Maximum bulk bagging rates are achieved when using a pre-weigh system.
Pre-weighing refers to weighing the payload of product to be placed in a bulk bag in a separate bin or hopper above the bulk bag filling machine.
Doing so eliminates the time required to precisely weigh the product as it flows into the bulk bag on the filling machine. Rather, the pre-weighed 'shot' can be dropped into the bulk bag as quickly as it can be made to flow through the pre-weigh hopper outlet.
So, instead of a fast feed and dribble feed cycle with weighing conducted on the filler that, at its fastest consumes 50-55 seconds, a pre-weigh system can fill a bulk bag in approximately 15 seconds.
Removing 40 seconds from the bulk bag filling cycle time dramatically increases the bulk bagging rate.
Bulk Bag Filler vs. Pre-weighing
Let's examine the numbers in more detail:
| Task | Filler Weighing
(seconds) |
Pre-Weigh (seconds) |
| Rig bulk bag | 30 | 30 |
| Tare | 5 | 5 |
| Fast Fill | 40 | 15 |
| Dribble Fill | 15 | NA |
| Final densification | 15 | 25 |
| Remove filled bag | 15 | 15 |
| 120 seconds | 90 seconds |
Note that the Filler Weighing cycle time is only 120 seconds - that equates to 30 bags per hour.
That is a very high rate and is possible with many products using high speed bulk bag filling equipment. However, as can be seen, adding a pre-weigh system to this type of bulk bag filler increases the bagging rate considerably.
A 90 second cycle time means that a properly designed pre-weigh system is capable of filling 40 bulk bags per hour!
Also note that the final densification time has been increased. This compensates somewhat for the reduced amount of total densification time compared to the Filler Weighing cycle where the bag would be densified for most of the Fast Fill task.
In our next article we will dive into the design issues that must be considered to properly implement a bulk bag pre-weigh system.
