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ABSTRACT
RESEARCH OF RESONANCE PROCESSES IN HAULING CHAINS OF SCRAPER CONVEYORS ON EXAMPLE OF THE SPС-26 CONVEYOR
Has been developed the mathematical model of determination the resonance rates of movement the chain of scraper conveyer taking into account the unevenness of its load
Problem and its communication with scientific and practical tasks
A bottomhole conveyor renders most influence on probability of faultless work of the mechanical complex. Presently a scraper conveyor is an irreplaceable transport vehicle at delivery of coal from breakage coalface at coal mines. On it is more than a 55% duration of outages the coalface, thus 50% of outages the scraper conveyers and 53% of labour intensive the removal of refusals are for a hauling chain. Depending on external environments the term of service the chains can change in wide limits: in excavation with aggressive waters chains fall out through 1-1,5 months. The middle terms of service the round-link chain on the conveyers of type SP make 5-8 months. The task of improvement of operating parameters of the hauling chains has the important value and is one of most actual.
Analysis of researches and publications
Scientific bases of theory of perfection the construction and methods of calculation the hauling chains are devoted I.G.Shtokman's , A.О.Spivakovskiy's, L.G.Shakhmayster's, L.N.Eppel's and many other scientistes's researches, both in our country and abroad. Organizations such are engaged in this question as: Dnepropetrovsk's mountain academy, Moscow's mountain academy, Donetsk's national technical university, Zaporozhian's national technical university and many others.
All from foregoing scientists and organizations affected the question of destruction the links of chain from the offensive of the resonance mode in the process of its work. In particular I.G.Shtokman developed the most complete method of calculation the resonance of chains; in works of L.G.Shakhmayster the terms of offensive the parametritic resonance are described; L.N.Eppel set were influence work in the resonance mode on longevity of hauling chains. In foregoing works at the calculation of the resonance mode the real degree the load of conveyor is not taken into account, and it is suggested to use the average value.
Raising of task
For achievement of this purpose set the following basic tasks. Are part:
- development of the mathematical model of forming loading of scraper conveyer and determination the resonance rates of movement the hauling chain;
- drafting of the algorithm the program calculation of loading and resonance speeds;
- development of the method treatment the results of design.
Material and results exposition
Permanent length of coalface implies, that entry and ventilation drift are strictly parallel in one plane. There in actual fact the types of drifts have some curvature, and, length of coalface is a variable. From here is a necessity to conduct the calculation of resonance speeds and at subcriticality, and at the supercritical pull of hauling chain.
Рiс. 1 - The charts to the calculation of vibrations of hauling chain at supercritical (а) and subcriticality (б) pulls
We designate through 2τ period of external indignation, equating which with the period of own vibrations, we get the condition of resonance for basic tone subsequent overtones. At the supercritical pull
2L0/a=2τ L0/aτ=1
L0/a=2τ L0/aτ=2
2L0/3a=2τ L0/aτ=3
For a chain hauling organ at hooking with an asterisk
τ=l0/v
where l0 – chain step, m; v - chain rate
movement, m/s.
At substitution we determine the values of resonance speeds:
v0=l0a/L0
v1=2l0a/L0
v2=3l0a/L0
At the subcritical pull we have the following values of resonance speeds:
v0=l0a/2L0
v1=l0a/L0
v2=3l0a/2L0
where L0 – length of the chain contour, m.
At these speeds the dynamic loadings achieve the maximal values. Value of speed (v0 + v1)/2 and (v1 + v2)/2 correspond to the antiresonance mode (own and forced vibrations are opposite on a phase). Thus the dynamic loadings achieve the minimum.
For determination of resonance speeds it is necessary to know the value of middle speed of distribution the resilient wave taking into account the degree of work-load the conveyor
a=(L0 агр апор)/(L1 агр + L2 апор),
where L1 and L2 – lengths of areas of chain contour without a load and with a load accordingly, m;
агр и апор – speeds of resilient wave distribution on the loaded and unloaded areas accordingly, m/s.
