Air Entrained Refractory: Will it Float ?

Which late night comedian did the "Will it Float" segment.

Anyway.  I used the original mix, #1 in the test, that subs silica flour for sand and mixed it up like the air crete people do.   I am not sure if it will be as light as it could be.  I made the foam with an electric mixer like one used to make a cake.

It looks like the top of the refractory is right at the water line. Given that there is the added weight of the container and water that will evaporate maybe it will. 

At any rate it is close.   Need to play with the foam and such to see if I can make it lighter.

Prior to doing the air entrained refractory I mixed up a bit of aircrete.  1:32 dawn:water,  1:2 water to Portland cement, and equal amounts of the wet cement and foam.

Maybe the cement could have been thicker.  Some bubbles escaped.  And it seems quit hungry for water.   Much more so than the refractory mix.   It rather fragile so adding water without messing up the surface takes some care.

Later in the day I became impatient and removed the air entrained refractory sample from its cup/mold.

It is starting to harden but I suspect it is drying rather than setting or curing.  I am thinking of doing a test with additional Portland cement in several steps.

The puck has been fired to 800C.

OK I had to see if it would float.  I did not think it would be all that interesting and did not record it.  The air-crete floated with the water just below the top of the slab.  The air entrained refractory was much more interesting.  It initally floated much like the air-crete.   But it started absorbing water and soon when to the bottom.  I may dry it out and record it.

I plan to try this again but with no perlite and maybe samples with a bit more Portland cement.

The puck did not seem like it was fired.  So I have loaded it and both parts of the original non air entrained brick into the oven and am firing to 850C for one hour after reaching temp.  At 830C I noticed something rising from the stuff in the furnace so I open the vent.   Not sure that the smoke/steam whatever is actually from the stuff I am firing.   Just the same I am going to fire it for another hour.
Yeah should have written down times.   Begs the question why I have not setup a controller so I can use firing schedules yet.

Another version of the sand snake, sand fluffer, rotary muller ?

From Rupert's Hobbies

"Components are a 1/4hp 1725 rpm motor mounted inside a large coffee can (the can
keeps the sand out of the motor, and old canner, an old salad bowl and angle iron to make
up the frame. The wheel shown is a steel disk 8" in diameter with a2 1/2" expanded metal
ring welded to it. The mesh could be replaced with studs spaced an inch or so apart."

This one looks easier to build than the 'sand snake' I have been working on.    





















Found more info at http://schoepp.hylands.net/fluffer.html

          

First Electric Furnace Design

I would like the furnace be used both for casting as well as tempering parts to large to fit the Kerr 666 burnout oven.  This suggests a rectangular shape.   Thinking about a shape that is tall, narrow and deep.  Big enough to fit a cruciable into and deep enough to temper stock to long to fit in the Kerr 666. Just thinking.  Don't want it to be too big and slow heating.  If I feel confident about it set it up so it can be rotated 90 degrees to make a wide low instead of a narrow tall.

Lets consider the design from the inside out.

For some time I have been thinking about casting the floor and ceiling with grooves to accept the sides and back.  The back would have a groove on each vertical edge to accept the ends of the sides.  This design would provide a free standing interlocking shell without casting it in one piece.   The channels for the heating coil will be created by gluing Styrofoam strips to the forms.   After the refractory dries these can be removed with flame or solvent.   The shell will be fairly thick to accommodate the cavities for the coils which I plan to run around the sides and back.

The shell will be surrounded by perlite.  I am not sure if it will be loose or bonded with sodium silicate.   Maybe a bonded section for the floor to rest on and the rest packed loose around the shell.

I am currently working on a refractory variant of air crete. 

Research Notes aka Book learning

My notes are in purple.

B. Thermal Shock (1)
This is measure of the refractory property when the refractory is exposed to alternate heating and cooling. It is an important property for a refractory material.Most high-temperature processes experience heating and cooling. Both refractory grains and the bonding system expand while being heated and contract during cooling. Having similar grains in the structure, the thermal shock resistance depends on the matrix bonding the grains. Thus, refractories having structures with built-in micro cracks of defects show better thermal shock resistance than with rigid systems. In some refractories, the bonding system, by nature, possesses micro structural defects or cracks that provide better thermal shock resistance.

