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ГИАБ. Горный информационно-аналитический бюллетень / MIAB. Mining Informational and Analytical Bulletin, 2021;(3):17-27 ОРИГИНАЛЬНАЯ СТАТЬЯ / ORIGINAL PAPER
УДК 621.926.3 DOI: 10.25018/0236-1493-2021-3-0-17-27
АНАЛИЗ ОТКАЗОВ ЭЛЕМЕНТОВ КОНУСНЫХ ДРОБИЛОК И ПРИЧИН ИХ ВОЗНИКНОВЕНИЯ
Н.В. Белов1,2, М.Б. Бородина2, О.А. Смирнова2, А.С. Часовских2
1 АО «Стойленский ГОК», Старый Оскол, Россия 2 Старооскольский технологический институт им. А.А. Угарова (филиал) НИТУ «МИСиС», Старый Оскол, Россия, e-mail: [email protected]
Аннотация: Цель исследования заключается в выявлении и анализе наиболее характерных отказов и причин их возникновения в элементах конусных дробилок, используемых на всех стадиях дробления руды на горнообогатительных комбинатах. Это позволит определить направление дальнейшей разработки эффективных способов предотвращения выхода из строя конусных дробилок. В работе использованы статистические данные по отказам конусных дробилок Стойленского горнообогатительного комбината. Изучение этого материала позволило выявить отказы, периодически возникающие в элементах дробилок. Анализ характера и особенностей работы оборудования и случаев выхода его из строя, позволил определить причины отказов. Кроме того, исследуя разрушения элементов конусных дробилок, было выявлено три типа отказов по степени их прогно-зируемости: прогнозируемые отказы, слабо прогнозируемые отказы и внезапные отказы. На базе проведенных исследований определены приоритетные направления модернизации дробилок: прогнозирование отказов первого типа для определения межремонтного периода и увеличение межремонтного периода путем повышения качества изготовления броней, разработки новых форм и материала броней, способных дольше сопротивляться износу; предотвращение второго и третьего типа отказов путем разработки и внедрения в привод агрегата предохранительных устройств и упругих элементов, эффективно снижающих амплитуду динамических нагрузок в процессе загрузки материала и дробления, а также размыкающих связь привода с дробящим конусом при перегрузках. Ключевые слова: конусная дробилка, измельчение горной породы, зона дробления, отказ, износ, динамические нагрузки, предохранительные устройства.
Для цитирования: Белов Н. В., Бородина М.Б., Смирнова О. А., Часовских А. С. Анализ отказов элементов конусных дробилок и причин их возникновения // Горный информационно-аналитический бюллетень. - 2021. - № 3. - С. 17-27. DOI: 10.25018/0236-1493-20213-0-17-27.
Failure analysis of main components of cone crushers
N.V. Belov12, M.B. Borodina2, O.A. Smirnova2, A.S. Chasovskikh2
1 JSC «Stoilensky GOK», Stary Oskol, Russia 2 A.A. Ugarov Stary Oskol Technological Institute, National University of Science and Technology «MISiS» branch, Stary Oskol, Russia, e-mail: [email protected]
Abstract: The study aimed to identify and analyze the most characteristic failures and their causes in components of cone crushers used at all the stages of ore crushing at mining and processing plants. This can help route further R&D on effective prevention of cone crusher failure.
© Н.В. Белов, М.Б. Бородина, О.А. Смирнова, А.С. Часовских. 2021.
The failure analysis used statistical data on cone crusher failures at the Stoilensky Mining and Beneficiation Plant (Stoilensky GOK). The analysis revealed the types of intermittent failures in the components of cone crushers. The studies into the operation mode of the equipment and its failure cases made it possible to determine the major failure causes. Furthermore, the failure types were distinguished in terms of their predictability: predictable failures, weakly predictable failures and spontaneous failures. Based on the implemented studies, the priority ways of upgrading of cone crushers include: prediction of the first-type failures to determine the overhaul period; extension of overhaul period through improvement of manufacturing quality of liners as well by development of new forms and material for liners capable of longer wear resistance; prevention of the second- and third-type failures by engineering and introduction of new drive safety gears and elastic elements for efficient reduction of the amplitude of dynamic loads during feed and crushing, and also to break connection between the drive and the cone in case of overloading.
Key words: cone crusher, crushing, crushing zone, failure, wear, dynamic loads, safety gears. For citation: Belov N. V., Borodina M. B., Smirnova O. A., Chasovskikh A. S. Failure analysis of main components of cone crushers. MIAB. Mining Inf. Anal. Bull. 2021;(3):17-27. [In Russ]. DOI: 10.25018/0236-1493-2021-3-0-17-27.
