Paddles make sense, right? What do you do when ingredient won’t come out of a bag or a bin? You hit it. That’s what paddles do to bulk bags: they manually manipulate the bag to induce ingredient flow.
Intuitively, that makes sense. However, as you will see, when we peer beneath the concept there are a number of problems with paddle style bulk bag unloaders that render their use much less than effective.
How A Paddle Style Bulk Bag Discharger Works
- The bulk bag rests on a flat surface comprised of a plate, bars or the paddles.
- The operator reaches up through an access box and an iris valve to reach the bottom of the bag.
- The outer flap is untied and the outlet spout (tied with its own tie) is pulled through the iris valve into the access box.
- The iris valve is closed.
- The outlet spout is untied (the closed iris valve prevents ingredient flow).
- The access box door is closed.
- The iris valve is opened thereby allowing flow.
- The paddles are actuated to induce flow.
Now lets investigate the details of how a paddle style bulk bag unloader functions and the problems inherent in its design.
Paddle Style Bulk Bag Unloader Ergonomics and Safety
As noted above, the operator must reach up through both the access box AND the iris valve to get to the bottom of the bulk bag.
No matter how you approach this task it is a long and awkward, blind reach requiring the operator to bend and stoop and manipulate the outer spout tie with both hands without the benefit if being able to see what she/he is doing.
So, what happens? Well before the end of their first shift, operators learn to untie the outer flap and pull down the outlet spout ‘goose neck’ before the bag has come to rest on the paddle style discharger.
That means they have their arms between a suspended load and a steel frame. This is unsafe and would cause a safety inspector to, at best, demand that the procedure be changed or, worst case, immediately shut down the process.
Even if operators use the paddle style discharger as intended the awkward reach is a recipe for back and/or shoulder repetitive motion injuries.
The reality is that many companies turn a blind eye to this serious safety hazard and operators are endangered every day. Significant liability is the result along with the likelihood of serious injury.
Another factor to consider is that the paddle mechanism is a potential safety hazard relative to pinch points. Some paddle style dischargers feature elaborate guards to prevent this - others do nothing to prevent operators from inadvertently getting fingers, hands or loose clothing caught in the mechanisms.
Paddle Style Big Bag Discharger Dusting
The access box either has a dust vent to be connected to a dust collection system or it has an integral dust collector.
Either way the paddle style bulk bag discharger’s access box can be maintained under negative pressure.
Again, conceptually, that is a good thing. However there is a serious problem with this design:
Because the outlet spout of the bulk bag typically ends somewhere in the access box, as can be
seen in the accompanying photo, the box’s interior is covered in ingredient or could even be partially filled with product. When the bag is changed and the door is opened the negative pressure collapses and ingredient will fall off the door or even spill out of the access box.
This is a recognized problem with paddle style unloaders. Regardless of how good the dust extraction system is, the area around the discharger will be contaminated with product.
Paddle Style Bulk Bag Unloader Flow Inducement
As mentioned at the beginning of this article, this style of discharger is characterized by its method of inducing flow: manual manipulation of the bag using paddles.
However, depending on your ingredient problems may arise because the bag essentially sits on a flat surface and the paddles contact a relatively limited portion of the bag.
Often, product hangs up in the corners and yield drops - not all of the ingredient in the bag is discharged or operator intervention is required to obtain 100% yield.
Some paddle style dischargers feature spring loaded top frames that lift the bulk bag as it empties to try and promote better flow and complete emptying. Unfortunately, as the bag is lifted the partially or completely looses contact with the paddles. This can impair flow and yield instead of increasing them.
In general, paddles can be effective at inducing flow with some ingredients. However, the relatively small paddle contact area and the bag resting on a flat surface are inherent limiations.
Paddle Style Bulk Bag Discharger Outlet Spout Clamps
A relatively recent ‘innovation’ added to paddle style big bag unloaders is the outlet spout clamp.
Simple in operation, (the outlet spout is clamped to a downtube as shown in the accompanying photo) outlet spout clamps have become popular in an effort to solve a number of the above mentioned problems:
- Outlet spout clamping eliminates dusting at the onset of product flow and throughout the duration of the discharge cycle.
- The addition of a clamp eliminates the need for an iris valve and access box thereby solving the dusting and ergonomic problems noted above.
Interestingly, the first version of the outlet spout clamp was patented by Control and Metering in the early 1990s. Today it forms an integral part of our Iso Flo bulk bag discharger used by many companies in the food, pharmaceutical, chemical and other industries.
While the clamp is an improvement to be sure, it does nothing to solve the flow inducement problems inherent with paddle style dischargers and it suffers from a simple issue regarding dusting: at the end of the discharge cycle the clamp is raised and ingredient coating the inside of the outlet spout will fall onto the area below.
The photo shows a typical paddle style discharger with outlet spout clamp and the ingredient that
has accumulated below the spout. Note that we are in the process of retrofitting this unit by replacing everything but the frame.
Outlet spout clamps have their place, but they must be enclosed in a negatively pressurized chamber to be truly dust free.
Effective Alternative To Paddle Style Bulk Bag Dischargers
There is an alternative to using paddle style dischargers that provides:
- Excellent dust containment without having to resort to outlet spout clamps and isolation chambers.
- Superior flow inducement with any indgredient.
- Safe and easy to use ergonomics.