Thuyết minh đồ án BK2012

7/31/2019 Thuyt minh n BK2012

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GVHD: Ths. Nguyn ThNgc Huyn

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MC LC

L ...4

......6

I: L THUYT ......61.1. Cc khi nim cbn....6

1.2. Phn loi ma st... 7

1.3. Cc nh lut c bn v ma st.... 9

1.4. Bn cht ca ma st ngoi...13

1.5. Tnh ton h s ma st....18

1.6. Ma st ln....21C II: L THUYT V MN......24

2.1. Cc khi nim v nh ngha c bn...25

2.2. Mt sc ch hnh thnh phn t mn...35

2.3. Phn loi dng mn.....39

2.4. Cc nh lut c bn v mn.......59

2.5. Bn cht ca qu trnh mn....65

2.6. Mt s phng php tnh cng mn ca cp ma st...75

2.7. Tnh mn cp ma st theo thuyt phn t...84

III: ..91

3.1. Lch s pht trin ca cng ngh bi trn...91

3.2. Phn loi cc dng bi trn ....94

3.3. Bi trn thy ng......96

3.3.1. Khi nim v phn loi....96

3.3.2. Nguyn l ma st bi trn thy ng trn gi ...97

3.3.3.Bi trn thy ng tip xc..98


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3.4. Du bi trn..105

IV:

....110

1. Cng nghc truyn thng1102. Cng ngh cn dnh cc lp lim loi....111

3. Cng ngh hn n to bng hai lp kim loi....112

4. Cng ngh luyn hp kim bt......113

5. Qui trnh cng ngh ch to bc bimetal ti nh my c kh Ng Gia

T...115

BIMETAL BK 2012.122

NAM..122

1.1. Cc dng bc c trn thtrng Vit Nam......122

1.2. Bc Bimetal ch to ti nh my c kh Ng Gia T......126

1.3. Phm vi cc loi bc cn th mn...127

II: T

BIMETAL.128

2.1. Nhu cu v tnh cp thit ca vic thit k ch to my th mn bcBimetal.128

2.2.Cc phng n v s th mn ...1312.3.Tnh ton khnng ti v cch t ti cho bc ..136

2.4. Nguyn l lm vic ....1402.5. Cc thng s lm vic ca my o mn.....140

2.6. S t ti....141

2.7.Tnh ton s b cc cm chi tit chnh143

2.8.Bn v thit k cc chi tit chnh ca my..154


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: 166

IV: THNGHIM MY185

..191

TI LIU THAM KHO...193PH LC..194


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Ngy nay cng vi s pht trin mnh m ca khoa hc k thut, ca ngnh

cng ngh ch to my ni chung, ngnh ma st hc Tribology ni ring v ngha

ln lao ca n i vi s pht trin ca nn kinh tt nc. Yu cu bc thit tra i vi mi cn b, sinh vin c kh l phi tp trung nghin cu, ng dng

nhng thnh tu khoa hc k thut vo thc tin sn xut gip cho nn khoa hc

k thut v kinh t ca t nc ngy cng pht trin theo kp cc nc tin tin

trn th gii, p ng mc tiu n nm 2020 a Vit Nam c bn trthnh mt

nc cng nghip pht trin. Vi yu cu chng em nhng sinh vin nm cui -

B Mn My& Ma st hc - Vin C Kh - Trng i Hc Bch Khoa H Ni

chn ti Nghin cu, thit k, ch to m mn metal BK2012,

ng dng kim tra bc xe Hyundai vi mong mun c nghin cu v tm hiu

thm v nhng c sv l thuyt chung ca ma st hc c p dng vo thc t.

Cc nghin cu thc tin cho thy phn ln cc my mc, thit bc kh b

hng khng phi do gy m do mn v h hng b mt ma st trong cc mi lin

kt ng. phc hi my mc, thit b phi tn ph nhiu tin ca, vt t, cngsc ca nhiu b phn sn xut. V vy nghin cu ma st v mn a ra cc

phng n ti u gim ma st, mn ang ngy cng l mt yu cu bc thit i

vi mi phn xng, mi nh my, mi ks cng ngh ch to my.

Mi loi h chi tit cn kim tra cng mn u cn thit phi thit k

mt my o mn ring vi yu cu g, h thng ng lc ring. My o mn

c nghin cu, thit kl my o mn dng cho h chi tit dng bc trt taybin - trc khuu ng c t trong. Bc bin l loi bc ch to bng bacbit gm

hai na thun tin khi lp ghp trn trc khuu v u to thanh truyn ng c

t trong. Vi iu kin lm vic khc nghit ti trng ln, nhit cao bc bin

mn rt nhanh. V th ta tin hnh kim tra bc trc khi lp hoc sau mt thi gian


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chy a ra la chn ti u ci tin bc, cng nh chn chbi trn hp l

gim mn. Ngoi ra c tho h s ma st ca bc th bng cch o gc ma st.

Trong ni dung n tt nghip ca sinh vin ngnh ch to my, vi s

hng dn tn tnh ca cc thy c hng dn Thc c Bo v Thc Nguyn Th Ngc Huyn B Mn My & Ma St hc, i hc Bch Khoa H

Ni. Chng em chn ti Nghin cu, thit k, ch to m mn

Bimetal BK2012 , ng dng kim tra bc xe hyundai ph hp vi kh nng

cng nh thi gian thc hin.

Chng em xin chn thnh cm n cc thy c B Mn My & Ma St hc,

i hc Bch Khoa H Ni gip chng em trong qu trnh thc hin ti.

c bit l hai thy c hng dn nhit tnhhng dn chng em hon thnh tt

nht ti.

Do phm vi kin thc v kinh nghim cn hn ch nn khng th trnh khi

nhng sai st trong qu trnh thc hin ti, nhm nghin cu chng em knh

mong cc thy nhn xt v bxung cho ti chng em them hon thin.

Chng em xin chn thnh cm n!

H ni, thng 06 nm 2012

Nhm SV thc hin n:

Trn n u

Tn

Tn Tn Trun


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PHN I : CSL THUYT CHUNG

1

L THUYT MA ST

1.1. Cc khi nim c bn1.1.1Ma st ngoi

Ma st ngoi l qu trnh tiu hao nng lng khi hai vt th rn c chuyn

ng tng i vng tip xc thc di tc ng ca ti trng ngoi.

Ma st l qu trnh rt phc tp v ph thuc vo:

- Bin i ca cc qu trnh din ra trn din tch tip xc thc v lp bmt mng trong qu trnh chuyn ng tng i ca mt vt th trn b

mt vt th khc.- Cht lng b mt khi tham gia ma st.- iu kin v mi trng ma st.- Cht lng ma st c nh gi bng lc ma st.Lc ma st l lc c xu hng cn trchuyn ng tng i ca cc vt

rn, xut hin ti cc im tip xc thc, khi vt th ny chuyn ng tng i

trn b mt vt th khc.Lc ma st khi ng l lc ma st xut hin trong cc dch chuyn ban u,

cn gi l lc bm dnh, xut hin trong cc khp ma st trt chuyn ng khng

lin tc.

Lc ma st tnh l ton b lc ma st ti thi im chuyn t trng thi dch

chuyn ban u sang trng thi trt hon ton.

Lc ma st ng l lc ma st xut hin trong qu trnh chuyn ng tng

i vng tip xc.

Lc ma st trt c xu hng cn trchuyn ng theo phng tip tuyn

vi b mt tip xc.


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Hnh I. 1.1.Sph thuc ca lc ma st vo gi tr dch chuyn L sau trng

thi dch chuyn bn u l trn t trtn nh vi Fms= Const

1.1.2. ln trn a ma st :

Trong k thut s dng 3 i lng c trng:

-

H s ma st: t s gia lc ma st v ti trng php tuyn :f = Fms/N (1.1)

- H sma st khi va p: t s ca sthay i v mt ng lng ca vtththeo hai hng tip tuyn v php tuyn.

fvd = (1.2)

- H s mt mt nng lng do ma st:Fw = Wms/Wtng (1.3)

1.2. Phn loi ma st1.2.1.Cn vo dng chuyn ng

Ma st trt: ma st xy ra gia hai b mt c chuyn ng trt tng i.


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Ma st ln: ma st xy ra gia hai b mt c chuyn ng ln tng i

Ma st xoay: ma st gia hai b mt c chuyn ng xoay tng i

Ma st hn hp:

Hnh I.1.2. Cc dng ma st theo chuyn ng1.2.2.Cn vo u kin bmt

Ma st khng c cht bi trn: l ma st ca hai vt rn trn b mt khng c

iu kin khng nh r rng cht bi trn hay bt k cht no,i khi cn c gi

l ma st kh.

Ma st gii hn: l ma st ca hai vt rn c tn ti gia lin kt ca chng

mt lp bi trn cphn t dn 0,0001mm, n c tnh cht hon ton khc vi tnh

cht ca ton khi cht bi trn

Ma st t: l ma st gia hai b mt c phn tch bi cc lp cht lng c

chuyn ng tng i vi nhau, trong ng sut tip to thnh lc ma st.

Ma st na t: l ma st ng thi c cma st t v ma st gii hn.


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1.2.3.Cn vo u kin lm vic

Ma st bnh thng: l ma st xut hin ch lm vic bnh thng (n

nh) . c trng bi s cn bng ng gia ph hy v phc hi lp mng oxit c

tnh bo v trn b mt ma stMa st khng bnh thng: l ma st xut hin ch lm vic khng bnh

thng. N thng c th hin nhit ca cp ma st, Cn bang ng gia

ph hy v phc hi b ph v.

1.2.4.Cn teo ng lc hc tip xc

Ma st tnh xut hin trong qu trnh dch chuyn ban u, lc ma st ngncn bin dng lp b mt

Ma st ng xut hin trong qu trnh chuyn ng tng i lc ma st

ng sthc y qu trnh bin dng trn lp b mt tng Ar

1.3. c nh lut c bn v ma stCc nh lut v bo ton nng lng, chuyn ng v cc nguyn l cc tiu

c p dng trong iu kin ma st v mn bnh thng, ngha l quan h gia

cc dng tng tc khc nhau trong qu trnh ma st mang tnh cht hong ton xc

nh.

1.3.1.nh lut thnht

Cng ca lc ma st ngoi bng tng nhit sinh ra v cc nng lng c

hp th (ch yu do kim loi).

A = Q + E (1.4)

- ACng ca lc ma st- Qnhit sinh ra- Enng lng hp th ca kim loi


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Cng ca lc ma st khng bao gibin hon ton thnh nhit: A > Q

Nng lng hp th khng bao gibng khng: E 0

E/A = f(p,v,c). hm nng lng hp thtng i ca b mt ma st ph thuc

vo tnh cht ca vt liu v iu kin ma st

V vy: C khnng iu khin qu trnh ma st bng cch iu chnh cn bng

nng lng c t s E/A nh nht v n nh.

1.3.2.nh lut thhai

Lc ma st l tng ca cc lc thnh phn c dng lm tin trin cc

qu trnh c l ha tt yu, ng vi iu kin tip xc nht nh ca cc vt th ma

st.

Fms = F1 + F2+ F3+ F4+ .+ F8+ F9kbt+ F9bt+ F10 (1.5)- F1 : Lc ma st trong cc lp thy kh ng,- F2 : Lc ma st ta thy ngbn trt (cc lp bin)- F3 : Lc cn trt trong cc lp gii hn- F4 : Lc to di tip xc trong lp b mt rt mng- F5 : Lc to ra dao ng n hi trong cc lp di b mt-

F6 : Lc lm bin dng cc th tch b mt v m- F7 : Lc ph hy cc lin kt bm dnh, khuych tn- F8 : Lc tng tc trng phn t, trng Vandecvan, trng b mt vi

cc khuyt tt ca cu trc phn t

- F9kbt : Lc ph hy thtch v m ca kim loi- F9bt : Lc ph hy khuyt tt tch ly v cc cu trc th cp- F10: Nng lng b khuch tn ra ngoi (pht x, dao ng m)

F1 v F2 xy ra khi bi trn thy kh ng

F3n F9bt , F10 xy ra trong qu trnh ma st bnh thng

F6n F9kbt , F10 xy ra trong qu trnh ma st khng bnh thng


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Qu trnh ma st bnh thng v khng bnh thng tng ng vi cc dng

lin kt khc nhau.

