New repair method for steel drum

New repair method for steel drum

Xin Qiaojuan

In the production process of steel drums, it is inevitable that there will be leakage of welds and upper and lower “big circles” (ie, the bottom of the barrel, the top of the barrel and the mechanical crimp of the barrel). However, with the further development of the market economy, the ISO9000:2000 standard will focus on the customer's focus on the standard of the Big Eight management principles. Meeting the customer requirements has become the goal of steel drum enterprises, otherwise the production and operation of the company will be in crisis.

Recently, I visited several barrel factories. Everyone complained about the higher quality requirements of customers. They said that the customer requirements are too high. The steel barrels can be welded without any welding. The national standards allow welding. Oh, why aren't the current users and so on? In fact, I have encountered these problems every day at work. At present, many customers require the appearance of steel drums to be dazzling, and there are no problems such as welding shovel, paint sag, peeling of paint and pits on the surface of steel drums. Even if the weld is repaired by the argon arc welding machine (the welding is very small, it is almost invisible after grinding), but it is still difficult to achieve the "zero defect" in the barrel enterprise, which is mainly Limited by the level of management of industry companies. The steel drum industry is currently unable to meet the requirements of zero-defect production conditions, regardless of personnel quality, equipment status and management level. Therefore, we are looking for a method that does not affect the appearance quality of steel drums and prevents them from leaking. Bonding has already been used by several steel drum companies.

Most of the leakage of the steel drum is at the bottom of the barrel, the top of the barrel and the mechanical crimping of the barrel; the second is the seam welding of the barrel. Very few are leaks due to defects in the steel sheet raw material itself such as blisters, interlayers, and the like. Adhesive substructure bonding and non-structural bonding. An important feature of structural bonding is that the bond is subjected to mechanical loads for a long time; non-structural bonding refers to non-mechanical load bonding such as sealing, encapsulation, positioning, and repair. Therefore, the bonding of steel drums belongs to metal non-structural bonding. Let's discuss the bonding process and method of steel drums:

First, the choice of glue bonding for steel barrel repair

To choose a reasonable and appropriate adhesive bond, we should first understand the properties and characteristics of the adhesive. In general, the adhesives we use to bond steel drums are synthetic adhesives. Synthetic adhesives can be divided into chemical reaction type and physical solidification type, or they can be classified into thermosetting and thermoplastic according to their state at different temperatures. Once the former is cured, it will not dissolve or melt, forming a cross-linked network structure; the latter will become soft with increasing temperature, when the temperature is higher than the temperature of a certain material (such as crystallization temperature or The glass transition temperature), they are able to flow viscously, and once the temperature is lowered, they re-solidify. Thermoset adhesives are generally chemically reactive, while thermoplastic or thermoset adhesives are generally chemically reactive, while thermoplastic or hot melt adhesives are generally physically solidified.

Thermosetting adhesives have higher strength and stiffness and less tendency to creep. Thermoplastic adhesives have greater plasticity and toughness and better fatigue properties.

Depending on the characteristics of the adhesive and the environment in which the steel drum is used, we usually use an epoxy resin glue called epoxy glue as a repairing adhesive for steel drums.

Epoxy adhesive has high bonding strength, good processing performance, convenient preparation and use, small volume shrinkage after curing, stable product size, wide temperature range, and no toxicity to human body. Epoxy adhesives of various grades are not only commercially available, but also can be formulated by themselves or modified as needed. Therefore, epoxy adhesives are called "universal adhesives".

Second, the surface treatment before the steel barrel repair

Before the steel drum is bonded, the most important point different from the welding is that the surface of the steel drum to be bonded has a certain degree of roughness and cleanliness, and also requires a certain chemical or physical reactivity on the surface of the bonded steel drum. In order to ensure the bonding quality of the steel drum. Therefore, the cleaning and surface activation treatment of the surface of the steel drum must be carried out before the bonding, which is collectively referred to as the pretreatment of the surface of the steel drum.

The common process for surface treatment of steel drums is as follows:

Solvent, lye or ultrasonic bath degreasing

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Machining, grinding, polishing, sandblasting

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Chemical corrosion treatment and anodizing

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Coating primer treatment, etc.

The following points should be considered when performing the surface treatment of steel drums:

1. The surface of the steel drum is contaminated, including the thickness of the contaminated layer, the tightness of the contaminated layer, and the type and nature of the surface pollutant. For example, the surface of the steel drum is painted, electroplated or mineral, vegetable oil, and the like.

