An overseas company had a cold rolling process where they would make metal sheets of different thicknesses and widths. They were having issues with their machine removing the excess coolant from the surface that was used in the process. Like with too many applications, they made their own home-made air knives. They found that they had reduced production rates, increased quality failures, and amplified noise levels. They contacted EXAIR to help resolve these issues.
To go into the details of the application, the cold rolling process uses work rolls to “squeeze” the metal to a thinner gauge. This squeezing creates heat up to 350oF (177oC). So, before each work roll, they would spray a coolant to help remove the heat. The amount of coolant is very important to get the proper cooling and metal gauge. After the work rolls, the coolant has to be removed before the next work roll operation. Their system was designed for 3,300 ft/min (1000 m/min), but they could only run it at half the speed as they could not remove enough coolant from the surface. For each work roll, they used three homemade compressed air knives that were made from 54” (1372mm) pipes with drilled holes. They laid one on top and one on bottom just after the work rolls. After the trial, they had to add another one on top to try and remove the remaining coolant that was missed by the first one. Each home-made knife used 440 SCFM (744 M3/hr) of compressed air at 100 PSIG (6.9 bar) during the cold rolling operation.
With similar solutions, EXAIR has a great product for non-contact wiping for flat surfaces, the Super Air Knives. They use compressed air to generate a force at varying degrees. With the engineered design, we are able to add free ambient air at a rate of 40:1. For every one part of compressed air, we can entrain 40 parts of ambient air. By adding this mass to the airstream, we can generate a hard-hitting force. Generally, with a drilled pipe, they have an entrainment near 4 to 5:1 which requires more compressed air to get that same force. Also, with the Super Air Knives, we can generate a laminar flow to give an even force across the entire length.
For this application, I was worried about the setup of their home-made air knives. With the position of being straight across, the coolant liquid could build up to a heavier amount in front of the knives, which could allow for some of the coolant to bypass. This would be the reason for the second drilled pipe on top. The bottom unit worked fine as gravity was helping to remove the coolant from the surface. But they were using a lot of compressed air with high noise levels. I was able to help them to create a more effective blow-off design and to save a lot of compressed air.
In my discussion, I mentioned that with high-speed operations, the setup is important for great non-contact wiping. For this customer, I recommend the Chevron style which mounts two Super Air Knives as an inverted “V”. Now we can cut the amount of coolant in half. Half of the sheet means half of the weight of coolant. For the top, I recommend two pieces, model 110036 36” (914mm) Aluminum Super Air Knife, and a single piece, model 110054 54” (1,372mm) Aluminum Super Air Knife, for the bottom. We were able to solve their issues with their cold rolling process.
As they started their operation, they were able to increase the production rates, and removed the need for the extra air knife. With the Super Air Knives, we were able to save them 877 SCFM (1,490 M3/hr) of compressed air at 100 PSIG (6.9 bar), as compared to the total amount of 1,320 SCFM (2,232 M3/hr) for the three home-made air knives. With a 24-hour operation, the Super Air Knives saved them a lot of money. The Return on Investment, ROI, was less than 30 days. As a note, the Super Air Knife only has a noise level of 72 dBA at 100 PSIG.
If you are looking to improve your blow-off application to increase production rates, reduce waste and improve safety, the EXAIR Super Air Knives can provide that solution. With the customer above, the development happened immediately with a short ROI. If you have a similar application and want to discuss it with an Application Engineer at EXAIR, you can contact us directly. We’d be happy to help you.
John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb
Photo: Steel Roll Alignment by Jean-Etienne Minh-Duy Poirrier. Creative Commons 2.0
