BS 1902-10 2-1994 Methods of testing refractory materials - Investment casting shell mould systems - Determination of permeability and standard air flow capacity at elevated temper.pdf

1、BRITISH STANDARD BS 1902-10.2: 1994 Incorporating Technical Corrigendum No. 1 Methods of testing Refractory materials Part 10: Investment casting shell mould systems Section 10.2: Determination of permeability and standard air flow capacity at elevated temperatures UDC 666.76.017:539.217:621.744.56

2、BS 1902-10.2:1994 This British Standard, having been prepared under the direction of the Refractory Products Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 March 1994 BSI 15 July 2003 The following BSI references relate to the work on

3、 this standard: Committee reference RPM/1 Draft for comment 93/301276 DC ISBN 0 580 22773 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Refractory Products Standards Policy Committee (RPM/-) to Technical Committee RPM/1, upon which t

4、he following bodies were represented: British Ceramic Research Ltd. British Industrial Ceramic Manufacturers Association British Steel Industry Refractories Association of Great Britain Refractory Contractors Association Society of Glass Technology The following bodies were also represented in the d

5、rafting of the standard, through subcommittees and panels: British Investment Casting Trade Association Department of Trade and Industry (National Engineering Laboratory) Institute of British Foundrymen Amendments issued since publication Amd. No. Date Comments 14426 Technical Corrigendum No. 1 15 J

6、uly 2003 Change to Clause 10.1BS 1902-10.2:1994 BSI 15 July 2003 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Definitions 1 3 Principle 1 4 Apparatus 1 5 Number and form of test pieces 6 6 Test procedure 7 7 Shell characterization: procedure A 7 8 Production/q

7、uality control procedure on a fired shell: procedure B 9 9 Production/quality control procedure on an unfired shell: procedure C 9 10 Calculation of results 10 11 Test report 11 Annex A (informative) Alternative calculation methods 12 Annex B (informative) Convention for tabular presentation of resu

8、lts 12 Annex C (informative) Convention of graphical presentation 13 Figure 1 Configuration of test equipment 2 Figure 2 Pressure-tight thermocouple/T-piece adaptor for thermocouple entry into air-stream 3 Figure 3 Detail of T-piece 4 Figure 4 Location of test piece 5 Figure 5 Sample former 7 Figure

9、 6 Four sample diameter measurement points 8 Figure C.1 Example of graphical presentation 14 Table 1 Test procedure: possible options 7 Table B.1 Temperature ramp phase 12 Table B.2 Temperature dwell phase at 1 200 C1 3BS 1902-10.2:1994 ii BSI 15 July 2003 Foreword This Section of BS 1902-10 has bee

10、n prepared under the direction of the Refractory Products Standards Policy Committee. It is one of two Sections covering the testing of investment casting shell mould systems, as follows. Section 10.1: Determination of resistance to deformation at elevated temperatures; Section 10.2: Determination o

11、f permeability and standard air flow capacity at elevated temperatures. To ensure the quality of castings manufactured by the investment casting process, the moulds used should have sufficient air flow capacity to obtain complete mould fill during casting. As the metal is poured into the mould, entr

12、apped air will be expelled through the mould walls to be replaced by the molten metal. Low air flow capacity will restrict this action and may result in incomplete filling of the mould. The significance of the values of standard air flow capacity (which is dependent on mould thickness) and permeabil

13、ity (which is independent of mould thickness) on the quality of the final casting will vary depending on, for example, the geometry of the mould, the temperature of the metal, the metalostatic head and the alloy to be cast. Generally speaking, the higher the standard air flow capacity and permeabili

14、ty the better, as long as other mould properties such as resistance to deformation are not adversely affected. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of it

15、self confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 14, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 1902-10

16、.2:1994 BSI 15 July 2003 1 1 Scope This Section of BS 1902-10 describes a method for determining the standard air flow capacity of investment casting shell moulds, and the inherent permeability of the shell material, at elevated temperatures. 2 Definitions For the purposes of this Section of BS 1902

17、-10 the following definitions apply. 2.1 permeability a measure of the ability of a material to allow air to pass through it which is the ratio of volumetric flowrate to the pressure gradient causing flow, at a given temperature NOTE 1 The value calculated is corrected for the viscosity of air and t

18、he geometry of the test piece. NOTE 2 This definition of permeability covers any fluid, but it is assumed that, in the context of investment casting, this fluid will predominantly be air. 2.2 air flow capacity a measure of the volumetric flowrate of air passing through a given shell mould at a given

