Evaluation of particulate contaminants

Details Evaluation of particulate contaminants Evaluation of particulate contaminants

1999-10-12

2001-05-15

Williams, Hezron (Department: 2856)

Measuring and testing

Liquid analysis or analysis of the suspension of solids in a...

Content or effect of a constituent of a liquid mixture

C073S863230, C073S061640, C073S864710, C422S082000, C422S105000, C210S340000

Reexamination Certificate

active

06230551

ABSTRACT:

The invention relates to a method of evaluating particulate contaminants and to a contamination monitor.
While many mechanical components appear “clean” they are not, as a result of their production processes, completely clean. Often many of the surfaces of a mechanical component will be covered in particulates of various sizes.
Where, for example, a component is to be used in a fluid flow system, there is the possibility of the fluid picking up such particles and carrying them elsewhere in the system. In certain applications, such as in the field of electronically controlled systems or where close tolerances are a critical factor, the presence of particulate contamination can damage the system.
As a result of this, there is a need to test mechanical components to determine the size and number of particulate contaminants on the component.
It has previously been proposed to collect particulate contamination for evaluation by the following methods. In a first method, the component is filled with clean fluid and then agitated for a set period of time. The fluid is then drained from the component and will contain particulate removed from the component. In a second method, the component is installed in a purpose-built pre-cleaned test rig and fluid circulated through the component for a set period of time. Again, the particulate will be transferred to the fluid.
The particles in the fluids produced by either method are then analysed. A first method of analysis involves using an optical counting microscope to view the particles in the fluid and assess their size and number. This is, however, time-consuming and it is not possible to apply this method to all of the fluid. Accordingly, local variations in particles in the fluid can produce misleading results. The method is also labour intensive.
A second method is to pass the fluid between a light source and a sensing cell and measure with the cell interruption of the light source to count the particles. This, however, can give uncertain results with multiphase fluids where, for example, water droplets in oil are counted as particles; with fluids with entrained air bubbles when the air bubbles can be counted as particles, with opaque fluids and with fluids with high particle concentrations where particles overlap on the light sensor and are counted as one larger particle. In addition, the light source and the sensing cell are mounted in a narrow flow channel and large particles can become lodged in the channel causing downtime.
A third method is gravimetric analysis. This is, however, well known as giving inaccurate results owing co the lack of clarity on particulate size or distribution.
A fourth method is to assess the particles through a microscope with an attached image analysis computer. This method, however, identifies only particle boundary outlines and does not therefore differentiate between overlapping or agglomerated particles and one large particle. Also translucent particles will not be identified.
According to one aspect of the present invention, a method of evaluating particulate contaminants in a fluid may comprise providing a flow of particulate containing fluid through a first screen. The first screen includes apertures of a single predetermined size for filtering particulate contaminants larger than the predetermined size. Further, the method comprises determining when the pressure drop across the first screen reaches a predetermined maximum corresponding to blockage of the first screen. After determination of blockage, a reverse flow of clean fluid is provided through the first screen. The reversed clean fluid with the particulate contaminants from the first screen is flowed through a second screen. The second screen includes apertures of a predetermined size greater than the predetermined size of the apertures of the first screen. The method also comprises providing a flow of the particulate containing fluid through the second screen. The greatest pressure drop during the particulate-containing fluid flow through the second screen is determined. Moreover, the method comprises providing a flow of a clean fluid without the particulate contamination through the first screen. During the clean fluid flow, the pressure drop across the first screen is measured. The method further comprises providing a flow of a clean fluid without the particulate contamination through the second screen. The pressure drop across the second screen is measured during the clean fluid flow. From the pressure drops, the number of particles in the fluid greater than the size of the apertures of the first screen and the number of particles greater than the size of the apertures of the second screen are determined.
According to another aspect of the present invention, a contamination monitor for evaluating particulate contaminants in a fluid may comprise a chamber, a screen, a pump, a pressure sensing system, and a control system. The chamber holds a fluid carrying a particulate contaminant. The screen has apertures of a single predetermined size. The pump is in fluid communication with the screen. The pressure sensing system is coupled to the screen to sense differential pressure across the screen. The control system is coupled to the pump and the pressure sensing system to pulse a flow of fluid across the screen in alternate reverse and forward directions and to determine from the pulsed flow the number of particles in the fluid greater than the predetermined size of the apertures.
According another aspect of the present invention, a method of evaluating particulate contaminants in a fluid may comprise providing a flow of particulate-containing fluid through a screen. The screen includes apertures of a single predetermined size for filtering particulate contaminants larger than the predetermined size. Further, the method comprises determining when the pressure drop across the screen reaches a steady value. The flow is pulsed across the screen in alternate reverse and forward directions. From the pulsed flow, the number of particles in the fluid greater than the size of the apertures is determined.
According to another aspect of the present invention, a method of evaluating particulate contaminants in a fluid may comprise washing an article with a fluid in a washing chamber including removing particulate contaminants from the article via the fluid. The method also comprises stirring the particulate containing fluid in a collection chamber. The method further includes flowing the particulate containing fluid through a screen. The screen includes apertures of a single predetermined size. The number of particles in the fluid greater than the size of the apertures is determined from the flow.
According to another aspect of the present invention, a method of evaluating particulate contaminants in a fluid may comprise flowing a particulate containing fluid through a screen. The screen includes apertures of a single predetermined size. The method also comprises determining from the flow the number of particles in the fluid greater than the size of the apertures. The method further comprises passing the particulate containing fluid through a filter having a pore size smaller than the size of the smallest screen aperture to a reservoir. In addition, the method comprises drawing a washing fluid from the reservoir.
According to another aspect of the present invention, a contamination monitor may comprise a chamber, a screen, at least one pump, a pressure sensing system, and a control system. The chamber holds fluid carrying a particulate contaminant. The screen includes apertures of a single predetermined size. The at least one pump provides a flow of a clean fluid without a particulate contaminant through the screen and provides a flow of the particulate containing fluid from the chamber through the screen. The pressure sensing system is coupled to the screen to generate a first signal corresponding to the pressure drop across the screen during the clean fluid flow and a second signal corresponding to the pressure drop across the screen during the particu

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