As machined parts require tighter tolerances, machine shops are starting to look at Swiss-type CNC machines. These types of machines are extremely accurate and very fast in producing small parts. But in order to reach that level of accuracy, the bar stock may have to be pre-treated by a centerless grinder.
Our customer was using Swiss-type CNC machines with guide bushings to produce a very tight-tolerance part. Because they were using guide bushings, the outside diameter of the bar stock had to be smooth and concentric. This helps to reduce any vibration when machining. A centerless grinder was used to accomplish this. The bar stock that they used was 10 feet long and it was placed into a bar feeder. They had to grind the bar to an outer diameter of 30mm with a surface finish of 32Ra. As they were loading the bar stock, they noticed that the surface finish was scuffed and marred. This was enough to affect the machining process and not meet the tolerance standard.
As they reviewed the possible causes, they found that after the bar was ground, some grinding remnants were sticking to the outside of the bar. As the rods were leaving the grinder and placed onto a roller-type conveyor, the oily film and metal shavings were sticking to the rollers. This would scrape and mark the rods as they traveled along the conveyor toward the Swiss-type machining center. As an attempt to remove this debris, they attached two copper tubes to blow compressed air onto the top and bottom of the bar. Not only was this loud and inefficient, it was not effective. They still had a dirty line along the sides of the rod that remained. They contacted EXAIR to see if we could help them with this dilemma.
In order to get a consistent blow-off force around the entire circumference of the rod, EXAIR Air Wipes were engineered to be an ideal solution for this kind of problem. I recommended the model 2482 Standard Air Wipe Kit. The Standard Air Wipe is designed to blow compressed air in a 360 degree flow pattern. This air pattern is directed at a 30 degree angle toward the center to blow the debris off of the bar stock. The Coanda effect maximizes the entrainment of ambient air into the compressed air. This makes the unit very efficient and powerful. The model 2482 Standard Air Wipe has an I.D. of 2” (51mm) which gives it enough clearance for the 30mm bar stock. It can be mounted easily near the exit of the centerless grinder to keep the grinding remnants inside the machine. The kit includes a filter, regulator, and shim set. The filter will remove contaminants from the compressed air system to keep from introducing any new grime and to keep the inside of the Air Wipe clean and functional. The shim set and regulator provide the ability to adjust the air to the ideal force level and remove any debris from the surface of the bar.
As they removed their home-made copper tubes and attached the Standard Air Wipe, they noticed some great improvements. The dark lines of debris previously along the sides of the bar stock were gone. The surface was clean around the entire circumference of the bar. The customer also noticed that the Standard Air Wipe was much quieter than their home-made solution, as it only has a decibel rating of 77 dBA. As an added benefit, the Standard Air Wipe was using much less compressed air than the copper tubes. This is due to its design to maximize the amplification ratio. With more of the “free” ambient air than the compressed air being moved over the target area, it will save money in compressed air usage. The ROI could be less than four months.