A£5 million (US$9관) investment in new equipment for the production and packaging of Ginger Nut biscuits has turned a largely manual operation into a highly automated one at United Biscuits’ Carlisle, England, plant.
While a portion of the investment went toward a new mixer and a controls upgrade on the oven, the bulk of the new equipment is packaging related. Productivity gains have been impressive since the line went into action last June. Five “technical operators” now package nearly 40% more product than the 25 operators that used to handle packaging before automation entered the picture. Dedicated to McVitie’s-brand Ginger Nuts—a “biscuit” in the U.K. but a “cookie” in the United States—the line runs around the clock five days a week.
An added benefit gained since the new line went in is improved shelf presence on primary packs thanks to a switch from roll wrapping to flow wrapping.
“A gusseting finger on the wrapper pushes the end seal in,” says unit manager Peter Scott. “On a conventional flow wrapper, the end-sealed portions are wider than the pack itself. This flow-wrapped version is a much neater pack.”
Supplied by Alcan Packaging, the new material used for primary packs is a two-layer adhesive lamination of 20-micron clear release polypropylene and 28-micron voided white PP. Graphics are reverse gravure printed in six colors on the clear PP substrate.
In selecting packaging machinery for the reborn Ginger Nuts line, UB went with an integrated-system approach. From the cooling conveyor at the head of the line to the robotic case packer that brings packaging to a close, the bulk of the line consists of equipment from Sigpack Systems (now part of Bosch Packaging Technology Co.). “We went with what is generally recognized as the best of its kind in the category,” says Glenn Allison, principal engineer at the Carlisle plant.
Individual pieces of equipment are each governed by a Rockwell ControLogix controller, which handles both logic and motion. Also distinguishing the line is that it is designed around Sigpack Systems’ Systegra concept, where all machines are tightly integrated over a communications network, in this case Profibus. As Scott puts it, “The whole line is intelligent. Each component communicates back and forth with the others along the communications network.”
Flexibility and rapid changeover were also important objectives in designing the line, partly because UB serves the needs of private-label customers as well as making its own-brand biscuits. “Rapid changeover is what lets you maximize opportunities,” says Allison. “A film change may take two or three minutes. Combine it with a change in slug size and case configuration, and it’s more like 45 minutes.” The slugs are produced in four sizes: 200-, 250-, 300-, and 400-g.
It begins on the ground floor
Packaging begins when the biscuits are conveyed from the ground floor mixing and baking operation up to the first-floor packaging line on a broad cooling conveyor. Dividing lanes channel the biscuits onto two separate belt conveyors, each leading to one of the two packaging legs on the line.
In Leg #2, biscuits move from collating to flow wrapping to accumulation to case packing to case taping. Film is brightly decorated with either the McVitie’s graphics or the graphics of whatever private-label customer UB is packing for.
Leg #1, which will be described here, is the same as Leg #2, except that it includes an optional spur that takes flow-wrapped biscuits to a rotary transfer wheel and then to a second flow wrapper that combines two slugs of biscuits in a single pack. Watching Leg #1 in action is all the more impressive knowing that biscuits used to be hand-fed into wrapping machines and then slugs of wrapped biscuits were case-packed manually.
One of the first tasks in packaging the flat Ginger Nut biscuit is that of coaxing each individual biscuit onto its edge. McVitie’s accomplishes this simply enough by putting vibratory channels a few inches beneath the upstream belt conveyor that feeds them. This short drop causes the biscuits to shingle, and as they are vibrated forward they gradually—and gently—orient themselves in an upright position ten rows across.
The first piece of equipment following the 10-lane vibratory infeed is a 10-across Sigpack ZHG system that portions biscuits into whatever portion is being packed. This task of portioning is done by measurement. For example, a 200-g slug of biscuits typically requires 20 biscuits. As soon as the right number of biscuits have been measured, a mechanical stop halts the further ingress of biscuits. The 10 groups just measured are then advanced into a feeding tray and then down into a flighted conveyor moving continuously at a right angle and leading directly into another right angle exchange leading directly into the Model HSS flow wrapper.
Capable of up to 140 packs/min, the flow wrapper has mounted on it a Markem Smart-Date thermal-transfer coding unit. The wrapper typically applies a cold-seal film that’s clear since the downstream flow wrapper in Leg #1 will shortly cover the primary packs in a decorated overwrap.
An Ishida combination checkweigher/metal detector, available in the United States from Heat and Control, sits a short distance downstream from the flow wrapper. Because Ginger Nuts are notoriously difficult to produce with perfect consistency, it’s not uncommon for slugs of 20 biscuits to be found too heavy or too light. The checkweigher detects this and sends a signal back to the ControLogix controller on the HSS flow wrapper. From here another signal is sent to the servo motor on the 10-lane ZHG feeder upstream telling it to increase or decrease the number of biscuits it is feeding into each portion in each of its lanes.
“The fingers on the machine adjust automatically thanks to the communications carried over the network,” says Allison. It is precisely this kind of integrated control that makes it possible to have just five people operating the two collators, three flow wrappers, one rotary transfer wheel, two accumulation systems, two case erectors, two case packers, and two case tapers that make up the two-legged packaging line.
Rotary wheel transfer
Feeding the slugs of biscuits from the HSM flow wrapper to the HBM overwrapper is a rotary feeding wheel. With an assist from Sick laser through-beam sensors that accurately identify the leading edge of the leading biscuit and not the clear film, the transfer wheel’s vacuum pickup heads transfer slugs of wrapped biscuits into a flighted conveyor that leads to another right-angle turn. Here, pairs of slugs take a right-angle turn into a flighted conveyor leading to the HBM overwrapper. Background-suppression photocell sensors, again from Sick, ignore the polished stainless steel of the conveyor track beneath the slugs and confirm that two slugs of biscuits are indeed in place and ready to be flow wrapped.
Exiting the second flow wrapper, which also incorporates a Markem Smart-Date coder, the twin packs are conveyed directly to a Sigpack TTL robotic top-load case packer—unless the case packer isn’t ready for some reason. In that case, a Sigpack FS Store first-in/first-out vertical accumulation system receives the twin packs until the case packer is ready.
“If the case packer needs to be cleared of a jam, the biscuits accumulate in the FS Store like cars in a multistory car park,” says Scott. “Should the FS Store be filled to capacity, it signals the wrapping machine to halt and in turn the ZHG collator/feeder, as well. Biscuits continue to fill up the 10 lanes of the vibratory infeed channels until the downstream equipment is freed up. It’s all tightly integrated.”
Complementing the TTL robotic top-load case packer is a Sigpack automated case erector that accommodates up to 13 different case or tray varieties. Regardless of the variety, it brings the case or tray into top loading position with the bottom glued. A change from one format to another takes minutes and is done by selecting from a menu of options on the HMI screen. Cases are taped shut and date coded by a Markem ink-jet unit before being conveyed to a remote palletizing area.
Handling nearly 7 million biscuits daily, the line has been running smoothly since its installation last June and is now being evaluated by other UB facilities that might also stand to benefit from an integrated-systems approach. None of this surprises engineering manager Allison. “We knew the quality of the system when we bought it,” he says.