11. May dao mot gau
a. Cong dung va phan loai
* Cong dung: May dao la mot trong nhung loai may chu dao trong cong tac lam dat noi rieng va trong cong tac xay dung noi chung. May dao chuyen lam nhiem vu khai thac dat va do vao phuong tien van chuyen, hoac chung tu dao va van chuyen dat trong pham vi cu ly ngan nhu dao dap kenh muong.
Trong cac cong trinh xay dung duong xa, de dap, thuy dien, khai thac mo v.v... may dao mot gau duoc liet vao may quan trong nhat. Theo thong ke o nhieu cong trinh xay dung, khoi luong dat do may dao dam nhiem chiem tren duoi 50% tong khoi luong.
Ngoai cac cong viec dao dat, xuc dat da, vat lieu xay dung v.v.. may dao con lam duoc nhieu cac cong viec khac nhu: truc cau cac thiet bi va vat lieu nang len cao, lam bua dong coc v.v. Nguoi ta thuong thiet ke them cac bo cong tac de may dao co the hoan thanh nhieu cong viec theo yeu cau cua dieu kien thi cong nhu thiet bi bo cong tac gau thuan, bo cong tac gau nghich, bo cong tac gau quang, bo cong tac gau ngoam, bo cong tac gau bao, bo cong tac can truc, bo cong tac bua dong coc.
* Phan loai: May dao co the duoc phan loai theo cac cach sau:
- Theo dac diem bo cong tac: may dao gau thuan, may dao gau nguoc, may dao gau ngoam, may dao gau keo (gau day quang), may dao gau bao...
- Theo he thong treo bo cong tac: he treo mem (cap) va he treo cung (xi lanh thuy luc).
- Theo he thong di chuyen: di chuyen xich va di chuyen banh hoi.
- Theo co cau dieu khien gom: may dao dieu khien co khi, may dao dieu khien thuy luc, may dao dieu khien hon hop.
- Theo dung tich gau dao nguoi ta chia ra cac loai:
+ May dao loai nho: co dung tich gau tu 0,15 den 1 m3.
+ May dao loai trung: co dung tich gan tu 1,25 den 4 m3.
+ May dao loai lon: co dung tich gau tren 4 m3.
b. So do cau tao va nguyen ly lam viec cua may dao mot gau.
Cau tao tong the cua may dao mot gau gom cac bo phan co ban sau:
- Thiet bi lam viec (gom: gau, tay gau, can).
- Thiet bi dong luc va truyen dong (dat tren san quay).
- Thiet bi di chuyen (banh xich hay banh lop).
+ May dao gau thuan (gau ngua).
May dao gau thuan thuong duoc dung de dao dat, da, quang o muc cao hon mat bang may dung, qua trinh do dat duoc xa qua day gau. Trong xay dung thuong su dung loai may co dung tich gau tu 0,153,2 m3, khi khai thac mo su dung loai may co dung tich gau toi 20 m3.
Bo cong tac cua may dao gom can, tay gau co lap gau voi mep cat lien hay co rang gau. Can co phan duoi noi voi san quay bang khop ban le. Gau thuong co dang hinh khoi chu nhat hoi rong ra o phia duoi, day gau co the dong mo nho co cau dong mo rieng. So do cau tao cua may dao gau thuan dieu khien bang thuy luc duoc cho o hinh 3.1. Hinh 3.1. Cau tao chung may dao thuy luc gau thuan
1- Gau; 2- Tay gau; 3- Xi lanh quay gau; 4- Can; 5- Xi lanh tay gau; 6- Xi lanh can; 7- Ban quay; 8- Xich di chuyen.
Qua trinh lam viec cua may dao gau thuan dien ra nhu sau:
Khi bat dau dao, gau duoc ha xuong, dong thoi dieu khien tay gau va gau dua gau ve vi tri cat dat. Tiep tuc dieu khien de tien hanh vua cat dat vua muc dat day gau. Khi gau day dat dua gau ra khoi tang dao, quay may dua gau ve vi tri do dat. Toi vi tri do vua ha gau vua mo day gau xa dat. Sau khi xa het dat gau duoc quay tro ve tang dao, luc nay do trong luong ban than day gau quay quanh khop, tao ra luc day chot vao lo, gau duoc day lai va tiep tuc chu ki dao dat moi.
