Best practices: Washing & classifying

Industry expert John Bennington discusses washing and classifying techniques with Pit & Quarry.

Headshot: John Bennington

John Bennington, product manager at Superior Industries, led an educational session on the basics and misconceptions of washing and classifying at the 2015 AGG1 Aggregates Academy & Expo. Bennington has been dealing with washing and classifying equipment since 1993. In the past, he has worked for Eagle Iron Works, GreyStone Inc. and Metso. Superior Industries hired him last spring to be its product manager of washing and classifying.

Pit & Quarry connected with Bennington to discuss the topic further.

P&Q: What are some common washing mistakes aggregate producers make?

Bennington: Washing equipment, for the most part, is pretty reliable. It does its job day in and day out. When mistakes happen, it’s usually because operators haven’t paid enough attention to them after months or years at a time. The two biggest mistakes I see operators make are either they don’t pay attention to maintenance of equipment, or they don’t notice how changes in certain parts and products will affect the washing side of things.

P&Q: To avoid maintenance problems on washing equipment, how often should washing equipment be checked?

Bennington: I always tell customers a daily walkthrough of the plant is not a bad idea. But they ought to at least walk around the entire thing to make sure all of the system is working. At least, I recommend a weekly walkthrough. These don’t have to be overly complicated. They can be done even while the plant is running.

P&Q: You mentioned during the AGG1 session that a dewatering screen should be able to last up to 12 years. How accurate is that? How should operators take care of dewatering screens?

Bennington: Dewatering screens will wear earlier if maintenance is not kept up on them. They usually won’t wear down, if they are of high quality. Most dewatering screens have a high quality. But you could end up with a broken screen if no one’s paying attention to it. That’s when they break prematurely.

P&Q: What is the difference between a dewatering cyclone and a sand screw? When should each of these be used?

Bennington: Traditionally, sand screws have been the way people in North America dewater sand. They’re reliable and low horsepower, running about 0.15 hp per ton. Go over to Europe, though, and they’re more inclined to use dewatering screens with a cyclone. That takes up about 0.7 to 0.8 hp, but the advantage is the material that comes off screens with cyclones is very dry. Basically no screen water comes off at all.

P&Q: Why is it uncommon to see sand screws in Europe?

Bennington: Europe has a much more urban environment than North America. Quarries over there tend to be surrounded by population, and most quarry operators don’t have space to let material dry. In America, we have more space. Producers have more space to build up tons of piles to allow drying space. And part of it goes back to cultures.

P&Q: Can you share some best practices for log washers?

Bennington: The main purpose of log washers is to remove heavy plastic clay. Plastic clays are clays that get slimy and are difficult to break down in water. What a log washer does is it takes two rocks and grinds them together so the clay between them actually gets worked on. You can vary the steepness on a log washer. When you have more clay or tougher clay material, steeper inclines do the work best. With less clay or lighter clay material, decreased inclines allow operators to do more tonnage.

P&Q: In your AGG1 session, was there anything else you think washer operators could take away and improve on? What are some poor washing habits that could be avoided?

Bennington: I think the biggest takeaway is that when you look at your plant, you need to look at its complete process. Individual pieces of equipment can be looked at, but the entire process also needs to be inspected. Make sure you’re checking everything with walkthroughs. I find when I go to customers, they sometimes will send me a picture saying one piece of equipment is the problem, but often another piece of equipment that works with that equipment is the main problem. For example, they’ll send me a picture of a sand screw they think is the problem, but I discover it’s really an issue with the screens that’s affecting the entire system. When problems arise, I suggest check the entire system.