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Closed moulding: A cheap solution to styrene emission
Closed moulding: a cheap s o l u t i o n to styrene e m i s s i o n As a major supplier o f unsaturated p o l y e s t e r a n d vinyl ester resins in Western Europe, DSM Resins has to face increasingly stringent legislation over styrene e m i s s i o n levels. This limitation will b e c o m e m o r e serious w i t h further r e d u c t i o n s in t h e a l l o w e d w o r k s h o p c o n c e n t r a t i o n . B e n Drogt, application m a n a g e r o f Structural Resins, l o o k s at o n e o f t h e m e t h o d s available to o v e r c o m e this p r o b l e m .
In m o s t cases the reinT h e r e are t h r e e principarts per million (ppm) f o r c e m e n t has b e e n preple w a y s to r e d u c e styrp o s i t i o n e d in the mould. e n e emission: developThese processes are m e n t o f resins w i t h a known under various lower styrene emission n a m e s as: (high solid resins and film f o r m i n g additives); • V a c u u m injection development of im• Resin transfer mouldp r o v e d ventilation and ing (RTM) air c l e a n i n g s y s t e m s ; • Structural r e a c t i o n inand development of jection moulding closed m o u l d i n g techni(SR~M) ques. Although DSM ReIn s o m e cases the reins i n s is v e r y a c t i v e l y ~ ~t~ oe Get~ ~j s~e~e~ ~ o ~ e . ~ e 6 a ~ ~s forcement fibres are i n v o l v e d in t h e first a d d e d to the resin bet w o fields it is the third fore injection: p r i n c i p l e w h i c h this reM a x i m u m a l l o w e d styrene concentration in the workshop. • Bulk m o u l d i n g c o m port will consider. pound injection Closed m o u l d i n g is defined as a t e c h n i q u e for p r o d u c i n g (BMC injection) j e c t e d into a closed m o u l d and for fibre reinforced thermosetting • Reinforced reaction injection that r e a s o n no direct e x p o s u r e o f parts in w h i c h resin will b e inm o u l d i n g (RRIM) the resin to the o p e n air will occur.
Reinforced Plastics March 1994
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0034-3617/94/$7.00( 1994, Elsevier Science Ltd
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I.ct us look me)re ch)selv at tilt: first three techniques. Apart from being c o m p l c m c n tarv in t i l t + i c c h n o l o g y ficlcl, the thrcc proccssing t e c h n i q u e s arc also c{mlt~iemcntary with r e s p c c t to cycle times and levels of inxestment. This can also lye i n t e r p r e t e d in terms of tile relationship bet w e e n series length and required investment as r e p r e s e n t e d in Figure 2. In this figure it is clear that thc t e c h n o l o g i c s arc c o m p l e n l c n t;iry aild c o v e r a large range of scries lengths from I to + SO 000 per year. T h e level of automation in each processing tcchnique varies. SRIM Cam be automated to a ver~' high Icvcl w h i c h results in a Io\v cont r i b u t i o n ()f the l;lbour costs ill t i l t f i n a l c o s t p r i c e o f t h e parts.
Vacuunl injection on the o t h e r hand is a relatively high labour consuming technique (comparable to hand laly-up), but tile contribution o f t o o l i n g :md e q u i p m e n t d e p r e c i a t i o n in tile cost price is low. In Figure 3 the cost breakd o w n of ,l specific part p r o d u c e d by the d i f f e r e n t t e c h n i q u e s is represented. It must be n o t e d that only the relative cost b r e a k d o w n is given, the absolute cost priccs :ire ¢liffcrcnt.
The closed m o u l d i n g techniques vacuunl injection, RTM and
10
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SRIM are cl;tssed as injcction tcch niques in w h i c h tile reinfl)rcement was put into place befl)rc closing the m o u l d and heft)re resin impregnation. This gives a high d e g r e e of control over tile a m o u n t and o r ientation of the r c i n f o r c c m c n t s o that localized stresses in a part can lye c o u n t e r e d by increasing the fibre loading. In c o m b i n a t i o n with m a t c h e d moulds, as used in RTM and SRIM, this control over the fibre loading gives a correspontting c o n t r o l over the fibre c o n t e n t s in t h e part. T h e c o n s i s t e n c y alld quality of parts, p r o d u c e d in v;lcuum injection. RTM or SRIM. is therefore very high. The Structural Resins (Stoup of DSM Resins w o r k s in three distinct areas as regards closed moulding injection tcchniques. These fields arc c o v e r e d by t h r e e o n - g o i n g projects within the d e v e l o p m e n t laboratories of I)SM Resins. These projects art': • Vacuum injection; • Low profile RTM; and • Hybrid resins. These projects c o v e r the technology field as previously described i.e., v a c u u m injection, resin transfcr moulding and structural reaction injection mouhJing. ~'c ~,~ill t/ox~ look at the p r o j c c t s ill more detail, starting with the v a c u u m injection project.
