If you are an engineer or a student of engineering, have you ever thought about how important bar screens are in many industrial processes? Even though these simple machines don't look like much, they are very important for separating large and small pieces of crushed rock, gravel, and other materials.
In this blog post, we'll take a closer look at bar screens and talk about how they're made, what they're used for, and how well they work.
No matter if you're an engineer in the mining industry or just want to know more about how machines work, you need to know what bar screens do.
So, let's dive in and learn more about this important piece of engineering technology that is often overlooked.
Introduction to Bar Screens
Formal definition:
A sieve with parallel steel bars for separating small from large pieces of crushed rock.
Bar screens are mechanical filters that are used to get big things out of wastewater, like rags and plastics.
In a wastewater treatment plant, they are an important part of the primary filtration flow.
Bar screens work like conveyor belts that use a bar or wire filter to pick up solids and let water pass through.
The filter is moved through and out of the water channel and to a motorized cleaning and trash area.
This can happen sometimes or all the time.
Types of Bar Screens
Bar screens can be either manually or mechanically operated.
Vertical bars that are 1 to 3 inches apart on manual bar screens let water through but stop big things.
On the other hand, mechanical bar screens are kept clean by a process that is done automatically.
Bar screens that are cleaned by hand have smaller holes and use electric motors and chains to clean themselves automatically.
Types of Screens for Separating Small and Large Pieces of Crushed Rock
Most of the time, vibrating screens or scalping screening plants are used in quarries or sand and gravel pits to separate small and large pieces of crushed rock.
Bar screens can also be used for this purpose.
Bar screens are often used in the mining industry and in plants that process aggregate.
In the first step of the process, they are often used to separate big rocks from smaller ones.
The space between the bars and the angle of the screen are both carefully thought out so that big and small things can be separated.
Static Grizzly Screens
Static grizzly screens are another type of screening system used to separate rocks.
They sort and classify rocks by size and get rid of anything that might slow down production.
Grizzly bars have holes punched in them, and steel rods go through the holes to hold the bars in place.
Between the bars, spacers made of cast iron with the right shape and size are put.
Different kinds of bars can be used for different things.
Manufacturers of Bar Screens
Large wastewater treatment plants can get coarse automatic bar screens from JC France Industrie.
These screens have an opening of 6 to 100 mm at the bars.
For small-scale private installations, a manual model is sufficient.
Duperon makes both large and small bar screens for wastewater that can be used in a wide range of situations and settings.
Experience the Thrill of Industrial Machinery with Bar Screens
Still hard to understand? Let me change the point of view a bit:
Are you tired of the same old things and want to spice up your life? Bar screens are what you need.
You'll be on the edge of your seat as you watch these metal marvels expertly separate big and small pieces of crushed rock.
It's like watching a high-stakes game of Jenga with industrial machinery! So get some popcorn, sit back, and get ready to be amazed by the world of bar screens.
Okay, that was just a joke made to look like a TV ad.
Now let's go back to the explanation.
Design and Maintenance of Bar Screens
Bar screens are needed in wastewater treatment processes to get rid of large particles.
To make sure the design works well, the following things must be taken into account:
Minimum Bar Size: For bar screens, the cross-section of bars, flats, or rods should be at least 10 mm x 50 mm.
Clear Spacing Between Bars: The clear space between bars, flats, or rods should be consistent and kept by a sufficient number of spacers that don't get in the way of the flow.
The distance between clear spaces should be between 15 and 75 mm.
Allowable Head Loss: 0.15 m is the amount of head loss that is allowed.
Minimum Approach Speed: The approach speed must be at least 0.3 m/s.
Flow Rate Through Screen Openings: The flow rate through screen openings should be between 0.6 and 1.2 meters per second.
Slope with Horizontal: Screens that are cleaned by hand lean 45° to 60° away from the horizontal, while screens that are cleaned by machine lean 60° to 90° away from the horizontal.
Submerged Area of Screens: The submerged area of the screens, including the bars and holes, should be about 25% to 35% bigger than the cross-sectional area of the approach channel.
When figuring out the area of a slanted screen, use the projected area normal to the flow direction.