19、 temperature 2.3 standard air flow capacity (SAF) a measure of the volumetric flowrate of air passing through a standard shell mould at a fixed gauge pressure of 10 kN/m 2(1.45 psig) at a given temperature 3 Principle The apparatus records the flow of air through a shell mould sample of known dimens

20、ions under a known pressure difference and at a given temperature. This information is used to calculate the permeability and the standard air flow capacity of the shell mould in question. 4 Apparatus 4.1 Test equipment, as shown in outline in Figure 1. NOTE If the pressure drop across the flow sens

21、or is very low the pressure regulator may be mounted before the flow sensor. This reconfiguration is acceptable because it does not have a significant effect on the regulation of air pressure at the test piece. 4.2 Air supply, which shall be clean and dry. The length of the pipework between the pres

22、sure regulator and the test piece shall be no more than 1 m, and the pipework shall have a bore of no less than 4 mm. NOTE This will minimize any drop in the regulated pressure up to the test piece. 4.3 Pressure regulator, capable of supplying regulated pressures in the range of 6.9 kN/m 2to 34.5 kN

23、/m 2 . The regulator shall be capable of maintaining a selected pressure to 3.5 kN/m 2throughout the period of the test. NOTE Pressure regulators are normally supplied in the UK with measuring scales graduated in pounds per square inch (psi). 1 psi = 6.9 kN/m 2 . 4.4 Thermal mass flow sensor, coveri

24、ng the range 0 ml/min to 2 000 ml/min. The sensor shall be accurate to 1 % of full scale deflection but shall not be used in any part of the range where the accuracy is less than 5 % of the true reading (this may prohibit the use of the sensor near the bottom of its range). NOTE 1 Certain materials

25、of low air flow capacity may require the use of a thermal mass flow sensor with a range of 0 ml/min to 1 000 ml/min as this may give better accuracy. NOTE 2 Flow rates of higher than 2 000 ml/min are not suitable for this type of test as chilling of the test piece can occur. 4.5 Pressure sensor, cap

26、able of covering the range 6.9 kN/m 2to 34.5 kN/m 2with an accuracy of 1 % of full scale deflection but shall not be used in any part of the range where the accuracy is less than 5 % of the true reading (this may rule out using the sensor near the bottom of its range). NOTE The pressure sensor shoul

27、d be connected close to the test piece to minimize any pressure drop between the test piece and the sensor.BS 1902-10.2:1994 2 BSI 15 July 2003 4.6 Test piece temperature indication, comprising the combined test piece thermocouple and indicator required to record the test piece temperature which sha

28、ll be accurate to 5 C. It shall be insulated in a sheath of nominal diameter 3.0 mm. The thermocouple and sheathing shall be sealed at the cold end to ensure there are no leaks from the system via the bore of the thermocouple sheathing. NOTE A suggested method of inserting the thermocouple into the

29、sample without causing any leakage from the equipment is shown in Figure 2 and Figure 3. 4.7 Programmable control furnace, capable of accurate temperature control as the time a test piece spends at elevated temperature is critical to the test results. The following conditions shall be met. a) The fu

30、rnace thermocouple, which is separate from the test piece thermocouple, and the temperature indicator shall have a combined accuracy of 5 C. The thermocouple shall be located as close as possible to the middle of the outer surface of the shell mould. b) The furnace shall be capable of applying a con

31、trolled heating rate of 20 C/min up to the given test temperature. When ramping up to the test temperature, above 500 C the furnace control shall be such that the furnace set point and indicated furnace temperature shall not differ by more than 5 C. c) On reaching a temperature dwell phase the indic

32、ated furnace temperature shall not overshoot the set point temperature by more than 5 C, after which the two values shall not differ by more than an indicated 2 C. The test piece shall be located in the furnace such that a minimum of 150 mm of the test piece (measured from the middle of the mould up

33、wards) shall be exposed to the furnace elements (see Figure 4). Figure 1 Configuration of test equipmentBS 1902-10.2:1994 BSI 15 July 2003 3 Figure 2 Pressure-tight thermocouple/T-piece adaptor for thermocouple entry into air-streamBS 1902-10.2:1994 4 BSI 15 July 2003 Figure 3 Detail of T-pieceBS 19

