Maritime University of Szczecin
Akademia Morska w Szczecinie
2011, 27(99) z. 1 pp. 112–117 2011, 27(99) z. 1 s. 112–117
The utilisation of non-contact temperature measurements
in technical diagnostics of belt conveyors
Zastosowanie bezkontaktowego pomiaru temperatury
w diagnostyce przenośników taśmowych
Vlastimil Moni
1, František Helebrant
21 VÚHU, a.s. Most
Instytut Badawczy Węgla Brunatnego SA Most 434 37 Most, Budovatelů 2830, e-mail: moni@vuhu.cz 2 VŠB – TU Ostrava
Wyższa Szkoła Górnicza – Techniczny Uniwersytet Ostrava
708 33 Ostrava-Poruba, 17.listopadu 15, e-mail: frantisek.helebrant@vsb.cz
Key words: belt conveyor, technical diagnostics, thermography, thermovisual measurements Abstract
The article deals with examples of thermography use (thermovisual measurements) to find out the technical state of belt conveyors and their equipment in open-pit mines. The measurements themselves are part of the grant project MPO FR-T11/537 “The Complex Diagnostic System for Belt Transportation”, basic output of which is a prototype of a diagnostic system on a model belt conveyor and prepared, certified and diagnostic services. All measurements are and will be verified as in situ measurements.
Słowa kluczowe: przenośnik taśmowy, diagnostyka techniczna, termografia, pomiary termowizyjne Abstrakt
W artykule przedstawiono przykład zastosowania termografii (pomiarów termowizyjnych) do oceny stanu technicznego przenośników taśmowych w kopalni węgla brunatnego. Pomiary zostały wykonane w ramach grantu zleconego przez Ministerstwo Przemysłu Czeskiej Republiki FR-TI1/537 pt. „Kompleksowy system diagnostyczny do przenośników taśmowych”, którego głównym celem jest stworzenie prototypowego syste-mu diagnostycznego na modelowym przenośniku taśmowym oraz przygotowanie certyfikatu dla usług dia-gnostycznych. Wszystkie pomiary są i będą weryfikowane w warunkach rzeczywistych.
Introduction to issue
Temperature contactless measurement has found its application in many fields. First, these are fields which can be called classical where everyone can imagine the need of the temperature measurement, e.g. non-destructive searching for thermo-techno-logical failures in building skins, quality check of thermal insulation, or surface heating are parts of the category. This measuring method is now often applied in less traditional activities like mining machines and devices diagnostics, observing and in-time detection of self-ignition of coal, tempera-ture measurement of a coal combustion process in
high temperature ovens, metallurgy process map-ping, and mining area aerial photo survey [1].
Physical methods, especially those using tem-perature changes, have started being used in larger scale at technological diagnostics in brown coal quarries in recent years. The dependency of the heating increase tendency was also very often used in past as one of fundamental physical indicators. The available technology enabled a direct – contact measurement by means of thermometers and ther-mistors with all disadvantages connected with this way.
A principal reverse of the possibilities of a wide use of the contactless method of temperature
change observation occurred after development of modern technology of temperature measurement.
A thermovision device measures and displays infrared radiation emitted by an object. The fact, that the radiation is a function of an object surface temperature, enables a camera to calculate and dis-play the temperature [2].
New thermovision devices (Fig. 1) can create more detailed temperature picture by means of an embedded display system, and temperature quali-ties of a measured object are described through the picture. Particular isothermal areas are diffe-rentiated by colour in a set palette which can be changed. A picture of the read object can be recorded on an attached recording device or can be saved as a picture (thermogramme) in a 14 bit dynamic range in a memory medium. All data on measurement conditions needed for thermo-grammes evaluation are automatically recorded by the camera. Object parameters mentioned above must be set in the camera e.g. emissivity, ambient temperature, relative humidity, and a distance between the camera and the object [3].
