Ken Mintz Composite Information pg.8 ==

	Composites Corner No. 8 - Hot Box Pictures and Dimensions  
  
	I gave a brief description of the hot box used to keep your resins and hardeners warm in Composites 
	Corner No. 6.  As noted there the box can be easily built from a sheet of 1/2 inch 4' x 8' sheet of 
	aluminized urethane foam house insulation.  The dimensions are chosen by the builder to cover the 
	resin and hardener containers used.  Usually these will be combined in the form of an automatic 
	dispenser that doles out the proper proportions of each material into the mixing cups.  In any case the
	resin and hardener need to be kept warm.  
  
	The dimensions of my hot box are 23.25" wide X 13" thick X 22" tall which covers my automatic 
	dispenser and allows additional room for the light bulb heater and various drip catching cups, etc.  It is 
	composed of six panels bonded together with a hot glue gun.  The floor panel is not bonded to the rest 
	of the box but is left to act as a drip pad for the dispenser from which the rest of the box can be lifted to 
	allow free access to the dispenser for replenishment and clean-up.  I cut an access door into the front 
	panel in order to permit operation of the dispenser without having to remove the whole box.  I even 
	bonded handles made from scrap foam and wood pieces to the top of the box and to the access door 
	to make moving them easier.  A smaller inspection door is cut into the front access panel to allow
	viewing of the thermometer glued to the resin tank on the dispenser.  All this cutting can be done easily 
	with a sharp knife or a hacksaw blade.  
  
	Vent holes are cut into the top.  These allow vapors to escape as well as hot air.  The latter is a crude 
	method of temperature control; however, I added an automatic thermostat to control the light bulb.  
	Vent holes are still advisable in case the thermostat fails and for the aforementioned vapor removal.  
	If you use heat leakage from the vent holes to control temperature you can cut enough holes to allow 
	too much heat to escape and then plug them back up until the correct temperature range is maintained.  
	As you can imagine this is done by trial and error and takes a fare amount of time to achieve.  The first 
	box I made used this method but the one depicted here has an automatic thermostat, a King Model PT-2 
	in my case, obtainable from any home supply store for about $10.00.  Any of them are rated high enough 
	to handle a light bulb but do check this out.  It is also set by trial and error but this can be done much 
	faster than using the vent hole method.
  
	The bulb used should be between 40 and 60 watts and no more.  The bulb should be no closer than 
	about 6" to any of the resin/hardener containers or anything else inside the box that could be heat 
	damaged or cause a fire.  It should not touch the walls of the box but can be within and inch or so of them.  
	Radiant heat from the bulb is the culprit here.  The thermometer should not be directly exposed to light 
	from the bulb nor in contact with the metal parts of the dispenser.  I glued mine to the plastic resin 
	container 	out of line of sight with the bulb.  The temperature range is usually between 85F and 95F but 
	can vary 	somewhat depending upon the type of resin used.  The manufacturer can usually supply this 
	information if it is not listed in your aircraft construction manual.
  
	During initial setup of the hot box check your temperature often until it stabilizes in the proper range. 
	Too hot and you will cook your resin especially the hardener.  It will often become thick and will not 
	pump easily from the dispenser.  Also its chemical characteristics will change affecting the quality of 
	the cure.  Resins and hardeners that get cold thicken up and also won't pump easily or at all but they 
	usually do not change chemically.   A gelled hardener can often be restored to useful fluidity simply by 
	heating it up slowly.  This can be done in your 	hot box or you can heat it up faster by placing its 
	container in another container of hot (not boiling) water - a double boiler without the boil.  Don't use 
	direct heat from a stove burner or torch or anything similar.  You will burn the hardener or resin. 
	 If it boils it is ruined for all practical purposes again especially the hardener.  Don't breath this stuff 
	either.  Once all this is done your hot box will be relatively trouble free.  Replace the bulb and clean it 
	up on occasion is about all that is required.  

	 
	 
  
	Ken Mintz
	Chapter 163 Tech Counselor
	Phone: (702) 567-1938
	Email Ken