--------------------------

BENEFITS OF CEMENT-LIME MORTAR (2)

1. Autogenous Healing - When hairline cracks develop in the mortar, hydrated lime reacts with carbon dioxide in the atmosp
2. here. This reaction produces limestone which helps to seal the crack and fill voids in the mortar. This explains the increased moisture resistance 
3. noted after six months of curing in two studies.
4. Extent of Bond - The extent of bond is the percent of brick to which the mortar adheres. The low air content and the fineness and stickiness of hydrated lime particles increase the extent of bond of mortar to brick. These factors allow cement-lime mortars to penetrate deeply into the brick and seal the brick/mortar interface.

Hydrated lime improves the strength of the mortar by several mechanisms:

1. Carbonation - Hydrated lime reacts with carbon dioxide in the atmosphere to form limestone.
2. Cementitious Reactions - Pozzolonic reactions can occur between hydrated lime and silica compounds in the mortar mix.
3. pH - Hydrated lime helps to maintain high pH levels in the mortar . This makes siliceous materials more soluble and reactive.

--------------------------
Pozzolan (3)

Pozzolans are a broad class of siliceous or siliceous and aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties.^[1] The quantification of the capacity of a pozzolan to react with calcium hydroxide and water is given by measuring its pozzolanic activity.^[2] Pozzolana are naturally occurring pozzolans of volcanic origin.

Reaction. The pozzolanic reaction is the chemical reaction that occurs in portland cement upon the addition of pozzolans. ... The pozzolanic reaction converts a silica-rich precursor with no cementing properties, to a calcium silicate, with good cementing properties. --------------------------

(5) Calcium Silicate Insulation

Over 1100 °C calcium silicates begin to sinter, therefore the
calcium silicates are limited to 1100 °C.

I need to take the oxy propane torch to a sample and see if I can break it down.  Need to know if the additional components will take it past 1100C.  200C more would make bronze casting easier.  OK looked up the melting point of Calcium Silicate.  2,130 °C (3,870 °F; 2,400 K)  NICE

we do advise heat curing, before the first use as a front
layer, as this will be beneficial and will ensure an even
longer working life for your insulation.



-------------------------- Silica flour aka silica fume is a pozzlan.   Are all the pozzolan bond based on water like the Portland cement bond ?   ANSWER NO see above

(4) Pozzolan a material that, when used in conjunction with portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. 

Clays → contain high amounts of silica & alumina but have a crystallic structure! (Do not possess pozzolanic activity) – However, by heat treatment, such as calcining ~700-900°C crystallic structure is destroyed & a quasi-amorphous structure is obtained.

Burned clay → possess pozzolanic property



Limestone breaks down at 825C but the temperature which calcified lime breaks down is over 4000C. (check this)   Things are looking good.
--------------------------

Thermal shock (1)
I was planning on making rings to test the refractories for resistance to thermal shock but this table has me wondering if this test only makes sense for dense refractories.  The 2nd entry "High thermal conductivity" is especially troubling.

On aggregates (1)

Given that my native sand has irregular edges that interlock well it may be a good choice. 

BENEFITS OF CEMENT-LIME MORTAR

This is regarding mortar and not refractory but parts may still apply.

Sources

1. Charles Schacht Refractories Handbook 2004
2. BENEFITS OF CEMENT-LIME MORTAR 
3. Wikipedia
4. aybu.edu  (best ref)
5. Calcium Silicate Insulation

Remember: Glucose in Sodium Silicate Cores 1/2%

From Martin.  Allows cores to be easily removed.

7 1/2 % Sodium Silicate
1/2 % Glucose
Power Mix
Riddle
Hand Mix

Refractory Experiment In progress

Further experiments.

Test ingredient variations. 

This is the formula by volume.  10 parts perlite  is a guess, it can be increased in a later experiment after these are evaluated.

10 : Silica Flour or Sand
  6 : Native Clay
  2 : Portland cement
  3 : Lime
  5 : Perlite

The variations from the mix are listed for each sample.  Play sand is a quartz sand.

