Bayern Ati584e Surface Texture

7232019 Bayern Ati584e Surface Texture

httpslidepdfcomreaderfullbayern-ati584e-surface-texture 116

Introduction

There is an ever increasing demandfor thermoplastic mouldings with tex-tured surfaces which resemble natu-ral materials such as wood leatherfabrics crystals etc thereby giving a

certain impression of better qualityThe surface of an injection mouldedpart is invariably an exact mirror im-age of the cavity surface To achievehigh gloss moulded parts requiresa great deal of extra work since thecavity surface must also be polishedOne disadvantage of highly polishedsurfaces is that they show up everyblemish sink marks and flow linesTextured surfaces on the other handlargely hide such defects provided ofcourse that both the mould and the

moulded part are satisfactory in otherways Such surfaces do howeverrequire bigger drafts than polishedcavity surfaces depending on theroughness height and position of thetextured areas If the draft is not bigenough or the mould not sufficiently

rigid the surface texture of the partmay become distorted when themould is opened The accuracy withwhich a textured surface is repro-duced by the thermoplastic mel tdepends on the thermoplastic materi-al itself its viscosity setting speedand processing conditions such asinjection rate injection pressure andmould temperature

This technical report deals with thetransfer of textures from the cavity

surface of an injection mould to thesurface of the moulded part Therecan be few subjects which lend them-selves so well to being explained bymeans of photographs as this one ndash and the more photos the better Theauthor hopes that by discussing the

sorts of problem which can arise andsuggesting ways and means of over-coming them it will help manufac-turers to avoid similar pitfalls

Methods used to finishcavity surfaces

Polishing

The rough surfaces of a mould cavitymust be smoothed by polishing tofacilitate easy release of the part For

this one normally uses emery paperand diamond polishing paste Polish-ing should be in the direction of ejec-t ion both the core and the cavitybeing treated If an opaque mouldingis to be given a high gloss surface themould may be polished with P 280to 400 grit paper or a diamond po-lishing paste with a particle size of30 microm

High gloss surfaces are preferred forobjects which must be easy to clean

for hygienic reasons such as kitchenappliances telephone receivers andthe like (Fig 1)

Plastics Business Group

Application TechnologyInformation

Reproducing textures from the cavity surfaceto the surface of the thermoplastic mouldingDieter Schauf

Th is inform ation an d o ur tec hn ica l ad vice ndashw he the r verbal

in w riting or b y w ay of trials ndashare g ive n in g oo d faith b ut

w itho ut w arran ty an d this a lso ap p lies w he re p roprietary

rig hts of third p arties are invo lved O ur ad vice d oe s n ot

relea se yo u from the ob lig ation to c he ck its va lid ity and to

tes t ou r prod uc ts a s to the ir suitab ility for the inten d ed

ATI 584eGeneral

processe s an d uses The a pp lication use an d processing

of our prod ucts and the p rod ucts m anu factured b y you on

the b asis of ou r tec hn ica l ad vice are b eyo nd ou r co ntrol

an d the refore en tirely your ow n resp on sibility O ur prod uc ts

are sold in a cc ordan ce w ith o ur G en eral C on d ition s of Sa le

an d D elivery

Fig 1 Food processor with Novodur 983214 (ABS) housingThis has a high gloss surface for hygienic reasons



Many firms have internal standardswhich should be submitted to thecustomer if possible in the form of pla-ques moulded in the actual thermo-plast ic material to be used Fig 4shows an ABS housing with a spark

eroded surface It is best not to choo-se too fine surface textures becausethese are somewhat difficult to pro-duce by EDM and also f inely tex-

If a brushed finish is required this canbe achieved with P 240 to 320 grit Fig 2 shows a shaver head with abrush-finish PC-GF surface

If an even higher gloss finish is re-quired fine grinding with P 500 grit ab-rasive must be followed by polishingwith diamond polishing paste This isnecessary in the case of transparentmouldings and involves extra timeand expense so that the total toolingcosts can rise considerably

If a high class finish is required egin transparent record player covers orfor lenses the steel used to make themould i ts heat treatment and thepolishing technique employed mustmeet all special requirements