Qu trnh ma st bnh thng c c trng bi h s ma st n nh v n

c gi tr nh nht.1.3.3.nh lut thba

Ba trng thi bin dng - ng sut: ng vi mt t hp cc thng s (vt liu,

mi trng) nht nh c mt vng ca thng sc hc (p,v), trong tch phn

ca hm nng lng hp thtng i trn b mt ma st ly trong ton th tch b

bin dng c gi tr cc tiu:

= min (1.6)Kt lun: Ba nh lut trn cho php phn tch qu trnh ma st phc tp v

ch ra min bnh thng trong gn nh ton b cng ma st bin thnh nhit .

Hnh I.1.3.S v tr cc vng ma st bnh

tn v kn bn tng

1.3.4.Quy lut mn thc nghim:

ng cong Stribech: Ph thuc ca h s ma st vo vn tc v p lc.

Ba trng thi bindng,ng sut


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Hnh I.1.4.Ph thuc ca h sma st vo p lc.

Hnh I.1.5. Ph thuc ca h sma st vo vn t trt.

IMa st kh

IIMa st gii hn

IIIMa st t

IVMa st khi bi trn ri

IVng n nhmnoxyhoa

IIVng chuyn tip

IIIVng bin dng vph hyMn khng

bnh thng (trc, cotrc)

IVng n nhMnoxyhoa

IIVng chuyn tipKhng bnh thng ng vitrc loi I (V < Vth)

IIIvng khng bnhthngkhng bnh thngng vi trc loi II(V>Vth)


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1.4. Bn cht ca ma st ngoi.Bn cht ma st ngoi rt phc tp, l tng hp ca cc qu trnh c, l, ha

din ra ng thi.

Ma st ngoi din ra trong din tch tip xc rt nhkhng quan st ctrc tip.

1.4.1.Bin dn k m st (n i hoc do).

Bin dng l phn ng chng li tc dng ngoi lc ca cc vt th vt l

Bin dng l qu trnh ch yu nh hng n ma st ngoi.

{ nh hng Fms , l nguyn nhn hnh thnh vng ma st c hc (s cn

trtrt ca cc lp v bin dng trong ma st trt)

1.4.2.Bm dnh v khuych tn khi ma st

Tng tc vt l ca cc b mt ma st c th hin bi hin tng bm

dnh v khuych tn. Xut hin cc lin kt gia cc b mt ca cc vt th ti vng

tip xc thc

- Bm dnh tnh: Sc cn chng tch ly ban u- Bm dnh ng: sc cn chng tch ly cc giai on khc nhau- Lc bm dnh l lc cn chuyn ng tng i ca hai vt th theo

phng vung gc vi b mt ma st. Lc phn t v lc bm dnh khng

sinh cng


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- Khuch tn l qu trnh thm nhp v phn tn cc nguyn t, phn tgia cc b mt tip xc ma st. Hin tng ny c p dng trong

phng php chuyn dch chn lc.

1.4.3.Ph hy khi ma st.

Kt qu cui cng ca qu trnh ma st l s ph hy b mt ma st bi s

bong tch hoc co xc to ra cc phn t mn.

- Do bin dng c lp i lp li nhiu ln- Do kt dnh v khuych tn c lp i lp li lm tng th tch cc phn

t chuyn di.

Lc ma st l tng lc cn trgy bin dng b mt ma st v lc lin kt

gia cc phn t trong lin kt bm dnh, khuych tn, bong tch,

Fms = Fch + Fpt f = fpt + fch (1.7)

- Thnh phn bin dng thng nh.- Thnh phn phn t c tnh cht quyt nhiu ny th hin r trong ma st khng cht bi trn:

- Thng c trt theo kiu bc nhy: rung khi khi ng, rt khi phanh,rung khi dao tin ct,

- Mng oxit v bi co nh hng rt nhiu n lc ma st: lc ma st phnt, din tch tip xc.

1.4.4.M st k b trn i hn.

Bi trn gii hn xy ra khi b mt ma st b phn tch bi mt cht bi trn

rt mng c chiu dy cphn tn 0,1m, c tnh cht hon ton khc ton khi

cht bi trn.

- Bi trn bng mng du


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MoS2: tng tnh Graphit dng nhit thp v trong chn khng.

Khi c m h sma st tng do s c mt ca lu hunh nhit 583oC

to thnh cc ht rn kim loi mm (khng b bin cng, khng to thnh dung dchrn) Babit, ng, Ch, hp kim ng mng kim loi mm c bn nn tt.

Khi c chuyn ng s dn n s ct trong kim loi mm, din tch tip xc

khng ln (nn cng)lc ma st gim.

1.4.5.M st k b trn t

B mt ma st b phn tch hon ton bi lp bi trn lng .

p sut du cn bng vi ngoi lc .

Cc lp du c khong cch > 0,5 m vi b mt chuyn ng t do vi

nhau .

Lc ma st ph thuc vo:

- nht ca du .- Gi tr bng tng lc cn ca cc lp du theo chiu dy ca mng

du.- Theo chiu dy ca mng du gm c cc phn t hot tnh hp th

vo b mt kim loi :

+ Lp gii hn

Cu trc tinh thGraphit:

Graphit: c cng vng phng vung gcvi mt phng ca lp trong mng tinh th xpx bng kim cng, bn cc phng song

song vi lp rt nh. H s ma st f = 0,03 0,04

Khi c m v mng oxit kim loi s tngcng bm dnh vo kim loi


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ptp lc chy

f = 0,170,2

o Cng thc R.kinh v Tabor:f = f0 + K.

(1.13)

Trong :

Kl h s thc nghim

Khi f0= 0 v K = 1 cng thc Taybor v Bowden

o Cng thc R.T.Spurr v T.P.Navcomb c mi quan hf =

(1.14)Trong :Dng knh mu th

dl chiu rng vt ng trt

o Cng thc Ranbinowic tnh h s ma st cho tip xc do:f =

(1 + ) (1.15)Trong :

v sc bn ct v gii hn chynng lng bm dnhgc nghingbn knh vng bm dnh

1.5.1i vi tip xc cc b (duy nht)

Khi tip xc do: Vi gi thit mt vt th rn tuyt i, cn vt th kia do

l tng. Khi < 0,5.T th h/r c th biu din qua ti, cng v h s ma st sl:

f =+ + (P2 = c.) (1.16)


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Khi tip xc n hi: H sma st c th hin bng phng trnh

f =+ + 0,44..Pr. (1.17)

Fms khi = 1,5.

(1.18)Trong : v thng s ma st ca thnh phn phn t

rbn knh cong ca nhp nh

h sn hi ca vt liu

h s mt mt do trtrtNti trng php tuyn tc dng ln nhp nhgii hn chy ca vt liuhchiu su thm nhp

1.5.2.i vi tip xc phn tn

Khi tip xc do:

f =+ + 0,55. .. (= c.T) (1.19)i vi cc b mt c gia cng ln cui, b=2 v v=2, khi h s ma

st s l:

f =+ + 0,52.

. (1.20)Khi tip xc n hi:

f =

.

+ 0,19.

.

.

.

.

Khi v = 2: f = + + 0,23.. . (1.22)

B mt sau chy r: v = 2: f = + (1.23)

(1.21)


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B mt c sng : f = + (1.24)

B qua thnh phn c hc

Trong : thng s t hp b mt

Vthng s ca ng cong phn bHbchiu cao ca sng

Rbbn knh cong ca sng

Pcp lc vng

= . . ; = .

(1.25)1.6. a st ln

Mt bnh xe ln trn mt nn phng cnh

- Khi n quay mt gc - Trc ca bnh xe dch chuyn tng i vi mt nn mt lng l R- Chuyn ng ca a trn c gi l ln thun ty. Trong trng hp ln

thun ty, im bnh xe tip xc vi nn s khng c chuyn ng tng

i.

Hnh I.1.9a.S ln a bnh xe trn nn cnh.

- Cc im ca bnh xe so vi tm quay tc thi O1 c vn tc gc l =


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- Trc i qua im O1 v vung gc vi mt phng ln ca bnh xe gi ltrc quay tc thi

- Trn thc t do bin dng ca cc vt th tip xc,im tip xc lnkhng nm trn ng trc quay tc thi m nm trn mt b mt nht

nh

- Nu bnh xe chu tc dng ca ngoi lc N vi phng ca lc l OO1m bo bnh xe ln vi vn tc khng i,cn phi t lc F0 ln, c

im t lc trn trc quay tc thi nh hnh v. Momen ca lc ny so

vi im O1 s cn bng vi Momen cn ln.

- H sma st ln k c xc nh theo t s ca momen chuyn ng Mvi ti php tuyn N

k = = (1.26)

- Nh vy h sma st ln khc vi h sma st trt, n c th nguyn ln vo chiu di.

- H s cn ln f vi c trng khng thnguyn c xc nh bng t sgia cng ca lc chuyn ng F0 trn mt dn v chiu di ng ln vti php tuyn

f = (1.27)- Khi mt trln u (trng thi cn bng) th momen tc dng M = F0.R

cn bng vi momen phn lc xut hin,tc dng ca phn lc N= N b dich chuyn mt khong cch e so vi phng ca ti tip tuyn,theochiu ca chuyn ng ln:

f = hay f = = (1.28)

Trong : Acng ca lc chuyn ng A = M.

Nti php tuyn

l qung ng chuyn ng l = R.Suy ra : F0.R = N

.e e = (1.29)Hay v mt gi tr :


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e = = k (1.30)

Tnh h s cn ln:

f= = {

- } (1.31)

Hnh I.1.9b.S ln ca bnh xe trn nn cnh.


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vt liu mi hoc lm xy ra qu trnh bin i vt l lp b mt tip xc ma st:

bm dnh, khuych tn hp th, hp kim ha, n mn, xm thc

Cc kt cu my cha cc cp ma st gi l cc kt cu ma st, chng c vai

tr r rt trong phn b p sut lm vic trn b mt cp ma st. Kt cu ma st ti

u phi l kt cu c p sut phn bu trn b mt tip xc ma st v l nh

nht, phi c iu kin ta nhit, bi trn v chng bi bn tt.

Mt trong nhng i lng quan trng nh gi mn theo thi gian

hoc theo qung ng ma st l lng mn U. N l gi tr mn ca cp ma st

trong mt khong thi gian hay trn mt qung ng ma st no . Lng mn

U c thnh gi theo chiu cao ca lp mn trn b mt ma st (theo phng

vung gc vi b mt ma st hay vung gc vi ng trt), hay theo khi lng

mt i ca cp ma st trong qu trnh lm vic hoc theo th tch mn ca b mt

khi hot ng.

Tc mn theo thi gian c s dng nh gi qu trnh mn v so

snh vi mn tiu chun, n l o hm ca lng mn theo thi gian hoc theo

qung ng ma st. Trong giai on mn n nh, tc mn l tg ca gc hp

bi thlng mn theo thi gian vi trc thi gian v c gi trkhng i.

Cng mn ca cp ma st I l i lng nh gi mn trn mt n v

chiu di qung ng ma st thng qua th tch mn, khi lng mn hoc chiu

cao lp mn. Ty theo tng trng hp c th sc cng mn thtch, cng

mn khi lng

Cng mn khng th nguyn Ih ca cp ma st l i lng mn m ti

xy ra h hng hoc khng c hiu qu kinh t nu s dng tip. Lng mn

gii hn ca cp ma st l tiu chun c bn xc nh tui th lm vic ca cp

ma st. Lng mn gii hn cng ln th tui th ca cp ma st cng di. Tuy


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nhin lng mn gii hn c quan h cht ch vi ch lp ghp m bo iu

kin lm vic bnh thng ca cp ma st nn khng thtng tdo c.

2.1.2. trn qu trnh mn

S ph thuc ca mn vo thi gian hoc qung ng ca ma st.

Khi cp ma st bt u lm vic chu k u tin s din ra qu trnh chuyn

ha t trng thi b mt ban u cn gi l b mt cng ngh sang trng thi b mt

lm vic hay trng thi s dng. Qu trnh chuyn ha i vi tt c cc cp ma

st gi l chy r hay thi k mn ban u. Qu trnh chy l c bit quan trng

trong vic m bo chuyn b mt ma st sang trng thi lm vic mt cch nhanh

chng, n nh v ddng, ng thi n nh hng n ton b hot ng sau ny

ca cp ma st nh: ch lp ghp khi lm vic, bin dng b mt ti u, tnh

cht c l ca lp b mt tip xc ma st.

Trong iu kin ma st mn bnh thng c th phn chia s ph thuc ca

mn (hay l lng mn) theo thi gian thnh ba giai on c bn:

Giai on chy r, giai on mn n nh v giai on mn khc lit.

