The use of foreign sealant and analysis of common problems (1)

At present, the performance of foreign imported sealants used in China is better than domestic ones. The main products are represented by GRATEX-made DAREX water-based compound sealants, which are suitable for foods and various types of products. The barrel seal of the oil product has better construction performance and sealing effect. After the sealant dries, it becomes an elastic rubbery liner. This liner forms a sealing ring in multiple crimps, which can effectively fill the small gaps that occur in metal seams. However, some companies have problems in storage and use. Most of them are caused by improper methods. Therefore, we need to discuss and analyze the storage and use of these sealants.

First, the storage of sealant

Taking Talis water-based compound as an example, it is necessary to pay attention to the influence of the ambient temperature during the storage process and store it in a place with a uniform temperature. In general, the temperature should be between 7.2°C and 32.2°C, and the storage temperature should not be lower than 0°C. Do not store directly in the sun, and should be away from heating equipment, because the heat will change the physical and construction properties of the sealant, heat will accumulate in the barrel, so that the viscosity of the sealant. The freezing temperature causes the sealant to agglomerate. In both cases, the sealant will become a permanent waste product.

When storing the sealant, it is important to take the principle of first use (ie first use first) in the first storage. Although the sealant can be stored for more than one year, if possible, the storage period is not more than six months. . In any case, the older sealant should be used first. If it needs long-term storage, the bucket should be inverted once a month to prevent the sealant from depositing. If the temperature difference between the storage area and the use area, the sealant should be placed in the use zone temperature for 24 to 48 hours before use.

Second, the preparation of sealant before use

Most sealants generally require slight agitation prior to use to make them uniform and to restore their original design fluidity. However, excessive agitation or too vigorous agitation reduces its viscosity and permanently changes its fluidity. However, if the sealant is stored for a long time, it is best to use a “pulping mixer” with a rotation speed of 60-80 rpm or an “S-type mixer” with a speed of 300 rpm. The sealant should be stirred with a mixer for 15 minutes before use. Or stir it by hand with a clean stir.

The fluidity of high-quality sealants is generally well-designed and suitable for the construction of various methods. Diluents are generally not needed and can be used directly. The physical nature of the liquid sealant has been carefully controlled, but there may be slight changes in the transportation and storage process; when using the glue injection machine, if the sealant is found to be too thick, a small amount of deionized water or distilled water may be added. Add 2%, you can add more than 5% if necessary. Sometimes the applicator needs to be diluted when the platen speed is slow or the lid diameter is small. When adding water, mix the sealant gently, but do not bring air into the sealant, otherwise it will cause problems with the glue. The water-based sealant contains ammonia. To prevent the ammonia concentration in the sealant from being diluted, the water incorporated into the sealant should contain about 5% ammonia.

Water-based sealants should not be diluted unless absolutely necessary. Some manufacturers use solvents to dilute the sealant, which is highly undesirable. The addition of the sealant to the solvent can cause condensation and can no longer be used. Therefore, do not use any solvents to dilute the water-based sealant.

General sealants have been filtered before leaving the factory. As an extra precaution, the sealant can be filtered once more when it is transferred from one container to another. For example, when the product is transferred from the factory vat to the glue injection barrel, and when the glue injection barrel is turned to the gluing nozzle, it can be filtered once. Such additional filtration can remove the impurities mixed into the barrel when the barrel is opened initially. To avoid nozzle clogging during glue injection.

30 mesh or finer stainless steel filters should be used for filtration. The filter should be cleaned from time to time, especially the filter between the glue barrel and the nozzle should be cleaned frequently. If particulate matter accumulates on the web and dries, the air pressure required to press the sealant out of the nozzle increases, and it becomes more difficult to maintain the proper amount of coating.

Third, the use of sealant

The distance between the sealant surface and the top of the bucket in the plastic barrel should not exceed three inches. In order to keep the fluid level from changing too much, sealant should be added frequently. The pressure at the nozzle is generated by the air pressure and the hydrostatic pressure of the sealant itself. Therefore, if the sealant surface changes too much, the amount of coating film will also change.

