Scheduling Preventive Maintenance to Determine Maintenance Actions on Screw Press Machine

PT. PAS is a company engaged in the manufacturing industry, is a company that manages palm oil into Crude Palm Oil (CPO) and Palm Kernel (PK) with a capacity of 30 tons/hour. The method used in this study is Reliability Centered Maintenance (RCM). This method can determine the actions of preventive maintenance activities on each component of the screw press machine. This study aims to provide proposals for scheduling preventative Maintenance of screw press machines using the Reliability Centered Maintenance (RCM) approach and determine appropriate maintenance actions in damage prevention. Based on the results of the research conducted, it can be concluded that in the Reliability Centered Maintenance (RCM) approach, it is known that five types of damage are a priority for repair. The types of damage included in the repair priority are worm screws, extension shafts, bearings, press cages, and oil seals. The proposed maintenance time for each critical component is a worm screw component maintenance time interval of 307.84 hours, and change-over schedules every 2035.3 hours. Component extension shaft maintenance time interval 279.5 hours, changeover schedule every 1824.5 hours. Bearing components have a maintenance time interval of 300.2 hours and a changeover schedule of every 1492.5 hours. Oil seal components maintenance time interval 286.1 hours, changeover schedule every 2769.9 hours. Press cage components maintenance time interval 250.72 hours, changeover schedule every 3277.8 hours. Actions are taken in the form of direct prevention of the source of component damage based on the time or age of the component.


INTRODUCTION
The machine is a tool with energy conversion to help facilitate human work [1]. The device must be adequately maintained to keep the production process running smoothly according to company expectations. Machine maintenance systems are generally divided into two, namely, Corrective Maintenance and Preventive Maintenance [2][3] [3]. Corrective Maintenance is a maintenance activity carried out after the component is damaged or breakdown, while Preventive Maintenance is carried out before the part is impaired [4]. The impact of periodic machine maintenance includes not achieving production targets, losing production time, high repair costs, and low productivity [5]. In addition, good Maintenance can extend the machine's life and prevent damage that can cause some losses [6].
The research was conducted at PT. PAS at the press station is a company engaged in the manufacturing industry, one of the palm oil processing companies. Found problems that occurred PT. PAS is the frequent occurrence of damage to the machine that causes the production process to stop. Damage to the production machine is caused because machine maintenance scheduling is not applied regularly [7]. At the press station, there are several machines: fruit elevator machines, cake breaker conveyor machines, digester machines, screw press machines, vibrating screen machines, and others [8].
One of the machines at the press station that most often suffered damage was the screw press machine. Some of the causes why the screw press machine becomes damaged, namely: the gearbox inserts rough objects such as iron chips with a diameter exceeding the size of the screw, worn bolt heads, the installation of the gearbox shaft and worm screw shaft is not suitable so that it can cause shaft breakage, and operator negligence can also cause damage to the engine For example, when the engine has vibrated violently, it can be ascertained that the engine has been damaged and the operator still forces the machine work. Damage due to interference with the Screw Press unit includes leakage in the seal, damage to the worm screw, wear on bearings, damage to the drive shaft, damage to the press cage, and short drive shaft screw press. The purpose of this study is to propose preventive maintenance scheduling for screw press machines and determine appropriate maintenance actions to prevent damage.
The method used in this study, Reliability Centered Maintenance (RCM), is a logical engineering process for determining maintenance tasks that will ensure a reliable system design with specific operating conditions in a typical working environment [9] [10]. For this reason, proper maintenance scheduling planning is carried out. Therefore, this researcher carried out machine maintenance system planning using the Reliability Centered Maintenance (RCM) method, and this method can determine the preventive maintenance activities on each component of the screw press machine [11].

METHOD Data Collection Primary Data
Primary data include production amount, machine maintenance system, causes of machine failure, frequency of damage, engine operating hours, last year's engine downtime data, engine repair time data, and engine change interval data [ 9] [10] [13]. c. Task Selection It is done to determine the policies that can be applied (practical) and select the most efficient task for each failure mode.

