Finding The Right Fit
Posted on 12/05/2018 | by The Orbitform Blog Team
You’ve decided on impact riveting as the best process for your application. With a fast cycle time and simple operation, you have the advantage over your competitors. Now you need to determine how to feed the rivets for installation. What are your options?
Standard Rotary Hopper
Most of Orbitform’s Impact Riveters come standard with a mechanically driven rotary hopper. The hopper barrel is spaced away from the hopper back with enough clearance for the rivet head to pass between the rim of the barrel and the hopper back. The barrel also has slots along the rim roughly equal in width to the rivet shank diameter. Each time the machine is cycled, the hopper rotates and the rivets tumble within the barrel. As they move around and bump into the rim and hopper wall, they will fall through the slots upon correct orientation. They will stack up between the barrel and a rivet guide, then fall into the feed track with each machine cycle.
Vibratory Hopper
An upgrade option for feeding is a vibratory hopper. A vibratory hopper uses a gentle vibration process to move parts around in the bowl. The bowl has internal tooling that guides the rivets up the bowl track towards the feed track transition point. Once they get to the top, a mechanism will knock off any rivets that are not in the correct orientation. Those that are in the correct orientation will continue through the feeding track to be presented to the tooling.
So, which is best?
For most applications, the standard rotary hopper will sufficiently feed the rivets into the equipment for installation. In some cases, however, a vibratory hopper is required:
- High capacity applications or automated processes may require a larger hopper. Depending on volume requirements, our standard hoppers may be too small in size capacity to meet specifications. Larger vibratory hoppers may be used to hold more rivets to meet the required volumes.
- Longer rivets may stack up on top of each other in our standard rotary hopper and restrict the movement of individual rivets, preventing any from falling through the slots in the rim of the barrel. With a vibratory hopper, the shaking motion separate the rivets as they move up the bowl.
- Lightweight rivets may have trouble falling out of the hopper barrel with the standard rotary hopper. Without enough weight to force them through the slots in the rim, they will just spin around inside the hopper. With a vibratory hopper, the gentle shaking motion of the bowl moves the rivets, and it is not dependent on gravity or weight.
- Rivets made of soft material may become chipped or scratched as they tumble inside the standard rotary hopper. With a vibratory hopper, the gentle shaking decreases the chances of bumping into each other and becoming damaged.
- Rivets that are nearly as long as the rivet head is wide may have difficulty feeding with our standard hopper. Ideally, the length of a rivet should be at least 1.5 times greater than the head diameter. The closer this ratio is to 1:1 (we refer to this as being “square”), the higher the risk of the rivet “tumbling” out of orientation. With the tooling design of the vibratory hopper, rivets that are not in the correct orientation will be knocked back into the bottom of the bowl.
- Rivets that are weighted towards the manufactured head may have trouble falling into the feeding track with a rotary hopper. Balanced rivets are ideal for rotary hoppers so that the shank sticks out of the bottom of the track and is in the proper position to be installed. Unbalanced rivets may tumble into the wrong position causing the track to jam or rivet to misfeed. A vibratory hopper will ensure the rivet is in the correct orientation, regardless of weight distribution.
- Shouldered rivets may also prove challenging to feed through a standard rotary hopper depending on the length of the rivet. The slots in the hopper need to fit the diameter of the shoulder. If this diameter is close to the length of the rivet, there may be a risk of the rivet "tumbling" out of orientation, much like with a "square" rivet as described above. With the tooling design of the vibratory hopper, rivets that are not in the correct orientation will be knocked back into the bottom of the bowl.
At Orbitform, we understand that each application, part, and rivet is unique, and work with you to find the best solution. Send us your part and rivet drawings, and we can help you determine what equipment and feeding method is fit for your application. Contact us today.