Note that web-based summaries of standard operating
procedures are not exhaustive.
Not all of the relevant safety information is included in this document. Further training is required for safe operation and will be provided in person. |
Use tool with 1/2" nubbin to push down on core and shim with the upper cylinder of the 250 ton hydraulic press. Pressure vessel (PV) should be right-side-up. In other words, the core and the shim should be pushed out the bottom of the PV. The bottom of the PV is the side where the shim is thicker. Use the hand-pump to push slowly, 25 tons of force (roughly 1000 PSI) were required to do this in January, 1998 (also, October, 1999).
Separate shim from core by pushing down on core in the 10-ton press. Use the now-empty 1/2" PV as a ring holder, so that shim rests on PV, but core is not supported by PV. Finally, put cracked core in a wooden box for a few hours, just in case it decides to explode.
Clean shim and inside of PV with acetone.
Check shim for cracks or major scratches. If the shim is cracked or heavily deformed, it may have to be replaced. Polish outside of shim and inside of PV with SiC paper and WD-40. Use 1200 or 600 grit paper unless there are marks too deep, in which case start with 320 grit paper and then move to 600 grit paper. Try to remove all scratches and irregularities. Gouge marks and partings may not be removable. Polish in a cross-hatched pattern, rather than radially or longitudinally. Clean with acetone and repeat polishing with 1200 grit SiC paper. (Optional: Finally, polish with 9 micron diamond film; blue-colored Buehler Carbimet disks.) CLEAN SURFACES THOROUGHLY with acetone.
Press new core into shim using the10-ton press. Make sure that core is flush with thick side of shim. Clean shim again. BE ABSOLUTELY SURE THAT SURFACES HAVE NO FINGER PRINTS or other oils.
(If new core does not fit snuggly into shim, fit core into shim by hand. AGAIN, MAKE SURE THAT THERE IS NO OIL ON EITHER SHIM OR CORE SURFACES.
Burnish surfaces with MoS2 powder (Belray microfine) using a soft, preferably chamois, cloth. (DO NOT USE MOLYLUBE GREASE. USE THE DRY MOLY POWDER!) Wear respirator masks and safety glasses while doing this, MoS2 comes as a very fine powder that is also highly toxic. Press hard and work each piece (the PV and the shim) for 1/2 hour each, at least. Surfaces should take on a bluish sheen.
Pushing core in. Do this with shielding doors closed.
Place shim/core on stack in PC A so that the thin part of the shim is facing up. Make sure that the shim and core are flush with each other. Fit PV on to shim/core (with wide part facing down) so that the endload ram will be pushing the PV and shim/core together by pushing the PV down. Core sticks out of PV about 1/2”. Use narrow (4" diameter) end-load spacer to push on shim/core. Make sure the latter is clean. DO NOT touch the finish on the shim, as the coat of MoS2 must remain undisturbed and even.
USE THE END LOAD (LARGE RAM) and the hand pump to push the core. The large ram valve should be slightly open so that pressure is allowed to build slowly. It may require 40-80 tons to push in. Peter McNutt says 45 tons is the theoretical minimum (i.e. if there were no friction). It took between 2500 and 3000 psi measured in the large ram gauge in Janury 1998; ~60 tons. (75 tons in August, 1998; 2200 psi or 58 tons for PV#2 in January, 1999; etc. Note added in 2005: Extensive experience suggests that 50-75 tons is about right). When core is moving, pressure will increase slowly and bleed back after each stroke. When core is no longer moving, pressure will build faster per stroke. The difference will be obvious. If you are done, this is good news. If the core is not yet in, this will be bad news. Core should push in noiselessly or with high pitched whining. Watch out for loud sounds and cracks. Generally, they indicate trouble. IF CORE STICKS BEFORE IT IS PUSHED ALL THE WAY IN, DO NOT FORCE IT! STOP, PUSH IT OUT, RE-POLISH AND RE-BURNISH AND START AGAIN.
Once core is in, pressurize to 5000-6000 psi for a couple of hours.Because of compression the ID of the WC core will probably be less than 0.500". The core ID needs to be 0.5015" + 0.0002" - 0.0000" (with a 12 microinch finish). It must be honed with a Sunnen hone using a diamond stone. (See note about Twin City honing below.) You can estimate the ID using the plug gauges. Wear gloves when handling the gauges. In January 1998 ID was between 0.490" and 0.500". In August, 1998, it was 0.498. Bore can be honed. If core/shim/PV are not flush, they may require grinding flat.
Tel: 952-894-1730.
12116 12 Ave S
Burnsville
MN 55337-1408