Conveyors are key

January 29, 2014

12 Min Read
Conveyors are key

Keystone Food Products has come a long way from its humble beginnings in 1946, when it produced fava beans, pistachio nuts and pumpkin seeds in a small family kitchen in rural Easton, PA. The company now has a 180,000-sq-ft plant running snack foods at 24,000 lb/hr on 10 production lines. The plant runs more than 300 stock-keeping units in bag sizes ranging from 3/4- to 32-oz.

"Our success is based on uncompromising freshness and quality, old-fashioned family tradition and a passionate commitment to personalized customer service," says president William Corriere. "In a word, the 'keystone' of our business is quality–quality ingredients, quality taste and quality service."

Initially, Keystone produced snacks under the private labels of other

Vf/f/s machine, above, incorporates a 14-head weighing system and runs a wide range of bag sizes at speeds to 140 bags/min. Protruding fingers, below, shake bags entering the case packer to evenly distribute product. Bags then go through a quality mangement system that checks them for defects.

food companies. However, product popularity encouraged Keystone to market its snacks under its own brand name as well. Today, its line includes more than 20 snack foods, including corn chips, cheese curls, pork rinds, carmel corn, baked tortilla chips, multi-grain chips, popcorn, onion rings, pellet-based snacks and the ever-popular "Original" Party Mix, all packaged in a variety of consumer-friendly sizes. The company packs for other well-known food companies, providing them with private label and contract packing.

With sales growing by leaps and bounds, last year, Keystone reworked a portion of its plant and installed three new high-speed packaging lines to run its most successful products. Utilizing conveyors from Hytrol Conveyor Co., the complex network was designed and line integration done by Hytrol distributor Stokes Material Handling System, who also installed the equipment. The system includes conveyors for empty and full cases of product as well as a rail system for a transfer car to move pallets from the palletizers to a stretch wrapper. "Transporting empty trays and cases from erectors to three case fillers, and then full trays and cases to two palletizers, was a challenge," says maintenance superintendent Todd Campbell. "Conveyors go over and under each other, and there are a lot of merging and diverting points."

V/f/f/s unit includes integral weighing system
All of the equipment on the three lines that Keystone installed is new except for one vertical form/fill/seal machine that was retained from the former installation. The other two vf/f/s machines are Model 2Ci Robag units from TNA North America. The machines were supplied with integral Yamato weighing systems, Markem Smartdate 3C ink-jet printers and Safeline metal detectors. All of these separate units on each machine are linked through TNA's Intelli-sys® control system, which uses proprietary software running under the Windows NT™ operating system. All components can be immediately changed using a touchscreen interface.

Keystone runs most of its products and bag sizes on these machines. Operating parameters for each of these, such as product weight, bag length and width and heat-sealing times are implemented automatically by selecting the appropriate product code on the touchscreen. Additional touches of the screen display settings currently in use, causes of operating problems, and maintenance requirements.

A Yamato Sigma Plus Series 14-head radial weighing system is mounted on a platform above each bagger. Product is delivered to the packaging lines on overhead conveyors and discharges onto the vibrating top cone of the Yamato weighing system. A programmable loadcell under the center cone turns the product discharge on and off to maintain the proper product level on the cone.

The Yamato weighing system consists of 14 individual weigh heads mounted around the vibrating top cone. Each head consists of three main components: vibrating feed pan, feed bucket and weigh bucket. Product discharges from the cone into the vibrating feed pan, which delivers product to the feed bucket. The on/off vibrating pan operates for a preset period of time to put a set amount of product into the feed bucket. The feed bucket, in turn, drops product into the weigh bucket. The amplitude of the vibrating pans changes automatically to adapt to product-flow changes and to maintain accuracy and efficiency. Individual programmable stepper motors open and close the feed bucket, and the weigbht bucket without the use of either external or internal springs.

