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Ceramic Washers

10/11/2013 5:20 PM

I just bought a ceramic washer meant to insulate a high temperature component that will be bolted to a heat sink. The vendors catalog says that the piece is not rated for hardness. The bolt will end up being torqued quite strong, I don't exactly know how much yet. I am confident that the washer will hold up but I was wondering if anyone has had any experience using them and if they break easily.

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#1

Re: Ceramic Washers

10/11/2013 5:41 PM

a call to their 1-800 number will clear up the mystery in a jiffy

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#2

Re: Ceramic Washers

10/11/2013 9:38 PM

Let me see if I understand you. You bought a ceramic washer with an unknown hardness to bolt to a heat sink. You do not identify the composition of this ceramic washer. You mention that the bolt that will compress this washer will be torqued to the highly imprecise setting of "quite strong" but you have no information on the temperatures the heat sink is anticipated to experience. You ask us if we have any experience with using them.

Yes. I have experience with ceramic parts. I have used ceramic parts on heat sinks that I've selected after careful analysis of the expansions and contractions that will dramatically change the loading on these brittle components during heat cycles. I have never offered a useful evaluation to someone that hides information from me but wishes an expert opinion.

Do what you wish with this ceramic toroid.

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#3
In reply to #2

Re: Ceramic Washers

10/12/2013 12:42 AM

Thanks fredred.. I suppose I deserved that.. I bought them because I just wanted to try them and they were cheap enough.. My philosophy these days is to "try it before you analyze it" because I have too many colleages who suffer from 'paralysis by analysis'..

Did wonders for my productivity ..

but you have to break and blow things up once in a while.

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#4
In reply to #3

Re: Ceramic Washers

10/12/2013 5:30 AM

What you recommend is an obsolete method since blind trying is not at all economical. The same endless analysis is too expensive the optimum is to verify by trial a spot you pinpointed by analysis. Reduces both eforts and costs a lot less. Analysis has NOT to be down to the last detail if the problem is not complex but in the case you mention a correct analysis takes may be 1 h and saves at least 10h in trials.

What you need are the mechanical and thermal properties of the washer you intend to use and as well the assembly mechanical and thermal properties where it will be used.

By assembly mechanical properties I understand as well the local stiffness of assemblid parts. If one is too compliant the contact pressure on the washer is not uniform and you could have peaks and following cracks on the hole ream.

Equations are VERY simple thus the shortv time and you make then ONLY one verification trial.

Red Fred is totally right.

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#5
In reply to #4

Re: Ceramic Washers

10/12/2013 7:18 AM

it has only been experienced since 1976 HVAC-rfg-GeoThermal (near-grade to 500ft depths) that I could not declare any less economics of a project always related to a 'blind' trial of some design or implementation. -throughout design to installlation-

one example was moving air bubbles throughout a smooth piping interior for not to have any air entrained air within a closed loop of recirculated fluids. Before long analysis, we noticed in reservoir-overhead of the pump and loops that air moved out off a T to the reservoir with a guessed velocity of over 3 ft per second, only based on other's research in chilled water coils (for also their other reasons, but "blind to us at that moment) stating "not over 4 to 5 ft per second; and around 3 ft per second in 1/2" Cu -Al fin0coils heat exchangers.

Quite economically all those 1980- to date water-source heat pumps, only confirmed WHY? later, did/do-to-date 'blindly' work well up to that info-guess, less-analyzed flow rate. Also without analysis, staging circulation worked well below reynolds numbers (Poly-E pipe inside tubing deformation w/turbulence) at just 1.4 ft per second, was found before it was known to be working at 1.4 ft per second, and we "let it go" as it just worked well (years later knowing these reservoir "pressureless" systems effervesced gasses from solution, all the while moved cling-on micro-bubbles at certain velocities).

Others at IGSHPA International Ground Source Heat Pump Assoc. training: - showed in clear tubing, they had to just keep watching, objectively, until the bubbles moved in a water only solution example and from first knowing (tables) GPM/ to piping diameter/ to feet per second in advance--- found over 2 ft per second at the model revealed results of moving most all the air in circulation.

