By Serge Raymond
Aggregate or mining facilities that rely on tensioned screen media for their vibrating screens have probably heard of the term “crown curve.” But what exactly is it, and why is it important?
What is the Crown Curve?
The crown curve, or camber, is a high point created in the middle of tensioned screen media by the clamp rails that hold the screen media down on either side. This curve is essential because it allows producers to maximize performance and wear life. Let’s break down how it works and why it’s so crucial for aggregate and mining operations.
What Does the Crown Curve Do?
The crown curve ensures equal distribution of weight across the screen deck during the screening process and helps set up the correct frequency for the wires. Think of the wires on the screen media like guitar strings – tightening them results in higher vibrations, while loosening them does the opposite.
Some screen media manufacturers help operations achieve the perfect frequency for their unique material. High-vibration screen media, for example, vibrates at a rate of 6,000 to 10,000 cycles per min., which is up to 13 times greater than a standard screen box. A proper crown curve helps these wires vibrate at a higher rate, increasing throughput and ensuring maximum efficiency from the screen media.
When Do You Need the Crown Curve?
Tensioned screen media requires a crown curve. Clamp rails hold the screening panels down on the east and west or north and south sides of the vibrating screen. The crown curve should be at a high point between the rails. The goal is for the material to hit the crown curve first to help disperse it evenly across the entire deck.
What is the String Test?
The string test is a simple way to check the crown curve of a screen deck. Here’s how it works:
1. Remove the crown bar rubber.
2. Put a string from corner to corner across the deck
3. If any part of the screen doesn’t touch the string, that’s where the crown curve sags.
Often, this test reveals that the clamp rails no longer hold down the screen media, which can happen for several reasons. Maybe the rail pulled away from the first bar, or the deck has been smashed down over time. When this happens, we send a technician to analyze the screen deck and provide a solution.
How Can You be Sure the Crown Curve is Correct?
Too low of a crown curve results in screen media flapping or breaking prematurely. Too high of a crown curve makes the material reach the sides of the screen media too quickly and results in premature wear at those points of the screen.
The string test will show if there are any areas of concern when it comes to the crown curve on a screen deck. A screen media technician from a trusted manufacturer can come out to a quarry or mine and help calculate the optimal crown curve for the vibrating screen. Some manufacturers also provide the required height of each support bar to redo the deck and suggest how to rebuild it to achieve the proper crown curve.
Optimize Screening Performance with the Crown Curve
The crown curve is a critical feature to optimize throughput on tensioned screen media. By distributing the weight evenly, the wear life of the screen media is improved and efficiency is maximized. Regularly testing the crown curve via the string test helps maintain the correct crown curve.
Consulting a manufacturer can further optimize the process, ensuring your aggregates or mining operation achieves the highest levels of performance and longevity from your screen media.
Serge Raymond is product specialist at MAJOR, www.majorflexmat.com.