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In tht+" c()I3ttfxt ()[ r e d u c i n g styrene emission levels, a solution has bt'en t+Icvt'h>pct+l to help lll;+llltlfacturcrs of glass rcinforct+'d lYlastic (GRI >) parts to s\vilch fi'om hantl lay-up ant+l s p r a y up tc~ a cost cfft'ctivc alternative producti fint+l a tneans by w h i c h largt+', high quality prot+iut'ts coeIM bc maclc w i t h o u t tile t+'mis sion of styrene t+hn-ing produt+'tion. A prerequisite was thitt the manufacturer shouM riot be forced to make large investments in (nov<) moulds or equipment. The result of this dexch)pmetlt is ;t cont+'cpt basctl on the resin injection technique in \vhich "c,icuum is u+cd ,is ,t t+triving force for the injection and ,t f l c x i h l e film is tlSt+'d ,1~ tilt+" ~>tllcr m o u M half: vacuunl injection. l+hc first half of the m()uM v+ill bc in most cases a slightly modified hand lay-uly or spray-up m o u l d The c~mccpt is sho\vil in Figurc t \ w i d e r,illgc ()t: rt'inforccnlcilts can bc d c c t i i l l l l l o d a t c d , fl'()ill chotypcd ~trand ghtss mat to woveil aranlid t)r carbon. The reinforc c m c n t Call bc p o s i t i o n c d v c r v prcciscly and inserts and stiffening rib,~ c;til bc intcgrcttcd into the lanlinatc such ;is corc materials ( p o l y v i n y l chlt~riclc (PV(;) or polyu r c t halle' ( 1:'1) foams ) aild
Rcintolccd lqa~qics March 19ql
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S-RIM
Depreciation tooling and equipment Labour costs Material costs I~TGI/RE 3: Relative cost b r e a k d o w n o f various closed m o u l d i n g techniques. "Ibe costs o f the parts h a v e been calculated f o r diflerent parts a n d di[]'erent series lengths that are specific lbr each processing technique. V a c u u m injection: s m a l l boat; length +_3 m; total weight 25 leg; series length 200; RTM.. body p a n e l s f o r coach; surface + 0.8 m-': total weight + 5 ~ ; series length 2000~year; SRIM.. structural parts o f car: surJace +_0.4 me; total weight ÷ .:I.6 kg; series letzgth 2 0 O00/.),ear
fasteners. T h e i m p r e g n a t i o n p h a s e itself d o e s not r e q u i r e any labour effort b e c a u s e the v a c u u m action d o e s the work. W e can t h e r e f o r e see that t h e r e are b o t h advantages and disadvantages. Advantages of the v a c u u m injection system: • No styrene emission. • Ve W clean w o r k s h o p . • I n c o r p o r a t i o n of c o r e s and inserts is possible. • Low i n v e s t m e n t in e q u i p m e n t ; hand lay-up and spray-up mtmlds can easily b e adapted. T h e disadvantages arc: • Reinfi~rcement m u s t always b e a mat ( w o v e n roving or c o m b i n a tion m a t ) w h i c h is a slightly more expensive than normal roving (but truly in c o m p a r i s o n w i t h spray-up). • T h e p o s i t i o n i n g of the mat and
Rcinfi~rccd Plastics March 1994
the film is slightly m o r e labour i n t e n s i v e t h a n , fl)r e x a m p l e , s p r a y - u p ( b u t c o m p a r a b l e to hand lay-up). T h e v a c u u m injection p r o j e c t has b e e n f o c u s e d tm four areas: raw materials, tools, p r o c e s s c t m t r o l and design a d a p t i o n w i t h the aim b e i n g to deliver a t u r n k e y technology to the market. W e not only tailored resins to this application
FI6'URE 4:
V a c u u m injection.
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but w e also d e v e l o p e d o t h e r dedicated system c o m p o n e n t s such as tools, application k n o w - h o w and films. For e x a m p l e , w c d e v e l o p e d and p r o d u c e d a special film (based on p o l y e t h y l e n e ) in c o o p e r a t i o n w i t h DSM P o l y m e r s in G e l e e n , T h e Netherlands. This special film has an elongation of 500%, is nonp e r m e a b l e to styrene and has a high p u n c t u r e resistance.
T h e target m a r k e t s s e l e c t e d fi)r the v a c u u m injection p r o c e s s are marine, transport, building and c o n s t r u c t i o n . DSM Resins' customers have been experimenting w i t h v a c u u m injection systems for hoat building since the 1970s and w e have c o n t i n u o u s l y s u p p o r t e d these d e v e l o p m e n t s as a result of the strate~" to c o - d e v e l o p p r o d u c t s with clients w h e n e v e r it is feasible. Some i m p o r t a n t p r o d u c t s that w e r e m a d e are:
the low proFde RTM system, no gelcoat is r e q u i r e d and t h e r e f o r e a m a j o r s o u r c e of styrene emission is eliminated.
• Boat p r o d u c t i o n set-up, small to large series • P r o d u c t i o n of high quality (e.g., s a n d w i c h side panels, i n t e g r a t e d s a n d w i c h panels for trucks and roofs for buses) • L a m i n a t e d sails for w i n d m i l l s (11 m e t r e s long w i t h a glass c o n t e n t of 68%) • Offshore s a n d w i c h panels • Roofs fi)r buildings ( s a n d w i c h construction with integrated cable trays) • Bath t u b s b a s e d on m e t h v l m e t h a c w l a t c (MMA) T h e v a c u u m injection t e c h n o l o g y is ideal for small to m e d i u m series (I to 1000 parts a year) of large parts ( g r e a t e r d3an 2 m e t r e s ) for which mechanical requirements are m e d i u m t() high.