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#8
In reply to #5

Re: Ceramic Washers

10/12/2013 12:10 PM

Thank you JP76 for the reply but since my English is very poor (being neither my mother not my father language) I did not understand what you wanted to explain. I presume it some important technical information so that I would be very thankful if you can reformulate your explanation in a way so that even I could get the point.

Thanks to you in advance.

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#12
In reply to #8

Re: Ceramic Washers

10/14/2013 7:11 AM

Thank you Nick:

Please start with a question at a line I wrote.

Tangent reference to wetted ceramic experience since 1980 was just about the survival rate.

I do not understand what "higher clamping " may mean as ther is in that comment above nothing to compare it to a "possible pressure per surface area " mentioned at all. So there is how I would understand what is not clear.

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#7
In reply to #2

Re: Ceramic Washers

10/12/2013 7:48 AM

when I initially read the question the 1st thought I had was.....ceramic and torque = breakage, right? I'm sure as an insulator these have merit but there must be recommendations on their proper usage and application or failure is almost certain at higher clamping forces.

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#6

Re: Ceramic Washers

10/12/2013 7:22 AM

Only experience with some Grundfos and other pump ceramic bearing surfaces:

Wetted ceramics can take a lot of wear to 26 years, has been found in small pumps 1/6-1/4 hp.

I suppose the slightest movement of a connection causing any wear would also relate to longevity depending on material and coating on a ceramic washer.

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#9

Re: Ceramic Washers

10/12/2013 11:19 PM

Dear Sir,

The ceramic washers can take compressive loads if and only if the load on washer is distrubuted uniformly.

You have to conduct surface grinding on the butting surfaces, do the blue match test for unevenness and produce perfectly matching surfaces. also take into account about the parallel surfaces of ceramic washer and check for unevenness on the surfaces also.

I hope the sink temperature does not cross even 100 degrees,

You can use a mica washer of 0.2 mm or o.5mm as a cushioning bed below the washer so as to take of any additional torque which might break the washer,

Mica washers can resist upto 1000 degrees temp.

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#11
In reply to #9

Re: Ceramic Washers

10/13/2013 2:27 PM

Thanks. I figured as much. The compressive load is around 600 MPa and I am planning on applying no more than 200 psi (1.3 mpa) on the bolt. Therefore, the distribution of the load is very important. Any suggestion on any thing I can use to make sure the load is distributed evenly, other than grinding ..

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#13
In reply to #11

Re: Ceramic Washers

10/14/2013 7:19 AM

Fastenal Corp and others alike will have various access to information on thin "springing" washers that can be placed between two other washers for a 'cushy' compression with even (more-even) distributed loading.

Side view some look as a metallic wave of a spring steel, or other materials , for the one in mind. Placed between , or at least the one side towards your ceramic - then separated by another washer after the spring washer, may be rigid enough of an interface to work evenly in the loading surface contacted.

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#15
In reply to #11

Re: Ceramic Washers

10/19/2013 1:03 PM

Use copper washers between ceramic and steel surfaces or any other alloy with a low E and yield strength.

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#10

Re: Ceramic Washers

10/13/2013 7:44 AM

If you use some thermal grease, you might not have to torque it down so hard to get good heat transfer.

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#14

Update

10/17/2013 11:33 AM

I was warned!
Didn't take much to break this damn thing into bits and pieces..
How much heat transfers through a screw anyway?
Its kinda of hard to figure out the contact areas, especially when fastened..
interesting question

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#16
In reply to #14

Re: Update

10/19/2013 1:15 PM

What happened was to be expected. There are several reasons one of them being the way the washer is loaded in shown configurations. The washer is subject to a BENDING due to unequal contact areas on both sides. The broken parts indicate such a failure. Further more the contact pressure could be too high.

As for the heat transfer the highest heat flow goes through the thread flanks, the bolt shaft and the head contact area. The bolt conductivity is usually the main factor. If you make a comparison the heat through the washers (AlO3 about 23 W/m²°K) is in your configuration, with a ream contact, could be lower. If the bolt is of SS then conduction is about 1/3 of the one for carbon steel.

Making usage of the copper washers as mentioned will also allow a better contact between ceramic and rest so that the contact heat resistance will be less.

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#17
In reply to #16

Re: Update

10/21/2013 2:17 PM

You are correct. Using SS washer has been deemed the best solution to this problem. The heat transfer is significant right now because we are using steel screws.

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