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C«ng nghÖ dËp nguéi
Ch ¬ng iii
Uèn
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3.1.Qu¸tr×nhuèn.- Uènlµnguyªnc«ngthênggÆpnhÊttrongdËpnguéi.
- §Æc®iÓmcñaqu¸tr×nhuènlµdíit¸cdôngcñachµyÐpvµcèi,ph«ibÞbiÕnd¹ngdÎotõngvïng®Ót¹othµnhh×nhd¸ngcÇnthiÕt.
- Phôthuécvµoh×nhd¹ng,kÝchthícvËtuèn,®ÆctÝnhcñaqu¸tr×nhuèntrongkhu«nmµcãthÓtiÕnhµnhtrªnm¸yÐptrôckhuûu,m¸yÐpmas¸thaym¸yÐpthuûlùc.
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3.2.Líptrunghoµ.Líptrunghoµ®iquÓntängt©mcñamÆtph¼ngtiÕtdiÖn,b¸nkÝnhuènnhádÇnth×tiÕtdiÖncòngthay®æi,do®ãtrongt©mcñatiÕtdiÖncòngdichuyÓndÇnvÒph¸it©muèn.
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VÞtrÝcñalíptrunghoµ®îcx¸c®Þnhbëib¸nkÝnhlíptrunghoµtheoc«ngthøc.
)2
.(..
S
rS
B
Btb
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Trong®ã:Bbt-lµbÒréngtrungb×nhBtb=(B1+B2)/2
B–lµbÒréngph«iban®ÇuBtb/B–lµtrÞsèbiÕnréng(tra b¶ng phô
thuéc vµo B vµ S).S–lµchiÒudµyvËtliÖu.-lµhÖsèbiÕnmáng(tra b¶ng phô
thuéc vµo r vµ S). =S1/SvíiS1lµchiÒudµyvËtliÖusauuèn.
r–lµb¸nkÝnhuènphÝatrong.
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TrongthùctÕkhidËpnh÷ngchitiÕtkh«ngcÇn®échÝnhx¸ccao,cãthÓdïngc«ngthøc.
=r+x.SVíixlµhÖsèthùcnghiÖmx¸c®Þnhkhoangc¸chlíptrunghoµ®Õnb¸nkÝnhphÝatrong.
(tra b¶ng phô thuéc vµo r vµ S).
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3.3.TÝnhph«iuèn.§ÓtÝnhto¸nchiÒudµiph«iuèncÇnthùchiÖnnhsau.
- X¸c®ÞnhvÞtrÝlíptrunghoµ,chiÒudµilíptrunghoµëvïngbiÕnd¹ng.
- ChiakÕtcÊucñachitiÕtuènthµnhnh÷ng®o¹nth¼ng,cong®¬ngi¶n.
- CéngtængchiÒudµicñac¸c®o¹n®ãl¹i,chiÒudµicñac¸cphÇnth¼ngkh«ngthay®æi,chiÒudµi®o¹ncongtÝnhtheochiÒudµicñalíptrunghoµ.
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3.3.1. Tr êng hîp b¸n kÝnh uèn r > 0,5S.
Gi¶söcÇnuènnhsau.
KhÝ®ãchiÒudµiph«i®îct×nhtheoc«ngthøc: )..(
180
.21 SxrllL
o
o
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Trongtrênghîptængqu¸:
x-lµhÖsèx¸c®Þnhkho¶ngc¸chgi÷alíptrunghoµ®Õnb¸nkÝnhuèn.(x tra b¶ng x = 0,23 – 0,5)
)..(180
.SxrlL iio
oi
i
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*Víitrênghîpuènnhh×nhvÏ.
Th×chiÒudµiph«i®îctÝnhtheoc«ngthøc:
).(2
2)..(180
.21 SrtgSxrllL
o
o
o
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*Khiuènnhh×nhvÏ.
Trong ®ã a ® îc tra b¶ng- Khi S nhá vµ r lín th× a < 0- Khi S lín vµ r nhá th× a > 0.
allL 21
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VD.TÝnhchiÒudµiph«iuènchochitiÕtnhsau.BiÕtr=2,S=4(r/S = 2 th× x = 0,45)
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25,412)2.45,04.(2.696
)2.4(2.66820282086
)..(180
90.
x
SxrlL iio
o
i
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3.3.2. Khi b¸n kÝnh uèn r < 0,5S.
