CA2057063A1

CA2057063A1 - Method of attaching appendages to blow moulded products

Info

Publication number: CA2057063A1
Application number: CA002057063A
Authority: CA
Inventors: Hans Schwochert; Wolfgang Weber; Andy Puempel; Hans Kogel
Original assignee: Individual
Current assignee: KAUTEX OF CANADA Inc
Priority date: 1989-03-15
Filing date: 1990-03-15
Publication date: 1990-09-16
Also published as: WO1990010532A1; GB8905919D0

Abstract

In a method for creating a blow moulded product comprising the steps of extruding a parison tube (3) into a cavity formed between opposite halves of a mould (5), pinching off end portions of the parison via crimping apparatus (7 and 9), admitting high pressure compressed gas into the inner portion of the parison tube via a gas blow pin or needle (11) for inflating the tube against the opposite halves of the mould and thereby create the blow moulded product, the improvement comprising the steps of projecting an undercut dowel (13) from an inner wall of at least one of the opposite halves of the mould such that the parison forms around and conforms to the shape of the dowel, retracting the dowel into the wall thereby leaving an undercut in the parison in the shape of the dowel, removing the blow moulded product from the mould and inserting pin portions (19 and 21) of an appendage (17) into the undercut prior to cooling of the parison whereby the undercut shrinks around the pin portions during cooling to form a secure connection of the appendage to the product.

Description

E'r~lOD O- AT'r~.CH. 'IG .~PI'E~DAGES TO BLOW MOULDED "RODUCTS
~echnical Fi- d ~ his ir.vention -elates in general to blow ~c~ld~.g of ~las~ic products, and mors particularl~ to a method or at_aching appendages to blow moulded articles.
aackaround Art ~ xtrusion blow mouldlng is a well Xnown process ~or ~abricatlng plastic products such as containers, rual tanks, etc. In op~ration, a parison i9 extruded through 1~ a d Q at ~ gi~;en melt temperature appropriate ~or the ra~
~aterial. A mould is sha? d in the for~ o~ a negat~ve image or 1he desir~d inal product out~r surrace. The extruded ~arison is pincned o~ at a bott~m portion thereo~ ~hile a narrow blowpipe i~ inserted from the lg bottom into the internal cavi~y o~ -the ~ube. Nexk, high pressur~ cJ2s is introduced into th~ parison ~.l.e. via a ~qedle or blow pin) ~uch tha~ the ~ruded parl~on ox~ands acJains~ the ~ould, ~or ~hapin~ th~ pla~-tlc to C~.
desi-~d produc~ ~om~try. Thl~ m~uld ~ th~n qp~n~d and the ~inal plastlc ~roduc~ is remo~r~d therefrom.
It is o~ten desirable to incorporate one or i more app~ndages such as handles, harneqs clip5 , etc., to ,~ the extruded pla~tic product.
According to prior art ~echniques, such additional appendages have be~n installed via post-moulding processing steps using ex~ensive dedic2ted plastic weld machinery. The use of additional down-line ~rocessing steps and machinery has been found to be labour intQnsive; and the cost or a typical down-line plasti- welding machine (per weld) can be in the vicinity of $100,000 Ccn (1989).
One prior art approach to attachin~ appendag~s to blow molded products is disclosed in U.S. Patent ~ 3,140,329 ~Nutting) in which a handle or othe~ attachment ; 3S me~b~r is mounted ln sp~cially d~signed Y~ce~s~s providcd in the mould cavity block~ ~o~ connection ~o ~he blow mclded prcduct sL~ultaneously with blow ~olding c~ the ,: . .
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,A .~ .' product. The Nutting apo2-2tus r~auires pr~-mounting or 'he h-ndle or other appendaga into the mold cavity.
U.S. P~t_nt ~,363,4;~ (Ralnfille) discloses a fur~hc- attachme~t scheme in which appendages ~~ other parts ^an be easily connected a.~d disconnected 'o a ~low mold d preduct by vi~tue or s~eclally designed ~nobs which e~ert a c~m action to stretc~ the entrance o~ a ~eCeSJ in ~h~ blo~ mould~d prcdu~:t. Accordingly, the apparatus dlsclosed in ~.S. Pat~nt 4,363,~15 is not 10 designed to prot~ide a secure and per~anent at_acr.ment of . ~, an appenda~e.
2isclosure or the Invention Accorcing to the ~res~nt invention, a s lmple : :' and inexp~nsiv~ process is ~rovi ed ~or attachln~
appendage~ such ag ~an~l~s or harnsss clips, ~tc. onto extrus1on mould~d products wi~ho~ ad~lt.ionn.l axp~nslv~
~t-mouLdineJ we!dlr;g ~qulp~n~. In ~ccord~n~ ~wlth an aspec~ o~ ~h~ pr~nc I .~v~n~lon, ~h~r~ I ~ prov1d~d a method ~or croa~1ng ~ '9ic~w rtlO~ . pr~c~ucc o~qmpr1s1ny t:~
steps Oæ extrudlng a pari30n tube (3) into a cavi~
f'ormed be~ween opposite halves of a mould (5), pinching ; o~f a topmost portion of said parison via cri~plng apparatus (7 and 9), admitting high pressure compresssd gas into the inner portion or' said parison tube via an s~5 blo~ pin (11) fo~ inflating ths tube agzinst said opposite halves of s~id mould and thereby create said blow moulded product, the improvement comprising the ~'~ steps of projecting an undercut dowel (13) from an inner all of at least one of said cpposite halves of said ~Guld such that said parison ~orms arou~.d and confor~s to i ~ the shape o~ said dow21 to thereby crea~e said blow moulded ~roduct, separatin~ said product ~rom said dowel thereby leaving an undercut in said parison in the shape o~ said dowel, removinq said ~low ~oulded produc~ ~rom sald mould and insertinq pln por~ions ~1~ and 21) o~ an appenda~e ~17) int~ said Un~erCUt prior ~o ~oollng Or said product whereby said undercu~ shrinks around said ~;~ÉE;~

