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INTRODUCTION
Throughout history, industrial and technological revolutions have provided an important modernization of industry which has been related to maintenance. In this way, new techniques have emerged that have given a new approach to organization and responsibility from within the industry, as well as greater importance to
volumes and the quality of products and services, as well as because of the constant appearance of new technologies quality, safety and environmental aspects, together with a high availability of equipment (Torres y Figueroa, 2010).
Historically, maintenance has evolved over time due to the need of increasing production, mechanization and automation of processes, that is, due to the growing development of the industry in general. Nowadays, industrial maintenance, and in general, all types of maintenance in a modern company, needs to be analyzed as a group of novel techniques and management systems that have direct consequences on the efficiency of production processes as well as on reduction of costs, profitability and competitiveness of the company, quality of the final product or service that is provided, and finally on customer satisfaction (del Castillo et al., 2009; Zambrano et al., 2015; Díaz et al., 2016; Amendola et al., 2017; Consuegra et al., 2017).
In contemporary industry there is a great diversity of possibilities for carrying out adequate maintenance of machines, equipment and facilities and, at the same time, there is a great shortage of financial resources that limit the application of certain techniques. Consequently, the selection of a specific maintenance policy is of a technical-economic nature and the application of mathematical methods and models, together with the progress made in the electronic processing of data, is an invaluable tool available.(Batista et al., 2000).
The maintenance evaluation within an organization allows analyzing the fulfillment of the objectives set, the status of the works and makes it possible to identify the aspects on which it is necessary to work to make this activity more efficient and developing actions for continuous improvement. All this can be achieved with the help of indicators, whose main function is to evaluate the operational behavior of the facilities, systems, equipment, devices and components, allowing the implementation of a maintenance plan aimed at improving said work. (Capote, 2014).
In the particular case of Cuba and specifically in the sphere of maintenance and repair in the industrial sector, maintenance management is carried out based on a single indicator: the technical availability coefficient, calculated at the end of each month through a method of momentary observation, which does not allow knowing the true behavior of the machinery in the real conditions of its exploitation, nor the effectiveness of the maintenance actions (Capote, 2014).
That is why proper maintenance leads to a good execution of the production process in a company or factory, taking into account the way it is carried out, and the factors that intervene in it in a certain machinery. To do that, it is vitally important to know the different maintenance implementation methods, especially in Bayamo Dairy Factory which uses these processes to manufacture its products that are exported from it, such as: ice cream, sweetened fluid milk and cheeses. And all these productions are achieved from agricultural raw materials like milk, soybeans, fruit and vegetable pulps.
This entity has a maintenance department which has the mission of ensuring the correct functioning of the machinery. That is performed through a maintenance plan indicated for each machine according to its technical requirements. This form of maintenance application is not optimal, since this equipment has more than 30 years of operation; therefore, its technical performance and availability are no longer the same. Another technique is required, but it is not applied due to the lack of technical training regarding the knowledge and application of these execution procedures necessary to carry out an adequate maintenance control of the production system equipment. Due to the aforementioned, the present work aimed to assess the quality of technical maintenance applied to the entity's equipment, through the application of world class indices.
MATERIALS AND METHODS
The following investigation was carried out in the maintenance workshop belonging to Bayamo Dairy Factory, located to the north of Bayamo City, on Jimmy Hirzel Avenue, Reparto Siboney, Granma. Its mission is the production and marketing of products derived from milk, soy, fruit and vegetable pulps and polyethylene sheets for food packaging.
Applied Methodology for World-Class Indicators
To carry out the research and assess the quality of maintenance of the equipment of the production system of the referred Basic Enterprise Unit (UEB), the methodology for the determination of world-class indicators referred by Tavares (2008) was used. In it, the main maintenance management indexes at international scale are summarized and it is based on the criteria established by other researchers. In addition, it collects precisely, the applicability of world-class indices from the analytical-mathematical point of view. Due to the complexity of applying this methodology to all the machinery of the factory, it was decided to carry out the study of the compressors of the production system, as they are the most directly linked to the production process. Although it could also be applied to other machinery to evaluate their operation as long as they are of the same type and brand as it is stated in the investigations. From now on, the four compressors to be evaluated are specified, these are identified by their inventory number. The indicators and mathematical equations for their determination are shown straightaway.
