 |
Apearance
after 5 min of sustained heat,
notice the cracking which has occured on the top layer
of unexpanded refractory. May be due to -------
-
Insuficiant drying
-
Thermal expansion
Click on image for video.
|
| An attempt to bind
the top layer together using glass
fibre tape. This has yet to be
tested , the top layer is not uniform I may have to redo this test.. The
diameter is approx twice the first test so the flame should not overlap
and heat the backing plate directly. Also I await a better small area contact
temperature probe. |
 |
 |
I have 2 of these
inexpensive thermometers one suffered from an open circuit thermister.
This was quite fortunate as I could use the lead to make
a contact probe from some NTC thermistors I got on ebay. The normal probe
is more suited to liquid temperature measurements.
These themometers are not very accurate but could
be
calibrated against my PRT. Refering to the video I repeated the test
,with the new probe and recorded a max temp of 50c from 17c over 5
mins. The liquid probe was highly inaccurate for this application. |
| This
piece has a double layer construction interleaved with glass webbing .
It has not cracked after 10min torch heating although the insulation
properties are not as good as the expanded material. However the
expanded material would disintegrate in the vacuum of space. It would
also be good if the emissability could be improved. |  |
 | The
difficulty has been finding a heat proof bonding material for the
vermiculite which will not conduct heat. This encourages the use of
layers.
On the rght we have vermiculite bonded with PVA this could be used up to 100c.
On the left a small amount of cement is used in addition to the usual bonding material. |
| The
expanded material gave the best insulation ,was very light and
responded well to intense heat. The next stage is to enhance the
expansion and moldabilty to greater than 3x whilst maintaining
strength. | Here is another test where the backing plate only rose 20 degrees C. |