The steel used should be as homoge-neous as possible Slag occlusionsshould be removed as far as possibleeg by vacuum degassing or betterstill by electrolytic refining This treat-ment also achieves a small particlesize within the metal so that polishingis made easier

Ease of polishing can be affected by

the wrong heat treatment eg exces-sive carbonisation or oxidation etc ofthe surface

The most important factor however isthe actual polishing process Thisrequires scrupulous cleanliness aspolishing proceeds to an increasinglyfiner finish The cavity surface must beabsolutely clean and a new polishingtool must be used Such tools can bemade of any hard material such aswood copper or brass The use of softpolishing materials such as felt caneasily produce ldquooverpolishingrdquo andultimately a so-called orange peeleffect

Optically perfect plain or curved sur-faces eg for making lenses can onlybe achieved by using special machi-nes

In the case of mould inserts of 50 mmdiameter the surface roughness of themoulded part which can be achievedi s lt0 02 microm and the fl a tnesslt003 microm The surface finish of thecavity surface can be determined bythe interference method whilst the

gloss of plastics surfaces is deter-mined with the help of ref lectormeasurements in accordance withDIN 67530

2

Fig 2 Brushed finish on the head of an electric shaver

Fig 3 Spark eroded textures according to VDI 3400 (produced by Microtechnik D-65835 LiederbachTaunus)

Electric discharge machine(spark erosion)

If the mould cavity is to be eroded byEDM (electric discharge machine) itmakes economic sense to producethe textured surface at the same timeVelvet-like to coarse-textured sur-faces can be produced in this way

depending on the intensity of theelectr ical discharge Fig 3 showstypical examples in accordance withVDI 3400



tured plastic parts tend to show upscratches rather more than roughlytextured ones Surfaces according tostages 30 to 36 VDI 3400 with Ra of3 to 6 microm have proved satisfactory(see also Fig 12) Fig 5 shows themagnified surface of a power toolhousing made of glass f ibre f i l lednylon 6 the mould cavity of which hadbeen spark eroded to stage 36 Sur-faces produced by spark erosionhave a relatively rounded-off texturewhich results in end products withgood scratch resistance if these arebased on low-viscosity polymer melts

Fig 4 shows an ABS housing witha scratch resistant stage 36 sparkeroded finish This has also madethe matt spot near the gate invisible

In power tools especially housingswi th spark eroded sur faces of feradvantages in that they are even hideblemishes and are scratch resistant(Fig 5)

If the spark eroded cavity surface isdamaged however it is difficult torepair because the electrode must be

placed in position with extreme pre-cision (tumble erosion is sometimespossible)

Fig 4 ABS housing with a spark eroded surface

3

Fig 5 Photographs showing the surface of the housing of an abrasive belt polisher made of nylon 6 containing 30 glass fibre The surface texture has been achieved by spark erosion (stage 36 Ra 63 microm)



Photoetching

Photoetching consists of dissolvingpart of a surface eg the cavity sur-face with acid Part of the metal sur-face which is not to be etched has tobe covered with acid resistant materi-al so that the acid will only dissolvethe exposed portions The texturedesign is applied photographically andthetechnique has becomefirmly estab-lished in the plastics processing in-dustry ndash indeed photoengraving is to-day the most important method of pro-ducing textured cavity surfaces

Fig 6 shows the various stages ofproducing a photoengraved texturedsurface Nowadays multiple etchingis mainly used in order to produce auniformly textured surface Thedegree of gloss can subsequently beadjusted by blasting the surface withglass beads for example Worn sur-faces can be restored to very neartheir original condition by this methodFig 7 shows some typical texturesproduced by photoetching thesebeing a selection of several hundredthat are now available

Nearly all the materials used to makemoulds can be textured photochemi-cally ie by photoetching It musthowever be remembered that steelswhich contain chromium are invaria-bly more difficult to etch than thosethat do not In general steels con-taining up to 5 chromium can still bephotoetched satisfactorily and steelswith up to 15 chromium can also beetched successfully although this ismore difficult

