Van Aarsen features the GD hammer mill with an automatic screen exchange system and frequency controlled motor, being the ideal solution to combine optimum grinding results with high grinding efficiency.
Hammer mills are used to grind the raw materials for animal feed. The raw materials are fed into the hammer mill where the impact of hammers rotating at high speed breaks them down into small particles. The efficiency of the grinding process depends on a number of variables, such as the breaker plate design, the hammer tip speed and the screen perforation.
Large breaker plates for optimal grinding efficiency
Van Aarsen designed its first breaker-plate hammer mill more than 65 years ago. The current hammer mill is equipped with a large breaker plate in the upper section of the grinding chamber: this exposes the product in the grinder to multiple impacts. Nowadays, this design is generally considered to be an extremely effective way of achieving high quality and grinding efficiency. The right particle size is achieved through the multiple impact action in the top section of the chamber, after which the ground product exits the mill through the screen at the bottom. This design avoids circulation of the ground product in the grinding chamber, which would reduce efficiency and cause an excessive amount of fines. The longer service life of the screens and hammers is an additional benefit.
Screen perforation and open area
The screens have a direct effect on end-product quality and the hammer mill’s capacity. The combination of the perforation size and open area (the number of holes) in a screen determine the particle size, particle variation and the grinding capacity. How larger the perforation opening, the coarser the ground product. How larger the open screen area, the greater the mill’s capacity.
Hammer tip speed
In addition to the screen perforation, the hammer tip speed also plays a role in determining the particle size of the ground product. A higher tip speed means a higher impact and will result in a finer grind. A lower hammer tip speed results in a ground material with a coarser structure. At the same time, the capacity of the hammer mill will seriously decrease. There is no such thing as one ideal tip speed; this setting depends on the base ingredients and the desired end-product. The hammer tip speed can be controlled via a frequency controller and this also influences the fineness of the grind.
Consistent use of the right screen and tip speed for optimal quality, speed and energy consumption
The desired quality, speed and energy consumption can be accurately managed through consistent use of the right screen. An automatic screen exchange system soon pays for itself when multiple screen perforations are used. Van Aarsen offers an automatic screen exchange system that holds 3 different screen perforations. Depending on the recipe in use, the screen exchange system automatically positions the right screen plates in the hammer mill screen holder, thereby reducing the screen changeover time from 20 minutes to just 1 minute. This results in a much higher grinding efficiency, capacity and reduced labor.
For full flexibility, an automatic screen exchange system can be combined with a frequency controller which regulates the hammer tip speed. By adjusting the hammer tip speed to suit the screen perforation, the ideal setting can be chosen for achieving the right particle size and variation while maintaining capacity at the desired level and keeping the energy consumption per ton of feed as low as possible. Van Aarsen’s GD hammer mill with the automatic screen exchange system is characterized by a low energy consumption of approximately 7 kWh/ton.
Automatic screen exchange – grinding efficiency
Intelligent design and low maintenance costs
In addition to the factors mentioned, the quality and position of the hammers, the feeding device and aspiration system also affect hammer mill performance. Thanks to intelligent design, Van Aarsen’s GD hammer mill scores well in all these areas.
- One of the unique features of Van Aarsen hammer mills is that the hammers can be rotated or replaced quickly and easily by a single person.
- The staggered hammer pattern increases the contact area and therefore grinding efficiency. The distance between the hammers and the screen is 25 mm. This prevents product from circulating in the grinding chamber and the resulting energy loss.
- The hammers used for the GD hammer mill are robust and have a long service life. They only need to be replaced when all 4 sides are worn. In combination with the wear-reducing breaker plates, the cost for the hammers amounts to less than 3 euro cents/ton of feed.
- The feeding device must deliver a steady flow of the raw materials. Because different materials have different grinding characteristics, a frequency control on the feeding device of the GD hammer mill always ensures the correct supply.
- As standard, the feeding device is equipped with a magnet and can also be equipped with a heavy parts separator for optimum safety and a longer lifetime of the screens.
With its compact design Van Aarsen’s GD hammer mill with automatic screen exchange can be integrated in new and existing situations.
Grinding: an essential process step
The feed production process has a significant impact on the nutritional value of animal feed. Grinding the raw materials to the required structure is an essential operation which affects both pellet quality as well as the animals’ digestibility. Size reduction increases the number of particles and the surface area per unit of volume which results in increased mixing homogeneity. In addition a finer grind has a positive effect on starch gelatinization which leads to improved pellet quality and increased pellet mill capacity.