CA1147918A - Combination thermoplastic and glass loaded thermosetting injection molding machine and method for operating same - Google Patents

Abstract

COMBINATION THERMOPLASTIC AND GLASS LOADED
THERMOSETTING INJECTION MOLDING MACHINE AND
METHOD FOR OPERATING SAME
ABSTRACT OF THE DISCLOSURE:
An injection molding machine which is capable of inject-ing both thermoplastic compounds and glass loaded thermosetting polyester compounds, wherein the machine is capable of rapid conversion from its thermoplastic configuration to its thermosetting configuration, and vice versa. The machine comprises an elongated charge forming barrel having a rearward thermoplastic feed opening, which is customarily supplied by pelletized thermoplastic material from a vertical feed hopper, and a thermosetting material feed opening extending into the barrel at a position forwardly of the thermoplas-tics feed opening. When processing thermoplastics materials, a conventional, fully flighted plasticizing screw is installed in the barrel so that the pelletized material is conveyed forwardly from the rear feed opening, and plasticized for subsequent injection. During thermo-plastics processing, the thermosetting feed opening is plugged. To convert the machine to process the aforementioned thermosetting materials, the second feed opening is unplugged, and the plasticizing screw is exchanged fox a deeper flighted conveying screw having flights extending from the forward end thereof to just behind the unplugged, second opening. A stuf-fer unit is then attached to the unplugged feed opening and dough-like glass loaded thermosetting material is forced through the second opening into the barrel by means of a reciprocating plunger, or the like.
The thermosetting material is conveyed forwardly and mixed slightly as the screw rotates.

Description

~7~

BACKGROUND OF ~HE INVENTlON
~ he pre ent invention relates to in~ection molding machines, and $n particular to such a machine which i5 capable of processing both thermopla~tic compounds and glass loaded thermosetting polyester compound~, such as bulk molding compound~, with easy conver~ion between the two modes of operation. The invention al~o relates to the method of conv~rt~ng the machine from the thermopla~tic mode to th~ th~rmo~etting mode, and vice versa.
Pl~tic~ materials which are becoming increa~ingly important and more widely used are thermo~etting polye3ter ~ompounds reinforced with gla3s fibers, and other type~
of fibers~ ~n i~portant application of component~
lS made of this type of molding compound i~ in the automotive indu~try where improved mileage requirement3 h~ve neces~itated the ~ubstitution of pla~tic part~ for those which have customarily been made of metal. For example, the headlamp hou~ing and front trim component for automobiles has cu~tomarily been made of a chrome plated metal, but, due to the streng~h and rigidlty afforded by fiber relnforced bulk molding compound~ (BMC), thls component can be made entirely of such a material. Although thi~ type of component can be m~de by compression mold~ng or tran~fer molding techniques, these technique~ are not particularly ~uited to high production due to the high degree of hand labor required and the long cycle time. The advantage~ of in~ection molding glas~
reinforced polye~ter compound~ ~r~ fa~ter cycle time, the elimination of hand labor, and a higher quality product having a better finish.
One of the disadvantages to making products of a ~iber loaded polyester molding compound is reduction of strength of the product due to fiber breakage.
One such thermosetting material i~ bulk molding compound, which comprl~es a thermosetting plastics material and gla~s fibers premixed to form a Qtarting material having a dough-like aonqistency. Although the use of conventional screw machines are advantageou~ from the Rtandpoint of short cycle time~, by feeding the bulk molding compound into the barrel through the normAl feed inlet which is at the r~ar end of the barrel, the shear force~ developed by a conventional pla3tic~zlng screw or even a deeper flighted conveying 8crew tend to break the glass fibers. This re~ults in lower product strength because the short, bro~en fibers are not as effective a reinforcing constituent as are longer fibe.rs.
In order to minimize fiber breakage, it i8 desirable 20 to limit, as much a3 possible, the di~tanoe in the ..
barrel through which the mater~Al is aonveyed, One technique for converting a standard injection molding machine from thermopla~tic operation to glass loaded thermo~etting operation i~ to replace the longer thermo-plastics barrel with a 3horter barrel. One problem with this i~ that it may take ~everal day~ to make this conversion, thereby resultlng in substantial machine down time and making conversion unfeasible except for very long run~. Furthermore, this requ$res the customer ~o stock both a thermopla~tic~ barrel and screw and a barrel and screw ~pecifically adapted 1~4~9~B

