Hey all, Am designing a gearbox to be used with a motor that gives 7700 rpm at it's rated conditions. This setup is to be used in a home appliance and for the purpose of it's application the gear reduction needs to multiply the torque to quite a large value (~6 Nm). As a consequence of this the final speed is also reduced to around 800 rpm. I have tried using a custom gear box manufactured by the motor supplier, however the vendor could only provide me with metal gears (alloy steel) and they were very niosy. To deal with this issue I designed a system using a two stage reduction with plastic gears (POM). This seems to be getting the work done, however the entire system is very noisy. I am new to designing gear-trains etc and have no idea how to reduce this/resolve this problem. The system has to go into a home appliance and the amount of noise at present is too much. I would really appreciate it if someone could help me out here. I am new to this forum and am not sure how the protocol here genreally works, but please reply back with any useful information that you might have. I would really appreciate it. Thanks in advance
Noise problems are very difficult to solve without seeing the offending equipment. Start with checking: -the gear intercentre distances are correct, -gear tooth finish, -spur or helical gears, -rigidity of gears, -gear concentricity, -bearings, ball or plain? -stability/stiffness of support shafting, -is support shafting parallel? -lubrication, -is noise with or without load? -the stiffness of the support casing, this could act as an amplifier. Gearbox noise begins with tooth meshing and the frequency noise generated, all other issues amplify this this noise.
At 7700rpm, the first mesh is going to be the problem area. You might have to use high helix ground gears to get around the noise problem. The alignment of the shaft axes, the fit of the gears on the shafts and correct amount of backlash should solve your noise problem. At the torque you have mentioned, nylon gears will not perform.Hope this helps you to figure out the solution.
Agreed, if your gears are straight cut, a switch to helical cut cogs is THE best solution (listen to the difference between a road car and a proper race car, or sportbike, for instance... lots of gear noise in the latter). The only other thing off the top of my head that I can think of (given the rest of your transmission is optimally designed) is a change to a softer gear material, so long as it can withstand the loads and temps imparted upon it.
Some noise is inherent to the very nature of gears, though it can be reduced substantially by hellicals. However, you can always try to reduce the noise coming out of the system by isolating and absorbing the noise and vibration on the way between the gears and the outside of the appliance. Probably your best bet is to do both.
