Up: Sediver
Sediver Catalog 1970
11 of 136
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When an exceptionally high corrosion resistance is necessary, we use
nickel-chrome stainless steels.
The caps which cover the heads of the dielectrics are usually of
black or white heart malleable iron, hot-dip galvanized, and sealed
onto the dielectrics, or they are of a zinc alloy die-cast directly
onto the toughened glass.
Besides the inspections made by our suppliers, we carry our reception
tests by lot on each incoming shipment of metal parts, before they are
used. For this, we usually use the tables of "U.S. Military Standard
105 D" or the WALD continuous sampling plans.
These inspections concern:
- the dimensions of the parts, by measurement or by gauge.
- their mechanical resistance, by means of destructive tests, by
sampling.
- the absence of cracks or internal defects, by the magnetoscopic
method.
c) the assembly material
To seal the metal parts onto or into the dielectrics, we use a
concrete of aluminous cement of which the main qualities are:
- a great mechanical resistance to shear under compression
- an excellent staying power in the face of corrosion
- a rapid hardening.
We have perfected a continuous sealing line based on the use of
high frequency vibrations. The risks of human error have thereby
been reduced and the efficiency of the control has been increased.
The quality controls concern:
- the granulometry and the specific surface of the cement
- the percentages of each of the constituents, the plasticity of the
mortar, and its mechanical resistance after artificial ageing.
The finished insulators
a) their quality control
The inspection operations are carried out as soon as the units, leaving
the assembly department, can be handled without risk of deformation.
We use control charts method for the interpretation of the results
obtained either by variable or by attribute.
The inspections cover:
- the shapes: dimensions are verified by measurements or by gauge,
to check the spacing, relative tilt of the metal parts and the
dielectric, the interchangeability of dimensions of the connecting
systems, either ball and socket or clevis.
- defects of appearance
- mechanical resistance: all cap and pin insulators are submitted
for 10 seconds to a tensile load of at least 40% of the rating. On
the same machine, electrical pulsators check the spacing of the
insulators, an important factor since it can reveal some sealing
defects.
In addition, we carry out, by sampling, systematic tensile loading
to failure on whole insulators and on stubs (the glass dielectric
having been broken), after having submitted them to artificial,
accelerated ageing.
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