The principle and design of packaging mechanical metering device
Release date：2017-06-30 17:29:27
With rapid economic development and technological improvement, people’s living standard and consumption level are constantly increasing. High precision pouch products are of higher and higher market demand due to its delicate package and convenience of carrying and using. Packing requirements for pouch products are mainly the following two: one is beautiful and attractive appearance and good protection of the product; two is accurate packaging with small deviation.
For small automatic packaging machines, measurement in volume usually has two types, namely measuring cup and auger. Measuring cup type can be further divided into constant volume and adjustable volume subtypes.
2. 1 Constant volume measuring cup
1- feed hopper 2- hood 3- guard ring 4- measuring cup
5- valve 6- main shaft 7- disk 8- scraper
Sketch 1 Constant volume measuring cup
Sketch 1 is constant volume measuring cup type. Material drops from feed hopper 1 to disk 7 by self-weight; on the disk evenly spreads several measuring cups 4 and corresponding valves 5. When main shaft 6 drives disk 7 to rotate, scraper 8 scrapes off extra material above measuring cups 4. When a measuring cup rotates to the discharge position, valve 5 under the measuring cup will be opened automatically. Therefore, the material in the cup will then be filled into the container under the valve due to self-weight, so as to realize the measurement of the material. The material volume in this type of measurement mechanism is determined by the measuring cup which cannot be adjusted. In case of needing to change volume, you have to replace the cup.
Series of measuring cups can be designed for choosing based on the specific gravity and package weight requirement of different materials.
2. 2 Adjustable volume measuring cup
1- feed hopper 2- upper measuring cup 3- lower measuring cup
4- hand wheel 5- adjusting bracket
Sketch 2 Adjustable volume measuring cup
Sketch 2 is adjustable volume measuring cup type. The obvious difference between this type and constant volume type is that the measuring cup of this type is made up of upper cup 2 and lower cup 3. Part of the upper cup is inserted in the lower cup, which can be moved up and down. The package volume is determined by both the upper and lower cups. When the package volume needs to be changed, the hand wheel 4 can be turned to move adjusting bracket 5 vertically. Then the adjusting bracket will drive the lower cup to move up and down to change the volume the lower cup. That means the package volume determined by both the upper and lower cups will also be changed. As to measuring cup type, the specific gravity of the material shall be stable because of the low accuracy of this type of measurement mechanism.
Sketch 3 is auger type constant volume measuring mechanism. This type uses the cavity of the auger to measure the volume of materials. Motor 3 drive screw shaft 6 to rotate via belt pulley 4; then screw shaft 6 drives auger 8 to rotate until the preset number of turns.
1&3- Motor 2- sprocket wheel 4- belt pulley 5- brake
6- shaft 7- stirring rod 8- auger
Sketch 3 Auger type volume measurement
As the measurement of the material volume is down by the cavity of the auger, relatively accurate volume value can be acquired by precise control of the number of turns of the auger.Auger type is applicable for solid granular materials of good fluidity, but it is not suitable for materials of large fluctuation of specific gravity.
3 Measurement in Weight
The accuracy of volume measuring type is not high, so it’s not suitable for those materials which are of bad fluidity, huge fluctuation of specific gravity or caking prone. For the above materials, weighing type is usually adopted with electronic weigher. Sketch 4 is electronic weighing mechanism. Material drops from feed hopper 1 onto belt 4 via gate 2, then the continuously running belt 4 conveys the material onto weigher 5; the weight of the material makes the supporting spring 7 under weigher 5 bend and deform and the weighing platform moves down correspondingly; this displacement signal is transmitted to weighing adjuster 3 by senor 6, so the weigher can immediately detect the material weight on this part of belt. If the weight is not right, weighing adjuster 3 can adjust the opening range of gate 2 according to the signal given by senor 6 to make sure the weight within a stable range. The performance of the weighing control system plays a decisive role to the accuracy of measurement.
1- feed hopper 2- gate 3- weighing adjuster 4- belt
5- weigher 6- sensor 7- blade spring
Sketch 4 electronic weighing mechanism
volume type is of simple structure, easy operation and wide application which is the first choice for low accuracy required materials; while weigher type, which is of higher productivity and accuracy, is suitable for materials of huge fluctuation of specific gravity. With the development of technology and the use of combination weigher, the metering speed of dynamic weighing mechanism is greatly improved. As the developing direction of packing industry, dynamic weighing packaging will surely improve and boom.