750 komatsu

[maytag]

Some of you that follow the ifps board know I'm working some on converting two Komatsu 750s into railmount scrap handlers. The four that are now operating are being driven with two Sundstrand 250cc(Sauer-Danfoss)series 51 motors and run open loop. These railmounts, the two scrap cars, charge buckets when loaded all tally up to about 700,000lbs or so. They are not using a hydraulic brake of any kind only using a metal to metal brake the is common on railroad equipment(at least thats what I'm told). I'm thinking about a brake valve for both A and B with a check in parallel as this a bi-directional application. Max flow is about 100-120gpm to each motor as they are in parallel and max pressure approaches 4000-4500 psi. I know a dedicated pump/motor closed loop system would be better but that is having to reinvent the wheel. Maytag

 

[EdDanzer]

You should have a spring applied hydraulic relies brake under the Sundstrand piston motor. If you need more braking additional spring applied brakes should be added. Do not depend on the motor as a parking brake. All motors have some leakage and will coast if under heavy load.

 

[maytag]

Ed,
thanks for the reply-we have had bad experiences with the brake that you mention and are trying to steer away from that. Parking brake is no problem as I mentioned in the first post we have the metal to metal brake shoe that is hydraulic applied to the railcar wheeels. At this time this is the only brake in use and it is not maintenance free. I've used the brake valve for other applications but not any as large a load or as high pressure as this railmount equipment. Maytag

 

[EdDanzer]

The brake problem is an inertia problem, and that mean you need a larger, possibly cooled brake. Typically the brake under the motor should be used only for parking. My guess is the acceleration time is much longer than the deceleration time, which requires more energy to be absorbed over a shorter time.

 

[kcj]

Is your brake spring applied, hydraulc release, or directly hydraulic applied? Loss of hydr pressure would mean loss of braking with direct brakes.

I assume your trainline or mechanical hand brakes are used for parking. Does it have an independant air brake direct control for decel when moving the crane, or relying on the motor/drive braking only?

Typically, a motor mounted Ausco or similar brake works well if heat is sized correctly. They can cause a jerk as the system might have to build up some pressure to release the brake, then the reduced braking causes a jerk in acceleration. Maybe the Ausco site/rep can assist.

How about pilot operated braking valves in both lines? These are basically pilot operated counterbalances with check built in. Sun has I believe, and SunSource makes standard packages with Sterling cartridges.

kcj

 

[maytag]

Kevin,
The only brakes that are in use now are metal shoes that are hydraulically applied and spring release-there is a 10 gal. accumulator dedicated to the brake and decoupler circuits. I am reluctant to use any friction disc brake such as you mentioned-we have had several failures in other applications using this type. I'm leaning toward the brake valve(C-bal,check)but know I will be generating heat everytime the travel DCV is returned to center. Maytag

 

[EdDanzer]

Maytag,
It would be helpful if you provided more information about the speed and deceleration time and what type of failures you had with the friction disk brakes.
This information will help us understand your problem and provide other options.

 

[maytag]

Ed, max speed is in the 12-15mph range. Right now there is no hydraulic decel as this is run open loop thru a float center DCV so there is only an accel mode and then a coast mode. The metal to metal brakes are applied as the only means to decel quickly and stop.
We have had the friction brakes to fail to release and fail to set both. These were spring set and hydraulic release. I'm not wild about the contamination generated with this type setup. With business as good as it is service intervals for these railmounts are becoming longer. Maytag

 

[EdDanzer]

One option is to add a valve to divert the deceleration pressure to a group of accumulators then the stored energy could be used for other functions.
Other choices include going to a DCV with A&B ports blocked in the center position and port relief valves. This like counterbalance valves will probably require an additional oil cooler if you are moving much.