Chapter 2 The bonding of the white zone 2.6 model cluster.


2.6.1Assembly of the model

The quality of the bond directly affects the quality of the casting, such as dimensional accuracy and internal quality. If the adhesive used in the bonding process is not suitable, it will cause a large amount of gas and a large amount of residue after vaporization, which can cause defects such as pores and slag inclusion. Another example is that the EPC model is not firmly bonded or the gap at the joint is not filled with glue, and the coating will enter the gap during the coating dipping process, which will cause coating slag inclusion. Therefore, in order to ensure that the casting can obtain the ideal modeling quality, the white mold bonding process requires module bonding, it must have the characteristics of uniform gluing, accurate bonding size, high efficiency and convenient operation. There are two kinds of bonding methods: manual bonding and mechanical bonding.

At present, most of the domestic vanishable white mold bonding is manually bonded, with manual bonding, the advantage of artificial bonding is that the capital investment is low, the controllability is strong. The shortcomings are also obvious. The bonding quality mainly depends on the operation level of the workers. If the adhesive is applied unevenly, the pressing force is not enough, which will cause the bonding quality to be poor. Manual bonding still occupies a dominant position in the domestic lost matrix industry. There are many successful lost matrix sites. Next, I will introduce the detailed process to you.

For example, in Shanxi Tianzhu site, the casting is a pressure pipe fitting. The whole casting is composed of flange and elbow part, and the elbow part is divided into two modules, which need to be bonded and assembled after docking, as shown in the figure.2-1:

Figure 2-1MountainWest press pipe fittings

During the bonding process, the die shall be bonded and assembled into a complete model in strict accordance with the drawing size requirements. This model is selected for hot adhesive bonding. Notes in the bonding process are:

1、Pay attention to evenly apply the glue, and during the process of applying the adhesive, use the adhesive as little as possible, and the application area is at the inner and outer edges of the bonding area. The purpose of doing this is to reduce the amount of gas and reduce the gap at the bonding area;

2、If the bonded part is a complex box part, the application area is concentrated in the inner area, because the inner gap cannot be maintained and cannot be repaired, try to make the adhesive bond the inner gap tightly without any gap;

3、Because this piece is symmetrical, there is no special relative position requirement. If there are corresponding requirements, it is necessary to mark the two modules before bonding according to the mark.

4、After the adhesive is applied and bonded, it is necessary to check whether there are gaps in the adhesive bonding. If there is a gap at the connection, it can be treated separately according to the size of the gap. Generally, it is divided into adhesive coating and paper tape sticking. If adhesive coating is used, it is simple and convenient, but it will have the disadvantages of large gas emission and easy to cause slag inclusion defects. If paper tape is used, the workload is increased compared with that of adhesive, and the paper tape may fall off during the coating process. This method has good surface quality and small gas emission, casting defects should be few. After the model bonding at Shanxi Tianzhu site is completed, as shown in the figure2-2:

Figure 2-2Bonded finish model

After the white mold is bonded, it enters the yellow area to apply paint, and the paint application process will be explained later. General castings and gating system were painted, brushing is completed and then through the design of a good combination of gating system, gating system design will be described in detail in the black area process. In the bonding process of components and gating system, there will be some castings with large weight, and the ideal bonding strength may not be achieved by using adhesive alone. You can choose to use clean steel nails without rust to connect. After model bonding, paint brushing and gating system combination, the finished product is shown in the figure.2-3:

Figure 2-3Model cluster after group type completion

In the process of grouping, some models will have relatively strict relative position relationship, that is, there will be relatively strict size requirements on the drawings. For example, the anode steel claws produced on site in Heqing, Yunnan, are used for electrolytic aluminum in an aluminum factory. The size of the electrolytic tank is fixed, and the position requirements for each claw are relatively strict, so the position of the steel claws needs to be controlled during the bonding process, however, the controllability of artificial bonding is poor, and corresponding bonding tooling needs to be prepared. The bonding tooling of this white mold is to use square wood to make square partition grooves with corresponding spacing according to the spacing of steel claws specified on the drawing. When in use, the claws of the steel claws are put into the tooling, and then the shoulder of the steel claws is bonded to the claws to ensure accurate size requirements. As shown in the figure:

   

      Figure 2-4White die assembly                             Figure 2-5Position the completed white die assembly

Here is just an example to illustrate the importance of tooling in the process of white mold bonding. The production of tooling needs to be made according to different castings according to the corresponding size requirements. Other types of castings should be made with corresponding tooling to ensure their important position dimensions.

