Mechanical Presses: Rebuild or Buy
What You’ll Get with a Rebuild
Typical mechanical-press rebuild time averages about six months, according to Peter Campbell, president of Campbell Press Repair, Lansing, MI. A rebuild typically runs 40 to 60 percent of the cost for a comparable new press.
Right off the bat, rebuilding entails removing excess clearances in bushings and wear surfaces, and replacing these parts to return them to original specs. These parts include main and connection bushings, ram wear plates, clutch, brake and air counter balance perishables. Sometimes during a rebuild you may find broken and damaged components such as crankshafts, connections and rams. These parts can typically be repaired and returned to service all in an effort to return the machine to working tolerance.
Also, the press may be disassembled down to its bare components—each inspected and replaced if necessary, along with replacement of all bushings, bearings, seals and gaskets. At another level, Campbell notes, press modernization may be in order.
“That may involve a new press-lubrication system, pneumatic system and controls,” he says. “Modernizing also includes addition of safety equipment such as light curtains and die-protection devices, tonnage monitoring and maybe even isolators to provide for leveling and vibration dampening.”
Making the DecisionA number of factors influence the rebuild vs. buy decision.
Press make, model and design. “Certain presses are designed better and built better than others, making them better candidates for rebuilding,” says Campbell. “We won’t bother quoting rebuilds on certain other presses because it is just not worth putting that kind of money into those presses.”
Certain press styles also influence the decision.
“Smaller OBIs, for example, say 75 tons and under, if they are more than 30 years old, probably are not worth the investment in a major rebuild,” Campbell says.
Press age not necessarily an indicator. “Sometimes the age of the press plays a factor, but mostly in regard to how a company wants to use the press,” according to Campbell. “If the press fits the operation and maintains the right speed for that operation, then age may not be a detriment when considering a rebuild. Also, older presses often have heavier-duty frames than do newer models, with extra capacity beyond the stated tonnage, built into the press frame.”
Similarity to other presses in the shop. “Some stampers may have several of a particular make and model of a press, easing maintenance,” Campbell says.
Compatibility with the process. “Perhaps newer presses offer capabilities that can’t be matched by a rebuilt press —servo drives, for instance,” Campbell says. “And newer presses may maintain tight tolerances in high-speed applications that are impossible to achieve with some older models. Finding a used press that meets a stamper’s specific current and future needs can be quite difficult, so a new one can be built tailored for those needs. A stamper that does primarily drawing and forming work for example, may start doing some blanking work. He then will need a press designed for blanking that can handle snapthrough and reverse tonnage, as opposed to a press designed for drawing. If needs change, perhaps press replacement is a better option than a rebuild existing equipment.”
Auxiliary equipment. “A stamper may have invested a great deal of time and money installing guarding, controls and automation for a particular press and specific application,” says Campbell. “That may justify a rebuilding a press that might not have been rebuilt with out the additional equipment.”
Down time. “A press manufacturer may have a new machine on its floor ready to go,” Campbell says, “so rapid delivery time may be a factor. “Perhaps downtime for three to nine months for a rebuild is not an option.”
|Here’s one of several Minster presses from the 1960s that were sent from a General Motors plant for rebuild and installation of new controls.|
Increase tonnage? No. “I don’t recommend trying to increase press tonnage via a rebuild,” Campbell says. “The press frame and component parts typically aren’t designed to handle any increase in tonnage.”
Change the stroke? Yes.
Change the shut height? Yes.
Increase speed? To some extent. “The speed can be changed but typically not by as much as most stampers want,” says Campbell. “A slight change in speed is possible, and that varies by the specific press.
Increase bed size? In most cases, no.
Retrofit a clutch? Yes. Changing from a dry to a wet clutch can increase the life span of a press,” says Campbell. “If stampers must frequently start and stop a press, a wet clutch provides much better performance. Also, safety is a concern, as some older presses with worn clutches may not achieve proper stop times, necessitating a switch to a wet clutch or a conversion to a newer-design air clutch.”
Increase rigidity? Yes. “We have added gussets and beefed up crowns, rams and beds,” says Campbell. “For example, due to unbalanced loads or the use of smaller dies in larger presses, cracks occur in the bed or ram that require repair. At that time we may reinforce the bed or ram, allowing the stamper to continue to run that type of work in the press while improving performance.”
Add overload protection? No. “Some older presses do not have built-in hydraulic overload protection, and that is very difficult to retrofit,” says Campbell. “Most new presses offer this feature, and if a stamper can’t buy new for whatever reason, tonnage monitoring can be added to the existing press to provide overload protection.”
Maintain and Inspect
“Presses can run for a long time with excess clearance, wear and even cracks in certain parts, but there will come a day of reckoning when deferred maintenance will catch up with you and shut your press down,” says Campbell, stressing the need for regular press maintenance and inspections.
Quick inspection services are available for stampers deciding whether to rebuild or buy. Stampers also can schedule inspections on used equipment before they buy it to gauge the shape of the press and how much money it will cost to make it production-ready. Also available, inspections on equipment for those looking to buy a company and interested in the shape of equipment before the purchase. MF
See also: Nidec Minster Corporation
Related Enterprise Zones: Presses
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