Safer product sampling

While planning the recent installation of a new processing line, engineers at Eastman Kodak's plant in Rochester, New York, envisioned a fully automated, completely closed system that would eliminate the need for manual control and contact with the product photographic emulsions. Although their design raised health, safety and environmental safeguards to a new level, while at the same time boosting productivity and process consistency, it also needed a totally new approach to quality control sampling one that would retrieve multiple samples automatically while keeping the system closed and samples in the dark.

Sampling of photographic emulsions essentially silver halide crystals and sensitising dyes suspended in a viscous gel solution is essential because of the number of individual ingredients that have to be dispersed with a high degree of uniformity. Depending on the type of film, an emulsion pack can contain up to 20 coatings of different emulsions and interlayers; a flaw in any one of these can ruin the finished product.

Different products

At Kodak, the emulsion-making process typically requires four to twelve samples, of approximately 100ml each, drawn during the process cycle to profile product composition and confirm completion. Different emulsions have different sampling and test specifications set by the formula engineer responsible for their product. Some tests are aimed at measuring performance criteria such as photosensitivity and reaction speed, while others check simpler physical criteria such as viscosity and concentration levels of silver and other key components.

One of the reasons for opting for a completely enclosed and automated system was to eliminate the manual spigot or ladle-dip sampling methods of older processing lines. These methods often require lights to be turned off while the samples are drawn a hazardous operation given the emulsion processing temperature.

Another key factor was to make the sampling procedure more consistent. Each formula specifies exactly when samples should be drawn and how much fluid should be taken, but when done manually, there was no assurance that it would be done according to spec every time and there was always the risk of spillage.

Such spillages do not present an environmental problem as such, since a central drainage system on the 1300 acre site diverts all spillage's and process effluent to a central holding tank, appropriately known as the 'Rich Pit', from which hundreds of tons of silver and other valuable chemicals are recycled each year. However, spillage is still a labour cost and anything that reduces it is welcome.

Automated sampling not only eliminates these problems, but minimises the time involved in retrieving samples as well, allowing shorter, more controllable cycle times. It also keeps the amount of emulsion withdrawn for testing consistent within each formula.

'To take full advantage of system automation', explains one of Kodak's senior engineers, 'we wanted each location to have a sample collection station that could gather a number of individual samples on command from a PLC and hold them in a light-tight enclosure so an operator could retrieve all samples in a single visit.'

Each sampling station also had to be compatible with automated CIP (clean-in-place) procedures planned into the new processing system. After each sampling cycle, cleaning solutions would flush the transfer lines and wash through the sampler, voiding directly into a Rich Pit drain.

After reviewing several types of sampling devices, Kodak chose Isolok samplers made by Bristol Equipment for two reasons, according to Kodak's senior engineer: 'first, the Isolok design works very well with our PLC control and CIP scheme; second, Bristol demonstrated the technical capability to custom-design and build the system we wanted.'

Each Isolok is installed at an access port built into the emulsion system pipeline and is mounted on top of a sample collection cabinet. In this cabinet is a rotary indexing tray that can carry up to 16 uncapped sampling bottles, with their caps resting in slots next to each bottle. Under PLC control, each bottle is moved into and out of the filling position under the sampler. The PLC also controls the activation of a plunger in the sampler body, which when injected into the process line captures 20ml of fluid in a sample spool for transfer into a sample bottle.

Triple elastomeric seals encircle the plunger at both ends of the spool to keep the access port closed regardless of plunger position. Unlike spigot valves, this isolating design prevents the sampling functions from affecting or being affected by process pressure.

At designated times during the process cycle, the system's PLC program triggers five plunger movements per bottle to deliver the total sample volume required. Then, in a single visit after all the samples are drawn, an operator retrieves the tray of filled bottles and inserts a new tray of empty bottles. If the samples are drawn for light-sensitive performance testing, a switch close to the sampling station allows the operator to turn out the lights momentarily and place the caps on to the opaque bottles, before taking the tray away.

Under normal automated operation, the only time an operator needs to enter the processing area is when samples are ready for harvesting. At each sampling station, a custom-built pushbutton control panel allows the operator to signal the PLC when the filled sample tray is being removed, and when the new tray of empty bottles is in place.

Samples are taken on their tray to a nearby receiving stations, where a technician logs them and sends them via pneumatic-tube to the testing labs in another building.