Hnh I.2.1. Biu din s ph thuc ca mn vo th n: I l on

chy r, II l on mn bn tng, III l giai on mn khc lit.


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Trong trng hp chy r, tha nhn thng s ca ng cong phn b nhp

nh b mt theo cao: b = 2, v = 2.

L thuyt ma st c phn t cho thy s ph thuc ca cc phn sc trng

cho tng tc ma st v thng s hnh hc vi m ca b mt ma st, n nh ca

nhp nh b mt trn vt rn tip xc ma st ph thuc vo bn lien kt, tng

tc phn t trn im tip xc, tnh cht n hi ca vt liu v ti trng php

tuyn. Khnng tnh ton v d kin nhp nh th cp ti u khi thit k cc

chi tit v cc kt cu ma st cho php s dng cc bin php cng ngh gia cng

b mt ph hp vi nhp nh xc nh, m bo mn ca cc b mt tip xc

ma st l nh nht khi chy r. Sau qu trnh chy r, cht lng b mt ca cp mast thay i hon ton vc l ha cng nh trng thi hnh hc b mt.

Giai on mn n nh II l giai on di nht v mt thi gian v c c

trng bi sn nh ca tc mn theo thi gian constdt

dU . Trong giai on ny

c s cn bng ng gia hnh thnh bin dng v s ph hy lp cu trc th cp

trn b mt tip xc ma st. Trong s t hp ca nhp nh b mt t ti gi trti u v khng thay i trong iu kin ma st nht nh. Do h s ma st ny

nh nht v n nh trong giai on ny, tc mn c quan h tuyn tnh vi thi

gian hoc qung ng ma st. Vi gi tr mn gii hn c xc nh trc c th

dbo c tui th lm vic ca cc ma st.

Biu hin bn ngoi r rng nht ca qu trnh mn n nh l sn nh

nhit ca cc ma st khi lm vic, n c trng c bn cho qu trnh mn bnhthng trong tip xc ma st.

Giai on mn khc lit III l giai on c trng ca stng vt nhanh ca

tc mn theo thi giandt

dUhay theo qung ng ma st

dL

dU.


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ng cong 1 c trng cho qu trnh mn trong nhng iu kin chy r

khng tt. Khi trong qu trnh chy r b mt ma st b trc mnh v khng tn

ti mng bo v, khng c bi trn y , dn ti vic hnh thnh cc vt xc

v cc cp h hng khc. Cp ma st b lm vic trong iu kin khng bnhthng.

Hnh I.2.3.Sty i nhp nh bmt trc khuu ph thuc vo thi gian

chy r; 1,2,3 tn ng vi t 100, 800, 1700 vg/ph

ng cong 2 c c trng tng qut cho qu trnh mn bnh thng theo

thi gian.

ng cong 3 c trng cho qu trnh mn trong iu kin chy r c ci

thin cht lng. Mn ca qu trnh chy r khng ln, cng mn v lc ma

st trong giai on chy r gim nhanh v t n gi trn nh trong thi gianngn. Hin tng trc khng pht trin, trn b mt ma st hnh thnh bin dng vi

m ti u v cc cu trc th cp chng mn.


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2.1.3.C ln trn qu trn mn

Qu trnh mn vi tc dng ph hy, xy ra trong th tch nh ca vt liu

cc lin kt ma st, ni din ra cc tc ng tng h mnh, hnh thnh din tch

tip xc thc ca b mt ma st v to cc phn t mn tch ra khi vng ma st.Thng thng gi trmn c nh gi theo s gim kch thc ca b mt ma

st theo hng vung gc vi b mt.

Trong ch tip xc ma st tnh din tch tip xc thc Arkhng thay i,

(Ar = const) theo thi gian. Khi chuyn ng trt tng i cc lin kt ma st

ang tn ti b ph hy lm pht sinh cc lin kt mi vi gi trng knh trung

bnh ca vt tip xc tng ng. Slng cc lin kt ma st ph thuc vo chu kti trng.

Th tch vt liu V tch ra t b mt dng phn t mn t l vi din tch

tip xc thc :

Ar: V ~ Ar.

S ph hy trn vt tip xc thc c th xem l tp hp ca cc s kin clp ng xc sut, v t l trong mi quan h ny c thnguyn l n vo chiu

di.

Khi trt trn ng knh trung bnh ca vt tip xc, ph hy ch xy ra

trong 1 phn ca din tch tip xc thc Ar, v c th gi thit tch ra 1 lp c chiu

dy h t mi vt tip xc thc:

V = h.Ar (2.1)

Trong mi quan h gi trh khng phi l gi tr mn thc s trong 1 vt

tip xc thc trn lp b mt vt liu. Vi quan nim cc ph hy trn tng vt


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tip xc thc ca b mt tip xc ma st s tp hp a n gi trmn tng ng

cui cng l H.

Ti mi thi im mn xut hin v b ph hy, qu trnh ny c din ra

vi Z lin kt ma st:

Z =h

H

(2.2)

Chia b mt mn thnh cc di nh dc theo hng trt vi chiu rng l d1

(kch thc trung bnh ca vt tip xc theo phng vung gc vi hng trt).

Chiu di ca mi di phi m bo trn xut hin Z lin kt lc ma st.

Tng s lin kt ma st xut hin khi ma st cho c b mt ma st l :

h

H

d

aN

1

0(2.3)

Trong a l kch thc ca vt thmn theo phng vung gc vi hng

trt.

Gi mt vt tip xc l:a

r

A

n (2.4)

Trong :r

rr

A

An

(2.5)

Tng s lin kt ma st xut hin trn din tch ma st:

1

1

h

Hdan (2.6)

Qung ng ma st c xc nh bng cng thc:

.

1

1dh

HL

(2.7)


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Va

r

r A

A

d

h

A

dd

L

H

2

21.

(2.8)

Trong : Ar - din tch trung bnh ca vt tip xc n v.

d2 - ng knh trung bnh ca vt tip xc theo hng trt.

c trng v m ca qu trnh mn l Ih:

L

HIh

(2.9)

c trng v m ca qu trnh mn l cng mn n in:

22.dA

V

d

Hi

r

n

(2.10)

Thng thng c th chp nhn nhp nh b mt c cc d1 = d2= d, do :

a

rh

a

rhh

A

Ai

A

AiI

4(2.11)

Ngoi 2 c trng c bn ni trn cn c cc i lng sau:

Cng mn theo khi lng:

L

GIg

(2.12)

Cng mn theo th tch:

L

VIv

(2.13)

Trong V v G l th tch v khi lng mn tng ng trn qung

ng ma st.


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- khi lng ring ca vt liu mn.

Cng mn ca cc vt liu ni chung nm trong khong:

133

1010

hI (2.19)

2.2. Mt sc ch hnh thnh phn tmn

2.2.1. Vai tr ca phn tmn

Qu trnh hnh thnh cc phn t mn khi ma st l mt qu trnh phc tp

v rt quan trng. Hiu c qu trnh ny s cho php lm sang tc ch ph hy

b mt vt liu khi ma st v xy dng phng php tnh.Vic nghin cu thc nghim rt phc tp do tnh c th ca qu trnh mn.

Xc nh chnh xc i tng ph hy, loi b tc dng ph hy ch l hin tng

n l, cn nhng ni xut hin ph hy th khng th dbo c.

Cc phn t ht mn l ngun thng tin quan trng. Nghin cu hnh dng,

kch thc, thnh phn, dng b mt, tnh cht c l cho php xc nh qu trnh

dao ng to thnh chng.

Vic tch cc phn t mn ra khi b mt ma st l kt qu ca mt ln hay

nhiu tng tc. Nu phn t mn tch ra l kt qu ca mt ln hay nhiu ln

tng tc th cng mn trong trng hp ny l v cng ln.

2.2.2. Mt s yu n tn pn t mn.

2.2.2.1. C bm dn.Tc giJ.Archard a ra c chmn bm dnh, a h s k vo cng thc

mn l s ln tng tc n cn thit to thnh phn t mn ( n = k-1 ), nu cc tc

dng tip theo vn thc hin trn cng mt vt liu th r rng s ph hy bt u

do kt qu tc dng ln th hai ch khng phi ln th nht.


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2.2.2.2. C mn do tr

Tc giN.P Suh a ra l thuyt mn do trc. Theo tc gi chiu dy ca lp

mn c xc nh theo suy gim chiu dy ca vng bin dng tp trung:

f

bGh

)1(4

.

(2.20)

Trong : G m un trt.

btenx Burgers.

- h s Poatxong.

f - ng sut ma st.

R rng t s G/f cng nh th chiu dy lp mn cng nh. Vt nt xut

hin trn b mt phn b song song vi b mt ma st. Tc xut hin vt nt

trong vt liu cng chm l do bn dnh ca vt liu cao. Mn ca vt liu c

cng cao, nhhn ca vt th mm.

2.2.2.3. C uyn r vt lu.

Phn t tch ra t b mt khng bin ngay thnh phn t mn. Phn t mn

ch ra khi vng ma st khi bm dnh nhiu ln vo v mt ma st.

M.Kerridge v J.K Lancaster s dng mt mu nhim xkhi trt trn vnh

dn hng bng thp dng c thy rng, on xut hin phn t mn xut hin

trc on chng tch t trn b mt vt thi. Slng cc phn t chuyn ri

tng dn cho n khi t ti gii hn chuyn ri. Cc th nghim pht hin trung

bnh mi ln phn t mn to thnh t 50 phn t ri.


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Nng lng b mt cn thit cc phn t b tch ra khi vt tip xc l:

2

...2

2dE as

(2.22)

Trong :a

- nng lng lin kt bm dnh.

iu kin chuyn ri b phn:sc

EE

Dn ti:

2

ma x.

.24

Ed ap (2.23)

Trong : dp - ng knh phn t bc tch.

Trong trng hp phn t nm khe hgia cc mt lm vic v khng th

bm vo b mt ta c:

2

max

2.

.6

E

Wd abh (2.24)

Trong : dh - ng knh phn t mn.

Wab - nng lng lin kt dnh.

- h s Poatxng.

i chiu gi tr min ca kch thc phn t tphng trnh (2.23) v (2.23)

c:

5

1

h

p

d

d(2.25)

Tphng trnh (2.25) thy rng th tch phn t mn ln hn 125 ln th

tch bong tch. Kt qu thc nghim v tnh theo cc cng thc (2.23), (2.24) c gi


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lp ghp chu ma st ca nhiu loi thit bc kh, ng lc, thy lc, kh nn, do

c cc ht mi cng lt vo vng ma st theo khng kh, du bi trn, nhin liu

hoc khi gia cng tinh ln cui bng dng c mi. Trong nhiu trng hp mi

mn cn do chnh cc phn tmn cng c hnh thnh trong qu trnh ma st.Nhng cu trc cng ca cc b mt ma st phc hp cng c tc dng gy mn

ht mi.

Dng v c ch ph hy c xc nh do tng tc ca b mt ma st i

vi mi trng c ht mi, v thc cht l trt ca cc ht mi cng gy bin dng

do kim loi, thm nhp vo nhau nhng ch tip xc, ph hy th tch b mt

khng tch phn t mn hoc to phoi t vi.

C 2 dng biu hin r rt ca qu trnh mi mn da trn c tnh tng tc

gia ht mi vi b mt kim loi.

Dng thnhtph hy c ha l ch yu: bin dng do ca th tch b

mt, s xi ha ca chng v s ph hy lp mng va hnh thnh.

Dng thhaiph hy c hc cc lp kim loi b mt chim u th, thmnhp ca cc ht mi, ph hy cc th tch kim loi b mt khng tch ht kim loi

gc hoc c th to phoi t vi. Dng ny thuc cc qu trnh h hng khng cho

php xy ra khi c ma st.

Trng thi b mt v cc lp kim loi b mt bh hng do tc dng ca ht

mi c cho trong bng di y:


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Cc tiu chun nh gi qu trnh Dng ph hy do mi mn

I II

Cp nhn b mt

su ca cc lp ph hy

Nhit lp hot tnh b mt

Thay i thnh phn ha hc v

pha ca lp b mt

Thay i tng i cng cc

lp b mt (Hs/hbd)H stng th tch ca lp b mt

ng sut trong lp b mt

Dng ph hy b mt

Tc qu trnh ph hy

Cc qu trnh ph km theo

712

n 2000

n 50C

To dung dch

rn cng tinh

xit

23sadsfsdfsggffgas

f

1,51,08

Nn v ko hn

ch

Dndo

Di 0,5m/h

510

n 0,20mm

n 50C

Khng

sdasdasdasdas

1,5

sdfasfasdfasdasd1

Nn

Do

0,550 m/h

xy ha nhit

thp

Bng 2.1.c tnh trng thi bmt v cc lp bmt tp k mn v

hng do tc dng ca mn ht mi.

