Cal Enterprises Ltd

High Temperature Insulation Tests

Apearance after 5 min of sustained heat,
notice the cracking which has occured on the top layer of unexpanded refractory. May be due to -------
  1. Insuficiant drying
  2. 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.