The sulphur content of steels must notexceed 003 since otherwise theuneven dispersion of the sulphur canlead to a patchy appearance of theetched surface The more homoge-neous the material of which the mouldcavity is made the more uniform willbe the textured finish Mould cavityinserts can be etched either before orafter hardening Saltbath nitriding canonly however be carried out afterphotoetching For the toolmaker it isimportant to use the same steel for allthe inserts intended for one particularmould cavity The steel should also befrom one batch and ideally have allbeen rolled in the same direction All

parts of the mould should have beensubjected to exactly the same heattreatment prior to photoetching Oneshould however keep in mind whenetching soft steels that ndash because of

Fig 6 Diagram showing the various stages of producing photoetched textures (after Wagner)

4

1 Degreasing chemical + manually

2 Coating sensitive to light

3 Explosure

4 Development

5 Correcting

6 Protecting

7 Etching

8 Cleaning

9 Result 1st

etching half matt finish

10 Protecting

11 2nd Etching

12 Result rounded matt finish

coat

film

coat

acid

dissolved surface 0 x

etching depth

surface loss

sharp edge

obtained surface


etching depth

round edges

dissolved surface 2 xFig 5

uniformtexture roughness

mould protectioncoating

Fig 4

texture roughness

etching bottom

Fig 3

mould protection

coating

Fig 2

Fig 1

light

remaining acid

resistant coat

Fig 7 Typical photoetched textures



Fig 8 Typical photoetching stages with post-treatmentAnnealed steel 2311 (silicone rubber impressions)

Fig 9 ABS housing made from a mould produced by electrodeposited nickel

the materialrsquos coarse particle structu-re ndash the valleys of the etched surfacewill show considerable roughness andplastics surfaces produced from suchsteels are very likely to become scrat-ched Fig 8 shows the classic pho-toetching stages in the form of photo-graphs of silicone rubber impressionstaken from the cavity Here one cansee that in the case of one photoet-ching operation the covered exposedareas retain their polished finish If anoverall matt f inish is required themetal must be etched at least twiceMulti-stage etching (see also Fig 26)results in a particularly good matt

finish in the case of higher viscositymel ts The mould cavi ty can besmoothed or roughened at a laterstage by sandblasting it with glassbeads or sil icon carbide the finalresult depending on the hardness ofthe cavity surface and that of thesandblasting agent

Apart from steel it is also of coursepossible to impart texture by this tech-nique to non-ferrous metals such ascopper aluminium and zinc Photo-etched surfaces can also be hardchromium plated

Special techniques

Other techniques can be employed toimpart textures to cavity surfaces be-sides those described above Theseare sandblasting matt chromium plat-ing the production of textured nickelshells made by electrodeposition andcasting of zinc or beryllium-coppermould inserts with textured surfaces

Sandblasting with hard materials suchas silicon carbide or soft ones likeglass beads is suitable only for cavi-ty surfaces that are mostly flat

Matt chromium plating of polishedcavity surfaces produces a matt wearresistant surface texture Plasticsparts made in such moulds have a finestructured surface which can be easi-ly cleaned

Textured cavities made by electrode-positon have the advantage that thestructure is more rounded and pro-ducts can be produced which ndash in con-trast to photoetching ndash are almostidentical to that of the thermoformedfoil This is important where for ex-ample injection moulded parts are

integrated wi th PU foam backedsheets (eg ashtray lids in a dash-board) Otherwise the method hasbeen largely superseded by photo-etching (Fig 9)

The casting of mould cavity inserts inzinc (Zamak983214 Z 430) and particularlyin beryllium-copper alloy has latelygained importance For examplecast ing of thermoformed texturedsheets with a subsequent secondarycasting utilising zinc or beryllium-cop-per a l loy can be used to producemould cavity surfaces which are iden-tical with the original pattern Partsmade from these have a roundedeven and scratch resistant surfacewhich also successfully conceals sinkmarks

photoetched 2 x photoetched

2 x photoetched and 1x photoetched andsandblasted (glass beads) sandblasted (glass beads)



Fig 10 shows a cast zinc mould for acar pillar trim made by this method

The transfer of cavity surfacetextures to thermoplastics

The reproduction of textures on cavi-ty surfaces depends on the type ofthermoplastic used the melt viscosityand processing conditions

Similar textures produced by sparkerosion and by photoengraving lookdifferent Spark eroded surfaces havea rounded appearance whereas sur-face textures produced by photo-etching often have a sharp-edged tex-ture depending on the structure of thetool steel This difference becomesapparent when the textures are trans-ferred to plastics surfaces especiallyin the case of low-viscosity thermo-plastic melts