Mi mn b mt ma st gn lin vi s c mt ca cc ht mi trong vng

ma st, n c th xut hin trong khong rt rng ca cc tc ng bn ngoi. S

xut hin dng mi mn c ha hay c hc ph thuc vo cc tnh cht c hc ca

ht mi, cng nh hnh dng hnh hc ca n vi cc lp b mt ca kim loi b

mi mn.


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S dng cc kt qu th nghim mn hin trng v trong phng th

nghim tng hp hoc kim im li cc d kin. Nhc im ch yu ca

phng php ny l s mu th nghim t, c kt qu chnh xc cao phi c thi

gian v chi ph.

Chi tit b mn In Ch thch

1 2 3

+ S mi xylanh

-ng c kiu M3 236

-t

1,8.10-12

2,5.10-12

(1,15,6).10-21

Xecmng

-M thic

-M crm

-Gang

+Xec mng

-M thic ca ng c

M3 236

-M crm ca ng c

M3 236

-ng c - 48T

2,5.10-11

2,5.10-12

4.10-11

S mi ca cc xylanhbng gang

Trc khuu ca ng c t+Ngng c bin

+Ngng c chnh

4.10-115.10-12

1,6.10-111,8.10-12

Thpbc hp kim

Ngng trc cam ng c t

ZIN130

1,8.10-9

1,6.10-9

-Bi trn

-M b mt,bi trn

Cc chi tit ca my xc

302: 305; 65t v cc my

khc

+Then hoa trn a quay

+Then hoa trn trc quay

+Rng ca bnh rng o chiu

-Trc

-Cn

8,6.10-20

5,3.10-11

1,5.10-11

6,3.10-12

7,3.10-12

Cc vt liu ca chi tit

my

Thp 50TWX15

Thp 40X - 35

Thp 40x45

Thp 4040x

Thp 4545


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Nh vy cng mn t l vi p sut v thng s b mt t hp vi s m

ln hn 1,khi h s ma st cng cao th cng mn cng ln,tnh nng c l ca

vt liu th hin trong cng thc trn bng tha s:

Khi cng v gin di tng i ti thi im ph hy cng cao th

cong mn cng nh.

2. 4. c nh lut c bn v mn

2.4.1.C n lut bn v mn

Ty theo nhng thng s lm vic p,v,tc ng l ha ca mi trng,tnhnng ca cc vt liu ma st c th l tp hp ca cc qu trnh c,l,ha khc

nhau.thng thng mt trong nhng qu trnh ny s chim u th,cn nhng qu

trnh cn li l th yu c nh hng khng ln.

2.4.1.1 n lut v mn t nt

Cc hin tng ma st v mn kim loi do cc qu trnh khc nhau gy

ra.nhng qu trnh ny din ra trn b mt kim loi v trong cc lp b mt c khiu l:P1,P2,P3 .,Pn vi vn tc ng l Vp1,Vp2,Vp3, ,Vpn.

Trong bt k qu trnh ma st no cng u c mt qu trnh din ra vi tc

ln nht Vpj.Qu trnh Pj ln t cc qu trnh khc v chim u th.

- n lut mn t nt:Dng mn c quyt nh bi qu trnh Pj din ra trn b mt ma st vi tc

ln nht : (n=1,2,n)y l iu kin cn nhng cha ,cn c thm iu kin th 2 dng

mn tn ti n nh l:


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Thay i ca p sut php tuyn v cc thng s ma st lm dch chuyn

min mn bnh thng.

- S ptu mn vo tn s m stTrong trng hp tng qut mn c quyt nh bi gi tr ca p sut

php,ca tc dch chuyn v cc iu kin ma st.

Cc thng s ma st quyt nh v tr ch yu ca hm I=f(v) v I=f(p).

I- vng chuyn dch ca mn n nh

II- vng cc qu trnh khng bnh thngQuy lut mn v h hng khi ma st ln :

Yu t chnh l p sut php tuyn v cc ng sut tip xc ca n,tc

dch chuyn tng i v nhit trong vng tip xc do n sinh ra,tc dng ca

mi mn c hc v l ha ca mi trng trong vng tip xc.

Tc dch chuyn tng i cng quyt nh qu trnh ph hy khi ma st

ln.ph thuc vo gi tr ca tc c th phn bit hai dng mn ch yu l

mn oxy ha bnh thng v qu trnh ph hy c bit do nhit(qu nhit).khi

nhit trong vng ma st vt qu nhit cho php du bi trn hot ng

bnh thng s gy nn hin tng do nng kim loi,khi kim loi b mm

i,lm gim tnh cht c hc ca thp c nhit luyn(ti).cc thay i v cu

trc,c tnh ca kim loi tip xc ma st lm cho qu trnh mn oxy ha bnh

thng chuyn sang qu trnh xc nng rt mnh m.s pht trin ca cc dngmn v h hng khckhi thay i tc dch chuyn tng i.

nh hng ca mi trng kh khi ma st ln l do cc thnh phn hot tnh

ca n c kh nng tng tc vi kim loi to thnh cc mng c cu trc th


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ma st. Do lm tng cng cc thnh phn cu trc cng trn b mt iu ny

c biu hin r khi mn babit.

2.5.3 Ty xy r do tn nt

Trong qu trnh ma st nhit ca cc lp b mt cao hn nhit kt tinh

li ca kim loi,lp b mt khng b bin cng m b ha mm dn n qu trnh

lm phng,lm nhn b mt.hin tng mm ha lp b mt khi ma st c th xy

ra trn ton b kim loi hoc ch mt phn hp kim.

Nhit cao ca lp b mt tip xc ma st kt hp vi bin dng do,to

iu kin thun li cho cc qu trnh khuch tn. c bit trong trng hp khi ma

st gia kim loi do thun khit.

Tnh ng ca khuch tn tng ln khi tng mc bin dng,ng thi qu

trnh khuyech tn khi ma st tnh v ma st ng cng khc nhau.

Trong iu kin ma st xc nh,nhit tng cc b ti cc vng tip xc

ng thi li b ngui nhanh b mt do truyn nhit vo khi kim loi xung

quanh,c th to thnh cc cu trc trn b mt nh khi ti,v km theo cc vt ntt vi. Bin dng do xy ra khi ma st kt hp vi Gradian nhit tng cao lm

thay i cu trc ca tng phn hoc ton b lp b mt tip xc ma st,s gy ra

ng sut trong lp b mt vt liu ma st. Trong mt s trng hp nht nh ng

sut ny c th lm ph v cc cu trc.

Trong iu kin tip xc ma st vi m ca cc cp ma st chu ti cao,nhit

ln khng nh kh nng to ra cu trc plasma.

Tng tc ca cc tip xc vi m xy ra trong thi gian rt ngn (t n s)vi mt nng lng rt ln. Cc nh lut nhit ng lc c in khngp dng c. Vt liu trn lp b mt tip xc ma st mng,b bin i trong


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vng ma st,va p to thnh macmaplasma. Qu trnh ny c th km theo s pht

x cc in t.

2.5.4. Ty xy r do t dn m trn xun qun

Mi trng khng kh hnh thnh trn lp b mt kim loi c lm sch khi

ma st cc mng mng oxit. Oxy ha b mt kim loi khi ma st l qu trnh ph

thuc vo trng thi b mt, cu trc v tnh cht ca cc b mt. Mng oxit bo v

b mt trnh b xm thc, khng ch trong ma st kh, ma st gii hn m c trong

ma st na t. N cn gp phn c bn lm gim cng mn ca cp ma st.

Kim loi nn v oxit c tc dng c hc ln nhau: Trong oxit thng xut

hin ng sut nn khc nhau l s xut hin khnng bong tch mng oxit khi kim

loi dc b mt phn cch. Khi trn b mt phn cch c lc tc dng (lc ma st

tip tuyn), ty thuc vo bn mng oxit v gi tr bm dnh ca mng vo lp

kim loi, c th xy ra bong tch lp mng oxit theo ranh gii vi kim loi hoc

ph hoi mng ny theo phng tip tuyn,trn b mt cc nhp nh.

B mt kim loi ca cc cp ma st khi tc ng vi cc hot ng pha trongdu(ph gia), to thnh cc mng hp cht ha hc c vai tr tng tnh mng

oxit. Cc mng s bo v b mt chng mn khi tc hnh thnh chng ln hn

tc mn.nhit cao, cht bi trn b phn hy, khi c khnng xy ra bn

ha b mt bng nguyn t cacbon.

Cc cht lng v kh c tnh hot ng cao c xu hng lm tng mn.

2.5.5 P y b mt m st

Cc dn bn ca sph hy cc bmt m st n su:

1. Sct v m


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Tia nh hng n h s ma st v cng mn. Khi tng liu lng chiu

tia len p lyetylen (PE) th h sma st v cng mn u gim. Nu tip tc

tng th cc c tnh ca polyme s gim.

Nhit cng nh hng n qu trnh ma st gia kim loi v polyme. Khi

nhit tng,tnh n hi v do ca vt liu gim. Ty theo nhit c th xy

ra cac qu trnh l ha ca s phn hy cht lin kt hu c hay bn thn vt liu.

Ngoi ra, khi nhit tng,stng ca lc ma st s ph thuc vo bm dnh

ca cht do vi kim loi.

Khi ma st nhng vt liu n hi cao bh hng, v s ph hy mi ca

cc lp b mt di tc dng ca ng sut php v lc ma st, bng con ng bc

ra. Nhng vt liu t n hi hn bh hng bi s ct vi m, trc v tch.

Trong qu trnh mi mn ,nhng yu t ha hc biu hin rt c o, khi

b mt polyme bh hng xy ra s ph hy nhng chui phn t ring bit gii

phng cc gc ha tr t do v cc nguyn ttrng thi nguyn t. Do , kim

loi va polyme s tc dng ha hc vi nhau. Hp cht to thnh b ph hy v li

xut hin .v.v

Ni chung, c ch mn ca vt liu phi kim loi khng khc c ch mn ca

kim loi. Nhng qui lut ring l do c im cc tnh cht c l ha v s bin i

trong qu trnh ma st.

2.6. t s phng php tnh cng mn ca cp ma st

Cng mn ca ma st ph thuc vo vt liu ca n, tnh cht ca lp

b mt tham gia ma st, cng nh iu kin ma st nh: ti, nhit , cht bi trn.

v.vCn c qu trnh xy ra trong tip xc ma st th thy rng qu trnh mn

khng phi l mt hin tng n gin, n l tng hp ca nhiu hin tng. Cc

hin tng ny nh hng qua li ln nhau, c th h tr nhau hoc khng ch


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2.6.1. Tn mn p m st teo t nm

Bng thc nghim quan h gia cng mn v p sut danh ngha

c xc inh qua cng thc :

(2.48)Trong : -p sut danh ngha.

H- cng.

m-ch s mn(khi mn c ha thng m=1).

k-h s t l c xc nh thc nghim.

Cng thc (6.1) thng p dng cho bin dng n hi vi ti ln v cng

ln. Th tch mn ca cp ma st c thc xc nh thng qua ti v cng khi

tm c h s t l thc nghim (R.Home).

W=Z.N/HB (2.49)

Trong : Wth tch vt liu mn.

N-ti trng php tuyn .

HB- cng Brinen.

Z-h s t lc ly t thc nghim ,khnng tch cc phn

t khi b mt ma st khi gp b mt i tc.

Nu gi thit phn t mn tch ra c dng cu vi bn knh bng bn knh

ca vt tip xc th th tch c thc tnh theo cng thc (J.Farchard)

W= (2.50)


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Trong k l h s kn khnng tch cc phn t ra khi b mt tip xc

:k=10-2 10-7.

2.6.2. Tn mn p m st teo nn ln.

Trong qu trnh tip xc ma st ,phn t mn s tch ra khi b mt ma st l

lp b mt ca vt liu tip xc ma st tch ly ni nng d tr. Phn ln

cng ma st c khuch tn di dng in nng, ch cn mt phn nh t 9 n

16% tch ly trong vt liu di dng ni nng. y chnh l nguyn nhn dn ti

ph hy b mt tip xc ma st (Et.Fleisder).

Nng lng ma st b mt c xc nh theo cng thc: (2.51)Trong : Vd - th tch vt liu mn.

WT - cng ma st, WT=f.N.L

F - h s ma st.