• I ) e v e l o p m c n t of an RTM resin system for Class A surface quality parts • I)evclopment of processing k n o w - h o w of RTM at h i g h e r temperatures • Evaluation of injection equipmerit • Establishment of joint p r o j e c t s w i t h clients T h e o b j e c t i v e of the low profile RTM p r o j e c t is to offer c u s t o m e r s a resin s y s t e m t o g e t h e r w i t h t h e t e c h n o l o g y to p r o c e s s the resin to p r o d u c e high surface quality parts.
T h e target m a r k e t s for this resin are in t r a n s p o r t and building, and o t h e r areas w h e r e a high surface quali D, is required. The different development fields for the entire system (consisting not only of the resin but also the processing know-how and h a r d w a r e k n o w - h o w ) are:
A g o o d e x a m p l e of w h e r e the rcsin and RTM t e c h n i q u e has b e e n i n t r o d u c e d to a client is at Indupol, a m a j o r p r o d u c e r of GRP parts in Belgium. lndupol set up an RTM
p r o d u c t i o n line fl)r w h e e l covers fi)r BOVA luxury c o a c h e s (see Fig u r e ~). lndup,:)l d e c i d e d to prod u c e t h e s e panels in RTM h e c a u s c of the h)wer styrene emission, b e t t e r reproducibility ()f the parts and the r e d u c e d cycle time. 1)SM Resins d e v e l o p e d a range of h y b r i d r e s i n s b a s e d o n t h e c o m h i n a t i o n of p o l y e s t e r and polyu r e t h a n e t e c h n o h ) g y : the l)aron h y b r i d s . T h e c h a r a c t e r i s t i c s ()f these resins art: • h)x~ viscositx (2()0-,i()0 MPa.s ;It roolll t e m p e r a t u r e ) • high curing s p e e d ,tt low temp e r a t u r e s (gel-time of I m i n u t e ;it ~() (~) • high mcch.trdcal p r o p e r t i e s (i.e.. ch)ngati(m at b r e a k + -"'~,, c()mbined with high strcngth and nlodulus). Considering t h e s e characteristics it is clear that the I)aron 19vbrids are well suited to application in structural RIM p r o c e s s e s (SRIM). The short curing Iinles and the low viscosity m a k e injecti(m processing at short cycle times possible. In its laboratories I)SM Resins invcstigated the high s p e e d prod u c t i o n ~)1 parts using thcse hybrid rcsins. J()illt tc'~t p r ( ) g r a m m e s with
Resin transfi'r m o u l d i n g can b e defined as a resin injection techniq u e at low p r e s s u r e levels (0.30 6 MPa, making use of m e d i u m cost moulds). Recent d e v e l o p m e n t w o r k carried out bv I)SM Resins has r e s u l t e d in Svnolitc "741--tt-1, a resin system w h i c h gives a high quality (Class A) finish. This resin system is based on a low profile additive d e s i g n e d for optimal perfi)rmancc at -'0 C, thus giving the possibility of using it at t e m p e r a tures that arc m u c h l o w e r than k n o w n low profile s y s t e m s fi)r example sheet moulding comp o u n d (SMC) ( 140- 160 C ). At present, in m o s t cases, a gelcoat is used to create a reasonably g o o d surface quality but by using
FIGURE 5: REll wheelcovers,fbr B()tL4 l u x u O, coclches prodi;ced I~1, lndtq~*~k
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Rcintorccd I>lastics March 109i
K & C MOULDINGS (DOWNLAND) LTD Passer d'une appilicatron manuelle a une production par puJverisatlon peut sembler un grand pas mais avec de bons consells et un soutient adapte, c'est un pas en avant facile a effectuer. Les advantages soot rmportants: un processus de production plus rapide et plus facile beaucoup radios de gaspillage de matiere et un moulage fini de bien meilleure qualite. Ayant plus de vingt ans d'experrence darts la fourniture de systemes de pulverisation GRP (resines/fibres de verre) un service d'installation et de rem~se en mares complet et un systeme de commande de pieces "par retour" K & C Mouldings peut veritablement affirmer ~tre la meilreure societe chez qut acheter votre systeme Des demonstrations de la gamme de purverisatlon 'Downland 1991' et de tout autre equipement 'Downiand - peuvent~trefacilementorgantsees.
FIGURE 6." T h e r m o f o r m i n g
suppliers of injection equipment (i.e., Cannon, Italy and Aplicator, Sweden) have also been carried out.
Apart from the injection equipment, a production line for high volume structural SRIM parts will consist of: • a reinforcement preforming unit • the production mould • a clamp force unit • an injection machine A reinforcement preforming unit is necessa W in an industrialized SRIM process to have preforms available for a production cycle time of just a few minutes. Currently t w o processes for preforming have emerged or are emerging. The first is to thermoform continuous strand mat (or another form of reinforcement)
and to consolidate this preform with a binder. Essentially a reinforcing pack of mat will be heated (normally with infrared heaters) above the melting point of the binder and then transferred rapidly to a cold pressing mould (Figure 6). The second method is Directed Fibre Spray Up. This is a further development of the existing process of making a preform with an air f l o w t h r o u g h a screen. C h o p p e d f i b r e s and a small a m o u n t of p o w d e r binder are sucked onto a screen (which has the product shape) and are consolidated to a preform by melting and cooling the binder. Today's robotized version of this process allows p l a c e m e n t of the fibres where required (Figure 7).
