DC Injection brake modules

[Rigpig]

*problems

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[SheffSimon]

Nope, but some of us on here do this design stuff for a living, and we follow the correct process mainly because we want to do it right, but also because we don't want to end up on wrong end of an HSE investigation.

 

[Darkwood]

1 point i do remeber is we received a flash report not to fit them to milling machines. Presumably this was due to the pronlems you mention above @Darkwood

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The problem is more to do with use and size of the lathe and gearing and control and unless you have a full grasp of its use, its motor type and duty, is the lathe used only for a specific task etc (possible in certain industries or workshops)... then possibly DC injection is an option, the downfall of using DC injection is the heating effect of the windings and if you get your timings wrong or start/stop duty is too high then expensive problems can occur, also I have seen DC injection units fail where they continue to inject long after the motor has stopped due to timerboard failures - consequently the motor windings burn out. With an electro-magnetic braking (my personal choice), a timer unit failure at worse would just see the brake on constant (power on units) or no timer board at all to fail (power off units) and dependent on control circuit it should stop a restart of the lathe but if of an older design it would mean motor would trip on start up or when it was put in gear, also some lathes have constant run motors with clutch control for the spindle to run so on the occasion DC injection would be pointless as that is not how the lathe works, another common motor type on lathes are 2 speed motors, again this comes with its own problems when using DC injection.

Im not saying using DC injection on a lathe is a no-go but trying to hi-light the problems and the considerations you need to take into account before you would spec' as a control method, if it was the only option for me then I would possible design a control system that may use a rotation sensor as the timer for injection with a background timeout for redundancy in case the rotation detector falls out of position or fails then at least it won't cook the motor, a warning light would then alert the user to an issue.

When your braking method is been fitted for safety then you really need to know you can rely on it even with component failure, this cannot be achieved if the DC injection module fails but can be if you have a power open electro-mechanical break, if its control fails and it loses power or even on a power cut then you know the brake will operate, this is why for the OP's situe' and because he is been asked to do this as a safety measure that I am advising on said method.

 

[Rigpig]

Thanks for the comprehensive response Darkwood.
In our ships case the dc injection module worked a charm but as you correctly point out it may not suit all situations/lathes.
As an aside i recall now the reason the injection modules were not to be used on milling machines was that on one of the other rigs the sudden stopping of the bit caused it to shatter sending shards flying. Or at least that was the "official "report..... wether that was the actual case is unknown

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[Carl S]

A spinning lathe like this?

https://www.youtube.com/watch?v=XsCFze4zkzk

Some don’t have a positive grip on the workpiece but rely on friction. Be very careful what you do as you could launch the workpiece.

Discus throwing was used in warfare, you may have found a way to automate it.

 

[joel89]

it is just a chuck connected to a shaft and motor no gearing !!! 1500rpm direct to the chuck.....it is a type of lathe but not a conventional one its a spinner.. for spinning a gas cylinder neck on with burning torches on

 

[joel89]

https://www.youtube.com/watch?v=Z8R-I5I1Dgo

doing the same process, skip to 2mins 20secs

this is the same machine as ours... spinning lathe

 

[joel89]

I have priced up a new motor with a brake built in electromagnetic, coming in at £500 probably go this option cures everything then

 

[netblindpaul]

I have priced up a new motor with a brake built in electromagnetic, coming in at £500 probably go this option cures everything then

Wrong again, sorry, it does not solve anything.

What do the assessments say?

In a little bit more detail, is the chuck threaded?

You can't just pick random solutions like this and hope they work, they MUST be correctly designed and engineered to the correct outcome.
You are "playing" with Statute Law, get it wrong enough, and you will become a Criminal and you can be jailed and subjected to unlimited fines.

 

[Carl S]

Ever seen a chuck come off a lathe at 1000RPM? I did when I was at engineering college, it went through two brick walls.

The foot brake is there for a reason, it gives a controlled stop.

 

[Carl S]

I have priced up a new motor with a brake built in electromagnetic, coming in at £500 probably go this option cures everything then

What make of motor?

SEW Eurodrive will supply different compression springs for their brake units. You need to attend their training centre to know how to set them correctly.

DC injection as you originally proposed sheared the shaft off a 75HP hoist motor. I’ll leave it to your imagination the damage it caused when the skip ran away.