Application of the Month
Production Flexibility in Machinery Design
April, 2009 - View all Application Examples
Providing production flexibility in machinery design, to manufacture or process different product sizes for example, is becoming more of a necessity with today’s desire for shorter runs and quicker deliveries. With our consultative approach and some unique capabilities, we were able to help a recent customer achieve the flexibility he needed.
A prospect recently contacted us with interest in our spiral bevel gearboxes with hollow output shaft. His task was to feed material through two counter rotating drums or rollers. The kicker was that different material sizes where required, meaning the center distance between the rollers had to change by several inches, sometimes a couple of times a day. His idea was to insert a connecting shaft with key inside the hollow bore of two boxes. Then when the center distances had to change he would slide one the boxes along the shaft and tighten it back down.
To drive the rollers at the necessary 100-200 RPM he planned on driving in on the through shafts of the 1:1 bevel boxes with a speed reducer in 8:1 or 9: ratio. He’d then inverter control the speed within the needed range. This gearbox would be independently mounted and connected to the bevel boxes in a manner that was yet to be determined at the time of the initial discussion.
Our first comment to the customer was that we didn’t believe using an insert shaft with key was the best option for what he wanted to do. Because adjustments had to be made fairly often we were concerned the key would begin to show wear from the sliding action.
Our suggestion was to use a square sided spline shaft, which effectively has six or more “keys”. This shaft design is more commonly used for adjustments of distance and where key load sharing is desired. Expanding universal joint line shafts come to mind as an example where this concept is used. The spline shaft shares the load better than a single keyed shaft, depending on tolerance accuracy. We have several profiles and tolerances available to choose from.
To use the spline shaft we recommended our HWK model of hollow shaft gearbox. This is one of four versions in the Tandler hollow output shaft series. This design, along with hollow bore with keyway, hollow bore with involute spline, and hollow bore with shrink disc, provides more shaft insertion design flexibility than is available from any other bevel box manufacturer. Each version has it’s advantages.
With only one of the bevel boxes needing to be moved to achieve the desired center distance adjustment, and that being the second box in line, the standard hollow bore with keyway, series HW, was actually the best choice for the first box in the line of two. This was primarily because we had another necessity, that being to capture the spline insert shaft so it wouldn’t move axially as we slid the second HWK bevel box along it’s length when adjusting the gap.
As part of our capabilities we were able to design and fabricate the customized spline shaft. On one side it featured a turned down end with key and shoulder to insert into the first gearbox. The key provided the torque transfer and the shoulder assured no axial movement in the direction of this gearbox.
The other side featured a turned down end to accommodate an independent thrust bearing to limit any axial movement in the opposite direction. The length of the fabricated shaft was configured to make mounting the thrust bearing an easy task while allowing plenty of leeway for sliding the adjustment gearbox back and forth.
Using a standard hollow shaft box in the first position created both a challenge and an opportunity. The dilemma was that with no shaft extension there was nothing to connect to the output shaft of the main drive speed reducer that was originally considered by the customer. The opportunity was that this allowed us to offer a complete solution as an entire assembly.
Our recommendation was to use our Watt Drive helical bevel right angle gearbox, also with a hollow output shaft, as the main drive reducer. The offer was to fabricate a custom input flange that would be piloted and bolted to the input of the bevel box and then mated to the optional bolt-on output flange available with the helical bevel reducer. This would allow the alignment necessary to incorporate a fabricated shaft that could be inserted into the two hollow bores, connecting the boxes without the need for a shaft coupling.
This concept of a two-gearbox “assembly” had another advantage. Instead of requiring structure to mount both the main drive reducer and the first bevel box only one mounting surface was necessary. This saved the customer the extra cost of both additional framing and component assembly.
The result of consulting with the customer in the beginning of the design process, and determining his needs for the entire drive design instead of just the components he expressed interest in, generated several benefits for the customer.
Instead of them going with an initial design idea that could have led to wear issues down the road, we were able to suggest a more reliable design idea. Instead of considering five components from as many as four different suppliers, they now had to mount only three major components, all from a single source. And instead of expending design and drawing creation time we were able to provide a complete assembly drawing, supported by individual standard and custom component drawings. In the end the customer purchased the system and had a better machine design because of it.
DieQua works with most of its customers in this manner. It’s through our consultative approach that we can be most helpful. While the products we offer are of outstanding quality, it’s the assistance we provide to best utilize them that our customers realize the superior value that is The DieQua Advantage.
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