Mean Time Between Failures (TMEF):
Relationship between the product of the number of items and their operating times and the total number of failures detected in those items in the observed period.
Where:
● NOIT: |
Number of items. |
● HROP: |
Operation time (hours) |
● NTMC: |
Total number of failures detected in these items. |
This index must be used for items that are repaired after the occurrence of a failure
Average Time to Repair (TMPR): Relationship between the total time of corrective intervention in a set of items with failure and the total number of failures detected in those items, in the observed period.
Where:
● HTMC: |
Total time of corrective intervention in a set of items (hours). |
● NTMC: |
Total number of failures detected in these items, in the observed period. |
Mean Time to Failure (TMPF): Ratio between the total operating time of a set of non-repairable items and the total number of failures detected in these items, in the observed period.
Where:
● HROP: |
Total operating time of a set of non-repairable items (hours). |
● NTMC: |
Total number of failures detected in these items, in the observed period |
This index should be used for items that are substituted after the occurrence of a failure.
Equipment availability (DISP): Ratio between the difference between the number of hours in the period considered (calendar hours) and the number of hours of intervention by maintenance personnel (preventive maintenance by time or by status, corrective maintenance and other services) for each item observed, and the total number of hours in the period considered
Maintenance Cost per Billing (CMFT): Ratio between the total maintenance cost and the company's invoicing in the period considered.
Where:
● CTMN: |
Total accumulated maintenance cost. (CUP) |
● FTEP: |
Billing of the company in the period considered (hours). |
Maintenance Cost by Replacement Value (CMRP): Ratio between the total accumulated cost of maintaining a certain piece of equipment and the purchase value of that same new equipment (replacement value).
RESULTS AND DISCUSSION
Figure 1 shows, by means of a bar graph, the values obtained from the mean time between failures for the compressors analyzed. Of these, the compressors with inventory number 32 759 and 326 005 are those that obtained the highest operating values without the technical failure occurring, with magnitudes of 79.63 h and 82.47 h of mean time between failures, respectively. Researchers such as Mesa et al. (2006); Amendola et al. (2012) & Christensen (2013) refer that the higher the value of this indicator, the greater the reliability and availability of the equipment.
When comparing the values of this indicator with that referred to by Zegarra (2016), it can be said that the result for the four compressors is in the range of hours reported by this researcher (between 60 and 80 hours on average), which confirms the adequate fulfillment of maintenance activities in the observed period. The target values of this indicator will depend on the correct application of the maintenance that can be applied to said equipment.
It should be noted that the compressors evaluated have more than 30 years of operation as average, with continuous work 24 hours a day, except for an unforeseen event or failure which required some technical support. However, the result of this indicator can be classified as acceptable; indicating that the maintenance applied is adequate, although better management will be required to further increase the time of appearance of failures.
In Figure 2, the mean time for repairing (TMPR) for the compressors studied is shown. Of these, the compressor with inventory number 32 759 had the lowest TMPR in the period analyzed with a value of 8,62 h. Christensen (2014) & Zambrano et al. (2015) stated that this indicator should be as low as possible so that the equipment has more time to produce and availability increases.
The results found for this indicator ranged between 8,62 hours and 15,13 hours, higher than those referred by Zegarra, (2016), which establishes that this indicator should range between 3 and 6 hours on average, for maintenance management to be adequate. High values of TMPR indicate that many hours are invested in repairing the machines, such as those reported by compressors with inventory numbers 306 008, 326 005 and 32 477.
Christensen (2013), referred that the TMPR is improved with three characteristic points that are:
It is necessary to point out that, despite those values obtained for the case under study, it does not demonstrate the maintenance management is inadequate or inefficient, since the evaluated equipment has more than 30 years of operation. Consequently, operators must dedicate more time to keep that equipment operating properly.
In Figure 3, it is observed that the equipment with inventory number 306 008 and 32 477, showed a time for the occurrence of the failure greater than 80 h.
The TMPF is determined taking into account that it is calculated for those failures that were presented in the pieces of the equipment and it was not possible to be repaired, and consequently, it was necessary either to redesign or to replace it by a new one. According to Tavares (2008), this indicator is only determined for items that are not repairable after the occurrence of a failure.
It can be seen that the compressors with inventory number 306 008 and 32 477 are those that obtained the highest TMPF with an average value of 84,23 h, a result that confirms the behavior of these equipment in the event of failures, which occur every 3 days considering those that are not repairable, such as those that have been addressed for the calculation of this indicator.
