3.5. C bt v ry

Bt

Cc c bt c quy nh da vo cc s ca ry. Tr khi c ch dn khc, khi quy nh dng mt ry xc nh c bt th khng c c di 97% khi lng thuc bt qua c c ry . Khi quy nh dng hai ry xc nh c bt th mt ry ln trn ry kia v tin hnh ry; khng c c di 95% khi lng thuc bt qua ry c s ry cao hn v khng c qu 40% khi lng thuc bt qua ry c s ry thp hn.

Ngi ta dng nhng k hiu sau y quy nh cc c bt:

Bt th (1400/ 355) l bt m khng t hn 95% phn t qua c ry s 1400 v khng qu 40% qua c ry s 355.

Bt na th (710/ 250) l bt m khng t hn 95% phn t qua c ry s 710 v khng qu 40% qua c ry s 250.

Bt na mn (355/ 180) l bt m khng t hn 95% phn t qua c ry s 355 v khng qu 40% qua c ry s 180.

Bt mn (180/ 125) l bt m khng t hn 95% phn t qua c ry s 180 v khng qu 40% qua c ry s 125.

Bt rt mn (125/ 90) l bt m khng t hn 95% phn t qua c ry s 125 v khng qu 40% qua c ry s 90.

Ry

Li ry c th dt bng si kim loi hoc si cc vt liu khc thch hp v dt thnh nhng mt vung. Li ca ry dng ry bt thuc c phn loi bng nhng con s, Chng biu th kch thc l ry quy nh tnh bng mm.Vt liu lm li ry khng c to ra mt phn ng no vi nhng bt em ry. Khi ry, trnh ko di thi gian v s lm tng mn ca bt. Khi khng dng vo mc ch phn tch, c th dng ry c mt trn, c ng knh trong bng 1,25 ln chiu rng mt vung ca ry c c tng ng.

i vi bt th hoc na th th ly 25 g ti 100 g bt th. Cho vo ry thch hp, lc ry theo chiu ngang quay trn t nht 20 pht v ry ti khi xong. Cn ng s lng cn li trn ry v s thu c trong hp hng.

i vi bt na mn, mn hay rt mn th tin hnh nh bt th, nhng mu bt ly th khng qu 25 g v lc ry t nht 30 pht ri ry ti khi xong.

Trng hp phi ry nhng cht c du hay nhng bt khc c xu hng bt mt ry th trong qu trnh ry thnh thong chi cn thn mt ry, tch ri nhng ng t li khi ry.

Bng 3.5. C ry (kim loi) 

S ry*

 

C mt ry

(mm)

ng knh si dy

(mm)

2000

2,000

0,900

1400

1,400

0,710

710

0,710

0,450

500

0,500

0,315

355

0,355

0,224

250

0,250

0,160

180

0,180

0,125

150

0,150

0,100

125

0,125

0,090

90

0,090

0,063

75

0,075

0,050

 

 

 

45

0,045

0,032

* S ry biu th kch thc o bng mm ca mt ry.

Nhng quy nh mt ry bng si kim loi ch yu c la chn t trong tiu chun ISO 565 - 1975.

Ghi ch: i vi dc liu c khi cn dng cc c ry to hn so vi bng c ry trn, trong trng hp ny ch cn nu r kch thc ca c mt ry.