Eren ALKAN Service Manager - Yemser Makine Predictive maintenance practices are performed to ensure that the equipment, machine or systems fulfill the functions expected of them at the desired level. These methods help to ensure that all equipment in the enterprises operates optimally and thus; • Cost of the machinery in enterprises decreases, • Production becomes more efficient, • Profitability increases.

METHOD AND COST OF MAINTENANCE An integrated, proactive maintenance planning strategy begins with identifying the current situation of value and maintenance management of the enterprise.

Today, maintenance costs are high. Maintenance costs can be listed as follows; • 65% corrective maintenance • 30% preventive maintenance, 60% of it is unnecessary • 5% predictive maintenance MAINTENANCE SCHEDULE We can examine the maintenance schedule in two main groups as “identifying the current situation" and “determining realistic targets". When realistic targets are determined, attention should be paid to proactive maintenance, unplanned downtimes, production volume, labor costs and profit margins. When the maintenance schedule is being prepared, a unique solution is created depending on the needs of each enterprise. It is necessary to eliminate the factors that have a negative effect on the enterprise and to apply the proactive maintenance method. However, it is necessary to establish an appropriate situation monitoring method with the experts. Sharing of business culture and achievements and improvement and development of processes are among the most important tailor-made solutions.

We can study proactive maintenance under 4 headings: • Predictive maintenance • Condition monitoring • Oil analysis • Machine operating deflection shape analysis (ODS)

VIBRATION ANALYSIS Vibration is the reaction that the parts of the machine give to the forces coming in and out. When performing vibration analysis, the frequency and amplitude (magnitude) are checked. Thanks to this analysis, problems such as imbalance, axial misalignment, bearing damage, mechanical looseness, lubrication, resonance, electric motor malfunctions, gear damage, hydraulic flow problems can be detected. However, before analyzing the vibration, it is absolutely necessary to learn about the machine's previous situation. Moreover, it is necessary to know what kind of maintenance is done to the machine and what has changed before the vibration analysis. When performing vibration analysis; At the 1st STAGE, the problem should be defined. To do this, firstly a database about the machines should be created and possible causes of excessive vibration should be identified. Following the trend of increase in vibration, the frequency of damage to rotating equipment (bearings, gears, couplings, seal, etc.) should be monitored and the damage status of the chassis, connections, and assembled equipment should be identified.

At the 2nd STAGE, machine details such as machine speeds (rpm), types of bearings, number of pump-fan blades, number of teeth in gears, coupling types, critical speed / natural frequency of the machine and past sources of vibration are required to be identified.

At the 3rd STAGE, particularly loose or missing bolts should be checked and, it should be observed whether there is any crack in the chassis, basis, and welds. In addition, sealing components, abrasions on the belt, excessive and established corrosion should be kept under control and visual checks should be completed while running at low speeds.

At the 4th STAGE, attention should be paid to the control of suction and discharge lines in subsequently added pumps. The externally mounted equipment should be checked, the harmony of assembled equipment should be observed and soft check for the machine frame.

In order to be able to collect high-quality and accurate data, the measuring points must be clean and machine point definitions must be accurate and continuous. Parameters at the measurement stage must be calculated well, and sensor selection should be appropriate. The measuring staff should be competent in the measurement techniques and importance should be placed on the appropriate use of the probe and the instrument.

Before starting the measurement, the measurement parameters, the optimum frequency range (Fmax), the alarm levels (Total and Bands), the resolution setting and finally the average number of measurements must be clearly defined.

Measurement Locations & Points When measuring locations and points are selected, the concept “SAFETY FIRST" should be taken as a basis before and during the measurement. Moreover, measurements should be taken as close to the horizontal and vertical axes as possible, and the axial measurements should be parallel to the shaft. Features, LOCATIONS OF BEARINGS AND SEALS SHOULD NOT BE CONFOUNDED, the measurement should not be done on protection elements such as covers etc. Care must be taken to use the correct machine name and numbering system and a common language that will not change. The numbering must follow a sequence from the rear of the motor to the drive side so that the correct letters indicating the measurement directions can be used in the correct order. For example A-Axial, H-Horizontal, V-Vertical Identifying Vibration Limits The most effective factor when determining the vibration limits is the previous measurement experience. In addition, the manufacturer's recommendations (Warranty) must not be ignored. Vibration values and overall alarm charts may be available on the manufacturer's machine cards. These limits can be established by comparing similar equipment and by monitoring the vibration levels that occur during long periods of time.

