Don't get complacent about shop safety

[Tyrone Shoelaces]

Most facing slides on the modern Hor-bores I worked on would stop within a rev even with 32” facing slides. They’re as big as a chuck. An electromagnetic brake is your friend.

Regards Tyrone.

 

[eKretz]

DC injection is definitely a fast stop. Same setup VFDs use for rapid stopping. The size of the machine doesn't really matter so much because the bigger the motor, the more the braking power it has. It's not something you want to use over and over at high settings, (it can overheat the motor with repeated use, apparently) but in an emergency or even at lower settings it is pretty good stuff. The same thing can be used on a DC motor in a little different way by shorting the motor poles together. They stop WAY faster that way.

 

[Bill D]

WHEn using compressed air to blow a clog out of a gasonline line make sure any flames are out before pulling the trigger. Leno is lucky he has his eyesight. I assume the hair is a wig now.
Bill D

 

[Joe Gwinn]

I’m not an electrician but what I believe happens is that DC current is injected into an AC motor.

That is exactly how it works. Think of it this way:

A 3-phase induction motor generates a magnetic field that rotates at the frequency of AC power (50 or 60 Hz on the line, variable from a VFD), and heavy currents are induced in the squirrel-cage rotor if it isn't rotating at the rotation speed of the magnetic field.

The magnetic field from DC does not rotate at all, so the squirrel-cage rotor is quickly forced to that speed, which is zero rpm.

 

[johansen]

A vfd can stop a motor a little faster than it can start it, but rarely does anyone run them that hard.

When that motor is geared down 10:1, as in a 200rpm drill press with a 1760 rpm 10hp motor.. I find it no surprise DC injection braking can stop the spindle within half a turn. This would take a 5th of a second and would qualify to most folks as "instantly".

In reality it's not instant.

Just for fun I can plug my (reconfigured for delta) 2hp 138vac 3600 rpm motor into 208v 3 phase and use an oscope to capture how long it takes to reach 3550 rpm. Because to my eye it really did start instantly. But it didn't. I think it had to have reached 3500rpm in less than a third of a second.

Most vfds can only DC injection brake at 150% nominal "amps". This might be enough to stop a variety of "drill press" applications within one turn of the output shaft. But it's not instant.

There are other ways to get instant..such as ignorant brake pads (channeling my inner thermite).

 

[Limy Sami]

That's a scary experience you had! It is amazing that you were able to get away unscathed. It is a great reminder of how important it is to follow safety protocols when working with machines. Before starting a project it's important to always conduct a pre start health and safety review. This should include assessing the specific hazards associated with the task identifying the appropriate safety protocols, and ensuring that the necessary safety equipment is in place and being used correctly. Taking the time to do this beforehand can help prevent potentially dangerous situations.

Spam spam spam, (and yes I know its health and safety)

 

[redlee]

Ever seen one of the big places with the sign "3512 Days without an injury"......the refinery was like that ,any contractor employee got hurt had to be taken outside the refinery for an ambulance to pick him up..........if you put the board back to zero....you would never work there again.

When I was working we had a similar system the guys hid injuries. And if you were caught hiding them you were written up.

 

[eKretz]

Spam spam spam, (and yes I know its health and safety)

Canadian bacon spam, according to the IP address. Canned now...

 

[Milland]

Spam spam spam, (and yes I know its health and safety)

And a delicacy in Hawaii. And Guam.

And a thread about a thread - how meta...

 

[Ox]

Spam spam spam, (and yes I know its health and safety)

And since you quoted it, it's still here...


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Think Snow Eh!
Ox