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~in po -ions during coolinq to form a secure connection o. saia appendage t~ said product.
According to another aspect of the invention, a blow ~oulding apparatus for creating a blow moul~ed product 3 -~i.h appendage comprising a cavi~ formed between cpposite halves o~ a mould (5), means _or ex-ruding a ?arison tube (3) into said c~vity, crimpi~g apparatus (7 ar.~ 9) Cor pinc~ing o~f ~nd portions of said parison, a blow pin ~ or admitting high pressure compressed gas lnto the inner portlon o~ said parison tube ~or inflating said tube against said opposite hal~res of said mould and . thereby creating sald blow moulded product, undercut j dowel ~13) disposed within an inner wall of at least one of sai~ opposi~e halves of said mould, and means ~or select~f31y projecting and retracting said undercu~ dowel ~r-m sa~d inr.er wall such tha~ said pari~on Eorms around an~ con~or~s ~o the shape of ~ald dowel respon~i~r~ ~o : pro~ection ~h~r~or, and ~wher~h~ an unflarcut i~ form~d 1.
i ~al~ produc~ in the 5h~p~ oæ sald cl~wal r~pon~ r.o ;- 2' .r~trac~lon th~_co~ ~or ~acilltatlny ln~er~lon o~ pin portlons (lg and ~.) o~ an appendaye ~17) therein, and wherein said dowel is charac~erized by undercut forming d.~a~.eters B and D, where B ~ D ~or~s an upper diameter .; limi~ and D S ~B ~orms a lower diameter limit.
Best Mode o~ CarrYina Out the Invention Figure 1 is a cross sectional view of standard extrusion blow processina equipment incorporating a hydraulically retractable dowel in accordance with the present invention;
- 30 Figur 2 is an enlarged cross sectional view of the dowel illustrated in Figure l;
Figures 3A-3D illustrate a handle for . .
attach~ent to a plastic product in accordance with the . present invention; and Figure 4 is a detailed view of the dowel .;
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illustrate~ in ~igures 1 and 2.
3es~ ~oGe For Carr~ina Out the Inv2ntlon : Tur~ir.g to Fi~ure 1, st~da-d extrusion blow ?~ocessi~.g equi?~en~ is shc.-n comprising an accumulator head 1 fo~ extrud~ng a heated rluid plas~ic parison 3 into a ~ould 5 cor.sisti.~g of t-~o cavitiss. The parison is pinched of~ at top and bottom ends thereo~ via crimping apparatu~ 7 and 9 (e.g. pinch plates). .~ neeclle or blo~" pin 11 e~tends into the extruded parison ~or admit~ing a hi.:. press -e ~low o~ comor`essed gas for inflatir.g the plastlc ~ube against the shaped w211s of the mould 5.
The above described process and apparatus is W211 known prior art.
~owev~, in accordanc~ with the pre~an~t inv~ntion, a dowel 13 e:~t~n~s throu~h an ap~rture ln th~
moulcl ~ such ~hac ~he blown pl~ ~Lc tub~ ~n1r~1~p~ and con~o~m~ ~o ~h~ ~h~p~ Oæ th~ dowei, ~or-~ln~ ~n un~l~rc~
in the 5ur~ac~ o~ the ffloul~d ~la5~1~ pr~duc~, as shown best with re~erence to Flgure 2.
Once the parison has been blown against the ~ mould wall3 and around dowel 13, the dowel 13 is b,'~ hydraulically retracted via a hydraulic cylinder (not ~; shown), the mould S is opened, and the product is removed.
It is kno~n that blow moulded plastic products shrink approximately 2-~% duri~g cooling. Thus, in .: accordancs with the present invention, upon removal of : the plastic product .rom the mould, any appendages such as ths handle 17 sho~-n in Figures 3A-3D, should immediat-ly be attached ~o the plastic produc~ by . inserting pin por~ions 19 and 21 into correspanding positioned undercuts ir the product w~ile the plastic is still shrinking. ~us, the undercu~ e ~ectively shrinks during coolin~ around ~ho plns 19 ror~ing a ~ecur~A
connection o~ the handle or~other ap~endage, without ~i requiring expensive post-~ould w21ding equipment, etc.

s~J~,ST~ s ; ' ' .

