In this blog post, we will take a closer look at why uniformity is important in the powder mixing process and how it is measured and controlled.

What is “uniformity”?

To keep product quality consistent, it’s super important to mix raw materials evenly. This is especially true for complex chemical products made from a mix of different powders, where the ratio of each ingredient needs to stay the same across all products. The standard for evaluating this is called “uniformity.”
Uniformity is an indicator of how consistently the content ratio of ingredients is maintained between products when powders of different ingredients that do not react chemically with each other are mixed to make a single product. In particular, in mass production systems, it is common to mix large quantities of raw materials and then divide them into equal masses for packaging and shipment. At this point, uniformity becomes a key criterion for determining product quality consistency.

Uniformity management begins with the mixing process

Uniformity should not be evaluated simply at the end of the mixing process. It must be systematically managed throughout the entire raw material mixing process, as it is difficult to correct deviations from the standard value once they occur.
Therefore, the ratio of each ingredient must be accurately adjusted before the raw powder is added, and uniformity must be continuously checked while mixing is in progress inside the mixer. During this process, mixing is stopped at regular intervals to collect samples and analyze the ingredient content ratio.

Traditional uniformity inspection methods and their limitations

The traditional method of checking uniformity in the mixing process is the “sample analysis method.”
This method involves stopping the agitator at regular intervals, randomly collecting several samples of the same mass, and analyzing the content ratio of each component. Based on the data obtained in this way, the variance of each component can be calculated, and the uniformity of the mixture can be quantified. In general, the smaller the variance, the higher the uniformity.
When this process is repeated according to the stirring time, the variance values show a downward curve and gradually converge to a stable level. At this point, the mixing process is terminated when the preset standard value is reached. Stirring beyond the standard value is not only unnecessary but may even deteriorate the uniformity depending on the characteristics of the powder.
However, this conventional method has clear limitations.
The biggest problem is that it takes a long time. In order to analyze the collected samples, a pretreatment process is required to prepare them for chemical analysis, and this process itself takes time. In addition, chemical analysis methods using reagent reactions also take a long time, so restarting the mixer without the analysis results will not accurately reflect the mixing state. In other words, there is a dilemma between time delay and accuracy.

Physical properties that affect mixing uniformity

It is not only the mixing time and the performance of the mixer that affect uniformity. The physical properties of the powder itself also act as important variables.
Powders with similar physical properties in all aspects are relatively easy to mix, but when there are differences in physical properties such as particle size, density, three-dimensional shape, and surface adhesion, similar physical properties tend to gather together during the stirring process and form specific areas. This phenomenon is called “particle separation.” When this phenomenon occurs, no matter how long the stirring continues, the mixing uniformity may actually decrease.
In particular, while particle size and surface characteristics can be controlled to a certain extent in advance, density and three-dimensional shape are difficult to adjust in practice, so it is very important to evaluate the physical properties and develop response strategies before the mixing process.

Latest technology: Real-time uniformity analysis using a spectrometer

In order to overcome the limitations of traditional methods, real-time analysis techniques using spectrometers are gradually becoming mainstream. This method has the great advantage of allowing real-time monitoring of the mixing state even while the agitator is in operation. A
spectrometer is attached to a transparent window installed at the optimal position of the agitator, and when the powder passing through the agitator passes through this window, light is emitted and the reflected spectrum is analyzed.
Since the intensity of the reflected light varies depending on the content of the components, the content ratio of each component can be converted into the intensity of a specific color of light. The data obtained in this way is transmitted to a computer in real time, and the dispersion value is calculated at set time intervals or for each sample.
When the dispersion value reaches the set standard, an automatic stirring stop signal is sent, allowing the mixing process to be completed efficiently. This innovative method achieves two goals at once: time savings and accuracy.

Conditions for improving the accuracy of the mixing process

In order to accurately evaluate uniformity, it is also very important to have a sample collection strategy that reflects statistical standards.

• Number of samples: Too few samples can lead to underestimation or overestimation of the dispersion value, resulting in errors.
• Mass per sample: It is desirable to set an upper limit based on the standard mass of a single final product.
• Sample collection location: Samples must be collected randomly and evenly in both the horizontal and vertical directions to accurately reflect the overall mixing state inside the agitator.

Conclusion

Uniformity in the powder mixing process is not just a simple quality indicator. It is a key factor that determines product reliability, safety, and ultimately customer satisfaction. Traditional sample analysis methods boast high accuracy, but they have limitations in terms of time consumption and process efficiency. In contrast, real-time analysis technology using spectrometers overcomes these issues and is gaining attention as a future-oriented quality control method.
Ultimately, in order to successfully manage uniformity, all processes, from raw material selection to mixing equipment operation, physical property evaluation, and real-time monitoring, must be organically connected. A precise process system built in this way will be the shortest route to stable production of high-quality products.