ASTM D1896-1999(2004) Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds《热固化合物传递模塑试样的标准操作规程》.pdf
《ASTM D1896-1999(2004) Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds《热固化合物传递模塑试样的标准操作规程》.pdf》由会员分享,可在线阅读,更多相关《ASTM D1896-1999(2004) Standard Practice for Transfer Molding Test Specimens of Thermosetting Compounds《热固化合物传递模塑试样的标准操作规程》.pdf(4页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: D 1896 99 (Reapproved 2004)Standard Practice forTransfer Molding Test Specimens of ThermosettingCompounds1This standard is issued under the fixed designation D 1896; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 of ther-mosetting molding 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 val
4、ues stated in eachsystem may not be exact equivalents; therefore, each systemshall be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thispractice.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with
5、its use. It is theresponsibility 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 similar, or equivalent, ISO standard.2. Referenced Documents2.1 ASTM Standards:2D 731 Test Met
6、hod for Molding Index of ThermosettingMolding PowderD 883 Terminology Relating to PlasticsD 957 Practice for Determining Surface Temperature ofMolds for PlasticsD 3123 Test Method for Spiral Flow of Low-PressureThermosetting Molding CompoundsD 3795 Test Method for Thermal Flow and Cure Propertiesof
7、Thermosetting Plastics by Torque Rheometer3. Terminology3.1 Definitions:3.1.1 GeneralDefinitions of terms applying to this prac-tice appear in Terminology D 883.3.1.2 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 D 731, D 3123, andD 3795. For this reason, a material may mold satisfactorilyunder one set of fixed parameters, while the same type ofmaterial with a different p
13、lasticity may require a different set ofparameters to produce satisfactory test specimens.4.2 The mold shown in this practice provides for a set offive specimens. However, if only certain specimens are desired,the other cavities may be blocked by inserting gate blanks.4.3 Typically, breathing of the
14、 mold may not be required torelease trapped volatile matter as the gas is free to flow fromthe vent end of the mold. This is a particular advantage for1This practice is under the jurisdiction ofASTM Committee D20 on Plastics andis the direct responsibility of Subcommittee D20.09 on Specimen Preparat
15、ion.Current edition approved Nov. 1, 2004. Published January 2005. Originallyapproved in 1961. Last previous edition approved in 1999 as D 1896 - 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStanda
16、rds 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.heat-resistant compounds and re
17、duces the tendency for moldedspecimens to blister at high exposure temperatures.4.4 Flow and knit lines in a molded piece are often sites ofmechanical or electrical weakness. Knit lines may be found insome degree of severity throughout the molded piece. Thesemisolid molding compound passing through
18、the gate issubject to non-Newtonian flow and, consequently, wrinkles andfolds as it travels down the mold cavity. Fibers and otherreinforcements in the molding compound align with the flowpattern and, consequently, may mold perpendicular to the axisof the bar at the center and parallel at the surfac
19、e of the bar.Mold temperature, thermal conductivity and plasticity of themolding compound, degree of preheat, and plunger pressureare parameters that influence the time to fill the mold cavitiesand the formation of knit lines.NOTE 3If the temperature of the mold is held constant and the plungerpress
20、ure varied for a designated 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 wi
21、ll fill fast, the outside 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 compound
22、s containing long-fiber 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 stre
23、ngth of transfer molded 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 fle
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