Planning to Purchase a Hot Runner System? What You Need to Know Before You Get Those Quotes

While they are certainly not a necessity in the moldmaking industry, more and more molders are discovering the numerous benefits hot runner systems offer the molding process: faster cycle times, no waste in the sprue and runner system and elimination of additional operations such as grinding the scrap material.

The capital investment is what may deter some molders from purchasing the equipment, but the benefits far outweigh the expense and the equipment pays for itself in approximately six to eight months, says Dirk Vandernoot, vice president of Gunther Hot Runner Systems (Buffalo Grove, IL). "You need to look at the long-term benefits," he states. "It is a capital investment, but you save a lot of money in the long run - especially with high-priced resins."
Since the investment is such a large one, a molder needs to know exactly what hot runner equipment can do for them and how to go about purchasing the proper equipment.

Why Buy?

According to David Boxall, vice-president and GM of Dundee, IL-based Ewikon Hot Runner Systems of America Inc., the most obvious advantage of using a hot runner system is the material savings that can be achieved by the elimination of the cold runner. 

"Also, more molded parts are requiring less regrind and consequently many applications do not allow the molder to use all of the regrind that is generated by cold runners," he explains. "In those instances the molder is required to use the regrind in other applications, or dispose of it through a re-claim company or send it to landfill. These of course, have costs associated with them.

"The second area that many people do not consider is the cycle time improvement that can be achieved with a hot runner, particularly for smaller parts," Boxall continues. "In many cases, the cycle time is driven by the size of the runner. A thicker runner requires a longer cooling time, and consequently if one can eliminate the runner then the wall thickness of the part becomes the driving factor of the cycle time in many applications, which can achieve shorter cycle times."

Purchasing Pointers

Ewikon's Boxall recommends a little soul searching before picking up the phone or surfing the Internet. "First of all, you need to ask yourself what you are trying to achieve with a hot runner and are you trying to directly gate onto the part," he says. "If so, this may narrow down the manufacturers you can address. "Or, you can address the application," Boxall continues. "If it happens to be a sub-runner application where you are molding a short runner attached to a part, most hot runner companies have systems that will achieve that kind of solution."

Vandernoot of Gunther feels the application is the most important factor to take into account. "We look at the application very carefully," he emphasizes. "We have several systems and depending on what application is each system's best we can determine what hot runner system is best suited for a particular application. In other words, if spacing is extremely close, say the injection points are a half-inch apart, we will use one type of hot runner system then let's say, a standard of two-inches apart.

"Or, for instance, if the temperature is more than 600xF with some of the engineering resins then we are going to go with a high-performance series of nozzles rather than one with less temperature," Vandernoot continues, "so we really try to size and fit the system to the application, and depending on how difficult the application is, that's how expensive it is going to get."

Another consideration is the type of material that is being molded and the quality requirements of the part, says Boxall of Ewikon. "This further narrows down the types of hot runner systems that can be used," he says. "In that same category one has to consider if he plans to mold different colors of the part, and if so, how frequent are the color changes. If color change is a consideration, one should pay particular attention to the design of the manifold and also to the design of the nozzles that are being used."

According to Boxall, while many custom molders specialize in a certain type of molding, some run the gamut. "If they offer a broad range of parts, it would be in the molder's best interest to consider a range of hot runner systems," he recommends. "I'm a firm believer that there isn't one hot runner system on the market that can mold every application. This type of molder may want to select a hot runner company that can offer a full range of product offerings. Alternatively, he/she may elect to find hot runner companies that specialize in each of the different segments of the molds that he or she may build."

Gunther's Vandernoot concurs. "Every mold has its own hot runner system and every application has its own hot runner system," he states. "No two molds - unless the molder is making the identical part - are going to be the same." Vandernoot offers a final piece of advice. "A lot of moldmakers just grab the book, look at it and say, yeah this one will fit," he says. "That's not the way to do it. Get the hot runner company involved from the get-go because that will solve a lot of headaches at the end. If there is a mold to be built get the hot runner company involved for advice, suggestions, how to size the runner and how to build the mold."