15. May ui

a. Cong dung - Phan loai:

* Cong dung:

May ui thuoc loai may chu dao trong nhom may dao, van chuyen dat voi bo cong tac ui. May duoc su dung rat hieu qua de lam cac cong viec sau:

- Dao van chuyen dat trong cu ly toi 100m, tot nhat o cu ly 10 - 70m.

- Lap hao, ho va san bang nen mong cong trinh.

- Dao va dap ne cao toi 2m.

- ui va san rai vat lieu nhu da ram, cat, soi...vv

Ngoai ra, may con co the lam cac cong viec chuan bi mat nen nhu: bao co, boc lop tang phu, ha cay, nho goc cay.... May con lam nhiem vu keo hoac day cac phuong tien khac.

* Phan loai:

- Dua vao ket cau bo di chuyen: may ui banh xich va may ui banh lop.

- Dua vao co cau dieu khien luoi ben: may ui dieu khien bang co hoc, loai may dieu khien bang thuy luc.

- Dua vao ket cau luoi ui va kha nang thay doi vi tri cua luoi ui:

+ Loai may ui thuong (khong quay)

+ Loai may ui van nang

- Tuy thuoc vao do lon cua cong suat dong co va luc keo danh nghia o moc keo cua may co so, may ui duoc chia thanh cac loai: rat nang (CS tren 300ML, luc keo tren 30T), nang (150-300ML, 20-30T), trung binh (75-150ML, 13,5-20T), nhe (35-75ML, 2,5-13,5T), rat nhe (toi 35ML, toi 2,5T).

b. Cau tao - nguyen ly lam viec cua may ui:

* cau tao:

Hinh 4.1: Cau tao may ui

a. Cau tao chung; b. May ui luoi co dinh; c. May ui luoi quay; d. May ui xoay trong mat phang dung; e. Cac loai luoi ui thay the. 1. Khop quay; 2. Khung ui; 3- luoi ui; 4. Thanh chong xien; 5. Xi lanh nang ha luoi ui; 6. May keo co so co bo di chyen xich; 7. Khop dich chuyen thanh chong xien; 8. Xi lanh nghieng luoi trong mat phang dung; 9. Khop cau; 10. Luoi ui co rang xoi o giua; 11. Luoi ui co thiet bi bat mai; 12. Luoi ui co rang bua

- May ui thuc chat la mot may keo co lap bo cong tac ui. Bo cong tac ui nay duoc che tao tu ket cau thep voi moi ghep han, cac cum duoc lien ket voi nhau chu yeu nho khop xoay.

- Cau tao may ui duoc the hien tren hinh 4.1.

- Bo cong tac ui thuong (hinh 4.2): khung ui co ket cau don gian va duoc tach roi thanh hai phan giong nhau.

- Bo cong tac ui van nang (hinh 4.3): khung ui co ket cau lien khoi, doi xung va duoc noi khop cau voi luoi ui.

* Nguyen ly lam viec

Qua trinh lam viec cua may ui co the mo ta nhu sau:

Ha luoi ui sao cho bap xuong nen dao; cho may tien, dat dan dan tich tu lai truoc luoi ui. Khi da tich day dat, tien hanh van chuyen khoi dat da dao duoc bang cach nang luoi ui len mot muc (chua thoat khoi nen dao) voi muc dich dao them chut it de bu luong hao phi khi van chuyen.

Neu muon rai deu khoi dat da van chuyen thi phai nang luoi ui len theo chieu day muon rai va tiep tuc cho may tien.

c. bien phap nang cao nang suat cua may ui.

* Bien phap nang cao nang suat:

+ Nang suat cua may ui

Nang suat may ui trong mot ca may duoc xac dinh theo cong thuc sau:

, m3/h

Trong do:

ktg- He so su dung thoi gian (thuong lay ktg= 0,750,85);

V- The tich khoi dat truoc luoi ui, m3;

Tck-Thoi gian mot chu ky lam viec, s;

kd- He so ke den anh huong ve do doc cua dia hinh (bang 4-1).

kx- He so toi xop dat (bang 4-2).

