Everything You Wanted To Know About Dumet Wire

Quality control system

Quality control system consits of following quality assurance processes.

  1. Raw Material Incoming Inspection
    1. Filament
    2. Base
    3. Bulb
  2. Tests on Wire-terminal Lamps
    1. Aging Test
    2. Initial Charateristics Test
  3. Tests on Lamps after Assembly
    1. Construction Inspection
    2. Characteristics Test
    3. Visual Inspection
  4. Test on Packing Material
    1. Pressure Test
    2. Humidity-resistance Test

The above processes can be summarized into the flow-chart as below :

Each quality assurance process has the following specifications:

Raw Material Incoming Inspection

A. Filament

When each lot of the filament has been produced, 50 to 100 pcs of it are made into wire-terminal lamps. The filament is protected by a non-oxidizing condition, either a vacuum or an inert gas, inside a glass bulb.

The filament is mounted between two electrodes made of dumet wires which provide mechanical support and pass out through the glass bulb for electrical connection. Thus-made wire-terminal lamps are tested to confirm the electrical characteristics such as voltage, current and luminosity (M.S.C.P or lumen).

The filament has to pass the heat-resistant test as well to see that it resists the incandescent heat and maintains the operative condition for the duration of life-time required by ANSI/IEC standards. The filament shape has to be uniform with coils evenly spaced and free of twist or shortening.

The filaments which are proven to be of proper quality through such tests are used for bead-mounting or stem-mounting on the actual production line.

B. Dumet Wire

Dumet Wire is a low resistant material consisting of a copper sheath around a nickel-iron core. It is given a special surface treatment permitting an air-tight seal to be made where the electrodes pass through the glass.

The dumet wire is visually inspected before production. The dumet wire the copper sheath of which is peeled off or which is wholly or partially oxidized can not used for production.

The dumet wire is carefully checked after bead-mounting or stem-mounting for wire-terminal lamp samples to see that it does not cause any slowly-developing air-leak on the spots where the two electrodes pass out through the glass bulb.

C. Glass Bulb

Glass bulb is visually inspected to see that it does not have nay deformity, crack or any foreign material on its inner or outer surface. Fragility is tested to see that it is strong enough `to resist outer shock, vibration or incandescence heat.

D. Bead or Stem

Bead or stem carries one or more piece of molybdenum wire, which are formed around the filament to provide additional mechanical support. Both bead and stem must have the same expansion coefficient of the glass bulb so that any crack or deformity may not be caused when they have been welded together at the bottom of the bulb.

Manufacture of wire-terminal lamp

  1. When the filament, dumet wire, glass bulb and bead (or stem)are proven to be of proper quality through specific tests and inspections, they are used for manufacture of wire-terminal lamps on actual production line. Thus-produced wire-terminal lamps are aged for 15 to 30 minutes for initial characteristics test.
  2. Initial characteristics Test: The wire-terminal lamps which have been aged for 15 to 30 minutes are tested to check the voltage, current, luminosity and life. The lamp is measured by an ampere meter to see that it stays within the tolerance ¡¾10% at the rated voltage.      
    Its luminosity is tested by a photometer to see that it has brightness within the tolerance ¡¾25% at the rated voltage. Its life is tested at over-voltage when it is impractical to run life tests at rated voltages. The relationship between accelerated life values and rated life values is generally determined as a function of the 12th power of voltage change
  3. The wire-terminal lamps which have passed the voltages, current, luminosity and life tests are brought to actual production line for assembly with base by using cement.


A. Base is visually inspected and checked for dimensions acceptable by ANSI/IEC standards.

B. Cement

Cement is tested to see that it has proper cementing power and has electrical conductivity in case of assembly of slide base lamps. It has also to see that its cementing power does not vary with the ambient temperature of the environment where lamps are being used.

When the wire-terminal lamps are assembled with base by the cement, the cement is baked by an electric oven for 60 to 90 minutes at a temperature of 200-220 degree Centigrade.

After the baking process, the lamp is cooled slowly inside the oven to prevent the cracking phenomenon caused by sudden exposure to a cool temperature outside the electrical oven.

When the lamps is removed from the oven,it is checked to ensure the proper cementing power.

Construction Inspection

  1. Dimensions of the lamp are checked to see that they meet those specified by ANSI/IEC standards
  2. Center of filament is checked to see that it stays within the center 1/3 of the bulb.
  3. Bulb has to be clear with no foreien materials or glass chips inside.
  4. Lamp has to be capable of operation and storage at temperatures from -65 degrees C to +100 degrees C without degradation
  5. The position of pins on midget bayonet base and the pitch on screw base have to meet ANSI/IEC standards.
  6. When the lamp needs a marking on the base, each piece of lamp is checked to ensure a clear marking on the base.
  7. For a construction inspection, sometimes a vibration test is performed on the lamp to see that it is not vulnerable to shock and vibration failure. Bayonet base is recommended over screw base where vibration exisists.

Characteristics Test

The finished lamp goes through tests on voltage, current, luminosity and life-hours once again before being shipped to customers.

The results of test on sample lamps before shipment are recorded on  "Lamp Test Report (TR-3A/95)" to be kept in our file for a lot trceability in the future.

Visual Inspection

The results of visual inspection are also recorded on "Lamp Test Report(TR-3A/95)"


  1. Lamp is packed in containers suitable to prevent breakage during shipment and transportation.
  2. Proper amount of foam or sponge is used to cover the lamp so that the lamp may not break by outer shock or sudden fall.
  3. When the lamp is exported, a humidity-resistant carton of export standard is used for packing.

From http://www.seillamps.com/english/index/content/qualitysy.html