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REXSON GRAVIMETRIC DISPENSERS HAVE SEVERAL KEY ADVANTAGES OVER VOLUMETRIC DISPENSING SYSTEMS:
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 INSENSITIVITY TO MATERIAL PROPERTIES
As volumetric systems rely on the material occupying a volume, any gas, air pockets or material density variation will affect accuracy. Changes in viscosity due to variants such as temperature may affect filling properties and thus completeness of priming. This results in inherent inaccuracies and a need for regular, often daily, re-calibration procedures.
As gravimetric dispensers weigh the dose of individual components as they are dispensed, they are invulnerable to such changes.
GREATER ACCURACY
Rexson's modern weigh scales can resolve to 1 in 3,000,000 of their maximum load. This gives a precision order of magnitude greater than achieved by volumetric dispensing, which is often around 1% of the amount dosed.
For example: Rexson typically provide units to dispense 5gallon batches to a repeatability of 0.1gram or even 0.02gram and 55gallon batches to 1gram.
SELF AUDITING PROCESS
The Gravimetric process records the actual amount dispensed, which will be within a tolerance band defined by the user (i.e. 0.1gram or 0.1%). This gives data for use in future quality audit processes (an ISO audit trail or batch tracking) and gives self-checking to indicate correct performance. Typically our customers will dispense a batch, put on the lid and send it out - with no QC checking!
With volumetric systems, only the target dose can be recorded – there is no feedback loop. No record of actual doses into a batch can be created or made available. This leads to a higher level of QC checking to confirm that the dispense is acceptable.
REDUCED NEED FOR CALIBRATION
For Gravimetric dispensers, a yearly calibration of the weigh scale is all that is needed to guarantee the continued accuracy of the system.
Volumetric systems need to account for material properties and performance settings, and need to be calibrated regularly (often daily) to maintain their precision – without regular calibration, inaccuracy can drift to several percent of amount dosed. If the formula colour is quality checked and is found to be outside of tolerance, which ingredient was dosed incorrectly? Was it just one ingredient or did they all dispense incorrectly? What do I add to correct it back to the right shade? This all consumes time of skilled colour matchers and QC personnel - creating a production bottleneck and all adding to the turnaround time of an order!
GREATER RANGE OF DOSE AMOUNTS
By using 1, 2 or more scales, Gravimetric systems can dose to a given accuracy – 0.1% of amount dosed, for example – over a huge range of dose volumes (from 1/2 litre to over 2,000 litres). This provides maximum flexibility for production. For example, one Rexson dispenser could produce lab samples in quart cans as well as 1gallon buckets, 55 gallon drums and bulk Tote IBC batches!
By design, volumetric systems tend to have a much narrower range of volumes dosed to the stated performance.
PRODUCTION SPEED
Although a volumetric dispenser can sometimes dose products quicker or dose more than one component at a time, due to the level of inaccuracy most batches will require a QC check. This may highlight shade errors which will need investigating and resolving. This time spent checking and correcting batches often means that the time taken to produce a batch volumetrically is longer than producing it gravimetrically.
A Rexson gravimetric dispenser can dose a batch in as little as 2 minutes - with no need for any QC checks!
PRODUCT RATIONALISATION
Volumetric solutions often require multiples of the same product to cope with varying dispense volumes or high accuracy tints. For example, systems may have to run two black pigments - one high strength, one low strength. Gravimetric accuracy means only one of every required base pigment or colorant is required - simplifying the process and minimising errors.
PRODUCT RECIRCULATION
Rexson gravimetric dispensers can automatically pump products around the fluid pipework and through the dispense valves to maintain a materials consistency and prevent settling out of any pigments or additives - meaning no 'stale' material or 'dead spots'. This results in consistent quality of the products being dispensed.
By design, volumetric systems cannot recirculate through the valve chamber as this is used to meter material doses - and as such the material must be static.
FREEDOM TO CHOOSE
Rexson gravimetric dispensers can dispense any colorant paste or dispersions so do not require 'approved' or 'tested' colourants. Therefore, our customers are free to choose whose products they run on the machine and can change suppliers in future, if required. |
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Computerised, gravimetric dispensing systems are essential
to produce consistent and accurate formulations with
guaranteed repeatability and a full audit trail for quality control.
Automatic dispensing leads to savings through maximum cost
and time efficiency in the management of raw materials and
reduced wastage.
Find out more advantages of Rexson gravimetric dispensing.
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Q10580
BS EN ISO 9001:2000
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