Thermogrammes made by a thermovision ca-mera have a scale on their left margin, which scale divides a set range of measured temperatures into
isothermal intervals in energy levels given in “iso-thermal units”. An associated photography can be taken by a digital camera for each thermogramme. Modern large computer software (e.g. Therma-CAMTM Reporter 2000 Professional) is used for
further processing and analysis of pseudo-colour thermogrammes (pictures of an observed object where each colour corresponds with a defined tem-perature range) uploaded together with photographs to a PC [4].
Measurement of current connections of electric equipment of driving stations of long distance conveyors
The diagnostics of electric devices by means of the thermovision is based on detecting places with increased transition resistance or decreased insula-tion resistance, which result in a temperature in-crease. The temperature increase changes a colour tone of the picture on the camera display at the thermovision measurement. The thermal diagnos-tics of electric devices of HV distribution substa-tions made by means of thermovision has been proven a very efficient way of fault detection (Fig. 2). Computer aided processing of results
Fig. 2. Detected fault of a current connection on a belt conveyor [5] Rys. 2. Wykryty błąd bieżącego połączenia na przenośniku taśmowym [5]
27,6 °C 63,8 °C 30 40 50 60 LI01 Fault (SP01) SP02 Fig. 1. Advanced thermovision devices [2]
enables an objective evaluation of the device’s technical state and present checks of electricity distribution substations showed eligibility of those. Detected faults can be corrected at next planned stop or thez can be observed when it is not possible to mend them and when they can cause a failure of the device [5].
A methodology of measurement of current con-nection of electricity distribution stations of drives of belt conveyor long distance transport was de-signed according to results of long term measure-ment of the current connections and contacts which uses the thermovision technology, as well as assessment of detected faults, and forms were designed for recording the obtained results [6].
Diagnostics of rotating parts of belt conveyors
The system of observing and maintaining of conveyor transport is carried out according to inten-tions of mining companies’ internal regulainten-tions which respect state legislation (standard and decrees). Actual state of long distance belt con-veyor transport can be objectively valuated based on non-dismounting diagnostics of drive bearing and/or tooth wheels of gear boxes. The size of repa-rations or reconditions at regularly annual revisions of technology complexes is determined from the actual state found out such way at driving stations of belt conveyors [7].
Smooth rollers of the upper branch of a con-veyor belt and disk rollers of the lower branch of a conveyor belt are an important element influenc-ing total operational reliability of a technological complex. The technical state of the rollers influ-ences tear of a conveyor belt and total main and secondary resistance by a global fiction coefficient f change from the ideal 0.016 value to the 0.03 value for a limiting state.
Stopping rotation of a roller after its seizing is another threat on coal belt lines and coal dust can self-ignite from a temperature increase by steel coat friction with rubber belt surface causing thus an emergency state mostly at a random conveyor stop [7].
This short analysis implies that the technical state of belt conveyor roller can have a fundamental influence under certain conditions on operational safety, power consumption, and total economy of technological complex operating.
At present, technological state of rollers is checked visually and by a manual rotation by main-tenance workers at stopped conveyor before start-ing a revision. This way is time consumstart-ing and can be easily influenced by a human factor – experi-ence, carefulness, time available, etc.
Due to rollers position in their bearings, an incorrect function of the bearing increases a friction coefficient which implies a surface temperature increase near the bearings (roller faces) (Fig. 3).
Fig. 3. Belt conveyor rollers [7]
Rys. 3. Rolki przenośnika taśmowego [7]
16,4 °C 22,0 °C 18 20 22 17,3 °C 23,5 °C 18 20 22
This incorrect function of roller bearings can be continuously observed by a thermovision device along all belt conveyors at operation. This was repeatedly proved by experimental measurements in the past [8].
