High-speed Production Line Modernized without Downtime

Although use of plastic—rather than glass—bottles is the current consumer trend, Longslow Dairies Group thinks otherwise. It holds that, in this new age of environmental friendliness and recycling, products in glass bottles will give consumers a sensible, cost-effective environmental form of milk packaging.




  • Slaves under central master PLC

  • Real-time speed synchronization

  • Dual product processing

Although use of plastic—rather than glass—bottles is the current consumer trend, Longslow Dairies Group thinks otherwise. It holds that, in this new age of environmental friendliness and recycling, products in glass bottles will give consumers a sensible, cost-effective environmental form of milk packaging. To this end, it has installed the U.K.'s first, totally automated, milk-bottle packing operation at its Central Dairies plant at Colwyn Bay.

"Easy to use and easy to maintain" was the mandate given to Dawson, the Heckmondwike-based filling-cleaning-and-handling systems manufacturer that designed, built, and installed the system. A simple solution was created that requires no manual interaction to run. Although the initial order was only to automate parts of the system, as the system was installed, Longslow was so impressed with the results that it expanded the system to automate the whole plant.

Andy Bethel, Longslow's area-engineering manager, had no problem in justifying spending for the new automation. He said, "Before the automated system was installed, we were running at about 60% efficiency; with the new system, we are averaging 87%. Throughput has also increased by 30% due to the improved control of the plant. The increased data we now receive back from the plant is much more accurate, allowing us to identify throughput restriction areas and correct them to make the system even more efficient in its operation."

Modular construction

To facilitate modular plant construction, Dawson chose CC-Link fieldbus technologies. Said to offer high immunity to noise and a flexible additional station insertion system, CC-Link became the communication backbone among sections of the newly automated plant. Longslow was Dawson's first CC-Link installation. Ease of adding sensors and stations to the CC-Link system simplified adaptation to changing customer needs—inevitable during new equipment installations.

The plant system is divided into seven basic sections. Each is controlled by a small PLC. It, in turn, controls all local operations and connects to a central master PLC using CC-Link. Using intelligent slaves—rather than one large PLC to control the whole plant—allows sections to continue operation, even if other plant areas have problems. This ensures high throughput and increased section efficiency. The central master PLC coordinates all communications. CC-Link's 10 MB/sec data-transfer speed and flexible, deterministic data-packaging was deemed crucial to the system's success, Dawson noted. Using CC-Link for distributed control permits simultaneous controlled shutdowns of even remote sections and makes warm startup of the production process much easier.

System installation took only six weeks, with Dawson working around the dairy's daily production requirements. CC-Link was said to drastically reduce wiring installation time, which was critical, as they could only install the system at night, or during shutdown periods.

Continuous 'big gulp'

The bottling line has two feeds, one each for returned and new bottles. Each returned bottle is re-used up to 15 times. This makes the packing process much more environmentally friendly than with disposable plastics. Used bottles are input to the system in crates of 20 bottles each. Crates are stacked up to seven high, with as many as 44 crates at a time input into the system. After entering the system, the crates go into a 600-bottle-per-minute Dawson de-grouper, which unstacks the crates and puts them into a single stream that is fed into the bottle de-crater.

Bottles then move into the soaker-washer machine. It sprays high-pressure water into the bottles to remove debris. Then, the bottles spend 10 minutes in a soak tank, prior to being rinsed of all trace elements from the cleaning process.

During the soaker-washer stages, the bottles are heated to 36 °C in the pre-soak, and then slowly raised to 73 °C in the soak tank. Temperature rise and subsequent drop must be smooth as temperature shocks can cause bottle fracturing. Sterilized bottles leaving the cleansing cycle are given a final chilled-water rinse to reduce bottle temperature to an acceptable level for filling. New bottles supplement clean ones to fill the production requirement by a combination conveyor system, where new and cleansed bottles combine into one line ready for inspection.

Line sensors match the speed of the single-line conveyor (via a variable-speed drive) to the exact spacing requirement needed for the inspection of the empty bottles. A Prism scanner scans (up to 14,000 times/sec) each bottle with three separate cameras and detects bottle dimension irregularities or deviations down to 0.5 mm, along with any residual water from the rinse cycle. Reject bottles are diverted off the production line. Glass is highly abrasive and, as the bottles pass along the stainless steel conveyors, synthetic oil lubricates their bases. Oil reduces friction on the conveying process, preventing wear to the bottles and the steel conveyor.

Immense pressure can develop from pushing bottles along a conveyor; a modulated variable-speed conveyor keeps this at a tolerable level as bottles leave the scanning section. The modulating conveyor checks the pressure the bottles are exerting, adjusts speed, reducing pressure by a third, decreasing bottle breakage to nearly zero. That increases efficiency by reducing the number of times operators must stop the flow to remove broken glass.

After inspection, bottles enter the Dawson carousel. There, they are filled at a constant 4 °C with milk or orange juice. Foil capping seals the liquid in the bottle. Milk used in the bottling process is processed on site; a tanker delivers the orange juice. Using CC-Link on the filler carousel allowed removal of control equipment from the machine. This diminished filler system size, and reduced the number of items to clean, improving the overall process cleanliness and lowering downtime for cleaning.

As bottles leave the filling station, a Dawson re-crating machine puts them back into the same delivery crates. These have been high-pressure washed automatically and then sent to the re-crater to be loaded with filled bottles.

The crate-washer control system is linked to the bottle filling process. The system intelligently washes the required amount of crates as needed, reducing water consumption and saving energy.

Dawson's re-crate machine can process 500 bottles per minute. CC-Link communication between filling and re-crating avoids bottlenecks in the production process.

Automating all process sections allows system parts to work seamlessly. High data processing of CC-Link's communications among sections ensures that all parts of the process are real-time speed synchronized, at any production speed. Communications among sections reduces energy waste; sections only run as fast as needed.

The production process' last stage transports the crated product to a restacking machine. There, five crates at a time are stacked for easy dispatch to waiting trucks. Since on-site space is at a premium, the whole process is "just in time." Requirements are set daily based upon orders. As plant capital cost was a major concern, all equipment in the automation process was second hand. Dawson located, refurbished, and reengineered the required machines to meet the new automation requirements.

No reconfiguration

Flexibility is very important, and the system supplied by Dawson can produce any type of bottled milk without reconfiguration. Using CC-Link's flexible-station-recognition system allows stations to be taken off-line without errors and introduced at any time without fuss. Switching the system from milk to orange juice takes 20 minutes, including wash-downs and physical changeover of the filler carousel for orange juice.

After 12 months of increased efficiencies, Dawson, collaborating with Longslow, will expand the system by linking it to Longslow's high-level management system and installing remote, maintenance, and diagnostics tools. This is expected to increase control and further reduce downtime.

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