The weight of product going into a box is one of the most questioned values on a packing line: underfill brings complaints, overfill quietly gives product away. The semi-automatic box filling scale balances the two with a load cell based, two-stage fill. This article explains how the target weight tolerance forms on the machine and how to follow it through a shift.
01
How does weight tolerance form on the machine?
According to the catalogue record, the weighing system is load cell based and filling runs in two stages, coarse and fine. In the coarse stage product flows fast and most of the box is filled. In the fine stage the flow slows down and the target weight is approached under control. Tolerance comes from setting the two stages together: the earlier the coarse stage is released, the longer the fine stage works and the more comfortably the target is reached, but the time per box grows.
The target weight tolerance is set together during commissioning. So tolerance is not one magic number but a set of adjustments built around the product, the box and the target weight. Which values suit a given job depends on the project; exact values are fixed in the quotation.
02
What shifts the weight?
The same setting does not give the same result for every product. In dried fruit, piece size, moisture and surface stickiness directly affect flow. The main causes of drift are these:
- 01Product character: as pieces get larger or moisture rises, the last piece falling into the box becomes less predictable.
- 02Tare difference: if the empty box weight varies between batches, the weighing zero point shifts.
- 03Mechanical vibration: vibration from a nearby machine or the floor can leak into the load cell reading.
- 04Build-up: product residue collecting on the weighing surface and the arms adds to the weight.
- 05Feed pattern: if the supply from the hopper changes in continuity, the amount remaining after the coarse stage changes.
If a pre-station fills boxes by hand, the way product reaches the scale also matters. For that role the catalogue offers the manual box filling hopper, a companion machine in the same group.
03
How is tolerance followed during a shift?
A correctly commissioned machine does not hold tolerance by itself. Tracking needs a short, repeatable routine. In practice the following order works:
- 01Zero check at shift start: with an empty weighing surface, does the scale read zero?
- 02Reference weight check: place a known weight on the weighing system and compare the reading.
- 03Sampling: filled boxes are weighed at intervals on a separate check scale.
- 04Records: each sample is written down with the shift, product and target weight.
- 05Trend reading: look not at single deviations but at whether the records drift in one direction.
Sampling frequency and the acceptable deviation are set in the plant's own quality plan. That is why this article gives no figures: the product, the packaging and the customer specification decide them, not the machine catalogue.
04
In what order do you look when a deviation appears?
When records drift in one direction, changing the setting at once often makes things worse. Simple causes are ruled out first, then the fill setting is revisited.
| Symptom | Look first at | Next step |
|---|---|---|
| All boxes above target | Zero point and residue on the weighing surface | Reference weight check, then calibration |
| All boxes below target | Box tare difference, arm friction | Check the box batch, clean the arms |
| Scattered results | Feed continuity and vibration | Review the coarse to fine switch setting |
| Deviation only on a new product | Piece size and moisture | Set the target adjustment again together |
Calibration and fill parameter changes should be made by an authorised person and logged with the date. Otherwise nobody can tell, on the next shift, why the result is different.
05
How do cleaning and maintenance affect tolerance?
All product contact surfaces of the machine are AISI 304 stainless steel, and the structure is designed to be easily dismantled and hygienic. Refitting dismantled parts correctly after cleaning matters for weighing accuracy too. The drag arms move over the weighing system, so their position and any residue on them show up directly in the reading.
For that reason the same check is repeated after every cleaning: zero reading, reference weight and a few trial boxes. On a line that skips the post-cleaning check, a tolerance problem is usually noticed only on the next shift.
06
What kind of filling job suits this machine?
A semi-automatic scale is set up for box filling where weight must be held closely and the operator takes part in placing and checking boxes. The drag arms move boxes forward at even spacing and safely, which reduces manual handling. Motor, gearbox, bearings and electrical equipment are standard parts of their own class, and control is run from a specially programmed electronic panel.
The machine runs on a 380 V / 50 Hz supply. Capacity is adjustable depending on the product and target weight and is set per project.
07
Next step
If you send your product, box size and target weight, we can settle the tolerance tracking routine and the station list together. You can leave details through the quotation page or look at the machine's technical page.