2, the performance requirements of the bonding structure, such as short-term requirements do not leak, that is, emergency treatment or long-term non-leakage, after the leakage of the steel drums are all treated with this method, it is required to reach the level of the new steel drum.

3. The economics and necessity of the materials used. That is, the type of surface of the bonded steel drum (paint bucket, plating bucket, galvanized bucket or cold white bucket), the type of adhesive, the performance requirements and the surface treatment process should find the best economical one. The compromise point.

In general, the following methods are commonly used in the surface treatment of steel drums:

Degreasing liquid: trichloroethylene or gasoline

Treatment liquid: orthophosphoric acid (85%): ethanol = 1:2 (weight ratio)

Treatment method: 1, solvent degreasing

2, medium coarse sand cloth hair

3. Soak in the treatment solution at 60 ° C for 10 min, then use a nylon brush to wash the surface contamination in the running water, rinse with distilled water, and dry in air at 120 ° C for 1 hour.

This method is most effective for surface treatment of steel drums that are not sprayed.

Third, the steel barrel repair bonding process

The general contents and procedures of the steel barrel repair bonding process are as follows:

Surface treatment of leakage parts of steel drums

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Applying adhesive to the surface of the treated steel drum

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Curing

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test

Steel pipe leakage is generally done by manual construction bonding. The following points should be mastered when hand bonding:

1. Select the appropriate glue application such as brush, spray gun or injection needle according to the type and nature of the adhesive. The glue should be even and free of air bubbles, and the thickness of the film should be within 0.2~0.5mm.

2. After the glue is applied, the open time should be controlled within the allowable opening time of the adhesive. At the same time, the open film should be prevented from adsorbing dust or being contaminated. This requires that the amount of adhesive should be appropriate each time. Otherwise, it will not be used and will not be used after the reaction.

3, the correct choice of curing parameters

The curing process of the adhesive is a chemical melon process, and it is important to properly select the curing process parameters. The theoretical basis for controlling the chemical reaction type adhesive curing process is chemical reaction kinetics, and the basic parameters are reaction time, reaction temperature, opening time and the like. The impact is as follows:

1 reaction time

When the temperature of a chemical reaction is constant, the concentration ratio of each component of the reactants in the system will change as the reaction time increases. At the beginning of the reaction, the concentration of each component of the reactants is the highest, and the reactivity of the system is the largest, so the reaction rate is the fastest. As the reaction time increases, the reaction rate decreases exponentially; at the final stage of the reaction, the reaction rate is very slow, and the cohesive strength of the adhesive is basically established. Therefore, when the reaction is generally considered to be about 90%, Curing is complete.

2 reaction temperature

Temperature is the most sensitive parameter affecting the chemical reaction rate. Generally speaking, for every 10 °C increase in reaction temperature, the reaction rate is increased by about one time. In addition, the temperature of the reaction product will also affect the structure and properties of the reaction product (such as the degree of crosslinking, Cohesive strength and adhesion strength, etc.).

Many adhesives have a wide range of reaction temperature adjustments, so the desired mechanical properties can be achieved by adjusting the temperature parameters of the curing reaction.

3 opening hours

The opening time is the continuation of the time during which the components of the adhesive are uniformly mixed until the mixture can no longer be used, ie the maximum time allowed to remain in the air after the adhesive is dispensed. The length of the opening time depends on the curing reaction rate of the adhesive system. Generally speaking, the faster the curing reaction speed of the adhesive, the shorter the opening time. In actual work, the opening time can be determined by measuring the gelation time of the adhesive, or by continuously stirring the adhesive and judging the degree of curing by experience, thereby roughly determining the opening time. In order to ensure the performance of the adhesive, it is best to use it in principle, and how much to use.

Fourth, the quality inspection after the steel barrel repair

The mechanical properties of the steel drum after repair and bonding shall be tested, inspected and analyzed in accordance with national standards or relevant international standards. The basic test content of structural bonding is the tensile strength, peel strength, impact strength, tensile strength of the joint, and uneven tear strength of the single-sided lap bonded sample. The most important of these is the test of tensile shear strength.

The national standard GB7124-86 specifies the tensile shear strength test of metal and metal single-sided lap joints. This standard can be used to test the strength of the steel drum after bonding repair.