Cleaning and Maintenance of Bar Screens
Operators can clean and maintain bar screens to make sure they work at their best by following these steps:
Visual Inspection: Look at the equipment often to find problems before they get worse.
Lubrication: On single-arm bar screens, grease the rack and pinion gear.
Cleaning: Look at the top of the screen and wipe it down.
Wash Water Pressure: Make sure that the pressure of the wash water is right.
Adjusting the control: Set the control so that it works best.
Chain Inspection: Look for wear and make sure the tension is right.
Inspection and Replacement of the Screen: Check, clean, and replace sections of the screen.
Clearance: Leave enough space in front of the screen at the discharge end or behind it at the feed end so that screen sections can be changed out.
Stationary Structures: Give stationary structures enough space around them.
Vibrating Frames: Don't let moving frames hit things that aren't moving.
Rear-Return Bar Screen Design: Use a rear-return bar screen design that uses brushes and spray nozzles to help clean the bar scrapers of debris before sending them back down the "clean" side of the screen.
This reduces the need for maintenance and can make it easier to get rid of debris.
Effective screening can cut down on pump damage and maintenance further down the line.
It can also cut down on how often and how much it costs to clean out clarifiers and digesters.
Mechanical maintenance can be easy to do once a year if the design and construction are solid.
For example, a top-of-unit bearing can be oiled every three months, and planned or emergency replacements can be made.
Alternatives to Bar Screens
Alternative Technologies for Solids Removal
In wastewater treatment plants, there are several other ways to get rid of solids besides using bar screens.
Some of these are:
StepScreen: This bar screen has a unique design that uses thin lamina as the "bars" to make a large amount of open space and allow nominal spacing as small as 1/8 inch.
It works best in places that don't get a lot of sediment most of the time.
Manual Bar Screens: These screens have their limits and are best for small systems, but there are several automated options to reduce the amount of work that needs to be done.
Chain-Driven Screens, Catenary Screens, Reciprocating Rakes, and Continuous Belt Screens: These options also often use vertical bars to catch solids and move them away with an automated raking system.
Drum screens use cylinders that turn to separate trash from wastewater streams.
Disc filters use a series of discs stacked on top of each other to remove debris from wastewater streams.
Microscreens are used to filter out trash from wastewater streams.
They are made of fine mesh or fabric.
Choosing the Right Screening Technology
The choice of screening technology depends on things like the size of the plant, the type of waste stream, and the available budget.
It's important to choose the right screening technology for each application to make sure that it works well and performs at its best.
Comparison of Bar Screens, Mesh Screens, and Vibrating Screens
Solids can be taken out of water streams with the help of bar screens, mesh screens, and vibrating screens.
But there are differences in how well they work and how much they cost.
Bar screens are automated mechanical systems that take out big things from water streams, like cans and driftwood.
They work better with higher concentrations of solids and have a simple and cheap way to remove floatables and visible solids because their holes are big and they can clean themselves.
Mesh Screens: Steel wire mesh or plates with holes can be used to make mesh screens.
Smaller particles will be caught by finer filters when they are used to filter.
But you can't say enough about how important it is to choose the right media for any screening application, because the media affects how well a screen works in terms of capacity, efficiency, and cost-effectiveness.
Vibrating Screens: The motion of a vibrating screen in the vertical plane ranges from +/- 3.5 to 6 g or more.
Linear-motion screens help producers because they cost less to install than circular- or elliptical-motion screens because they need less headroom.
Cost-effectively, both bar screens that are cleaned by hand and modular polymer screens have wear life benefits.
When choosing a screening method, it's important to think about what the plant needs.
Bar Screens for Other Applications
Bar Screens for Wastewater Treatment
Bar screens are a common way for wastewater treatment plants to get rid of big solid objects in the water.
They are a type of coarse screen that takes out rags, plastics, papers, metals, and other large floating objects that could clog the treatment process.
Bar screens are made of vertical steel bars that are 1 to 3 inches apart.
They keep waterways from getting clogged and dirty, which slows down the whole treatment process.
Alternatives to Bar Screens
In wastewater treatment plants, other separation methods are used to separate slurry particles and remove oil from the fluids that are made.