Figur~s 3A-3D show a preferred form of handls .or attach~ent to a plastic p Gduct (e.g. vehicle fuel ~ar.k, contair.er, etc.), in accordance with the process or th2 present in~;on~ion. ~owever, the process and ~pp2ra us o~ the present invention may advantageously be - used ~o attach ~ir~ually ~ny othe type of appendage such as clips, straps, etc. Also, whereas the dowel 13 is indicated above as being hydraulically operated, o~her ;~ mechanical or electro-~echanical dow~l operation means ma~ be used.
Wit~ rsaerence to Figure ~, a detailed view o~
the undercut dowel 13 is shown with optimized undercut forming diameters of B and D in the range of ~rom B < D
(upper limit) to D ~ 4B llower limit). For dimensions of ; 15 a equal to or gr=ater than D, th~re will be no lip on the undercut such that ~he und~rcut wil.l be ess~ntially c-~l nd~ical and ther~ear~ insu~ictant to r9t~in th~
assocla~&d pin3 19 o~ the appendag~ a~t~r sh~lnkaq~
~he dimen~ions o~ D ar~ gr~tar than ~, bh~ llp on ~h~
undercut ~111 be ~oo gr~t, r~ultln~ ln ~ por~ on o~ the product ~eing ripped out upon separation ~rom the dowel 13 within the blow processing equipment.
~ ccordinq to a success ul prototype, the dimensions were D ~ 3 mm and B ~ 6.5 mm.
Industrial A~plicabilitv In summary, the process of the present invention makes use of the approximately 2-4~ total shrinkage of a blow extruded plastic product during -~
cooling, to implement a process for creating an undercut in ~he plastic product during blow extrusion and ;~ attachi.g appendages thereto by means of app~opriate di~ension pi..s inserted into the undercut while the product is cooling, such that the undercut shrinks around `~ the ap~endage pin forming a secure connection.
Other embodiments and variations a~e contemplated.

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Ss ~sT~ A~

For e~2mple the di~ensicns or D and a can be greater or less than 2S discussed with reference to the succe~s~ul pr~tot-;pe, Drc -ied the relation therebet~een ; confo~ms to the abo~e disc~ased upper and lower limits.
As a f-1rther alterna-ive, one or mo~e ejector ins ~2y ~e housed ~i~hi~ the ~all of the moulding and ejected there~rom for ~orcing the produc~ awa~ from the dowel 13 and the ~ould wall within the vicinity of the dowel, instead of retracting the dowel into the wall.
.~11 such modifioaticns and embodiments ~re ~elieved to be within the sDhere and scope o~ the present in~Jention as derined by the claims appended hereto.

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Claims

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

1. A method for creating a blow moulded product with appendages comprising the steps of extruding a parison tube (3) into a cavity formed between opposite halves of a mould (5), pinching off end portions of said parison via crimping apparatus (7 and 9), admitting high pressure compressed gas into the inner portion of said parison tube via a gas blow pin (11) for inflating the tube against said opposite halves of said mould, projecting an undercut dowel (13) from an inner wall of at least one of said opposite halves of said mould such that said parison forms around and conforms to the shape of said dowel, to thereby create said blow moulded product, separating said product from said moulded leaving an undercut in said product in the shape of said dowel, removing said blow moulded product from said mould and inserting pin portions (19 and 21) of an appendage (17) into said undercut during cooling of said product whereby said undercut shrinks around said pin portions during cooling to form a secure connection of said appendage to said product, and wherein said dowel is characterized by undercut forming diameters B and D, where B < D forms an upper diameter limit and D ? 4B
forms a lower diameter limit to ensure a lip on the undercut sufficient to retain the pin portions but not is large as to cause any portion of the product to be ripped out upon separating said product from said dowel.

2. The method of claim 1 wherein said step of separating comprises retracting said dowel into said wall by hydraulic means.

3. The method of claim 1 wherein said step of separating comprises extending one or more ejector pins through said wall adjacent said dowel for forcing said product away from said wall and said dowel.

4. The method of any one of clams 1 to 3 wherein said appendage is one of either a handle or a clip.

5. A blow moulding apparatus for creating a blow moulded product with appendage comprising a cavity formed between opposite halves of a mould (5), means for extruding a parison tube (3) into said cavity, crimping apparatus (7 and 9) for pinching off end portions of said parison, a blow pin (11) for admitting high pressure compressed gas into the inner portion of said parison tube for insulating said tube against said opposite halves of said mould and thereby creating said blow moulded whereby an undercut is formed in said product in the shape of said dowel responsive to retraction thereof for facilitating insertion of pin portions (19 and 21) of an appendage (17) therein, and wherein said dowel is characterized by undercut forming diameters B and D, where B < D forms an upper diameter limit and D ? 4B
forms a lower diameter limit.

6. The apparatus of claim 5 wherein D = 8 mm, and B = 6.5 mm.

7. A blow moulded product and connected appendage produced in accordance with the method of claim 1.