High-availability process control solution as a cross-discipline core of a newly erected smart factory where glass bottles are manufactured for the pharmaceutical industry
Within the international glass industry, Zippe is renowned as the contact of choice for batch and cullet plants. Owner-operated in its fourth generation, the company was formed in 1920 and supplies everything from one source, from planning to commissioning. Forty-five experienced individuals are responsible for the realisation of modern, high-performance automation and control systems.
“Within our industry, successfully completed reference projects are frequently the deciding factor for being awarded an order, or not. It is therefore imperative that we deliver systems with a high level of availability, which are efficient and easy to operate,” Joachim Ullrich department head, Zippe, who places great value in selecting suitable hardware and software solutions, explains.
Glass production plants usually remain in operation for ten to 12 years, without interruption. Even if the plant only has to run for 16 of 24 hours, longer shutdown periods are still not an option. “A maximum of three hours, then production has to continue,” Ullrich confirms. He adds that reliably functioning systems are one of the main requirements of the glass industry. Especially as the Zippe plants are directly connected with the centre of the entire production system, the glass melting furnace.
“We take care of everything that has to happen prior to this step: From the delivery of the raw materials to their dosage and weighing, in some cases requiring precision to the exact gram,” Ullrich says. Across the almost 100-year corporate history, a total of approximately 600 batch plants as well as more than 1,000 cullet plants have been designed and implemented by Zippe in accordance with customer requirements.
Zippe is globally renowned for a wide range of skills. The ability to modernise existing plants during continuous operation is one of the major strengths of the Wertheim-based company. Plant designs, which provide precisely what the final customer envisages, are another specialty of the house.
Greenfield plant
During a greenfield project in France, Zippe was contracted to deliver a batch plant with mechanical conveyor technology and a cullet return system. With regards to the execution of this project, the following requirements had to be met: The plant should be designed to supply two furnaces with a total of 130 tonnes of mixture in 16 hours. Output reserves were requested, and the facility should allow three different types of feeding – big-bag filling, filling with silo trucks and mechanical loading. The plant had to be erected within one year and put into operation with the supreme satisfaction of the final customer. Finally, the utilisation of a PlantPAx ready system as a higher-level process control system was demanded – PlantPAx is Rockwell Automation’s distributed control system. This should ensure a uniform look and feel at all operating and monitoring stations of the entire factory.
“We have already been working with Rockwell Automation in a highly successful manner for many years,” Ullrich says. “We were already supplying plants with Allen Bradley control systems as early as back in the 90s. The demand is increasing, especially in Australia, America and South Africa.”
The PlantPAx ready system is virtually predestined for sensitive applications, in which reliable around-the- clock operation is a requirement. This is because this process control solution not only guarantees a high level of availability via the redundancy of system components, but also by means of a device level ring topology in the EtherNet/IP network.
“The major advantage of the PlantPAx ready system is that it acts across different disciplines and combines the different areas – i.e. the continuous furnace control and the batch plant – into a joint network,” Ullrich continues. “Devices that actually communicate over a different protocol, such as, for example, the electronic systems for weighing or the barcode reader, can also be easily integrated into the higher-level process control system.” Ullrich is satisfied with an engineering-friendly solution that enabled Zippe to make an entire batch plant with mechanical equipment, with conveyor belts, with feed units, with motors, with screw feeders, with a large 4,000 litre mixer, and the entire automation technology including control cabinets fully operational in only one year.
Ullrich adds that shortly after they were awarded the order, Rockwell was there and actively supported them in the selection of the appropriate components and in the design of the plant network. “The final customer is very satisfied with what we have realised together,” he adds, especially since enough reserves were planned and included on the system. The first small expansion, to integrate an additional raw material weighing system into the process control system has already been implemented.
The pre-furnace silo, that is the silo upstream of the glass melting furnace, demands replenishment in a fully automated manner if a certain threshold value has been on the batch plant. The supplies of sand, soda, dolomite and limestone are generally among the most important ingredients found in the production of glass and must be 100 per cent according to the recipe.
Varied mixes
The Zippe batch plants, however, need to potentially weigh other ingredients, in some cases with to-the-gram precision. “Every single one of our customers has his own special and secret recipe when it comes to the mixing ratio of the raw materials contained in his glass,” Ullrich explains. “The important thing is that the individual components are weighed precisely and within a certain period. This enables a new batch to be produced every five minutes.”
Consequently, in addition to the ‘calling signal’ of the pre-furnace silo, the weight signal of the weighing vessel is one of the most important pieces of information processed by the process control system.
