1、BRITISH STANDARD BS1902-10.1: 1993 Methods of testing Refractory materials Part10: Investment casting shell mould systems Section10.1 Determination of resistance to deformation at elevated temperaturesBS1902-10.1:1993 This British Standard, having been prepared under the directionof the Refractory P
2、roducts Standards Policy Committee, was published underthe authority of the Standards Board and comesintoeffect on 15 May1993 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference RPM/1 Draft for comment92/36027DC ISBN 0 580 21650 0 Committees responsible
3、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 the following bodies were represented: British Ceramic Research Ltd. British Industrial Ceramic Manufacturers Associ
4、ation British Steel Industry Refractories Association of Great Britain Refractory Contractors Association Society of Glass Technology The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Investment Casting Trade Association Department
5、of Trade and Industry (National Engineering Laboratory) Institute of British Foundrymen Amendments issued since publication Amd. No. Date CommentsBS1902-10.1:1993 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Apparatus 1 4 Test pieces 2 5
6、 Procedure 3 6 Draw back procedure 3 7 Calculation of results 3 8 Test report 6 Annex A (normative) Measurement of temperature distribution in thetestpiece 7 Annex B (normative) Calculation of stress/strain and load-bearing capacity/deflection 7 Annex C (normative) Presentation of results 8 Annex D
7、(normative) Calculation of standard deviation 8 Annex E (informative) Presentation of results 8 Figure 1 Test piece, showing application and bearing edges 2 Figure 2 Pattern for test piece 4 Figure 3 Load/deflection curve 5 Table 1 Stabilization times at typical test temperatures 3 Table C.1 Example
8、 of stress 8 Table C.2 Example of load/deflection 8BS1902-10.1:1993 ii BSI 08-1999 Foreword This Section of BS1902-10has been prepared under the direction of the Refractory Products Standards Policy Committee. It is one of a series of three covering the testing of investment casting shell mould syst
9、ems, as follows: Section10.1:Determination of resistance to deformation at elevated temperatures; Section10.2:Determination of permeability and standard air flow capacity at elevated temperatures; Section10.3:Determination of thermal profile. A British Standard does not purport to include all the ne
10、cessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pag
11、es1 to8 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS1902-10.1:1993 BSI 08-1999 1 1 Scope This Section of BS1902-10describes a method for determining the resis
12、tance to deformation under constant loading rate, at elevated temperatures, of investment casting shell mould systems, thus providing a meaningful measurement of shell mould performance during casting operations. The test is applicable to all types of refractory shell moulds used in the investment c
13、asting industry. 2 Principle The test is designed to measure the hot deformation resistance of shell mould systems at relatively low levels of strain and is not therefore a test to failure. The resistance to hot deformation of a shell mould is a measure of its ability to resist shell mould wall move
14、ment at low strain levels at high temperature. Consequently two strain values are selected as the criteria for comparison:0.075% and0.25% strain. The stress levels at these strain values are thus ascertained from the test. This test essentially measures the intrinsic strength of the shell mould and
15、the result is not dependent on the mould thickness, which can vary considerably from operation to operation depending on the application. Thus materials for making shells, including binders, fillers and stuccos, can be readily compared. However, the test procedure also determines the load-bearing ca
16、pacity of the shell mould, which does depend on the mould thickness. Again this is determined at two levels of deformation. Two deflection levels are selected at0.2mm and0.5mm. Thus for the same composition of shell mould, the influence of the number of shell coats, as related to shell thickness, ma
17、y be discerned in relation to the ability to resist shell mould wall movement. Test pieces cut from an investment casting shell mould are placed on a test fixture located within a furnace which is already at a designated test temperature. After the test pieces have stabilized at the test temperature
18、, they are loaded at a constant rate until the higher of the two strain values is passed. If the test piece fractures before the upper strain level is reached, then the test stops and the lower strain level is utilized. During the test the load and deflection values are continuously recorded, allowi
