|
I recently had the problem of a water leak that showed up about 24 hours after mold startup. This particular mold had several circuits and was difficult to troubleshoot. I finally made a trip to my local grocery store and purchased a small package of various food colorings. Next, I began segregating each cooling circuit and adding one of the colors to that particular circuit along with some water. I then closed off the exit end of the circuit and pressurized the inlet side of the circuit with 60 psi of air pressure. When I began to mold parts, I checked for the colored water residue in the mold or on the parts. I continued this process with each circuit until the leak showed up.
My problem turned out to be leaking pipe plugs caused by brass baffle blades that were too long for the bore depth. The pipe plugs felt like they were very tight hut actually were compressing the longer baffle blade into the bore depth, thus preventing the taper of the pipe plug threads from sealing. The gradual seeping of the water would collect between the core insert and backup plate, eventually migrating onto the ejector pins and into the
cavity.
-Dave Svohoda, Venture Plastics Inc., Newton Falls, OH, (330) 872-5774.
One of the causes can be imprecise fits between cavity and mold plates (radially or longitudinally). Under clamping or injection pressures a slight shift can take place, loosening the seal of the 0-rings. There is no way to test for leaks on the bench, and the mold usually needs to be reworked to improve the fit of the seals.
Another cause can he hairline cracks in the cavity that cannot he easily seen with the naked eye, but will open up under clamping or molding pressure.
The third cause we found relates to running high-temperature materials. The 0-rings harden with time, but still retain enough resilience to seal on the bench. They need to he changed
frequently.
- C. Mattke, Nylomold Corp., Rochester, NY, (716) 647-3880, gmattke@nylomold.com
First, when testing for water leaks on a table, remember that you are not applying the same stresses to the mold that you are when it's in the press.
We have found that leaks are caused by mold deflection and occur on toggle machines in particular. Try using a dial indicator on the stroke piston that moves your injection unit forward or backward. The indicator will tell you the degree of deflection if it is large enough to cause a
leak.
-C. Wells, I)J Nypro, El Paso, TX, (915) 771-0900, genew@djinc.com
It's important to use high-strength bolts between mold plates and to tighten them as hard as you dare. Also, explore the option of adding more bolts between the plates. Most molds do not have enough because (1) plates are not as flat as you think they are in molds that have been worked; and (2) water pressure with a mold heater added can be well over 100 psi. This means there is 100 lb of force pushing the plate apart per square inch of water area.
If the 0-rings move each time clamp force is applied and removed, they will leak. Also, if your water pressure varies, this will cause leaks as well. All molds will leak at a high enough pressure; conversely, no mold will leak at 0 psi.
As a test, I suggest increasing pressure by 25 percent more than the mold would experience, and then pulsating from full pressure to no pressure 50
times.
-P. Allen, Logic Corp., Sandy Hook, CT, (203) 426-6500, logic@logicseaI.com
First, make sure your 0-ring depth is correct. Next, try lubricating new 0-rings with silicone so they don't dry out. Since leaks occur only when the mold is under tonnage, you may have small cracks in the steel. Check for these using a two-part crack detector kit similar to those used on engine blocks (should he available at an auto parts
store).
-B. Lowe, De Ster ACS, Thomaston, GA, (706) 647-2205.
|
|
