Fastest 2x72 grinder ever?

Interesting- my disk grinder loses almost all its torque as I dial the VFD down- time for some research, I guess.
It's not too big an issue, since slow grinding tends to be light pressure, but it's still odd, I thought it was part of the package.
 
elementfe said:
Interesting- my disk grinder loses almost all its torque as I dial the VFD down- time for some research, I guess.
It's not too big an issue, since slow grinding tends to be light pressure, but it's still odd, I thought it was part of the package.
Click to expand...

It's worth checking your VFD settings.

As a rule, we tend to use a constant torque characteristic for most of the stuff we want to run: the Voltage and frequency increase together and linearly from minimum to rated speed.

At rated speed, the voltage is as high as the motor can accept, so the VFD only increases frequency from rated speed to maximum speed. We get constant torque below rated speed and constant power above it.

Many VFDs have a selection of curves pre-programmed and the one that best fits the application is selected on commissioning.

One of the other common curves is for fans. Fans follow the fan laws and the torque changes as the square of the speed (power changes as the cube of the speed). If you have the fan curve (sometimes called quadratic) programmed, the torque will drop away sharply as you reduce speed.
 
You're right, most of the VFD drives I installed in chemical plants were for fans or pumps, which slow speed required low HP, so it was never a problem. I'm using a TECO VFD, model JNEV-101-H1 on the lathe. If you can reference me to the parameter in the setup that would give full hp at low RPM it surely would be helpful.

Looking thru the manual with new eyes, on page 22, there is a C23, Torque Boost Gain function - is that one place you're referring to increase low speed torque/power?
http://www.tecowestinghouse.com/Manuals/ev_operating_manual.pdf

Ken H>
 
Last edited:
It's not a VFD I am familiar with, so please don't assume I know what I am talking about.

It looks like you want C14 set to 000.

This looks to be the setting for Sensorless Vector mode and should automatically adjust the voltage to maintain the power factor for the motor. On most (all?) of the SV drives I've used, the power factor is one of the settings taken off the motor rating plate. I assume this drive works it out from the rated speed and frequency, as set in F43 to F47?

It looks like F48, F49 and F50 can then be fine-tuned to maybe give you a little more.
 
Yes, you are right, it should be F48 rather than the C23 function - the F48 is for vector mode which is factory default setting and where I'm running. I'll tweak around with those 3 settings and see if that doesn't increase low end torque a bit.

Thanks for taking time to look it over,

Ken H>
 
Ken H> said:
Darrin - you say you have to turn your grind down to less than 400 SFPM to lose any torque? Have you tried to "bog" the grinder down at theses lower speeds? Just a fact of physics, the motor is producing less HP at those lower speeds (lower frequency), than at 100% speed. At 150% speed (90hz) the motor is still only producing name plate HP.

As I mentioned, with my 1 hp lathe with the speed turned low for threading it requires shallow cuts to prevent motor from bogging down, while at higher speeds the same depth cuts wouldn't even load the motor.

Ken H>
Click to expand...

Ken, I have to really bear down HARD to bog it above 400 SFPM. It does happen occasionally but not often. I'm guessing that its because I rarely use that much pressure unless I'm hogging. I rarely use it below 500 unless I'm grinding a super thin (.002"-.003") edge with a 220X or higher belt.
However, I have noticed that it seems to bog a little easier when cold than it does after it warms up. Does that make any sense or is it all in my head?
 
bladsmth said:
No, the belt has the momentum from a few ounces as it hit your face. My body would have the momentum from 180 pounds. If the belt weighed .1 pound, that would make the momentum 1800 times ( .05%) less than me falling off a motorcycle at 102MPH. (p=mv) .

That is roughly like comparing the carbon content of 1005 steel with 1095.

You really should stay awake in your physics class :)
Click to expand...

yeah but it could papercut you bad enough to slice open your jugular...
 
I really wish I knew 13 years ago, when I started working where I do, that materials cost so much, or that anyone might want them. There are literally tons of all SS scrap in the boneyard from when they built the new factory. The company that built it, a SS welding company, is still based on the premises to this day. It's all still there, only difference is that the head engineer that let me take whatever I wanted passed away a few years back from asbestos exposure. :(

It would be a piece of cake to source enough steel for ALL of you to make several pieces of equipment, let alone a simple grinder frame.

Oh well, hindsight is a mofo.
 
You must log in or register to reply here.
Back
Top