Design

Dryer Wheel

PEEK or Torlon Could Be The Answer To Your Wear Problem!

A number of years ago a large company came to us because their wheel was the number one warranty claim in the entire company’s product line.

The big problem they had was with the oil impregnated sintered bronze bushing which leaked oil and made terrible noise.  The other problem was with the rubber on the outer edge which took a compression set from sitting in their warehouse.  When the owner would use the product for the first time a rumbling noise would come from the unit because the wheel was no longer round.

We were told that the part had to survive a 1500 hour life test.  Our solution was to replace the bronze bushing with a high performance wear grade material.  We also used the same grade of rubber as the original wheel on the outer part of the wheel, but used less of it and reinforced it with the spoke material between the bushing and rubber.

The result?  Our polymer bushing showed no wear after the life test and our rubber design did not compress. We were told by the project engineer that no bushing, including the current production one, has ever passed the life test.  This metal to plastic conversion of the bushing and the redesigned rubber part would save the company millions of dollars per year in warranty claims.

 

International Plastics specializes in the molding of all grades of PEEK and Torlon.  There are many new wear grades of PEEK and Torlon just now available.

Contact International Plastics today to discuss enhancing the wear performance of your product.

Runner Sizing

Runner Sizing

Runner Sizing

One of the least understood elements in mold design is runner sizing. The equations that govern plastic flow are nearly unsolvable in their classical form. However with the aid of computers, sophisticated computational methods, this task can be accomplished quickly and quite accurately. While this software ( Moldflow TM) costs a small fortune to acquire and the training to use the software correctly is extensive, there are other ways to accomplish the task.

Dupont developed a program 15+ years ago called ‘Skinny Runners’. While this program only does runner design and not cavity filling analysis, it is a very powerful tool. Simple to use and easy to understand this software was a computer implementation of a Dupont Engineering bulletin that presented a straight forward method to manually calculate runner sizes. I was fortunate enough to get my hands on a copy of this program many years ago. Comparing ‘Skinny Runners’ to software I had developed to solve the runner sizing problem. I found that their system was overly simplified and did not allow for more advanced design concepts.

Skinny runners calculated basic pressure drop and shear, for a limited number of predetermined runner configurations under static viscous conditions. The program I developed for International Plastics’ allows for any configuration of your choosing and accommodates non-linear viscosity behavior like that which happens during real molding. The in-house program did several other things that “Skinny Runners” did not, like constant shear design, minimum volume design, and auto-balancing of non-symmetric runner systems. Shear balancing, thermal balancing and ‘what if’ capabilities have been added over the years.

Dupont got great results from the application of their program to customer runner problems, making runner systems more efficient. International Plastics also got tremendous results on even more complicated runner geometries.

The first application of our software was on a new mold we built for a customer. The mold was a 4 cavity that was replacing an old worn out 8 cavity that had half of it’s cavities blocked off. The runner on the left is the original runner from the 8 cavity mold only running 4 cavities. The runner on the right was the new runner designed specifically for the same part molded in the same material. Even if you only consider half of the old runner (4 cavities) and compare it to the new one (4 cavities) there is still a huge difference, over an 88% reduction in runner weight. While not every example is as dramatic as this, it is safe to say that every existing mold we have encountered we have been able to reduce the runner size by calculating the proper runner size for the application.

The best advise I can give is don’t let you mold maker design you runners, I have not found a mold maker that understands the subject no matter how well intentioned. I have had molds built by some of the biggest and the best mold makers on three continents and have not found an exception to this statement. Also, find out if the mold designer uses competent software to design the runners, if he uses the good old ‘rules of thumb’ you can kiss your productivity, and quality good-by forever.

Proper runner design will insure years of quality, productivity, and reliability.

weld-lines

Weld Lines – The Overlooked Defect

Several years ago a customer transferred an old single cavity mold to our facility. The part was a very simple rectangular ring. It had two sub-gates, one at each end of the part on the short side of the rectangle. The material was glass filled and made a very strong part.

We made our first sample submission and were approved for production immediately. The next day we delivered the first parts for their order. A couple of hours after the parts were delivered I received a call from our customers General Manager thanking us for the very fast service, then he went on to say none of the parts were usable because they did not pass “the hammer test”. The first words out of my mouth were “what is the hammer test? And why wasn’t this test requirement talked about before this”. I drove over to the customer’s plant and observed the hammer test. It was quite simple; the part was set on a metal table so it stood up resting on its long axis. A technician then proceeded to beat the daylights out of the part with the pointy end of a steel masonry hammer.

The part broke in the very middle of the long side. I examined the part and asked if they had this problem before. The general manager said this happens all the time and it is a major problem. As it turned out the hammer was used to seat a metal piece between two of the plastic parts to make the assembly. The metal pieces were to stiff to assemble by hand so the hammer was used.

My further examination showed that the failure had occurred at one of the weld lines in the part. Weld lines occur when plastic flows around a core and then joins back together. The solution was very simple, the problem was that no one looked at the way the part was gated and how the part would be assembled. I told the GM that I would be back that afternoon with parts that would not break.

I had one of our mold makers take the mold apart and we simply blocked off one of the two gates. This meant that all the material would flow through one gate and the single weld line that resulted from the new flow pattern would be on the short axis. The old flow pattern produced a weld line in the middle of both of the long sides. We tested the parts with our own hammer and could not produce a failure. I immediately took the newly re-gated parts to the customer and asked them to test them with their hammer. They could not break the parts either. I took the first parts back and scrapped them and we delivered the new parts thenext morning.

The customer never had a weld line failure again. We had solved an assembly problem that had existed for years, saving time and money on every assembly.