Thit k & ch to h thng thot kh

Thit k - ch to h thng thot kh

1. H thng thot kh :

Lng khun th lun cha khng kh , khng kh ny phi c thot ra trong sut qu trnh in y. H thng thot kh l cung cp nhiu con ng khng kh b mc kt trong lng khun thot ra nhng khng cho nha nng chy i qua.

Nu khng c hay h thng thot kh khng c thit k tt th s gy ra mt s khuyt tt nh b ng hn, vt chy, chi tit khng in y,...

H thng c dng ph bin nht l cc rnh thot kh trn mt phn khun v mt mi quanh ti li (ti y) sn phm. Ngoi ra, kh cng c th thot ra ngoi qua ng nc lm ngui, cc khe h nh ca h thng trt, phn ghp (cc cy).....

2. Kiu thot kh :

a. Phn loi kiu thot kh:

Cc phng n thot kh c th c s dng, ty thuc vo kt cu ca lng khun, v tr cng phun, kh nng gia cng, p sut phun,...

Mt s phng n ang c s dng rng ri hin nay gm:

Thot kh qua rnh thot kh trn mt phn khun.

Thot kh qua h thng y trn khun.

Thot kh qua h thng ht chn khng.

Thot kh qua h thng lm mt, insert, slide

b. Rnh thot kh trn mt phn khun (parting line venting)

Rnh thot kh c b tr mt phn khun v d gia cng v v sinh.

Rnh lm nhim v nh mt cu ni gia lng khun v mi trng ngoi a khng kh ra khi lng khun.

Rnh thot kh

Cu to ca rnh thot gm hai phn chnh: rnh dn v rnh thot.

Kch thc h thng thot kh trn mt phn khun

Thot kh trn mt phn khun

c. Rnh dn (vent land):

Nm phn u ca rnh thot kh.

Thit k khng cho vt liu chy vo cc l thng hi trong sut qu trnh in y.

Rnh dn

su ti v tr u ca rnh thot kh thng nh trnh vt liu chy ra ngoi. Ty thuc vo nht ca tng loi nha th c su khc nhau. V c cho bng sau :

Loi nha

Chiu su (INCHES)

ABS

0.001-0.015

ACETAL

0.0005-0.001

ACRYLIC

0.0015-0.002

CELLULOSE ACET, CAB

0.001-0.0015

ETHYLENE VINYL ACET

0.001-0.0015

IONOMER

0.0005 -0.001

LCP

0.0005 - 0.0007

NYLON

0.0003 - 0.0005

POLYPROPYLENE

0.0005 - 0.00 2

P C (RIGID)

0.0006 - 0.001

PVC (FLEXIBLE)

0.0005-0.0007

POLYETHYLENE

0.0005 - 0.0012

PET, PBT, POLYESTERS

0.0005 - 0.0007

POLYSULFONE

0.001 - 0.002

rng ca rnh trong thc t n nm trong khong 3.175 12.7 mm.

Chiu di rnh (l): 0.762mm 1 3.175mm

Khi thit k rnh dn cn ch cc iu sau:

S rnh ty thuc vo lu lng v tc in y.

Khi cn tng thot kh th c th tng thm rnh thot kh hay m rng cc rnh.

d. Rnh thot (relief slot):

a khng kh t rnh dn thot ra ngoi.

Chiu su v b rng ln hn rnh dn, gim p sut v m bo khng kh thot ra ngoi hon ton.

Thng c kch thc 20 x D.

Cch b tr:

t ti nhiu v tr khc nhau dc theo h thng knh dn v ng bao chi tit. c bit nhng v tr c in y cui cng, l nhng khu vc xa cng vo nha nht. c khng kh b nn li v hnh thnh cc by kh nn n c b tr ti y.

Cch b tr rnh thot kh

B tr rnh thot kh nhng ni d to ra ph phm do khng kh khng thot ra c, nh: l kh, vt chy...

Cch b tr rnh thot kh

Thot kh thong qua l kh & knh dn hnh vnh khuyn

S lng rnh thot kh cn thit:

S lng rnh thot kh ph thuc vo chu vi ca chi tit nn khng th b tr qu nhiu. Tng chu vi rnh thot kh phi gn bng 30% chu vi ca chi tit m bo kh nng thot kh.

v d c 12 rnh thot kh, chng c th c t cch u nhau nh hnh, hoc bt u bng cch t mt rnh thng hi mi bn gc, mt trc tip i din cng v rnh thot kh khc bng nhau cc vng cn li.

Cch b tr rnh thot kh

B. H thng thot kh trn knh dn (runner)

B tr thm h thng thot kh trn knh dn tng thm kh nng thot kh khi lng khun.

Rnh thot kh c b tr thnh 1 vng khp kn quanh chu vi knh dn v dn ra ngoi bi cc rnh thot.

Nha c dn vo knh dn s dn thm khng kh trong knh dn vo trong lng khun do trong knh dn tn ti khng kh t trc.

