RFT SpA ensures quality in the seal manufacturing process

The SKF Group is one of the leading global suppliers of products, solutions and services in the area comprising rolling bearings, seals, mechatronics, services and lubrication systems. The Group's service offering also includes technical support, maintenance services, condition monitoring, and training. SKF does business mainly through three divisions - Industrial, Automotive and Service - each of which serves the different sectors of the international market.

SKF has 110 manufacturing sites across the world, one of which is the facility at Gazzada Schianno in Lombardy, Italy. Owned by RFT SpA, a member of the SKF Group, this plant manufactures bearing seals and rotary and sliding shafts for the Automotive and Industrial sectors.

"The machines at this production site," says Davide Mischiatti, Machinery Development Manager for RFT SpA, "are capable of producing seals with a diameter of 0.6” and above. They are rubber molding machines, mostly designed in the 1970s and 1980s, that have been subject to continuous technological developments aimed at enhancing their efficiency and, at the same time, reducing their environmental impact."

"The SKF Group," Mischiatti continues, "is very conscious of ethical and environmental issues. For example, as a replacement for the original pneumatic motors, the Group has adopted Omron brushless spindle motors in the pick-and-place system that unloads the finished parts from the machine. This solution was implemented largely to solve the problem of bottlenecks during this phase but, in addition to the expected increases in speed, precision and flexibility with regard to programming movements, we have also noticed a small reduction in compressed air consumption. The need for maintenance has also fallen."

One of the most significant upgrades to the molding machines concerned the mold heater control system. To understand its importance, it is useful to briefly outline how this machine works.

The mold heater is a large-diameter, rotary table system on which is placed a varying number of molds, depending on the size of the product. The machine includes a range of heaters and thermocouples to measure its temperature. The molds are largely heated using conduction.

The pre-treated rubber and metal components are loaded into the mold. The mold is then closed and the edges are pressed together to form a seal. Both the table and the molds must be maintained at a preset temperature, which at times can exceed 460°F. This temperature must be completely constant and each section of the table must be kept at the same temperature: any variation, however small, can compromise the quality of the molded product, either by changing the properties of the vulcanized rubber or by reducing the adhesion between the rubber and the metal support.

Improving the temperature control system by reducing the variation over time would therefore assist in the reduction of quality issues during the molding process.

To improve the machine's performance, RFT SpA decided to adopt our CelciuXº (EJ1G) temperature controller with built-in Gradient Temperature Control (GTC) algorithm. The heaters were spread across the 12 areas independently controlled by the CelciuXº (EJ1G).

The CelciuXº (EJ1G) is not just a multi-area control system, but also offers a significant advantage over a conventional PID controller, this is because the GTC algorithm measures interference between heating areas and eliminates temperature differences between them, therefore ensuring a uniform temperature over the whole two-dimensional area.

The result achieved is a reduction in the temperature gradient, which consequentially improves the quality of the end product.

"By implementing the Omron EJ1G temperature controller with built-in GTC algorithm," says Mauro Alberti, Manufacturing Process Development Manager for RFT SpA, "we have been able to offer our clients better quality guarantees on our products by eliminating the causes of faulty seal manufacture at the source."

The benefits of adopting GTC do not stop there; as well as ensuring the quality of molded products, the CelciuXº (EJ1G) also considerably reduces the time taken for the machine to heat up after it is switched on, improving machine efficiency as a consequence. For example, after a routine maintenance shutdown, using the previous solution it used to take approximately an hour for the machine to reach the correct temperature for production. With the CelciuXº (EJ1G), however, the correct temperature is reached after just one rotation of the machine - just 90 seconds!

Yet another of the system's advantages over the previous solution relates to heater fault monitoring: the CelciuXº (EJ1G) temperature controller can be used to instantaneously identify faults in the heating system. This substantially decreases the number of predictive maintenance inspections required.

"We're pleasantly surprised every time we look at the real-time temperature display," concludes Mischiatti. "It's so still it looks like a static image, not the reading from the table temperature sensor! Given the many benefits it has brought us, the EJ1G has definitely been a good investment."