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INTRODUCTION
The modern line technological and
automated lines, inters hop transport demand application of various types of
the hoisting-and-transport mechanisms providing a continuity and cyclist of
productions. For this reason the
hoisting-and-transport equipment now plays the main role in efficiency of
modern manufacture. That is why to reliability and durability of mechanisms
make special demands. The modern high-efficiency load-lifting and transport
machines working with bigger speeds and possessing high carrying
capacity, require a lot off care, especially in units with rubbing surfaces.
The actuality of the theme
On metal works the basic vehicle is
the bridge crane at which mechanisms of movement are exposed to greater
loadings. The basic lack of it is: fast deterioration and failure of rotating
parts, especially plain bearings.
The
purpose and problems
The given problem can be solved
having replaced bearings on bearings of sliding that will lead to increase of
durability of the mechanism of moving and will give economic benefit by way of
service and replacements of units of moving. The purpose and research problems: the Purpose is to increase
durability of bearing’s units of the mechanism of moving of bridge cranes. The
object in view can be reached by realization of following private(individual)
tasks:
-
Definition
of durability developed bearing unit with application of bearings containing fluoroplastic
materials;
- definition of economic efficiency from application bearing
units of a new technological level.
Practical
value
Necessity of maintenance of working
capacity of various devices at extreme temperatures and at presence of bigger
loadings stimulates wide industrial development self-greased radial spherical
bearings.
Unlike the
metal hinges used with lubricant, self-greased hinges carry out mainly from antifriction
materials of type metalfluoroplast and fabric materials with fluoroplast a
fibre. Self-greased materials have in the basis, as a rule (fluoroplast-4).
Wear resistance and the lowered value of forces of friction at use metalfluoroplastic
a material is provided with friction fluoroplastic, high durability is reached
due to the steel basis, fast heat removal at friction takes place owing to
application of a porous layer bronze skeleton. Unlike the metal hinges used
with lubricant, self-greased hinges carry out mainly from antifrictional
materials of type metalfluoroplast and fabric materials with fluoroplastic
fibre.
The review and the analysis of
literature
Loading the hinge is characterized
by the attitude of the enclosed loading to the area of a projection basic
surface on a plane, perpendicular to a direction of action external loading, -
average (conditional) pressure:
Pk= , (1.1)
Where N -
equivalent radial (normal) loading; dss = d1 - diameter of the spherical
bearing (d1 - diameter of an internal ring); b - length of the bearing (the top
ring) (pic.1.1).
Actually average and the
more so the maximal contact pressure will surpass calculated on the
above-stated equation. Definition of the intense condition in a place of power
contact, the sizes of a platform of the contact, the maximal pressure and size
of rapprochements of adjoining bodies for the specified composite materials
represents a challenge which is necessary for solving, combining settlement
methods with specially put experiments.
Figure 1.1. Self-greased
radial spherical the bearing (animation: seven images, seven repeats).
On bearing N, considering
simultaneous action radial Nr and axial Na loadings it is possible to define
equivalent loading under the formul:
N=Nr ,
(1.2)
On conditions of normal
operation it is desirable, that the attitude (relation) of axial loading to
radial did not exceed 0,6. If during one half-cycle loading on the bearing
changes from Nmin up to Nmax equivalent loading we shall find from expression:
N= . (1.3)
Static bearing ability
(contact pressure) for motionless (inactive) are defined from a condition of
absence of residual deformations and destruction of antifriction elements
(rings), its value does not exceed usually 250 ÌPà. At vibrating influences
and change of a direction of loading admissible average pressure it is
necessary to reduce at 2-10 time.
Dynamic
characteristics of bearing
Number of expected cycles (fluctuations) n∑,
falling a full cycle (a corner 2β) (ðiñ.1.2), it is
defined under formulas:
n∑= or n∑= , (1.4)
where S – way of a sliding friction, sm; υ
– number of
fluctuations (full cycles) in a minute min-1; υs
– way of a
sliding friction, sm/sec; [h] – admissible deterioration, sm; Jh – average intensity.
Figure 1.2.
Kinematic scheme.
Let's express intensity
of wear process on a way of sliding friction S and on time τ dependences:
 ;  (1.5)
where h – deterioration; Jh
– intensity
of wear process (on a way of friction);
Jhτ – Intensity of wear process (on a way of time).