Introduction
The mining industry features flow-line production. Therefore, failure of one section of a production line often results in suspension of the entire production process. Unscheduled stoppage of crushers affects the rate and output of production since the product of the crushers the the feed of the subsequent ore concentration stages. Consequently, an increase in the mining equipment reliability leads to a highly productive and faultless operation of a whole mine and, thus, is a relevant task.
One of the most important processes in mining and processing is crushing of ferruginous quartzites. Crushers operate in difficult conditions due to the high hardness of this rock (hardness as per the Protodyakonov scale is 17-18). At Stoilensky GOK's processing plant, cone crushers are capable to perform coarse, medium and fine crushing.
In cone crushing, rock is broken in the crushing chamber formed between the liners of the cone and bowl. The description and operating principle of cone crushers are presented in detail in the literature
[1-4].
Failure statistics
For the failure analysis of main components of cone crushers with a view to determining their causes leading to the equipment breakdown, the data on failure statistics of cone crushers at Stoilensky GOK as well as at other local plants were collected and studied.
The statistics analysis revealed major causes of failures leading to long downtime. Each cause of failure was analyzed individually to develop appropriate precautions.
Damage of crusher cone
and bowl liners
There are three types of damage to liners:
• Surface wear;
• Cracking;
• Compression marks (dents) from un-crushable materials.
In the cone crushers, rock is broken in the crushing chamber formed by the liners of the crushing cone and immobile bowl. Crushing results from the action of compression, abrasion and bending. The bending forces may be very high due to the cir-
Fig. 1. Types of wear in liners: critical wear at the bottom of liner in medium-crushing bowl (a); through wear of liner in fine-crushing bowl (b)
Рис. 1. Виды износа броней: критический износ футеровки чаши среднего дробления в нижней части (а); сквозной износ футеровочного кольца чаши мелкого дробления (б)
cular surface of the crushing chamber. The liners of the bowl and cone are subjected to loads that mainly lead to mechanical hardening, abrasive wear and chipping-off [4-6].
It should be noticed that the beneficial effect of surface hardening only occurs in crushing of materials with hardness lower than the hardness of the hardened layer.
Table 1
In the impact and abrasive wear, the liner surface undergoes chipping-off, and the hardened layer is gradually regenerated deeper into the wall of the wear part, down to the through wear (Fig. 1).
Furthermore, an important performance constraint for eccentric crushers is their high sensitivity to the nonuniformity of feed, both in terms of weight and particle
Operating time (OT) of liners in crusher no. 1, hours Наработка броней дробилки № 1 (в часах)
Date Cone liner OT (341-342), h 1255.05.341 Certificate Comments
labeling No Date
13.03.2017 2655.5 110 105 515 23.09.2016
18.04.2017 1438.672 116 121 594 05.01.2017 Crack in liner
01.06.2017 2197.149 115 120 673 26.12.2016
21.07.2017 2334.283 122 147 478 13.06.2017
14.09.2017 2282.812 126 159 740 30.08.2017
08.11.2017 2342.516 123 147 477 13.06.2017
24.12.2017 2250.387 131 170 636 31.10.2017
05.02.2018 1900.976 132 173 662 23.11.2017 Crack in liner
01.03.2018 1293.829 135 180 608 12.01.2018 Crack in liner
19.03.2018 955.771 134 179 080 26.12.2017 Shaft broken
24.04.2018 1779.727
13.05.2018 880.231 137 188 424 07.03.2018
17.06.2018 1975.365 143 201 083 30.05.2018
07.08.2018 142
Fig. 2. Cracks in cone liner: vertical (a); horizontal (b) Рис. 2. Трещины в броне конуса
size distribution. In this case, a crusher operates unevenly, with peak stresses in the parts and in drive units, and liners undergo riffle scuffing, with coarse particles falling into these riffles. Aiming to avoid this phenomenon, some factories undertake mechanical treatment of liners (once or twice in lifetime), which increases the operating cost of crushers but ensures profitability through the increased productivity [4].
Sometimes liners fail ahead of the end of life due to cracking. By way of example, Table gives the liner performance data of crusher KKD 1500/180 No. 1 at Stoilensky GOK. Alongside with planned maintenance over a period of 1.5 years, there were 3 unscheduled replacements of the cone liner due to cracks and one unscheduled repair of the crusher due to the broken shaft.
All cracks in the cone liners at Stoilensky GOK can be grouped into horizontal and vertical cracks (Fig. 2).
The analysis of the liner performance led to the conclusion that vertical cracks appeared due to uncrushable bodies. The causes of the horizontal cracks were of two types: deviations from the technology of cavity filling between the liners and basic parts; surface damage from uncrushable material (scratches, chips) resulting in reduced strength and further destruction.
