a portion of said mating surface of said first half, an internal conical surface associated with the innermost ring of said rings and mating with the conical surface of said element, and resilient means impelling said element into a projected position in relation to the other portion of said mating surface of said first mold half.

15. A mold according to claim 13, in which each cavity has a fixed marking which differs from the fixed marking of each of the other said cavities.