High Temperature Mechanical Compression system

Hi,

don't use screws, use a weight.

Or: Add big (helical or other type) springs or replace the bolts by springs.

Else you will have considerable work to match the CTEs as these depend on temperature.

RHABE

What is the block material, perhaps we can suggest a tie rod material that matches the CTE of that.

At 1000°C the rods you use will turn to mush and the load will go away. The only way to do this experiment is to apply the compressive load using hydraulic pressure through the oven wall all the while cooling the piston rods to keep them from failing and mushrooming from the temperature. A stack of thin, heat resistant materials like Inconel 800HT, interleaved with an insulator, like mica or silica aerogel can cut down on the heat loss. There is no material I know of capable of withstanding tension loads at these temperatures from which to make the tie rods. CTE is the least of your problems.

Did you consider ceramics ? Only thing that can stand that temperature is the ceramics. And it is not clear - what is the torque on tie rod ? you want to put a load on the component isn't it ? what load ? how many lbs or a pressure of how many psi ? can it be used by gravity ie by putting a weight over the top plate and may be reduce the x-section of the component to generate the pressure at a comfortably handlable weight ?

Other way may be to put ceramic rods suitably designed and using a hydralic cylinder to generate the load. The cylinder may be insulated from the ambient easily - provided the baking period is not large - then though thermally inulator, still ceramics will slowly heat up as will the mineral wool or what-ever you use for thermal insulation of the cylinder will.

If expansion is troubling, how about using it to our advantage?

Top View:

The idea is to tighten the Tie Rod nuts during the heating process.

Levers are attached to tie rod nuts as shown. Suitable Expander is held between these levers.

On heating the Expander rotates/tightens due to its expansion.

If concept is convincing, the shape, dimensions and materials can be worked to compensate the relative expansion between the job and tie rods.

Hi, yesyen!

I don't think it will work, because if the tie rods are losing tesile strength during the heating process, they are not suitable for the job.

But I ADMIRE the concept, and the ingenuity of it just blows me away! Excellent thinking.

GA, even if I don't think it will work, for the innovative thinking.

Mark

Mark thanks for your credit.

Yes, I agree at this high temperature no ordinary alloy would retain the pre-stretch nor even the shape.

If at all any exotic alloy can be thought of, then one more possible arrangement could be:

Central Stud is covered by suitable Insulation and housed in an Outer Tube as shown.

The relative expansion of the outer tube must be more than the insulated inner stud. The net direction and force should favorably press the work down towards holding it.

Hi, Guest!

I read that you do not want the applied pressure to be affected in any way during the test.

Is there some way to heat the block without also heating the tie rods? Or to reinforce the tie rods with a pre-measured tying material that would e.g. clip on to the pressure plates and retain the pressure without being affected by the heat?

I don't think that inside-the-furnace thinking is going to solve this one.

Mark

Just as a passing thought, is it you want to bake the thing at a certain pressure ? What is the duration of the Baking you didn't mention since that is the most critical information after the constant pressure that you want to maintain.

Check if it is possible to locally heat the component without affecting the other portion - may be experiment with Induction heating (conductor) or even check microwave or other means It all depends on the material of the block, duration, pressure etc- If you keep thermal inulator materials as pressure plates and properly focus the energy you may have your solution (think of our good old microwave ovens)

Any sort of tie rod arrangement will be inaccurate since the clamping force depends on the coefficient of friction and that is, in each instance, unknown. In addition, the clamping plates will also be at 1273K and will deflect easily and most likely not distribute the force evenly.

The hydraulic press suggested previous will obviously work very well and is a great solution. There is also a simpler form.

You don't provide dimensions or values, but, based on the torque given, you probably require something on the order of 5000 lb force to hold the two pieces together. If that is the case, simply load the top with a 5000 lb weight. That requires some modification of the furnace, but should be easy enough to do.

If this is a production process, the weight would be left hot.

A snapper-up of unconsidered trifles - The Winter's Tale