Replaced Liner Just Isn't The Same As The Old

Q. We have an Osrotron 10-cu-ft bowl. Our operators like the low rim height and ease of loading and unloading by hand. The liner wore out—after about 20 years—and we decided to reline rather than purchase a new machine. When we got the bowl back with the new liner, we could not adjust the machine to the same good action we had before. The parts don’t travel around the machine and some parts turn to the outside of the bowl, while others bang against the center post and don’t submerge unless we push them down. Our supply vendor is a general supply house and is not qualified to help with this. We don’t know where to turn for assistance since Osro is out of business. S.W.

A. You bring up a sore point shared by many operating people in manufacturing: The unfortunate trend by large companies to price buy. Qualified vendors who offer technical support are being turned away. The short term winners are jack-of-all trade suppliers, and managers compensated by commodity type purchasing. The long term losers are the companies. A recent survey of suppliers to the automotive industry made it clear that vendor relations are inversely proportional to corporate success. The slow and painful demise of the largest American corporations is a high price to pay for cheaper goods.

Your Osro Osrotron SB-10 is a fine, operator friendly, flat bottom bowl. The down side is that it is very difficult to adjust. I’ll walk you through the procedure for setting the weights and the lead angle. You will see that it is a quirky design with appeal, perhaps, to a mechanical tinkerer with lots of time on his hands.

First, let’s get the motor rotating in the right direction. Most flat bottom machines rotate the parts clockwise around the center post. Some, like the Osrotron, can be set to go in either direction. Whichever way you want the mass to travel, the motor should run the other way. I suggest setting it for clockwise parts rotation, so wire the motor for counter-clockwise as viewed from the top.

The weights are lobe shaped, somewhat like a single leaf of a clover. These are mounted on the motor shaft, two for the top and two for the bottom. Each can be rotated on the motor shaft and then locked into place. You can lock the relationship of the pairs of weights to one another. If you place the pair so that the weights are exactly 180? apart, they will balance each other and there will be no eccentric force when they rotate. If you place them exactly one over the other, the eccentric force potential will be at its maximum. In this case, the force vector will be concurrent with the centerline of the two weights. Easy so far. Now, suppose you don’t want 100% of the available eccentric weight. Let’s say you only want half of that. You would then set the weights so that the centerlines of the lobes strike a 90? angle to each other. The resultant vector of the force equally divides the center line projections of each segment. You can see that by opening and closing the angle between the two segments you can have any eccentric potential from zero to the total of the two weights. And, the vector force of this resulting weight will create equal angles with the centerlines of each weight.

Using this technique, you can adjust for a different eccentric force potential on each end of the motor. Start with about 1/3 as much eccentric force on the top as on the bottom. Later, you can fine tune these settings for the desired action in the bowl.
Next comes the lead angle setting, which is the angle by which the bottom weights lead the top weights as the motor rotates. This is easiest done by aligning the vector of the bottom weights to point at some fixed spot on the machine. Then, when adjusting the top weights, be sure the motor does not rotate. Move both top weights in unison until their force vector trails that of the bottom weights while rotating counterclockwise. The trailing angle is the lead angle. A good starting point in your operation will be a 60º lead angle.

The topic of top to bottom weight ratios and lead angles is rather lengthy and was discussed in this column in October 1994. Let me know if you want a copy.