Ullrich explains that this higher-level intelligence ensures that the silos are loaded correctly. “With the help of technical aids, we can ensure that sand does not end up in the soda silo,” he says. “By scanning the barcodes on the delivered raw materials, the control system sets the correct path. A wrong selection is then no longer possible.”
The system also proves itself to be very user-friendly when it comes to monitoring adjustable frequency drives. Drives are displayed on the visualisation stations with icons and faceplates and managed on the asset management level. In addition, disaster recovery functionality enables the system to automatically backup and restore the drive configuration as well as logging of changes. Extensive diagnostic information is delivered directly to the user on the HMI level.
The RA Process Library contains ready-to-use control and diagnostic objects. This allows the entire production process to be easily monitored. “Thanks to a seamless EtherNet/IP network structure, the technicians can route through right up to the variable frequency drives to retrieve individual variables or current signal states,” Ullrich adds, stating the benefits of the faceplates for diagnostics and maintenance. Alarm indication and parameterisation are also simplified by the RA Process Library.
By utilising a PlantPAx ready system as a higher-level process control system, a modern Smart Factory to produce brown glass bottles and ampoules has been erected in France. It is intelligently and redundantly networked via EtherNet/IP and offers real-time visibility on all the currently running production processes. It is simple to expand and offers a wide range of connection options. Thanks to PlantPAx, all operating stations exhibit a uniform look and feel with standardised icons for visualisation purposes.
This reference project has entered operation as scheduled. “We generally want to ensure that our customers can get started with the plants supplied by us as soon as possible,” Ullrich concludes. “This is why we test all control systems in detail before they leave the company. We work with virtual production data, enter different recipes, produce thousands of batches and simulate an entire monthly production in order to avoid any ambiguities or errors in advance.”
Having passed these tests with flying colours it is no surprise that Ullrich is thinking of increasingly utilising this process automation solution in Zippe’s batch and cullet plants.
Extra Information – The bottle-making process
The batch house is the initial location where raw glass material is housed in large silos before entering the glass furnace operations phase.
After leaving the batch house, the mix is fed continuously into the furnace or tank where it is melted into glass. The glass depth must be controlled to within ±0.01 inch for proper forming machine operation.
Furnaces consist of three main parts, the melter, refiner and regenerators or checkers. Most furnaces are designed to use natural gas but can use alternate fuels-oil, propane and electricity if necessary. Furnaces range in size from about 450 to more than 1,400 square feet of melter surface.
A properly operated and well-maintained furnace will last for ten years or more with just one partial repair and will produce over 1,000 tons of glass per each square foot of melter surface over the life of the furnace.
The melter is a rectangular basin in which the actual melting and fining (seed removal) takes place. In a side-fired furnace, the batch is charged into the furnace through the doghouse, which is an extension of the melter, protruding from the back wall. Along each side of the melter, above glass level, are three to seven ports, which contain the natural gas burners and direct the combustion air and exhaust gases.
The melter basin is separated from the refiner by the bridge wall (throat end wall). Glass passes from the melter to the refiner through the throat, which is a water-cooled tunnel that extends through the bridge wall.
The refiner acts as a holding basin where the glass can cool to a uniform temperature before entering the forehearths. The melter and refiner are covered by crowns to contain the heat.
Feeder and delivery molten glass flows with the help of gravity from the refiner through the forehearth.
From there it is carefully cooled to a uniform temperature and viscosity prior to reaching the feeder. Using the pull of gravity, the hot glass flows through the orifice at the bottom of the feeder. Glass flow is controlled by the height of a ceramic tube in the feeder; a raised tube creates a heavy flow while a lowered tube results in a reduced flow. The glass flow undergoes a mixing action created by the rotation of the ceramic tube. This helps to make the temperature consistent while the downward motion of the plunger accelerates the glass flow.
This pumping action is timed with the shearing of the glass flow as it falls beneath the feeder to shape the falling gobs. After the gob has been sheared from the feeder it falls into a series of chutes where it is delivered to the blank mould on the Individual Section II machine. This is designed to ensure efficient production so that operators can take one or more sections out of production for repairs without shutting down production in other sections. Gobs enter the I.S. machine and are formed into containers through a process of controlled shaping and cooling of the glass. The total time needed to produce a container varies, but beer and soda bottles take approximately 10 seconds. Depending on the container’s size and shape, the machine’s production speed may be as fast as 700 containers per minute.