Crushers with hydraulic control of the discharge opening have become widespread in the recent years as size of the output product (fraction) can readily be adjusted in this case and the hydraulics can also serve as a safeguard (compensator) to prevent overloads when a hard-to-crush (uncrushable) product enters the crushing cavity [2]. When an uncrushable material enters, the load increases while the hydraulic mechanism regulating the size of the discharge opening lowers the crushing cone down and widens the discharge open-
Fig. 3. Dents from uncrushable bodies Рис. 3. Вмятины от недробимого тела
ing until the uncrushable material falls out of the crushing zone. During this period of time, the motor, transmission and the main parts of the crusher experience significant overloads as removal of the uncrushable body takes place with the running motor. The pressure between the liner and the uncrushable material increases very fast, and the uncrushable body makes dents in the liner up to the outlet through the discharge opening (Fig. 3).
Dents in the liner from uncrushable materials significantly accelerate wear and tear of the liner and often cause cracking.
Breaking of cone shank
and bevel pinion shaft
This type of damage is associated with the loss of torsional strength of shafts. It is known that the loss of strength can be of two types: the loss of static strength and the loss of fatigue strength [7].
The loss of static strength is caused by overloading when an uncrushable material enters the crushing zone, as is noted above. In this case, the torques applied to the cone crusher shafts can reach or even exceed the critical moments.
The loss of fatigue strength results from prolonged exposure to intense dynamic loads, right down to impacts. In this case, spontaneous failures are prevented by the timely scheduled replacements.
However, in sudden fracture of the cone shank (Fig. 4), the cone failed long before the scheduled replacement. The chemical analysis of the fracture point showed that the quality of material met all requirements. The failure cause was assumed to be the increased intensity of dynamic loads and short-term impact overloads, which resulted in the loss of fatigue strength ahead of the scheduled time.
Current loads can be estimated using the time-capacity variation in operation of the motor (Fig. 5), which is displayed on the operator's monitor in the framework of the real-time motor capacity control during operation of crusher KKD 1500/180 at Stoilensky GOK.
Although the torque in the asynchronous motor is not proportional to the power, the nature of the change in loads of the motor shaft agrees with the nature of the motor capacity variation within a small range of the shaft spin rate.
From the analysis of the curves, the crusher operation can be divided into several stages:
• Idle run — crusher capacity is constant, approx. 60 kW;
• Feed — jump in capacity up to 725 kW (Fig. 5, b) with subsequent power fluctuations;
• Crushing — aperiodic fluctuations of capacity at the level of 400 kW.
Fig. 4. Cone shank fracture Рис. 4. Излом шейки конуса
Fig. 5. Time-capacity profiles of crusher motor in operation for: 1 h (a); 1 minute (b)
Рис. 5. Графики изменения мощности двигателя дробилки: в течение 1 ч работы (а); в течение 1 мин работы (б)
The motor power fluctuations are composed of low frequency and high frequency oscillations. It is found that low frequency fluctuations depend on the feed nonuni-formity, since right after feeding, the amplitude and period of these fluctuations are
maximum. High frequency fluctuations are caused by the process of crushing, and their amplitude depends on the hardness of the feed.
When these fluctuations superimpose, the motor capacity reaches 650 kW.
Fig. 6. Failure of eccentric surface Рис. 6. Разрушенный слой эксцентрика
Given that the crusher motor is designed for a rated power of 400 kW, it can be concluded that the crusher motor is constantly subjected to short-term loads that are 1.825 times the rated load during feeding and up to 1.625 times the load during crushing. At the same time, the revealed dynamic loads affect all components of crushers and reduce their service life, which leads to the loss of fatigue strength.
Damage of babbitt-coated eccentric
This type of failure (Fig. 6) occurs when the lubrication temperature in an assembly rises significantly and the oil film is displaced from the contact area [8]. In this case, particles of the babbitt coat and steel interface are bound together (adhesion) and, as a result, the surface layer suffers dynamic failure.
These phenomena are usually caused by overloading or by a series of intense dynamic loads often associated with passing of an uncrushable material through the crushing zone.
Damage of bevel pinion teeth
During operation of bevel gear, its teeth experience loading and friction. At each tooth, stresses change in time within a zero-to-critical-stress cycle by jumps [8]. The repeated stresses cause fatigue failure of the teeth in the form of breakage and chipping-off. Friction in engagement caus-
Fig. 7. Breakage of pinion teeth Рис. 7. Излом зубьев шестерни
es surface wears and jamming of teeth. Breakage of teeth (Fig. 7) is most often caused by the repeated bending stresses in the teeth, resulting in the loss of fatigue strength and subsequent overloading.