+ May xuc gau nguoc (gau sap)
Hinh 3.2 May dao thuy luc gau nguoc
a- So do ket cau; b- Cac loai gau; c- Qua trinh lam viec; d- So do dong hoc co cau di chuyen; e- So do dong hoc dan dong cac bom thuy luc; g- Co cau quay san; 1- Banh sao chu dong; 2- Hop giam toc ba cap; 3- Dong co thuy luc; 4- Bom co dieu chinh; 5- May phat dien; 6,8- Bom khong dieu chinh; 7- Dong co diezen; 9- Dong co thuy luc; 10- Banh rang trung tam; 11- Banh rang hanh tinh; 12- Vanh rang; 13- Banh rang; 14- Vanh rang toa quay; 15- Truc-banh rang.
May xuc gau nguoc thuong duoc dung de dao ranh, kenh muong, ho mong... noi ma nen dat dao thap hon mat bang may dung hoac co the dao dat o muc cao hon mat bang may dung nhu doi voi gau ngua, qua trinh do dat duoc xa qua mieng gau. May dao thuy luc gau nguoc duoc su dung pho bien hon so voi may dao dieu khien bang cap.
Viec bo tri xi lanh thuy luc voi bo cong tac cua may dao gau nguoc co nhieu loai khac nhau nhung pho bien nhat la so do bon khau. Dieu khien can, tay gau va gau la cac xi lanh luc. Tuy theo loai dat gia cong co the dung cac loai gau co hinh dang khac nhau.
Qua trinh lam viec cua may dao thuy luc gau nguoc dien ra nhu sau: Rut can pittong xi lanh gau 5 va xi lanh tay gau 3, tay gau 4 quay nguoc chieu kim dong ho. Can 2 cung voi tay gau 4 dua gau 6 ve phia truoc va ha xuong khong chi do trong luong bo phan cong tac ma con do luc cua xi lanh can 1. Quay tay gau ve phia may bang xi lanh can 3 hoac quay gau so voi tay gau bang xi lanh gau 5. Co the dieu khien duoc chieu day phoi cat nho xi lanh can 3. Sau khi gau da day dat duoc keo ve phia can hoac quay quanh tay gau sao cho dat khong bi do ra ngoai. Nang gau khoi tang dao nho xi lanh can 1 va quay gau cung voi toa quay ve cho do. Dieu khien xi lanh gau 5 va xi lanh tay gau 3 de do dat. Tiep do quay gau ve vi tri dao va thuc hien chu ki dao dat moi.
+ May dao gau ngoam
Hinh 3.3. Bo cong tac may dao gau ngoam
1- Doi trong; 2- Puly; 3- Can; 4- Cap nang gau; 5- Cap dong mo gau; 6- cac ma gau; 7- Cap giu gau; 8- Thanh ngang; 9- Cac thanh giang; 10- Palang gau; 11- Puly.
May dao gau ngoam thuong dung de dao dat mem, dat ho mong, dao gieng, vet kenh muong, xuc cac loai vat lieu nhu cat, da dam, soi.
Tren hinh 3.3, gau gom hai ma gau, lien ket voi dau duoi (co gan puly 11) va voi thanh giang 9 bang cac khop ban le. Khi may bat dau lam viec, gau nang len cao o trang thai mo do cap dong mo gau 5 duoc nha ra. Tha dong thoi hai cap nang 4 va cap dong mo gau 5, gau roi xuong, rang gau cam vao dat. Keo cap 5 len, rang gau cung voi hai nua gau khep lai, ngoam dat vao trong gau. Khi keo cang cap 5, gau duoc khep kin, keo cang dong thoi ca hai cap 4 va 5, gau duoc nang len cao. De gau khong bi lac, cap khong bi xoan, nguoi ta dung cap giu 7, vong quanh puly 2 va duoc giu boi vat nang 1. Vat nang co the di chuyen theo can 3. Khi quay may den vi tri do, nha cap 5, hai nua gau mo ra, dat roi vao noi do dat. Sau khi xa dat xong, quay may ve vi tri dao de tiep tuc chu ki lam viec moi.
