Figuring out the best way to obtain the perfect blend is the goal of every material processor. However, the pursuit of a uniform mix can sometimes lead to unintended consequences, particularly when it comes to overmixing.
We sat down with Senior Application Engineer Bill Noonan recently to talk about the phenomena of overmixing and how he helps customers overcome this challenge.
Q: What is overmixing and why is it something material processors need to watch closely?
A: Overmixing happens when you start a mix and everything seems like it’s running the way it’s supposed to. After say two minutes, your coefficient variations look perfect. Then, all of a sudden, your materials start to separate or unmix.
It’s a big concern because you’re damaging the material at that point but you are also not making any new product – you’re just running that mixer for no reason when you could be starting on that next batch. You could also be needlessly kicking up dust, which becomes another particle inside of your mix. You’re changing the character and cross-section of the material.
Q: Are some industries or materials more susceptible to overmixing than others?
A: Bakeries are prone to overmixing. Especially when shortenings are added. If you overwork that mix, those shortening additives will smear inside your mix. In the building materials industry, overmixing can change the color or color shade of colored grouts. Industries that tend to have a lot of ingredients, such as nutraceuticals where you have 10-20 ingredients inside a mix, are also very concerned about overmixing.
Q: We talked about some of the problems you can encounter when mixing dry materials. Is it a common problem with wet materials as well?
A: Yes, because you could be changing the moisture content of your mix. For example, if you start overmixing drywall mud, you can make it more liquidity and possibly trap more air in your mix as well. If you think about the consistency of pancake batter, too much air is bad. So too much mixing could ruin that batch of drywall mud as well as products with similar characteristics.
Q: What is the best way to tell if you are overmixing your product?
A: Most of the time, the signs aren’t visual. You’re going to have to do some internal analytical coefficient variation studies, or take those samples to a lab to make sure you have the right percentage of your ingredients in there.
Q: Can the design of a mixer contribute to overmixing?
A: It could if you are using a mixer that was not designed to handle certain mixes. For example, mixers with fluidizing paddles run twice as fast as mixers with traditional paddles or ribbon agitators. If you run that fluidizing paddle for the same length of time as a more traditional mixer, then you could damage or separate materials in your mix.
The same goes for high-speed choppers. Those are running so high and fast that they put a lot more energy into material. With mixes that have a lot of shortenings, we need those choppers to break up those agglomerates, but we don't want those running the full, three minutes because that’s constantly adding more unnecessary work to the material.
Ribbon agitators work on sheer and can grind salt down too finely and alter its properties, which could lead to an uneven distribution in the mixture. Look at salt under a microscope and you’ll see it has rough and jagged edges. With too much unnecessary work, these surfaces get worked away. This is now dust. You just changed your mix characteristics!
Q: What other factors contribute to overmixing issues?
A: Sometimes just the ambient temperature of your material can have an impact. January and August are two different extremes in ambient temperatures. For example, when you are making pie crust, you want your dough cool, otherwise it’s going to smear. So that’s why you keep it chilled so it doesn’t cling to your rolling pin.
Q: How can Marion help customers prevent overmixing?
A: For starters, by asking the right questions. Like how are they getting material in and getting material out so they are not damaging the material? Some customers think they have to add this huge mixer and then are amazed to find out it’s going to take 30 minutes to fill it, so figuring out how they can streamline what happens upstream and downstream of the mixer is key.
Marion’s Testing Centers are also an excellent resource for anyone who wants to make sure they’re getting the most out of their mixing equipment. For customers with new applications especially, it’s very helpful because they don’t necessarily know how to achieve the right mix yet. It also helps us to make sure we’re supplying them with the right piece of equipment with the right agitator, so they don’t overwork or underwork their material. This is another way we can help guide them on the right path.
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About Bill Noonan
Bill Noonan has worked in sales at Marion Process Solutions for 27 years. A graduate of the University of Northern Iowa, Bill is a self-proclaimed process junkie who loves seeing and discussing the manufacturing process.
