Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2000-07-19
2001-10-09
Beck, Shrive P. (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S294000, C427S430100
Reexamination Certificate
active
06299933
ABSTRACT:
FIELD OF THE INVENTION
The present process and apparatus relate to controlling the extent of impregnation of porous parts during the impregnation thereof. In particular, the present process and apparatus provide for control of the extent of impregnation by measuring the change in effective volume of impregnant during the impregnation process.
BACKGROUND OF THE INVENTION
Impregnation of porous parts is a common technique employed in a variety of industries for a variety of reasons. Stone, brick, ceramic, wood, polymer, aggregate, cermet., and porous metal parts, for example, are commonly impregnated. Commonly, a sealant is impregnated into the part because the porosity is undesirable in the intended end use of the part. In some applications, it is only necessary to seal the pores on the surface of the part. In other applications, thorough impregnation of the part is necessary. Further, in certain applications, it may be possible to over-impregnate a part, so the level of impregnation should be carefully controlled.
For example, separator plates are a component of fuel cells, including solid polymer electrolyte fuel cells. Separator plates are electrically conductive and substantially impermeable to the fluid reactants and/or coolants used in the fuel cell or fuel cell stack. They are commonly made from graphitized carbon, carbon-resin composites, or graphite. The plates are typically impregnated with a resin that assists in imparting the necessary impermeability and mechanical stability. The plates should be thoroughly impregnated with resin.
Expanded graphite sheets, such as the material available from UCAR Carbon Technology Corp. (Danbury, Conn., U.S.A.) under the tradename GRAFOIL, may be used to form separator plates for fuel cells. Expanded graphite sheets are useful in this regard because they are relatively light, flexible and amenable to lowcost manufacturing methods, such as embossing. Separator plates made from expanded graphite sheet may be impregnated with a suitable resin in order to achieve the desired impermeability and mechanical stability discussed above. It is important that such plates be sufficiently impregnated to meet performance requirements. At the same time, it is possible to over-impregnate the plates, resulting in degradation or loss of desired structural and/or functional properties. Accordingly, impregnation process control is an important aspect of separator plate manufacture.
Conventional impregnation process control methods typically rely on a consistent time to sufficiently impregnate a part. Based on such methods, an optimum time can be selected to ensure adequate impregnation without much wasted time or expenditure. However, where relatively subtle process and/or material changes can drastically affect the proper impregnation time necessary to achieve the desired impregnation level, such methods are unsatisfactory. For example, the variability of different grades, lots and batches of expanded graphite sheet, as well as variations in separator plate processing or design, has made it virtually impossible to determine an appropriate impregnation time beforehand for a given lot of separator plates.
Current methods use the impregnation time from the previous batch of plates as the initial time estimate for impregnation of the next batch, taking into account other factors such as plate thickness and density. Since the level of impregnation can only be assessed after the impregnation process is complete, entire batches of parts may have to be scrapped due to incorrect estimates of the impregnation time. This approach is costly in terms of time and materials, and is poorly suited to high-volume production methods.
Accordingly, a method of controlling the impregnation of porous parts that allows the extent of impregnation to be predictably controlled is desirable.
The present process and apparatus address one or more of the problems associated with the prior art impregnation control processes. Specifically, the present process and apparatus allow the extent of impregnation of a porous part to be controlled during the impregnation process.
SUMMARY OF THE INVENTION
A process for impregnating at least one porous part with an impregnant is provided comprising:
(a) immersing at least one porous part in a fixed volume of impregnant;
(b) measuring at least one parameter indicative of the effective volume of impregnant as it impregnates the at least one porous part; and
(c) interrupting impregnation when the at least one measured parameter indicates a desired level of impregnation is achieved.
The at least one measured parameter may comprise the change in effective volume of the impregnant, the rate of change in effective volume of the impregnant, or both. Preferably, the measured parameter is measured continuously. Impregnation may be interrupted when the change in effective volume exceeds a predetermined threshold value and/or when the rate of change in effective volume falls below a predetermined threshold value. The measured parameter may be compared to a reference parameter value and impregnation interrupted when the measured parameter varies from the reference parameter value by less than a predetermined threshold amount. For example, impregnation may be interrupted when the measured parameter indicates that at least 85% of the void volume of the porous part(s) is impregnated, or alternatively, when the measured parameter indicates that at least 95% of the void volume of the porous part(s) is impregnated.
The process may further comprise sending an output signal representative of the at least one measured parameter to a controller. The controller may comprise a display for displaying the at least one measured parameter represented by the output signal and impregnation may be interrupted in response to an output signal from the controller.
The porous part(s) may comprise carbon plates, for example. The carbon plates may be graphite plates, and more specifically, may be expanded graphite plates. The impregnant may comprise a resin, such as a resin selected from the group consisting of phenols, epoxies, melamines, furans and methacrylates.
The porous part(s) may be impregnated at any suitable pressure. For example, the porous part(s) may be impregnated at ambient pressure, at a pressure less than atmospheric pressure, at a pressure greater than atmospheric pressure, or any combination thereof.
An apparatus for impregnating porous parts is also provided, comprising a vessel for holding at least one porous part and a fixed volume of impregnant, and at least one device for measuring the change in effective volume of the impregnant within the vessel. The measuring device may be a series of graduations on a wall of the vessel or a depth gauge, for example. The measuring device may also comprise a level sensor such as linear hall effect sensors, linear encoders, linear variable displacement transducers, and digital probes, for example. The measuring device may also comprise a pressure transducer associated with the interior of the vessel.
The apparatus may further comprise a pump fluidly connected to the vessel for reducing the pressure therein below atmospheric pressure, or for increasing the pressure therein above atmospheric pressure, or both.
The measuring device preferably generates output signals representative of the measured change in effective volume, the measured rate of change in effective volume, or both. The apparatus may further comprise a controller for receiving output signals from at least one measuring device and for displaying the change in effective volume represented by the signals.
REFERENCES:
patent: 4183963 (1980-01-01), Brimelow et al.
patent: 4311735 (1982-01-01), Young
patent: 4384014 (1983-05-01), Young
patent: 4873102 (1989-10-01), Chang et al.
patent: 5019426 (1991-05-01), Noe et al.
patent: 5348774 (1994-09-01), Golecki et al.
patent: 5776372 (1998-07-01), Saito et al.
patent: 5985114 (1999-11-01), Sekhar et al.
patent: 5993892 (1999-11-01), Wasserman et al.
Ballard Power Systems Inc.
Barr Michael
Beck Shrive P.
McAndrews Held & Malloy Ltd.
LandOfFree
Control process for impregnating porous parts and apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control process for impregnating porous parts and apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control process for impregnating porous parts and apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2577606