Research objectives are:
- Determining the causes of the destruction of an extended rope rope-block
system of thin rope, exposed to the atmosphere;
- Development of methods to protect cables from damage.
work the rope in the block:
But the definition of AI Dukelsky in the strands, but the stress
tension, with rounding blocks have additional
bending stress and xcontact stress in the field
xcontact between the outer wires with the rim of the block. These bending and
xcontact stresses are pulsating in nature, they disappear
by straightening the rope. The result is a metal fatigue,
and after a certain number of kinks begin to break down the wire
firsxtexternal and then internal, until, finally, does not occur
complete destruction of the rope.
Design Guidelines CABLE-block system.
We give some advice from various sources,
concerning the choice of O unit, depending on the O line.
Prof. Dukelsky AI "Rope the road ...»:
1) Use wire ropes with gB = 160 ... 180 kg / mm 2 is considered
optimal for increasing the longevity of the ropes. We had
used rope with gB = 165 kgf / mm 2.
2) The main significance for the longevity of the block have the value O
and tensile stress gp. Endurance of the rope in the other
equal proportional changes
(D / d * 1/Gr) ** 2
3) Recommendations regarding the selection ratio D /d:
with a> 20 * D / d> 60 ... 80
where a - angle of wrap block
(We had a D / d = 32, with a = 90 *)
«installation and safe operation of cranes»:
Heavy duty D / d> 30
The maximum value of D / d> 35 is set for a very heavy
modes, in other cases it is much less.
And Marhel. And "Crane Ropes":
1) The flexibility of the rope determines its capacity for inflection on the block
within the elastic deformation due to internal sliding
wires. Flexibility is characterized by the coefficient. Flexibility:
By flexible = dc / d, where d - the maximum diameter of wires in the rope, mm.
d to - rope diameter, mm.
For crane ropes: For flexible> 6.11
(We have to flexible = 1.2/0.45 = 2.7)
2) Rigid cables (with a large O and small wires to the hybrid) is more
resistant to wear. (We - Tight ropes).
3} The definition of durability is based on the use of long-term
observations of similar cables in operation.
MA Bukshteyn "Steel ropes "»:
Durability ropes determined by the ratio:
K = D / d, where D - diameter of the unit (drum)
d - wire diameter.
In the recommended designs: K = 450 (We have K = 38 \ 0.4 = 95)
If we take K = 450, then the rope d 1,2 requires D = 450 * 0.4 = 180 mm)
general recommendation of all the authors:
Lining unit elastic material (nylon, rubber ...) is much
(1.5 ... 2 times) increases the durability of the ropes (decrease
(We - groove block - steel)
features of our unit design:
1) The ratio D / d = 32 for the unit conforms to the recommendations
"Rules for the design and safe .... cranes;
2) margin of safety rope np = 60;
3) rope diameter 1.0 ... 1.2 determined by the requirement of minimum
the inertia of our tether-block system;
4) The unit is installed on the hinge (3 degrees of freedom) that, according to
recommendations of the "Design and operation of the constant network ..."
reduces wear on the rope.
5) The rope hard, which guarantees its high durability
6) Low reliability of our rope is a result of lack of
experience in building similar systems such extent and
expressed in an underestimation of the influence of operating conditions on the fatigue
strength of the ropes.
1) The data for weather stations in our area:
Average wind speed - 14m / s
max - 25 m / s
Data on the frequency of wind gusts in there.
According to the book "Design and operation of the xcontact
Network ...", wind loads in overhead wires can cause
a) self-oscillation f = 40 ... 60 1/min - fight with them is
the installation of special damping devices;
b) vibration f = 100 1 / s - the fight against it is to strengthen
the junction of the wires with the supports special springs;
NATURE OF FRACTURE ROPES:
A survey of damaged kanatav was installed
cause breakage of wires ropes
- "Typical fatigue fracture with no signs of fraying wires"
(See table damage
ropes MA Bukshteyn "Steel Ropes"), and 30% of all injuries
located at the vanishing point with unit horizontal branch of ropes:
The impact of wind load on the rope may have the following character:
I) vibrations of the rope (without turning blocks):
2) Cranking blocks (due to the lifting and lowering the balances)
with increasing length of the branches AB and BC:
3) The rotation balances:
We estimate the magnitude of wind effect on the vertical branch of the rope.