Von der Handgun- zur Spr,tzgu#produkbon mag es als ein gro~,er Schritt erschemen -- aber mit der richtigen Beragtung und Unterstutzuog ist es ein Schritt, den man bequem machen kann Und die Vorteile sind erheblicher Natur Ein weitaus leIohterer und schnelrerer Producktionsvorgang Sehr viel weniger Abfallprodukte Und ein Formgul~ yon emer qualitativ weitaus besseren Fertigung Mit 0ber 20 Jahren Erfahrung bei der Lieferung von GRP Spritzgu#systemen und emem kompletten Kommlssions- und Instarlationsservice und eing Ersatzteile-Bestellsystem mit der nachsten Post, Kdmmen K & C Mouldings rail Recht von sichbehauptendiebesteFirmazusem beiderSie rhr System kaufen Konnen Vorf0hrungen der 1991 Downland Spritzgul}kollektion und aller anderen Gerate yon Downland -- K0nnen je nach Bedarf vereinbart werden Posiblemente parece un gran paso desde la preparacion manual hasta la producc~on por rocio - pero siguiendo los consejos y el apoy correctos resulta ser un paso que se puede hacer sin dificultad. Y los beneficios son cuantiosos. Un proceso de produccion much mas f a c i l y rapido Mucha mends perd~da de material Y una p~eza moldeada acabada de una calidad muy superior Contando con m~ts de 20 argos de experiencla en el suministro de sistemas de roc[o de GRP (ph~stico reforzado con libra de vidrio), un servlcio comprensivo de instalacion y puesta a punto y un sistema de pedido de piezas de repuesto para entrega inmediata, K & C Mouldings puede, con razon, considerarse la melor compar~[a para ele suministro de sus requisitos Con mucho gusto organizariamos una demostracion der la gama de rocio Downland 1991 - o culaquier otro equipo Downland
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FIGURE 7." Directecl f i b r e preforming.
Reinforced Plastics March 1994
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with press moulding since low cost tools and clamp force unit can be used • improved product strength through total control over a m o u n t and orientation of fibres The drawbacks of SRIM are: • higher level of investment compared to hand lay-up and sprayup • t e c h n i q u e is only economically viable for m e d i u m and large v o l u m e series T h e target markets for SRIM are transport, building, c o n s t r u c t i o n , and electrical and electronic goods, w h e r e g o o d m e c h a n i c a l p r o p e r t i e s and s h o r t cycle times are required.
FIGURE 8: SRIM processing e q u i p m e n t
Certain products, such as fiat shapes, may not n e e d a p r e f o r m i n g o p e r a t i o n and p r e f o r m s can also often be fabricated off-line, in an inh o u s e o p e r a t i o n or by a subcontractor. T h e p r o d u c t i o n mould can be made from various materials. GRP tooling is e x p e c t e d to find limited use because of its m o d e s t lifeume. SRIM is suited to volumes u p w a r d s of several t h o u s a n d parts per year w h i c h calls for nickel shell tooling or alternatives made from aluminium or metal alloys. T h e advantage of metal (faced) tooling is the e x c e l l e n t heat transfer, ensuring the highest product i o n s p e e d s . T h e DSM R e s i n s a p p r o a c h is to avoid steel tooling, t h e r e b y offering a substantial inv e s t m e n t r e d u c t i o n c o m p a r e d with c o m p r e s s i o n moulding. SRIM also does not require steel tooling, since t h e t e m p e r a t u r e and p r e s s u r e s involved are relatively low. T h e clamp force unit can be any unit capable of carrying a mould and c l o s i n g this m o u l d t i g h t l y during injection. Injection is carried out at relatively low pressures
Reinforced Plastics March 1994
that typically do not e x c e e d an average value of 1 MPa. The injection m a c h i n e is used to m e t e r the t w o p r e m i x e s ( w h i c h c o n s t i t u t e a Daron hybrid resin system), and to mix and inject this s y s t e m into t h e h e a t e d mould. Mixing is a non critical operation, w h e r e considerable ratio deviations are tolerable. The s c h e m a t i c set up of an injection m a c h i n e for Daron hybrids is r e p r e s e n t e d in Figure 8. T h e cost for an injection machine is s o m e w h e r e b e t w e e n that o f a s p r a y u p u n i t ( w h i c h is essentially a similar two c o m p o n e n t dispensing unit) and a PU mixing unit ( w h i c h allows a higher level of a u t o m a t i o n o f the process). The benefits of SRIM with Daron hybrids are: • no styrene emission because of the closed moulding p r o c e s s • i m p r o v e d and c o n s i s t e n t product quality because of the industrialized manufacturing process • p r o d u c t s have two s m o o t h sides (no fibre pattern on reverse) • savings in labour • lower investments compared
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DSM Resins has long b e e n at the f o r e f r o n t in the d e v e l o p m e n t of low styrene emission resins and the investigation of improved air handling systems for workshops. Closed moulding t e c h n i q u e s are clearly a n o t h e r s o l u t i o n to the styrene emission problem. T h e s e t e c h n i q u e s , specifically v a c u u m injection, resin transfer m o u l d i n g (RTM) and s t r u c t u r a l reaction injection moulding (SRIM), m e a n practically zero styre n e emission. The t h r e e t e c h n i q u e s are similar as regards cycle times, r e q u i r e d investment and optimal series length. With its e x p e r t i s e in the develo p m e n t of resins for closed moulding i n j e c t i o n c o m b i n e d w i t h processing know-how, DSM Resins is well positioned to help clients to start closed m o u l d processing or to help t h e m switch from traditional hand or spray lamination methods.