May dao gau ngoam dieu khien thuy luc (hinh 3.4) gom can 6, tay gau 5, thanh giang 7, xi lanh dong mo gau ngoam 4, xi
lanh tay gau 1, ong dan cung 2, ong dan mem 3 cung cap dau cho xi lanh thuy luc dieu khien dong mo gau nam o phan tren cua gau ngoam.
+ May dao gau day
Hinh 3.5. May dao gau day
1- Con lan dan huong; 2- Tang nang can; 3- Tang nang gau; 4- Cap nang; 5- Can; 6- Puly dau can; 7- Gau; 8- Cap keo can; 9- Xich keo can.
May dao gau day (gau keo hay gau quang) thuong duoc dung de nao vet ao, ho, song, kenh, rach, dao ho mong rong hoac de gom vat lieu o noi thap hon mat bang may dung.
Bo cong tac cua may dao gau day (hinh 3.5a) gom can 5 co chieu dai lon hon cac loai may dao noi tren, gau 7, cap keo gau 8, cap nang 4. Cap nang vong qua puly dau can 6 toi toi nang can 2. Cap keo duoc dan huong bang con lan 1 va cuon vao toi keo 3. Gau duoc mac voi cap keo boi xich keo 9 (hinh 3.5b) va voi cap nang bang xich 13. Thanh ngang 12 dat giua xich nang de khong can tro gau trong qua trinh lam viec. Xich 13 duoc deo o hai ben thanh gau, noi voi hai dau thanh ngang 12 de nang gau nho cap nang 4. Khi keo cang cap 8, xich 13 nang gau len vi tri nam ngang hoac hat len (tuy thuoc vao do nang cua cap 4), khi cap 8 trung gau
o vi tri chuc xuong. Cap giu gau 10 co mot dau moc voi quai gau phia tren, con dau kia bat o cum xich keo sau khi vong qua puly can bang 11 o cum cap nang de bao dam cho gau thuc hien duoc cac vi tri cong tac trong chu ki lam viec, khong de gau bi xoay, lat hoac xoan.
Chu ki lam viec cua may dien ra nhu sau: dua gau ve vi tri I, nha cap 4 va 8, gau duoc ha xuong va cam vao dat. Muc do cam sau vao dat cua gau phu thuoc vao trong luong, ket cau, loai va trang thai dat. Keo cap 8 dan ve phia may khi cap nang duoc noi long, gau tien hanh cat dat va tich vao gau (vi tri II). Tiep tuc keo cap 8 cho den khi gau day dat, giu cang cap keo, dung cap nang dua gau ve phia can (vi tri III), quay toa xe toi vi tri do dat dong thoi dieu khien cap nang va cap keo dua gau ve dau can. o cuoi nguyen cong nay ta tha long cap keo, gau bi lat up va dat roi xuong (vi tri IV). Xa xong dat quay may ve vi tri ban dau de thuc hien mot chu ki lam viec moi.
+ May dao gau bao
May dao gau bao dung de san cac cho map mo tren be mat thi cong.
