Rubber manufacturers have knowledge advantage in processing LSR

Twinsburg, Ohio — If you're a rubber product manufacturer, you bring some key advantages should you decide to enter the realm of liquid silicone rubber.

As a thermoset material, LSR bears similarities to other kinds of elastomers in the way it's molded, and having a deep knowledge of what to expect comes in handy when processing LSR, according to Bernie Stritzke, chief technology officer at Q Holding Co. The Twinsburg-based firm makes LSR products as part of its Qure Medical unit, as well as its QSR business, which serves automotive and industrial customers.

"If you have an arsenal of other thermoset molding capabilities, all of a sudden you set yourself apart from the plastic injection molders that happen to stumble across LSR molding," Stritzke said. "We can offer other types of molding materials and processes to create the same part. LSR molding is kind of a sexy art when you think about the ability to mold as fast as you can in a thermoset process. It's a very quick way of molding something, but it's not always the only way of molding something."

LSRs bring some unique challenges to the table for a molder, Stritzke said. As its name implies, it's a very viscous material, which prevents molders from being able to use molding methods that might work on the plastics side, like using knockout pins to eject a tool. Eventually, the rubber will find its way into the gaps of those pins and render them useless.

Another is handling the material. Because of its liquid state, getting the gooey compound into a press and the mold is difficult, if not impossible, without some form of a pumping unit. Stritzke said not being able to physically pick up the material and place it in a tool is unconventional to typical thermoset molding.

But the heat is arguably the biggest challenge, especially for companies used to the opposite process — cooling a material to make a part. LSR needs heat in order to activate the cross-linking, and as the material gets hotter, physics dictates it will expand. Stritzke said a balance is required to minimize the amount of flash. Some tricks molders can use include minimizing the temperature differential from pump to mold, or allowing the LSR to expand so flash does not occur in critical areas.

"It's a thermoset, and it has to operate in that fashion as a thermoset," Stritzke said. "You're introducing heat into the mold to cause that cross-linking to take place. Having a background in molding rubber or thermoset elastomers is going to be an advantage in that regard."

Stritzke added that he does not believe LSR is a difficult product to mold.

"I don't think the plastic companies have some type of inferiority to a thermoset molder," Stritzke said. "A lot of this all depends on what these companies want to do. I've seen some very successful plastic injection companies embrace LSR molding. It's like anything else: If you do the same types of products over and over again, you become successful at it. If you have a wide variety of different LSR products, it would probably be a challenge to just go from plastics to LSR. But if you hone all your experience into one type of product that's very similar, there are some inherit advantages."

The material's low viscosity makes it easy to flow, and it has a very quick cure time as opposed to some of the other heat-cured rubbers on the market. But Stritzke said the key to success with LSR, like with any other material, is establishing a consistent process. Especially when it comes to tooling.

"You have to have other means to remove products and tooling," Stritzke said. "With a quicker cycle time, most people want to try to automate LSR. But the challenge with elastomer products is a lot of them have deep undercuts that are impossible to de-mold in the thermoplastic environment because there's no give in the material. The tooling in those regards needs to be designed in some really creative ways in being able to manipulate the part to get it out of the tool because people come up with creative designs for elastomers.

"To really be effective at it, your tool and your process need to be honed together into one."