Hydraulic extrusion presses have a history of developing cracks and defects. If these defects are not detected at their incipient stage, they could propagate and result in extensive damage to the press and extended outage resulting in loss of business.
Recently, I visited couple of large Aluminum extrusion facilities and found that all the extrusion presses had cracks and defects going back several years. In one instance the tie rod actually broke deflecting the front and rear platens.
A close review of the operating history of the presses, maintenance, testing procedures and business continuity programs, I found:
- In most cases, the presses were over 25 years old and the manufacturer was not is business.
- The plants had a comprehensive annual NDT program to monitor the cracks and if it was found the crack had propagated, welded repairs were done. Often the repaired areas developed secondary cracks. Sometimes, the cracked and welded areas had to be rewelded.
- There was no documented contingency plan in place to transfer the production to other sister or independent plants. Verbally, it was stated there were several independent plants that could be contacted to handle the production at additional cost. The additional cost factor was not calculated. It should be considered that most extruding operations are customer specified and often the dies are owned by the customers. Even if the independent companies had similar tonnage presses, there is no surety the dies would fit the press.
- None of the plants I visited considered reducing the operating tonnage and/or increase the monitoring of crack propagations.
It should be noted there is no scientific method of predicting the geometry of propagation of cracks and predicting the failure mode and time period before breakage. If a component has developed cracks, it should be replaced. This could sometime mean rebuilding the press.
During the Equipment Breakdown inspection visits, the operating history of the press should be discussed, and the inspector must ask for copies of NDT reports for minimum of three years and do a close review.
If welded repairs have been completed, as a minimum, the material should be identified to select proper weld alloy and procedure.
The welders should be qualified in the welding procedure.
The crack should be completely excavated.
The excavation should be made at an angle wide enough to permit confident welding.
Surfaces to be welded should be ground smooth.
The area should be preheated to a minimum of 200 F and maintained throughout welding.
Extra surface reinforcement should be added to areas where cracks initiate.
Final weld should be tapered and ground smooth.
Stress relief heat treatment for weld 2” or more thickness.
Increase visual examination to weekly while press is offline with written reports for each inspection that details inspection points and results
Increase NDE to quarterly with all cracked areas inspected and a report issued
The NDT program should utilize straight and angle beam Ultrasonic (UT) and Magnetic Particle (MT) methods as appropriate.
The components to be NDT should include front and rear platens, side cylinder rods and hot container shift cylinder rods, main pullback cylinders and hot container shift cylinders, main rams, ram stems and ram stem bolts, main hydraulic cylinders, valve – to – main cylinder bolts.
Laser press alignment should be completed annually.
The lead time for major components such as tie rods could range from 3 to six months based on the tonnage of the press. Platens, container housings, rams, power cylinder could exceed 12 months. Often, they have to be manufactured either from drawings or actual measurement of the components if drawings are not available.