Production Machining

NOV 2018

Production Machining - Your access to the precision machining industrial buyer.

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CONTRIBUTOR Barbara Kanegsberg and Ed Kanegsberg Ph.D., consultants with BFK Solutions, specialize in critical/precision and industrial product cleaning. For questions or to receive their newsletter, call 310-459-3614 or email info@b„ By Barbara Kanegsberg and Ed Kanegsberg Ph.D. The Importance of Drying Parts fter Cleaning D rying should get the respect it deserves. At least in the world of parts cleaning. Most cleaning processes consist of three steps, not two: wash, rinse and dry. at drying step is absolutely necessary for everything from product nishing to product performance to eective throughput to product quality. In simple terms, the goal of drying is to remove water and/or solvent residue from parts. is goal must be reached without incurring physical damage or undesirable surface modication of the part, promoting corrosion or depositing soils back onto the part. Residue that is adsorbed into product surfaces can outgas and damage other products or, especially in medical applications, harm people. Outgassing is, in eect, delayed drying of a surface that appears to be dry. Drying is often under- funded or ignored, and it is often the rate-limiting part of the cleaning process. Consider the impact of drying and cool-down times on process €ow: To build a truly cost-eective drying process, an operation must plan, evaluate and budget accordingly. Drying techniques can be divided into physical and chemical approaches. It is important to review the types of drying and consider all the options. A manufacturing process might even require more than one type of drying. Physical drying methods. In most physical drying processes, air is used to displace rinse water from the part. Examples of physical drying are blow-o, convection, forced air, radiant heat, centrifugal, desiccant and vacuum. Manual air blow-o uses shop air to dry parts. It is sometimes automated as the nal step in an in-line cleaning system. Once the drying nozzles have been appropriately placed relative to the product, and once the velocity and temperature have been set, the conveyor belt's length and speed essentially controls the drying process. Convection oven drying is controlled by gravity or is mechanically controlled. Gravity convection works on the principle that warm air rises, and while less expensive, there can be large temperature variations within the oven. In mechanical convection, a fan stirs the air for more uniformity, but the air €ow still may not reach blind holes. Vacuum drying involves radiant or conductive heating and tends to be costlier than other methods. It is eective for drying blind holes, but it isn't necessarily faster. e vapor pressure of the liquid is determined by the tempera- ture, so while the liquid may boil at a lower temperature, the rate of evaporation is not faster. Chemical drying methods. Solvent drying or solvent displacement typically is used to remove water or a high- boiling rinse agent. Isopropyl alcohol, methyl alcohol or acetone may be used to remove traces of rinse water. Where even more drying is desired, materials such as hydro€uorocarbons or hydro€uoroethers may be used to displace alcohol. In such applications, the drying agent may also function as a wash or rinse agent to remove thin lm or particulate contamination. In some instances, supercritical carbon dioxide is necessary. While drying is important, high temperatures can cause surface damage or product deformation, so it's also impor- tant to make sure the solvents at the temperatures used for drying are compatible with construction materials. Also, the drying process itself can be a source of contami- nation. If shop air is used for blow-o drying, point-of-use ltration is essential to avoid particles or oils being depos- ited on the parts. In vacuum drying, silicone pump oil can be a contamination source. Also, don't assume that solvent displacement means it is not necessary to worry about contamination. Check the cleanliness of the solvent, including looking for chemical and thin-lm contamination. With all drying systems, it is important to check that air quality is adequate and that the system is powerful enough to cope with product conguration or throughput. Drying system capacity should also be considered. As with wash and rinse tanks, drying chambers can be overloaded, so be realistic about drying capacity. Finally, once the part is clean and dry, take steps to store it correctly; ship it in the right packaging. e more time between product drying and product nishing, the more opportunity there is for recontamination. The drying step is necessary for product performance, finishing, effective throughput and quality. COMING CLEN 42 PRODUCTION MCHINING :: NOVEMBER 2018

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