Fig 11 shows the differences in tex-ture for nylon 6 the spark erodedspecimen being the top half of thepicture the photoetched one under-neath this If one compares spark

eroded and photoetched cavity sur-faces as reproduced by high viscositypolymers such as ABS (Novodur983214)and PC (Makrolon983214) as well as by thelow-viscosity nylon (Durethan983214) andPBT (Pocan983214) one can see (Fig 12)that the spark eroded surfaces resultin a rounded ie scratch resistantsurface in both instances

Fig 10 Cast zinc mould for a car pillar trim produced from thermoformed foil

6

spark eroded 50 microm

photoetched 50 microm

Fig 11 Comparison of a nylon 6 surface moulded in a cavity with a spark eroded (top) and photoetched (bottom) surface



Fig 13 Photoetched surfaces of Durethan and Novodur


Fig 12 Spark eroded mould cavity reproduced by ABS (Novodur 983214 )

PC (Makrolon 983214 ) nylon 6 (Durethan 983214 ) and PBT (Pocan 983214 )

Photoetched surfaces such as shownin Fig 13 are reproduced sufficientlyaccurately by higher viscosity meltssuch as ABS and PC (Novodur andMakrolon) although rounded whilstlow viscosity melts such as those ofPP PE nylon and PBT reproduce thetexture with extreme precision so thatdeep matt part surfaces are producedwhich however are fairly susceptibleto scratches Fig 14 clearly showshow much better surface texture isreproduced by nylon (Durethan) thanby ABS (Novodur)

The accuracy with which surface de-tail is reproduced depends not only onthe melt viscosity of the thermo-plastic but also on processing con-ditions particularly the mould tem-perature inject ion speed and theeffective cavity pressure during thefirst few seconds after the mould fill-ing phase

7

Novodur 100 microm Makrolon 100 microm

Durethan 100 microm Pocan 50 microm



Durethan 200 microm Novodur 200 microm



Fig 15 shows the effect of mould tem-perature on the gloss of an ABS mir-ror housing The higher the tempera-ture of the cavity the more accuratelywill the texture be reproduced thereflected light is scattered more even-ly and the surface has a higher mattappearance

The cavity pressure and temperaturehave a decisive effect on the accuracyof sur face detai ls reproduct ionFigs 16 and 17 show a housing for abattery cover with evidence of vary-ing surface gloss Shiny spots are pro-duced at low mould temperatures andinsufficient pressure which preventsthe surface being accurately repro-duced The higher the mould tempera-ture injection speed and injectionpressure the better will be the mattsurface The gate thus also affectsthe surface finish

From what we have discussed aboveit follows that differences in surfacegloss may be expected on a mouldedpart depending on how close to orhow far from the gate a particular area

is F ig 18 shows an ABS vacuum

cleaner housing with two switch unitsmounted on the housing The cavitysur faces for the swi tch uni ts andhousing have been photoetched in thesame way and a silicone cast takenfrom these two areas shows almost nodifference in surface finish Never-theless the surface of the switch unithas a much more pronounced texture

Fig 16 Battery cover made of ABS ndash left shiny right matt The difference is due to differences in injection pressure and mould temperature

Fig 17 Magnified section of the cover shown in Fig 16

Fig 18 Vacuum cleaner housing with varying surface gloss

Fig 15 Effect of mould temperature on gloss (ABS)

8

shiny matt 500 microm

mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt



Figs 19 and 20 Differences in texture in regions of sudden wall thickness differences with two different moulds (ABS)

9

than that of the housing The cause ofthis increased gloss is the fact that thispart of the housing is further awayfrom the gate so that the melt passesover this area with less pressure In-terestingly the part once again has amatt finish at the end of the flow pathThis is due to pressure building upagain within the cavity at this pointresulting in improved reproduction ofthe cavity surface texture The pro-blem was solved by using a sparkeroded cavity whose rounded texturehas the effect of making pressuredifferences less obvious

Moulding surface defects andtheir prevention

The main types of surface defects are

1 Variation in gloss due to abruptchanges in wall thickness

2 variations in gloss due to heavysection or ribs

3 degassing problems which pre-vent accurate reproduction of thesurface

4 variations in gloss caused byinadequate etching(single double or triple etching)