N - ti trng php tuyn.

L - chiu di qung ng ma st.

Nng lng b mt ma st c th c xc nh theo cng mn :

T

h

eI

(2.52)

Trong : - lc ma st ring,=f.Pa.

Ihcng mn.


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Trnh by s ma st vi m hnh chm cu cng trt trn b mt bin

dng ni xut hin thnh phn ng sut phc tp.Kt qu l s xut hin bin thin

ng sut theo chu k trong th tch vt liu b mt, mi chu k tng tc ma st

s hnh thnh h hng tch ly mn do ma sat mi l dng ph hy c bit do ngsut ma st thay i theo chu k, gi tr bin khng vt qu gii hn n hi

ca vt liu.

S chu k dn n ph hy ph thuc vo bin ca ng sut tc dng:

onstf

c tn

(2.63)

Trong : - lc ma st ring.

Tf - s m ca ng cong mi c xc nh t thc nghim.

S chu k dn n ph hy n c trng cho qu trnh mi ca vt liu lp b

mt. Theo ng cong mi Veler, s chu k dn n ph hy s gim khi tng bin

ca ng sut tc dng .

Bng thc nghim xc nh c s ng dng gia ph thuc cas chu

k ph hy v ng sut tc dng ca ton khi ca vt liu ph thuc s chu k ph

hy vo ng sut ma st ca b mt. Hai ng mi trn th Logarit lun song

song v cch nhau mt khong nht nh.

S chu k ph hy ca ton khi vt liu c xc nht theo cng thc :

btoankhoi

n

t (2.64)

Nh vy hng s const trong cng thc pahir c dng : const= b


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S chu k ph hy do ng sut ma st c th hin bng cng thc :

.

ft

bms

nk

(2.65)

Trong : - lc ma st ring .

K - H s ph thuc trng thi ng sut v bn cht ca vt liu :

i vi vt liu gin k=5; i vi vt liu do k=3

tfThng s ma st tip xc ma st mi.

B mt tip xc ma st c nhp nh thay i theo cao.Do ng sut mast xut hin trn nh nhp nh bin thin ngu nhin ph thuc vo cao khc

nhau ca nhp nh.Tha nhn quy lut phn b xc xut ca ti khng n nh trn

vt tip xc v p dng gii thuyt cng tuyn tnh cc tng tc mi a n vic

Hnh I.2.14.Ton x n TV


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danh ngha v cng ca vt liu mm hn trong ma st.Vi gi thit th nht

:ch c th tch b mn tham gia vo cc tip xc ma st nhp nh.Th tch vt liu

Vbc tnh thng qua vic s dng ng cong mt phn b nhp nh b mt.

Hnh I.2.15.M n tp x vt rn np n b mt v mt pn

vt lu bn dn n .

tb=b. b (2.70)

trong :- dch cn tng i,=h/Rmax

h - Khong cch t mt phng n nh nhp nh cao nht.

b, vThng s c trng cho ng cong nhp nh.

RmaxChiu cao ln nht ca profil b mt.


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E(kG/cm2)

22 2,110 3,0

28 1,460 3,4

32,5 8,500 3,6Cao su lm vng bt 1,600 3,4

Polyformaldehyle 1,470 1,3

Polycacbonate 8,400 2,9

Nha epoxy 1,800 4,6

K82 14,200 3,1

Cht do florua cp 4 630 5,0Retinax K-240 11,840

Retinax A-3AM 27,300 2,9

Caprolon 6,300 2,6

n 2.4. G tr tn s tp x m st m tfk trt trn tp kng t b

trn tron m trn kn k.

Trong phng trnh mn c bn () tha s th nht th hin su thm

nhp tng i ca nhp nh b mt, su thm nhp ny quyt nh dng bin

dng trong tip xc ma st.i vi vt liu n hi n nh hn 10-2i vi kim

loi en. V nh hn 10-4 i vi kim loi mu. Cn phi lu rng vi t s

h/r>0,5 th khp ma st ngoi khng hot ng. Trong trng hp thm nhp cng

vo b mt vt th bin dnh n hi (vt th b mn),nhp nh b mt c c

trng bi thng s t hp v thng s ca ng cong phn b nhp nh b mt.

Gi tr ca h/r c tnh theo cng thc:

1

12

22

.c

r

ph

r p

(2.74)


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hng III

3.1. Lch spht trin ca cng ngh bi trn

Trc thk 20 :

Hin tng ma st c con ngi bit n v s dng tlu i. Sng

chu tin l vo khong nm 4000 trc cng nguyn l cc thanh ln v xe y

dng chuyn chcc vt nng. Tri qua nhiu thin nin kngi ta ci tin v

b sung cc cng c tuy th s m tin dng v gim nh sc lao ng cho

con ngi.

V mt l thuyt, pht minh u tin thuc v Leonard de Vinci (1452 -

1519) trn cc hiu ng ma st v khi nim v h s ma st. Nhng s v

nguyn l nhm gim h s ma st ca ng vn mang tnh thc tin cho n ngy

nay. Cuc cch mng khoa hc ln th nht (1500 - 1750) ghi nhn s pht trin

quan trng ca ngnh ma st hc trong c kh, p ng yu cu ch to trang thit

b ngy cng phc tp. Tiu biu trong thi k ny l cc cng trnh ca Berlidor

(1697 - 1761) v k thut dn hng v nng, ca Euler (1707 - 1783) v tnh tonh s gc ma st, v hiu ng nhp nh b mt.

Cng nghip pht trin vi tc ngy cng cao y nhanh tc nghin

cu v ng dng vma st v bi trn. Vn c t ra y hn trong cng

trnh ca Charles Augustin Coulomb (1736 - 1806) : ma st hc kn tnh cht

vt liu v hiu ng bi trn, mi quan h ti trng v c tnh tnh v ng cc

cp ma st. T ma st hc ngy cng c nghin cu rng v su hn; c thkn cc cng trnh ca G.A Hirn (1815 - 1890) ... Trong lnh vc bi trn v c

hc giai on ny ni bt l cc cng trnh v m hnh ha cc dng chy cht

lng n gin ca Stokes, hnh thnh phng trnh tng qut chuyn ng ca cht

lng ca L.H Navie (1785 - 1836), lut chy ca J.M. Poiseuille (17991869). V


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c bit l phng trnh tng qut ni ting trong bi trn thy ng c cng b

nm 1886 bi Osborn Reynolds (18421912)

Phng trnh Reynolds nh du bc pht trin nhy vt v n l nn mng

trong mi nghin cu vbi trn cho n hin nay. Xut pht tphng trnhNavie Stockes v vi cc gi thit v dng chy ca mng du bi trn, dng

quen bit ca n l:

L thuyt ca Reynolds c s dng rng ri bt u t th k 20 trong

vic nghin cu cc c hbi trn: cc h thng thy ng, bi trn thy ng

n hi, bi trn vi cc dng chy v vt liu khc nhau. Hn na n cn thc y

cc lnh vc nghin cu lin quan n k thut bi trn nh ha hc, gia cng c

kh, phng php tnh ton ..

u t pt trn v tn tu tthk 20 n nay:

Nghin cu v ma st hc (Tribology) l khoa hc nhm li ng thi cc

yu t ca ba lnh vc khoa hc: Bi trn, ma st v mi mn. Thc cht n l ni

dung nghin cu v cc thnh phn sng, tc l cc b phn tip xc c thchuyn ng trong cc my mc v thit b cng nghip.

K thut bi trn nh mt ngnh u tin c nghin cu rt mnh trong

khoa hc v ma st hc. Trc ht l cc cng trnh v phng php gii phng

trnh Reynolds. Nm 1905, A.G. Michell (1870 1959) ch ra c s gim p

sut phn bin ca mng du bi trn gia hai tm phng kch thc hu hn.

Vo nm 1904 J.W. Sommerfield (1868 1951) a ra phng php gii bnggii tch cho di v hn vi iu kin bin mang tn ng. Tuy nhin do cha tnh

n sgin on ca mng du nn p sut ca vng ra mng du khng thc t (

p sut m). Nm 1914 L.F. Gumbel (1847 1923) ngh b qua min p sut

m trn khi tnh . Sau nm 1923 H.B. Swift (1894 1960) xc nh c


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vng p sut bo ha ca mng du v nh ra iu kin bin ca Reynolds.

chnh l c scho thut ton gii s ca Chrirstopherson c tnm 1941.

Bng phng php tng tin, nm 1931, A. Kingsbury 91863 1943)

trnh by phng php gii gn ng phng trnh Reynolds. i vi c chiudi nh so vi ng knh, gii php b qua gradien p sut theo chu vi ca F.W.

Ocvirk (1913 1967) c ra nm 1953. Cui cng, gii tng qut v trn

vn phng trnh Reynolds dng vi phn o hm ring ngi ta s dngphng

php s; cc phng php u tin c trnh by bi Cameron v Wood nm

1949 ri n Pincus, Raimondi v Boyd nm 1958. n nay, nhvo s pht trin

phi thng cc cng c tnh ton nn cc li gii cho kt cu bi trn c gii

quyt nhanh chng.

Cc hiu ng khc trong bi trn cng c nghin cu c th. Mc d hiu

ng nhit c Kingsburry cp tnm 1933, nhng phi n nm 1962 phng

trnh tng qut nhit thy ng mi c vit ra ln u bi D.Dowson. Tuy nhin

tnh nhit cho tt c cc trng hp cho n nay vn cn ni dung cn gii

quyt.

Vic s dng cht bi trn c nht thp hay tng tc trt trong bi

trn thy ng sinh ra hiu ng lm thay i ch chy ca mng du. Cc phn

tch u tin vbi trn vi dng chy xon v ri thuc v nghin cu ca G.I

Taylor nm 1923. Cng thc tnh n lc qun tnh ca mng du y c trnh

by bi Slezkin v Targ nm 1946 v ca D. Wilcook nm 1950. Trong bi trn

lu bin ng , tnh cht chy ca loi vt liu ny dc c trng bi lut ca

Bingham tu th k, nhng ng dng trong bi trn c ghi nhn trong cccng trnh ca R. Powell v H. Eyring nm 1944 v A. Sisko nm 1958. C rt

nhiu cng trnh nghin cu v hiu ng trn ch chy ca mng du trong bi

trn; nhng do phng trnh m t dng phi thuyn, nn vic xem xt c h bi

trn y vn lun l vn thi s.


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hiu qu nu khng c cc loi du bi trn thch hp,v vy vic bi trn tt s

lun m bo cho my mc, thit b hot ng n nh, gim chi ph bo dng,

nng cao tui th s dng v tin cy ca chng trong nn kinh t.

Nhn chung cc chc nng ca bi trn l:

- Lm gim ma st, gim cng mi mn, n mn ca cc b mtma st nhm m bo cho ng c, my mc t cng sut ti a.

- Lm sch, chng tt c cc loi mi mn m bo tui th s dngca ng c.

- Lm mt.- Lm kn.

3.2.2.Pn lo dn b trn

Cc phn loi c bn vbi trn.

Theo dng ma st, ngoi ma st kh c cp phn mnma st chng

ta c bi trn na t (thng gn vi vic cung cp du mnh k) v bi trn

t.

Theo vt liu bi trn c cht bi trn rn ( graphit hay bisunfure molybene),

cht bi trn lng ( nc, du, m) v cht bi trn kh.

Vi bi trn ma st t c nghin cu nhiu nht c hai dng ch yu l bi

trn thy ng v bi trn thy tnh.

Trong bi trn thy ng ty theo sReynolds c bi trn tuyn tnh, bi trn

lu bin ng phi tuyn (thng i vi cht bi trn mi c R nhhay nhi

cao) v bi trn ri (i vi cht bi trn l nc hay kh)Bi trn p lc cao sinh ra bin dng ca cc b mt ma st c bi trn thy

ng n hi ( bi trn ln, chu ti ln hay cp bnh rng)


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khi vn tc nh hoc p lc ring khng ln. Th d: trc tay quay, trc my cng

tc cng sut nh. Cc thuc nhm (I-2) l nhng c bi trn lin tc bng

m, bng pht du, m du. Chng l loi d tho c. Ngi ta thng s

dng trong cc thit b rn, rp, c , cn, .Cc thuc nhm (I-3) l nhng lm vic chbi trn thy ng.

Chng chu ti trng nng, va vi trc c vn tc nh, thay i. Ngi ta thng

s dng chng trong ng c v hp tc .

Nhng nhm (I-1) l thy ng, chu ti nh v vn tc trt ln,

chng thng c dng trong cc turbin hi nc, kh v bm li tm.