Cracking and failures
in spider arm assembly
Failures in spider arm assembly occur (Fig. 8):
• when coarse ore enters the upper zone of the crushing chamber, which transfers crushing loads to ribs of the spider arm assembly in any possible zone;
• in abrasive wear and tear of the outer surface of the spider arm assembly, when feed ore particles and dust fall in the space between the cone shaft, cone liner nut and
Fig. 8. Failures of spider arm assembly: breakage (a); outside wear (b)
Рис. 8. Разрушения траверзы: излом траверзы (а); износ наружной поверхности траверзы (б)
the lower boss of the upper hanger of the spider arm assembly.
The first type failure is prevented by size control of the feed.
Failure of sliding bearing
The major cause of failure in sliding bearings is overheating as in the case of the babbitt-coated eccentric. Besides, surface
Fig. 9. Scheme of failures and failure causes in cone crusher components
Рис. 9. Схема отказов элементов конусных дробилок и причин их возникновения
of bearings wear out in operation, and the impact of variable loads typical of crusher operation lead to fatigue chipping-off of these surfaces, which requires regular replacement of the bearing shell [9].
Motor failure
Motor can fail when the crusher continuously transfers momentary overloads commonly connected with the entrance of uncrushable bodies in the crushing zone. Most often, this failure type is avoided by installing a more powerful motor, which disagrees with the modern energy saving standards.
Damage of safety element
of drive pin coupler
As a rule, overloads can be prevented using a safety coupling with shear ties capable to transfer high torque. Such couplings are disadvantageous for the necessity to be restored after the action. The couplings act in case of long-term transmission of moment overloads from the crusher to protect thereby the drive. However, there can be so-called "false" actions under high-intensity impact loading, most often during feed of the crushing zone, or as a result of the loss of fatigue strength in the shear ties.
Conclusions
The failure analysis of components of cone crushers shows that there are three types of failures (Fig. 9):
• predictable failures of equal periodicity (liner wear), given persistent quality of liners; prevented by timely replacement during scheduled repairs;
• weakly predictable failures, due to the loss of fatigue strength under dynamic loads; prevented by periodic monitoring of the condition of the crusher components, as well as by reduction in the amplitude of dynamic loads;
• spontaneous failures, either due to overloads, which are most often caused by feed of uncrushable material in the crushing zone, or due to impact loads at the moment of crusher feed.
The first type failures are only prevented by the timely replacement of liners as their wear is conditioned by the crushing process. Therefore, one of the top-priority tasks currently is to increase the time between overhauls through the improved manufacturing quality of liners and by development of new liner forms and materials capable of longer wear resistance [10, 11].
Prevention of the majority of the second and third type failures is achievable with protection of crusher components from jump overloads and dynamic loads using safety gears and elastic elements to reduce the amplitude of dynamic loads during feed and crushing as well as to break connection between the drive and the crushing cone in case of overloads. Elastic elements that protect against dynamic loads are inserted in the safety couplings, but such elements feature low and unadjustable yielding. To this end, the present paper authors suggest equipping the drives of the cone crushers with a safety gear with a hydromechanical actuating mechanism of increased yielding and self-recovery [12, 13].
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ИНФОРМАЦИЯ ОБ АВТОРАХ
Белов Николай Владимирович1 - аспирант, e-mail: [email protected];
начальник цеха технического обслуживания и ремонта
обогатительного оборудования, АО «Стойленский ГОК»,
Бородина Марина Борисовна1 - канд. техн. наук, доцент,
e-mail: [email protected],
Смирнова Оксана Андреевна1 - аспирант,
начальник отдела науки, e-mail: [email protected],
Часовских Андрей Сергеевич1 - студент, e-mail: [email protected],
1 Старооскольский технологический институт им. А.А. Угарова (филиал) НИТУ «МИСиС».
Для контактов: Бородина М.Б., e-mail: [email protected].
INFORMATION ABOUT THE AUTHORS
N.V. Belov1, Graduate Student, e-mail: [email protected]; Head of Processing Equipment Maintenance and Repair, JSC «Stoilensky GOK», Stary Oskol, Russia, M.B. Borodina1, Cand. Sci. (Eng.), Assistant Professor, e-mail: [email protected],
O.A. Smirnova1, Graduate Student, Head of Science Department, e-mail: [email protected],
A.S. Chasovskikh1, Student, e-mail: [email protected], 1 A.A. Ugarov Stary Oskol Technological Institute, National University of Science and Technology «MISiS» branch, 309530, Stary Oskol, Russia. Corresponding author: M.B. Borodina, e-mail: [email protected].
Получена редакцией 10.03.2020; получена после рецензии 08.09.2020; принята к печати 10.02.2021. Received by the editors 10.03.2020; received after the review 08.09.2020; accepted for printing 10.02.2021.
