Cranes – Design, Practice, and Maintenance phần 5 ppsx

120 Cranes – Design, Practice, and Maintenance

4. Lowering speed of the load:

û (m
min) ûG60 m
min

5. Wire rope speed on the drum:

ûdG2 · û (m
min) ûdG2 · 60G120 m
min

G(2 · û) : 60 (m
sec) G120 : 60G2 m
sec

6. Nos. of rev
min of the drum:

ndGûd: (π · Dd ) (rev
min) ndG120 : (π · 1,2)

G31,84 rev
min

7. Nos. of rev
min of the

motor:

nmotorGnd · igb (rev
min) nmG31,84 · 24,6

G783 rev
min

8. Inertia moment on the

motorshaft from:

motor(s); brakesheave(s)

and gearbox:

JrotGJmCJbCJgb (kg m2

) JrotG24C16C6

G46 kg m2

9. Reduced inertia moment on

the motorshaft from the

weight of the spreader plus

load:

JLG(L · û

2

d · ηgb) :ω2

1 (kg m2

) JLG(31 350 · 22 · 0,94):

783 · 2 · π

60

2

JLG117 876 : 81,952

G17,55 kg m2

10. JtotalGJrotCJL (kg m2

) JtotG46C17,55

G63,55 kg m2

Brakes 121

11. After pushing the emergency

button, the load is

accelerated by M1 during ∆t

sec (activating time for the

brake) with ∆ω2 (rad
sec):

∆ω2G∆t · M2

Jrot

(rad
sec) ∆ω2G(0,3 · 7051)

46 G46 rad
sec

12. The activated brake starts

mechanical braking after

∆t sec with a rotational speed

on the motorshaft of:

ω3G(ω1Cω2)(rad
sec) ω3G

783 · 2π

60 C46

ω1G(nm : 60) · 2π (rad
sec)

G81,95C46

G127,95 rad
sec

13. The numbers of rev
min of

the motor- and brake-shaft is

then:

n2Gω3 ·

60

2π

(rev
min) n2G128 ·

60

2π

G1223 rev
min

14. The wire rope speed on the

drum is then:

ûd2G n2

nm

· ûd (m
sec) ûd2G1223

783 · 2G3,123 m
sec

15. The effective brake moment

is:

MbeGηb · Mb (Nm) MbeG0,95 · 19 000

G18 050 Nm

16. The effective braking time is:

tbrakeG ω3 · Jtotal

MbeAM1

(sec) tbrG 128 · 63,55

18 050A7051G0,740 sec

17. Total braking time:

tG(∆tCtbr) (sec) tG0,3C0,74G1,04 sec

122 Cranes – Design, Practice, and Maintenance

18. Wire rope displacement on the

drum during braking:

SdG∆S1C∆S2 (m)

∆S1Gdisplacement on the

drum during ∆t (m)

∆S2Gdisplacement on the

drum during

deceleration whilst

braking in tbr sec.

∆S1GûdCûd2

2 · ∆t (m) ∆S1G2C3,123

2 · 0,3G0,768 m

∆S2G3,123

2 · 0,74G1,155 m ∆S2Gûd2

2 · tbr (m)

SdG0,768C1,155G1,923 m

19. Total displacement of

spreader and load during

emergency stop: in lowering

direction (see Fig. 4.2.2)

SsprCLGSd : 2 (m) SsprCLG1,923 : 2G0,96 m

Note:

– The winch has: 2 motors;

2 brakes;

1 gearbox;

2 drums.

– The spreader and the load are suspended by eight ropefalls; 4 of

which are fixed on the boom end; the other 4 falls run via wire

rope sheaves to the 2 wire rope drums.

– ∆t can be taken as ∆tG0,3 sec

the worst case for ∆tG0,5 sec.

– The maximal peripherical speed of the brake disc must be

controlled.

The allowed number of brake cycles in an emergency stop can be calcu￾lated as follows:

Dissipated energy per brake cycle: WBGMbr · n2

9,55 · tbr

2000 (kJ)