The a u t h o r wishes to t h a n k Frits D o l l e m a n , Gerard v a n den H o n d e l a n d R i c h a r d Pieters o f DSM Resins, Zwolle, The Netherlands, a n d P a u l Brittles o f DSM Resins UK in Ellesmere Port f o r their collaboration.
In m o s t cases the reinT h e r e are t h r e e principarts per million (ppm) f o r c e m e n t has b e e n preple w a y s to r e d u c e styrp o s i t i o n e d in the mould. e n e emission: developThese processes are m e n t o f resins w i t h a known under various lower styrene emission n a m e s as: (high solid resins and film f o r m i n g additives); • V a c u u m injection development of im• Resin transfer mouldp r o v e d ventilation and ing (RTM) air c l e a n i n g s y s t e m s ; • Structural r e a c t i o n inand development of jection moulding closed m o u l d i n g techni(SR~M) ques. Although DSM ReIn s o m e cases the reins i n s is v e r y a c t i v e l y ~ ~t~ oe Get~ ~j s~e~e~ ~ o ~ e . ~ e 6 a ~ ~s forcement fibres are i n v o l v e d in t h e first a d d e d to the resin bet w o fields it is the third fore injection: p r i n c i p l e w h i c h this reM a x i m u m a l l o w e d styrene concentration in the workshop. • Bulk m o u l d i n g c o m port will consider. pound injection Closed m o u l d i n g is defined as a t e c h n i q u e for p r o d u c i n g (BMC injection) j e c t e d into a closed m o u l d and for fibre reinforced thermosetting • Reinforced reaction injection that r e a s o n no direct e x p o s u r e o f parts in w h i c h resin will b e inm o u l d i n g (RRIM) the resin to the o p e n air will occur.
Reinforced Plastics March 1994
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0034-3617/94/$7.00( 1994, Elsevier Science Ltd
1
10
100 Cyclelime (rain.) :
1
1000
I.'I(,'I.'RI:' I.. (.)'cle li#*#es versus req/m'eU i,/vesl#Hents ¢~/closeU *#/ollld i#{ie(+lio*# h'('/~##iqlles.
I.ct us look me)re ch)selv at tilt: first three techniques. Apart from being c o m p l c m c n tarv in t i l t + i c c h n o l o g y ficlcl, the thrcc proccssing t e c h n i q u e s arc also c{mlt~iemcntary with r e s p c c t to cycle times and levels of inxestment. This can also lye i n t e r p r e t e d in terms of tile relationship bet w e e n series length and required investment as r e p r e s e n t e d in Figure 2. In this figure it is clear that thc t e c h n o l o g i c s arc c o m p l e n l c n t;iry aild c o v e r a large range of scries lengths from I to + SO 000 per year. T h e level of automation in each processing tcchnique varies. SRIM Cam be automated to a ver~' high Icvcl w h i c h results in a Io\v cont r i b u t i o n ()f the l;lbour costs ill t i l t f i n a l c o s t p r i c e o f t h e parts.
Vacuunl injection on the o t h e r hand is a relatively high labour consuming technique (comparable to hand laly-up), but tile contribution o f t o o l i n g :md e q u i p m e n t d e p r e c i a t i o n in tile cost price is low. In Figure 3 the cost breakd o w n of ,l specific part p r o d u c e d by the d i f f e r e n t t e c h n i q u e s is represented. It must be n o t e d that only the relative cost b r e a k d o w n is given, the absolute cost priccs :ire ¢liffcrcnt.
The closed m o u l d i n g techniques vacuunl injection, RTM and
10
100 1000 Series length (palls/year)
lO,OgO
lOli,OOO
KI(,I'Rt:" 2: Series lesl,gl/~s i'm'sits rcq/li#'eU iP/veslJ#letlls ¢?/('l+Js(>~l *#m/lid i#{ieclhm h ' c t , liq#,'s
SRIM are cl;tssed as injcction tcch niques in w h i c h tile reinfl)rcement was put into place befl)rc closing the m o u l d and heft)re resin impregnation. This gives a high d e g r e e of control over tile a m o u n t and o r ientation of the r c i n f o r c c m c n t s o that localized stresses in a part can lye c o u n t e r e d by increasing the fibre loading. In c o m b i n a t i o n with m a t c h e d moulds, as used in RTM and SRIM, this control over the fibre loading gives a correspontting c o n t r o l over the fibre c o n t e n t s in t h e part. T h e c o n s i s t e n c y alld quality of parts, p r o d u c e d in v;lcuum injection. RTM or SRIM. is therefore very high. The Structural Resins (Stoup of DSM Resins w o r k s in three distinct areas as regards closed moulding injection tcchniques. These fields arc c o v e r e d by t h r e e o n - g o i n g projects within the d e v e l o p m e n t laboratories of I)SM Resins. These projects art': • Vacuum injection; • Low profile RTM; and • Hybrid resins. These projects c o v e r the technology field as previously described i.e., v a c u u m injection, resin transfcr moulding and structural reaction injection mouhJing. ~'c ~,~ill t/ox~ look at the p r o j c c t s ill more detail, starting with the v a c u u m injection project.
