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Retrofits for aging extrusion lines

At 30 years old and approximately 75-ft long, the Black-Clawson two-station extrusion laminator that dominates the Amgraph production floor has made the switch from analog drives and drifting system variables to a modern all-digital system.

As customer requirements surpassed the capabilities of the existing system, Amgraph faced several choices for supplying flexible packaging solutions for the food industry. It could spend millions on a new machine, settle for lower productivity and product diversity, or retrofit the equipment with modern controls. Amgraph opted to replace its analog control system with high-efficiency motors, digital drives and updated controls.

As a result, Amgraph now produces a wider variety of coated plastic and foil flexible food packages, was able to cut material expenditures and improve throughput, and boost productivity.

RetrofitTension Control
Circonix, a Siemens system integrator and solutions partner that specializes in web handling applications, was contracted by Amgraph to redesign its packaging machine's automation system.

"Initially, the machine had four different motors with analog drives and controls, each with their own wiring harness and relay logic, which really made the machines a challenge to maintain," says Andrew Alaya, vice president of engineering for Circonix. "Only one of the sections was capable of tension control, which forced Amgraph to operate the extrusion machine in draw mode. This meant that the machine could only handle certain types of coatings without breaking the web and going down. Improving that uptime through better tension control was the main goal of the project."

Circonix engineers decided to retrofit the extruder's four existing analog drives with Siemens motors and Sinamics S120 drives, while adding four load cells inline and a new Fulton Machinery dancer to the machine's two unwind spindles. Two Vetaphone treaters were also added inline as part of the retrofit. These effectively eliminated the need for the primer coater, and served as pull stations for the machine, also now driven by Siemens motors and drives. These modifications allowed the machine to work in closed-loop tension control mode.

By changing values on the HMI and PLC (provided by Wonderware and Rockwell Automation, respectively), Amgraph can now precisely control the speed and thickness of the web, turn various systems such as treaters, laminators and tension control systems on or off, and apply thinner coatings to package materials without worrying about additional web breaks and downtime, or thicker coatings to meet special customer needs.

Retrofit 2"Now that we have more control of the system, we're looking at replacing the thicker films that we used to purchase from other vendors with extruded materials we make ourselves, which saves us money," says David Rand, production manager at Amgraph. "Our initial trials have been successful."

The new motors, upgraded digital drives and new controls also increased the extrusion machine's uptime, throughput and productivity. The high bandwidth of the Sinamics S120 digital drives allows for improved speed regulation and faster response, both of which are key to improving tension control. Amgraph set aggressive goals of 95 percent uptime for the retrofitted extrusion machine.

In addition to increasing uptime and the number of products the machine can handle, Rand says the retrofit has increased throughput up to 20 percent, depending on the product line. "We've definitely increased production speeds," he says. "We're happy where we are now, but we still have opportunities to improve throughput."

Addressing Retrofit Concerns
The primary issues with the original system centered on the analog drive system and system variables that drifted, so the challenge was moving to an all-digital system. Sections of the older system used draw control, developed by using the speed differential from one section to another, rather than direct tension control on the individual axes.

Load cells for direct tension control were added to sections that originally used draw control, and the final configuration provided an ability to use either draw or tension control. This is important when you have an extensible web, because it is easier to use draw control and a speed ratio to develop tension on the material. But if the web doesn't have modulus in it, the resolution of the speed differential becomes more critical. If the accuracy of the drive, which provides speed regulation, is not as good, that also complicates the application.

Induction motors were used for the application, with the drives providing an ability to run in a servo mode. On several converting applications (due to torque requirements), many engineers still use high-performance induction motors. The drive offers a servo mode which increases dynamic performance to reduce motor current more quickly and provide optimized performance with a standard NEMA induction motor in the 30 to 40 hp range.

Retrofit 3Retrofitting large production machinery like the Black-Clawson extrusion laminator machine rarely progress as scheduled, because changing a machine from discrete analog to digital control systems with the latest energy-saving ac induction motors presents significant electronic and mechanical engineering challenges.

Customers also typically want to use specific equipment providers for certain systems. In this case, Amgraph specified a third-party HMI and PLC technology, which meant Circonix needed to interface the Sinamics S120 drives with third-party systems. Using Siemens' Starter drive engineering and commissioning software, and integrating the Sinamics S120 drives using the electronic nameplate capabilities of Drive-Cliq for motor and drive components, the project was able to be delivered to Amgraph on time and within budget.

"We used Profibus to tie the drives together and an SST module in the PLC to talk to the Siemens drives," Alaya explains. "With the Siemens dc bus lineup, all the drives fit in a single cabinet that was smaller than the space of one of the previous motor control systems. We were able to eliminate the wiring mess and relay logic that came with the older analog controls as well, which significantly simplified maintenance and troubleshooting for the customer while improving performance and uptime."


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