For decades (more than 70 years) KAHL pelleting presses have been applied successfully for compacting organic products such as compound feed, straw, dried forage, dried beet pulp, wood and other more.
The product is pressed through a die by pan grinder rollers, formed into endless strands, and then cut to the desired particle length by means of knives.
We are constantly developing our machines in order to improve their capacities and economic efficiency. KAHL pelleting presses are particularly appropriate for products which are difficult to pellet.
The current production range of KAHL presses consists of 12 different sizes
Die diameter 175 - 1,500 mm
Drive motor 3 - 500 kW
Roller diameter 130 - 450 mm
Pellet diameter 2 - 40 mm
Output 2 kg/h – 30 t/h
The small presses are driven by slip-on gears, the big presses by low-noise and low-wear worm gears with preceding belt drives.
A CONVINCING TECHNOLOGY
1. The product is fed by gravity. The large pelleting chamber avoids blockings.
2. The low roller speed of approximately 2.5 m/s ensures a good deaeration of the product.
3. As a result of the low speed, the press noise is below 70 dbA.
4. The thick product layer between the pan grinder rollers and the large die surface results in a high throughput, even in case of products which are difficult to pellet.
5. The roller gap can be adjusted during operation, thus the pellet quality can be controlled.
6. Permanently lubricated roller bearings with special seals prevent the product being pelleted from contamination by lubricating grease as well as grease losses.
7. Quick die changing increases the availability of the complete plant.
8. Liquid variations in the product are permissible.
9. Mixtures with high levels of fat and molasses can be effectively pelleted.
10. Each pelleting press is tested before supply under full-load simulation.
The material is directly fed to the press vertically from above by gravity without passing any deflectors and without the use of mechanical aids (forced feeding). Thus the danger of blocking or bridging due to inadvertent compaction, particularly with materials having a low bulk density, is excluded.
For material feeding and acceptance by the pelleting tools a large press interior is available. The maximum effective diameter of our dies is 1,250 mm. A large feeding area is especially necessary for materials with a low bulk density. The compaction ratio in case of straw, for example, is 15:1, i.e. about 15 m³ of input material must be processed to achieve 1 ton of pellets.
PAN GRINDER HEAD
The pan grinder head forms one unit comprising roller axles and rotating pan grinder rollers. Number, diameter, width, shape (cylindrical or conical), and surface of rollers are selected to best suit the material to be pelleted. Materials with a low bulk density are handled with fewer rollers to provide more space.
The circumferential roller speed of 2.5 m/s is relatively low which makes it easier to force the material between the rollers and the die. Furthermore the material can be deaerated more easily, the risk of roller slip is reduced and the press can operate under a noise level lower than that of the drive motor.
The hydraulic pan grinder head adjusting system makes it possible to optimise the distance between rollers and die during operation. The thickness of the material layer can therefore be influenced in such a way that the most economic press capacity is achieved. Thus it is possible to optimise the quality of the pellets.
The distance between pan grinder rollers and die is preselected, entered into the computer and automatically adjusted for each feed mixture. The electronic control system keeps the value constant. Press output, pellet quality, security of operation, service life of the die and rollers and availability of plant are thus considerably improved. The hydraulic system in connection with automatic load control allows deblocking of machine while running.
The Distamat system determines the gap between the pan grinder rollers and the die after the assignment of zero between pelleting press and measuring cylinder (the taring process). For the gap measurement, a measuring cylinder is installed in the oil supply line of the hydraulic nut of the press. A displacement of the pan grinder head causes a displace¬ment of the measuring cylinder. This is measured by a displacement sensor and processed as actual value by the control system. The displacement sensor emits a signal of 4-20 mA = 0-100 % to the control system. In the control system, this signal is calibrated in mm by means of a conversion factor.
The task of the Distamat is to maintain the gap between pan grinder roller and die constant according to a preset setpoint value, independent of the product quantity. The gap is indicated in mm for an easier understanding. The values of the gap are indicated as repeatable values under the same measuring conditions - though they are no real measuring values. Deviations between the indicated gap and the measured values are possible due to the indirect measuring method. A constant gap between pan grinder roller and die is an essential prerequisite for the pellet quality as well as a stable operation. The resulting pressure is due to the load of the machine (modification of throughput, of humidity, or of product).
As it keeps the contact between pan grinder roller and die to the technically necessary minimum, the Distamat minimises the wear. In addition, several safety functions for the pelleting press are realised using the Distamat.
For the functioning of the Distamat the correct mechanical assembly of the pelleting press according to the operating instructions, the tightness of the unit, as well as a good condition of the wear parts are basic prerequisites. Functioning of the hydraulic pan grinder roller adjusting system: on the left in the rest position, on the right in working position.
Die thickness plus the number, shape, and diameter of the holes as well as the roller track width can be varied according to the material to be processed. A high specific press output with low energy consumption per unit is among other things greatly influenced by the retention time of the material inside the effective bores.
The specific roller track area varies between 25 and 30 cm² per kW of the installed power depending on the intended use and requested material compaction. Only with large specific perforated die areas can the installed power be completely converted into throughput.
The shearing forces produced by the pan grinder rollers when running on the product layer between rollers and die result in a better pre-compaction, less crumbling and drilling of the material, better intake characteristics, shorter length of the effective bores as well as smoother, harder, and tougher pellets with the same power consumption. Conical rollers can be used for materials whose nature does not allow them to be subjected to additional shearing forces or which causes excessive wear on the die. Due to the direct material feeding, the large press interior, and the shearing effect of the rollers even very coarse material can be processed. With some products, e.g. waste, one size reduction stage can be saved by operating the existing grinding plant using a bigger mesh size. The net result is a saving of energy, a reduction in investment costs, and a simplified sequence of operation.
CHANGE OF PELLETING TOOLS
The dies are supported on the full circumference of the press case. The pan grinder head is seated loosely on the main shaft and is connected to the latter by feather keys. From above the pan grinder head is held in place by the adjustable hydraulic nut.
Changing dies is therefore very easy and rapid, because except for the hydraulic nut no screws or clamps need to be loosened. The pan grinder head and die can easily be lifted by means of an electric chain hoist and be replaced without any need to clean the interior.
AUTOMATIZATION FOR OPTIMUM PRODUCTS
Switch and control panels for all plant sizes are designed, built, and installed by KAHL. Our electrical engineers develop custom-made application software for ensuring a high degree of operating safety and efficiency.
The EAPR is the pelleting press control system for an optimum, automatic operation of the flat die pelleting presses of the company KAHL. It consists of a local control cabinet with a graphic operator panel (OP) and an S7-PLC by Siemens as central components. The EAPR controls and regulates all the relevant process parameters.
• Optimum operation of the pelleting press
• Low manpower requirements
• High availability due to the use of proven quality components
• Optional field bus system saves installation work
• DISTAMAT for continuous adjustment and control of the roller gap (option)
PRODUCT TESTS CAN BE CARRIED OUT IN THE KAHL PILOT PLANT
In the last few years more than 5,000 products have been pelleted successfully in the KAHL pilot plant.