With the continuous enrichment of the variety of solid preparation powder products, the types of mixers, as one of its main production equipment, have also become varied.

1. Mechanism of powder mixing

Powder mixing is a process to reduce component heterogeneity. Mixing has many forms of movement. Convective mixing is the main method in solid preparations. Its particles move from one spatial position to another, or more than two components move in the space occupied by each other, in order to achieve uniform distribution of each component.

2. Classification of mixing equipment

Mixing equipment uses different fabrication of various mixing devices to make relative movement between powder materials, continuously change their relative positions, and continuously overcome the trend of material stratification caused by object differences.

According to the acting force on the powder, there are mainly three types: container return transformation, container fixed type and composite type. Due to different operation modes, there are two types: gap type and continuous type. However, in the powder and particle of solid preparations, the most widely used is container transformation, mainly including mixers such as double cone, V-shaped, three-dimensional motion, two-dimensional motion and square cone hopper.

3. Characteristics of each mixing device

In the past, there were many double cone mixers (Fig. 1) and V-type mixers (Fig. 2) in solid preparation mixing equipment. The double cone type only moved in one direction, with poor material fluidity, incomplete mixing and poor mixing effect, which has tended to be eliminated. There are two kinds of V-type mixing, one is symmetrical V-type mixing. Its disadvantages are high rotation height, easy dead corners on the tailor-welded lines of the two barrel bodies, easy cross-contamination, inability to clean thoroughly, and long mixing time caused by only transverse and longitudinal flow in movement. Another kind of asymmetric V-shaped mixing, the two sides of the V-shaped container are highly asymmetric, its advantages are that the repeated doping of the container materials on both sides achieves good mixing effect during movement, and its disadvantages are large volume, large rotating space, difficult full polishing inside to form dead corners, and easy cross contamination.

Fig. 1: Double cone mixer                               Fig. 2: V-type mixer                                              Fig. 3: Two-dimensional motion mixer               Figure 4: 3D Motion

In addition, although the barrel mixer has the characteristics of compact structure and small occupied area, the charging coefficient is only about 50%, the mixing effect is worse than other forms of mixing, and the mixing barrel is inconvenient to load and unload, the mixing barrel is not easy to clean and the machine transmission is exposed, so it is generally not suitable for the use of clean factory buildings.

In view of the above disadvantages, two-dimensional and three-dimensional motion mixing equipment appeared later. The two-dimensional motion mixer (Fig. 3) is also called a rock mixer. On the one hand, the mixing barrel spins around its axis of symmetry, and on the other hand, it swings around a horizontal axis orthogonal to its axis of symmetry. In addition, the inner wall of the barrel is welded with a copy plate, which can make the materials copy to the space, thus making the materials mix more fully. Two-dimensional motion mixing is characterized by large mixing amount, convenient discharging, stable and reliable operation and small occupied space, which is suitable for large quantities and long-term varieties. Three-dimensional motion mixer (Fig. 4), some people call it a multi-directional motion mixer. The materials make three-phase compound movement in the mixing barrel in the circumferential, radial and axial directions, and the materials flow, diffuse and mix with each other through complex movements such as rotary flow, translation and inverted falling body, so that the materials can be fully mixed. Three-dimensional motion mixing has the characteristics of small occupied area, convenient operation and simple structure. It can make the mixing homogeneity reach more than 99%. At the same time, there are no dead corners in the barrel, easy discharging, easy cleaning and low noise. Therefore, it is one of the preferred mixing equipment for clean factory buildings.

Hopper loading and unloading mixer solves the problems of material charging, conveying and discharging dust. It is also called hopper mixer. It has the characteristics of a three-dimensional motion mixer. The hopper mixer uses the angle between the turnover of the square cone barrel body and the left and right barrel wall axes to make the object turn up and down, enlarge and reduce, and the left and right doping achieve uniform mixing effect when rotating, and its charging coefficient can reach 80%. This kind of mixing and lifting equipment is integrated, which can facilitate batching and cleaning, and is a feasible mixing equipment for basically realizing dust-free production and a total mixing equipment for solid preparations.