for glass loaded thermo~etting compound~, an expense which i8 not afforaable unle~s a ~ub~tantial portion of the proce~Ror's output is ~uch thermosetting compounds.
SUMMARY OF THE INVENTION
_ _ _ The pre~ent invention overcomes the dlsadvantages ~nd problems of prior art apparatus for injectlng BMC and other glass loaded thermosettlng material~
by providing an injection barrel having a normal thermo-plastlc~ feed openlng at the rear end of the barrel, and al~o a second feed opening forwardly of the thermoplastics feed opening so that ~uch thermo~etting molding compound introduced into the barrel through the second opening will be conveyed within the barrel through a ~ubstantially ~horter di~tance than i~ the ca~e wlth thermopla~tics ~aterials. Thus, the 3ame barrel can be util~zed for both BMC and thermopla~tics proces~ing, and, as will be seen, conver~ion from one mode of oparatlon to the other i8 relatively e~sy.
When proces~ing thermopla~tic~ materials, the thermoset feed opening i9 plugged by mean~ of a ~pecially adapted plug having a concave inn~r ~ur~aca which conform~ to the curvature of the inner surface of the barrel. A aonventional pla8tici8$ng ~crew i3 installed ln the barrel, and th~rmoplast~cs material fed through the rearward openlng by mean~ of a con-ventlonal hopper are conveyed forwardly and pla~ticized by the rotatlng ~crew and then in~cted into the mold a~ the ~crew is rammed forwardly. To convert the machine to glass loaded thermo~et operation, the plasticizing ~crew i~ removed and replaced with ~1~79~8 a deeper flighted, conveying screw suitable for conveying the thermosetting material forwardly ln the barrel w$thout undue ~reakage of the fiber~. Thi~ screw preferably i~ flighted for forwara conveyance only a~ far back as the thermo~et inle~, with the rear port~on of the screw being unfltghted or, alterna~vely, rever~e flighted ~o that any material whlch may leak rearwardly in the barrel will be conveyed out of the rear end of the barrel before it has a chance to set up. The thermoset feed opening i~ unplugged, and a conventional stuffer unit 1~ attached thereto.
The material is then forced into the barrel through the unplugged openlng and con~eyed forwardly by the screw for ~ubsequent in~ection into the mold a~ the ~r~w is rammed forwardly.
To convert from glas~ loaded thermo~et to thermo-plastic operation, the reverse ~t~p~ are per~ormed.
Specifical~`y, the present invention contemplates an injection moldlng machine for alternati~e gla89 loaded thermo~et and thermoplast$~ operation comprising an elongated barrel having a generally cylindrical bore therein, ~n elongated scre~ rotatably and axially reciprocably received within the bore of the barrsl, ~ first feed opening ne~r the rear end of the barrel extending into the bore through the s~de wall of the barrel, a se~ond feed openlng intermed~ate the first feed open~ng and the forward end of the barrel extending into the bore through the barrel side wall, and a cover attachable to the barrel for alterna-tively closing and opening the se~ond feed opening.