34、02-10.2:1994 BSI 15 July 2003 5 NOTE Dimension is in millimetres. Figure 4 Location of test pieceBS 1902-10.2:1994 6 BSI 15 July 2003 5 Number and form of test pieces 5.1 Number For the purpose of assessing any shell system at least two test pieces shall be tested and the results averaged. If two te

35、st pieces only are tested, and the permeability differs by more than 10 % under the agreed conditions, then further test pieces shall be tested until any two results differ by less than 10 %. Where there is no obvious fault in any test piece, such as cracking, then the result presented shall be the

36、average of all the individual test results. The number of test pieces tested, and the reason for testing that particular number, shall be noted in the test report. 5.2 Test piece former 5.2.1 General The test piece former shall be manufactured as indicated in Figure 5. The tube shall penetrate the h

37、ollow plastics ball by between 5 mm and 20 mm. A small fillet of wax shall be used to bond the tube to the ball and to act as a sealant. The amount of wax used shall be kept to a minimum and have as smooth a surface as possible. 5.2.2 Tube material and dimensions The tube material shall be non-porou

38、s, capable of withstanding the test temperature without support and possess a thermal expansion coefficient similar to that of the shell mould. NOTE 1 Impervious mullite is recommended. The tube dimensions shall be between 6 mm and 7 mm internal diameter and 10 mm outer diameter. The length of tube

39、required will vary depending on how the apparatus is arranged, but it should be long enough to conform to 4.7. NOTE 2 Thermal expansion incompatibility between tube and shell may cause cracking of the shell and invalidate the test result. 5.2.3 Hollow plastics ball The ball shall be an International

40、 Table Tennis Federation (I.T.T.F.) approved 3 star table tennis ball. Balls which qualify for I.T.T.F. approval have a diameter no less than 37.2 mm and no greater than 38.2 mm. The mean ball diameter lies between 37.4 mm and 38 mm. For the purposes of this test the ball diameter shall be assumed t

41、o be 37.7 mm. NOTE Some additives to the slurry bath may attack the table tennis ball. If this occurs the test is invalid and wax may be used instead of the table tennis ball, although this may entail the construction of a special die with ensuing extra cost. In addition, it may prove difficult to c

42、ompletely drain the wax from the shell mould. If wax is used, however, it should be removed from the test piece following the normal de-waxing procedure for investment casting shell moulds and carefully inspected for cracks prior to testing. 5.3 Shelling Prior to shelling, the test piece former shal

43、l be degreased in the same manner, and with the same degreasants, as used for investment casting wax assemblies. The test piece former shall be shelled beyond the ball by between 25 mm and 75 mm along the length of the tube. 5.4 Burn-out Prior to testing, the test piece shall be burnt out at 700 C f

44、or 5 min to completely remove any trace of the table tennis ball. The test piece shall be placed in a furnace with a suitable extraction system at room temperature and heated at a rate of no more than 7 C/min. NOTE Rapid heating of the combined table tennis ball and shell mould test piece may cause

45、it to rupture.BS 1902-10.2:1994 BSI 15 July 2003 7 6 Test procedure The test can be either: a) a full characterization of a shell system by monitoring it as it is heated from room temperature through a simulated firing and casting cycle (procedure A); or b) as an aid to production/quality control, a

46、 simplified test which generates less information but allows test pieces to be analysed more quickly, which can be carried out on either fired (procedure B) or unfired (procedure C) material. Table 1 gives the possible options. Table 1 Test procedure: possible options 7 Shell characterization: proce

47、dure A 7.1 Measurement of shell test pieces Measure the test pieces using a knife-edge vernier calliper accurate to 0.02 mm. Record and average four readings, taken at approximately 45 intervals around the diameter of the test piece as shown in Figure 6. Calculate the thickness of the test piece by

48、subtracting 37.7 mm from the mean value and then dividing by two (see 5.2.3). NOTE As the surface of the test piece can be very irregular due to the nature of the process, care should be taken, where possible, to avoid including any unrepresentative peaks or troughs in the measurements. 7.2 Connecti

49、ng test piece to apparatus and performing leak checks 7.2.1 General Check 1 (see 7.2.2) shall be carried out before every test and check 2 (see 7.2.3) shall be carried out after 10 test runs or a period of 3 months, whichever is the sooner. NOTE Dimensions are in millimetres. Figure 5 Sample former Purpose of test Shell condition Procedure Shell characterization Unfired A Production/quality control Fired B Unfired CBS 1902-10.2:1994 8