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| агр = |
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where E0 – longitudinal inflexibility of chain, N ;
q – linear mass of load, kg/m ;
q0 – linear mass of chain with scrapers kg/m;
с – coefficient of participation of the transported load in longitudinal vibrations (the communication of scrapers with the hauling chain is harder more than), for the scraper conveyor с = 0,3 – 0,5.
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| апор = |
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The resonance speeds of basic tone taking into account the unevenness of load the conveyor are determined the following
Рiс. 2 – The chart of conveyor for resonance speeds determination
T=T1+T2=L1/апор+L2/агр
аср=L0/T=L0/(L1/апор+L2/агр)=L0аграпор/(L1агр+L2апор)
с=l0аср/2L0
Vдокр=l0аср/4L0
We put the value of аср in the formulas of resonance speeds for the supercritical and subcritical pull of hauling chain
Vзакр=l0аграпор/2(L1агр+L2апор) c
We put
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| агр = |
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| апор = |
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and L1 = L0 – L2 or L1 = L + Li , and L2= L - Li
where L = L0/2 – length of conveyor, m
Li – position of combine on the conveyer, m
L1 – area of chain without the load, m
L2 – area of chain with the load, m
we get
|
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| Vзакр = |
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Vдокр=Vзакр/2
The calculation was produced by the computer program written in the VBA language with the use of the Excel appendix for the chains of 24x86 conveyor SPC-26 in terms 10th north coalface at the mine "Ukraine". As a result of calculation the ranges of resonance speeds for basic, the 1th and the 2nd tones were obtains, and the graphs of dependences of sizes the resonance speeds depending on position of combine on the conveyor have been built, and - from the degree of load (pic. 3).
Рiсt. 3 – The graphs of resonance speeds for the chains of the SPC-26 conveyor depending on position of combine on the conveyor for two hollow cycles
The conclusions and direction of further researches
As a result of calculations for two hollow cycles the ranges of resonance speeds have been obtained for the SPC-26 conveyor and it has been exposed, that the speed of movement the hauling chains on this conveyor is near to resonance speeds of the 1th and the 2th tones at the supercritical pull of hauling chain (special in the end and beginning of hollow cycles). From it is here possible to come to the conclusion, that in these terms and at this productivity of conveyor it is extremely undesirable to have the supercritical pull of hauling chain from point of view of resonance. The resulted calculations and recommendations can be used for the choice of the mode the operations conveyer.
At the subcritical pull of hauling chain basic, the 1st and the 2nd tones have the following intervals:
basic tone - (0,16 - 0,23) m/s;
1st tone - (0,32 - 0,48) m/s;
2nd tone - (0,5 - 0,7) m/s.
At the supercritical pull of hauling chain:
basic tone – (0,32 – 0,48) m/s;
1st tone – (0,67 – 0,92) m/s;
2nd tone – (0,98 – 1,4) m/s.
It is thus visible, that avoiding resonance in this case is possible, choosing the speed of movement of hauling chain in the range (0,92 - 0,98) m/s. However at other cycles of load of nonresonance interval it can not be. It is possible to come to the a conclusion, that at this length of conveyor it is difficult to avoid the phenomenon of resonance in one or another period of cycle.
LITERARURE LIST
1. Галкин Н. А. Усилия в звеньях тяговой цепи на звездочках скребкового конвейера // Изв. вузов. Горный журнал. - 1980. - № 3 . - С. 76-79.
2. Спорыхин В. Я., Сноведский В. М. Эксплуатационные параметры тяговых цепей скребковых конвейеров // Уголь Украины. – 1983. – № 7 . – С. 28-29.
3. Леусенко А. В. Нагрузки при транспортировании угля забойными скребковыми конвейерами с направляющими // Изв. вузов. Горный журнал. – 1987. - № 5 . – С.47-49.
4. Штокман И. Г., Ляховский С. И. Расчет тяговых цепей конвейеров на усталость // Приложение к сборнику “Горные машины ” №4., - 1978. – С.3-10.
5. Соснин А. Г. О динамических усилиях в скребковых цепях многоприводных конвейеров // Приложение к сборнику “Горные машины ” №4., - 1985. – С.10-15.
6. Штокман И. Г., Эппель Л. И. Прочность долговечность тяговых органов // М., “Недра”, 1967 – 231с
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