Page 20 - MetalForming April 2012

Rebuild or Retrofit
stronger hoses and couplings have vir- tually eliminated leaks and greatly min- imized maintenance. Even hydraulic fluids exhibit increased effectiveness due to new additives, promoting improved pump performance. Also, state-of-the-art pumps and motors operate more quietly than do their aging counterparts, and they use off- the-shelf replacement parts, whereas replacing components of older pumps and motors can take 12 weeks or more.
Another recent development is the use of soft motor starters or variable- frequency drives ( VFDs). These devices allow the motor to ramp up to full speed, decreasing the inrush current. A hydraulic press with a VFD will start the motor when the press is ready to per- form work, and then shut the motor off when platen movement is not required, including during press idle times. This technology can run the motor at slow- er speeds when the press is idle, to allow for accumulators to be charged and the oil to be cooled or filtered.
Finally, new options for increased press safety might include adding light- curtain circuits, presence-sensing devices, gates and barriers. Solid-state relays for anti-tiedowns on press buttons is another consideration.
Pressing for Change
Metalformers ready for some type of hydraulic-press upgrade should care- fully evaluate their goals in relationship to their costs. Here are checklists to help determine whether a retrofit or entire rebuild will prove most beneficial.
Retrofits/Upgrades
• Upgrade to the current ANSI B11.2- 1995 (R2010) standards for safety.
• Build in speed control for han- dling hard-to-form materials and to increase cycle rates.
• Add closed-loop pressure and dis- tance control.
• Improve accuracy and repeatability.
• Integrate automation components (robotics, feeders, etc).
• Add the ease-of-use and accuracy of touchscreen controls with recipe storage.
Rebuilds
Rebuild services replace existing hydraulic, mechanical and electrical components. If some of the following are needed, it may be time for a rebuild.
• Replace old, complex piping/valve systems with a single, consolidated and easy-to-troubleshoot manifold system.
• Replace or rebuild pumps and motors.
• Replace leaky hydraulic pipe- thread technology with oil ring seals (ORS and SAE).
• Rewire electrical systems.
• Rebuild cylinders.
• Replace worn-out platen guides/
slides.
• Strip down and repaint surfaces. • Replace ram gland rings and seals.
Case Study:
Going Green for Efficiency
For a look at the benefits that come from a complete press rebuild, con- sider an automotive customer operat- ing a 1997-vintage gap-frame press. The company recently required an upgrade to make the press ANSI-com- pliant, while providing all of the qual- ity, flexibility and maintenance advan- tages of today’s technology. Greenerd replaced all of the hydraulics and elec- trical components to a modern PLC, ANSI-compliant configuration. The only elements remaining intact were the frame and steel components, which will last indefinitely.
A significant benefit was derived from synchronizing the two auxiliary side cylinders on the press. A master slave control on both sides uses servo- quality proportional direction valves mounted directly to each cylinder to achieve 0.001-in. position tolerance. Prior to this rebuild, the customer was using hardened stop blocks to hit the hard stop. This older process is prone to error because after the press cycles, the parts may move out of tolerance, requiring manual repositioning of the blocks. MF
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© FOTOLIA - © DANIEL CHASLERIE
18 MetalForming/April 2012
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