Moving from Powered Roller Case Conveyors to Plastic Modular Chain Case Conveyors
Uptime is critical within the high-speed food packaging and beverage industries. One key area is in case handling between case packers and palletizers. Upgrading from powered rollers to plastic modular conveying chains not only increases line uptime and efficiency, but also increases flexibility, quality and safety.
1. Shifting packaging trends
One major trend is cost savings through the use of lighter-weight and higher quality packaging materials, and even the elimination of some packaging. This results in cases of containers that can be unstable and much more susceptible to damage. For example, most PET soda and water bottles are now only shrink-wrapped with no cardboard sheet or tray on the bottom. This makes them impossible to be conveyed on conventional roller conveyors. Another example is 12-packs or smaller packages of cans are usually packed in very thin lithographed cardboard packages. When conveyed on roller conveyors, these cases bounce, causing the cans to wear “rings” on the bottom of the case, which, in turn, ruin the package appearance. The lithograph printing also wears off these packages and deposits heavy build-ups on rollers, which can result in damaging the packages.
Another packaging trend is an increase in the variety of packages, including small, hard-to-handle cases. These shorter cases cannot be easily transferred between many conventional conveyor sections.
Plastic modular chains:
• Easily handle unstable packages; packages with uneven bottom surfaces, and multiple package sizes
• Eliminate any case bouncing via smooth, stable case transport, resulting in minimized package scuffing and damage
• Simplify case accumulation with minimal sensors and no external activation devices
• Mitigate lithograph buildup
2. Increasing production speeds
Even though beverage containers and packages are getting thinner and less stable, production speeds continue to rise. With bottle filling speeds of 1,200 bottles per minute and can filling speeds up to 2,400 cans per minute, the case conveyor speeds can be as fast as 200 to 300 feet per minute. At these speeds, rollers now wear out very rapidly, causing package damage, reducing uptimes and increasing maintenance/replacement costs. Plastic modular chains can easily run at these high speeds for many years while protecting the packages and improving production efficiency. While food processing speeds are slower than beverage, delicate products such as chips, cookies, crackers, pastries, cakes, and pies can be damaged from vibrations caused by roller conveyors. Additionally, damaged components in the drive system (belts, rollers, etc.) cause dead spots that may affect product quality on timesensitive products in refrigeration and freezing areas.
3. Safety precautions
Safety precautions are a critical consideration when it comes to production line setup:
• Pinch points typically occur every 3 inches with roller conveyors, whereas with plastic modular chain, pinch points only exist at the end of each conveyor
• Plastic modular chains operate at significantly lower noise levels even at high speeds; this reduces overall noise levels, helping to achieve permissible OSHA exposure limits
• Sliding chain returns eliminate sagging chain which can pose a serious danger to workers in the vicinity
4. Reduction of unscheduled downtime
Powered rollers wear out rapidly and need continual replacement. Belt-driven roller systems require tensioning and tracking adjustments. Line shaft systems require continual replacement of O-rings that increase general maintenance costs and potential unscheduled downtime. A major benefit of plastic modular chain is that any maintenance or repair is usually limited to just that damaged chain section, without the need to replace the entire chain.
When comparing the two types of conveying methods more specifically, plastic modular chain:
• Uses sprocket teeth to positively drive the chains, versus friction-driven belts or o-ring driven line shafts, resulting in no chain slippage
• Provides edge guides to track the chains in a straight path to eliminate damaged chain edges
• Eliminates the need for take-ups and their associated maintenance
• Does not have any O-rings to continually replace (compared to line shaft driven rollers)
• Eliminates the need for large inventories of repair parts; the only replacement parts required are sections of chain and a few sprockets
By Bob Bigoness, Application Engineer, Rexnord and Chuck McGrady, Application Engineer, Rexnord