Cc thuc nhm (II-2) l nhng lm vic chbi trn thy ng,

chng chu ti trng nng, va vi trc c vn tc nhngi ta thng s dng cho

my nng.

3.3.2. Nguyn l vm st b trn ty ng trn g .

Cht bi trn l mt loi vt liu c khnng lm gim ma st, mi mn,

tng cng khnng hot ng n nh v bo v chi tit my. Chng ta cn phi

hiu r snh hng ca l tnh v ha tnh gia du vi b mt bi trn, c nh

thmi lm vic n nh v tng cng tui th ca chng.

Trong qu trnh lm vic ca my mc thit b c cc chbi trn: ma st

kh, ma st t, ma st thy tnh, ma st thy ng v ma st n hi thy ng lc

hc.

nh hng ca ma st bi trn thy ng ln

L thuyt v bi trn thy ng:


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c trng bi mt ng lt hnh tr bao quanh ngng trc. Du bi trn c cung

cp bi bn ua vo qua mt ltm ca mt bn.

ph thuc vo chuyn ng ca trc to thnh p sut do ti trng tc

dng ln du bi trn. Dng hnh hc ca c cho hnh 1.1 trc thngquay khng ng tm vi lt . Khong dch chuyn ca tm trc so vi tm lt gi

l lch tm, v tr lch tm ca trc so vi khong trng ng lt ph thuc vo

ti trng tc ng. Gi tr lch tm thay i cho n khi ti trng c cn bng

vi p sut du bi trn sinh ra. Khi p sut mng du sinh ra cn bng vi p sut

do du bi trn sinh ra. Khi p sut mng du c sinh ra cn bng vi ti theo

hng knh, lc ny ngng trc s chuyn ng l lng trong lp du bi trn.

L thuyt tnh ton bi trn thy ng.

trn khi hot ng mt mng du c hnh thnh bao quanh ngng trc.

V ngng trc quay nhanh v lp du ngn cch b p sut c sinh ra v chng ta

c c bi trn thy ng.

Trong qu trnh tnh ton trn c m hnh ha l 2 tm phng song song

cch nhau mt khong S, vi mn du c nht gia 2 mt phng nh hnh

di y. Gi mt mt phng cnh, y l mt phng nm di, trong khi mt

phng cn li (mt phng trn) chuyn ng vi vn tc U. S c nhng lp du

tip xc vi tm di chuyn chuyn ng vi vn tc U v cng c nhng lp du

tip xc vi tm cnh ng yn. Vn tc ca cc lp du gia bin thin tuyn

tnh t0 n U nh hnh v.

dx

dy xy

Th tch kho st

x

y

Uu

S


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Chng ta xt trng hp c dng chy tng hnh thnh gia hai tm phng

song song di v tn. Cc tm phng c xem nh di v tn theo phng z v

khng c s bin i no v tnh cht lu cht theo phng ny. Chng ta cng bit

rng thnh phn theo phng x ca vn tc bng khng c tm trn v tm dido iu kin khng trt vch bn.

Chng ta c cc iu kin nh sau:

u = 0 khi y = 0

u = U khi y = S

V dng chy c pht sinh trn vn, vn tc khng ththay i c theo xnn ch ty thuc vo y, do chng ta c:

u = u(y)

Thm vo , khng c thnh phn vn tc theo phng y hoc theo phng z

nn: v = = 0

phn tch m hnh , chng ta chn th tch vi phn kho st c kch thc dv

= dxdydz v vit phng trnh momen ng lng theo thnh phn ta x vi lc

vt th trn thtch n v bng khng. = d

Vi gi thit dng chy bnh n v pht sinh trn vn, lc b mt do psut to thnh v cs l b mt kho st.

i vi dng chy pht sinh trn vn, thng lng momen ng lng thc

xuyn qua b mt kho st bng khng, v khng tn ti cc lc vt th theo

phng x, phng trnh moomen ng lng gim thiu thnh:

= 0


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K tip chng ta ly tng ca cc lc tc ng vo th tch kho st theo

phng . Chng ta bit rng cc lc php tuyn (lc do p sut) tc ng vo mt

tri v mt phi v cc lc tip tuyn (lc ct) tc ng vo mt trn v mt y.

Nu p sut trng tm phn t l p, lc p sut trn b mt tri l:

( ) V lc p sut trn b mt s l:

( )

Nu ng sut ct trng tm phn t l , lc ct trn b mt y l: ( )

V lc ct trn b mt trn l:

( ) Chng ta s dng vi phn ton phn cho ng sut ct v ng sut ct l mt

hm ch c bin y (do u = u(y)). Tng ca cc lc trn tc ng vo mi mt ca

th tch kho st bng khng nn:

= 0=

+

Sp xp li chng ta c: - = 0Hay


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Theo nh lut Newton v dng chy nht, ng sut ct ( ) c sinh ra trnlp lu cht ti khong cch y tnh t tm phng cnh c cho bi

Trong : = l Gradien vn tcMt khc, lc ct bng ng sut ct nhn cho tit din ca tm phng.

Kho st trng hp chiu dy khe hlu cht l b, do dng chy c m

hnh ha tng tnh dng chy gia 2 tm phng song song di v hn.

p dng cho b mt , ta c lc ct (lc cn nht) c cho bi:

= (Dl)= (Dl)Lc cn nht c thc biu din di dng: = c.u

Trong : c: l hng s

u: l vn tc lu cht

T hai h thc trn, chng ta c c hng s gim chn c ca thy ng l :

c = (DL)

Trong : s: khe hgia v ngng trc

D: ng knh ngng trc

L: chiu di ca thy tnh

: nht tuyt i ca du

3.3.3. B trn ty ng tip xc


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Khi lm vic, gia cc b mt tip xc ca ngng trc v c ngn cch

bi lp du, bao ph hon ton hoc mt phn (v db truyn bnh rng). Lp

du gia khe hs c chiu dy thay i.

Lp du gia cc bmt tip xc

Lp du gia cc b mt tip xc di tc dng ca lc lin kt gia hai lp

du v kim loi, lc ma st trong xut hin gia cc b mt tip xc. Du s chuyn

ng theo phng chuyn ng ca b mt tip xc. Khnng chu ti ca lp du

s cn bng vi lc nn v b mt tip xc. Nhng nh hng ch yu n kh

nng chu ti ca lp du l:

1. Bn knh cong cng nh th vng khe htip xc cng nh, p lc xut hintrong lp du cng ln, p lc theo ng cong ny gim i cng ln khi

chiu cao h tng ln. Kt qu l khnng chu ti gim.


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2. nht ca du cng cao, ni lc ln, khnng chu ti ln. nht trongvng tip xc thay i rt ln, snh hng rt ln n kh nng chu ti

ca mng du tip xc.

3. Vn tc b mt tip xc cng ln th ng nng ca du cng ln.4. Gi tr khe h cng nh, lng thu hp khe h cng ln (khi dng

ng cong b mt) nh vy p lc d cng ln, nhng khng cgim xung qu gi trcho php. Khi khnng chng mn km.

Phn tch k qu trnh chy ca du gia cc b mt tip xc v nht thay

i l bi ton phc tp, cn phi gii quyt ng thi cc phng trnh thy ng,

l thuyt n hi v nng lng.

3.4. Du bi trn

3.4.1.Tng quan

Du bi trn l vt liu quan trng trong nn kinh t ca mi quc gia.Tt c

cc my mc,thit bcc dng v cc kch ckhc nhau s khng th thc hin

c chc nng ca mnh hiu qu nu khng c cc loi du bi trn thch hp.

Do c rt nhiu chng loi t du bi trn c cp cht lng thp n rt cao

c dng nhm p ng cc nhu cu s dng tc bit n cc loi du a dng,

dng rng ri trong nhiu lnh vc.

Cc nc trn th gii sn xut du bi trn theo cc tiu chun, quy nh

ring ph hp vi iu kin s dng my mc nc . Thng thng vic bi

trn my mc phi s dng du do nh ch to ra chng quy nh.

Trong thc t, vic tun thcc quy nh v du bi trn m nh ch to

ra l rt kh khn. V vy bi trn cc loi my mc, thit b do cc hng canc khc nhau ch to, chng ta c th thay th bng cc loi du bi trn c cc

tnh nng tng ng vi du mdo cc hng quy nh.

V vy, vic s dng vt liu bi trn ni chung, du mbi trn ni ring

v quy trnh bi trn ph hp vi quy nh ca nh ch to thit b, s gp phn rt


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ln m bo cho my mc, thit b hot ng n nh, gim chi ph bo dng,

nng cao tui th s dng v tin cy ca chng trong nn kinh t.

Bi trn l bin php lm gim ma st n mc thp nht, bng cch to ra

gia b mt ma st mt lp cht (cht bi trn). Cht bi trn c thdng lng(du nhn hay cn gi l du nht), dng c (mbi trn) hay dng rn......

Trong s chim a phn l cht bi trn dng lng, kn l cht bi trn dng

c, sau cng l dng rn. Cht bi trn dng ny thng chim rt t v ch p

dng trong mt vi trng hp ring bit nh bi trn cc trc c nhit rt cao

hoc trong chn khng, nhng ni ny khng th dng du hay mbi trn c.

m bo cho du bi trn c th thc hin tt cc chc nng nu trn, du

bi trn phi c phm cht tt. C th l du bi trn phi c tnh bm dnh tt,

phi c nht thch hp, phi c bn ho hc, c hc, sinh hc..., phi c

dn nhit tt, khng gy n mn ho hc, ty ra phn tn tt cc cn,mui... sinh

ra trong qu trnh s dng ng c thit b.

Vic la chn, s dng du bi trn thch hp ng vai tr ht sc quan

trng trong vic m bo cho du bi trn thc hin c cc chc nng ca mnh

mt cch tt nht. C squan trng la chn du bi trn thch hp l da vo

nguyn l bi trn:

+ i vi cc chi tit lm vic c chuyn ng nhanh cn dng du c

nht thp v ngc li.

+ Khe hgia cc b mt chi tit lm vic cng ln th du bi trn cng

cn c nht cao.

+ Nhit lm vic cao th dng du c nht cao.+ S vng quay ln, p sut trn trc nh th dng du c nht thp.

+ p sut trn trc ln, s vng quay nh th dng du c nht cao.

+ Phm vi thay i nhit ln th dng du c tnh nhit nht tt (ch s

nht cao)


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+ Mi trng lm vic tip xc vi khng kh, kh chy nhit cao th

dng du c tnh chng oxy ho v chng n mn.

+ Mi trng lm vic tip xc vi nc v hi nc th chn du c

tnh chng to nh v chng to bt.+ Thi gian s dng du lu, chn du c tnh chng oxy ho tt, tnh n

nh cao.

- Nguyn liu ch yu sn xut du mnhn l du m v du thc vt.

Du gc c sn xut t du m thng qua cc qu trnh ch bin c gi l du

gc khong v du c ngun gc t thc vt c tng hp qua cc qu trnh tng

hp ha hc c gi l du gc tng hp. Thnh phn c bn ca du bi trn l

du gc v cc phgia c pha trn nng cao cht lng ca du bi trn. Bn

cht ca du th v qu trnh ch bin s quyt nh tnh cht vt l v ho hc ca

du gc to thnh.

3.4.2. Du gc

Cc phn on du th thch hp cho sn xut du gc s cho ra cc sn

phm c khong nhit si khc nhau nhqu trnh chng ct chn khng. chng

cha cc hydrocacbon sau:

- Parafin mch thng v mch nhnh- Hydrocacbon no n v a vng(neptan) c cc cu trc vng

xyclohexan gn vi mch nhnh paraffin

- Cc hydrocacbon thm n vng v a vng ch yu cha cc mchnhnh ankyl

- Cc hp cht cha vng napten, vng thm v mch nhnh trongcng mt phn t

- Cc hp cht hu c c cha cc di nguyn t, ch yu l cc hpcha lu hunh, nit v nhm.

Phn loi du gc:


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IV

KHO ST CNG NGH CH TO HP KIM NHIU LP

LM B T

4.1. Cng nghc truyn thngTrc nm 1950 cc nc cng nghip pht trin ch to a s cc loi

bc trt ngi ta dng phng php c hp kim chu mn m ch yu l hp

kim ngch trong khun phi kim loi hoc khun o thp dng sn phm n

kim (mnlit). Thng thng chiu dyban u ca phi hp kim chu mn phi

c ln hn t 3-5 ln kch thc ca bc trt sau khi gia cng c kh mi m

bo c cht lng yu cu. Do vy, cc sn phm ch to theo cng ngh cinny, c bit l mt s vt liu chu mn khng qua gia cng bin dng do c

th khng p ng yu cu k thut cao ca chi tit my dung trong my mc thit

b hin i, v chng c kch thc hnh hc tng i ln, khnng chu ti trng

v tc trt trong bi ma st cha cao, h s s dng nguyn vt liu thp.

