The hottest solid material is filled

2022-08-12
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Solid material filling (Part 1)

solid materials have a wide range, which can be divided into powder, particle and block according to their forms; According to viscosity, it can be divided into three categories: non viscous, semi viscous and viscous

non viscous materials. Such as dry grains, seeds, rice, sugar, coffee, granular salt, crystal rock sugar and various dried fruits, these materials can flow freely, dump on the horizontal plane, and naturally pile into a conical pile, so they are also called free flow materials, which are the easiest to fill; Semi viscous materials, such as flour, powdered monosodium glutamate, milk powder, soft white sugar, washing powder, penicillin powder, etc., cannot flow freely. During filling, they will bridge or pile up in the storage hopper and lower hopper into an arch shape, which makes filling difficult, and special devices are needed; Viscous materials, such as brown sugar powder, candied fruits and some chemical raw materials, are more difficult to fill. They not only stick together by themselves, but also stick to the metal wall and the surface of polytetrafluoroethylene coating (commonly used in the maintenance of steel bar zigzag testing machine with the popularization of gold reduction testing machine knowledge, protecting less friction between materials and metal wall, increasing the wear resistance of material bucket), so it is more difficult to fill, Some cannot be filled automatically by mechanical means at all. It should be pointed out that some loose powder and granular materials will become sticky after the temperature rises or gets damp. Therefore, the temperature and humidity of the workshop should be controlled during filling

the filling methods of solid materials can be divided into three categories: one is the weighing filling method, which is to measure the quantity of filling materials by weight; The other is volume filling method, which calculates the quantity of filling materials by volume; The third type is counting method, which is usually used for collective packaging. The filling of solid materials with block and granular materials is a method to measure the static quantity of various springs or the quantity of single packaging pieces based on the number of block and granular solid materials at ordinary times

I. weighing and filling method

weighing and filling method is applicable to the filling of materials that are easy to absorb moisture, easy to agglomerate, uneven particle size and large specific gravity. This kind of filling method is divided into net weight filling and gross weight filling

1. Net weight filling method

this method weighs the materials first, and then fills them into the packing containers. The weighing result is not affected by the weight change of the container, so it is the most accurate weighing and filling method. As shown in the figure, the filling result is that a feeder 2 is used to transport the materials from the storage hopper to the metering bucket 3, and the materials are continuously weighed by the scale 4 which can be widely used in high-tech fields such as military industry, aerospace, electronics and so on. When the material in the metering bucket reaches the specified weight, the material is discharged through the drop hopper 5 and enters the packaging container. The feeding can be completed by rotating feeder, belt, screw pusher or other methods, and the weighing is controlled by mechanical scale, electronic scale or combined scale. It can be controlled by mechanical device, photocell or limit switch to reach the specified weight

in order to achieve high filling accuracy, the method of graded feeding can be adopted. During weighing, most of the materials enter the metering bucket at high speed, and the rest enter the metering bucket slowly through the micro feeding device. In the case of computer control, the coarse feeding and fine feeding can be weighed, recorded and controlled respectively to make up for the difference

due to the high weighing accuracy of net weight, such as 500g materials, the weighing accuracy can reach ± 0.5g, that is, the accuracy can reach ± 0.1%, so it is widely used in precision requirements or valuable free flowing solid materials, and it can also be used for materials that are not suitable for volume filling and packaging, such as expanded corn, fried potato chips, fried shrimp chips, etc. However, the filling speed of the net weight method is slow and the price of the machine used is high

2. Gross weight filling method

after loading the material into the container, weigh it together with the container, and the weight is the gross weight. The machine used in this method is simple and cheap. The disadvantage is that the weight change of the packaging container directly affects the specified weight of the filling material. As shown in the figure, it is different from the net weight weighing in that there is no measuring bucket, but the container is placed on the scale for filling. When the specified weight is reached, the feeding is stopped, and the weighed weight is weight

this method is not only suitable for free flowing materials with general price, but also commonly used for the filling of viscous materials, such as bagged brown sugar, pastry powder, etc., because even if the viscous materials sometimes stick to the lower hopper, it will not affect the final filling weight

gross weight filling is not suitable for occasions where the weight of packaging containers changes greatly and the weight of materials accounts for a small percentage of the whole weight. For example, the weight change of a glass bottle containing 25g pepper powder is 5.9%, which is accurately weighed by the gross weight and must be reflected in the final packaging weight

second, volume filling customers have chosen many product methods of this series

this method measures the quantity of filling materials based on volume. Because there is no need for weighing device, the machine structure used is simple, and the filling speed can be improved. However, the filling accuracy depends on the stability of the specific gravity of the material, which is generally lower than that of weighing and filling, ranging from ± 1.0% to ± 2.0%

there are many kinds of machines to realize volume filling, but in principle, they basically belong to two kinds

1. control the flow or time of filling materials to ensure the filling volume

(1) the timing vibration filling machine has the lowest accuracy, but the structure is the simplest and the price is cheap. Its principle is shown in the figure. A vibrating tray feeder 2 is connected to the lower part of the storage hopper 1. The feeder vibrates according to the specified time to fill the material directly into the container. The filling quantity is controlled by the vibration time

(2) screw filling machine can obtain high filling accuracy. Its principle is shown in the figure. There is a cylinder at the conical bottom of the storage hopper 1, which is equipped with a feeding shaft 2 with spiral surface and an agitator 3. When the feeding shaft rotates, the mixer will mix the materials evenly, and the spiral surface will squeeze the materials to the required density. The screw shaft can output a certain amount of material every revolution. The number of turns of the screw shaft is controlled by the clutch, which ensures that each container is filled with a certain amount of material

if filling small bags, a rotary table can be installed under the screw feeder to cut off dense materials, and then mix them with air to form free flowing materials. After filling, vibrate the bag and tamp the loose materials

(3) vacuum filling machine. In the filling process, the container is kept vacuum, the materials are relatively dense, and the bridge void (i.e. the materials support each other to form an arch) phenomenon is reduced. Therefore, the filling accuracy is higher than that of timing vibration filling machine and screw filling machine. Its principle is shown in the figure. Each packaging container is vacuumized by filtration, so the container and vacuum head must be sealed during filling. Materials enter the container by gravity. In order to control the filling quantity, a screw feeder is installed in the storage hopper to feed the vacuum head

when the vacuum filling machine is used for semi-rigid packaging containers of thin-walled plastic bottles, a rigid sealing sleeve should be used outside the container to prevent wrinkles in the packaging container during the filling process. The disadvantage of vacuum filling machine is that in some cases, the filling weight is affected by the change of packaging volume. For example, the change of glass container wall thickness will lead to the change of filling volume

2. Measure the materials with the same measuring container to ensure that the filling volume is

(1) gravity measuring cylinder filling machine. This filling machine is suitable for free flowing solid materials with low filling price and low filling accuracy. As shown in the figure. The lower part of the feeding bucket 1 is equipped with two or more measuring cylinders 3, which are evenly distributed on the rotating horizontal circular plate. There is a telescopic cavity 4 on the upper part of the metering cylinder, which can make the upper and lower telescopic to adjust its volume. When the metering cylinder passes under the feed hopper during rotation, the material falls into the metering cylinder by gravity. Then, when the discharge port under the metering cylinder is aligned with the round hole on the fixed plate under the cavity assembly 5, the materials are discharged into the packaging container through the discharge pipe 6. In order to make the material flow into the container quickly, sometimes the container must be vibrated

(to be continued)

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