The invention also ~ontemplate~ a method for 7~

converting the injection molding machine from theinjection of a thermoplastics compound to a gla~
reinfQrced thermose~ting polyester compound compri~ing:
providing an i.njection molding machine having a barr~l with a rotating and axially reciprocable plasticizing screw therein, the barrel having a first feed opening and a 3econd feed opening forwardly of the first feQd opening with the second feed opening clo~ed, feeding thexmoplaQtic compound in~o the barrel through the first feed openin~ whereupon the material i8 conveyed forwardly and pla~ticized by the rotating ~crew: with the machine stopped, removing the plasticizing ~crew and in3talling a glass loaded thermosetting compound conveying screw in the ~arrel for rotat~on and axial reciprocation;
opening the second feed cpening; and orcing a glas~
loaded thermo~etting polyester compou~d into the barrel through the second feed opening whereupon the thermo3etting compound is conveyed forwardly as the thermo~etting compound conveying screw rotates.
The converse Bt~p8 are performed for converting from ~hermo~etting to thermopla~tic operation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagrammatic top view, partly in section of an injection molding m~chine configured for glass loaded thermosetting operation in accordance wi~h the present invention;
FigurG 2 is a fragm~ntary ~ide elevational view of the machine ~hown in Figure l;
Fi~ure 3 i8 a ~ectional view taken along line ~7~8 3-3 of Figure 1 and viewed in the direction of the arrows and wherein the screw h~s b~en omitted;
Figure 4 i~ a top view, partl~y in section, of the machine o~ Figure 1 but configured for thermopla~-tic operationS
Figure 5 i8 a sectional view taken along line S-S of Figure 4 and viewed in the direct~on of the arrows, wherein ~he screw has been omitted, and Figure 6 i~ a sectio~al view taken along line 6-6 of Figure 5 and vlewed in t~e direction of the arrows.
D~TAILED DE~CRIPTION
With reference now to the drawing~, there is illustrated in Figur~ 1 a~ in~ection molding machin~
8 ~ompr~sing an elongated barrsl 10, which may be, for example, a 20:1 barrel, secured to feçd cham~er 12. ~arrel 10 is supported for recipro~al movement ln the horizontal directlon by convçntional apparatu~
well known ln the injection molding art, and i3 connected to feed chamber 12 by nut 56. Nozzle 14, having flow pa~sage 16 therein, i8 secured to the forward end 18 of barrel 10, and ~erYes a~ the mQans for conveying the softened plasti~ mat~ri~1 to the mold a~embly (not ~hown). A plural$ty of heat~ng or cooling bands or unit~ 20 are po~itionçd around barrel 10 for the purpo~e of he~ting or ~ooling the plastics material ~ it i~ aonveyed forwardly within barrel 10.
In~action ~yl~nder~ 22 have injection pi3tons 24 received th~rein Eor re~iproc~tion in the horizont~l 7~8 direction. Strain rods 26 are ~ecured to rams 24 and extend through openin~ 28 in cyl~nder~ 22.
Feed chamber 12 is secured to stra:in rods 26 by nuts 30.
The injection molding mach~ne 8 illustrated in Figure 1 i~ conf~gured for the proc~ing of a thermosetting polyester matexial, such a~ a bulk molding compound (BMC), whlch i9 reinforced with gla~ fibers. The bulk molding aompound h~s a s~icky, dough-like con~istency in it5 initial state, and for this rea~on, only convey~ng of the material ls necessary. Plastlc~zing and melting of the mat~rial i~ not ~ece~sary, as i~ the ca~e with a thermopla~tic~
Received within barrel 10 i~ a screw 32 particularly adapted for ~onveying the bulk molding compound forwardly. The rear end 34 of sarew 32 i~ connected to a hydraulic motor 36, which rotates ~crew 32 about its longitudin~l axi~. By mean~ of conventional cyllnder~ 22 r~iproc~ting over pi~tons 24, ~crew 32 is reciprocated longltudinally within barrel 10 80 that the charqe of pla9 tic~ mater~al can be injected into the mold a~sembly.
Screw 32 compris~s a series of continuous flights 38 having a pitch ~uch that~ when screw 32 is rotated 2S counterclockwise when view~ng the ~rew from the forward end 18 of barrel 10, th~ thermo~etting material with~n barrel 10 will be con~eyed forwardly. It will be noted that flights 38 are somewhat deeper than the flights of a conventional pla~t~cati~g ~crew, becau~e the primary funct~on of screw 32 3~

