Discussion on application technology of steel drum sealing material
Beijing Huade Sealing Material Industry Co., Ltd. Yang Lianji
With the development of China's foreign-oriented economy, the export volume of commodities has continued to grow. Since the implementation of the International Maritime Dangerous Regulations, all steel drum factories across the country have attached great importance to improving the quality of steel drums. In order to meet the requirements of Class I of the International Maritime Dangerous Regulations, many manufacturers of 200L steel drum products have begun to use the seven-layer round crimping technology. At the same time, the selection and application method of steel drum sealing materials and its understanding of the importance of product quality It is also deepening. Here, I will talk about some shallow understanding of this issue for reference.
First, the role of sealing materials in the manufacture of steel drums.
A very important quality indicator for steel drums is the â€œleakage rateâ€. Leakage is a fatal lack of filling in steel drums. In the steel drum manufacturing process, in order to reduce the leakage rate, it is necessary to carry out the whole process management of cutting, seam welding and coil sealing. It is easier to control the quality of the blanking and seam welding, and the quality of the sealing of the barrel and the bottom cover is much more difficult. In the whole process of winding, to improve the sealing quality of the ring seam, in addition to ensuring the geometrical dimensions of the crimping, the key issue is the filling of the sealing material (except of the welding method of the barrel and the bottom cover, of course).
What is the role of sealing materials?
1. The sealing of the barrel and the bottom cover of the steel drum is accomplished by bending the steel sheet by mechanical external force in the cold state. Whether it is a rectangular bead or a round bead, it is inevitable to form a void in its section.
If the cavity is not filled with a sealing material, it is difficult to ensure that no leakage occurs after the steel drum is made.
2. Steel drums are the final packaging for petroleum, chemical, food and other products, many of which are liquids. In the transportation process, it plays the role of preserving and protecting the contents. Therefore, the steel drum must have certain impact resistance. Although the impact resistance of the seven-layer round-edged barrel is relatively high, the curling is caused by the bending deformation of the steel sheet, and it does not form a whole like welding. When the steel drum is impacted by external force, it will cause a certain degree of looseness in the curling part. If there is no kind of sealing material with certain elasticity in the curling edge to make up the position, the liquid material in the barrel will seep out, causing pollution and waste.
3. If there is no sealing material, the top of the barrel of the large open barrel cannot meet the requirements of the International Maritime Safety Regulations. It is not a complete product because it cannot realize the function of holding and protecting the contents.
It is not difficult to see from the above analysis that sealing the packing plays a decisive role in preventing leakage of the steel drum.
Second, the types and choices of steel barrel sealing materials
According to the performance requirements of steel drums for sealing materials, a good sealing material must have the following properties:
1. Have certain chemical resistance;
2. The material itself has a certain strength and elasticity after curing;
3. Have a certain adhesion to the steel plate;
4. Good workability.
At present, the level of steel barrel sealing materials produced in China is still relatively low, and the range available for steel drum manufacturers is relatively narrow, especially for the effective sealing materials for steel drums containing strong solvents.
The steel drum sealing materials seen on the market are broadly divided into two series: rubber series and plastic series.Bucket bottom sealing material Rubber series Glue-made rubber series Plastic powder plastisol (commonly known as plastic paste)
Large opening steel barrel top sealing material After molding, rubber-filled sealing strip Rubber molding sealing strip Plastic molding sealing strip After injection molding, plastic paste, plastic styrofoam
Because it is not resistant to the corrosion of the chemical contained in the product, it will not function as a seal. Therefore, when selecting the sealing material, the chemical resistance should be first determined. However, there are many types of barreled chemicals that must be identified in advance if they are certain.
Usually the liquid makes the sealing material after curing:
1 The liquid is absorbed by the cured sealing material (generally referred to as "swelling").
2 The soluble component is withdrawn from the cured sealing material.
3 chemical reaction with the cured sealing material.
The end result is a change in volume (ie, an increase or decrease in volume). Therefore, it is generally accepted that the test is conducted by a volume change test. Because the top of the barrel and the sealing material at the bottom of the barrel are applied differently on the steel drum, the specific test method is:
1. Bucket bottom sealing material. The general practice is to make the sealing material into a thousand test pieces, and after soaking in the chemical for seven days, observe the volume change before and after the soaking. It is a good product that does not change or has no obvious change in volume, and a slightly swollen volume becomes an edible product, and the test piece is dissolved or the volume is reduced to be a banned product.
2. Barrel top sealing material. The chemical was placed in a small can, and the dry test piece made of a sealing material was used to cover the mouth, and then pressed with a lid, and the volume change was measured after being left for a long time (35-70 days). It is a good product that the volume does not change significantly, and a slightly larger swelling volume is available, and the volume of the test piece is reduced by more than 30% as a banned product.
Secondly, a sealing material with a high solid content and a certain strength and elasticity should be selected. Because the same amount of wet glue is sprayed on the top of the barrel (bottom), the film with a high solid content will be thicker and the sealing effect will be better. At present, the solid content of domestic rubber series sealant is within the range of 35-55%, while the similar solid content of foreign products is up to 70%.
The choice of construction performance is extremely important for improving production efficiency and simplifying production equipment. The so-called construction performance refers to whether the use of the sealing material is convenient. For example, some sealants must be heated to 60-80 Â°C before use to spray, which is more troublesome than spraying at normal temperature. Some adhesives have high viscosity and can only be painted by hand, and can not be sprayed, which causes construction limitations to be too large. For example, the curing conditions of the glue, the curing time, etc. belong to this category. It is not as convenient to cure at room temperature as the heat curing, and the curing time is not as easy as the curing time is short.
