Search Results for household appliances

Numerous protective covers, used in conjunction with an electrical appliance, failed during assembly with the mating components. The failures were traced to a particular production lot of the covers and occurred during insertion of the screws into the corresponding bosses. The parts had been injection molded from an ABS resin to which regrind was routinely added. Inspection of both the failed covers and retained parts, which exhibited normal behavior during assembly, included visual inspection, micro-FTIR in the ATR mode, and analysis using DSC. The FTIR results indicated the presence of contaminant material exclusively within the ABS resin used to mold the failed covers, and the thermograms suggested contamination with a PBT resin. Further TGA analysis showed the contamination was estimated to account for approximately 23% of the failed cover material. The conclusion was that the appliance covers failed via brittle fracture associated with stress overload. The failures, which occurred under normal assembly conditions, were attributed to embrittlement of the molded parts, due to contamination of the ABS resin with a high level of PBT. The source of the PBT resin was not positively identified, but a likely source appeared to be the use of improper regrind.

Housings (being tested as part of a material conversion) from an electrical appliance failed during an engineering evaluation. They had been injection molded from a commercial polycarbonate/PET blend. Parts produced from the previous material, a nylon 6/6 resin, had consistently passed the testing regimen. Grease was applied liberally within the housing assembly during production. Investigation included visual inspection, 24x SEM images, micro-FTIR in the ATR mode, and analysis using DSC. No signs of material contamination were found, but the thermograms showed a crystallization of the PET resin. The grease present within the housing assembly, analyzed using micro-FTIR, was composed of a hydrocarbon-based oil, a phthalate-based oil, lithium stearate, and an amide-based additive. The conclusion was that the appliance housings failed through environmental stress cracking caused by a phthalate-based oil that was not compatible with the PC portion of the resin blend. Thus, the resin conversion was the root cause of the failures. Additionally, during the injection molding process the molded parts had been undercrystallized, reducing their mechanical strength. More importantly, the resin had been degraded, producing a reduction in the molecular weight and reducing both the mechanical integrity and chemical-resistance properties of the parts.

This article reviews the most common reasons for failures and the purpose of a failure investigation. It discusses the nine steps for the organization of a good failure investigation. The three basic tools that are helpful in any failure investigation, namely, a fault tree, a failure mode assessment chart, and a technical plan for resolution chart, are reviewed. The article briefly describes failure investigation pitfalls and concludes with information on the other common tools used for failure investigation and root cause determination.

Plastics or polymers are used in a variety of engineering and nonengineering applications where they are subjected to surface damage and wear. This article discusses the classification of polymer wear mechanisms based on the methodologies of defining the types of wear. The first classification is based on the two-term model that divides wear mechanisms into interfacial and bulk or cohesive. The second is based on the perceived wear mechanism. The third classification is specific to polymers and draws the distinction based on mechanical properties of polymers. In this classification, wear study is separated as elastomers, thermosets, glassy thermoplastics, and semicrystalline thermoplastics. The article describes the effects of environment and lubricant on the wear failures of polymers. It presents a case study on nylon as a tribological material. The article explains the wear failure of an antifriction bearing, a nylon driving gear, and a polyoxymethylene gear wheel.

This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

This article discusses the organization required at the outset of a failure investigation and provides a methodology with some organizational tools. It focuses on the use of problem-solving tools such as a fault tree analysis combined with critical thinking. The discussion covers nine steps to organize a good failure investigation. They are as follows: understand and negotiate goals of the investigation, obtain a clear understanding of the failure, identify all possible root causes, objectively evaluate the likelihood of each root cause, converge on the most likely root cause(s), objectively and clearly identify all possible corrective actions, objectively evaluate each corrective action, select optimal corrective action(s), and evaluate effectiveness of selected corrective action(s). Common problems detrimental to a failure investigation are also covered.

This introductory article describes the various aspects of chemical structure that are important to an understanding of polymer properties and thus their eventual effect on the end-use performance of engineering plastics. The polymers covered include hydrocarbon polymers, carbon-chain polymers, heterochain polymers, and polymers containing aromatic rings. The article also includes some general information on the classification and naming of polymers and plastics. The most important properties of polymers, namely, thermal, mechanical, chemical, electrical, and optical properties, and the most significant influences of structure on those properties are then discussed. A variety of engineering thermoplastics, including some that are regarded as high-performance thermoplastics, are covered in this article. In addition, a few examples of commodity thermoplastics and biodegradable thermoplastics are presented for comparison. Finally, the properties and applications of six common thermosets are briefly considered.