Operating time of the
hinge we shall express dependences:
 (min);  (hour).
(1.6)
Using parameters of
intensity of wear process of a material and admissible deterioration, we shall
find an expected operating time:
 (hour).
(1.7)
Average speed sliding
(sm/sec) in contact of rubbing rings we shall define(determine) under the formula:
Vs= 2,9 10-5
ddsβυ,
(1.8)
where dds – diameter of sphere, mm
At expression of speed of sliding in m/mines it is had:
Vs=
1,74 10-5 dds β υ.
Supposed
deterioration metalfluoroplast material.
Reliable forecasting of
durability of the hinge mainly depends on correct definition of intensity of
wear process of materials in expected conditions of operation. With a view of
preliminary orientation to fig 1.1. The area which approximately characterizes
value and its dependence on a primary factor – average pressure is given. In
real conditions of operation self-greased bearings intensity of wear process
changes approximately in range Jh= 5*10-7 – 10-9. Admissible deterioration
for metalfluoroplastic materials makes
[h]≈0,05-0,2 mm.
The factor of a sliding
friction on experimental data decreases with growth of average pressure and
temperatures and increases with increase of speed of sliding. The approached
calculation of factor of a sliding friction can be carried out under the
formula:
(1.9)
Factor of a sliding friction usually measure in a range f=0.025
– 0.35.
Development on the theme
Figure 1.3. Dependence of intensity of wear process fluoroplast a layer
from average pressure.
Figure 1.4.
Dependence of speed of sliding on average pressure.
CONCLUSIONS
On the basis of the
executed calculation it is possible to formulate following conclusions:
1.
Optimum
set of properties have so-called metalfluoroplast the bearings consisting of a
strong constructional basis, a porous layer of the antifrictional alloy
(bronze) impregnated by fluoroplast.
2.
2. At
loading Pk=246 MPà that corresponds(meets)
to loading on bearing unit of the bridge crane carrying capacity 250t., for
annual operation at maximal fluoroplastic layer h=0,2mm, intensity of wear
process is in admissible limits Jh = -
 is equal Jh= .
3.
At
the received value of speed of sliding Vs=0,204 sm/sec the factor of friction
is equal f=0,204, that is in a range of factor of a sliding friction f=0,025 -
0,35.
PROSPECTS of the FURTHER RESEARCHES
To investigate(research) parameters metal and not metal bearings. On
carrying capacity of the crane to choose optimum parameters of the bearing. To
develop new unit of movement of the crane.
LITERATURE
1. Âîðîíêîâ Á.Ä. «Ïîäøèïíèêè ñóõîãî òðåíèÿ».Ì.:Ìàøèíîñòðîåíèå,1968,140ñ.
2. Òðåíèå, èçíàøèâàíèÿ è
ñìàçêà : Ñïðàâî÷íèê.  2-õ êí./Ïîä. ðåä. È. Â. Êðàãåëüñêîãî, Â.Â.
Àëèñèíà. – Ì.: Ìàøèíîñòðîåíèå, 1978 – êí. 400ñ., èë. Â ïåð.
3. Ðàñ÷åòû ãðóçîïîäúåìíûõ è
òðàíñïîðòèðóþùèõ ìàøèí. Èâàí÷åíêî Ô.Ê. è äð. Èçäàòåëüñêîå
îáúåäèíåíèå «Âèùà øêîëà», 1975, 520ñ.
4.
Ñåìåíîâ À.Ï., Ñàâèöêèé Þ.Ý. «Ìåòàëëîôòîðîïëàñòîâûå ïîäøèïíèêè». Ì.:Ìàøèíîñòðîåíèå,1976,192ñ.
5.
×åðåíêåâè÷ Ë.Â., Ìåðêóëîâ Þ.Ý. «Ôòîðîïëàñòîâûå ïîäøèïíèêè ðàáîòàþùèå áåç ñìàçêè»,ËÄÒÏ,1959,31ñ.
6. Ãàåâèê Ä.Ò. «Ïîäøèïíèêîâûå îïîðû ñîâðåìåííûõ ìàøèí».Ì.:Ìàøèíîñòðîåíèå,1985. - 248ñ.,èë.
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