Preventive Maintenance Scheduling Planning.
Maintenance scheduling planning is usually done at planned time intervals. The level of equipment or machine and load conditions determine this interval distance. Preventive Maintenance can help extend engine life (up to 3-4 times) and reduce unexpected damage. The RCM (Reliability Centered Maintenance) method performs interval policy and machine maintenance activities. This schedule keeps the preventive maintenance program organized and neat and does not interfere with the production process or other activities. 3. Proposed Maintenance System Improvement.
It is the proper maintenance system improvement plan to be implemented by the company from the research results. The data processing flow diagram in this study is shown in Figure 1.

Failure Mode Effect Analysis (FMEA)
FMEA determines consequences and decides what to do to anticipate, prevent, detect, or improve them. The FMEA results of the Screw Press Machine are shown in Table 1.

Logic Tree Analysis (LTA)
Logic Tree Analysis (LTA) is a qualitative measurement for classifying failure modes. Determine LTA priority in the following way: Evident, that is, does the operator know there has been a disturbance in the system under normal conditions? Safety, that is, does this damage mode cause safety problems? The outage, i.e., does this damage mode result in all or part of the machine stopping? Category, namely the categorization obtained after answering the questions asked. The arrangement for selecting actions for critical components can be shown in Figure 2.  Table 2.

Task Selection
Action selection is the final stage of the RCM process. A list of effective actions from each damage mode is created. The Screw Press, Machine Selection Task, is shown in the table3   The Probability Density Function (PDF) closest to the downward shifting line is the most appropriate to the data, and it can be said that the data has followed that distribution pattern. To see the corresponding distribution can use the information from the text output, which can be seen in Table 4.

Mean Time to Failure (MTTF) and Mean Time to Repair (MTTR)
Mean Time to Failure (MTTF) is the average time of component damage used only on frequently damaged components and must be replaced with new or good components. At the same time, the Mean Time to Repair (MTTR) is the average time to repair these engine components. The following is the Mean Time to Failure (MTTF) and Mean Time to Repair (MTTR) from the critical component data of the Screw press machine.
The following Mean Time To Failure (MTTF) of critical component data of the Screw press machine through output calculations from easyfit 5.6 professional software is shown in Figure 8 to Figure 12.

Determination of treatment time intervals
The determination of the maintenance time interval is aimed at finding out the optimal Time for the Maintenance of components, the calculation of which is as follows:  Table 5.

Preventive Maintenance
To avoid downtime on the machine, the proposal is in the form of preventive maintenance component maintenance using the Average Time To Failure as the maintenance schedule. At the same time, the Maintenance of components with the proposed actions is shown in Table 6.  [31] research, optimal inspection frequency is two times in one month and availability of 98.87%. There are two results of suitable maintenance activities: time-directed life-renewal task and time-directed life-renewal task & Failure finding task. The Mean Time to Failure (MTTF) for bearing component damage is 1492.5 hours. And the maintenance time interval for bearing components is every 300.2 hours. Preventive Maintenance of bearing components can be carried out by replacing bearings regularly according to a schedule and not exceeding the service life of the components. These results are reinforced by [32] research results, namely maintenance time intervals and optimal replacement of Spring Carbon Brush components on Callender machines that have a value of the highest reliability is 85% and occur in 35 days. The most optimal replacement time interval is 18 days, and 16 component repairs occur in 1 year. • Savings on downtime and costs incurred when carrying out preventive Maintenance for 35 days with 16 treatments of Rp. 2,880,000,-. Compared to before using the Age Replacement method, the company paid a fee of Rp. 4,590,000

CONCLUSION
Five types of damage are priority repairs. The types of damage included in the repair priori are worm screws, extension shafts, bearings, press cages, and oil seals. The