Delrin or Teflon Alternative

Ceramic.

Not nearly enough information.

Thermolon may work. Their website could use some improvement though.

This is coating system with some metal base substrate.

At this high of a temperature (≈600°C) you have to specify your atmospheric environment. If you are in even a marginally oxidizing atmosphere (air) I suspect many metals could be reduced. Forget about trying to use any plastic at these temperatures, regardless of environment. You may have to consider ceramics at this temperature.

If you are in even a marginally oxidizing atmosphere (air) I suspect many metals could be reduced.

?????

But Both the plastic you are talking About do not withstand that temp (1100⁰F). You should think of metal.

I don't know where my last comment went but here it is again,

This is to mount an accelerometer to a clamp around a vessel at an oil refinery. I want to insulate or isolate the accel from the high temperatures while limiting the damping. I was thinking about fastening the block of whatever I come up with to the steel clamp either with some type of epoxy or bolt it to it. I would only be talking about an area of about 2X2 inches. But need about 50 of them.

Hope this helps.

Design for the maximum temperature your accelerometer can handle, not the highest temperature in the vicinity of this part. At 1100°F all solders I've seen used in electronics will melt.

The temperature you have written in your original post as 1100F. Did you mean 110ºF instead? That would make a big difference.

You're correct that 110°F would be a significant difference, but Delrin and Teflon will easily handle 110°F. So we once again have confusing data to work with.

I hear you! Maybe when that Green Bastard comes back in from the field, he will set this all to rights.

Now, OP is silent. But I don't think he means 110 deg F. 110 is just little warmer than body temperature. Why he need to post the problem (and think of teflon) for such low temperature.

consider then mounting the Accelerometer on a ceramic insulator inside a mirrored vacuum container. you don't want to use a polymer anyway as it would absorb too much vibration energy anyway. the mirrored surface will reflect the IR energy and the vacuum will prevent conduction/convection. the accel will stay nice and cozy. if vacuum is not possible, consider argon or something with poor heat transfer.

If it's really 1100°F, I agree, ceramic is the only way to go.

BTW, I don't think a vacuum will affect conduction of heat, just convection.

ever seen a vacuum heat treating furnace? if there is no air to conduct heat, the only conduction path is the ceramic standoffs.

True, the only path for heat to travel is the ceramic conduction path. However, with the only thermal path being to a very hot item, things will still get eventually very hot.

On a hunch spurred by The Green Bastard's picture I decided to investigate ICE exhaust gas temperatures, the safe limit for an engine is 1200°F. Now why he would want to put an accelerometer in this hot gas flow is anybodies guess.

probably flow induced vibration is breaking stuff is my guess.

"the only conduction path is the ceramic standoffs." and radiation.

Except the mirrored surface facing the vacuum/argon would reflect the radiation back away from the accelerometer just as the reflective radiant barrier in a vacuum furnace reflects the radiation back to the part being heated.

Oh, that.

Never mind.

Why not mount it magnetically? There are some very strong permanent magnets available. Are the pressure vessels not of steel? Much vibration involved? If the accelerometers have mounting tabs, why not tack-weld them in place and remove them later?

Don

Go to the pros: High-Temperature Plastic Materials provided by Professional ...

Not an endorsement.

Graphite?

As per my knowledge, Teflon, Peak and PFA can work upto 260 deg C(500 deg F). (and not Delrin)

No other plastic goes beyond this.

No plastic works at 1100 deg F

I have used polyimide for limited duration at 1100 degrees C. The silver metal it was in contact with was molten. Look for trade names vespel, meldin, kapton or plavis. This is pretty pricey stuff. Celazole PBI may be another material that could work for you.

Check out Keramab/Insulcon, a company specialized in this domain.

They have different materials, can do the machining if required.

I worked with them for junction box stands for heat tracing applications in this domain.

LOL

I posted this late in the afternoon before I went home, the OP was in bed while you were making comments.

Here is some more information.

The accel will be mounted on overheating process piping at a refinery and the typical operating temperature will be realistically around 750 degrees F.

