SECTION 5 – DETERMINATION OF FILLER CONTENT OF FILLED WAXES
Scope
This method is used for the determination of filler content in filled waxes
Definition
Filled waxes are those pattern waxed with filler added to provide properties to the wax pattern to ensure strength, dimensional stability, lower thermal expansion, and minimal shrinkage
Summary of Method
The weighed wax sample is placed in a Buchner funnel along with a solvent. The wax is dissolved from the filler and separated from the filler through the filter by vacuum. The remaining material on the filter is the resultant filler
Safety
  • Organic materials may be irritant or cause sensitization. Materials should not be manually handled without gloves. Wash hands after contact.
  • This test involves Petroleum Distillate (Safsol, Toluene, Isopar C) skin contact should not occur.
  • Work area should be free of sources of ignition.
  • Hot plate is very hot and should be handled with care.
  • Solvents should be disposed of according to local disposal regulations
  • Filter cake may be disposed of to normal bin.
  • Safety glasses and lab coats must be worn at all times.
  • This test should be performed in fume cupboard with face shield at appropriate height.
Equipment and Materials
  • a. Top pan balance (reading to two decimal places)
  • b. 1 Buchner filter funnel - 11 cm internal diameter
  • c. 1 Buchner flask - 1000 ml capacity (see Figure 1)
  • d. No.1 filter paper
  • e. 500 ml of Safsol 2 (or a similar aliphatic hydrocarbon solvent)
  • f. Thermometer
  • g. Hot plate
  • h. Vacuum pump
  • i. Circulated oven @ 120°C (240 ˚F)
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Figure 1 - Buchner Flask
Procedure
  1. Record weight of the filter paper plus clean dry vessel, place the Buchner funnel in the oven to warm through. Note: Record all weights to two decimal places
  2. Break up the sample of casting wax into 1 cm diameter pieces. Weigh 50 g of the wax into a 1 liter can and add 250 ml of solvent.
  3. Place the can on the hot plate and, with continuous stirring, dissolve the waxy fraction. Raise the temperature of the can contents to 80°C.
  4. Heat 250 ml of solvent to 80C in the other can.
  5. Remove the hot filter funnel from the oven and connect to the vacuum pump. Vigorously stir the solvent/wax/filler mixture in the first can and pour it into the Buchner funnel.
  6. Quickly rinse out this can with a little hot solvent and pour the washings into the funnel. Use the remaining hot solvent to wash the filter cake then draw air through it for a few minutes to remove excess solvent.
  7. Disconnect the vacuum pump. Carefully transfer the filter cake and filter paper to a pre weighed clean, dry vessel and place in the oven at 120°C for 30 minutes to remove residual solvent.
  8. Cool the extracted filler and paper to room temperature and weigh. Determine the weight of filler by difference and express as a weight percentage of the initial sample of wax taken.
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Figure 2 - Buchner Funnel with filled wax & solvent
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Figure 3 - Buchner Funnel after filler separation
Reporting
Report the average from the two individual rings as the softening point, quoting to the nearest 0.1°C. Record sample ID, results and date in an appropriate fashion.
In general, discard a pair of results if they differ by more than 1.0°C and rerun the test with fresh samples.
Precision and Bias
According to ASTM E28-99 (2004), the following precision data might be expected from a resinous material having a 75°C softening point:
  • Repeatability limit, 95% (within laboratory): 0.8°C
  • Reproducibility limit, 95% (between laboratories): 5.9°C
Given the lack of accepted references, no bias statements appear to have been made for the determination of ring and ball softening point as described.
Considerations
The method described above is largely manual. Several automated ring and ball softening point systems are available. These appear to work well but are more expensive to procure and require regular calibration and maintenance.

Whichever test system is utilized, new users should be aware that considerable operator experience is necessary to generate consistent results that can be reliably compared with those from other established laboratories.
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