Home About us Contact
|
Home About us Contact | ||
|
|
||
Molding Compound (molding + compound)
Selected AbstractsOptimizing injection gate location and cycle time for the in-mold coating (IMC) processPOLYMER COMPOSITES, Issue 5 2002Mauricio Carbera-Rios The standard practice when compression molding Sheet Molding Compound (SMC) exterior automotive body panels is to in-mold coat (IMC) the parts. Consequently, IMC needs to be considered an integral part when improving the process. Selecting the proper IMC injection gate location to obtain a defect-free coated part and properly setting the IMC processing conditions to reduce its cycle time are both key decisions for the IMC process. In the present work, an optimization method that involves metamodeling through either linear regression or artificial neural networks is explored with two purposes: first, to select the injection gate location(s) with the objective of minimizing the potential for surface defects in the coating; and second, to set the mold wall temperature and the initiator concentration to minimize the cure time for a given minimum required flow time. [source] Recycling of the solid residue obtained from the pyrolysis of fiberglass polyester sheet molding compoundADVANCES IN POLYMER TECHNOLOGY, Issue 2 2009A. Torres Abstract This paper is part of a project devoted to study the pyrolysis process as an alternative for recycling sheet molding compound (SMC), a thermoset composite of polyester and fiberglass. A standard SMC was pyrolyzed under nitrogen, at 300, 400, 500, 600, and 700°C, for 30 min in a 3.5-dm3 autoclave. This paper focuses on the possibilities of reusing the fibers and fillers contained in the solid residue obtained from SMC pyrolysis. The solid pyrolysis residue was recycled in another thermoset composite, bulk molding compound (BMC), of polyester and fiberglass. The mechanical properties of BMCs prepared with different proportions of the solid residue (fiber + CaCO3 filler) from SMC pyrolysis were compared with those of BMCs prepared with the same proportions of virgin fiber and CaCO3. In summary, pyrolysis can be an appropriate technique for recycling SMC, with 500°C, the most suitable temperature for the process. Solid residues of 75 wt%, composed of 65 wt% of powdery material (mainly CaCO3) and 35 wt% of fiberglass, were obtained. Such solids can be recycled in a proportion of 6 wt% in BMC to replace virgin filler and fiberglass, with no detrimental effect on the BMC mechanical properties. © 2009 Wiley Periodicals, Inc. Adv Polym Techn 28:141,149, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20150 [source] Yield stress and rheological characterization of the low shear zone of an epoxy molding compound for encapsulation of semiconductor devicesPOLYMER ENGINEERING & SCIENCE, Issue 4 2008Masaki Yoshii In encapsulation molding of IC packages, the melt flow inside the cavity is generally controlled in a low shear to prevent wire sweep, and other molding defects. Therefore, it is important to evaluate the rheological properties of epoxy molding compounds (EMC) in a low shear zone including determining the yield stress. In this study, a newly specialized Parallel-Plate Plastometer for EMCs was built up. Using this plastometer, the yield stress and its temperature dependence were clarified, and the rheological properties in the low shear zone were evaluated. As a result, the rheological properties in a low shear zone of 0.1,10 s,1 were characterized using the Herschel,Bulkley viscosity model which introduced the yield stress, the Castro,Macosko equation as a dependency model of cure, and the WLF equation as a dependency model for temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Chemorheological analysis of an epoxy-novolac molding compoundPOLYMER ENGINEERING & SCIENCE, Issue 2 2000T. H. Hsieh The chemorheological behavior of an epoxy-novolac molding compound was studied by a combination of differential scanning calorimetry and dynamic rheological measurements. Based on a modified version of Kamal and Sourour's kinetic expression, a procedure aiming at the phenomenological description of cure kinetics was developed. In combination with our kinetic study, an empirical Arrhenius-type expression was adopted for the description of the dependence of complex viscosity on temperature, frequency, and conversion by allowing the pre-exponential factor and the flow activation energy to be frequency- and conversion-dependent. At low conversions (, < ,0.05), the system behaves approximately as a thermoplastic material; at higher conversions, the rheological behavior of the system was dominated by the extent of cure reaction. [source] Effects of defrosting period on mold adhesion force of epoxy molding compoundASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009Hwe-Zhong Chen Abstract In integrated circuit (IC) packaging, when epoxy-molding compound (EMC) is filled in the mold cavity and cured in the mold, adhesion occurs in the interface between EMC and the mold surface. Too large an adhesion force can cause many problems. For