Low Mass Glass Kiln

Specifications

Requirements

  • Large hearth: 3x6 feet
  • Operable to 1800F+ (for casting)
  • Limited power supply: 80 Amps at 240 VAC, or about 19kW
  • Affordable

Design Overview

  • 3x6 foot hearth shifts design from clamshell to top hat to provide better access
  • Top and bottom elements for more even heat distribution
  • Bottom elements imply a high thermal conductivity hearth
  • Ceramic fiber insulation to reduce lid weight and lower power consumption

Design Details

  • Heating elements all inserted from a detachable top
  • Kanthal AF elements, 11 AWG, on 1" OD mullite tubes
  • 3 Ohms total resistance yields 18.4 kW
  • Fiber insulation implies a floating hearth
  • Recrystallized silicon carbide tiles for hearth (2x3 x 18x18")
  • Individually adjustable mullite hearth support posts (10)
  • 2300F rated end-cut ceramic fiber insulation modules, 6" thick
  • Gold coated quartz viewport windows
  • SG-70 composite panels support internal machined ceramic parts
  • RA330 alloy internal metal parts
  • Mild steel frame with expanded steel mesh tension panels
  • Lid lift mechanism: 2-ton screw operated lift jacks
  • 6 top vents under computerized control
  • Watlow CLS 208 ramping controller with 50A PWM solid state relays
  • Thermal profile equalized via element positioning and resistance 



Kiln Design

Initial CAD



















Finished Kiln with viewports











 

 Construction

Hearth frame skeleton, with silicon carbide tiles on mullite posts









Hearth supports











Nickel Plated Frame











Insulation

Schematic











Insulated hearth bed, with 2 hearth tiles

 










With hearth elements

Sub-hearth detail - heating elements, fiber, supports, and hearth posts 









Fiber wall modules and silicon carbide hearth


 







Insulation dance

















Top Elements - Kanthal on mullite tubing










Element support hooks: RA330 versus carbide router bit












Electricals


Watlow CLS208 controller and thermal cutoff


 

 

 
 
 







50A SSR switches & main power cutoff relays


Control Station 













Power Busses

As Dr. Frankenstein imagined them









As Igor deployed them



Ceiling Vents






Threaded rod tails






Simulations

Thermal Simulation

1505F - 1509F



2F variation









Mechanical Simulation


0.01" Deflection of frame when fully loaded









Final Assembly/First Firing

Hearth rolled out

















First Glass - even heat at 1400F