5 variations in gloss in front of orbehind apertures and at the endof flow paths

6 prominent and badly positionedweld lines

7 poor scratch resistance

In addition there are defects whichare produced during ejection (seesection on ejecting) Surface defectscaused by a poorly designed or posi-tioned gate eg matt spots jettingetc or by overheating of the polymerduring processing (coloured streaksand streaking caused by shear mois-ture etc) are beyond the scope of thispaper and are therefore excluded fromthe discussion

Let us now consider some of the sur-face defects mentioned above

identical photoetchingsteel 12713 steel 12311(55 Ni Cr Mo 4) (40 Cr Mn Mo 7)

matter surface

where wallsare thinner

mould I mould II

S = 4 mm

S = 2 mm

200 microm



Fig 21 Poor part design resulting in gloss differences

A common problem is gloss differen-ces in textured surfaces caused bysudden changes in wall thickness andby the use of different steels Fig 19shows two identical mouldings madein different moulds some parts ofwhich have thinner walls Differenttempered steels were used to makethe mould inserts both however beingphotoetched in the same man nerWhere the walls have their normalthickness of 4 mm both moulds pro-duce the same surface texture A mat-ter finish was obtained where the wallswere thinner when using the mouldwith the more sharply etched surface(Fig 20 bottom) This fault was rec-tified by smoothing over the matt areawith a glass brush

Variations in gloss also occur wherethe walls are thicker Fig 21 shows anABS cover where f low aids weremachined into the mould originatingfrom the gate in order to minimisesinking far away from the gate The re-sult is that the runners on the back areclearly visible

Figs 22 and 23 Trapped air in a bumper made of modified PBTThis causes a shiny strip at the centre (bottom picture)

10



Fig 24 Glove compartment lidphotoetched once and sandblasted (ABS)

Fig 26 Triple-etching results in matt diffused surfaces Fig 27 Elimination of rough surface by coarse spark eroded surface texture (ABS)

Fig 25 Glove compartment lidphotoetched twice and sandblasted (ABS)

I f air is trapped between two f lowfronts the melt will be unable to accu-rately reproduce surface textures inthe weld line region This problem isi l lus tra ted i n F igs 22 and 23 InFig 23 a shiny strip is clearly visiblein the centre

Improved etching methods

Excessive gloss coupled with glossvariations is sometimes caused byincorrect etching Fig 24 shows asingle-etched surface Fig 25 one thathas been double-etched and Fig 26 atriple-etched surface Multiple etchingwhich gives a superimposed terrace-like effect produces a higher matt sur-face This type of photoetching hasbeen developed in the last few years

Tear drops and other rough blemishescan also sometimes be eliminated bymeans of coarse textures Fig 27shows a brush with handle where thetear drop has become invisible (smal-ler picture)

11

cavity surface cavity surface



Textured surfaces usually manage toconceal flow or weld lines to a large

extent If however the textured sur-face is very sharp-edged so that thetexture is not very accurately repro-duced pressure will tend to build upalong the weld line resulting in thisbeing more accurately reproduced sothat the weld line will appear to havea higher matt surface in the finishedpart This problem is demonstrated inFigs 28 and 29 This effect can bereduced by means of a rounded tex-ture

Examples of correctly designedtextures

In an ABS pocket calculator housingwith numerous holes for the keys itwas possible to completely concealthe weld lines by means of a sparkeroded texture (stage 36) (Fig 30)

Fig 30 Calculator housing without a visible weld line

Figs 31 to 33 Profiled textures conceal linear ribs(31 and 32 ABS 33 PP)

12

Figs 28 and 29 Radiator grille made of ABS showing pronounced weld line The picture on the right shows the matt weld line in close-up

Fig 31

Fig 32

Fig 33



Profiled textures to simulate laminatesin combination with design are some-times able to hide sink marks andsimilar defects as shown in Figs 31to 33

The scratch sensitivity of a surfacedepends on the kind of thermoplasticused and the texture of the cavity sur-face As we have pointed out beforethe roughness in the valleys of theetched design plays an important partIf for example the mould material has

a generally coarse structure rough-ness at the bottom of these valleys willbe inevitable The lower the melt vis-cosity of the plastic the more critical

will this roughness be Fig 34 clearlyshows scratches resulting from dam-age to the textured surface