39
In tht+" c()I3ttfxt ()[ r e d u c i n g styrene emission levels, a solution has bt'en t+Icvt'h>pct+l to help lll;+llltlfacturcrs of glass rcinforct+'d lYlastic (GRI >) parts to s\vilch fi'om hantl lay-up ant+l s p r a y up tc~ a cost cfft'ctivc alternative producti
Rcintolccd lqa~qics March 19ql
4 ¸i l ! ( ? :
iiiiiii!ilil!i
RTM
S-RIM
Depreciation tooling and equipment Labour costs Material costs I~TGI/RE 3: Relative cost b r e a k d o w n o f various closed m o u l d i n g techniques. "Ibe costs o f the parts h a v e been calculated f o r diflerent parts a n d di[]'erent series lengths that are specific lbr each processing technique. V a c u u m injection: s m a l l boat; length +_3 m; total weight 25 leg; series length 200; RTM.. body p a n e l s f o r coach; surface + 0.8 m-': total weight + 5 ~ ; series length 2000~year; SRIM.. structural parts o f car: surJace +_0.4 me; total weight ÷ .:I.6 kg; series letzgth 2 0 O00/.),ear
fasteners. T h e i m p r e g n a t i o n p h a s e itself d o e s not r e q u i r e any labour effort b e c a u s e the v a c u u m action d o e s the work. W e can t h e r e f o r e see that t h e r e are b o t h advantages and disadvantages. Advantages of the v a c u u m injection system: • No styrene emission. • Ve W clean w o r k s h o p . • I n c o r p o r a t i o n of c o r e s and inserts is possible. • Low i n v e s t m e n t in e q u i p m e n t ; hand lay-up and spray-up mtmlds can easily b e adapted. T h e disadvantages arc: • Reinfi~rcement m u s t always b e a mat ( w o v e n roving or c o m b i n a tion m a t ) w h i c h is a slightly more expensive than normal roving (but truly in c o m p a r i s o n w i t h spray-up). • T h e p o s i t i o n i n g of the mat and
Rcinfi~rccd Plastics March 1994
the film is slightly m o r e labour i n t e n s i v e t h a n , fl)r e x a m p l e , s p r a y - u p ( b u t c o m p a r a b l e to hand lay-up). T h e v a c u u m injection p r o j e c t has b e e n f o c u s e d tm four areas: raw materials, tools, p r o c e s s c t m t r o l and design a d a p t i o n w i t h the aim b e i n g to deliver a t u r n k e y technology to the market. W e not only tailored resins to this application
FI6'URE 4:
V a c u u m injection.
42
but w e also d e v e l o p e d o t h e r dedicated system c o m p o n e n t s such as tools, application k n o w - h o w and films. For e x a m p l e , w c d e v e l o p e d and p r o d u c e d a special film (based on p o l y e t h y l e n e ) in c o o p e r a t i o n w i t h DSM P o l y m e r s in G e l e e n , T h e Netherlands. This special film has an elongation of 500%, is nonp e r m e a b l e to styrene and has a high p u n c t u r e resistance.
T h e target m a r k e t s s e l e c t e d fi)r the v a c u u m injection p r o c e s s are marine, transport, building and c o n s t r u c t i o n . DSM Resins' customers have been experimenting w i t h v a c u u m injection systems for hoat building since the 1970s and w e have c o n t i n u o u s l y s u p p o r t e d these d e v e l o p m e n t s as a result of the strate~" to c o - d e v e l o p p r o d u c t s with clients w h e n e v e r it is feasible. Some i m p o r t a n t p r o d u c t s that w e r e m a d e are:
the low proFde RTM system, no gelcoat is r e q u i r e d and t h e r e f o r e a m a j o r s o u r c e of styrene emission is eliminated.
• Boat p r o d u c t i o n set-up, small to large series • P r o d u c t i o n of high quality (e.g., s a n d w i c h side panels, i n t e g r a t e d s a n d w i c h panels for trucks and roofs for buses) • L a m i n a t e d sails for w i n d m i l l s (11 m e t r e s long w i t h a glass c o n t e n t of 68%) • Offshore s a n d w i c h panels • Roofs fi)r buildings ( s a n d w i c h construction with integrated cable trays) • Bath t u b s b a s e d on m e t h v l m e t h a c w l a t c (MMA) T h e v a c u u m injection t e c h n o l o g y is ideal for small to m e d i u m series (I to 1000 parts a year) of large parts ( g r e a t e r d3an 2 m e t r e s ) for which mechanical requirements are m e d i u m t() high.
• I ) e v e l o p m c n t of an RTM resin system for Class A surface quality parts • I)evclopment of processing k n o w - h o w of RTM at h i g h e r temperatures • Evaluation of injection equipmerit • Establishment of joint p r o j e c t s w i t h clients T h e o b j e c t i v e of the low profile RTM p r o j e c t is to offer c u s t o m e r s a resin s y s t e m t o g e t h e r w i t h t h e t e c h n o l o g y to p r o c e s s the resin to p r o d u c e high surface quality parts.