The amount of product delivered to each weigh-bucket is about one-third to one-sixth of the weight of the finished package, depending on that weight. For each weighment, the control system selects the combination of three or four buckets (for small bags) and six or seven buckets (for large bags) that comes closest to the total bag weight without being under that weight.

Typically, the system achieves accuracies of about 1 to 11/2 g overweight. Each discharge is displayed on the computer monitor, showing the fill weight, exactly which scales released product, and statistical data for each production run.

Not only is the Yamato weighing system easy to operate and extremely accurate, it's also very easy to clean and maintain. Product contact parts can be removed quickly and easily without tools, and each weigh head actuator, which includes stepper motors, loadcells and controls can be removed as one unit without undoing any cables. Scales discharge product through the Safeline metal detector, which is mounted just below the scale platform and above the bagmaker. The unit automatically calibrates itself for bulk product as it passes through the system, tracks the product and continuously compensates and updates itself for optimal sensitivity.

Two rolls of bag film are mounted on spindles on the back of the machine. One roll is actually running, while the second is a backup. The machine is equipped with a sensor that detects when the film is running out, and it shuts down the machine before this happens. An operator splices film from the new roll to the film from the old roll and restarts the machine. Film is pulled through the machine by a combination of front and rear drive rolls and friction drive belts mounted on both sides of the fill tube below the forming collar. Vacuum inside the belts is transmitted through the belts to help ensure positive contact between the belts and the film.

Snack product packaging lines

Click here for an enlarged view.

The Markem ink-jet printer applies a date code to the film as it leaves the roll. An encoder continuously measures the speed of the film and automatically adjusts the printing speed to correspond to the film speed.

The film passes over a series of rollers and dancer bars at the top of the machine, and these, plus an air bladder in the film spindle, maintain the proper back pressure on the film as it moves continuously through the machine. The film passes around a forming tube on the front of the unit, and a hot band sealer produces the vertical overlap seal. Snacks drop intermittently through the forming tube into the continuously moving formed tube of film as it leaves the vertical forming section.

Next, the film passes through the sealing section, which consists of tube closers, product strippers and rotary sealing jaws. The tube closers are horizontal rods that move in against the film and prevent product from falling into the sealing section. The product strippers are curved pieces of metal mounted on the rotary sealing jaws that push product downward out of the sealing area. Finally, the sealing jaws rotate against the film and induction-heat a horizontal seal across the film. As the jaws move away from the film, blades on their tops interact like scissors to cut the bag loose.

A sensor mounted on the film carriage detects the eye mark on the film and initiates the start of each cycle. It compensates for any slight changes in the film length and ensures that the film for each bag will always be in perfect registration. This system basically tells the horizontal sealer and cutoff knife when to energize and tells the code dater when to operate. The machine is controlled by a programmable logic controller and incorporates three servo drives that operate the film drive, the pulling belts, and the rotary jaws, respectively.

After filling, cases are conveyed to a top sealer that folds the flaps and applies tape.

There are occasions when either Keystone or one of its customers wants to apply an auxiliary label to the bags of snacks. To accomplish this, the company installed an EPI labeler to apply pressure-sensitive labels. The roll of labels is mounted horizontally on the back of the f/f/s machine. The web containing the labels travels around the machine to the front, labels are stripped from the web for application to the bag, and the web then travels back to the take-up/rewind drum, which is mounted next to the supply reel on the back of the machine.

Unique case packers overlap bags
Each of the v/f/f/s machines discharge to a Model CP-4600 case packer from Nor-Reg AS. This machine incorporates unique product settling and placement techniques to enable an impressive number of bags to be loaded into the smallest possible case. "This case packer is the heart of the packaging line. You can't place the same number of bags into the case manually," says Corriere.

