Dureable Grippers Grab Bottles Around The Clock

By John Moore

John Moore, Territory Manager
Parker Hannifin Corp.

Reliability and cycle time are critical to any manufacturing process. Rocheleau Tool & Die Co., Inc., a family owned and managed business, stakes its reputation on the quality and performance of the small to mid-sized plastic blow molding machines the company designs and manufactures.

When grippers on a line of the OEM’s machinery began failing in the field, managers reacted immediately to correct the problem. Parker Hannifin was already supplying Rocheleau with pneumatic cylinders and linear slides, so the company contacted Parker about providing replacement grippers. The machinery, used for blow molding plastic bottles used in the dairy and soft drink industries, is often in production around the clock and requires trouble-free operation.

The shapes and sizes of the plastic bottles produced by the machinery vary tremendously. Combined with continuous operation, and you have an application that demands low maintenance, quality components. After explaining the process to the Parker team, the OEM tested Parker’s GPK Series Grippers to ensure they would meet the application demands.

Grippers on this plastic blow molding machine are programmed to pick and place 10 bottles per each six- second cycle.

The pneumatic grippers feature precision linear bearings and hard coat anodized parts to offer millions of trouble-free cycles, just what Rocheleau needed to resolve the gripper failures occurring on its machines. Dirty environments, with airborne dust and wide temperature swings, are often home for these machines. The grippers’ inner mechanisms are protected against harsh environments.

The grippers are involved in a two-phase process. Plastic is inserted into a hollow tube and blown into shape in the mold. The grippers are programmed to pick and place 10 bottles per each six-second cycle. Traditionally, machines in these applications grab bottles from the molding area by the tail section on the bottom of the molded bottle. In a unique process developed by Rocheleau, the bottles are gripped from the top. The dome of the mold is cut from each bottle, and then moved to the second phase, which is the trimming cycle.

“We selected Parker GPK Grippers because they are robust, reliable, and save space because of their small footprint, ” explains Jeff Rocheleau. “We’re not talking about a big payload, so we didn’t need a strong grip force for this application. But we did need durability and reliability.”

In a unique process, the grippers grip the
plastic bottles from the top rather than from the molding area by the
tail section on the bottom of the molded bottle.

Thrust slides position collection bins that
transport the bottles to a conveyor, then return the bins to the
machine to collect a new batch of bottles.

The grippers have maximum strokes of 25-50 mm and a total grip force of 20-90 lbs. Custom 2 mA pneumatic cylinders move the grippers into position during a process. A linear position sensor provides position feedback. These back-to-back duplex cylinders provide three positions instead of the standard two. The first stroke aligns the gripper to grab the dome of the molded bottle. The second stroke positions the bottle to be stripped of excess plastic from the die edge. The bottle is then dropped into the collection bin and moved to the next step of the process. The third stroke returns the cylinder to its home position.

This controlled pick and place process increases production, in part, because grabbing the bottles from the top means that they drop into the collection bin straight – not on an angle or sideways – which makes more bottles move quickly to the next process stage. Extrapolated over an eight-hour shift, that translates into a significant increase in production.

Parker HBT and HBC thrust slides are used on Rocheleau machinery as well, for medium and short guided linear travel. The bearings are pre- lubricated for millions of trouble-free cycles. With low friction, and virtually no mechanical vibration, the thrust slides provide precise linear motion.

Rocheleau employs these slides for two purposes. The HBC slides position collection bins that transport the molded plastic bottles to a conveyor for the next stage of the process – then return the bins for a new batch of bottles. The HBT slides are used in a punching operation that strips excess plastic from the die edge.

The Parker grippers are a little more expensive than what they replaced, but their quality and longevity will reduce maintenance costs and improve uptime, which translates into increased product production.

:: Design World ::