T h e target m a r k e t s for this resin are in t r a n s p o r t and building, and o t h e r areas w h e r e a high surface quali D, is required. The different development fields for the entire system (consisting not only of the resin but also the processing know-how and h a r d w a r e k n o w - h o w ) are:
A g o o d e x a m p l e of w h e r e the rcsin and RTM t e c h n i q u e has b e e n i n t r o d u c e d to a client is at Indupol, a m a j o r p r o d u c e r of GRP parts in Belgium. lndupol set up an RTM
p r o d u c t i o n line fl)r w h e e l covers fi)r BOVA luxury c o a c h e s (see Fig u r e ~). lndup,:)l d e c i d e d to prod u c e t h e s e panels in RTM h e c a u s c of the h)wer styrene emission, b e t t e r reproducibility ()f the parts and the r e d u c e d cycle time. 1)SM Resins d e v e l o p e d a range of h y b r i d r e s i n s b a s e d o n t h e c o m h i n a t i o n of p o l y e s t e r and polyu r e t h a n e t e c h n o h ) g y : the l)aron h y b r i d s . T h e c h a r a c t e r i s t i c s ()f these resins art: • h)x~ viscositx (2()0-,i()0 MPa.s ;It roolll t e m p e r a t u r e ) • high curing s p e e d ,tt low temp e r a t u r e s (gel-time of I m i n u t e ;it ~() (~) • high mcch.trdcal p r o p e r t i e s (i.e.. ch)ngati(m at b r e a k + -"'~,, c()mbined with high strcngth and nlodulus). Considering t h e s e characteristics it is clear that the I)aron 19vbrids are well suited to application in structural RIM p r o c e s s e s (SRIM). The short curing Iinles and the low viscosity m a k e injecti(m processing at short cycle times possible. In its laboratories I)SM Resins invcstigated the high s p e e d prod u c t i o n ~)1 parts using thcse hybrid rcsins. J()illt tc'~t p r ( ) g r a m m e s with
Resin transfi'r m o u l d i n g can b e defined as a resin injection techniq u e at low p r e s s u r e levels (0.30 6 MPa, making use of m e d i u m cost moulds). Recent d e v e l o p m e n t w o r k carried out bv I)SM Resins has r e s u l t e d in Svnolitc "741--tt-1, a resin system w h i c h gives a high quality (Class A) finish. This resin system is based on a low profile additive d e s i g n e d for optimal perfi)rmancc at -'0 C, thus giving the possibility of using it at t e m p e r a tures that arc m u c h l o w e r than k n o w n low profile s y s t e m s fi)r example sheet moulding comp o u n d (SMC) ( 140- 160 C ). At present, in m o s t cases, a gelcoat is used to create a reasonably g o o d surface quality but by using
FIGURE 5: REll wheelcovers,fbr B()tL4 l u x u O, coclches prodi;ced I~1, lndtq~*~k
43
Rcintorccd I>lastics March 109i
K & C MOULDINGS (DOWNLAND) LTD Passer d'une appilicatron manuelle a une production par puJverisatlon peut sembler un grand pas mais avec de bons consells et un soutient adapte, c'est un pas en avant facile a effectuer. Les advantages soot rmportants: un processus de production plus rapide et plus facile beaucoup radios de gaspillage de matiere et un moulage fini de bien meilleure qualite. Ayant plus de vingt ans d'experrence darts la fourniture de systemes de pulverisation GRP (resines/fibres de verre) un service d'installation et de rem~se en mares complet et un systeme de commande de pieces "par retour" K & C Mouldings peut veritablement affirmer ~tre la meilreure societe chez qut acheter votre systeme Des demonstrations de la gamme de purverisatlon 'Downland 1991' et de tout autre equipement 'Downiand - peuvent~trefacilementorgantsees.
FIGURE 6." T h e r m o f o r m i n g
suppliers of injection equipment (i.e., Cannon, Italy and Aplicator, Sweden) have also been carried out.
Apart from the injection equipment, a production line for high volume structural SRIM parts will consist of: • a reinforcement preforming unit • the production mould • a clamp force unit • an injection machine A reinforcement preforming unit is necessa W in an industrialized SRIM process to have preforms available for a production cycle time of just a few minutes. Currently t w o processes for preforming have emerged or are emerging. The first is to thermoform continuous strand mat (or another form of reinforcement)
and to consolidate this preform with a binder. Essentially a reinforcing pack of mat will be heated (normally with infrared heaters) above the melting point of the binder and then transferred rapidly to a cold pressing mould (Figure 6). The second method is Directed Fibre Spray Up. This is a further development of the existing process of making a preform with an air f l o w t h r o u g h a screen. C h o p p e d f i b r e s and a small a m o u n t of p o w d e r binder are sucked onto a screen (which has the product shape) and are consolidated to a preform by melting and cooling the binder. Today's robotized version of this process allows p l a c e m e n t of the fibres where required (Figure 7).