Similar situation concerns drums of driving and return stations of belt conveyors. Technical state of the drums is much influential on operational reli-ability of belt conveyors and it is one of key design elements. Rolling bearings of the drums have
Fig. 4. Tension drum of a belt conveyor [7]
Rys. 4. Bęben napinający przenośnika taśmowego [7]
Fig. 5. Thermographic measurement of conveyor belt [7] Rys. 5. Pomiar termowizyjny taśmy przenośnika [7]
10,8 °C 37,6 °C 15 20 25 30 35 SP01 SP02 LI01 SP03 SP04 SP05 0,3°C 27,6 °C 5 10 15 20 25 SP01 SP02 LI01 SP03 SP04 SP05 4,7°C 78,4 °C 20 40 60 SP01 1,9°C 15,9 °C 5 10 15 SP01 SP02 LI01 SP03 SP04 SP05
a great influence on the operational reliability. It means, that diagnosability of the rolling bearings must be dealt with either independently or as a part of a driving unit of the belt conveyor. An example of a surface temperature anomaly measured on one side of the tension drum can be seen in figure 4 [7].
An example of uneven belt load and lateral deviation of a belt detected by a thermovision device is shown for completeness (Fig. 5). These matters have an influence on belt upper and lower coat layer wear and thus on the life time of con-veyor belt as well.
Driving motors and gearboxes
Thermovision measurement of surface tempera-ture of driving motors and installed gearboxes
of long distance belt transport enables to determine a surface temperature of drive units and to detect eventual faults of these key devices (Fig. 6).
Operational surface temperature is calculated from percentage representation (histogram) of tem-peratures of selected area of a thermogramme con-taining whole area of interest of the measured mo-tor or gear box. The determined temperature can be compared to the interval of usual temperatures of these devices. Eventual anomalies can be gathered from colour and contrast distribution [5].
Conclusions
By including the non-contact temperature mea-surement by thermovision device into technological diagnostics of belt conveyors a way has been found
Fig. 6. Thermal measurement of a drive and a gearbox [5] Rys. 6. Pomiar termograficzny silnika i skrzynia biegów [5]
Fig. 7. Belt conveyor operational temperature [7] Rys. 7. Temperatura pracy przenośnika taśmowego [7]
21,5 °C 55,9 °C 30 40 50 LI01 (SP01) SP02 AR01 5 1 0 1 5 3 5 4 0 4 5 5 0 5 5 IR 0 1 AR 0 1 °C Th r e s h o ld : 0 .0 °C , Ab o v e : 1 0 0 ,0 0 %,... 20,7 °C 46,0 °C 25 30 35 40 45 LI01 (SP01) SP02 AR01 25 30 35 40 45 li01 Lin e Min Ma x ... li01 22,5°C 47,0°C °C IR 0 1 20,0 °C 35,9 °C 20 25 30 35 Tření pásu o OK – 148,7 °C Tření pásu o OK – 66,5 °C Ohřátí horního válečku – 39,8 °C
Ohřátí dolních válečků – 48,6 °C Teplota povrchu OK – 17,9 °C
Friction of the mesh waist – 148.7C Upper heat roller – 39.8C
Lower heat roller – 48.6 C Friction of the mesh waist – 66.5C Temperature of the surface mesh – 17.9C
how to get information on operational temperatures of structural parts and how to use this information for determining actual technological state of these parts. Processing thermogrammes made at regular operation of long distance belt transport eventual thermal anomalies can be detected which mean a fault of the operated device. This can be seen at figure 7 which shows operation temperature levels in a part of a belt conveyor. Looking at it, a remark arises “what all can happen at a sudden stop”. The picture shows unambiguously an operational tem-perature of rotating idlers, i.e. we have knowledge of a temperature which lubrication stuff of the roll-ers must stand, etc.
Applications of the results of non-contact mea-surement of surface temperatures of devices and parts of belt conveyors have proven that a ther-movision apparatus with no doubt belongs to that measuring temperature by means of which the actual status of electricity distribution stations, belt conveyors driving stations, technical state of all rotating parts and drives can be observed.
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This contribution originated under support of the project MPO FR-TI1/537 “Complex diagnostic system for belt transport”.
Recenzent: dr hab. inż. Witold Biały, prof. PŚl Politechnika Śląska
