As most mold maintenance audits reveal, water leaks, both internal and external, continue to be one of the frontrunners in unscheduled mold downtime, and this company suffered no differently. The simple act of electrons of one steel migrating to another wastes thousands of company dollars per year—not only through excessive repair hours and tooling, but also press idle time, scrapped parts and missed or late orders. Molds and components are sent to the junk yard that could have—and should have—made thousands of more cycles and parts, if only specific precautions had been taken to prevent or at least slow down the erosion.
While pinched, cut or missing o-rings and other assembly oversights share responsibility as root causes for water leaks, rusted and pitted o-rings glands (grooves in plates and tooling) continue to be the main factor with molds built and run with no corrosion prevent measures taken in mold design or maintenance practices to save money.
Rust Never Sleeps
Though I doubt Neil Young had mold maintenance on his mind when he conceived this phrase, it fits well. Working 24/7 and nourished by heat, pressure, water and oxygen, rust takes no time off as it slowly eats away our molds.
The resultant issue of this electrochemical reaction is that the eroding steel usually goes untreated until the leak is sufficient to stop production, then a spotlight is shone on the problem and questions arise. From there, the focus of maintenance efforts will revolve around what is necessary to quickly get the mold back into production—or stopping the leak versus how to stop the rust.
Stopping the leak is usually a matter of:
• Stuffing a larger o-ring in to the pitted gland
• Stuffing two o-rings in to the gland whose combined cross-sections are slightly larger than the single o-ring.
• Clean up the pits by milling the gland area with an endmill (sharpened with a flat face) and resize the o-ring.
• Filling the pitted gland with silicone
• Filling the pits with epoxy
These are the cheap and short-term fixes. If any of them work … yippee. If not, then we try again and again.
Products Can Dictate Repair Method
With critical parts, as in medical products, any kind of water leak that could possibly migrate to the product is cause for shutting down. On other products, there are major water leaks simply re-directed into buckets or an area around the press to keep the mold in production as long as possible. Is this shop floor ingenuity or poor molding practices? Depends on in which culture you were raised.
||Count||Count Labor Hours
||Labor Cost||Tooling Cost
|X-Internal Water Leak
So as to not lose site of reality here, there are companies that have molds whose yearly volume requirements leave little money to repair a leak professionally and permanently. So the mold is set with rags tied where necessary to absorb and redirect the dripping water, with little thought given to related issues that come with operating in this type mode. It is assumed to be a better business decision to just let’r leak.
Then there are the tweeners. These are molds where a misguided choice is made—even with the higher volumes—to just deal with the random leaks when they occur, by pulling and performing one, or all, of the steps outlined above.
More involved but permanent repairs include grinding plates and tooling (usually involving dimensional restacking) welding, brazing or nickel plating for future protection. If the leak is unfixable (cracked water lines or tooling) you can skip the repairs and just buy a negative pressure thermolator that draws water through versus pushing it through.
Common Affected Areas
In molds, most water leaks occur around static seals where dissimilar metals, such as a P-20 plate contacts hardened steel tooling such as A2, D2 or S7. This dissimilar contact sets the stage for the formation of Fe203, the reddish form of iron oxide that we know as rust. The oxide is a larger molecule than iron, so it puffs up and cracks which exposes more bare metal. Mobile oxygen in the metal moves deeper into the base steel continuing destruction and creating the rust lives methodology.
Cavity blocks and cores are the typical victims where the walls and bottoms of glands pit and erode until the o-ring can no longer conform to the depth of the pit and water seeps past. The leaks can be enhanced by a mold’s opening and closing, acting as a virtual pump by slightly moving or shifting tooling with every cycle, and by opening stress cracks that would normally not leak during a static bench test of the circuits.
|Mold||Part Description||Configuration||Stop Reason||Count|
|6169||Closure Cap “C”||Standard||Internal Water Leak||6|
|6749||Top Cup “D”
||Standard||Internal Water Leak||4|
|6989||Port “R”||Standard||Internal Water Leak||3|
|6870||Top Cup “C”
||Standard||Internal Water Leak||3|
|5990||Threaded Sleeve||431||Internal Water Leak||2|
|6942||Round Cup||Standard||Internal Water Leak||2|
|6382||15 ML VHC “K”||Standard||Internal Water Leak||1|
|6471||18 ML VHC “L”||Full Thread||Internal Water Leak||1|
|6492||12 ML VHC “E”||Standard||Internal Water Leak||1|
|6723||Crank Handle||Standard||Internal Water Leak||1|
|5918||Outer Flange||Standard||Internal Water Leak||1|
|6717||3-Hole Locking Switch||(3 Hole)||Internal Water Leak||1|
|6816||Top Cup “B”||Standard||Internal Water Leak||1|
|6948||Large Ring “D”||Standard||Internal Water Leak||1|
|Stop reason count.|
But is anybody going to arbitrarily send the mold out to get the leaks fixed correctly just because it’s the right thing to do? Hardly. Not unless there is proof of profit in it, which is why it is important to assign an accurate cost with any problem a mold suffers.
Analyzing water leaks in the company as a whole, or as a mold stop reason from a collective costs perspective is seldom done because there is no easy means to collect and analyze this data, plus it’s easier for those inclined to sit in their offices not to worry about a water leak until they get one. But the numbers can be convincing that something needs to be done to eliminate water leaks from your list of unscheduled mold stops when viewed as a whole, and compared to your entire unscheduled stop list.
Let’s take a look at this company’s water leak costs for last year through their 2007 Defect Analysis report. This company discovered some startling facts about the overall costs of the simple water leak as seen in Chart 1.
Twenty-eight molds in all for the year were stopped for internal water leaks and four more for external leaks (not shown here) where hose lines popped off, were too short or worn through (which soaks the entire mold versus just one area). We can see from the Stop Reason Count list in Chart 2 that the problem was spread among 14 different molds with two molds accounting for 35 percent of the total leakers in frequency and costs.
Additional Downtime Costs
Direct tooling and labor costs are only part of the total expenses. The total labor hours (173.25) also can be applied to press idle time, in this case $45.00 per hour for another $7,796.25. Add in 3 hours (average) for each of the 28 stops for mold pull, reset and start-up times and you can tack on another $4,200.00 giving them $23,468.75 in total costs for water leak issues. Doing the math then pushes the Total Defect Cost at about $4,000.00 each per year for the top two leakers (6169 and 6749) shown in Chart 2.
Now What? Selecting Your Target
As you can see from Chart 2, the worst actor (6169) accounted for six stops, so this is a good place to start. Further review of the Corrective Action history revealed the mold had four o-ring groove locations that were pitted and in need of welding, refacing and then stripping and plating the entire 18" x 24" x 2" thick plate in nickel. The cost of this repair was $675.00 to weld and spot face the four grooves and another $300.00 to apply nickel plating for a repair cost of $975.00, making the ROI for this repair about four months, since volumes were to remain constant in 2008. Looking at it from this perspective makes the repair decision a no-brainer.
It is not a good decision to automatically assume that the cost of putting up with random water leaks is a less expensive means of dealing with them versus eliminating with them. When you see the total costs of this common problem, it becomes an easy, justified decision to fix the mold. Now you have one less issue to worry about, and can proceed onto the next most frequent/costly defect your molds suffer and eliminate them also, one at a time. Before you know it, you have reduced your costs of unscheduled downtime by 50 percent or more, which means thousands of dollars in savings, increased capacity and less stress in the shop and on the molding floor.