Bng phng php cng nghc hp kim chu mn cin ny c t 80-90% cc

kim loi mu qu him b loi bdng phoi tin khi gia cng tinh bc. p

ng nhu cu pht trin ca k ngh ch to my v tit kim kim loi mu qu

him, sau nm 1950 cc nh cng ngh th gii chuyn hng sang s dng bc

trt 2 lp thp + kim loi ng, thp + hp kim nhm. Bc trt 2 lp c th ch

to bng cng ngh truyn thng c hp kim chu mn, ch yu l hp kim ng

ch, ngchthic, ngthickm trng thi tnh hoc ng. Phi

ng thp phi c lm sch b mt tip xc vi lp hp kim chu mn, nung nng

n nhit t 800-850oC, c nhng vo dung dch hn the nng chy, sau mi rt hp kim chu mn vo khe hgia ng thp v li khun (c trng thi

tnh) hoc vo pha trong ng thp c quay trn g chuyn dng (c ly tm).

Khi quan st thy b mt hp kim chu mn ng c, phi lm ngui tht nhanh

trnh hin tng ch v cc hp kim ha khc b tht thot trn b mt ca phi


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gia cng nhit m bo cc chtiu c l tnh cn thit i vi tng chng loi

bc trt.

4.3. Cng ngh hn n to bng hai lp kim loi.Mt trong nhng cng ngh tin tin khc to bng hp kim loi nhiu lp

c nghin cu p dng nc ngoi l cng ngh hn n. Hn n xt theo kiu

nng lng a vo, c lin quan n nhm qu trnh c hc lin kt cc kim loi.

Khi nng lng ha hc chuyn ha ca lng thuc n dng sn phm kh n

c chuyn thnh nng lng c, lm cho mt phn ca vng hn trong cc tm

kim loi dch chuyn vi vn tc rt ln. ng nng va p ca phn chuyn ng

vi b mt ca phn c nh, c dng lm cng bin dng mm hn hp ca cc

lp tip xc ca cc kim loi (2 kim loi cn hn), dn n vic hnh thnh lin kt

hn hay mi hn.Cng bin dng mm chuyn thnh nhit, nhit ny do hu qu

tnh on nhit ca qu trnh, do vn tc ln c th t nng kim loi vng lin

kt cho n khi t nhit kh cao (cho n khi to nhng vng nng chy cc

b).

S nguyn l hn n c 2 dng: dng song song v dng khng song song

(to gc).Vi vic kch n thuc, s xut hin mt mt trc (mt tin) ca sng

dn n v n lan truyn vi vn tc D, ph hp vi vic chn thuc n, tnh cht,

khi lng, trng thi, s trong khong 2000-8000 (m/s). mt sau (mt hu)

to thnh nhng sn phm n dng kh trong khong thi gian rt ngn theo qun

tnh chng s bo ton th tch trc kia ca thuc n nm trn di p sut

100-200 nghn at, sau vi vn tc 0,5-0,7D chng s m rng ra theo hng

vung gc vi nhng mt phng t do ca khi thuc n. Vic ny to ra vng kimloi di xung lng no , xung lng ny s cun ln lt tng khong th

tch kim loi th nht vo s chuyn ng hng ti b mt ca tm kim loi c

nh v va p vi n vi vn tc - vn tc va p. Trong qu trnh ny, tm kim

loi th nht (tm gi l kim loi bay) s b b cong hai ln. Phn nghing ca n


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a. Ch to bt kim loi, hp kim hay phi kim c thnh phn ng vi yu cu dng bt rn v mn. Thng sn xut bt kim loi theo phng php

nghin, phun tia kim loi lng di p lc cao vo mi trng ngui nhanh,

in phn, hon nguyn.b. To hnh: theo thit k sn phm ly cc loi bt theo t l xc nh v trn

ln tht u ri a vo khun p nn di p lc 100- 1000 MPa. Mun c

khi lng ring ln v ng u phi p di plc cao ng thi rung c

hc.

c. Thiu kt : p xong em nung nng n nhit v trong khong thi gianxc nh trong chn khng hoc trong mi trng kh bo v. S xy ra qa

trnh kt tinh li to ra cc ht mi a cnh, cc ht lin kt bn vng vi

nhau lm tng c l tnh ca sn phm n gi tr mong mun. C th kt

hp p to hnh v thiu kt ng thi vo mt bc t c mt

cao nht.

c im ca phng php :

a.Nguyn liu c s dng gn nh trit (h hao nguyn liu t).b. Sn phm ra c tnh ng nht cao v t phi gia cng.c. Cu trc t vi :khng xt cht lun c l rng. xp thay i t 2

n vi chc % ty theo phng php cng ngh v yu cu ch to

sn phm.

C nhiu sn phm ch to theo phng php kim loi bt s r hn nhiu

so vi phng php truyn thng.Phng php p nng ng thi vi qu trnh

thiu kt hn hp kim loi bt ch to 1 s loi bc trt c u im c bit lc th gim thiu ti a kim loi mu qu him, nng lng dng cho gia cng

sau to phi n thnh phm nh khng cn nhiu nguyn cng gia cng c. Nu

iu kin thit b khng cho php, c th to phi lm bc trt theo cng ngh p


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4.5.2.Qui trnh cng ngh chto bc bimetal c n my k N G T

Qui trnh cng ngh chto bc bimetal c n my k N G T:

* Kt cu vt liu(Composition): Bc lt trc kim loi kp thp-ng hp kim h

(BMT) s dng k thut cng ngh luyn kim tri mt lp ng ln b mt tmthp v thiu kt trong mi trng nhit khng oxy ha lm cho hai kim loi gn

kt bn chc vi nhau.

*Cu to bc Bimetal(Structure):

* c tnh k thut(Features):

Tnh nng vt l(Physical properties)

Thnh phn ha hc(Chemical composition)

Khiu

Nhn mchp kim

Label alloy

Mt

Density

cngHardness

Pb Sn Zn Cu Tpcht

BMT CuSn6Zn6Pb3 >7,8 >60 2-4 5-7 5-7 Dlng

0,7-1,3

Hnh I.5.4: u o meal


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- Ph ti tnh ( stating load rating): >310 Mpa- Ph ti lc vn hnh (Dynamic load rating): >120 Mpa- cng ca lp hp kim ng(Hardness copper: >HB60 ?- H s ma st kh (Factor of friction): 0,3-0,4- H sma st khi bi trn (Factor of friction oiliness): 0,04-0,12- Nhit lm vic cao nht( Max temperature working): 2800C

* Kiu rnh du(Oil groove): Rnh cha du vi nhiu hnh dng khc nhau trn

b mt vt liu ng hp kim p ng nhu cu bi trn a dng ca chng loi sn

phm.

Hnh I.5.5: C ku rn du b trn

HnhI.5.6: tn k tut b bmetl.


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Nguyn cng to cc dng bmt ma st cho bc

Nguyn cng dp phi theo bin dng cn thit un


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Nguyn cng un phi va dp trn my uyn dn to bc


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II:

I

CC DNG B T C TRN THNG VIT NAM

1.1. Gii thiu s lc mt s loi bc sn xut trong nc.

Bc l mt chi tit ph bin thng dng trong c kh.

Bc c bn c th phn lm 3 loi theo 3 chc nng:

- Bc chn: loi ny lp trn cc trc v gp phn chn chuyn ng dc trc ca

cc chi tit khc lp trn trc. V dnh chn bi, chn bnh rng.... Khi mt

u bnh rng, bi c chn bi gtrc, 1 u s b chn bi bc ny.

n II.1.1: n b

- Bc lt: loi bc ny c s dng nh 1 chi tit trung gian. V dnh chi tit A

lp ln Trc B v gia chng c chuyn ng tng i. Lc ny trnh mn cho

trc ngi ta lp bc lt vo gia 2 chi tit. Bc lp cht vo trc v khi s ch

cn chuyn ng gia A v bc.


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n II.1.2: lt tr

- Bc : bc ny dng cc trc trong trng hp trc di, cn tng cng

cng vng, trnh cong vng trc. Bc gm 1 ng lp trn , ny bt cht bng

bulong ln cc thnh hp, thnh my cn trc c lng qua cc ng .

n II.1.3. Trt dn tron ty n


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Vit Nam c nhiu nh my c kh sn xut c nhiu loi bc cung

cp cho thtrng trong nc. in hnh c nh my c kh Ng Gia T chuyn

sn xut cc loi bc: Bc nhp t, bc cn bng, bc lt trong ng c t, my

cng trnh, khai khong Trong khun kh n th ch nghin cu v bc trt.Babit (White Metal) l vt liu ph bin nht lm bc trt.

Babit l tn chung ca cc hp kim chu ma st, nn thic, ch c cho thm

antimon, ng v cc nguyn t khc. Babit c dng c cc trt dng

thp bimetan c h s ma st nh, chu ti trng v tc trt ln. c gi

theo tn nh sng ch Hoa K Babit (Babbitt; 17991862).

c tnhC h s ma st nh vi b mt trc thp, gi du tt, truyn nhit tt,

mm nn t lm mn c trc. Ty thuc hm lng kim loi chim t l ln trong

babit m ta c cc loi: babit thic, babit ch, babit km, babit nhm.

C 2 loi:

1. Babit ch: khong 85% ch, cn li l thic, antimo v ng .

2. Babit thic: 95% thic, cn li l ch, ng v antimo

Vit Nam c cng ty TNHH MTV BaBit chuyn cung cp cc sn phm bc

babit. Sau y l 1 s loi bc do cng ty sn xut :

Hnh II.1.4: bn 80do n ty MT bt sn xut


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Hnh II.1.5: bn 120 do n my MT bt sn xut


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1.2. Bc bimetal do nh my c kh g ia ch to

nh my Ng Gia T th sn xut c bc bimetal, l loi bc kim loi kp

thp ng hp kim h. Kt cu vt liu ca bc dng kim loi kp thp ng

hp kim h s dng k thut cng ngh luyn kim tri 1 lp bt ng hp kim lnb mt tm thp c thu kt trong mi trng nhit khng oxy ha lm cho 2

kim loi ny gn kt mt cch bn chc vi nhau.

n II.1.6: B bmetl do n my k N G Tsn xut


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1.3. Bc trt sdng trong my o mn

Bc s dng trong my o mn l bc trong tay bin t. Bc bin b mn

lm tng khe hgia bc v c trc, dn n lng du phun ra vt qu gii hn.

Khi khe hdu tng gp i, lng du phun ra tng xp x 5 ln so vi khe hbnh thng. Khe htng gp 4 ln bnh thng, du phun tng khong 25 ln so

vi mc bnh thng. Trc c quay lm cho du phun ra tun hon. Nu mc phun

du qu nhiu, cc xc mng du khng gt ht, lm du lt vo v b t chy

trong xylanh.

Bc mn cn lm xut hin ting g. Vt liu lm bc trc km, du bi trn

khng , ng c qu nng, my thng xuyn qu ti, nhng sai st khi gia cng

c kh l nhng nguyn nhn lm tng tc h hng bc .

n II.1.7: ty bn dn t mn


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II

THMN BC BIMETAL

2.1. Nhu cu v tnh cp thit ca vic thit k ch to my th mn bcBimetal

2.1.1Nhu cu v tnh cp thit c ti

Xut pht t yu cu thc t cn o v kim tra mn cho cc chi tit c kh

ni chung v bc trt ni ring nh gi tui th ca chi tit v thit bngi ta

ch to cc my th mn chuyn dng thc hin nhim vny. i vi mi loi

h chi tit khc nhau ta phi thit k mt loi my th mn ring v mi loi chi tit

yu cu g t v ch ti trng v bi trn khc nhau. y c thl bi trn

thng xuyn hoc nh k hoc khng v th cn nghin cu v thit k ring cho

tng chi tit. i vi loi chi tit dng bc trt cng yu cu phi thit k mt loi

my thmn ring xc nh lng mn ngay sau khi xut xng c th nm

c cng mn, tui th ca chi tit chu mn c phng n xl v iu

chnh thch hp. Nguyn tc lm vic ca my th mn bc trt y l kim tra

cng mn ca bc sau mt thi gian chy th vi ti v vn tc cnh

nh gi tui th ca bc v kim tra xem bc cn t yu cu khng.

