Re: Pulley Alignment Tolerance
NEVER, NEVER, NEVER use a pulley for tracking a belt. They need to be square and level to the frame to the tolerances as specified by CEMA. If the contractor is using a tape measure to achieve this you need a new contractor that understands conveyors.
There are many laser tools that can create very a accurate alignment. Place a spirit level across the frame side to side then place the spirit level across the pulley is a good check, they must be the same, shim only to achieve the same. Even a square placed on the mounting frame and across the face of the pulley is more accurate than using a tape measure. Once the proper alignment is achieved then you can adjust idlers by shimming or knocking to track the belt. Always think of "riding a bicycle" when knocking idlers. If you steer the bike one way that is the way it will go. So if you want to steer the belt away from the side you are on knock the idler on the side you are on in the direction of belt travel. The other way to bring the belt towards you.
Moving a pulley to align a belt is a very lazy mans way of troubleshooting tracking issues.
What you describe as the belt "going up to the bend" tells me you must have a vertical gravity take up. If your tracking changes through the take up then first thing to check is if the take up guides are vertical and level in both directions.
Another thing to check about tracking. If the mistracking is constant then it is a pulley alignment issues. If it mistracks for a while an then goes back to normal or flips side to side then it is a splicing issue that is out of square.
Build up of material on the pulley face and/or worn lagging can also cause tracking issues. Inspect for those issues.
Good luck. ■
Gary Blenkhorn
President - Bulk Handlng Technology Inc.
Email: garyblenkhorn@gmail.com
Linkedin Profile: http://www.linkedin.com/in/gary-blenkhorn-6286954b
Offering Conveyor Design Services, Conveyor Transfer Design Services and SolidWorks Design Services for equipment layouts.
Re: Pulley Alignment Tolerance
Gary,
Thank you very much for your advice.
A quick question on vertical take up guides - is it better to try and have the take up hang free (an air gap between the guides and take up assembly) or have guides rigidly hold the take up in place (take up assembly would have wheels that constantly contact guides)? I have only seen the later one time and was told that it was very difficult and constant problem to keep the guides true.
Finally, I tried clicking on your web site link but it appears to be broken. ■
Re: Pulley Alignment Tolerance
Personally I would not use wheels on a vertical take up as the wheels could freeze up (bearings failure, wheel wear, etc.) and cause misalignment as one side drags more than the other.
The way I design them is typically a vertical round HSS mounted on the floor (ground) and on the frame of the conveyor set completely plumb. The moving take up frame would have a slightly larger round HSS mounted on the moving frame. This acts as a mainly friction-less guide and will maintain good take up pulley alignment. Typically I use a 5"Øx1/2" wall for the guide and a 6"Øx3/8" wall on the take-up frame. This does a very good job of limiting the movement of the take up but gives it great freedom to travel.
Sorry about the link still in my sig. I will remove the link as I shut down my website a while back. I am somewhat retired now and only work from my home based office for conveyor design and consulting. You can look me up on LinkedIn at https://www.linkedin.com/in/gary-blenkhorn-6286954b/ if you wish. ■
Gary Blenkhorn
President - Bulk Handlng Technology Inc.
Email: garyblenkhorn@gmail.com
Linkedin Profile: http://www.linkedin.com/in/gary-blenkhorn-6286954b
Offering Conveyor Design Services, Conveyor Transfer Design Services and SolidWorks Design Services for equipment layouts.
Pulley Alignment Tolerance
I am hoping some experienced people here can give me some guidance regarding pulley installation tolerance. I am familiar with CEMA +/- 1/32" square and level to belt line. As a practical guideline how much error can there be before having issues such as belts running off pulley?
In my particular case I have a conveyor with good tracking on head and snub then starts to track off through the take up and even further as it goes up and over the last bend pulley. The tracking changes under load so clearly the structure is moving. My question is how much differential movement/error is tolerable? Is it only +/- 1/32" or as practical mater can it be more?
In this case the last bend pulley is very close to lateral bracing of the structure. Is it possible the head pulley is moving but still tracking well and the problem showing up at the last bend because it is not moving relative to the head?
For bend pulley tracking is there a way to tell the difference between tracking errors caused by out of level vs out of square by observing the belt?
A secondary question is how is it possible to achieve +/- 1/32" using only standard bubble levels and tape measures? In the US most tape measurers have 1/16" increments so you would have to be dead on to achieve total tolerance of 1/16". This particular conveyor has had several contractors work on it and all report making corrections but I can't understand how they can achieve +/- 1/32 with the tape measure methods they are using. Secondly I see them using shim plates at 1/4" thick increments - which also seems to me that they can't be within 1/16" total if they moved it in 1/4" increment, unless they got really lucky. ■