Tubular containers for snack foods - for example, a well-known brand of circular crisps - are established and well known. Similar containers can also hold heavier goods such as bottles, but the largest potential for this packaging medium is with snack foods. Such containers (known as ‘cans’) must be hygienic and airtight, and are usually made with two layers of paper and an inner liner of aluminium foil, with product graphics applied to the outside of the tube.
Dewsbury based cardboard tube forming machine specialist, C Perkin has developed a finished can with both a paper base and a paper top – the latter feature being something of a market innovation. The foil-lined ends are rolled into the end of the tube for load bearing strength and then heat-sealed. This arrangement is significantly lower in cost than alternative plastic or metal caps, much more environmentally friendly and actually looks better. Once the can is opened the paper top (which includes an inner foil seal for transport and storage purposes) can reseal thanks to its tight fit around the can body.
The company’s recent order from Los Angeles called for a machine capable of producing cans for tacos at the rate of 120 per minute. The process begins with a tube winder, which rolls two narrow strips of cardboard, together with a foil lining, on a mandrel, with glue being applied to connect the layers. The mandrel is driven by a Lenze geared motor and inverter. This tube is cut at one metre intervals by a flying saw, powered by a Lenze servo drive and motor.
Cut tubes are then passed to the next stage, the composite can labeller (CCL), which is a servo-driven machine that applies glued labels to the finished length. The CCL processes are based on the mechanical concept of a four-mandrel ‘turretting’ head. At the first position the 1m long tubes from the winder are automatically loaded. At the second turret position, a glued label is applied and wrapped around the full 360° of the tube. The label is fed from a separate unwind and gluing station, and is handled by vacuum rolls. At the third turret position the tube is cut to length by a pre-positioned rotary knife, the motion of which is controlled by a Lenze servo-driven linear actuator. In the final turret position the finished can bodies are automatically unloaded.
The complex, high-speed motions of the CCL require five servo axes and two inverter axes, all of which were supplied by Lenze. The ‘Application’ version of Lenze’s ECS drive was selected for the servo axes. This has powerful PLC functionality built in, offering free programmability via IEC 61131-3 compliant languages. All the motion control in the drives was configured using an internal ‘cam’ software library, which allows the profile shapes to be easily defined by following an intuitive set-up routine.
In the leading drive, Lenze created a virtual master axis, which is followed by all five servo axes. The first of two CANbus connections is used to synchronise all drives and a ‘telegram’ from the master axis ensures that there are no position errors. Each axis holds its own cam profile, and operators can adjust profiles on the fly – fine tuning the can length, for example. Homing is only needed once on each machine power-up. Any subsequent problems that require a restart benefit from an instant reset to the virtual master.
A second CANbus connection on the drives is used for process control, basic on/off commands, and so on, as well as linking to the operator station HMI. Remote monitoring of machine performance is possible from a standard laptop PC connected via Ethernet to all the hardware. All the machines in the taco can production line are linked by this Ethernet connection, enabling remote diagnostics from anywhere in the world. Fault diagnostics and the application of software patches can be enacted from the UK, thus avoiding expensive and time-consuming service trips.
The next machine in the production line is the ‘Flange, Disk and Bellnose’ (FDB), which creates the base disk of paper and foil layer that is inserted into the end of the can body. Prior to this, the end of the can is flanged, increasing its diameter slightly in order to accept the disk. The base is heat-sealed in a crimp process and then rolled to achieve a finish that is both load bearing and smart in appearance. The FDB is a complex mechanical system, driven by four servo axes (Lenze ECS units) and a further two inverter axes.
Completing the production line is a multiple flying knife that cuts tube to the relatively short lengths required for cap body, and then a finishing machine similar to the FDB that completes the cap with a foil lined disk.
C Perkin director, Michael Kirby, pays tribute to Lenze and a partnership that has given his company a foothold in a very significant market for packaging machines. “From cardboard strip to a high specification food container, the all-paper composite can has given us the lead in the snack food market, and the partnership with Lenze has enabled us achieve the high-speed motion control we needed for this application.”