Mixes tested.

1. ✅  the formula aka control
2. ✅  local sand instead of silica flour 
3. ✅  play sand instead of silica flour
4. ✅  silica flour without Portland cement
5. ✅  play sand without Portland cement
6. ✅  local sand and silica flour 5 each
7. ✅  local sand and silica flour no Portland cement

𝥷   Not started     ⑇    Dry mixed     ✅ Drying     🔥  Firing

Whats wrong with this picture ?  6 and 7 are identical but 7 lacks portland cement so it is lighter.  So yeah, I knew which one it was. LOL

If all goes well tomorrow I can hydrate them and move the flags to ✅
Currently thinking a day of natural drying in the house then bake them below the boiling point of water till dry.   Then fire.  This is a bit of a rushed schedule and I reserve the right to change my mind. LOL

Aside:  I knew a geneticist who said "It's all book keeping".

All were hydrated in one afternoon.  Containers were covered with snap on lids assumed to be mostly air tight.  Solo brand containers.

In addition to the normal sample and additional one was made with 1 spoon of sodium silicate.  Total of 14 sample.   I should have enough to make 1 or 2 more samples from each bottle.

It took considerable time to create these samples.  I am now thinking a week to dry.

The perlite is not of a uniform size.  I think it would be better to sieve it so a more uniform sample could be made.

 It would also work better to add the perlite to each sample as it was hydrated.  That would ensure a more even distribution.

---------------
Its the next morning about 12 hours after the tests were cast. 
Moved the labels to the lids as they were not going to make the trip on the sides.

Took the lids of the samples which we heading in the direction of dry.  So I gave each 2 teaspoons of water.  Shortly after casting I had given each sample a dribble of water.  It will be interesting to see if the absorb this water and how long it will take.

If you are thinking the water is only needed to hydrate the Portland cement you might be mistaken.  The samples with no Portland cement were just as non-wet, don't want to say dry.  It may be that water enables processes that unlike the Portland cement bonds are not destroyed by heat.  If this is or is not the case adding water will at worst waste my time.   And if you look at it this way I should have gone out and purchased chimerical refractory.  But at this juncture I  have more time than money.

The original tile/brick was mixed to a consistency of peanut butter.  I would call that ramable refractory.  These were slightly more fluid maybe more along the line of a castable.

It seems that ramming the refractory produces better mechanical interlock between the particles.   This provides additional strength in the green and fired stages.     However if you are using a commercial refractory follow the makers instructions.   This is about DIY.

Again with not so good image of my sand.

It looks like the sand particles would interlock when forced together.  A good thing.  But note that the original test tile/brick was made with silica flour instead of sand.

---------------
48 Hours after cast

IB needed water
2B and 5B were soon to need, and were watered

B is identical to A but has a small spoon of sodium silicate added.  Adding sodium silicate to this mix may flux it so maybe a bad idea.

1. A B 
2. A B
3. A B
4. A B
5. A B
6. A B

I would not read anything into this.  Too little data and not enough control over how much water was added.  Different samples had different mixes with different weights and densities.   Even if all had the same amount of water to start it would not have usable meaning.  I record it here because it is an observation and multiple observations can provide clues which can be investigated.

Why am I bothering to keep these moist when the Portland cement bonds will break down anyway?    The lime and possibly the sand may form pozzolan type bonds which need water to form and may not break down with heat.

---------------------------------

Saturday November 17th.

Interesting difference between sample 4 and 5.

1. ✅  Mix from previous video
2. ✅  local sand instead of silica flour 
3. ✅  play sand, quarts, instead of silica flour
4. ✅  silica sand without Portland cement
5. ✅  play sand without Portland cement
6. ✅  local sand and silica flour 5 each
7. ✅  local sand and silica flour no Portland cement

Both lack Portland cement. But sample 4 with silica sand is much firmer than sample 5 with play/quartz sand.   

Sample 5 show no signs of firming up, it is about the same as it was mixed.  I had been thinking it was the lime which was doing the bonding but apparently the silica sand is.  Strange because the lime only sample from a video or two back dried/set into a nice puck not unlike the refractory.   Interesting.