Bags from the vf/f/s machine drop onto a conveyor that delivers them to a short product-settling conveyor where protruding fingers palpitate the bags to distribute the product in them. The bags then travel to Nor-Reg's Pack Quality Management system, which checks for bags that are over- or under-inflated, grossly misorientated, too long, too short, open or leaking. The checking system consists of an enclosed chamber containing upper and lower band conveyors that transport the bags between them. The first section applies pressure to the bag to remove air if it has a leak, and the second section measures the thickness of the bag. The minimum and maximum acceptable thicknesses, as well as acceptable bag lengths, are entered into the unit's control system. Bags outside of these dimensions are quickly rejected.

The unit provides real-time feedback of the results, and also maintains long-term statistical data about the number of acceptable and rejected bags, as well as the number rejected for each reason. Settings for each package running through the system are pre-set into the unit's control system and the proper values are selected for each product by entering the sku number into the control menu. The system also provides real-time information on flexible film waste levels and tracks the percent of film waste, so that corrective actions can be taken.

Bags then enter the first section of the Nor-Reg case packer. This consists of a pivoting conveyor that moves back and forth to place the bags in the proper configuration in a collation chamber. Bags are placed side-by-side and may or may not be overlapping, depending upon the final pack pattern. Once a row of bags is completed, they are moved onto a steel plate.

Empty cases or trays (the machine can run either) enter the packer by gravity, and are indexed to the loading station. The case or tray is tipped 90 deg, so the open top faces the row of bags, and the plate places the assembled layer of bags in the case. The case or tray is then lowered, and the plate inserts a second layer of bags. This continues until the case or tray is filled, at which point it is tilted back upright and discharges from the packer.

"The plate presses down slightly when it is in the case, so it helps keep the bags flat and provides space for the next layer," says Corriere. "The top layer would never fit into the case if the plate wasn't in there pressing down."

The tops of the cases are sealed by two O/K Supertaper-1A case sealers that fold the top flaps of the cases and seal them with tape. The units incorporate a tape monitoring system that alerts the operator when the tape supply reaches a set level. Code dates are then applied to the cases by Hewlett Packard ink-jet printers.

"We've had Nor-Reg case packers on some of our other lines and they've done an excellent job for us. Their ability to fit the maximum number of bags into each case or tray gives us a significant increase in the weight of product we can load on a truck and significantly reduces transportation costs," says Campbell. Other significant advantages of the CP-4600 packer include quick changeover and the ability to pack product in either a standard RSC case or a display tray.

Case packer overlaps bags in a case so the case will hold more bags.

Cases are set up from blanks by two O/K International Superformer case erectors, while trays are set up by a Nor-Reg tray erector.

Finished cases and trays are conveyed to two Columbia floor-level palletizers–a Model FL100 rated at up to 20 cases/min, depending on case size and pallet pattern, and a Model FL150 rated at 30 cases/min. Pallets are picked up at the discharge of the machines by a shuttle that runs on rails past the two palletizers. The shuttle car transports the pallet to a Lantech S1503 stretch wrapper. The shuttle car system was part of the material handling system from Stokes Material Handling Systems.

More information is available:

Conveyors: Hytrol Conveyor Co., Inc., 870/935-3700. Circle No. 223.

Conveyor distributor and system integrator: Stokes Material Handling Systems, 215/340-2200. Circle No. 224.

Vertical f/f/s machines: TNA North America Inc., 972/462-6500. Circle No. 225.

Weighing systems: Yamato Corp, 262/236-0000. Circle No. 226.

Code daters: Markem, 603-352-1130. Circle No. 227.

Metal detectors: Safeline Inc., 813/889-9500. Circle No. 228.

Labelers: EPI Labelers, 717/235-8344. Circle No. 229.

Case packers, tray erector: Nor-Reg AS, 47/3211-6700. Circle No. 230.

Top tapers, case erectors: O/K Intl, 508/303-8286. Circle No. 231.

Printers: Hewlett Packard, 650/857-1501. Circle No. 232.

Palletizers: Columbia Machine, Inc., 800/628-4065. Circle No. 233.

Stretch wrapper: Lantech, Inc., 502/267-4200. Circle No. 234.

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