The tich khoi dat truoc luoi ui duoc xac dinh:

Trong do: L - Chieu dai luoi ui;

H - Chieu cao luoi ui;

Knd- He so phu thuoc vao tinh chat cua dat va ty so .

Thoi gian mot chu ky lam viec duoc xac dinh:

Trong do: l1,l2,l3 - Quang duong may ui dao, van chuyen dat di xa va quay tro ve, m;

v1,v2,v3 - Toc do lam viec tuong ung voi cac qua trinh tren, m/s;

t0 - Thoi gian ha luoi ui, t0= 1,52,5 s;

ts - Thoi gian thay doi so, t1= 45 s;

tq - Thoi gian quay may, t2= 815 s.

Chu y: Khi ap dung cong thuc nen ket hop voi kinh nghiem thuc te de chon cac yeu to cho thich hop. Moi doan thi cong can tinh duoc nang suat trung binh.

Nang suat may ui khi lam cong tac san bang dia hinh duoc tinh theo cong thuc:

m3/h

Trong do: S - Chieu dai doan dia hinh san bang, m

L- Chieu dai luoi ui, m; 0.5m - ke den loi san trung nhau;

 - Goc nghieng lech cua luoi ui so voi truc doc cua may;

n- So lan may ui di lai qua mot cho khi san;

v- Toc do san, m/s.

+ Bien phap nang cao nang suat may ui:

Qua cong thuc tinh nang suat tren ta thay: muon tang nang suat can tang khoi luong dat truoc luoi ui (tang V), he so giu kgt va giam thoi gian lam viec mot chu ky (tck).

Mot so bien phap nham nang cao nang suat la:

- Dao va van chuyen dat theo chieu doc. Cach thi cong nay da duoc chung minh qua thuc te va lap duoc do thi tuong quan giua nang suat va do doc duong van chuyen (hinh 4.14)

- Han che so lan quay vong cua may ui, neu van toc tien va van toc lui cua may gan bang nhau thi chi nen cho may tien va lui khong can quay vong.

- Khi thi cong noi dat xop (dat nhe) nen dat hai tam chan (canh ga) o hai ben luoi ben de tang the tich truoc luoi ui va dat do roi vai khi di chuyen. Tam chan phai dat cao hon luoi ben tu 23 cm de de cat dat.

- Dao dat va van chuyen dat theo tung ranh. Ranh dao no cach dao kia tu 0,60,7 met. Cac go dat duoc tao thanh nay la cac tuong chan de giu dat khoi roi vai ra bai ben trong qua trinh dao va van chuyen dat (hinh 4.15)

- Su dung hai may ui cung song hanh trong qua trinh dao va van chuyen dat. Khoang cach giua 2 day ui tu 0,30,5 met, nhu vay se tao mot the tich phu o giua hai ben (Hinh 4.16).

- Khi thi cong o noi dat cung (ran) co the lap luoi ben co thiet bi rang xoi phia sau. Rang xoi nay co chot giu, khi may ui tien de dao dat thi rang xoi chay truot tren mat dat, khi may ui lui thi thanh xoi bi thanh ben giu lai tro thanh cac rang cat va xoi dat (hinh 4.17)

- Chuyen dat theo tung chang. Neu khoang cach giua noi dao tuong doi xe (tren 80 met) thi so dat chuyen duoc cang ve cuoi cang roi vai nhieu. Truong hop nay ta chia quang duong van chuyen ra tung chang. So chang can chia tuy theo chieu dai van chuyen dat dai hay ngan (thuong lay cu ly van chuyen moi chang khong qua 60 met). Nhu vay, khoi dat chuyen tiep cua moi chang la so dat cua hai hoac ba luot gap lai cua chang dau.