Kiln Elements

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Kiln Elements Design

• Phil Hamling
• 9-23-08

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Heating element for use in kilns are available in
many types

• Metallic Wire
• Iron Chrome Aluminum
• Nickel Chrome
• Platinum
• Silicon Carbide
• Moly Disilicide

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Hobby Kilns

• Most commonly use Iron - Chrome Aluminum
  metallic Wire.
• In the form of coiled elements
• There are many, many manufacturers throughout the
  world.
• Kanthal makes the premium grades.
• A, AF, A1 APM

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Guidelines for Industrial Furnace

• May or may not be applicable to hobby kilns
• Serve as valuable reference material

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Major Guidelines

• Surface Loading (w/in.2 or w/cm2)
• 14.5 w/in.2 at 1300ºC (2372ºF)
• Coil Geometry
• Diameter Ratio
• Coil / wire 5 to 8 X wire diameter
• Stretch Ratio
• Length of stretched coil loop 2 to 3 X wire
  diameter

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Element Issues in an LL e23s

• Original 1.2 mm APM elements failed after only 69
  10 to 11 cycles.
• Improvement in life was sought.
• Possible alternate wire sizes were evaluated.
• Real Estate limitations!!!

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Element Analysis
  Original         Revised  
Wired Parallel Parallel Series Series Series Series Series
Wire dia. (mm) 1.2 1.5 1.5 1.7 1.8 2 2.2
Total wire mass (lb) 1.30 2.02 0.82 1.35 1.70 2.59 3.74
Power density (w / sq cm) 3.42 1.75 6.76 4.64 3.92 2.86 2.21
Wire surface (in2) 107.3 209.0 54.2 78.9 93.6 128.3 168.7
Power density (w / in2) (14.5 Target) 22.0 11.3 43.6 30.0 25.3 18.4 14.2
Stretch ratio (2 Target) 2.8 1.5 5.6 3.9 3.3 2.1 1.7
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Element Selection

• 2 mm wire was chosen.
• Power density was lowered from 22 to 18.4 w/in.2
  (Still above 14.5 w/in.2 though)
• Stretch Ratio maintained above 2.
• What is really needed is more real estate to
  lower the power density effectively.

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Wiring Change

• Changing from parallel to series wiring
  configuration was needed.

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The e23s kiln just completed its 87th Firing
with 18 firings on this Revised set of elements.
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Element Related Topics

• Many sizes and types of heating coil are
  manufactured at ZIRCAR Ceramics, Inc.

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Element Related Topics

• Many are custom shaped to fit unique heater
  designs

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Element Related Topics

• Annealing takes the springiness out and helps
  them hold shape.

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Element Related Topics

• Some are hand fitted on specially shaped
  insulation to form complex heaters

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Element Related Topics

• Others are set on vacuum forming molds

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Element Related Topics

• To make both small and large custom heating
  elements

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The Grand FinaleHeating Element Coil Winding
Demonstration