i~ to convey the material forwardly, rather than plas~icizing the material ~y ~he application of ~hear forces, a~ i8 the case with tharmoplastlc materials. Connected to the forward end 40 of ~crew 32 is an annular flow nonreturn valve 42 comprising a retainer 44 threadedly sec~red to screw 32, and ~ check rl.ng 46 slidably keyed to reta~n~r 44 by pin 48. The purpose of nonreturn valve 42 i~ to prevent the backflow of material during injection.
The r~ar portion 50 of screw 32 i8 al~o preferably flighted, and comprises a series of continuou~ fl~ghts 52 having a pitch which i~ rever~ed to that of flights 38 su~h ~hat material wi~hin the rear portion of barrel 10 will be conveyed rearwardly out the rear end 54 of the barrel 10 b~fore it has a chance to set up. Seal 58, which compri~e~ a pl~rality o~
integral, annular rib~ 60 having close clearance~
with the inner wall 62 of barrel 10, prevent or greatly minimize the flow of material rearwardly in barrel 10. Barrel 10 al80 includes a thermopla~tics feed opening 64 extending through the cide wall of barrel lQ and communicating with bore 66.
conventional hopper 68 i~ connected to barrel 10 50 a~ to feed thermopla~tics material through opening 64 into barrel 10 when the machine 8 ls configured for thermoplastic~ processing.
In Figure 1, however, the machine illustrated i8 configured, not for thermspla~tic~ processing, but for processing glas~ loaded thermosetting polyester compoundsO For this purpose, barrel 10 i~ provided 79~L~

with a second feed opening 70, which i5 generally circular in ~hape and positioned ~ubstantially forwardly of thermoplastics feed opening 64. The thermosetting material, ~uch as a bulk molding compound, is fed into barrel 10 under pressure ~hrough opening 70 by means of a conventional stuffer unit 72~ With reference ~o Flgure 3, the ~tufer unit 72 i9 conneeted to opening 70 by means of liner 74 held against rotation by dowel 76, the latter extending through an opening in the flange portion 78 of liner 74 into a groove 80 in barrel 10. $iner ?4 is held in place by ~leeve 82, which is threadedly ~ecured to barrel 10. Liner 74 is hollow and generally cylindrical 310ng its axis, and the inner ~urface 84 thereof is generally aoncave such that it confcrms to the contour of barrel inner surfa~e 62. Sleeve 82 is ~ecured to the flange 86 of ~t~ffer elbow B8 by retainer 90 ~nd screw~ 92.
Stuffer unit 72, which i9 merely exemplary and doe~ not itself form a part of the invention, will QOW be described w1th reference to Figure 2, whereln the external portion~ of the 3tuffer 72 are illustra~ea, and to Figure 1 wherein the int~rnal ~tructure i8 illu~trated ~omewhat diagr~matic~lly.
The ba8e plat9 ~3 of stuffer unit ~2 i~ supported on the ~led 94 o~ tha in~ectior~ molding machine 8 by mean~ of ~pacar~ 96. Plate~ 98, 99 and 100 are weldsd to ba~e plate 93, and ~upport the main ~tuffer barral 102, elbow 88 and main hydraulic cyllnder 104. A hopper 106 i~ ~ecured ~o barrel 7~