TrongthùctÕkhiuènvíib¸nkÝnhuènnhá,chiÒudµiph«ibÞkÐodµiravµchiÒudµyn¬iuènbÞmáng®i.GãcuèncµngnhávµcãcµngnhiÒugãcuènth×hiÖntîngkÐodµicµngrârÖt.
C¸cc«ngthøcgÇn®óngtÝnhchoc¸ctrênghîpcôthÓ®îctratrongb¶ngtracñasætaydËpnguéi.
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3.4.b¸nkÝnhuèn.B¸nkÝnhuèncñavËtuènph¶i®ñnhásaochovËtuèngi÷®îch×nhd¸ngkhilÊyrakháikhu«n,vµ®ñlín®Ókh«ngbÞ®øttiÕtdiÖnëvÞtrÝuèn.
Trong®ã:-lµm«®un®µnhåikÐoKg/mm2
T–lµgiíih¹nch¶yKg/mm2
-lµ®éd·ndµit¬ng®èi%
T
Sr
2
.max )1
1(2min
S
r
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*Nh÷ngyÕutè¶nhhëng®Õnb¸nkÝnhuèn.
- ¶nhhëngc¬tÝnhcñavËtliÖu:VËtliÖudÎoth×cãb¸nkÝnhuènnháh¬nvËtliÖudßn.
- ¶nhhëngcñagãcuèn:Khinháth×vïngbiÕnd¹nglín,ph¶it¨ngb¸nkinhuènnhánhÊtchophÐp.
- ¶nhhëngcñathíkimlo¹i.- ¶nhhëngt×nhtr¹ngmÆtc¾tvËtliÖu.
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3.5.tÝnh®µnhåikhiuèn.-KhibiÕnd¹ngkimlo¹ilu«ntånt¹ibiÕnd¹ng®µnhåivµbiÕnd¹ngdÎo.
- TÝnh®µnhåi®îcbiÓuhiÖnkhiuènvíib¸nkÝnhnhá(r<10S)b»nggãc,khiuènvíib¸nkÝnhlín(r>10S)th×ph¶itÝnh®Õnc¶sùthay®æib¸nkÝnhcongcñavËtuèn.
- Khir<10Sth×gãcuèn®îcx¸c®Þnhtrªnc¬sëthùcnghiÖm(södôngc¸clo¹igi¶n®å)
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o
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3.6.Lùcuèn.Lùcuèntrongkhu«ndËpbaogåmLùcuèntùdovµlùclµph¼ngvËtliÖu.
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-Lùcuèn®îcx¸c®Þnhtheoh×nhd¸ngvµtr¹ngth¸iuèn.
- Khiuènh×nhch÷V.
l–lµchiÒuréngmiÖngcèi.mmB–lµchiÒuréngvËtuèn.MmQ-¸psuÊt®Ólµph¼ngkG/mm2.F–lµdiÖntÝchlµph¼ngdíichµymm2,phôthuécvµogãc
FqBl
SkP bc .... )(kG
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- Khiuènch÷U,vËt®îc®Èyquacèith×.
- Khiuènch÷U,kh«ng®Èyquacèi,cãlµph¼ngcuèicïngth×:
B–lµchiÒuréngvËtuèn,mmF=(L–2r).B–lµdiÖntÝchlµph¼ngdíichµy,mm2
bc SBP ..4,0 )(kG
FqSr
SBP bc .
..7,0
2
)(kG
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3.5.kÕtcÊukhu«nuèn.KÕtcÊukhu«nuèncãlo¹i®¬ngi¶nvµphøct¹p.
*Khu«nuènch÷V®¬ngi¶nkh«ngcãdÉnhíng.
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*Khu«nuèn1gãccãtrôdÉnhíng
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*Khu«nuènch÷Uvíigãcuènnháh¬n90o
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*Uènvßngtrßn.
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KÝchthíc®îctÝnhnhsau:
Khi = 90o th× R2 = R1 khi ®ã 3 cung cã b¸n kÝnh uèn b»ng nhau.
)(2
sin
)(2
sin2
.1180
22
12
12
RRa
RRl
RRo
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*Khu«nuènvßngë2®Çuthanh.
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*Khu«nuènphøct¹pcãm¸quay.
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*Uènèng.
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*UènvËtliÖutÊmtrªnm¸y3trôc.
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