The 1100 comes from one area that will not have an accel, but is in the vicinity of the measurement points, therefore we posted the worse case scenario situation.

Hope this helps clear things up!

Amateur potters kilns are made with a light weight ceramic fibre 'board' about 2" thick. The outside temperature after 12 hrs firing is about 100c ( guess only i'm afraid ).

I mentioned damping a while ago and although it is important to have a rigid surface to mount on, the vibration is low amplitude and low frequency something with the consistency and size of a hockey puck would be OK.

I still suspect that you are providing us some erroneous information. I do not believe the temperature of the solid material you wish to measure motion is at 400°C (aka 750°F). I do believe that on the interior side of this solid the chemistry of this refinery places the reactants at 400°C. Likely the interior surface of this solid does reach close to these temperatures but I'm certain the exterior surface where you could mount an accelerometer will not be at this temperature. If you really do have to measure the kinematics of an object at 400°C that could achieve 600°C (1100°F) temperatures I do not believe you can do this with a directly connected accelerometer that is nominally rated for a maximum temperature of 120°C. I expect that I could find an accelerometer that might operate at 200°C but not 400°C.

Getting back to your specific initial question, I think you should refer to a white paper from Zeus Industrial products on high temperature plastics. Notice the Ashby chart provided by Granta Design on page four. The only materials that have a maximum service temperature in the range of 400°C to 600°C are metals and ceramics. All plastics will fail at these temperatures. If you really must measure acceleration at these temperatures I expect that you will have to do this indirectly. A possibility will be to reflect a laser off of your hot object and do an interferometer measurement but this will certainly not be cheap.

Surface temps measured with infrared thermography read 650 to 750 Degs F consistently.

OK, so more important than the rigid metal and ceramic pieces you use to attach your accelerometer, you will have to do a careful thermodynamic analysis to keep the accelerometer at a cool temperature. Or you could consider an indirect approach like my interferometer suggestion.

Hello,

I am new member joined due to this question (After 2-3 years from reader.)

The Delrin/teflon material is required for frictionlessness. The temperature resistance required for high temperature withstanding property.

Cast iron/ cast iron with additive material used for piston rings with be suitable lubrication should help.( Just like in IC engines)

=================

Outstanding is standing out.

Maybe you could use a product called generically "thermal millboard." As the name suggests, it comes in sheets of useful thickness.

check out "sealinfo.com" This is the webpage for"Interface Solutions." This stuff is good up to 2500 deg. F. It is an asbestos substitute.

Embarassingly, I can't seem to paste the link.

I was dreaming about this problem last night and i think i may have a solution.

A piece of thin 2" square section stainless steel tube cut so that it has wings to make a stegasaurus heat sink. Two of these bolted together with a 4" Sq mica heat deflection shield between them. The whole then strapped to the pipework with a stainless steel BAND iT and another mica sheet between it and the pipe.

The accelerometer can then be attached to the outside. If this isn't cool enough, the dimensions can be increased to allow more surface area to transfer heat to the air or a small fan fitted nearby.

Im working with Vesuvius, so high tempreture is kinda our thing. I dont really understand your design but, if insulation that you need, ive been dealing with temp up to 1600degC furnaces. ceramic fiber blankets, ceramic wool, fire brick, refractories and ceramic fiber boards can be use. Depend on the design, any tempreture is possible to be insulated.

You might look up a material known as tefzel. Good up to near 400°F. Depends on your application there are even better materials being used in O-ring manufacture.

Don

Still thinking, I decided against the millboard and am in the process of getting a quote on 50 ceramic "cups" 1/2 inch in thickness and mount the accel inside of it. This will protect all sides from heat and keep the weather off it for the most part.

Keep posting, something might come up that is easier and off the shelf and not custom made!

So what is the maximum operating temperature for your accelerometer? How will you communicate and provide power to your accelerometer? You will have to also consider getting the cabling some how to and from this high temperature environment.

