Cleanliness and Wear Monitoring by Modern Particle Measurement Technology

In fluid power systems, the oil is regarded as a structural element that satisfies the most diverse tasks. It transmits power, takes over the lubrication, the heat balance and transports dirt to the filters. Although there are many causes for failure in fluid power systems, besides mechanical fatigue or overload of individual components especially the condition of the oil comes into focus. Here, in particular, particles are the major cause of wear and damage to components.

The undesired particles can enter the system from the outside, e.g. by ventilators or seals, or they are generated by wear in the system itself. Consequences of particle contamination are increased wear, failure of components and reduction in system performance and lifetime. The particle contamination of the oil thus causes high costs for the owner, this is why different high-quality filters should be used to keep fluid power systems clean.

To further reduce costs, there is moreover a great interest to detect increased wear at an early stage and to prevent damage or standstill. For this purpose, there are different sensors and instruments for particle measurement available, enabling an effective and inexpensive monitoring of almost all applications.

In addition to the wear monitoring, a growing field of application for the particle measurement is the control of the cleaning or rinsing processes. Here, more and more often it must be proved that the rinsed parts or systems satisfy the specified purity requirement. Producers and users of cleaning equipment take account of this demand by integrating particle measurement technology in their facilities, allowing them to document each cleaning process.

Manufacturers can monitor the proper use and service of their equipment by regular measurement of particles and thus reduce warranty costs. From the information obtained, optimization potentials in the system design may be identified in reverse, in order to improve the own products. Furthermore, the use of particle measurement technology has proven itself as a development tool for the evaluation of wear on pumps, gears, bearings etc. Here, both, the necessary purity of the test medium, as well as any wear of the component itself, are measured.

When considering which method is best suited for monitoring, economic considerations are in the foreground. Here not only the costs of analysis of the single sample play a role, but also how high the risk of failure and the costs for any damage or standstill are.

Particle Measurement
Automatic particle sensors indicate the best price-performance ratio, allowing measurement of the size and number of particles in real time online. Alternative manual procedures such as microscopy or gravimetry are complex, error-prone and inefficient, compared to online measuring.

The advantages of online measurement to conventional laboratory analysis do not only lie in the simpler handling and the lower total costs, but especially in the gapless measurement. The measured data do not reflect an arbitrary snapshot but detect the continuous change. Thus, a state-dependent predictive maintenance can be realized.

Furthermore, the accuracy of the oil analysis itself is largely determined by the care taken in the sampling and analysis. Particularly with regard to the particle concentration, improper sampling and analysis can lead to a significant distortion of the measurement results. Automatic particle measuring instruments guarantee optimum repeatability and only thereby the comparability of measurement results.

Optical Particle Measurement
As standard for online particle measurement, the optical method by light blockage principle according to ISO 11500 has prevailed, because it is inexpensive and very reliable.

Here, the particles to be counted are separately optically measured in a capillary. If there are no particles in the measurement cell, the light shines unhindered on the photodiode. If a particle passes the measurement cell, the light beam is blocked, whereby a shadow is generated on the opposite photodiode. The size of the shadow is proportional to the size of the particle and thus enables to characterize the particles.

Subsequently, the measured number of particles is related to the measurement volume and reported as concentration. This allows a representation according to different standards, which can be selected in the measuring instrument. In addition to the common standard ISO 4406:1999, the devices of ARGO-HYTOS also offer SAE AS 4059, GOST 17216 and NAS 1638.

Particle Counters
Particle Counters are particularly suitable for extremely accurate measurement of oil contamination in the laboratory or in the field. With the OPCount, ARGO-HYTOS offers a Particle Counter of the latest generation, which has been designed for use in hydraulic machines. The integrated volumetric particle measuring cell guarantees, in conjunction with first-class components, that each particle flowing though the sensor is accurately measured.

The internal pump allows online, bottle and tank measurements. The device can thereby intuitively be operated via a touch display and convenient measurement profiles. Measuring data and additional information about the sample, such as e.g. temperature, viscosity or oil type can be stored and printed directly. Any accessories required for measurement can be neatly stowed away at the device, which greatly facilitates handling.

The Particle Counter OPCount is often used for routine monitoring, for quality control or failure analysis. It enables the creation of databases, with the help of which the history of the oil of a machine can be understood. From this, valuable information on the cleanliness and condition of the equipment can be obtained.

Optionally, it is also possible to connect an ARGO-HYTOS Condition Sensor from the LubCos range to the OPCount. This allows the inclusion of other parameters such as temperature, humidity and oil quality.

Particle Monitor
For systems where the particle measurement is to take place not only automatically but also durably, a device is needed that can permanently be installed. Here, compact and robust Particle Monitors are recommended that can easily be integrated into a hydraulic system.

The demands to a stationary or mobile measurement can be high. Amongst others, attention has to be drawn to high pressures and temperatures, dirt, humidity and vibrations. Therefore, a robust design of the measurement equipment is essential to its long-term operation. That is why all components, such as e.g. light source, detector or housing, have to meet high technical requirements. With an IP67 protection class and corresponding shock and noise immunity, the ARGO-HYTOS Particle Monitor OPCom is also suitable for demanding applications.

A proven area of application for the online particle measurement is the monitoring of oil cleanliness in heavily loaded industrial applications such as presses or injection molding machines. The figure below shows an example of a particle measurement during the cleaning of an injection molding machine. Here, the machine was cleaned with a mobile off-line filter unit and the particle concentration was recorded.

Inductive Particle Measurement
For selective detection of ferromagnetic wear particles, inductively measuring metal particle detectors are used. A specifically for gears designed economical alternative for conventional metal particle detectors, is the Wear Sensor OPCom FerroS.

The Wear Sensor OPCom FerroS works on the principle of a magnetic plug and accumulates ferromagnetic particles by means of a permanent magnet. A coil in the sensor head detects the accumulated particles and generates a measurement signal proportional to the accumulated amount. For continuous measurement, the sensor can be cleaned automatically.

The proven measuring principle enables easy integration of the sensor directly in the system. In contrast to comparable sensors, no flow must be generated.

Summary
The use of modern particle measurement technology makes new service and maintenance concepts possible by which oil change intervals can be extended, problems can early be identified and downtime can be reduced. Today’s sensors detect changes early and make it possible to detect wear and damage in time. The ease of use and the high added value therefore make particle sensors a proven means for reducing operating costs of machinery and equipment.

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