In short, the choice of sealing materials should be based on the equipment level of each plant. It is necessary to use a sealing material with good sealing effect, convenient use, easy management, small consumption, reasonable price and harmless to the operator.
Third, the comparison of construction methods of sealing materials
The application of packaging steel barrel sealing material is divided into two parts: one is the barrel top of the closed steel barrel, the bottom of the barrel and the bottom of the barrel of the large opening steel barrel. The second is the top of the barrel of the large open steel barrel.
The application method of the former sealing material can be roughly divided into three methods: manual painting, mechanical spraying and dip printing. Manual and mechanical injection are common methods, and the dip method is only a special method of applying glue to the bottom of the square barrel. That is, the glue which is carried by the film of the same size as the square bottom cover to be glued is left in the position where the bottom cover needs to be glued. This method is relatively old, low in efficiency, uneven in coating, and it is difficult to ensure the cleaning of the bottom cover. The better square bottom cover glue injection machine is made by the injection nozzle to make a square track movement to complete the glue injection work.
Here, the focus is on the application of the glue on the top of the round bucket. Due to the uneven level of equipment in China's steel barrel industry, and most of the manufacturers are born and raised, relying on self-reliance and hard work, the performance in the process of injection molding is more prominent. Because the top of the barrel (bottom) is rolled up in the process of implementing the seven-layer round crimping technology, many manufacturers still retain the manual coating method in the application of sealing materials. The following compares the two methods of manual brushing and mechanical jetting.
In the steel barrel manufacturing process, which station is the top glue coating process? I think that the top of the barrel and the bottom of the barrel of all steel drums should be subjected to the pre-filling process. It is advisable to enter the steel drum assembly line after the glue is cured.
At present, many factories still use the method of brushing and spraying the steel drums while assembling the seals. The disadvantage of this method is that the sealant is in a liquid state. After the seal is sealed, the glue is not easily cured by air, and it is difficult to exert a sealing effect. The second is that the liquid substance generally has different degrees of shrinkage after being solidified, and even after curing, it can be cured after being sealed. The shrinkage in the volume of the sealing material also reduces its compensating ability and the sealing effect is not good. Therefore, the process of setting up the injection molding glue first coats the top of the barrel and then assembles it into a barrel after it is solidified, which is very effective for improving the quality of the steel barrel sealing.
At present, there are two methods for applying glue; one is manual brushing, which is of course simple, but has many defects:
1. The film coating is not uniform;
2. The amount of glue applied to each bottom cover is difficult to control accurately;
3. It is not possible to apply the glue to the most probable area.
The method of mechanically applying the glue is ideal. The top of the barrel (bottom) after the mechanical injection of the glue, the filling position of the sealing filler and the shape after curing are ideal, and can be controlled in advance. Its location is exactly the center of the curl. In addition, after curing, it is assembled into a barrel, and the pressure applied during the sealing process causes the sealing packing to generate a pre-stress which is expanded to the periphery. Once the steel barrel is subjected to an external force and the curl is loose or deformed, the sealing packing is sealed. It will quickly compensate according to its own flexibility to achieve the purpose of sealing and improving impact resistance.
1. The top and bottom of the steel drum should be filled with glue. After the filler is solidified, it can be assembled into a barrel to improve the quality of the joint.
2. It is advisable to use a mechanical pre-filling glue for the injection molding method.
For the sealing of the top of a large open steel drum, the construction method is divided into:
1. Put into shape after molding.
2. Glue injection molding.
At present, more applications are made by processing rubber or plastic into a circular gasket or a sealing strip which is adhered to the lid of the barrel by an adhesive, that is, after being formed into a method. Disadvantages of this method: higher cost; more difficult to put in; easy to fall off. The injection molding method is ideal, especially after the injection of the styrofoam, the obtained sealing ring has good elasticity and excellent sealing effect. The process is extremely simple, which is an indispensable process in the manufacture of internationally-used tapered steel drums. It is undoubtedly extremely beneficial to transplant it into the manufacturing process of all large open barrels.
Fourth, the application of HDF type PVC styrofoam.
Beijing Huade Sealing Material Industry Co., Ltd. introduces HDF-type PVC styrofoam produced by foreign advanced technology, which is an indispensable quality sealing material for large open bucket tops. The styrofoam is made of polyvinyl chloride resin as the main raw material. When used, the styrofoam is injected into the groove of the top of the bucket and placed in a heatable baking equipment. After a certain period of time, the styrofoam is plasticized and The plasticized sealing strip uniformly generates tiny bubbles, making it a sponge-like elastomer. The degree of softness is proportional to the temperature of the heating in time.
The styrofoam plastic molding temperature is between 170 Â° C and 210 Â° C. If the temperature is too high, the color of the sealing strip will become darker or even coke. The plasticizing time varies with the size of the top of the barrel (bottom) and the amount of glue injected. Take the 20L steel bucket top as an example: the injection amount is 10.5-llg, the baking temperature is 170Â°C-175Â°C 0C, and the baking time is about 5 minutes.
Due to the wide application of HDF type PVC styrofoam, the top sealing effect of the large open barrel barrel will be improved, and the large open steel barrels of each steel drum factory will become high quality packaging goods.
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