1、Designation:D 796-87a 4sb Standard Practice for Compression Molding Test Specimens of Phenolic Molding Compounds This standard is issued under the fixed designation D 796;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of l
2、ast rzvision.A number in parentheses indicates the year of last reapproval.A superscript epsiion(c)indicates an editorial change since the last revision or reapproval.1.ScQpe 1.1 This practice describes procedures for compression molding of Izad or Charpy impact,flexure,tension,com-pression,water ab
3、sorption,modulus in tension or flexure,heat aging,electrical tests,and heat-deflection temperatures(Note).1.2 The values stated in SI units are to be regarded as the standard.The values in parentheses are given for informa-tion oniy.1.3 This standard may involve hazardoits materials,oper-ations,and
4、equpmertt.This standard does not purport to address all o f ttie safety problems associated with its use.It is the responsibility o f ttie user o f this standard to establish appropriate sajty and health practices and determine the applicability o f regirlatoiy liinitations prior to use.NOTE-The uti
5、lity of this practice has been demonstrated for the molding of phenolic molding compounds exhibiting higher-viscosity,non-Newtonian flow.2.Referenced Documenfs 2.1 ASTM Standards:D 638 Test Method for Tensile Properties of Plastics2 D 647 Practice for Design of Molds for Test Specimens of D 65 1 Tes
6、t Method for Tensile Strength of Molded Elec-D 958 Practice for Determining Temperatures of Standard Plastic Molding Materials2 trical Insulating Materials3 ASTM Molds for Test Specimens of Plastics 3.Significance and Use 3.1 The conditions under which samples are molded influence the properties of
7、the specimens.In determining whether a given compound meets the specification require-ments,it is important to hold to a standard set of conditions.This is also necessary for a valid comparison of properties obtained with different compounds,or between lots of the same compound.3.2 If the molded spe
8、cimens show evidence of lowdensity areas due to trapped gases,the specimens should be dis-carded.In molding new specimens,the mold should be opened slightly just after it is closed.It should be closed again within 2 to 3 s.It is critical to keep this mold reopening step This practice i s under the j
9、urisdiction of ASTM Committee D-20 on P l a s t i c s and is the direct responsibility of Subcommittee D20.09 on Specimen Preparation.Current ediion approved Nov.27,1987.Published January 1988.OnginaUy published as D796-44.L a s t previous edition D 796-87.Antirial Book ofASTbf Standards,Vol 0 8.0 1
10、.Antirial Book ofASTh Standards,Vol 10.01,to a minimum to avoid precurhg the material in the mold before full pressure is reapplied.Precured material in the molded specimen would cause poorly knitted areas that would not have the potential full strength.This mold reopening,commonly known as a“breath
11、e”step,allows any excess gases to be vented.4.Apparatus 4.1 Molds:4.1.1 Chrome plating of compression molding cavities is recommended,but not necessary.4.1.2 For molding impact and flexure specimens,use the single-bar,single-cavity positive mold shown in Practice D 647.4.1.3 For molding tension spec
12、imens,use the positive mold shown in the Mold for Tension Test Specimen figure in Practice D647 to make specimens required for Test Method D 651.Use the positive mold shown in the Five-Cavity Transfer Mold figure in Practice D 647 to make specimens required for Test Method D 638.4.1.4 For molding wa
13、ter absorption specimens,use the 50.8-mm(2411.)positive mold shown in the Mold for Disk Test Specimens figure of Practice D 647.4.1.5 For molding specimens for electrical tests,use the 101.6-mm(4411.)positive mold shown in the Mold for Disk Test Specimens figure of Practice D 647.4.2 Press-The hydra
14、ulic press shall be such that the molding pressure on the specimen can be maintained at 13.8 to 34.5 MPa(2000 to 5000 psi).4.3 Heating System-Use any convenient method of heating the press platens or molds,provided the heat source is constant enough to maintain the mold temperature within rC3”C(5F)a
15、cross molding surface.4.4 Either a thermometer or pyrometer as specified in Practice D 958 may be used to record mold temperature.5.Conditioning 5.1 Except for referee tests,prior conditioning of phenolic molding materials is required only for electrical tests(see 5.2).For referee tests,condition a
16、sufficient sample of the molding material,spread to a maximum depth of 12.7 mm(Y2 in.)in an open container,for 72 h in a Standard Laboratory Atmosphere(23 f 1”C,50 f 2%relative humidity)for flexure,impact,tension,and water-absorption test specimens.5.2 For molding electrical test specimens,condition a sufficient sample of the molding material in loose-powder form for 30 min at 90*3C(194 f 5F)in a circulating-air oven and mold it immediately after conditioning.While NOTICE:This standard has eithe
