Reason and Solution for bottom-sticking pots during sample ball milling

When we do planetary ball milling in the laboratory, we will find that some samples, such as moist soil materials, asphalt ore, activated carbon, metal powder, certain chemicals and other viscous materials, will be deposited in the ball mill after grinding. There is also a lot of material stuck to the bottom, inner wall and lid of the ball mill tank, which is difficult to clean.

In addition, once the sample sinks to the bottom and sticks to the can, the grinding balls can only act on the surface of the material, making it impossible to grind the internal materials. The particle size distribution of the ground sample is uneven, which greatly reduces the sample grinding effect.

Next, Kingda Ceramic will take you to see the reasons and solutions for why laboratory sample planetary ball mills tend to sink to the bottom and stick to the cans.

Five reasons why ball milling samples tend to sink to the bottom and stick to the can.

1. The planetary ball mill used is a vertical planetary ball mill. The ball milling tank of the vertical planetary ball mill can only rotate in the horizontal direction. Affected by gravity, the sample is easy to accumulate at the bottom of the tank. The grinding balls in the ball milling tank make a spiral upward motion. After reaching the top of the tank, Drop it and pound the material firmly.

2. Samples are highly viscous. Some samples are highly viscous. Coupled with the extrusion of the grinding balls, they will easily stick to the inner wall of the ball mill tank. Or some types of samples may undergo cold welding or chemical reactions during the grinding process. Reactions and other conditions make the originally non-viscous raw materials turn into viscous materials. Materials with high viscosity will reduce the kinetic energy of the grinding ball and affect the grinding effect.

3. Samples become damp. In a humid environment, samples tend to absorb moisture in the air and become damp. This causes the materials that were originally easy to grind to clump together. Under the high-speed impact of the grinding balls, the materials begin to agglomerate and become difficult to grind.

4. The configuration of the ball mill tank and grinding balls is unscientific. A similar bottom sinking phenomenon will also occur when the material of the ball mill jar and the grinding ball easily reacts with the sample or one of the substances, is corroded by the sample, or forms an alloy layer on the wall of the ball mill jar. In addition, the density and hardness of the sample to be ground and the grinding ball must be different, so that there is a speed difference between the two when they rotate, and the grinding ball squeezes and rubs the material. Otherwise, the sample will gradually form agglomerates during the grinding process and sink to the bottom of the pot.

5. Research related to ultra-fine dry grinding shows that if the sample is dry-ground to 25 μm, the particle size will be difficult to reduce due to the influence of van der Waals forces and intermolecular forces. On the contrary, it is easy to agglomerate and accumulate, causing sinking and sticky pots.

Solution for bottom-sticking pots during sample ball milling:

With many years of industry experience, Kingda technical staff have summarized several solutions to the problems of sample sinking to the bottom and sticking to the can caused by the above factors.

1. Replace with an full directional planetary ball mill
The all-round planetary ball mill is an improved and upgraded version of the conventional planetary ball mill. While the sun disk (i.e. the main disk) performs planetary motion, it also performs a 360-degree all-round flip with the flipping assembly. This movement method makes the ball mill The samples in the tank can be turned over continuously to minimize sinking and sticking to the tank.

2. Increase sample dryness
For damp samples, we must try our best to dry them to remove the moisture inside, otherwise they will easily stick together and accelerate the sticking of the samples to the bottom.

3. Add grinding aids for wet grinding
After adding grinding aids to the ball mill tank, the sample particle size can often be ground to a smaller size. Common grinding aids include ultrapure water, anhydrous ethanol, n-hexane, etc. We can also select appropriate grinding aids based on the actual sample. Among them, absolute ethanol is used more often, and it is easy to dry after grinding.

4. Scientific and reasonable selection of ball mill jars and grinding balls
The ball mill jar and grinding balls are in direct contact with the sample and act directly on the sample, so many aspects such as material, density, and proportion must be considered.
In terms of materials, it is necessary to ensure that the sample will not react with the tank and ball under contact and high temperature environment, and will not cause contamination to the sample;
In terms of density, the density of the grinding ball needs to be greater than the sample powder. This can ensure that the powder is pressed into the grinding ball when it hits the bottom, and avoids the accumulation of samples. For example, high-alumina ceramic balls cannot be used for grinding alumina, the two have the same density, which will cause serious bottom sinking problem;
In terms of ball-to-material ratio, there is a big difference between metals and non-metals. The ratio of metal samples to grinding balls is 10:1 and above, while the ratio of non-metal samples to grinding balls is around 2:1.

5. Correctly choose grinding conditions
There are many types of laboratory samples, and the grinding conditions applicable to each sample are different. We need to explore in specific experiments, such as the length of grinding time, the speed of the ball mill, etc. Generally, for brittle samples, low speed often The material will not sink to the bottom, and for some samples, high speed will prevent the material from sinking to the bottom.

The reasons and solutions for laboratory samples that are prone to sinking and sticking to the pot in planetary ball mills are shared here. Before we use planetary ball mills to grind samples, we may wish to refer to the above methods to reduce such problems probability of occurrence.

For more information or any inquiry, you can contact our salesperson:
Shirley Liu (Mr.)

Email: Sales4@kingdacera.com
She will provide you with customized services.