Groove measurmentgreenspun.com : LUSENET : Elevator Problem Discussion : One Thread
Diameter of sheave groove.
To check a sheave groove diameter one usually lays a straight edge along the top of the ropes and sheave and looks for excessive difference. However, on the better installations the maximum groove discrepancy is .004 inch (at one time factory made brake drums using drop-hold brakes were cut to that tolerance). Method to determine the amount of material to be machined or cut from the groove to make every groove the same diameter is, in the mining, trade, called a collar to collar test. Few elevator companies will utilize this method because duration of a service contract precludes cutting grooves to such accuracy. Most companies cut so that all grooves appear eaqual and thats good enough. In any case here is the method of making the proper determination.
1.Have the car make one full trip from the lowest to the highest level of travel.
2. Lower the car to the mid-point of the shaft and stop.
3 Install a staging at the top of the shaft. Clean a short part of the hoist ropes on the car side and spray paint the ropes at the cleaned length.
4. Using a bubble level, draw a line across the ropes at the same level in the mid point of where the spray paint was added.
5. Raise the car slowly so the marks will go around the drive motor and down towards the counterweight.
6. Stop the car when the marks are easy to get at from the staging previously installed.
7 Place the bubble level at the highest mark (the mark closest to the hoist motor). That rope has the groove with the smallest groove diameter.
8. Measure and record in inches the difference between the level and each of the marks on the ropes.
9. Calculate a constant for the job------
C = 2 X distance of marks traveled (in feet) divided by the motor sheave diameter (in feet). 10. Divide each of the discrepancies in #8 above by the constant C
Here is an example: Assume the sheave diameter is five feet. Distance marks traveled was 30 feet.
Discrepancies obtained in step in #8 above --- rope #1 = 1 rope #2 = 0.5 rope #3 = 0.0 rope #4 = 3.0
Constant C = 2 X 30 = 60 and that divided by 5 which equals 12
Then from groove number 1 remove, 1 divided by 12 which equals a little over 83 thousands of an inch (0.083in) .
From groove #2 we divide ).5 by 12 which gives 0.041 inches to be removed From groove # 3 we remove nothing and,
From groove #4 we divide 3 by 12 and get 0.25 thousandth. Different?
Do you know that in the installation of deep mine elevs that the direction of the earths rotation must be taken into account to reduce comp rope sway?
-- Tom Grosch (firstname.lastname@example.org), March 30, 1997
Have not had much experienc deteriming the size of a sheave groove, but have had considerable experience making sure sheaves are true. It seems that in the early 70's late 80's the metal being used for drivers by some manufacturers was extrmely soft. Just by the cable slipping traction on an emergency stop could place the driver out of round. How much have I found these drivers out of round.As much as 80 thousandths. Even as little as 10 thousanths on a 1200 fpm car is noticable especially with a comp sheave with mono mass. What happens is the car will start to bounce which causes the comp to bounce and this whole scenario gets amplified, the longer the run. How we would rectify this was to take a dial indicator measurement of each groove to check for trueness. Then use a specially made cutting tool to fit on the bed plate to cut the grooves true while the car ran high speed.
-- Rolland Harrison (email@example.com), March 31, 1997.
I take care of a new 6 rope basement machine with an undercut driver.The Titan machine is just over a year old. We got a call that the car was above the floor at the top floor landing just far enough to hit the top O.T. limit. This happened again the next month and then 3 weeks after that. We looked at rope tension with the standard torsion type device and found some ropes unequal. After equalizing the ropes, the call-back resurfaced 2 weeks later. Again the ropes were re-tensioned. 3 weeks later, you guessed it. We applied a rope traction lube after checking the grooves and it's been over 2 months with no slip. The boss was a little leary of adding lube to slipping ropes, but now he's a believer. I can't help but wonder what the real problem is though. There is a second new machine in this building just like this one with one exception. It has 5 ropes. So far no slip on this guy. Can you have too many ropes? Could removing one of the 6 give greater traction? Do I think about my job when I'm off the clock? What do you guys think?
-- Timothy J. Wahl (firstname.lastname@example.org), April 02, 1997.
The thing that first pops into my mind , Tim is counter-balancing. I don't think you can have too many ropes as far as traction is concerned. Especially with a new job and all the drivers appear to be identical. Once knew of a job that had similar problems for years. The mechanics solution was to keep applying Comet to the ropes. It was finnally determined that counterbalancing was the real culprit.
-- Rolland Harrison (email@example.com), April 03, 1997.
Tim, I don't believe there can be too many ropes as long as you have the right amount of compensation. I used to maintain a job that was underslung basement traction and we had a slipping problem and still do! The rope lead off of the machine sheave did not allow enough wrap around the sheave for traction. The trick was to make shure the cables were clean and lube. We never had the problem with a load. P.S. I remember meeting your dad. He helped me set up a Haughton brake for the first time.
-- B.T.(Tommy) Herrity Jr. (Elevatorman@compuserve.com), April 22, 1997.
Dear Tom, Its so good to know your still out there with those brain busters..
I often see Anna and ask her how are you doing.I have coffe with Alex Parshooto and often hear great stories on your training methods...thanks again for all you do,,,god bless ...Dan Wiegand
-- DAN WIEGAND (DANOTIS@AOL.COM), March 09, 2003.
Hi Guys, Firstly traction is number of ropes independent with the exception of out of the maximum out of ballance being increased with more ropes. (If no compensation is used). The formula is T1/T2.T1 being the heaviest weight. The allowable ratio is speed dependant. Some of the major elevator manufacturers forget to account for out of ballance rope weight when calculating for basement machines roped 2:1. This very often results in a sheave with an undersized undercut in the grooves hence rope slippage. The 'permanent' cure is to widen the undercut by remachining.
-- Helmut Meuris (firstname.lastname@example.org), October 11, 2003.