Under normal circumstances, the use of water-based sealant when applying 10 to 20 pounds (0.7 to 1.4 kg/cm2) of air pressure; pressure of 10 pounds or less, even slight fluctuations in air pressure will make a significant amount of coating Change; In addition, if the air pressure is far more than 20 pounds, the sealant will overflow or overlap.

In most cases, when the lid is glued, 30% of the sealant is applied to the "planar" position of the bucket hook, and 70% is applied to the pre-rolled groove. The location of the sealant depends largely on the following two factors:

1, nozzle position. In order to achieve 70% in the ditch and 30% in the plane, the nozzle should be as close as possible to the “shoulder” where the lid is stretched, ie away from the pre-rolled groove.

2, chuck speed. Sealant can be distributed from the position on the lid to the flat surface and into the groove, which is the centrifugal force generated when the chuck rotates. Some problems that arise during glue injection can be solved by increasing or decreasing the centrifugal force; the centrifugal force depends on the rotational speed of the chuck.

All water-based sealants are filled with ordinary steel, stainless steel, or enamel containers and cannot be packed in tinplate or galvanized steel containers. If the sealant is filled with the above-mentioned containers, especially after long-term storage, its viscosity will change, and even become jelly-like, which makes the sealant more sensitive and easier to condense. All valves and fittings in contact with the sealant must be made of iron or steel. Copper or galvanized fittings must not be used. All containers must be kept clean and the solid particles of the sealant must be removed. The dry sealant can be cleaned with water, but it is difficult to remove the dry sealant. and so. All containers, filters, funnels, etc. should be cleaned immediately after use.

Water-based sealant construction methods generally have two, one is the use of nozzle plastic injection machine for spraying, generally applicable to larger steel barrels, and more circular; another type of mold-printing machine for printing Glue is generally suitable for smaller drums or shaped buckets.

1, nozzle injection. Generally semi-automatic or automatic injection machine for spraying. The method of controlling the amount of glue to be injected is that the amount of glue should be checked at least once per hour on the nozzle dispenser. The film thickness is controlled by (a) increasing or decreasing the air pressure on the sealant cylinder; (b) raising or lowering the ejector pin; (c) increasing or decreasing the nozzle hole. Usually changing the air pressure is enough to adjust the amount of glue injected.

2, mold printing plastic. Semi-automatic and fully automatic die-stamping machines are generally used for printing. The method for controlling the amount of glue to be printed is that the amount of glue printed on the edge of the lid depends on the width of the mold used and the distance between the mold and the lid at the place where the glue is printed. Whether or not the mold stamping machine can fully function depends on whether the machine can be kept absolutely clean. Molds should often be wiped with a damp cloth to prevent excessive build-up of dry sealant. The accumulation of dry sealant on the mold increases the effective width of the mold surface, and the amount of printed glue increases.

All water-based sealants are best dried by drying. The recommended drying period is 10 minutes and the temperature is 104°C. The temperature and drying time are variable, depending on the dryer type and how the lids are arranged in the dryer. The crimping process must begin after the sealant has completely dried. Prior to crimping, the dry lid should preferably be parked for 48 hours. This allows the sealant film to harden, minimizing the occurrence of "squeeze" during crimping. Gas (or electric) forced-air ovens that use the principle of air circulation are the most effective dryers.

In the coating production, all hoses, nozzles, ejectors, containers, etc., should be washed with cold water. After the hose is flushed with water, it can then be probed into the tube with a hard brush to remove any pieces of sealant attached to the inner wall. The build-up of sealant on the machine can be removed with a damp cloth. Special note: Never remove the sealant with solvent in any case. In addition, care must be taken to prevent solvents or oils from coming into contact with the liquid sealant, as these can cause the sealant to coalesce.