The mechanical gearbox is an integral part of a production line, providing power and propulsion. When the gearbox fails, parts are not being made, calling for machining to bring the parts back to square.
Sometimes, when parts are not stamped properly, it's not the die that's at fault; it's that the press has become out of square or alignment. Machining the bolster, bed plates, uprights, crowns, and gearboxes can get a worn press back to square. Although the bolster, bed plates, and uprights often can be machined on-site, the gearbox usually has to be disassembled and moved to another location to be machined and completely cleaned and repaired.
The gearbox is an integral part of a mechanical press, providing power and propulsion. When the gearbox fails, parts are not being made. Following are the steps a repair shop takes to rebuilds a stamping press gearbox or other types. (This specific gearbox was in a rubber plant.)
1. At a pre-project meeting, the crew goes over safety and fills out a job safety analysis.
2. Any guards and obstructions are removed to enable access to couplings.
3. Alignment checks on motors to the gearbox, and gearbox to the mixer are conducted and findings recorded. Based on the findings, a report is generated at the end of the removal phase of the project.
4. A soft foot check is done while the gearbox is still attached to motors and mixer.
5. Alignment is checked again when the couplings are apart. This will show any stress that might have happened during the gearbox installation.
6. Another soft foot check is performed after the alignment process has been completed.
7. The removal process begins. Any obstructions in the way of gearbox path out of plant are removed.
8. To keep costs down, the customer uses its preferred rigging vendor with a gantry crane and fork trucks to remove any special rigging for the removal of the gearbox.
A thorough cleaning of the gears and other elements removes debris.
9. The gearbox is removed using the customer’s preferred equipment and relocated to the building deck.
10. The crane vendor rigs and loads the gearbox onto the truck for shipping.
11. The gearbox is shipped to repair shop for repair/replacement.
Once the gearbox arrives at the repair shop, inspection and teardown begins.
12. First, the gearbox is unloaded from the trailer and set level before teardown.
13. Next, the gearbox is inspected before removing the cover.
14. Covers are removed from the gearbox after they are match-marked for their locations.
15. The cover is stowed away.
16. Float checks and contact checks are done before the gearing is removed.
17. Next, the high-speed bearings are removed and cleaned for teeth inspection, which involves looking for heavy transfer marks caused by improper tooth wear, misalignment or bearing failure; cracks, and improper pitch. The bearings are inspected for scars, tracks, or pits caused by limited in-play/floats, misalignment, presence or absence of lubricant, and inner/outer race.
The gearbox must be removed to be realigned.
18. The intermediate gear/low-speed pinion and bearings are removed, cleaned, and inspected as in previous step.
19. The low-speed gear/secondary pinion and bearings are removed, cleaned, and inspected as in previous step.
20. Any gearing damage is brought to the customer’s attention for repair recommendations.
21. The lower half of the gearbox is cleaned and checked for cracks. The upper half of the gearbox is cleaned and checked for cracks.
22. The lower half of the gearbox on is set up on a mockup frame the in-repair shop and leveled using laser measuring equipment.
23. The soft foot and shimming are inspected.
24. The part line is laser-checked for straightness.
25. The upper half of the gearbox is positioned onto the lower half to marry the two.
26. The part line bolts are tightened to the correct specs from the equipment manual.
27. The core lines are laser-checked in the gearbox. This will ensure parallelism and correct spacing among pinions.
Disassembly is a challenging and complicated process.
28. A report is generated on the findings at this phase of project.
29. A report is written identifying the root causes found in phases 1 and 2 and given to the customer.
30. Bearings are installed on high-speed, intermediate, low-speed and jumper pinions.
31. The low-speed pinion is installed and free float is checked.
32. The jumper pinion is installed and free float is checked.
33. The intermediate pinion is installed and free float is checked.
34. The high-speed pinion is installed and free float is checked.
35. The cover plate is installed on the low-speed and jumper pinions. This involves checking the float on the jumper pinion while hand-tightening the bolts on the bearing cap. Then, pinions are checked at 50% of torque value, then at 100% torque value. Float is checked with indicator and the readings are recorded. Float is checked on the low-speed pinion.
