ASTM D1896-2009 Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds.pdf
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1、Designation: D1896 09Standard Practice forTransfer Molding Test Specimens of ThermosettingCompounds1This standard is issued under the fixed designation D1896; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisio
2、n. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a general procedure for the transfermolding of mechanical and electrical test specimens of ther-mosetting mo
3、lding materials.NOTE 1The utility of this practice has been demonstrated for themolding of thermosetting molding compounds exhibiting intermediateviscosity non-Newtonian flow.1.2 The values stated in either SI or inch-pound units are tobe regarded separately as standard. The values stated in eachsys
4、tem are not always exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in nonconformancewith this practice.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is th
5、eresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 2There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D731 Test Method for Molding I
6、ndex of ThermosettingMolding PowderD883 Terminology Relating to PlasticsD957 Practice for Determining Surface Temperature ofMolds for PlasticsD3123 Test Method for Spiral Flow of Low-Pressure Ther-mosetting Molding CompoundsD3795 Test Method for Thermal Flow, Cure, and BehaviorProperties of Pourable
7、 Thermosetting Materials by TorqueRheometer3. Terminology3.1 Definitions:3.1.1 GeneralDefinitions of terms applying to this prac-tice appear in Terminology D883.3.1.2 transfer molding, na method of forming articles byfusing a plastic material in a chamber and then forcingessentially the whole mass i
8、nto a hot mold where it solidifies.3.2 Definitions of Terms Specific to This Standard:3.2.1 breathing, vthe operation of opening a mold or pressfor a very short period of time at an early stage in the processof cure.3.2.1.1 DiscussionBreathing allows the escape of gas orvapor from the molding materi
9、al and reduces the tendency ofthick moldings to blister.3.2.2 cavity (of a mold), nthe space within a mold to befilled to form the molded product.3.2.3 clamp pressure, nthe pressure applied to the mold tokeep it closed, in opposition to the fluid pressure of thecompressed molding material.3.2.4 fill
10、 time, nthe time required to fill each cavity usedin the mold. Fill times can be critical to well molded parts (seeNote 3 under 4.4).3.2.5 minimum plunger pressure, nthe minimum pressure,on the ram, required to just fill each cavity used in the mold ata specified temperature and reasonable fill time
11、.3.2.6 vent, na hole, slot, or groove provided in a mold ormachine to allow air and gas to escape during molding,extrusion, or forming.4. Significance and Use4.1 Transfer molding is particularly suited to thermosettingmaterials of intermediate plasticity. Fixed molding parameterscannot be specified
12、for each type of material. Molding com-pounds of the same type come in many different plasticitiesmeasured in accordance with Test Methods D731, D3123, and1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.09 on Specimen Prep
13、aration.Current edition approved Dec. 1, 2009. Published December 2009. Originallyapproved in 1961. Last previous edition approved in 2004 as D1896 - 99(2004).DOI: 10.1520/D1896-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.or
14、g. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States
15、.D3795. Consequently, for a given material type, the moldingparameters required to produce satisfactory test specimens willoften vary dependent on the plasticity of the specific materialgrade.4.2 The mold shown in this practice provides for a set offive specimens. However, if only certain specimens
16、are desired,the other cavities can be blocked by inserting gate blanks.4.3 Typically, breathing of the mold is not required torelease trapped volatile matter as the gas is free to flow fromthe vent end of the mold. This is a particular advantage forheat-resistant compounds and reduces the tendency f
17、or moldedspecimens to blister at high exposure temperatures.4.4 Flow and knit lines in a molded piece are often sites ofmechanical or electrical weakness and can be found in somedegree of severity throughout the molded piece. The semisolidmolding compound passing through the gate is subject tonon-Ne
18、wtonian flow and, consequently, wrinkles and folds asit travels down the mold cavity. Fibers and other reinforce-ments in the molding compound align with the flow patternand, consequently, can orient perpendicular to the axis of thebar at the center and parallel at the surface of the bar. Moldtemper
19、ature, thermal conductivity and plasticity of the moldingcompound, degree of preheat, and plunger pressure are param-eters that influence the time to fill the mold cavities and theformation of knit lines.NOTE 3If the temperature of the mold is held constant and the plungerpressure varied for a desig
20、nated thermosetting molding compound, twoextreme characteristic conditions can be obtained. If the pressure is low,then the vent end of the cavity will not fully fill, and weld lines will formby incomplete knitting of the material. If the pressure is too high, the moldcavity will fill fast, the outs
21、ide of the specimen will case harden while thepressure is still forcing material out the vent, and a ball-and-socket grainstructure will be obtained. A ball-and-socket structure is an indication ofthe molding condition, and lower test data will result.4.5 Thermosetting compounds containing long-fibe
22、r fillerssuch as glass roving, chopped cloth, or shavings can be usedbut are not recommended for transfer molding. These fillermaterials tend to break, tear, or ball in passing through thegates of the mold, thereby not optimizing their potentialstrength.4.6 The Izod impact strength of transfer molde
23、d specimensof molding compounds containing short fibers will generally belower than the values obtained using compression-moldingmethods. Quite often the impact strength will vary along theaxis of the bar due to molding parameters, flow pattern, andfiber orientation.4.7 The flexural and tensile stre
24、ngth of transfer moldedspecimens of molding compounds containing short fibers willgenerally be higher than the values obtained usingcompression-molding methods. Flexural tests are particularlysensitive to transfer molding due to the thin resin skin formedat the surface of the bar during the final fi
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