Hinh 3.6 the hien cau tao may dao gau bao thuy luc kieu ong long. Bo cong tac gom khung can 2, hai doan can co dinh 4 va di dong 6, gau 8. Can duoc bat voi toa quay bang khop ban le. Xi lanh 1 cho phep nang ha can trong mat phang dung. Doan can co dinh duoc lap tren khung may cho phep no co the xoay quanh duong truc doc may do doan can nay ti vao vanh 3 va qua truc 9 ti vao thanh sau cua khung 11. Tren hinh 3.6a the hien mot trong nhung phuong an cua co cau quay nho xi lanh thuy luc 12 lam quay cap banh rang gom vanh rang 13 va banh rang 10. Banh rang nay lap tren truc 9, con vanh rang gan o phan tren cua thanh sau cua khung. Doan can di dong keo dai 6 co the dich chuyen trong doan can co dinh 4 nho xi lanh thuy luc 5. Gau duoc lap o dau can bang khop ban le va co the quay quanh dau
can nho xi lanh thuy luc 7. Nhu vay gau co the thuc hien chuyen dong quay so voi can, dich chuyen theo doan can di dong, quay theo doan can co dinh so voi duong truc doc cua can va quay theo toa quay. Voi kha nang co the dieu chinh vi tri gau trong khong gian nen may co the thao tac chinh xac cac nguyen cong san bang, don sach be mat thap hon mat bang may dung, cac be mat nam ngang, nam nghieng, tham chi ca thanh ben cua ranh va ho mong.
De lam bang va don sach mat bang nguoi ta co the dung gau co mieng rong, khong co rang (hinh 3.6b). Khi ay no co the thuc hien cong viec dao, boc do hang thong thuong. Cac thong so co ban cua may dao gau bao la ban kinh dao toi da Rmax, chieu sau dao va chieu cao dao toi da H'max va H"max va chieu cao do toi da.
c. To chuc thi cong may dao mot gau
+ Chon loai may dao mot gau
Viec chon loai may dao mot gau cho thi cong la nhiem vu quan trong cua nguoi can bo phu trach to chuc thi cong. Nang suat co cao, hieu suat su dung co tot hay khong mot phan la do nguoi can bo ky thuat quan ly su dung may nam vung tinh nang ky thuat va dieu kien su dung may den muc do nao. Doi voi viec chon lua may dao mot gau, ta can quan tam den cac yeu to: khoi luong cong tac, dang cong tac, loai dat, dieu kien chuyen cho, thoi han thi cong. Tuy tung dieu kien cu the ma chung ta lua chon thiet bi cong tac lap tren may dao mot gau cho hop ly. Vi du:
- May dao gau thuan co ket cau bo cong tac chac chan, luc dao lon, dung co loi khi dao dat va do vao xe van tai de cho di xa. May dao gau thuan chi lam viec tot khi nen dat noi dung may kho rao. May dao gau thuan dao duoc nhung ho sau va rong, theo nhieu tang, moi tang co nhieu ranh dao.
- May dao gau day co can dai nen co the do dat tu ho dao di kha xa. No dung tu tren cao de dao nhung ho sau (toi 10 hoac 20 met) va dao dat o nhung noi co nuoc nhu vet bun v.v... So voi may dao gau thuan thi may dao gau day co nang suat thap hon (neu cung mot dung tich gau) vi kho huong cho gau do dung vao phuong tien van chuyen, thao tac de xuc day gau kho khan hon may dao gau thuan. Dung may dao gau day dao roi do thanh dong hoac do truc tiep vao noi can dap thi nang suat cao.
- May dao gau nguoc chi dao duoc nhung ho nong (may dao co dung tich gau 0,5m3 thi chieu sau dao toi da la 5,5 met). Dung may dao gau nguoc de dao muong mang nho, dao ranh dat duong ong, duong day cap dien v.v... Voi nhung cong viec nhu tren nguoi ta thuong chon may dao gau nguoc co dung tich gau q=0,15; 0,25, 0,35; hoac 0,50 m3. Cung co the dung may dao nhieu gau.
- Khi dao nhung ho sau va dat tuong doi mem, neu su dung may dao gau thuan thuong phai dao them nhung con duong len xuong cho ban than may dao va cac phuong tien van tai. Khoi luong dat dao cua cong viec nay cung kha lon, cho nen trong truong hop nay ta co the thi cong bang may dao gau day lai kinh te hon.
Trong cac truong hop thi cong sau day nen lua chon may dao banh xich:
- Khoi luong thi cong dat tap trung, khong can di chuyen may nhieu;
- Thi cong tren nen dat yeu (may on dinh hon khi lam viec va di chuyen);
- Khi thi cong dat da nham (banh lop se mon nhanh hon).