36. Cover plates are installed on the intermediate gear and floats are checked with an indicator.
37. Cover plates are installed on high-speed and floats are checked.
38. Tooth contacts are checked after low-speed and jumper pinions are centered in relation to each other.
39. Tooth contact is checked between the low-speed gear and intermediate gear.
40. Tooth contact is checked between high-speed gear and intermediate gear.
41. All covers are removed and the upper half of the gearbox is married to the lower half.
42. Covers are installed on the output side using new seals.
43. Covers are installed on the input side using new seals.
44. All remaining blank covers are installed.
45. The float check is repeated after the lid and all covers are installed.
46. A report is generated for phase 3 of the project and given to the customer.
47. The rebuilt gearbox is loaded onto the truck for shipping back to the customer’s plant.
48. The gearbox is unloaded with help from the customer’s preferred crane vendor.
49. The gearbox goes back to the flight deck and is staged to its previous location.
50. The customer’s preferred rigging vendor installs the gearbox.
51. The gearbox is rough-aligned to the mixer using conventional measuring, such as dial indicators.
52. The gearbox is fine-aligned using a laser measuring instrument.
53. After alignment is done, repair company removes all soft foot while holding alignment.
54. All inspection covers are removed and tooth contacts are checked.
55. Once all tooth contacts reach 75% or greater, reinstallation is complete.
56. Motor alignment is checked. If it needs to be moved, that will be a separate scope of work.
57. All parts that were removed during deconstruction are re-installed.
58. A lube cycle is performed for bearings/elements.
59. Break end time for bearing temperature checks is performed.
60. A report is generated for phase 4 of project and given to the customer.
Note: A final report containing in-depth detail of measurements, floats, teeth contacts, and temperature readings is furnished to the customer. Another section of the report will describe the root cause in detail.
A repair company inspects the evidence, follows the clues, and interviews witnesses in an effort to identify the root cause of press gearbox failure.
Ladies and gentlemen, the story you are about to read is true. The company name has been changed to protect the innocent.
This is the pressroom. We work here. We’re a press service and gearbox repair company. We can help you. Press crowns and mechanical presses are similar. What seems to be the problem? Just the facts, ma’am.
It was 10:00 p.m., Sunday, July 5, 2020, when we received a phone call from a large manufacturer. The gearbox housing and baseplate was torqued on its existing bolts. We scheduled a conference call with the company that night.
We inspected the bed plate for possible gearbox misalignment. It matched the drawing, so no design problems were apparent. From what was discussed in the phone call, it appears that the previous bolt locations were not aligning to the 19-bolt pattern in the new base plate.
The manufacturing company opted to slot the gearbox holes first, and then to slot the baseplate only if necessary. It will use the smallest-diameter nuts to mount the gearbox. The company is exploring opening the holes in the north-to-south direction by ½ to ¾ in., depending on the hole and stud. It will investigate enlarging the holes in the north, south, east, and west directions. The engineer is finishing the layout drawings for approval.
11:32 p.m. that same night: We conducted a conference call with several plant personnel from the company headquarters. We spent an hour investigating options with them. One option was to remove duct work and production to clear the area to gain access to the studs and thoroughly clean the area for a hot work permit. We decided to drive or cut the studs from the existing foundation, only opening the holes in the bedplate and gearbox to the smallest diameter. The goal is to remove only one stud from the gearbox, eliminating the requirement to obtain a hot work permit.
9:03 a.m., Monday, July 6: We arrived at Plant No. 2. We toured and previewed the plant. We viewed the gearbox job site and took measurements. We noticed that three holes showed signs of bolt-bound mounting studs and another hole was slotted.
12:00 p.m.: We held a meeting with the electrical engineer, mechanical engineer, and two engineering managers. The mechanical engineer reviewed and confirmed the layout drawing.
We all determined that four studs could be adjusted, and the rest should align properly—one being slotted to match the existing 2-3/4-in. depth by 4¼-in. width. We explained this to the plant manager. The manufacturing company is going to start modifying the foundation to remove the four studs/sleeves but will also be prepared to modify extra studs as needed up to 19 studs/sleeves.
We scheduled a review meeting to confirm that fire watch is approved and that sleeve removal is in progress.
1:37 p.m.: We took more measurements and visual of hole layout at gearbox location. We notice that three studs were up against the can. This obstructed movement in one direction. We proposed to remove those studs and reposition them.
9:10 p.m. that night: On arrival, we saw that the second shift had decided to remove all the studs. We began prepping for the baseplate/gearbox installation.
11:00 p.m.: The rigging company started rigging the baseplate/gearbox.
2:32 a.m., Tuesday, July 7, 2020: The rigging company set the gearbox in place.
5:00 a.m.: The company started rough alignment on the gearbox.
11:30 a.m.: It was rigged and staged the bull gear on the third level.
12:30 p.m.: The top half cover of the box was rigged on the third level.
2:00 p.m.: We inspected the bull gear. During inspection, we found a roller bearing that had popped out. We put the roller back into the bearing race. The rigging company continued to flush out the bearing to remove any debris.
3:05 p.m.: We cleaned the gearbox and elements.
1:02 a.m., Wednesday, July 8: We inspected the bearing on the bull gear. The inspection showed that the outer bearing race was offline. Because of the bearing’s weight and the slack in it, the roller had space to fall out. We did a visual inspection and there was no damage to the bearing and no debris in the roller surface. After aligning the bearing back to the manufacturer’s specified position, we installed and aligned the roller without problems.
2:31 a.m.: We started staged the bull gear for lift. After staging was complete, we started rigging the bull gear. When the lift started, there was enough head room to raise bull gear.
3:10 a.m.: We started tearing down the crate underneath the bull gear to make enough room for the lift.