“To drive or not to drive, that is the question.” This question can only be answered if you understand how the bowed roller works as we described in great detail in our Web101 class. Also, this question can only be answered by knowing how the bowed roller does NOT work as was described in our class and outlined in the last clip. However, just because you have a motor does not mean that the spreader will operate better. In fact, a poor drive may well be worse than no drive at all. Few people know whether a drive is helpful and how the motor must be programmed. Here we will give you the clear answer.
***201.44c – Bowed Roller Failure Modes – Poor Drive Strategies
04 Slides Duration 04.19 v 15.08.26
201.44c.01 – Title Slide
Welcome to web handling. My name is Dave Roisum. In this clip we continue our series on bowed roller failure modes by looking at when and why and how a drive might be helpful as well as why a poorly tuned drive could make things worse.
201.44c.02 – Traction Circle
Last year I gave a half hour paper on traction as it affects the many spreader types and even more spreader modes. The basic idea comes from a life-saving practice that all race car drivers and motor cycle riders and in fact every driver should know and practice to the point of becoming subconscious. That is, you brake before entering a corner and when in the corner your hand or foot is on the gas just enough to counter drag and thus maintain speed. More gas or more brake from this one special setting robs from total available traction and leaves that much less for the number one task of cornering, that is cornering.
201.44c.03– Available Traction
Perhaps the most important as well as least understood by the general practitioner is whether to drive a bowed roller and how to manage the drive setting if you do drive it. Here I will give an abbreviated discussion of the why of drives. The details of the how were given in our Web101 class.
The first case is when a combination of light webs and light wrap angles are coupled with a high bowed roller drag coming from the sum of bearing drag and cover hysteresis. Here, the bowed roller will break loose everywhere across its width and the roller will either come to a stop or perhaps turn slower than web speed. Here, bowed roller mode spreading is not possible. Only bent pipe spreading is and that is an entirely different discussion. Here we will just observe that it is a pretty expensive way to get bent pipe spreading and that you will quickly ruin the cover due to wear.
The second case is less severe, but a similar combination of light webs and wrap angle coupled with a high bowed roller drag, but not enough to break it loose entirely. Here, the amount of available sideways spreading force is reduced.
The third case is optimum. Here, a drive motor is provided and properly tuned such that drive torque precisely matches drag + inertia as we covered in Web101. Here, all of the traction is available to do spreading work.
Finally, the fourth case is an improperly tuned drive that is common enough because most drive people don’t have web handling training. Here, the motor overdrives and pulls on the web and causes a loss of spreading work because some traction is used up just tugging on the web. In all cases of a mechanical belt drive slaved to some other roller, the drive will be less than optimum and quite probably worse than no drive at all except in extreme application cases such as tissue that must run in the bent pipe mode to due exceeding light tensions and tractions.
201.44c.04– Thank You
Thank you so very much for watching this module in my plant practical video clips. Stay tuned in the next clip where we will show trying to jam a bowed roller into a cramped space can make things worse than no spreader at all.