Nen lua chon may dao banh lop khi:
- Thi cong tren nen dat co kha nang chiu tai cao;
- Khoi luong thi cong khong tap trung;
- Thi cong trong thanh pho co yeu cau thuong xuyen di chuyen may.
Theo kinh nghiem viec chon may xuc con dua vao khoi luong dat thi cong. Khi khoi luong dat dao lon thi nen dung loai may dao co dung tich gau lon. (khi lua chon may co the tham khao cac bang chon trong tai lieu).
+ Cac so do thi cong may dao mot gau
Tuy theo dia hinh thi cong ma ta co cac so do dao thich ung.
Doi voi may dao gau thuan thuong co cac cach dao sau:
- Dao doc do ben: (hinh 3.7) khi duong truc di chuyen cua may dao song song voi duong di chuyen cua xe van tai. Cach dao nay bao dam xe dung lay dat va may dao lam viec khong phai ngung tre. Duong di chuyen cua may dao va o to co the tren cung do cao hoac may dao co the dung thap hon o to mot it.
- Dao doc do sau (hinh 3.8): cach dao nay doi voi nhung khu vuc truong doi doc theo huong chay cua xe van tai, hoac nhung khu vuc tuong doi doc theo huong chay cua xe van tai, hoac nhung khu vuc thanh tang, thanh bac. De giai quyet goc quay do cua may dao qua lon (toi 1700) thi ta co the mo rong khoang dao cho xe o to vao duoc de dang dong thoi giam thoi gian chu ky lam viec cua may dao.
- Dao ngang (hinh 3.9): cach dao nay thuong ap dung khi khai thac dat da nui, khai thac than lo thien. Ta thay hinh thuc dao nay cac phuong tien van chuyen thuong dung lay dat gan vuong goc voi truc di chuyen cua may dao. Trong truong hop khoang dao sau vuot qua chieu cao cua may dao thi ta phai chia thanh ranh (tang) dao.
Doi voi may dao gau nguoc
Dung may dao gau nguoc de dao nhung ho mong, ranh dao, muong dao v.v... Voi khoi luong dao dat khong lon, tinh chat cong viec khong phuc tap, loai dat khong ran lam, dung tich gau xuc thuong nho; ta dung may dao gau nguoc la tien loi va kinh te khi dao va do dat sang ben canh ho dao. Khi ay may dao dung dao doc voi ranh dao va do dat sang hai ben ranh dao hoac mot ben ranh dao (hinh 3.10).
Khi dao va van chuyen dat vao o to de cho di xa, ta co hai hinh thuc thi cong:
- Neu chieu rong ho dao khong lon (khong vuot qua ban kinh dao cho phep cua may xuc) ta se co hinh thuc dao ngang, nghia la huong di chuyen may dao song song voi ho dao.
- Neu chieu rong ho dao lon va thuan tien de o to vao lay dat ca hai phia thi ta co hinh thuc dao doi dinh, nghia la may xuc vua dao vua lui doc theo ho dao.
Doi voi may dao gau day
May dao gau day co ban kinh lam viec tuong doi lon nen no co the truc tiep dao roi do dat vao nen dap, hoac do dat thanh dong. No thich hop dung de nao vet bun, khai thong song, ngoi, muong ranh. Noi chung thi cong voi dat mem, uot thi may dao gau day co nang suat cao. Chieu sau dao khong nen vuot qua 50% chieu dai can.
Tuy theo dia hinh thi cong va dieu kien dat dai ma co cac so do lam viec cua may dao khac nhau.
Thi du, voi dieu kien o to khong the dung duoi ho dao de lay dat duoc, ta co so do thi cong nhu (hinh 3-11).
Tren so do nay, ta thay truc dao cua may xuc luon luon song song voi truc duong o to dung lay dat. Vi tri dung cua o to lam sao cho goc quay do cua may dao la nho nhat, de giam thoi gian chu ky lam viec cua may dao, dong thoi de dam bao an toan trong khi may dao quay do dat vao thung o to, thi nen cho thung o to huong vao phia quay can do cua may dao. Cac kich thuoc cua khoang dao se tuy thuoc vao tung loai may dao va o to.