13

Fig 34 Scratches produced on a nylon surface by finger nails

In the case of certain thermoplasticsthe additives contained in them maybe deposited on the mould cavity sur-face eg flame retardants lubricantsetc This increasingly leads to shinyspots especially in the areas near theend of the flow path The problem canbe alleviated by ensuring adequatemould venting higher mould tempe-ratures and minimum shear of the meltthrough the gate ie gates should beas large as possible

Draft and wearof textured surfaces

The draft that is necessary is a con-stantly recurring point for discussionFor highly polished mould cavities or

for those with a brushed finish in thedirection of ejection it is generally con-sidered that the minimum draft forunf i l led thermoplast ics should be05 deg For filled thermoplastics (fibre ormineral fillers) the draft should be atleast 075 deg The minimum draft x degforselected materials can be read off asa function of roughness height inFig 35 These figures apply to a sparkeroded texture or a rounded etchedsurface for a wall thickness of 2 mmFor glass fibre reinforced filled ther-

moplastics the draft should be onestep higher

Draft angel x degCharm No Ra microm asymp Rz microm PA PC ABS

12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60

Fig 35 Minimum draft x degas a function of roughness height for a wall thickness of 2 mm for a spark eroded texture For glass fibre filled materials choose one step higher



The condition is that the two mouldhalves fit properly ie that there is nomould misalignment and that themould should be rigid If the texture istoo deep and the walls too thin thetexture wil l be damaged when themould is opened as is clear fromFig 36

If the theoretically necessary draft isimpracticable for design reasons it ispossible in special cases to still applyan external texture In such cases thecore should be f i rst withdrawn onmould opening whi lst the partremains in the cavity so that the partcan shrink away from the texturedcavity surface as it cools and can thenbe ejected Fig 37 shows this methodfor an ABS moulding with a sparkeroded textureThe draft for photoetched texturedsurfaces should if possible not bebelow 3 deg The necessary draft is spe-cially dependent upon the type of tex-ture ie whether it is in line of draw orin the form of isolated areas as wellas on the type of thermoplastic usedpart wall thickness (the thinner this isthe greater will the draft have to be)and mould rigidity

The fol lowing tab le 38 l i sts theroughness height and draft for twoABS mouldings

Fig 37 Ballpoint pen housing for which the core had a greater draft (05 deg)than the outside

14

Fig 36 Mechanical damage to textured surface during ejection due to

insufficient draft

Type of moulding Max roughness Average Mean roughness Draft Commentsheight roughness indexRMmicrom height RTmicrom RAmicrom

Radiator grille 1 58 49 85 3 deg Gloss difference due toinsufficient roughnessheight

Radiator grille II 71 59 11 3 deg Degree of mattnessacceptable

Dashboard I 174 152 35 5 deg Demoulding problemsbetter 7 deg in some cases at 5 deg

Dashboard II 85 72 20 4 deg

Table 38



Wear of textured surfaces

Polished cavity surfaces do not showany abrasive wear with unfilled ther-moplastics provided they are suf-

ficiently hard Cavities with hardnes-ses of gt55 HRC were found to be ca-pable of producing more than 1 milli-on shots

Textured surfaces are by their verynature more prone to wear Wear ofvelvety f ine-textured surfaces byglass fibre filled thermoplastics andthose with high pigment contentsbecomes apparent fairly soon throughshiny patches on the moulded partThe cavity used to produce a shaver

housing with a velvety fine-texturedfinish and made of a highly pigmentedgrade of ABS had to be re-workedafter every 10000 shots The cavitysurface hardness was measured andfound to be 47 to 50 HRC By in -creasing this to 55 HRC it proved pos-sible to prolong the life fivefold

Fig 39 shows a photoetched surfaceafter prolonged use Signs of abrasivewear are clearly visible near the edgesof the mould insert which was madeof tempered steel

If the mould insert surface is not hardenough a noticeable change in thetexture can become apparent after9000 cycles as is shown in Fig 40

