Performance and Improvement of Filled Wax-Wax Mold for Precision Casting

2022-08-11 10:50:00 353

Investment wax is a kind of mixed wax, which can be customized according to specific properties to meet the market demand. Nowadays, the market demand has changed, and the larger and more complex castings make the traditional unfilled wax unable to meet the requirements. Wax filling will lead the wax manufacturing technology and shell manufacturing technology. The wax filled shell has low shrinkage, low settlement rate, firm shell, stable size and fast manufacturing time. This report will make an in-depth study on the properties of filled wax.


In the initial stage of lost wax precision casting, unfilled wax was used, natural wax was used first, and then synthetic materials were used. With the appearance of the later mold, the unfilled wax can't meet the requirements, so the filled wax is used.


Adding special materials to filled wax can improve the performance of wax and solve the problems caused by unfilled wax. The filler is not affected by wax raw materials and operating temperature. Filling wax can effectively reduce linear shrinkage and sedimentation rate.


Over the years, many different types of fillers have been developed and applied. Now let's take a look at the commonly used filler XLPS (Crosslinked Polystyrene). The material has strong thermal stability in wax base, low ash content and similar density, which helps to reduce sedimentation, does not affect the surface smoothness of wax, reduces cost and improves production efficiency. Therefore, when using fillers, we tested how to affect wax and wax molds, and the results are as follows:


Experimental wax


Add 20% filler. For comparison, we also added 40% filler to the same wax base. The test results of two wax samples are as follows.

physical property


Include indicators.


Filler content


ash


viscosity


Cone penetration (temperature 25℃, 100℃ G, 5 seconds)


condensation point


drop point


Wax mold size analysis


Under the same conditions, the same waxing tools are used for the three mixtures on the same machine. The test piece used is a test piece. "German specimen" is designed by Germany. It has been widely used in standard test design throughout Europe.


physical property 

Inspection method

Wax base

20% filled wax sample

40% filled wax sample

Viscosity @ 100 ℃

93

180

630

Viscosity @ 90 ℃

143

270

885

Viscosity @ 80 ℃

233

402

1400

softening point

68.3

69

68.5

Dropping point

67

67

68

freezing point

65

65

64

Cone penetration @ 25 ℃

7.0

6.5

5.5

Filler content

0

19.7

40.1

ash content

0.005

0.012

0.012

The dropping point may be different due to different test methods. The freezing point is consistent, so we can say that it is not affected by the filler added.

As expected, the wax becomes stronger with the addition of filler.

The effect of filler on viscosity. The test results clearly show that the more fillers are added, the higher the viscosity. This experiment did not test the influence of different types or sizes of fillers after adding wax base, but we can infer that the better the filler added, the greater the influence on viscosity. The smaller the filler particles, the greater the impact on the wax, and the higher the viscosity, because it can be completely integrated into the wax itself.

Wax viscosity is an important parameter of any mixed wax material, and also a very important feature of precision wax casting. If the viscosity is too high, the waxing machine will not wax, or the wax mold with poor surface finish will be produced. If the melt viscosity is too high, the waxing speed will be very slow, which may lead to shell cracking. For industries that only focus on the use of non filled waxes, the viscosity of the filled waxes we introduce will be shocking. Even so, filling wax can also produce high-quality wax models. Most waxing temperatures are between 50-70 degrees. Within this temperature range, the viscosity will reach a peak. The change of wax casting at different waxing temperatures will not be repeated here., Very low ash content is also the result of our pursuit. The ash content of wax base and filler is very low, so this kind of filler wax is used for very sensitive alloy casting, such as titanium casting.

Size change

Experimental wax

40oC

67oC

100oC

Wax base

2.06


7.81


10.77

20% filling wax

1.61


6.46


8.90

40% filling wax

1.50


5.35


7.36

It can be seen from the above results that the filler significantly reduces the expansion rate of wax. The wax filled with 20% wax decreased by 17%. 3%, and the expansion rate at 100 ℃ was only 13%. 8%. At 67 ℃, the wax filled with 40% wax decreased by 31%. 7 At 100 ℃, the wax filled with 40% wax decreased by 29 ℃. 5%.