Thit k thm h thng thot kh trn knh dn thot khng kh ra ngoi hn l y thm khng kh vo lng khun trnh nha vi nhit v p sut cao cng vi nhit v p sut sn c s tip tc gy nn hin tng qu nhit lm

Cch b tr rnh thot kh knh dn

u im:

D gia cng v v sinh.

C th b tr bt k v tr no trn mt phn khun.

Nhc im:

Phi thit k rnh thot kh sao cho khng kh thot ra ngoi nhng nha khng chy ra khi lng khun.

Ph thuc vo tc v lu lng dng chy khi b tr h thng thot kh.

Khng b tr c h thng thot kh trn chi tit qu mng, c gn (rib), rnh ct (blind holes).

C. Thot kh qua h thng y trong khun:

Trn cc ty y ca h thng y trn khun , thit k cc rnh xon t khng kh trong khun s theo cc rnh ny s i ra ngoi.

B tr rnh thot kh trn ty y

Mt mi trn ti li (ejector pin): lp rp ca h thng y phi trt dc trc y chi tit ra ngoi l lp rp c h. Chnh v vy m da vo khe h khng kh c th thot ra ngoi loi b cc by kh.

B tr rnh thot kh trn ty y

Khi s dng h thng y vo vic thot kh th cn lau chi hng ngy loi b nhng vt lm ngn khng cho thot kh. Cn c thay th hay tho ra lm sch khi b tc.

u im:

Thit k chung vi h thng y nn c th tit kim chi ph.

Nhc im:

i hi chnh xc cao mi c th thot kh tt.

i hi h thng y c bng cao.

D. Thot kh qua h thng ht chn khng :

H thng ht chn khng ang c s dng rng ri trong ngnh cng nghip khun mu do vic s dng nhng phng php thot kh truyn thng l khng trit , do kt cu lng khun phc tp, c nhiu im cht khin khng kh khng th thot ra ngoi hon ton. Phng php ht chn khng khc phc c nhng vn ny.

Cch b tr h thng ht chn khng

Hnh trn trnh by s lc v cu to ca h thng, bao gm:

Cc rnh dn a khng kh ra 1 rnh cha kh bao quanh chu vi ca lng khun.

Khng kh bn ngoi khng th lt vo khun do c 1 vng m bng cao su cch ly gia mi trng ngoi v bn trong khun.

Ti rnh cha kh : thit k cc l thng ni vi bm chn khng.

a. Nguyn l hot ng:

Bm chn khng c m a ton b lng khng kh ra ngoi khun khi khun ng, to cho th tch bn trong lng khun hon ton l chn khng, nh vy khi nha c phun vo s khng b cn tr bi lng kh cn tn ng.

b. Thi im bt u m my bm chn khng:

Thi im bt u ht kh ra khi lng khun c xc nh bng cch tin hnh ng khun v t mt my o chn khng cui ming phun nha. Sau bt u m my bm chn khng v xc nh thi gian ht ton b kh trong lng khun ra ngoi. T thng tin ny gip cho vic xc nh thi gian m my ht chn khng cho hp l.

u im:

Hiu qu thot kh rt cao.

Khc phc nhiu khuyt im ca phng php thot kh truyn thng, c th thot kh nhng im cht (dead pocket).

Nhc im:

Thit k phc tp, tn km.

Kh gia cng khun v phi b tr rnh cha kh, l thng vi my bm chn khng.

E. Thot kh qua h thng lm mt,slide,insert :

p dng cho cc chi tit c gn

S dng lng khun kiu insert tn dng khe h lp ghp gia 2 mnh b tr rnh thot.

Cch b tr rnh thot kh ch ming ghp

Thot kh qua h thng lm mt

Hnh di y cho thy lng khun c lp vo 1 mnh insert c lm t kim loi xp, c kh nng dn kh t lng khun vo knh lm mt.

Cch b tr rnh thot kh thng qua knh lm mt

u im:

Thot kh tt cho sn phm c gn khc phc khuyt im ca thot kh bng mt phn khun v h thng y.

Gi r.

Nhc im:

Lng khun b tr phc tp.

Tiu ch

Thot kh qua mt phn khun

Thot kh qua h thng y

Thot kh dng h thng ht chn khng

Thot kh qua h thng lm mt, insert, slide

V tr

b tr

Ch c th b tr ti mt phn khun ca chi tit.

Ch b tr tch hp trong h thng y.

B tr nhiu v tr trong lng k c nhng im cht (dead pockets).

Thng b tr ti chi tit c gn khng th thot kh bng mt phn khun.

Kh nng thot kh

Thot kh tt ti v tr mt phn khun, khng thot kh c nhng im cht.

Ch thot kh nhng v tr c t h thng y.

Hu nh thot kh c ton b v tr trong lng khun.

Thot kh c bit tt cho sp c gn, lng khun kiu insert.

Kh nng gia cng

Nm trn mt phn khun nn d gia cng nhng phi m bo kch thc.

Ch phi gia cng trn h thng y.

Kh gia cng cch rnh dn v l thng ni my bm chn khng.

Khng phi gia cng nhiu do li dng khe h trong khun dng insert.

Tnh kinh t

R tin.

R tin.

t do phi gia cng v s dng my bm chn khng.

R tin.