15

Fig 39 Photoetched nylon surface showing worn texture But still scratch resistant (Steel P 20)

Fig 40 Change on part surface after 9000 cyclesSteel P 20

Fig 42 Stereo-scan taken of component surfaces containing 10 and 40 GF reinforced PC

Fig 41 Corrosion in cavity through entrapped air (Diesel effect)

In the case of glass fibre thermoplas-tics wear of polished surfaces is to beexpected caused by the melt as it hitsthe cavity wall on entering through thegate as well as by frictional forceduring ejection The factor most cru-cial in deciding how long a given tex-tured finish wil l last is the surfacehardness of the mould cavity The bestresults were obtained with sparkeroded surfaces coated with chro-mium carbide No visible changes

in the cavity surface were apparenteven after one million shots

When processing glass fibre fi l ledthermoplastics it is important to posi-t ion the gate correct ly to preventair being trapped inside the cavitycausing corrosive damage to the tex-tured surface

The use of high alloy steels with largechrome content and higher carbonamounts which results in the carboni-

sation of the insert surface finish canminimise the problem Fig 41 showsthe type of corrosion where here theair cannot escape on the tool partingline and so becomes trapped in the

cavity (Diesel effect with decomposedproducts = corrosion)

When processing glass reinforcedthermoplastics consideration mustalways be given to the possibility ofthe glass appearing at the surface ofthe component giving a ldquogreyingrdquoeffect The problem can be avoidedor minimised by use of higher tooltemperatures and higher injectionspeeds The problem becomes more

apparent with increasing amounts ofreinforcement or fillers

Fig 42 shows the surface finish of apart containing 10 glass fibres (PC-GF10) A further stereo-scan showsthe surface structure of a 40 glassreinforced thermoplastic (PC-GF40)

It is possible to produce high surfacegloss on finished components withglass reinforced materials This how-ever is easier to achieve with lighter

colours similar in shade to the glassf ibres than i t is possible with thedarker colours of the thermoplastics

moulding cycles

at the start 9000

PC GF 10 PC GF 40



Pu blished by K U -M artketing Techn ische R ed aktion 15061988 KU 48476e

Literature

Stoeckhert KWerkzeugbau fuumlr die Kunststoff-verarbeitung Carl Hanser VerlagMuumlnchen-Wien 1979

Vorbach GAnforderungen an das Spritzguszligteilaus der Sicht des Entwicklers undKonstrukteurs ReihebdquoDas Spritzguszligteilldquo VDI-VerlagGmbH Duumlsseldorf 1980

Christoffers K-EFormteilgestaltung verarbeitungs-gerecht Reihe bdquoDas SpritzguszligteilldquoVDI-Verlag GmbH Duumlsseldorf 1980

VDI-Gesellschaft KunststofftechnikGestalten von Spritzguszligteilen austhermoplastischen KunststoffenRichtlinie VDI 2006 Juli 1979

Menges G Mohren PAnleitung zum Bau von Spritzgieszlig-werkzeugenCarl Hanser VerlagMuumlnchen 1974 und 1983

Boumlhm DOberflaumlchenveredelung von Kunst-stoffteilen Reihe bdquoKonstruieren mitKunststoffenldquo TAELehrgang Nr 5807 1982

MOLD-TECH983214 PRO PLASTICOberflaumlchenstrukturenbdquoTechnische InformationenldquoStandard International GmbHKrefeld

Schauf DDie Formnestoberflaumlche ndash Herstel-lung und Auswirkung auf das Form-teil aus bdquoDas SpritzgieszligwerkzeugldquoVDI-Verlag 1983



Many firms have internal standardswhich should be submitted to thecustomer if possible in the form of pla-ques moulded in the actual thermo-plast ic material to be used Fig 4shows an ABS housing with a spark

eroded surface It is best not to choo-se too fine surface textures becausethese are somewhat difficult to pro-duce by EDM and also f inely tex-

If a brushed finish is required this canbe achieved with P 240 to 320 grit Fig 2 shows a shaver head with abrush-finish PC-GF surface

If an even higher gloss finish is re-quired fine grinding with P 500 grit ab-rasive must be followed by polishingwith diamond polishing paste This isnecessary in the case of transparentmouldings and involves extra timeand expense so that the total toolingcosts can rise considerably