Here we take 67 ℃ as the test temperature, and the same wax injection temperature is 67 ℃. This clearly shows that the shrinkage of 40% wax is reduced by 30%, which can effectively help the foundry to produce products with higher precision. At the same time, the shrinkage at 100 ℃ is reduced by 30%, which greatly reduces the problems of shell cracking caused by excessive pressure during shelling.

Wax injection test

Operate the wax injection machine according to the following parameters to make 10 wax molds.

Temperature 66 ℃

Pressure 320psi

Time 100 seconds

Hold time 60 seconds

Other indicators remain unchanged

Table 3 Linear shrinkage%

Mixed wax

A

B

C

D

E

F

Wax base

0.55


0.76


0.51


1.43


7.22


4.84

20% filling

0.62


0.81


0.49


1.19


4.70


2.38

40% fill

0.63


0.80


0.38


1.06


2.57


1.43

Table 4 Standard Deviation of Linear Shrinkage and Settlement

Mixed wax

A

B

C

D

E

F

Wax base

0.042


0.028


0.023


0.052


0.078


0.184

20% filling

0.029


0.019


0.026


0.057


0.032


0.133

40% fill

0.014


0.012


0.016


0.039


0.015


0.127

As the filler particles are very fine, avoid freezing liquid wax at the wax gate. All wax samples were injected under the same conditions at a temperature close to their freezing point. Under the same conditions, the surface viscosity of wax is high, so there is only a small amount of wax left in the mold. Under certain conditions, the effect of increasing the number of fillers on the linear shrinkage is also interesting.

It should be noted that all these waxes are injected under the same conditions. Results obtained from each wax sample. In this case, the results are only comparisons.

Many factors determine the change of shrinkage rate, such as temperature, time, pressure, waxing machine quality, gate size and location, etc.

The linear shrinkage deviation of filled wax is much smaller than that of unfilled wax. The slight difference is due to the failure to reach the wax state.

mechanical property 

The size of wax rod is not 9x9x90, and the data is shown in Table 5

Mixed wax

load

Fracture (%)

Elastic modulus (N/mm2)

Unfilled

68.5

-----

322

20% filling

65.6

108.8

400

40% fill

67.9

44.9

521

The addition of filler has a significant effect on the mechanical properties of wax. Adding filler can reduce the flexibility and elasticity of wax. The load has not changed much. These results show that the addition of filler can enhance the toughness of wax, reduce bending and softness. The addition of filler has a great influence on the mechanical properties of wax.

Surface finish

The surface finish of both waxes is very good, which is acceptable. Although the surface of non filled wax looks better than that of filled wax, it is acceptable.

Practicability of filling wax

If the foundry considers using filler wax, but only has experience in using non filler wax, the following matters should be noted. Liquid filled wax requires constant agitation. If mixing stops, the filler will sink to the bottom; In most cases, even if it sinks, it can be remixed evenly, but it takes a long time. At the same time, the size and horsepower of the mixer shall be suitable for the container for wax storage. The foundry will also consider wax compatibility, such as

Can I use both waxes at the same time? If its mechanical properties are sufficient to handle strict control procedures, they can be mixed.

Can the filling wax be reused? Of course, once the mold is dewaxed, the old wax can be sent back. We can recycle and supply filled or unfilled wax according to customer requirements.

Can filled wax and unfilled wax be shelled together? Yes, yes. The two waxes can also be recycled and supplied separately when mixed together.

What changes should be made in the system when using filler wax? No, the filling wax can be used in the existing shell making system.

Will my casting size change? As we introduced, the shrinkage of filled wax is different from that of unfilled wax.


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