102 and has any type of ~uitable automatic feeding means for cau~ing the thermoset~ing compound to be fed downward through opening 108 into barrel 102. An inner ~ealing ~leeve 110 is ~lidably received within barrel 102 and reciprocated by means of ~leeve carrier plate 112 to which are seaured conne~ti~g rod~ 114. The pistons 116 for connecting rods 114 are actuated within cylinder~ 118 by mean~ of hydraulic pre~suraG Carrier plate 112 slide~ over guide rod~
120, which are connected between ~top plate 122 and rear plate 100. Inner ~eal~ng ~leev~ 110 i~
periodically ~lid rearwardly pa~t opening 108 so that more material can be fed ~nto barr~l 102.
With ~ealing sleeve 110 clo~ed, main plunger 124 lS is urged forwardly by mean~ of the hydraullc pre~ure ~eveloped within cylinder 104 and acting again~t ram 126. The bulk molding compound within barrel 102 forwardly of plunger 124 will be forced through elbow 88, ~leev~ 82 and liner 74 tnto the bore 66 of barrel 10. As ~rew 32 rotate~, the flights 38 on the forward portion thereof will ~onvey the material forwardly within barrel 10. A8 thi~ occurs, screw 32 will travel r~arward}y under the pre~sure ~uilt up in front of nonreturn valve 42 in the conventional manner. When the de~ired charge ha~ b~en developed in ront of valve 42, ~crew 32 will be drlven forwardly and cause the charge ~o be in~ected into the mold as~embly through pa~aqe 16.
It will be noted that the thermoset feed opening 70 is located sub~t~ntially forwardly of thermopla~t~os feed openlng 64, for example at least one-third of the effective barrel length in front of opening 64. The ~eal 58 is located ~ust behind opening 70 when screw 32 is forwardly within barrel 10, and ~erves to prevent an undu~ amount of material from flowing rearwardly within barrel 10. ~ny material which does flow past æeal 58, however, will be conveyed out the rear end of barrel 10 by fligh~s 52.
~ecause the distance alonq which the maSexial 0 i9 conveyed by screw 32 is sub~t~ntially l~ss thsn that if the material werc fed into harrel 10 through the normal feed inlet 64, fiber breakage i greatly reduaed. Furthermore, the lower re~idence time within barxel 10 with the concomitant heating due lS to shear forces produced a~ screw 32 rotates, r~sults in a lower temperature rise, which iæ advantageous when molding wlth thermosetting materials. Although æome temperature rise within barrel 10 i~ desirable from the standpoint of shorter cycle time, too mu~h rise in temperature will cause prema~ure curing of the thermosetting material. When processing thermosetking materials, such as bulk molding com-pounds, barrel 10 is cooled by circulating a cooling medium, ~uch as water, through cooling bands or units 20. Conversely, if it i~ de~ired to heat barrel 10, then electric heating would be employed.
Heating/cooling units 20 are of con~entlonal design.
When it is deæired to process ~hermoplastics materials in injectiGn molding machine 8, it is I,ecessary ~o convert the ~achine to the configuration ~7~1B

illu~trated in Figures 4 through fi. Stuffer unit 72 i8 removed, and thermoset feed opening 70 i~
plugged by mean~ of plug 128, whi~h ha~ the identical ~hape a~ liner 74 but i5 solid rather than hollow.
The inner surface 130 i8 concave along a directisn parallel to the axi8 of barrel 10 so as to conform to the inner surface 6~ of barrel 10. Plug 128 includes a flange portion 132, which e~gages ~houlder 134 and is held again~t rotatlon ~y dowel 76. Plug 12~ ~ held in place by r~talner 136, which i~ threaded into opening 70.
Screw 32 i~ then removed, and replaced by a conventional pla~ticizing screw 138, which may have annular ~low nonreturn valve 42 or a ~on~ent~onal nonreturn valve threadedly secured to 1~ forward end 140. It will be noted that ~crew 138 is of convantional design having a de~per f1ighted conveying section 14~ extending forwardly from feed opening 64, a tapered transition section 144, and a shallow channel section 146 on the forward end for the purpose of achieving final plastication once the material ha3 been nearly completely melted. Screw 138 i8 reciprocated and rotated by the sam~ appar~tus ~
was described in connection with Flgur~ 1. Electric he~ting band8 or unit~ 20 impart additional thermal energy to the thermopla~tic mater~al thereby accelerating it~ ~elting.
The thermoplaYtic compound, ~hich may be in pelletized form, i~ fed from hopper 148 through feed opening 64 into the bore 66 in barrel 10.