If a high class finish is required egin transparent record player covers orfor lenses the steel used to make themould i ts heat treatment and thepolishing technique employed mustmeet all special requirements

The steel used should be as homoge-neous as possible Slag occlusionsshould be removed as far as possibleeg by vacuum degassing or betterstill by electrolytic refining This treat-ment also achieves a small particlesize within the metal so that polishingis made easier

Ease of polishing can be affected by

the wrong heat treatment eg exces-sive carbonisation or oxidation etc ofthe surface

The most important factor however isthe actual polishing process Thisrequires scrupulous cleanliness aspolishing proceeds to an increasinglyfiner finish The cavity surface must beabsolutely clean and a new polishingtool must be used Such tools can bemade of any hard material such aswood copper or brass The use of softpolishing materials such as felt caneasily produce ldquooverpolishingrdquo andultimately a so-called orange peeleffect

Optically perfect plain or curved sur-faces eg for making lenses can onlybe achieved by using special machi-nes

In the case of mould inserts of 50 mmdiameter the surface roughness of themoulded part which can be achievedi s lt0 02 microm and the fl a tnesslt003 microm The surface finish of thecavity surface can be determined bythe interference method whilst the

gloss of plastics surfaces is deter-mined with the help of ref lectormeasurements in accordance withDIN 67530

2

Fig 2 Brushed finish on the head of an electric shaver

Fig 3 Spark eroded textures according to VDI 3400 (produced by Microtechnik D-65835 LiederbachTaunus)

Electric discharge machine(spark erosion)

If the mould cavity is to be eroded byEDM (electric discharge machine) itmakes economic sense to producethe textured surface at the same timeVelvet-like to coarse-textured sur-faces can be produced in this way

depending on the intensity of theelectr ical discharge Fig 3 showstypical examples in accordance withVDI 3400









3




Photoetching







4



3 Explosure

4 Development

5 Correcting

6 Protecting

7 Etching

8 Cleaning

9 Result 1st


10 Protecting

11 2nd Etching


coat

film

coat

acid


etching depth

surface loss

sharp edge

obtained surface


etching depth

round edges




Fig 4

texture roughness

etching bottom

Fig 3

mould protection

coating

Fig 2

Fig 1

light

remaining acid

resistant coat









Special techniques


















6












7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature

















3




Photoetching







4



3 Explosure

4 Development

5 Correcting

6 Protecting

7 Etching

8 Cleaning

9 Result 1st


10 Protecting

11 2nd Etching


coat

film

coat

acid


etching depth

surface loss

sharp edge

obtained surface


etching depth

round edges




Fig 4

texture roughness

etching bottom

Fig 3

mould protection

coating

Fig 2

Fig 1

light

remaining acid

resistant coat









Special techniques


















6












7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature











Photoetching







4



3 Explosure

4 Development

5 Correcting

6 Protecting

7 Etching

8 Cleaning

9 Result 1st


10 Protecting

11 2nd Etching


coat

film

coat

acid


etching depth

surface loss

sharp edge

obtained surface


etching depth

round edges




Fig 4

texture roughness

etching bottom

Fig 3

mould protection

coating

Fig 2

Fig 1

light

remaining acid

resistant coat









Special techniques


















6












7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature
















Special techniques


















6












7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature


















6












7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature

















7

















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature




















8


mouldtem-perature

20 degC

60 degC

shiny matt

gate

shinymatt




9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature












9














matter surface


mould I mould II

S = 4 mm

S = 2 mm

200 microm







10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature















10










11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature


















11










12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature

















12


Fig 31

Fig 32

Fig 33







13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature















13








12 040 15 05 10 05

15 056 24 05 10 05

18 080 33 05 10 05

21 112 47 05 10 05

24 160 65 05 15 10

27 224 105 10 20 15

30 315 125 15 20 20

33 450 175 20 30 25

36 630 240 25 40 30

39 900 340 30 50 40

42 1250 480 40 60 50

45 1800 690 50 70 60








14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature















14


insufficient draft






Table 38










15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature


















15
















moulding cycles

at the start 9000

PC GF 10 PC GF 40




Literature












Literature









Documents

Bayern Ati584e Surface Texture