In addition to the tooling to ensure the position and size, there are also simple tooling to fix the module when cold glue is used for bonding. Such tooling fixes the module before the adhesive strength meets the requirements to prevent the module from moving relative to the position due to insufficient adhesive strength, resulting in deviation of position. This kind of tooling is relatively simple, divided into horizontal direction fixed and vertical direction fixed two types. The horizontal direction is generally selected with a widthThe rubber strip of about 10mm is wound and fixed. If the rubber strip is narrow, it will hurt the white mold. As shown in the following figure, it is a fixed horizontal tooling.

Figure 2-6Horizontal position fixing tooling

The vertical direction of the tooling, the general use of pressure block can be. For example, in the case of an anode steel claw, after the adhesive is applied to the shoulder, a metal compact can be placed on the shoulder to enhance the bonding strength.

There is also a very important link in the process of model cluster grouping. That is, the anti-deformation measures of the model. Because the white model type is different. Some simple parts can be directly buried after the completion of the box modeling, after the vibration casting, but there are also some models if you do not take anti-deformation measures in the vibration process, deformation phenomenon will occur, casting out of the finished product rate will be greatly reduced. Such castings are mainly thin-walled parts, box parts, flat parts, ring parts, for example, manhole covers, well rings, reducer housings, etc. Anti-deformation measures, that is, using wooden materials such as square wood or chopsticks (after pouring, it will burn without affecting the quality of the casting) to fix the deformed parts. The fixing method is shown in the following figure;

Figure 2-7Anti-deformation measures for manhole cover of sewer

According to the way the castings are buried, the anti-deformation measures will be different. The manhole cover of the sewer is cast horizontally, so the support is strengthened in the horizontal direction of the manhole cover to prevent the manhole cover from warping after vibrating. The manhole cover and manhole ring completed by horizontal casting are also shown in the following figure:

            

       Figure 2-8manhole cover                                   Figure 2-9Well ring

 

Figure 2-10Box burying process of well circle

Anti-deformation measures are not only applied to the model itself, but also need to be fixed between the model and the casting system in the molding process, because some gating systems use inner runner, the strength of the direct runner is not enough, and fracture phenomenon may occur in the vibrating process. If the gating system is broken, molten iron will involve the molding sand inside the casting during pouring, resulting in slag inclusion phenomenon, resulting in increased casting rejection rate. Common gating system fixed as shown in the figure below:

  Figure2-11 Anti-deformation measures for casting system

In addition, there are other anti-deformation measures for castings, as shown in the following figure:

   

Figure 2-12Other types of anti-deformation cases

The above is a more complex casting group, in addition to most of the castings with simple structure, such castings have not been internally bonded, and the volume is small, the group is more convenient, without taking anti-deformation measures, after the casting system is designed, as long as the casting and casting system are combined together, the buried box modeling operation can be carried out, as shown in the following figure:

Figure 1-13The mode of simple casting.

2.6.2Special adhesive for lost form

The above-mentioned introduction to the model is the bonding and group type of the model. Since it is necessary to bond, the adhesive is an indispensable and important consumable. As an important auxiliary material in the process of lost foam casting, the quality and effect of the adhesive will affect the quality of the casting. At present, the special adhesive for EPC bonding is divided into two types: hot glue and cold glue.

Considering the casting characteristics of the lost foam, the special binder for the lost foam shall meet the following requirements:

   1、Good quick-drying, and has a certain bond strength, so as not to damage the white mold during processing and handling;

   2、Moderate softening point, both to meet the process requirements, and convenient bonding operation;

   3、Decomposition, low gasification temperature, less residue after gasification;

   4、After drying, there is a certain degree of flexibility, rather than crisp hard rubber;

   5、Non-toxic or low toxicity, no corrosive effect on the white mold model.

Several common adhesives are as follows:

   a、White latex, which is water-soluble, was used more in the early manual molding. The bonding method is to apply the surface of the pattern and then fix it with tooling and send it to the drying room. The disadvantage is that the bonding strength is poor, the curing speed is slow, and the bonding strength must be obtained after the evaporation of water. Generally, a bonding cycle takes one day and night, and the work efficiency is poor, which has been basically eliminated;

   b、is abandonedEPS Foam Decomposition in Vinyl Acetate Monomer and Toluene MixingIn the solvent, an epoxy resin and.TDIAs a modifier, dioctyl ester was synthesized as plasticizer and cumene peroxide as initiator. It has strong bond strength, but it has certain corrosiveness to the white mold model, affects the quality of the white mold, and also has certain toxicity.

c,Lost vanish mold cold glue, the product is green water-soluble glue, with fine bonding assembly, small amount of gas, no carbon defects and other characteristics, applied to the bonding area of the larger white mold model, uniform coating, bonding model, bonding strength, is the use of a wide range of adhesives;Hot melt glue, the use of a wide range of hot melt glue stick, with the use of hot melt glue gun. It is applied to the white mold model with small bonding area, which is characterized by high bonding strength, high working efficiency and convenient operation.

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