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Volumetric & Gravimetric Feeders: What are the Differences

2019-10-29

So you want to buy blenders/feeders for your molding machines! Maybe, you’re just getting started in the field. Perhaps, you wish to enhance the quality of output while reducing the material cost. No matter the reason, getting familiar with the various types of blenders is advisable to make an optimal choice. Typically, you’ll find volumetric blender/feeder and gravimetric blender systems. Both the feeders deliver results. However, some molding businesses favor a volumetric feeder, whereas others endorse a gravimetric feeder. Let’s get familiar with both types of feeders and find out what suits you the best.

Volumetric feeder systems

The concept of feeding or blending volumetrically starts by filling the auger completely. The volume displaced by the auger, the rotational speed, and the auger’s pitch is known beforehand. So, an auger with a 1-inch pitch rotating at 100 revolutions per minute (RPM) will move the material (in volume) forward 100 inches in one minute.

As far as everything is okay and constant, the volume of the material dosed will remain the same throughout the operation provided the auger is full all the time. Keeping the auger’s pitch constant, you can change the volume of the material dosed in the machine by altering the rotational speed. Varying the speed offers linear control over the material (in volume) being dosed.


This method of feeding presents consistent, repeat metering with better linear control for materials that are termed as good powders. Good powders have consistency in bulk density with manageable characteristics. The problem in this method of feeding arises when the powder lacks consistency in bulk density.

Volumetric feeding/blending lags in capacity requirements if the bulk density of the material varies. Such materials will struggle to meet the feeding requirements. Consequently, the quality of the output will be affected. However, volumetric systems make a great fit for small scale industries where accuracy isn’t a matter of preference. Also, they’re far more affordable systems.

Gravimetric feeder systems

Gravimetric feeding (gain in weight or loss in weight) presents a way to dose by metering or weight continuously. It provides methods for tracking and recording materials used. Additionally, it could offer the means for running recipes for feeding/dosing systems. Since the system is mostly automatic and features a control mechanism, there are hardly any chances of errors.

A gravimetric blending/feeding system costs almost double the price of the volumetric blending system because it includes a control module, scale, and an HMI (microprocessor-based). Despite the high cost, a gravimetric model is essential for certain applications for accuracy, record keeping, and overall control.

In gravimetric feeding, each cycle of material dispensing is verified by weighing the material dose. The control system is meant to self-correct any mistake in dispensing on subsequent doses, on the basis of weighted results. The self-correcting operation measures the results of metering and adjusts itself for very high accuracy. Consequently, the quality of the output is greatly enhanced.

Although volumetric feeding is also a good way to dose materials, gravimetric feeding is an improved version over volumetric dispensing. Accuracy and self-adjustment of weighted doses are the highlights of gravimetric systems which make them hugely popular in fields where a higher degree of accuracy is desired.

Hengju-Volumetric Gravimetric Feeders: What Are The Differences

While both volumetric and gravimetric dispensing systems are meant for dosing materials into the machines, they differ in many respects. In volumetric systems, the user has to know the rate of dispensing of materials into the system. In the case of gravimetric feeding, the user doesn’t need to know this thing.

Volumetric blenders offer a good accuracy when the material in question has a consistent bulk density. Gravimetric blenders, on the other hand, render a very high accuracy even if the bulk density of the material varies.

In volumetric blending, the user needs to adjust the weight of the material. In gravimetric blending, the system automatically adjusts the weight. Volumetric blenders come at a lower price compared to gravimetric systems. Gravimetric blending delivers a high quality of output compared to volumetric systems.

Bottom line

Choosing the right kind of blender or feeder is imperative for any molding business. Although you can use a gravimetric feeder or volumetric feeder in most cases, each of the two feeders is unique in some respects. So, check out the working and benefits of these feeders in view of your particular situation. With handy information by your side, choosing an ideal feeder becomes a lot easier without doing much legwork.


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