19、ng an accurate characterization of the ability of the shell material to resist deformation under load at high temperature. 3 Apparatus 3.1 Test fixture, having two fixed lower bearing edges to support the test piece (the support bearing edges), and one moveable upper bearing edge for the application
20、 of the load (the load application edge). The three bearing edges shall be parallel to each other. The distance between the support bearing edges shall be76mm 1mm (see Figure 1), and the load application edge shall be placed centrally between them with an accuracy of2mm. These distances shall have b
21、een measured at room temperature to an accuracy of 0.5mm. The bearing edges shall have a radius of curvature of2.75mm 0.5mm and a length no less than25mm (see Figure 1). It shall be capable of applying a load (via the load application edge) normal to, and uniformly across, the centre of the test pie
22、ce and of increasing this load at a constant rate of5kg/min. NOTEThe bearing edges should be examined periodically (e.g.yearly) and replaced if they become flattened. 3.2 Load measuring system, capable of measuring the load throughout the test with a minimum accuracy of 5%, and calibrated over the f
23、ull range of the system at intervals of20% of full scale deflection. The interval of calibration shall not exceed10test batches or a period of3 months, whichever is the shorter (see4.1). 3.3 Deflection measuring system, capable of measuring the deflection of the test piece under load with a minimum
24、accuracy of5% within the range0mm to5mm, and calibrated over the full range of the system at intervals of1mm. The interval of calibration shall not exceed10 batches or a period of3months, whichever is the shorter (see4.1). 3.4 Furnace, capable of providing the overall heating of both the test fixtur
25、e and the test piece, and designed so that during the test no part of the test piece shall fall outside 10K of the test temperature (see Annex A). The atmosphere in the furnace shall normally be air. The use of a different atmosphere shall be stated in the test report. 3.5 Temperature measuring devi
26、ce, consisting of a calibrated thermocouple in the immediate proximity of the midpoint of the tensile face of the test piece (see Annex A). BS1902-10.1:1993 2 BSI 08-1999 4 Test pieces 4.1 Number of test pieces Test pieces shall be tested in batches. One batch shall consist of a number of test piece
27、s from the particular shell mould system to be assessed. The minimum number of test pieces in a batch shall be either: a) for a comparison between different shell systems, for example, to assess two or more shell systems, not less than10test pieces for any given temperature; or b) for the repeated a
28、ssessment of the same shell, for example, as an aid to quality control, not less than three test pieces for any given temperature. 4.2 Shape and size Test pieces shall be of rectangular or square cross section with a maximum thickness of18mm (thisdimension being dictated by the thickness of the shel
29、l mould to be tested), a width between10mm and18mm and a minimum length of85mm (seeFigure 1). NOTE 1The test pieces used are cut from manufactured investment casting shell moulds; they are not machined specimens. It is impossible therefore to give precise tolerances for the parallelism or taper in t
30、he test piece. As a general recommendation, the width and thickness of the test piece, should not vary by more than1mm along the length and the thickness of the test piece should not vary by more than1mm across the width. NOTE 2For ease of location in the test fixture, it is recommended that the wid
31、th of test piece is not less than the thickness. Figure 1 Test piece, showing application and bearing edgesBS1902-10.1:1993 BSI 08-1999 3 4.3 Preparation Test pieces shall be cut from flat sections of shell mould material of appropriate dimensions. NOTE 1An example of a suitable test piece pattern i
32、s given in Figure 2. The shell moulds shall have been produced in accordance with normal investment casting procedures. For an example of the relevant part of the process, see note2. The procedure used for producing the test pieces shall be reported and shall include details of the pattern used, how
33、 the shell is removed from the pattern, and the grinding or cutting method used. NOTE 2A wax pattern is produced from liquid wax being injected into a suitable closed die within which a perspex plate forms a central core. On solidification the pattern, now a thin uniform layer of wax covering the pe
34、rspex plate (see Figure 2), is removed from the die ready for investing. Investing involves successive dipping and stuccoing operations on the wax pattern until a sufficiently thick shell has been built up on the wax pattern. In this case, the test pattern is shelled up to the top of the wax using t
