Tooling Product News

How to select the right hot runner system for your
application by understanding what impacts the process

By Terry L. Schwenk

With the advancement of heater technology, for the most part all hot runner systems perform reasonably well under moderate molding conditions. The major differences between hot runner suppliers seem to be in the area of service and reliability.

To start the search, when choosing the hot runner vender make sure they are able to reliably service their products. Ultimately there will be issues, and what separates a good supplier from a bad one is how well and how quickly they respond to problems. Ask about their service network and spare part inventories. Make sure you understand what “guaranteed” actually means. This will give you a good indication about the company capabilities at the beginning of the process and reduce frustration when you are in full production.

One of the biggest keys to successfully select and specify the right hot runner is to take ownership of your project. Don’t expect hot runner suppliers to do your job for you. Yes, you are paying them to supply equipment for your molding operation but don’t expect them to know more about your operation more than you do. Be very open with information relating to the application and the production requirements. If you think you have a difficult application, make sure you relay that information.

Invest in education. The more your employees know about processing hot runners the better success you will have. There are several sources for training on hot runner technology and in some cases they are free. The only cost to you is the investment of time for you and your staff. Take advantage of these educational services and your production will benefit.

Now, what are the basic questions that need to be answered first? Each hot runner application can be addressed through an understanding of the requirements related to the project. So, here’s what you need to know.

1. What is the resin being processed?
2. What are your experiences with this resin?
3. What are the part requirements?
4. How is the part used?
5. What molding equipment is being used?
6. How well are your employees trained on the equipment?

As you can see most of the questions revolve around processing plastic. If your hot runner supplier isn’t asking these questions about your materials processing, then what is the likely-hood they will be able to select the right hot runner components for your application?

Document the process
In my travels throughout the industry I have observed on many occasions the lack of process documentation. Whether it was intentional because of trade secrets or that it just didn’t seem important, to successfully process plastic there no substitute for experience gained and lessons learned.

Less cost is not always less cost
Sometimes it seems the cheapest solution is the best solution. But what is the cost of not getting into production in a timely manner. Or worse yet, to have something that’s not running at all. If you don’t have a materials expert on staff, there’s no shame to seek out a professional to assist you with your application. I have always stated that I may not have all the answers for a particular situation, but I am the world’s foremost expert on what not to do. A little money spent up front to ensure smooth sailing through the project is well worth it.

Selecting the right gating method
Now that you have found a supplier that seems competent you need to determine the manufacturing and quality requirement for the part you are producing. This is important for selecting the correct gating method for the part. You ask, “Why this is important?”

Let’s say you think a hot tip is the way to gate this part. OK. Did you consider whether the part is going through an automated assembly operation, if so then gate vestige may be an issue; especially if the vestige causes the part to not track through the assembly equipment. Or maybe the material is a polypropylene homopolymer, which has a very high degree of stringing. The strings then cause issues with the assembly equipment.

It’s not a well known or documented fact that hot tip runnerless systems work well in low cavities, but are very challenging in high cavity scenarios. It also is not well known or documented that most gate wear with hot tip systems does not occur during injection phase of the resin, but rather at de-molding when the part moves away from the cavity and starts pulling at the gate before the material fractures.

The material could be glass filled polycarbonate requiring a large gate size. Initially the gate vestige isn’t an issue. However after a period of time, the gate wears resulting in a very high gate vestige that won’t allow the part to track through the assembly equipment.

So are these issues the fault of the hot runner supplier that didn’t understand the wear characteristics of glass filled PC? Or is it the fault of the tool builder that didn’t select the correct cavity steel? Or is it the fault of the processor who ran the tips too cold forcing a cold slug through the gate, damaging it?

The answer is all the above. Without experience and training, you won’t know what to fix. Worse yet, you fix the wrong thing and the problem keeps cropping up. The lost production time can never be recovered. The real cost of poor application integration never gets captured. The bottom line is reduced profit.

As you can see, it is critical to understand the complete manufacturing process to select the proper manufacturing components. These real day-to-day processing issues take us back to earlier discussions on education, knowing what your end result has to be and making sure the right questions are being asked up front.

In conclusion, when selecting the right hot runner components for your application make sure you’re asking the right questions and that the person who is answering the questions has a high degree of processing experience with hot runner technology. If that’s not the case, seek out those professionals in the industry that can assist you with selecting the right hot runner for your application.

Process and Design Technologies contact:

Terry Schwenk
Tel: (262) 237-2525
Email: tschwenk@processdesigntech.com
www.processdesigntech.com

About Process and Design Technologies
Process and Design Technologies was created to provide plastics companies with complete optimized processing solutions through efficiencies gained in engineering, manufacturing and processing. Company founder, Terry Schwenk has over 33 years of experience in the plastics industry, including more than 22 years of specialized experience in hot runner technology and tooling. An active member of SPE and holding the position of Past Chair for Mold Making & Mold Design SPE divisions, Terry has an associate degree in Business Administration and is accredited with several patents.

© Copyright 2009 Process and Design Technologies

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