Von der Handgun- zur Spr,tzgu#produkbon mag es als ein gro~,er Schritt erschemen -- aber mit der richtigen Beragtung und Unterstutzuog ist es ein Schritt, den man bequem machen kann Und die Vorteile sind erheblicher Natur Ein weitaus leIohterer und schnelrerer Producktionsvorgang Sehr viel weniger Abfallprodukte Und ein Formgul~ yon emer qualitativ weitaus besseren Fertigung Mit 0ber 20 Jahren Erfahrung bei der Lieferung von GRP Spritzgu#systemen und emem kompletten Kommlssions- und Instarlationsservice und eing Ersatzteile-Bestellsystem mit der nachsten Post, Kdmmen K & C Mouldings rail Recht von sichbehauptendiebesteFirmazusem beiderSie rhr System kaufen Konnen Vorf0hrungen der 1991 Downland Spritzgul}kollektion und aller anderen Gerate yon Downland -- K0nnen je nach Bedarf vereinbart werden Posiblemente parece un gran paso desde la preparacion manual hasta la producc~on por rocio - pero siguiendo los consejos y el apoy correctos resulta ser un paso que se puede hacer sin dificultad. Y los beneficios son cuantiosos. Un proceso de produccion much mas f a c i l y rapido Mucha mends perd~da de material Y una p~eza moldeada acabada de una calidad muy superior Contando con m~ts de 20 argos de experiencla en el suministro de sistemas de roc[o de GRP (ph~stico reforzado con libra de vidrio), un servlcio comprensivo de instalacion y puesta a punto y un sistema de pedido de piezas de repuesto para entrega inmediata, K & C Mouldings puede, con razon, considerarse la melor compar~[a para ele suministro de sus requisitos Con mucho gusto organizariamos una demostracion der la gama de rocio Downland 1991 - o culaquier otro equipo Downland
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Head Office & Sales Spa House, Shellanger, Diss, Norfolk IP22 2DF Tel: Diss (0379) 642600 Fax: (0379) 650304
FIGURE 7." Directecl f i b r e preforming.
Reinforced Plastics March 1994
~
44
with press moulding since low cost tools and clamp force unit can be used • improved product strength through total control over a m o u n t and orientation of fibres The drawbacks of SRIM are: • higher level of investment compared to hand lay-up and sprayup • t e c h n i q u e is only economically viable for m e d i u m and large v o l u m e series T h e target markets for SRIM are transport, building, c o n s t r u c t i o n , and electrical and electronic goods, w h e r e g o o d m e c h a n i c a l p r o p e r t i e s and s h o r t cycle times are required.
FIGURE 8: SRIM processing e q u i p m e n t
Certain products, such as fiat shapes, may not n e e d a p r e f o r m i n g o p e r a t i o n and p r e f o r m s can also often be fabricated off-line, in an inh o u s e o p e r a t i o n or by a subcontractor. T h e p r o d u c t i o n mould can be made from various materials. GRP tooling is e x p e c t e d to find limited use because of its m o d e s t lifeume. SRIM is suited to volumes u p w a r d s of several t h o u s a n d parts per year w h i c h calls for nickel shell tooling or alternatives made from aluminium or metal alloys. T h e advantage of metal (faced) tooling is the e x c e l l e n t heat transfer, ensuring the highest product i o n s p e e d s . T h e DSM R e s i n s a p p r o a c h is to avoid steel tooling, t h e r e b y offering a substantial inv e s t m e n t r e d u c t i o n c o m p a r e d with c o m p r e s s i o n moulding. SRIM also does not require steel tooling, since t h e t e m p e r a t u r e and p r e s s u r e s involved are relatively low. T h e clamp force unit can be any unit capable of carrying a mould and c l o s i n g this m o u l d t i g h t l y during injection. Injection is carried out at relatively low pressures
Reinforced Plastics March 1994
that typically do not e x c e e d an average value of 1 MPa. The injection m a c h i n e is used to m e t e r the t w o p r e m i x e s ( w h i c h c o n s t i t u t e a Daron hybrid resin system), and to mix and inject this s y s t e m into t h e h e a t e d mould. Mixing is a non critical operation, w h e r e considerable ratio deviations are tolerable. The s c h e m a t i c set up of an injection m a c h i n e for Daron hybrids is r e p r e s e n t e d in Figure 8. T h e cost for an injection machine is s o m e w h e r e b e t w e e n that o f a s p r a y u p u n i t ( w h i c h is essentially a similar two c o m p o n e n t dispensing unit) and a PU mixing unit ( w h i c h allows a higher level of a u t o m a t i o n o f the process). The benefits of SRIM with Daron hybrids are: • no styrene emission because of the closed moulding p r o c e s s • i m p r o v e d and c o n s i s t e n t product quality because of the industrialized manufacturing process • p r o d u c t s have two s m o o t h sides (no fibre pattern on reverse) • savings in labour • lower investments compared
46
DSM Resins has long b e e n at the f o r e f r o n t in the d e v e l o p m e n t of low styrene emission resins and the investigation of improved air handling systems for workshops. Closed moulding t e c h n i q u e s are clearly a n o t h e r s o l u t i o n to the styrene emission problem. T h e s e t e c h n i q u e s , specifically v a c u u m injection, resin transfer m o u l d i n g (RTM) and s t r u c t u r a l reaction injection moulding (SRIM), m e a n practically zero styre n e emission. The t h r e e t e c h n i q u e s are similar as regards cycle times, r e q u i r e d investment and optimal series length. With its e x p e r t i s e in the develo p m e n t of resins for closed moulding i n j e c t i o n c o m b i n e d w i t h processing know-how, DSM Resins is well positioned to help clients to start closed m o u l d processing or to help t h e m switch from traditional hand or spray lamination methods.
The a u t h o r wishes to t h a n k Frits D o l l e m a n , Gerard v a n den H o n d e l a n d R i c h a r d Pieters o f DSM Resins, Zwolle, The Netherlands, a n d P a u l Brittles o f DSM Resins UK in Ellesmere Port f o r their collaboration.