Methodology "Handbook of cranes":
qo = v2/16 n = 1.8 (H suspension = 40 ... 50 m)
a = 1.2
b = 2.0
g = 1.1
P = qo * n * c * b * g = (142 / 16) * 1.8 * 1.2 * 2.0 * 1.1 = 58.2 kgs/m2
F1 = 40 m * m * 0.0012 58.2 kg / m2 = 2.3 kg
f1max = q * l2 / (8 * s) = 2.3 \ 40 kg / m * (40m) 2 / (8 * 2.5 kg) = 4.6 m
F2 = PB * 0.5m * 0.1m = 2.9 kg
ie fi = 45 °
l2 = f2 = 4m
The "geodetic work in the construction of the Serpukhov
q = d * v2 / 8 = 1.2 * 142 / 8 = 29.4 kg / m
f = q * l1 ** 2 / (8 * H) = 29.4 * 402 / (8 * 25) = 2352mm = 2.3m
Let us assume that the curve «a» - a circle.
la = SQRT (l1 ** 2 + 16 / 3 * f1 ** 2) = 40.35m
delta l = la - l1m = 0.35m
n = delta l / (pi * D) = 350mm / (3.14 * 38mm) = 2.94
ie Block provernetsya for «n» turnovers.
EVALUATION OF THE INFLUENCE OF TYPE wind effect on the fatigue
DESTRUCTION OF ROPE:
Number of cycles N loading with the stress that G
can withstand the design is determined by the relationship:
(G / Go) m = No / N
Typically, m = 4 ... 10
No = 10 ** 6 ... 10 ** 7
Go = G-1 - the endurance limit of the sample at No (determined
as durability of N is inversely proportional to the voltage
during loading, then we define the stress arising in the rope
with various types of loading.
1). Bending of the rope due to rolling through the block. For straight
procrastination (by Dukelsky) we have:
G, = E * d / D = 2.1 * 104 kg / mm 2 * 0.4 / 1938 = 221 kg / mm 2
GB wire = 165 kg / mm 2
However, since in the rope has the form of a spiral, so the tension in her
We take G and = 100 kg / mm 2
2). Bending the rope swing with a counterweight:
f = 1m (real value).
For a single wire d = 0.4 mm
f = P * l ** 3 / (3 * E * Jx), hence P = 3 * E * Jx * f / l ** 3
M = P * l
G, = M / W = 3 * E * Jx * f * l / (l3 * Wx) =
= 3 * 2.1 * 10 ** 6 * 0.05 * 0.4 ** 4 * 100 * 400 / (400 ** 3 * 0.1 * 0.4 ** 3) =
= 787.5 kg / cm2
Gi1> Gi2 and, therefore, bending the rope on the block stand
far fewer cycles.
CALCULATION OF LIFE ON ROPE Dukelsky "Steel Ropes»
Collected papers vol 5 page 225:
Number of cycles:
I = k * Ao * (D / d) ** 2 * (NH-2) th cycle
k = 1, max value
Ao = 0.025 steel block
Ao = 0.059 polymer lining
NH-2 = 60 - 2 = 58 NH-margin.
For D / d = 30 I = 1 * 0.025 * 30 ** 2 * 58 = 1,305 thousand loops
For D / d = 80 I = 1 * 0.025 * 80 ** 2 * 58 = 9,280 thousand loops
2 months contain 5.1 * 10 ** 6 seconds
Thus, if the loading frequency 60 1 / min = 1 1 / sec
then 2 months to destroy even a rope with a "good" unit (D / d = 80)
and ruggedness NH = 60.
Note that all the dependencies and recommendations are made for
crane ropes d> 12 mm and have an empirical nature.
COMMENT ON QUALITY ROPES:
The certificate of quality on the ropes, GOST 3062, we have used
in construction, contrary to the requirements of GOST 3241-80 no xinformation
The test wires to a cyclic bending loading on
BACKGROUND xinfoRMATION ON LIFE ROPE:
I. Marhel "Crane ropes" life ropes
(Loaded at 60%):
1) Excavator - 1 ... 1.25 months;
2) port valve - 3 ... 4 months,
3) foundry crane - 2mes.
4) truck crane - 6 ... 8 months.
Collection of Steel Ropes ":
The service life of wire ropes: 6 ... 20 months.
1) The cause of breakage of the rope, in our case is a fatigue failure
section of the rope in the area of ??the block from bending stresses arising from
repeated rolling of the rope through the block under the influence of wind
Indicated is the result of a wrong choice of operating mode
2) To prevent breakage of ropes for the further operation of the stand
necessary in the long intervals between tests (more days)
counterweights to lift and put on a platform of service, and in the zone
blocks of both branches of each rope to fix the clip.
1) AI Dukelsky "cableways and cable cranes"
M. "Engineering" ed. 4
2) I. Marhel "Crane ropes" M. "Engineering" izd.2
3) IA Birger et al, "Calculation of strength ..." M. Mash. izd.Z
4) AI Dukelsky Handbook of cranes "izd.2
5) "Rules of construction and safe operation of cranes"
6) "Design, construction and operation of the xcontact network and air
Line AV Frayfeld ...
7) "Steel ropes" Collection of articles v.5, 6 Kiev "Technique"
8) MA Bukshteyn "steel ropes."
9) GOST 3062-80