Honing in on hydraulic cylinders

  • 08-Nov-2011 03:56 EST

The Sunnen HTA tube honing system used by Air Hydro Power handles parts with a mass up to 8000 lb (3629 kg) with ID ranges from 2.5 to 21 in (63.5 to 533 mm) and is available for 6- and 12-ft (2- and 4-m) part lengths.

Air Hydro Power started in 1961 in its founder's basement, and by 1965 was the third Vickers distributor in the U.S. Its Repair division services and repairs all brands of industrial and mobile hydraulic pumps, motors, valves, and cylinders. Work in its repair shop primarily focuses on refurbishing steel hydraulic cylinders used in construction equipment; material handling equipment; and other equipment such as cranes, oil rigs, and off-highway vehicles.

In 2007, its in-house honing capability consisted of hand honing with a half-inch chuck Milwaukee drill.

"Hand honing was physically demanding and a little tricky," said Perry Goldstein, Air Hydro's Director of Value Added Services. "If someone accidentally hit the reverse switch while adjusting the hone, the stones would bite the tube and rotate the drill, which is not good if you're the one standing next to it."

Other factors, such as inability to maintain stone pressure and having to deal with blind bores, relegated Air Hydro's in-house honing to low-end tasks such as taking out light scratches, deglazing, or polishing.

"Correctly honing a tube, maintaining accurate diameter, and keeping all the taper out is really difficult to do by hand," said Goldstein. Therefore, parts requiring more significant material removal had to be sent out at significant cost. Outsourcing also took out some control of meeting delivery dates.

"There were times when subcontracting came back to bite us," said Goldstein. "A third party may not have the same sense of urgency we do."

Ultimately, Air Hydro acquired a Sunnen HTA horizontal tube hone to repair and recondition hydraulic cylinders, allowing it to bring previously farmed-out honing work back in-house, helping it regain control of job turnaround times and save the company in outsourcing costs.

Approximately 80% of Air Hydro's repair work is done on cylinders 8 in (203 mm) or smaller in diameter; however, it has honing stone sets and holders that handle bores up to 18 in (457 mm). "Our largest lathe has a 3-ft swing and 15-ft bed," said Goldstein. "But, most of our work is done on our 22-in swing lathe. The HTA fits perfectly with our other equipment."

The Sunnen HTA tube honing system handles parts with a mass up to 8000 lb (3629 kg) with ID ranges from 2.5 to 21 in (63.5 to 533 mm). The HTA machine is available for 6- and 12-ft (2- and 4-m) part lengths. Air Hydro has the 12-ft (4-m) model designed for resurfacing and repair work where light-duty stock removal up to 0.030 in (0.76 mm) is required.

"Having the hone in-house allows us to look at the size and complexity of each job and determine if it's a repair or a replacement," said Goldstein. "Prior to the HTA, we'd rub a finger over the tube and determine the material removal to be 0.005 in, which means 0.01 in off the diameter. That would require us to make a new piston, new seals, etc., and we were better off just making a new tube."

What AHP discovered, however, is the grooves felt larger than they actually were due to the "finger test" reflecting raised material as well as missing material. "Now, we put that tube on the HTA, make a few passes and find that, once honed, the tube may be only 0.001 or 0.002 in over tolerance, and the seals can easily absorb 0.002 in, so we save the tube."

The HTA also comes in handy when building a cylinder from scratch, which requires the tube to have a trunnion mounted. When the trunnion is welded on, the cylinder will distort and cause a tight spot. Air Hydro hones the tube to eliminate the tight spot and allow the piston to pass. The shop also hones across all ports on the tube, which improves the life of the seals and wear bands.

The HTA includes a Siemens drive and PLC-control with touch-screen HMI for setting machine parameters such as stroke reversal point, spindle/stroking speed, and crosshatch angle calculation. The control features a load meter to determine areas of bore tightness and provides the ability to dwell the tool in multiple areas to correct part geometry.

A touch-screen-controlled hone provides a safer working environment and reduces operator fatigue. It also provides better quality parts by producing a controlled crosshatch pattern, which allows the honed surface to retain oil or grease, ensuring proper lubrication and ring seal of pistons in cylinders.

Transition to the HTA was easy, as the machine uses the same Sunnen ANR tooling the shop was using to hand hone.

"Generally, it takes us longer to set the machine up than to run it," said Goldstein. "We know how much material is removed for every minute the machine runs, so we calculate the surface area and set the time. Once we get it set, we can hit the go button, walk away for a few minutes, come back and measure, and we're done."

The shop will run anywhere from 2 to 15 parts per day through the hone. "We've got it down to where we will stage the tubes by grouping like sizes, so we can run it without changing the setup," he said.

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