|
The easiest way to deliver and mix x-ray
chemicals is to utilize an automatic chemical mixing station, or an
automixer.
You use an automixer in much
the same manner that you would use replenishment tanks.
Automixers are really dual mixers in that they have separate mixing
systems: one for developer and one for fixer. Both mixing systems
work in an identical manner. There are several different specific
gravity-type automixers on the market, all of which do basically the
same thing in the same manner. Since the automixer can mix both
developer and fixer, they have two sides: a developer side and a
fixer side. Automixers have one common electrical connection, but
everything is separate from there. Automixers are designed to fit
the bottles that you are using into �templates� so that you can�t
accidentally put developer
parts on the fixer side and fixer parts on the developer side. You
will remove the cap and place the bottle upside-down in the
�template.� (The bottles are sealed with a foil seal which prevents
the bottle from leaking when turned upside down in addition to
protecting the chemicals from exposure to air.) When inserted into
the template upside-down, a knife mechanism uses the weight of the
bottle to cut the foil seal and release the liquid in the bottle
into the mixer. When the chemical enters the water below from the
bottle you just inserted into the template, (remember that water has
a specific gravity of 1.000 and the concentrated solutions you are
mixing are much heavier than that) the specific gravity of the
resulting solution increases to a pointwhere a specific gravity
float-switch is lighter than the solution and begins to float. When
the floatswitch is boyant (floating) an electrical connection is
made in the switch which opens a solenoid valve allowing water to
flow into the mixture. As the water enters the mixture, the solution
gets lighter and lighter (closer to 1.0) until the float-switch no
longer has the ability to float. The float-switch sinks which breaks
the electrical connection in the switch and returns the solenoid
valve to its resting state which is normally closed, shutting off
flow of water. The float-switch is the key to accurate mixing. Each
float-switch is custom made by the mixer manufacturer and most are
made to be adjusted over a wide range of gravities. Most x-ray
chemicals are designed to be mixed to have a working strength
specific gravity of 1.075 and 1.085. In addition, at the proper
specific gravity most x-ray chemicals are designed to mix to exactly
five gallons. So, by measuring specific gravity with a calibrated
specific gravity float, you will be mixing accurately to five
gallons if the formula was designed for five gallons. The above
process is extremely easy, and except for placing the bottles on the
mixer, the process is all automatic and can be very clean. In
addition, automatic chemical mixers help to reduce the odors often
associated with x-ray chemicals which makes for a more pleasant and
potentially healthier working environment. There are some negative
features to using an automixer. Automixers are not always one
hundred percent accurate. In most cases you wont see extreme
variations from mix to mix, but the accuracy of automixers is
dependant on incoming water pressure variability, and incoming water
temperature. Water pressure which varies widely from time to time
can affect the way the chemicals are mixed by affecting the motion
of the specific gravity floatswitch. Variable incoming water
temperature will affect the specific gravity of the mixture itself.
As temperature increases, molecules expand causing the solution to
lose density or become lighter. As temperature decreases, molecules
get closertogether which causes the density to increase or get
heavier. Water temperature will not change rapidly from mix to mix,
or even from day to day, but in more northern climates, water
temperature can vary from 35 degrees F. in the winter to 70 degrees
F. or higher in the summer. In theory, such a larger jump in
temperature from one season to the next will cause the solutions to
become heavier in the winter and lighter in the summer and the mixer
should be calibrated twice per year as a result. Most mixers don�t
get calibrated after installation because the variability in
chemical density as a result of incoming water temperature is not
great enough to cause objections to film readability or processing
quality. However, in some cases, you may find a heavier build-up of
chemicals in the processor or even in the mixer during the winter
months as a result of more densely mixed chemicals. The biggest
negative feature to using an automixer is really more of a hurdle
than a negative feature: someone has to put the bottles on the
automixer. X-ray departments often see this as causing more work
when they are already overworked. It does take time to place the
bottles on the automixer, but probably no more than 60 seconds. Once
the x-ray department realizes that the work involved in using an
automixer really is no work at all, they love to use them. Using an
automixer means being able to store more concentrated chemicals
which decreases the risk of running out of chemicals. In addition,
because the chemicals are delivered in bottles sealed in boxes,
delivery and storage is much neater and more convenient. In
addition, the chemicals are delivered in the manner that the
chemical manufacturer has specified and you can depend of quality
chemical manufacturers to provide consistency from case to case and
from batch to batch and from year to year. So, an automixer allows
the x-ray department or facility the freedom from most mistakes and
the freedom to have cleaner more pleasant working environment.
|
