204
6. SECTION MOUNTING
Finally, one carbon tip is sharpened with a fine file and the other flattened as illustrated in Fig. 23(b). These tips are lined up carefully in the
carbonizing apparatus. When vaporization starts, then, a crater begins
to form in the central region of the flattened tip, and the tips evaporate
fairly uniformly. If the alignment has been sloppy, the crater may break
through the edge of the flattened tip and the tips be deflected. Thus, one
tip may glide past the other and effective contact be lost. Then one has
the frustrating experience of being unable to continue with the evaporation until the chamber has been opened, the tips readjusted and the
whole system reevacuated. Rarely is the adage of "haste making waste"
more applicable.
Ordinarily the object or objects to be coated with carbon should be
placed 5 or 6 in. away from the source to avoid excessive heat.
When the system has been suitably evacuated, carbonization can begin.
The current input probably will be controlled with a variable transformer in the primary circuit of the transformer which is to supply the
low voltage, high amperage current. Thus, as one turns a handle, the
current increases. It is perhaps best to begin slowly until the carbon tips
start glowing, then the operator knows that he has electrical contact. Next
he should increase the current rapidly until a few sparks begin to fly in
the chamber. At this point carbon presumably is or soon will be evaporating. One can see the film as it is deposited and judge its thickness by
the discoloration of a piece of white porcelain placed at about the same
distance from the carbon source as the objects to be filmed. The discoloration can be seen particularly well if a drop of vacuum pump oil has
been placed on the surface of the porcelain [Fig. 23(c)]. The area covered
by the oil will remain white as the carbon film builds up, and by its contrast one can quite accurately assess the amount of discoloration and
hence the relative thickness of the film [Figs. 23(d) and (e)].
Once carbon begins to be evaporated it comes rapidly so that the porcelain indicator darkens quite quickly. The operator must keep his eyes
on this and be prepared to turn off the current suddenly when it has been
suitably darkened. If evaporated carbon is being used to stabilize a plastic
film, only a very thin layer will be required, and the current should be
shut off as soon as a very light deposit has been built up on the indicator
[Fig. 23(d)]. In practice, this means shutting off the current just about as
fast as one can after the image of the oil droplet is first visible. If carbon
is to be the sole supporting film for sections, much thicker deposits are
6. SECTION MOUNTING
Finally, one carbon tip is sharpened with a fine file and the other flattened as illustrated in Fig. 23(b). These tips are lined up carefully in the
carbonizing apparatus. When vaporization starts, then, a crater begins
to form in the central region of the flattened tip, and the tips evaporate
fairly uniformly. If the alignment has been sloppy, the crater may break
through the edge of the flattened tip and the tips be deflected. Thus, one
tip may glide past the other and effective contact be lost. Then one has
the frustrating experience of being unable to continue with the evaporation until the chamber has been opened, the tips readjusted and the
whole system reevacuated. Rarely is the adage of "haste making waste"
more applicable.
Ordinarily the object or objects to be coated with carbon should be
placed 5 or 6 in. away from the source to avoid excessive heat.
When the system has been suitably evacuated, carbonization can begin.
The current input probably will be controlled with a variable transformer in the primary circuit of the transformer which is to supply the
low voltage, high amperage current. Thus, as one turns a handle, the
current increases. It is perhaps best to begin slowly until the carbon tips
start glowing, then the operator knows that he has electrical contact. Next
he should increase the current rapidly until a few sparks begin to fly in
the chamber. At this point carbon presumably is or soon will be evaporating. One can see the film as it is deposited and judge its thickness by
the discoloration of a piece of white porcelain placed at about the same
distance from the carbon source as the objects to be filmed. The discoloration can be seen particularly well if a drop of vacuum pump oil has
been placed on the surface of the porcelain [Fig. 23(c)]. The area covered
by the oil will remain white as the carbon film builds up, and by its contrast one can quite accurately assess the amount of discoloration and
hence the relative thickness of the film [Figs. 23(d) and (e)].
Once carbon begins to be evaporated it comes rapidly so that the porcelain indicator darkens quite quickly. The operator must keep his eyes
on this and be prepared to turn off the current suddenly when it has been
suitably darkened. If evaporated carbon is being used to stabilize a plastic
film, only a very thin layer will be required, and the current should be
shut off as soon as a very light deposit has been built up on the indicator
[Fig. 23(d)]. In practice, this means shutting off the current just about as
fast as one can after the image of the oil droplet is first visible. If carbon
is to be the sole supporting film for sections, much thicker deposits are