In general, these values behaved above 75 h, a result that can be considered acceptable for the compressors analyzed, which reveals the quality of maintenance applied to this equipment after the change of any of the parts that due to a technical failure that could not be resolved.
In Figure 4, it is observed that the compressors with inventory number 32 759 and 326 005 obtained an availability of 90,23% and 85,05%, respectively, in agreement with that described by Christensen (2006), which refers that the shorter the Time Medium for Repair (TMPR), the greater the availability of an equipment.
Other authors such as Mesa et al. (2006) & Amendola et al. (2012), reported that availability also depends on the Mean Time Between Failures (TMEF), since the higher this is, the reliability and availability of the equipment will be higher, since it will have a higher technical performance and consequently its useful life will be further lengthened.
These values are obtained through the relationship between the TMEF and its sum with the TMPR, and the entire expression multiplied by 100%, thus the technical availability of the compressors for that year can be obtained.
According to Tavares (2008), an equipment availability value that is between 81-90% can be considered acceptable, since it demonstrates the work efficiency under operating conditions, considering the operating time and the failures obtained in the period analyzed.
When observing the values (Figure 4), it can be seen that the compressors with inventory numbers 306 008 and 32 477 were those with the lowest technical availability, but they are still within the ranges reported by this researcher, yielding values of 83,06% and 82, 23% respectively.
In Figure 5, the Maintenance Cost per Billing (CMFT) is shown. Of the compressors under study, the one with inventory number 306 008 yielded a value of 65,83%; which implies an increase in maintenance costs, causing an overdraft in this indicator. The fundamental causes are given by the expenditure of material and financial resources.
However, this indicator in the rest of the equipment analyzed, behaved with values lower than 55% of the costs. This could be less, although in general, it does not exceed 48% of these. For equipment 32 759, 326 005 and 324 477 there was less expenditure or use of resources, as well as in the workforce assigned to carry out maintenance.
It can also be observed that the compressor with inventory number 326 005 presented a cost of 29,32% for this year analyzed, which is favorable, since it is given by the high values of equipment availability and mean time between failures reached in this year by it.
Figure 6 shows the Total Cost of Maintenance by Replacement Value (CTRP). Observing that this indicator in the analyzed compressors remained below 2%.
According to Tavares (2008), this indicator is the relationship between the total accumulated cost of maintaining a certain equipment and the purchase value of that same new equipment.
Taking this fact into account, it is evident that each of these compressors' price in the international market, and the value of the costs accumulated in the maintenance of each one during the year do not reveal a high expense tax in correspondence with its replacement value.
In general, it was possible to observe the indicators' behavior for each of the compressors of Bayamo Dairy Factory production system. Of these, the compressor with inventory number 326 005 was the one with the best technical performance and, consequently, to which adequate maintenance was applied, yielding acceptable values according to those referred by other researchers. The most significant are given by the correct management and application of the maintenance conceived to each one of the equipment in the observed period. It is important to clear out that despite they have more than 30 years of operation and the corresponding maintenance has been carried out for their proper functioning and durability, better performance would be available, if the necessary spare parts, the corresponding supplies and adequate training were offered. Then, a better implementation of maintenance could be carried out in the presence of failures. To achieve this, it is also necessary to take into account the control of the activities applied to each of the machines through the management indicators or world-class indices discussed in this research. That allows better control of the actions and at the time of execution of these, obtaining longer time interval for the presence of faults between one and another, and consequently, a higher availability in the compressors.
CONCLUSIONS
The quality of technical maintenance in the compressors of Bayamo Dairy Factory production system was assessed by calculating and analyzing world-class indicators.
The values of availability and maintenance cost per billing obtained are within the established ranges compared to those reported by other researchers, being these 85,14% and 47,35%, respectively as an average, so, the quality of the maintenance applied to this equipment in Bayamo Dairy Factory during the observed period can be valued as acceptable.
The Mean Time Between Failure (TMEF), Mean Time to Failure (TMPF) and Mean Time to Repair (TMPR) values could be better, if better management time is carried out for the execution of corrective maintenance, and supplies of higher quality were used to repair breakdowns.
Among the equipment analyzed, the compressor with inventory number 326 005 was the one that presented the highest technical performance and, consequently, it was the one that received the best maintenance during the period observed.
