Inline viscometer checks copier drum coatings

Hydramotion viscosity control is saving time and money and boosting productivity for Ricoh UK Products in Telford, Shropshire.

In 1972, Ricoh began development of the organic photoconductor (OPC) drums that are now a key component of the company's latest digital copiers.

This was Ricoh's first production plant in Europe and is still Ricoh's only OPC production facility outside Japan, producing up to 22,000 60 and 100mm diameter drums per month.

In the first stage of production, aluminium cores are automatically loaded onto a lathe where they are machined to the correct thickness and surface finish.

The drums are then given an initial inspection before being transported via conveyor to a degreasing line, which removes any remaining swarf, grease or coolant from the machining process and leaves the drums clean, dry and ready for coating with photoconductive material.

Three different layers of coating are applied to each drum.

It is vital that each layer is applied uniformly and to the correct thickness, and since this depends on the flow characteristics of the coating solutions, maintaining the correct viscosity directly affects the quality of the finished product.

This is where Hydramotion viscometers are proving invaluable.

A handheld Viscolite VL700 is used to make a preliminary check of the viscosity of the coating mix, which is made offline and used to supply the process dipping tanks.

Measurement is quick and simple: "We simply take a 500ml sample in a glass jar and insert the probe into the liquid", says Production Engineer Matt Surmacz.

This ensures that the coating solution has the required properties right from the start.

The coating stage, known as "dipping", is carried out within a clean room, which is classed as a hazardous area because of the flammable materials used.

The drums are lifted from a central conveyor by robot and dipped slowly into tanks containing organic polymer-based coating solutions.

A Hydramotion XL7 intrinsically safe inline viscometer is permanently installed on the dipping tank, enabling production staff to monitor the process liquid viscosity constantly.

This instrument also gives its measured output value to a PLC program that automatically dilutes the dipping liquid back to the required viscosity to compensate for solvent evaporation during the process.

"The maximum viscosity we have to measure is 500 centipoise".

"It's controlled at two different settings +/-3 centipoise, depending on the product we're making", explains Surmacz.

Temperature also has to be carefully controlled, since the liquid must be kept to within a degree of 20C.

Surmacz explains: "It is critical that the liquid is at the required viscosity at both the mixing and process dipping stages, because there is a direct relationship between the viscosity and temperature of the liquid and the robot dipping speed".

"So if any of these set-points are incorrect the coating thickness of the drum will be too thin or too thick and the drum will be scrap".

During the final stage of production a flange is inserted at each end, the drums are wrapped in black light-protective sleeves and finally boxed ready for sale.

"We learned about Hydramotion through recommendation of our existing viscometer supplier at the time", said Surmacz.

"We decided to purchase the instruments from Hydramotion as they were suited to our process requirements and were easy to use, giving an instant reading".

"They gave us the facility to put a live digital display in the hazardous area for the operators to monitor the viscosity, and they also gave us the facility to integrate it with our PLC software for the automatic dilution system".

The XL7 inline viscometer has given Ricoh the high level of process control it needed.

"This system now gives us a stable dipping process with no fluctuation in the viscosity".

"With a set lifter speed and liquid temperature we can now run this process with great efficiency".

Before discovering Hydramotion, Ricoh had to depend for viscosity measurement on an offline rotational instrument.

This had a number of disadvantages: it could not be integrated into the automated system and it had to be located in a lab away from the dipping process, which meant operators would lose time analysing the liquid.

Also, repeatability was adversely affected by the small sample size and solvent evaporation during the test.

"The Hydramotion viscometers are easy to use", says Surmacz: "and they give us instant results for our process liquids".

"They were easy to install using the hygienic fittings and clamps, and have required no maintenance".

"The only check we carry out is a measurement of a known viscosity standard every month to confirm their accuracy".

These checks have only served to reinforce the company's faith in Hydramotion.

"Since the viscometers were installed they have proved to be 100% reliable, with no fluctuation on the measurement of our liquids", Surmacz said.

"We would definitely recommend them to other companies considering buying them".

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