I think I'd make the "cup" (more like a truncated pyramid is what I'm thinking) out of bent and welded thin gauge (say 16 or 18 gauge) aluminum or stainless sheet and then mount the accel on plain old ceramic standoffs inside the cup. Make sure the outside surface of the cup is nice and shiny (and stays that way, why you might want to use stainless.) to reflect the IR away from the accel like a heat shield. mount the cup on another set of ceramic standoffs to whatever piping you are trying to measure.

Green Giant,

Ceramic can indeed withstand ultrahigh temps. but is also a really good conductor of heat, which means that you will be in essence mounting the sensors directly and without much thermal blocking. In looking up standard accelerometers, haven't found one that is good past about 250° F. Check out the following website, it may save you some grief:

www.pcb.com/aerospace/hightemperatureaccelerometer.asp

They claim their products will work @ 1,200°F. You could then go back to the simple banded direct mounting scheme. Don't know what 50 will cost, but it's better than burning up a hundred sttandard units and getting bad data in the process. They use the "charge output" method, where the temp-limiting electronics is housed safely away from the heat source.

Murphy doesn't always win!

WOW that's certainly some hot sensor. This seems to be just what Mr. Green needs.

The only nit I would pick is your assertion that ceramic is a really good conductor of heat. It is not. NONE of the ceramics are good conductors of heat, granted some are better than others, but they are all really poor conductors.

Re: thermal properties of ceramics.

Thermal transfer characteristics of ceramics vary with type from about 3 to about 150 W/m · K.

My kitchen stove top is ceramic. The heating element is beneath the ceramic and the cooking utensil goes on top. Water boils fairly fast on my stove top.

Not exactly, it depends on the ceramic chemical composition. High heat conduction is to be found in Al2O3 ceramics but other have a conduction coefficient as low as 2 W/mK ! Those are zirconium based ceramics. I used them with very good results. The problem is also depending on several factors as : distance to the hot wall, air temperature at the place where the sensor can be mounted. Of course the heat flow from the vessel wall has to be kept low but the "cup" will have at least the temperature of the environment. So distance is important and also the position if the sensor is sidewards or over or under the heat source. If the distance has to be important then a stainless steel tube will be fine as support since thermal conduction is low, combined with a plate of zirconia it will keep heat flow down. The tube can have holes to increase convection surface to environment if this is not too hot.

Thermal properties are in general seldom used and thus are not well known here a couple of graphs to give a right feeling:

So in other words, with the exception of Silicon Carbide, I was correct.

GB,

What type of accel are you using (mfr, model)? Most accelerometers have an ambient temp max rating far below your ambient. This is because the electronic parts of the sensor are mounted inside the unit. From this post, it appears that your application involves a vessel exposed to outdoor ambient conditions. Have you considered also attaching one to the ground near the vessel so that ambient surface vibrations can be zeroed out? If the ground shakes, will it not also shake the vessel?

Did you consider my previous suggestion of using a hi-temp accel with the electronics located remotely? Of course, you may already have solved your problem and have collected the required data. Perhaps you had stopped posting because of Hurricane Irene.

dgp1939

Mr. Grinch,

There are some laser accelerometers on the market that may resolve your dilemma without contact if space is not at a premium in the application. It seems to me that using any kind of banding around a pressure vessel would be a nightmare. The larger the vessel diameter, the greater the problem with that approach. Of course, you may already have spent the bucks for the contact-type. In that case, I'd consider the previously-suggested tack-welding solution if the customer will allow it.

"A recovering engineer is still an engineer."

It has been a few months and I thought I would give an update.

I used a relatively low tech apparatus, from Home Depot!

I tapped a hole in a 2 inch square piece of Phenolic board which I attached the accel to. Which in turn was securely fastened to the inside of an aluminum electrical box (for a dryer) which was layered with fiberglass insulation.

It has been 4 Months now and none of the accels are cooked!

The vibration is of low frequency and relatively high amplitude so damping isn't an issue!

Thanks for all the feedback!

TGB

Thanks for the update. Sounds not dissimilar to my post #19

Removed 64 of these accels from the unit in the fall of 2014 and sent them for calibration verification, one failed out of spec by a couple of percent.

I need to post more on here....