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The material i9 conveyed forwardly by ~crew 138 and plas~cated so that it is in molten form as it builds up in front of nonreturn valve 42. The increase in pressure in front of valve 42 causes screw 138 ~o retrac~, and once the desired charg~
ha3 been formed, screw 138 is rammed forwardly ~o a~ to in~ect the charge through nozzle 14 into the mold as~embly. The operation of the lnjectlon molding machine 8 in the thermopla~tic configuration ~hown in Figure 4 i~ completely convant~onal in nature.
In order to convert the machine bac~ to the glas~ loaded thermoset coniguration, al~ that i8 nece88ary, i8 to replace ~crew 138 with screw 32, remove plug 128 and retain~r 136 and replaae them with liner 74 and ~leeve 82, r~move the hopper 148 from barrel 10, and attach the ~tuffer unit 72.
As mentioned earller, thi~ conversion can be accomp~i~hed withln a matter of hour~, as opposed to prior art m~ch$nery whersin the replacement of the entire bArrel a~sembly requires days.
The present invention i8 not limited to the proceg8ing of BMC when in the configuration illustrated ln Figure 1, but 18 useful when it i~ desired that m~nimal shear forces be imparted to the materlal by the ~crew.
While thi~ invention has been de~cribed as having a preferred design, it will be understood that it is ~pable of furth~r modification. Thi~
application i8, therefore, intended to cover any variations, uses, or adaptation~ of the invention -~3-~ ~ ~ 7 ~

following the general princlples thereof and including 3uch departure~ rom the pre~ent d:i~clo~ure as come within known or cuBtomary practice in the art to which this invention pertain~ and fall within the S limit~ of the appended claims.

Claims (18)

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

1. An injection molding machine comprising:
an elongated barrel having a generally cylindrical bore therein, said barrel having a forward end and a rear end and a side wall, an elongated screw rotatably and axially reciprocably received within the bore of said barrel, a first feed opening near the rear end of said barrel extending into the bore through the side wall, a second feed opening intermediate the first feed opening and the forward end of the barrel extending into the bore through the barrel side wall, and cover means attachable to said barrel for alternatively closing and opening said second feed opening.

2. The apparatus of Claim 1 wherein said screw includes a front and a rear end and flights adapted for conveying plastics material forwardly in said barrel when said screw is rotated in a given direction about its axis, said flights extending Along said screw from a point near the front end of said screw to a point just behind said second feed opening when said screw is positioned forwardly in said barrel, said screw extending through the rear end of said barrel and being contoured rearwardly from said point just behind said second feed opening such that plastics material will not be conveyed forwardly by the portion of the screw behind said point just behind said second feed opening when said screw is rotated in said given direction.

3. The apparatus of Claim 2 wherein a substantial portion of said screw rearwardly of said point just behind said second feed opening is flighted with a reverse pitch with respect to said first mentioned flights.

4. The apparatus of Claim 2 including a seal means on said screw behind said point just behind said second feed opening adapted to prevent plastics material from flowing rearwardly in said barrel past said seal means.

5. The apparatus of Claim 1 wherein said cover means is insertable into said second feed opening and includes a concave inner surface contoured to conform to a portion of said bore.

6. The apparatus of Claim 1 including a stuffer unit for glass loaded thermosetting materials connected to said second feed opening, said stuffer unit including means for forcing glass loaded thermosetting mater-ial into said barrel through said second feed opening.

7. The apparatus of Claim 6 wherein said stuffer unit comprises a reciprocable plunger for forcing the thermosetting material into said barrel.