example, too large an adhesion force may damage an IC during ejection and cause the package to fail and thus lower the yield rate. To resolve mold adhesion problems, improving the mold design and applying suitable surface treatments, such as mold surface coating, are the common approaches. Applying suitable surface coating is a more popular and practical approach. Defrosting is a process to increase the frozen EMC temperature to room temperature, and to retain it at room temperature for some period before molding. It is a common practice to put EMC under required atmospheric environment during defrosting. It has been found by molding engineers that increased defrosting period will increase the frequency of mold cleaning. But there is no quantitative description on how much the adhesion force increases during the defrosting process. This paper describes the use of a semiautomatic EMC adhesion force test instrument to measure the normal adhesion force between the mold surface and EMC. By measuring the adhesion force, one can quantify how much adhesion force exists between EMC and the mold surface under different defrosting periods. The results show that it is best to use the EMC with 24,32 h of defrosting, to prevent excessive amount of mold adhesion force and it has been found that the adhesion force of the 24 h defrosting period will be 24% less than that of the 48 h defrosting period. Decreasing moisture absorption will decrease the increase in adhesion force for prolonged defrosting period cases. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Mechanism of fiber,matrix separation in ribbed compression molded parts,POLYMER COMPOSITES, Issue 4 2007Alejandro Londoño-Hurtado This paper presents a model that predicts fiber,matrix separation in ribbed sections of compression molded parts. The model combines a mechanical analysis of compression molding with some experimentally measured variables. It is shown that with a higher closing speed, the viscosity of the material will increase and fiber,matrix separation can be reduced. Specific applications for this method are compression molding of sheet molding compounds and glass mat-reinforced thermoplastics. POLYM. COMPOS., 28:451,457, 2007. © 2007 Society of Plastics Engineers [source] Yield stress and rheological characterization of the low shear zone of an epoxy molding compound for encapsulation of semiconductor devicesPOLYMER ENGINEERING & SCIENCE, Issue 4 2008Masaki Yoshii In encapsulation molding of IC packages, the melt flow inside the cavity is generally controlled in a low shear to prevent wire sweep, and other molding defects. Therefore, it is important to evaluate the rheological properties of epoxy molding compounds (EMC) in a low shear zone including determining the yield stress. In this study, a newly specialized Parallel-Plate Plastometer for EMCs was built up. Using this plastometer, the yield stress and its temperature dependence were clarified, and the rheological properties in the low shear zone were evaluated. As a result, the rheological properties in a low shear zone of 0.1,10 s,1 were characterized using the Herschel,Bulkley viscosity model which introduced the yield stress, the Castro,Macosko equation as a dependency model of cure, and the WLF equation as a dependency model for temperature. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Influence of chemical composition on the rheological behavior of condensation reaction resinsPOLYMER ENGINEERING & SCIENCE, Issue 2 2003M. Doyle In this paper, the chemorheological and dynamic mechanical behavior of melamine-formaldehyde (MF) resins of four different formaldehyde/melamine (F/M) molar ratios (1.25, 1.5 1.75 and 2.00) are investigated. MF resins polymerize via a polycondensation reaction involving formation of up to 10 wt% of H2O on cure. This typically results in rapid and extensive foaming of the resin when it is cured under atmospheric pressure. Experimental adaptation for the foaming behavior of MF resins is used to gather rheological information concerning the curing kinetics and the mechanical response of neat MF resins of different molar ratios. Likewise, the procedures developed allow curing of the resins under atmospheric pressure, hence allowing volatile evacuation as occurs during venting procedures (commonly used during compression molding of MF molding compounds) or as a result of absorption by hydrophilic fillers or substrates. The results show that increased moisture content in the B-stage leads to faster reaction rates and greater foaming. Gelation and vitrification times are identified for each molar ratio, and are found to increase with decreasing molar ratio. The dynamic mechanical behavior of carefully molded neat MF samples of different molar ratios is studied using DMTA. Tg is found to be 200°C for the resin with the lowest formaldehyde content (F/M = 1.25), and around 230°C for the other resins. The storage shear modulus above Tg is studied, and the results show that the crosslink density increases with increasing molar ratio. [source] | |||||||||||||