Hydrocyclones are devices that use gravity to separate slurry particles based on their weight.
They have a high throughput.
They don't have any moving parts, are easy to use, and are strong.
They have been suggested for separating animal cells in batch and perfusion processes.
To separate animal cells, though, they need to be made with special geometric proportions.
Centrifuges can get rid of very small oil drops, but they are more expensive than hydrocyclones and aren't used as often in wastewater treatment plants because of this.
Advantages and Limitations of Bar Screens
Bar screens are easy to make and have lower capital and operating costs than other technologies for separating.
They use the full width of the channel and take out big things like wood, cloth, paper, and plastic from the waste stream.
Automated bar screens cut down on labor costs, but there are other costs to think about.
Bar screens have a simple design, lower capital and operating costs, use all of the width of the channel, keep large solids out of the waste stream, and reduce labor costs with automated options.
But they have some problems, like the fact that you have to think about operational costs with automated options.
Other Applications of Bar Screens
Bar screens can be used for more than just treating wastewater.
For example, they can be used to filter water coming into power plants, desalination plants, and industrial processes.
Bar screens are also used in the management of solid waste along with other treatment equipment like comminutors and grit chambers, which are the next steps in the treatment process after screening.
Evaluating Bar Screen Performance and Safety
Guarding Moving Parts
All moving parts of bar screens, like flywheels, belts, and pulleys, should have guards put on them to keep people from touching them by accident.
This makes it less likely that employees will get hurt while doing their jobs.
Proper Training
Employees should get the right training on how to use equipment safely, how to use protective gear like gloves and safety glasses, and what to do in an emergency, like if something breaks or someone gets hurt.
Training should be given to all employees, even those who only work part-time or are in training.
Clean and Well-Ventilated Workspace
To avoid trips, slips, and falls, the workspace should be clean and free of clutter.
Also, the area around the bar screen should have good air flow so that pollution and carbon monoxide don't get in.
If maintenance or repairs need to be done, employees should follow lockout/tagout procedures to make sure that the equipment is properly turned off and can't be turned back on by accident while someone is working on it.
Evaluation and Optimization of Bar Screen Performance
To evaluate and improve the performance of a bar screen, many things must be taken into account, such as its design, how it works, how long it lasts, the flow rate, temperature, pH level, and chemical makeup of the wastewater.
The more debris it catches, the smaller the hole in the screen.
But the increased rate of capture means that the debris on the screen needs to be able to be taken off mechanically.
When choosing a screening system, it is important to think about how reliable this mechanism is.
Even though the SCR rating can help you decide what to do first, you should be very careful when judging a screen based on other important factors.
Other Safety Considerations
It's also important to make sure the area behind the bar isn't too crowded and that there are enough places to put things.
If a worker spends a lot of time carrying things or doing the same thing over and over, they should take breaks during their shifts to stretch or rest.
In general, safety equipment is needed to keep workers from getting hurt when it's not necessary.
Any part of a machine or process that could hurt someone must be made safe.
Awareness devices can warn workers when a danger is about to happen.
The first type of awareness device is an awareness barrier, which lets employees get to dangerous parts of a machine but alerts them when they are getting close to a danger point.
By thinking about these things and taking the right safety precautions, employees can work with bar screens in a safe and effective way that minimizes the risk of getting hurt or damaging equipment.
HUBER Coarse Screen TrashMax®: Animation + Video
Tip: Turn on the caption button if you need it. Choose “automatic translation” in the settings button, if you are not familiar with the spoken language. You may need to click on the language of the video first before your favorite language becomes available for translation.
Conclusion
As we wrap up our talk about bar screens, it's worth pausing to think about how important they are to our lives, even though they are often overlooked.
Bar screens are used in many industrial settings, from mining and the processing of aggregates to the treatment of wastewater and the management of solid waste.
Still, they are often taken for granted, and not much thought is given to the complicated engineering that went into making them and making them work.
But maybe that's the real beauty of engineering: being able to make machines and tools that make our lives easier and more efficient without drawing attention to themselves.
So, the next time you see a bar screen at work or in your daily life, take a moment to think about how cleverly it was designed and built.
And remember that the things that change our world the most are often the ones that look the least important.
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