8. An injection molding machine comprising:
an elongated barrel having a generally cylindrical bore therein, said barrel having a forward end and a rear end and a side wall, an elongated conveying screw rotatably and axially reciprocably received in said barrel, said screw having a forward portion and a rear portion and including conveying flights on the forward portion of said screw adapted to convey plastics material forwardly in said barrel when the screw is rotated in a given direction, the rear portion of said screw being contoured such that it is incapable of conveying material forwardly when said screw is rotated in said given direction, a first feed opening near the rear end of said barrel extending into said barrel through said side wall, a second feed opening intermediate said first feed opening and the forward end of the barrel extending into said barrel through said side wall, said second feed opening being in communication with the forward portion of said screw, and cover means attachable to said barrel for alternatively closing and opening said second feed opening.

9. The apparatus of Claim 8 including a second elongated conveying screw adapted to be rotatably and axially reciprocable in said barrel interchangeably with said first mentioned screw, said second screw including a forward end and a rear end and including flights thereon adapted to convey plastics material forwardly in said barrel when the screw is rotated in said given direction, the flights of said second screw extending from near the forward end thereof to a point at least as far rearward as said first feed opening when said second screw is positioned forwardly in said barrel.

10. The apparatus of Claim 8 wherein the rear portion of said screw is flighted with a reverse pitch with respect to said first mentioned flights.

11. The apparatus of Claim 8 including a seal means on said screw between the flights on said forward portion of the screw and the flighted rear portion adapted to prevent plastics material from flowing rearwardly in said barrel past said seal means.

12. In an injection molding process wherein a charge of plastics material is injected into a mold by means of a rotating and reciprocating screw, a method of converting from the injection of a thermoplas-tics compound to a fiber reinforced thermosetting compound comprising:

providing an injection molding machine having a barrel with a rotating an axially reciprocable plasticizing screw therein, the barrel having a first feed opening and a second feed opening forwardly of the first feed opening, with the second feed opening closed, feeding thermoplastic compound into the barrel through the first feed opening whereupon the material is conveyed forwardly and plasticized by the rotating screw, with the machine stopped, removing the plasticizing screw and installing a thermosetting compound conveying screw in the barrel for rotation and axial reciprocation, opening the second feed opening, and forcing a thermosetting compound having fibers dispersed therein into the barrel through the second feed opening whereupon the thermosetting compound is conveyed forwardly as the thermosetting compound conveying screw rotates.

13. The method of Claim 12 wherein the plasticizing screw is flighted for forward conveyance of the plastic material along nearly its entire length and at least forwardly of the first feed opening, and the thermosetting compound conveying screw is flighted for forward conveyance only on its forward portion and as far rearward as the second feed opening when the conveying screw is forwardly in the barrel.

14. The method of Claim 12 wherein the thermosetting compound is a glass loaded thermosetting polyester compound.

15. In an injection molding process wherein a charge of plastics material is injected into a mold by means of a rotating and reciprocating screw, a method for converting from the injection of a fiber reinforced thermosetting compound to a thermoplast-ics compound comprising:
providing an injection molding machine having a barrel with a rotating and axially reciprocable thermosetting compound conveying screw therein, the barrel having a first feed opening and a second feed opening forwardly of the first feed opening, with the second feed opening open, forcing a thermosetting compound having fibers dispersed therein into the barrel through the second feed opening whereupon the thermosetting compound is conveyed forwardly as the conveying screw rotates, with the machine stopped, removing the conveying screw and installing a plasticizing screw in the barrel for rotation and axial reciprocation, covering the second feed opening, and feeding thermoplastic compound into the barrel through the first feed opening whereupon the material is conveyed forwardly and placticized by the rotating plasticizing screw.

16. The method of Claim 15 wherein the plasticizing screw is flighted for forward conveyance of the plastic material along nearly its entire length and at least forwardly of the first feed opening, and the thermosetting compound conveying screw is flighted for forward conveyance only on its forward portion and as far rearward as the second feed opening when the conveying screw is forwardly in the barrel.

17. The method of Claim 15 wherein the thermosetting compound is a glass loaded thermosetting polyester compound.

18. The method of Claim 17 wherein the thermosetting compound is a bulk molding compound.