35、he desired investment casting shell moulding procedure. Typically, dipping involves submersing the pattern (or pattern assembly with more than one pattern) in a ceramic slurry, whilst stuccoing involves immersing the still-wet shell mould in either a fluid bed or a rainsander containing certain grad
36、es of refractory powder. After drying, the three narrow outer edges of the mould sample are cut off leaving two flat plate samples from which the test strips are cut. The perspex plate(s) can be re-used. NOTE 3Test pieces may be given a preliminary treatment prior to testing. The temperature and dur
37、ation of this heat treatment should be decided by the parties concerned and reported (seeclause8 f). 5 Procedure 5.1 Data collection Choose suitable scales for load and deflection for each test batch, such that the maximum readings taken during any single test exceed20% of full scale deflection. If
38、a computerized data logging system is used, select a sampling rate such that a minimum of50sets of readings are recorded for any single test. NOTEIf the test batch is of a shell system that has not previously been characterized, one or two samples should be tested first, prior to the actual test, to
39、 establish suitable scales and sampling rates for the recording device(s). 5.2 Heating With the furnace at test temperature place the test piece centrally on the support bearing edges with the inner mould surface (primary coat) uppermost. Allow the test piece time to stabilize at the test temperatur
40、e. NOTEA number of factors such as shell mould material, test piece dimensions and furnace temperature can result in slight variations in the time taken for the test piece to stabilize at the test temperature. It is not feasible however to determine the exact stabilization period for each test piece
41、. The times given in Table 1 are recommended at these typical test temperatures (based on a zircon/molochite shell13mm thick and14mm wide). Table 1 Stabilization times at typical testtemperatures 5.3 Loading Immediately the stabilization period has elapsed, apply the load to the test piece, at a con
42、stant rate of5kg/min, until either failure, or a deflection level greater than that equating to0.25% strain, is reached. 5.4 Measurement of shells At room temperature, measure the width and thickness of the test piece or broken section under the load application edge using a ball-nose micrometer acc
43、urate to0.01mm. NOTEThe ball-nose micrometer should have balls at the end of its spindle and on its mating face. A micrometer with a ball radius between2mm and 3.5mm is recommended. Record at least one measurement of width and three measurements of thickness. Calculate the average value of thickness
44、 and width from these results. 6 Draw back procedure Because of the uneven nature of the outer mould surface of the test piece, there can be a certain amount of “bedding in” as the load is applied at the start of the test. This is reflected in the load/deflection graph recorded during the test. If t
45、his effect occurs, extrapolate accurately from the curve back to the deflection axis to get a true value of zero (see Figure 3). If necessary, carry out this operation before taking any results from the graph. 7 Calculation of results Calculate the stress/strain and load-bearing capacity/deflection
46、in accordance with Annex B. Temperature C Stabilization time min 700 1200 1450 9 6 5BS 1902-10.1:1993 4 BSI 08-1999 NOTEThe test piece pattern is shelled-up to the top of the wax. After drying, the three narrow outer edges of the mould sample are cut off leaving two flat plate samples from which the
47、 test strips are cut. The perspex plate(s) can be re-used. Figure 2 Pattern for test pieceBS 1902-10.1:1993 BSI 08-1999 5 NOTEAll readings of load and deflection should be taken with reference to true zero. Figure 3 Load/deflection curveBS1902-10.1:1993 6 BSI 08-1999 8 Test report The test report sh
48、all include the following information. a) The name of the testing establishment. b) The date of test. c) A reference to this method of test, i.e.determined in accordance with BS1902-10.1. d) The designation of shell material(s) tested (manufacturer, type). e) The number of test pieces per material.
49、f) The procedure used for producing the test pieces. g) Any pre-heat treatment given to the samples. h) The distance between supports. i) The time that the test pieces were held in the furnace prior to testing. j) The test temperature and any use of atmospheres other than air. k) Tables of results of stress (at0.075% and0.25% strain) which give values for each individual test piece (see Annex C) and the mean value and standard deviation (see Annex D), with results quoted to two decimal places. l) Tables of results of load-bearing capac