Thinking I should try crumbling the lime only sample.  See if there is any bonding past drying going on there.  The silica sand only sample dried to a puck but easily crumbled to dust.

 I see I should have made a sample with local sand and no Portland cement.

lime mortar with perlite part 2

The sample has been kept wet for a week.

Yesterday I broke it in two and put one part in the. now heated, defunct wet freezer.  The other half was allowed to dry for a day then baked in the electric furnace.  Currently it is on its way from 550C to 750C.   I am not following an exact firing schedule.   Cooked of the water with temperatures below 100C.   One hour at 50, 75, 90,   Then one hour at 150, 250, 350, 450, 550, and 750.

For kicks and giggles I measured the oven temperature rate of change.  Came out to about  1C in per 10 seconds.  So about 2 hours from freezing to 700C.  But this is sort of useless in that the test tile have very little mass.  This is the time for an empty oven. It also assumes that the temperature climes at a fixed rate which is not true.   As the oven gets hotter it looses more heat.  But since this was done at the upper end of what I normally heat to it might be shorter.

And I turned the controller up to 800C.  Going to turn it off in two hours.  Let the oven cool with the door shut overnight.  Examine the tile in the morning.

My friend at Chirpy's Tinkering suggests adding 1 part talc to this mix.
"in very small amounts, it'll lower the vitrify temp, but in larger amounts, it takes the melting temp way up some clays react to it in different ways, but usually talc is used in pottery to change unknown clays with low melting temps to something more managable"

"I thought sodium silicate crackling was pretty cool but I believe the one guy made some refractory out of sodium silicate, sand, talc, and bentonite, and made a hot face to go over it with sodium silicate and talc, and he was doing brass castings for quite a long time with a propane burner, and the lining seemed to hold up pretty well"

Oven turned off 800C @ 10:50PM
                            90C @  3:15AM

Its morning.

And a video summing this up.

Tub Muller build II

While looking for a jack shaft I figured I'd check the slowest moving table.  The sit up table.   Instead of a jack shaft it had a 150:1 double worm gear reducer from Hub City.  If the input is driven at 3X the 1725 motor speed the output shaft will run at 35 RPM.  Or with a 3450 motor and 1:1 the speed is 23 RPM.


The gearbox may leak a bit of oil.  Need to check the level.



Maybe after the muller is built I will change seals.



It might be a bad idea to couple the gearbox output shaft too tightly to the sand muller drive axle.   Given the low RPM it need not be complex.  Just something that interlocks and stays centered.

Still thinking about using the left over new bearing from the HF concrete mixer repair.  They are 62mm outside and 30mm inside.  Quite good sized.  It maybe better to use tapered bearings like a car's front wheel but if they are good enough for the mixer they should work on the muller.   After all its what is running on the HF mixter to muller conversions.  Need to determine what is a suitable outer pipe and what to use for a drive axle.

I am musing about making the the base unit for several different machines.  Build the tub and related parts as a unit that can be removed from the base drive unit.

Tub Muller Build Starts

While tearing down one of the spa tables I found it contained 2 small right angle gear boxes.  From this image I dentified them as Hub City model ADS 05404-007 with a 2:1 gear reduction. 






They look like this.

But it does not stop there.  The frame and some other bits can be used too.










Unfortunately the output shaft is about 80 RPM.  I could put the 2 gearboxes in series and get 40 but I think I am going to go with a jack shaft and belts.

The drum will be stationary with the wheels and plow rotating within it.  A pipe will be fited to the center of the drum floor and a drive shaft will come up through it to power the rotating assembly. 

I have a tube of bearings ordered to replace the ones in the HF cement mixer drum.  They are 30mm ID, 62mm OD,   I may have to create a bushing to match the bearing ID's and the shaft OD.   But some sort of thrust arrangement would be needed so as not to load up the bearings in the right angle drive.   Perhaps a lawn tractor axle would serve as this shaft ?

I have an 18" diameter water heater tank to use for the tub wall.  Still need to find a tub floor and a pipe for the center.

Now to find shafting for the jackshaft and the vertical driv.