General machine failure frequencies are divided as follows; • 1xRPM – Imbalance • 2xRPM – Axial misalignment and looseness • Line Frequency • Blade or Channel Crossover Frequency • Gear Frequency • Bearing Failure Frequency

FAST FOURIER TRANSFORMATION ANALYSIS Each part of the machine has its own signal-frequency. For example materials such as every gear, bearing, shaft, rotor, stator and bearings in electric motor; spindle, bearings and fan blades on the fan, etc. have unique signals and frequency.

When we monitor the values of the vibrations, we can observe that values gradually increase over time in case of a problem. The reason for this increase may be that wear or corrosion occurring in rotating equipment (bearing, coupling, gear, etc.) affecting fan blades and balance. In addition to this, the effect of the deformation of the chassis to the axial setting, difficulties in flows due to the clogging of the filters, and besides worsening of lubrication may be among the factors.

Part replacements and some modifications (chassis, connections, foundation, etc.) with a change in machine speed and active load may cause the vibration to unexpectedly increase.

Frequency Frequency, in brief, is the measurement of the number of repetitive vibrations in a specific period. It gives information about the level of vibration. It is converted with 50 Hz and measured in Hz / CPM. CPM is directly related to RPM.

Speed RMS value is usually expressed in mm / sec in the metric scale. Vibration speed unit is directly related to material fatigue. Because the sooner a machine leans the sooner the material is fatigue.

Acceleration Large stresses at high frequencies will cause damage to the bearing due to oil film rupture. Stress or force is directly proportional to acceleration. Unit of peak to peak is g. It is suitable especially for frequencies over 120 kCPM.

Imbalance Operational conditions such as temperature, pressure, flow, etc. affect the balance. Imbalance situation should be corrected under normal operating conditions. We need to pay attention to the change in the pitch and the angle on the fan blades because this change in pitch and angle will create "Aerodynamic imbalance". Balance defect takes an important place among mechanical problems. The reason for its occurrence is that the geometric center line and the center mass line of the shaft do not overlap each other.

Axial Misalignment The Axis Misalignment is THE MOST IMPORTANT PROBLEM that we encounter. Operating temperature, defects in the chassis and foundation have a direct effect on maladjustment. Axial misalignment constitutes about 50% of rotating equipment failures. At the same time, it increases energy consumption.

There are 3 types of axial misalignments. These are: • Combined (the most common one) • Angular • Parallel or offset

Parallel axial misalignment; It has a spectrum similar to angular misalignment vibrations, but the phase difference creates vibrations in the high radial direction up to 180 ° on both sides of the coupling. Angular axial misalignment; angular misalignment can be identified with vibration in the high axial direction and 180 ° phase difference on both sides of the coupling. Vibration symptoms are similar to angular misalignment. Elimination of axis misalignment and imbalance situation will not solve the problem. The phase angle and the shaft will have twist movement towards down, right and left.

BEARING FAILURES Bearing failures occur at high frequencies and they are identified with acceleration measurement. If the Fmax is kept in a wide range, we can see that it may be on the spectrum seen in the high-frequency region. We can study bearing failures over 4 stages. At the 4th Stage, the bearing failure frequencies do not occur and it is replaced with general vibration distributed to the ground. 1XRPM will be seen as active again as it goes towards the end. The high-frequency noise amplitude is reduced but the gE values are still at high levels.

At the 3rd Stage, bearing failure frequencies and harmonics are observed. Many harmonics will be observed along with the sidebands due to abrasion and HFD will continue to increase from 0.5 to 1.0 gE.

At the 2nd Stage, failure initialization is observed near the bearing failure frequencies and these frequencies occur at a range of 30k-120k CPM. At the end of the 2nd stage, sideband frequencies begin to appear below or above the natural frequency (HFD example 0.25-0.50gE).

At the 1st Stage, the bearing will become unusable.