2.1.2.Yu cu thit k

M hnh th mn c cc thng su vo nh ng knh bc, lin kt ca

cp ma st (cp ma st A v B). y, A l trc v B l bc. Lin kt ma st c

c trng bi cc thng ssau: ng knh bc, c tnh ca vt liu ch to bc(

trnh by phn I), chiu di bc lt, nhn b mt trc v bc lt, tnh cht c,

l, ho ca loi vt liu lm bc, khe hlp ghp gia bc v trc. Ch lm vic(P, V) ca lin kt ma st. y P c trng cho ti trng tc dng ln .

Da vo cch s dng mt bEncoder c lp trn trc ng c ta c th

xc nh c tc lm vic ca ng c ch lm vic c ti n nh,t tc

ny da vo cng thc chuyn i ta tnh c vn tc gc trc ng c v do


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Xt 2 loi bc c trng trong di kch thc trn tnh l:

Bc th nht c: D1 = 76(mm); d1 = 70 (mm); L1 = 100(mm)

Bc th hai: D2=122(mm); d2 = 117(mm); L2 = 100(mm)

d1 = 70

D1 = 76

L1=

100

d2 = 117

D2 = 122

L2

=

54


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2.2. c phng n v s thmn kim tra mn ca bc khi hot ng, ta cn m phng li ch lm

vic ca bc trong cc iu kin khc nhau, lm c iu ta cn bit c

c im lm vic ca bc nh chbi trn, lai du bi trn, ti trng, phngtc dng ca ti trng

Trn thc t, bc lm vic trong chbi trn phc tp, ph thuc ngi

s dng v iu kin lm vic ca my. V vy ta s th mn 3 ch ring bit

l bi trn t-na t-v kh.

Vphng t, thc cht ti c t ln trc, nhng trong iu kin m

phng, vic t ti ln trc khng kh thi nn ta st ti ln bc. Cc phng n

t ti c thc thc hin nh sau:

2.2.1.Sdng b truyn t ti ln bc, c chiu nc vi chiu trng lc.

nh II.2.1: t t t d lnPhng n ny t ti c thc thc hin bng cch dng thy lc y

bc ln.

u m:

- Cch t ti bng thy lc to ra c ti tc dng ln v n nh.- Khnng iu chnh ti d dng v nhanh chng v c thiu chnh ngay

trong khi my ang hot ng.


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N m:

- Kh xc nh chnh xc phng ca lc i qua tm ca Oa v Oc .- Vic dng phng php t ti bng thy lc lm cho kt cu my phc tp

hn v gi thnh my cao hn.Phng n my:

nh II.2.2:PA1 t t t d ln

2.2.2.Sdng b truyn t t pn nn v pn nn 1

N m: Phng n ny kh thc hin v lm cho kt cu thm phc

tp, trn thc tphng n ny khng khc nhiu so vi cc phng n khc

m cn lm cho kt cu thm phc tp.


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nh II.2.3: T nn v pn nn 1 Phng n my:

nh II.2.4: PA2 t nn v pn nn 1

2.2.3.Sdng b truyn bn rn p gim tc ti cng chiu trng lc

Ta c nhiu cch t ti theo cch ny, c tht trc tip, hoc thng

qua b treo ti, di tc dng ca trng lc, phng ca P s i qua tm ca Oc

v Oa


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nh II.2.5: t t t trn xun trn u trn l

u m:

- Phng n ny kh hp l, khng gian nh gn, ti trng c tht c lkh cao. Ngoi ra chbi trn c thp ng c nhng yu cu ra

- D thc hin hn phng n 1, to c lc ln n nhN m:

- B tr b truyn hp gim tc lm cho kt cu my cng knh v phc tphn

- Tng gi thnh sn xut myPhng n my:

nh II.2.6:PA3 dn b truyn GTt t t trn xun trn u trn l


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2.2.4.t ti ln bc, chiu ca ti trng vi chiu ca trng lc

nh II.2.7: t t t trn xun trn u trn l

Ta c nhiu cch t ti theo cch ny, c tht trc tip, hoc thng

qua b treo ti, di tc dng ca trng lc, phng ca P s i qua tm ca Oc v

Oa

u m:

- Phng n ny kh hp l, khng gian nh gn, ti trng c tht c lkh cao. Ngoi ra chbi trn c thp ng c nhng yu cu ra

- D thc hin hn phng n 1, to c lc ln n nh

nh II.2.8: PA4 dn b truyn t t t trn xun trn u trn l


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T nhng nhn xt trn ta chn PA4 vi cch t ti ln bc vi phng

chiu ca ti trng vi phng chiu ca trng lc, ti c truyn n bc thng

qua b treo ti, trc thc dn ng tng c qua b truyn ai.

2.3. Tnh ton khnng ti v chn cch t ti cho bc2.3.1.Tnh ton khnn ti ln nht ca bc

tin hnh xc nh lng mn ca bc v a ra chtiu nh gia bc ta i

xc nh ti trng ln nht bc chu c tin hnh gia ti v th mn.

Theo bng 16.3 Trang 82[4] - Chi Tit My-Nguyn Trng Hip- NXBGD ta c

tr s p sut ln nht bc bin chu c l : [p] = 5 Mpa = 5.106 (N/m2)

Theo cng thc (16-13) Trang 82[4] p sut sinh ra trong khng c vt

qu [p] ta c ti trng ln nht m hai bc trn chu c l:

P/dl [p]

Suy ra : P [p].d.l

P max = [p].d.l

Ti trng ln nht m bc th nht (D1 = 76mm; d1 = 70 mm ; l1 = 100mm)

chu c l:

P1max = [p].d1.l1 = 5.106.70.10-3.100.10-3 = 3500 (N)

Ti trng ln nht m bc th hai (D2 = 122mm; d2 = 117 mm ; l2 = 54mm)

chu c l:

P2max = [p].d2.l2 = 5.106.117.10-3.54.10-3 = 3159(N)

Vy Pmax = P1max = 3500 (N)


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2.3.2.Chn cch gia ti cho bc th

gia ti cho cm chi tit bc bin v trc ta c cc cch sau:

- Bng in: dng nam chm ht i vi trng hp ti trng nh

- Bng c : s dng ti treo trc tip qua b phn treo ti c gn trc tip trncm bc v trc cn o. Ti c s dng khi cn ti trng tc dng trung bnh.

- Bng thy lc: s dng h thng thy lc gm xy lanh, piston, xylanh thy lc v

bm bnh rng. Ti thy lc dng khi yu cu ti trng tc dng ln.

- Vi ti trng tc dng ln cm bc bin v trc kh ln nn ta dng bin php gia

ti l thy lc.

Chn xy lanhpiston v ng cbm du :

Chn s bng knh piston l dpiston= 50(mm) th ng c bm du c chn

phi to ra p lc ln h xylanh- piston l:

Ta c :

P = p.S = p. (d l ng knh piton)

p = = = 1,78 (N/mm2)= 17,8 (bar)

T y ta c th chn c ng c bm du cng sut tha mn


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P: Ti trng tc dng

Trc (5) c ng knh d = 50 mm, mt u gn vi puly lin kt vi ng

c in dn ng qua b truyn ai, u cn li lp vi b bc trt thmn nh

hnh v. B bc lt,bc trt (7) c cnh bng cc bu long v bc hai na.

Hai ln (4,6) c lp trn cc gi . Cng mn ca bc trt sau thi gian

th vi ch lm vic ti P v vn tc V c o bng hai cch : theo khi lng

hoc theo kch thc, tuy nhin cch o cng mn theo kch thc d thc

hin v hay c dng hn.

2.4. guyn l lm vicKhi ng cu dao in, ng c in (1) quay, ko theo trc (5) quay nhb

truyn ai qua bnh ai chng (2) v bnh ai bng (3). Cm bc trt v bc

lt (7) c lp cnh vo trc( 5), cm chi tit ny quay cng chiu quay ca

trc do ma st sinh ra trong trc trong qu trnh my lm vic. Trc (5) quay vi

nhiu vn tc khc nhau nhb truyn ai (2,3). Bc trt chu ti trng P v c

vn tc trt tng i gia trc v bc l V.

Ma st sinh ra trong trc l ma st trt. M men ma st ny ph thuc voti trng P v vn tc trt V .

Nhit lm vic trong cm bc trt c khng ch bi lu lng cht

bi trn (du). Du c a vo trt qua lpha trn bc hai na. Sau khi bi

trn v lm mt du chy ra ngoi cm bc trt-trc qua khe htrc - bc.

2.5. c thng s lm vic ca my o mn

2.5.1. Cc thng su vo

Cc thng su vo

My o ma st Thng sura


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bc lt, trc v bc lt ma st trc tip vi nhau dn n cng hao mn trong

ln.

Ti nhit:

Nhit sinh ra do ma st gia trc vi bc trt (ma st trt) v ma st trong

ln (ma st ln).

V - Vn tc trt.

Mi trng lin kt ma st lm vic (c) gm c: cht bi trn v khng khbao quanh. Cc thng c bn v cht bi trn gm c: nht v nhit .

f() = f(P, V, c)

2.7. nh ton s b cc cm chi tit chnh

2.7.1. Tn ton n n

Vic chn ng c in cn tho mn cc yu cu c bn sau y:- S dng tin li.- Cu to n gin, kch thc nh gn.- Gi thnh ch to r.

Tin hnh chn ng c nh sau:Lc ma st sinh ra trong trt l: Fmsi = P .fms (N )

Bc trt c bi trn bng du nhng do cht lng b mt ca trc v

bc trt l khng cao nn chiu dy lp bi trn kh m bo ln hn tng s

mp m b mt ca cp ma st. Nh vy ta c ma st na t v tr s h s ma st

nm trong khong (0,010,1) theo gio trnh chi tit myGS.TS.Nguyn TrngHip-NXBGD - tp 2. Chn fms = 0,1.

Nh vy ta tnh c:


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Fms = P . f = p.S.f= p. .f = 17,8.105(N/m2). 6

2

10.4

50.14,3 (m2).0,1

= 349,325 (N)

M men ma st c xc nh bng cng thc sau:

Mms = Fms .2

d(N.mm)

Trong : Mms - M men ma st sinh ra gia trc v bc trt (N.mm)

Fms - Lc ma st sinh ra gia trc v bc trt (N)

d - ng knh trc (mm)

M men ma st sinh ra trong bc trt l :

Mms = Fms .2

d= 349,325 .

2

50= 8733,125 (N.mm)

= 8,733125 (N.m)

my c th lm vic c th momen xon sinh ra trn trc phi thomn iu

kin sau:

Mx K. Mms

Trong : K l h s an ton. Ly K = 3

Chn Mx = 3. Mms = 3 .8,733 = 26,199 (N.m)

Cng sut trn trc my o l: Nt = Mx .

Theo s liu thng k, ch lm vic ca h tay bin bc trt nm trong khong:

P = (0,050,3) (N/mm2)


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- ng c in mt chiu t, nhanh hng v khi lng sa cha ln hn ng c

xoay chiu, phi thm vn u t lp t cc thit b chnh lu.

- ng c in ng bba pha gi t, mmy phc tp, tuy c h s cos cao,

chi ph vn hnh scao hn loi ng c khng ng bnhng y yu cu cng

sut nhnn cc u im ca ng c ng b ba pha khng quan trng lm.

- ng c khng ng b ba pha gi r, cu to vn hnh n gin nht, mc trc

tip vi mng in xoay chiu khng cn thit i dng in, c th iu chnh

nhy cp vn tc bng cch thay i si cc t.

Chn ng n:

Ta tin hnh chn cng sut v tc ng c.

ng c cn chn sao cho c th li dng c ton b cng sut ng c.

Khi lm vic n phi thomn ba iu kin.

- ng c khng pht nng qu nhit cho php.

- C khnng qu ti trong thi gian ngn.

- C m men mmy ln thng m men cn ban u.

V vy ta chn ng c in c cng sut nh mc (Nm) ln hn cng sut

yu cu t ra cho n (Nycc).

So snh vi cc loi ng c in trn, nhn thy ng c khng ng b ba

pha c nhiu u im. Do chn ng c in c k hiu DK414 l loai ngc in khng ng bba pha roto on mch c nhm, do Vit Nam sn xut

theo Bng Ph Lc 1.2-T235-Tnh ton thit k h dn ng c kh T2-Trnh

Cht,L Vn Uyn - NXBGD


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Bng Thng skthut c n n.

Kiu

ng c

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