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

Yang Wenliang

At present, the performance of foreign imported sealants used in China is better than that of domestic ones. The main products are represented by DAREX water-based compound sealant produced by GRACE. The sealant is suitable for food and various types. The sealing of oil drums has good construction performance and sealing effect. After drying this type of sealant, it becomes a rubbery pad with elasticity. This gasket forms a seal within the multiple beading to more effectively fill the small gaps in the metal seam.

However, some enterprises have problems in storage and use, mostly caused by improper methods. Therefore, it is necessary to conduct some discussion and analysis on the storage and use methods of such sealants.

First, the storage of sealant

Take the Thales water-based compounding agent as an example, it should pay attention to the influence of the ambient temperature during storage, and it is required to be stored in a place with uniform temperature. Generally, the temperature is preferably between 7.2 ° C and 32.2 ° C and the storage temperature is not lower than 0 ° C. Do not expose to direct sunlight during storage, and should be kept away from heating equipment, because too much heat will change the physical and construction properties of the sealant, and heat will accumulate in the barrel, which will reduce the viscosity of the sealant. The freezing temperature will cause the sealant to agglomerate. In both cases, the sealant will become a permanent waste.

When storing the sealant, it should be noted that the first use of the first storage (first take first) principle is important; 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, you should use an older sealant first. If long-term storage is required, the bucket should be inverted upside down every other month to prevent the sealant from settling. If the temperature of the storage area differs from the temperature of the use area, the sealant should be placed in the temperature of the use area for 24 to 48 hours before use.

Second, the preparation of the sealant before use

Most sealants typically require a slight agitation before use to make them uniform and return to the original design flow. However, excessive agitation or excessively vigorous agitation will lower the viscosity and permanently change its fluidity. However, if the sealant is stored for a long period of time, it is best to use a "slurry mixer" with a speed of 60 to 80 rpm or an "S-type mixer" of 300 rpm. The sealant should be stirred with a blender for 15 minutes before use. Or stir by hand with a clean mixing hand.

The flow properties of high-quality sealants are generally designed to be suitable for a variety of methods. Generally no diluent is needed and it can be used directly. The physical properties of the liquid sealant have been carefully controlled, but there may be slight changes during transportation and storage. When using the glue injection machine, if the sealant is too thick, a small amount of deionized water or distilled water may be added. Add 2%, if necessary, add 5% or more. Dilution is also required when the speed of the applicator is slow or the diameter of the lid is small. Gently stir the sealant evenly when adding water, but do not bring the air into the sealant, otherwise the glue will be problematic. Water-based sealants contain ammonia. To avoid dilution of the ammonia concentration in the sealant, the water incorporated into the sealant should contain about 5% ammonia.

Water based sealants should not be diluted unless absolutely necessary. Some manufacturers use solvent to dilute the sealant, which is extremely undesirable. When the sealant is added to the solvent, it will agglomerate and can no longer be used. Therefore, do not use any solvent to dilute the water-based sealant.

Generally, the sealant has been filtered before leaving the factory. As an additional precaution, the sealant can be filtered once more when it is transferred from one container to another. For example, when it is transferred from the factory vat to the glue barrel, and when it is transferred from the glue barrel to the glue nozzle, it can be filtered once. This extra filter can remove the impurities mixed into the barrel when the barrel is initially opened. To avoid blockage of the nozzle during the injection process.

A 30 mesh or finer stainless steel strainer 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 net and is dried, the pressure of the air required to press the sealant from the nozzle increases, and it is more difficult to maintain a proper coating amount.

Third, the use of sealant

The distance between the sealant and the top of the bucket in the glue tank should not exceed three inches. In order to prevent the liquid 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 level changes too much, the amount of the coating will change.

Under normal conditions, 10 to 20 pounds (0.7 to 1.4 kg / cm 2 ) of air pressure is applied when water-based sealant is injected; even if the pressure is below 10 pounds, even a slight fluctuation in air pressure will cause significant coating volume. Change; in addition, if the air pressure is far more than 20 pounds, the sealant will be overwhelmed or overlapped.

In most cases, when the lid is glued, the sealant applied to the "flat" of the barrel hook is 30% and 70% is applied to the pre-roll. The location where the sealant is applied depends to a large extent on two factors:

1. The position of the nozzle. In order to achieve 70% in the groove and 30% in the plane, the nozzle should be as close as possible to the "shoulder" where the lid is stretched, that is, away from the pre-rolling groove.

2, chuck speed. The sealant can be distributed from the position coated on the lid to the plane and flow 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 magnitude of the centrifugal force depends on the speed of the chuck.

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

There are two kinds of construction methods for water-based sealant. One is sprayed with a nozzle glue injection machine, which is generally suitable for larger steel drums, and is mostly round; the other is printed by a type of stamping machine. Glue, generally suitable for smaller cans or shaped cans.

1. The nozzle is glued. It is usually sprayed with a semi-automatic or fully automatic glue dispenser. The injection amount is controlled by the injection molding machine, and the injection amount should be checked at least once every hour. The film thickness is controlled by: (a) increasing or decreasing the air pressure on the sealant cylinder; (b) raising or lowering the thimble; (c) increasing or decreasing the nozzle hole. Usually changing the air pressure is enough to adjust the amount of glue injected.

2, type die printing glue. Generally, semi-automatic and fully automatic die-printing machines are used for printing. The amount of printing glue is controlled by the fact that the amount of printing glue 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 printing press. Whether the type of printing machine can fully perform depends on whether the machine can be absolutely clean. The mold should always be wiped with a damp cloth to prevent excessive dry sealant build-up. The accumulation of dry sealant on the mold increases the effective width of the mold face and increases the amount of print.

All water-based sealants are preferably dried by drying. A drying cycle of 10 minutes is recommended and the temperature is 104 °C. The temperature and drying time are variable, depending on the type of dryer and the arrangement of the lid in the dryer. The crimping process must be started after the sealant has completely dried. The dry lid should preferably be parked for 48 hours before crimping. This hardens the sealant film and minimizes "extrusion" when the bead is joined. Gas (or electrothermal) forced-ventilated ovens that utilize the air circulation principle are the most effective dryers.

In the production of rubber coating, all hoses, nozzles, thimbles, containers, etc. should always be washed with cold water. After the hose has been rinsed with water, the hardener can be used to remove the sealant fragments attached to the inner wall. The sealant accumulated on the machine can be removed with a damp cloth. Special Note: Under no circumstances should the solvent be removed with a solvent. In addition, care must be taken to prevent solvents or oils from coming into contact with the liquid sealant as these will cause the sealant to coalesce.