Truong hop o to co the dung duoi ho dao de lay dat, khi do vi tri dung cua may xuc cao hon han o to thi ap dung so do dao con thoi (hinh 3-12).
Voi so do dao nay, goc quay do cua may dao la nho va may dao co kha nang lam viec lien tuc khong phai cho doi o to. Cach thi cong nhu kieu nay dam bao nang suat cao. Tuy nhien no co nhuoc diem la phai lam duong cho o to len xuong ho dao de dang.
d- Nhung bien phap nang cao nang suat may dao mot gau
- Cong thuc tinh nang suat dao mot gau:
(3.1)
trong do: N- nang suat cua may dao lam viec trong 1 gio
q- dung tich gau, m3; tck - thoi gian mot chu ki lam viec, s;
kd¬- he so day gau (la ty so giua the tich dat da thuc te xuc duoc day gau va the tich hinh hoc cua gau);
kx- he so toi xop cua dat;
ktg- he so su dung thoi gian; doi voi may dao thuong lay ktg= 0,20,25, cac he so kd¬ va kx co the lay theo bang duoi day:
- Cac bien phap nang cao nang suat may xuc mot gau
Hien nay o nuoc ta co rat nhieu loai may dao mot gau dang thi cong o nhieu cong truong vao cac cong viec khac nhau nhu: khai thac da, khai thac quang than, dao dat, v.v... Da co nhung don vi, ca nhan su dung may dao dat duoc nang suat cao, kinh nghiem nay chua duoc pho bien rong rai nen cung con nhieu noi nang suat lam viec cua may dao van thap (thuong hut chi tieu dinh muc). Nguyen nhan cua viec dat duoc nang suat cao phu thuoc rat nhieu yeu to, sau day la nhung yeu to anh huong den nang suat va bien phap nham nang cao nang suat cua no.
+ Nguoi cong nhan phai biet su dung thanh thao may, rut ngan chu ky lam viec bang cach ket hop cac thao tac mot cach toi da.
Thi du, trong khi cho may dao do dat da vao o to co the phoi hop them cac dong tac: keo tay gau ve phia may dao; nang gau len do cao can thiet de chuan bi do; dua tay gau ra phia ngoai truoc khi do; ha gau xuong vi tri can do; do dat, da khoi gau.
Khi quay may dao lai phia via dao co the phoi hop cac dong tac: keo tay gau lai phia buong lai; ha gau xuong de bat dau dao; do dat da ra khoi gau.
+ Chon phuong tien van chuyen tot, phu hop voi dung tich gau. Ty le giua dung tich gau may dao va dung tich thung xe o to la mot yeu to quan trong anh huong toi nang suat may.
Thi du, may dao CE-3 khi dung tich cua phuong tien van chuyen voi dung tich gau la 1:1 thi nang suat may dao chi dat 60% so voi may dao do vao phuong tien van chuyen co dung tich thung chua gap 8 lan dung tich gau dao. Thong thuong chon phuong tien van chuyen phuc vu may dao nen chon loai thung chua lon hon dung tich gau tu 4 den 5 lan.
+ Lap kich thuoc khoang dao hop ly (xem bang chieu cao dao hop ly cua mot so loai may dao), va cho dung cua cac phuong tien van chuyen chinh xac, sao cho goc quay trung binh cua may la nho nhat va hieu suat cua no lon nhat.
+ To chuc tot cac phuong tien van chuyen lam sao duoc lien tuc, khong de xay ra truong hop may dao phai cho o to.
+ Chuan bi cho dung lam viec duoc thuan loi, tranh go ghe va doc nghieng. Khi khai thac da, quang phai duoc lam toi, xop bang phuong phap no min.
+ Tuy theo moi loai dat, da ma thay the loai rang gau, kich thuoc gau cho hop ly. Thi du, voi dat mem, xop thi co the thay gau voi dung tich lon hon.