Production Machining

DEC 2014

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

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Depending on whether the process is carried out as immersion cleaning or as a spray cleaning application, there are several ways to introduce mechanical force. Agitation is an Efective Way to Clean Parts CONTRIBUTOR Doris Schulz is a freelance journalist specializing in the feld of surface treatment, and especially parts cleaning. Contact: CLEAN SLATE 42 PRODUCTION MACHINING :: DECEMBER 2014 N o matter if I want to lose weight, gain a clear mind or just stay healthy, my preferred way is to move, such as going for a walk, swimming or doing gymnastics. Tinking about that, I realize that there are also quite a number of other situations in daily life, when I use agitation to get rid of waste: shaking table- cloths or washing dishes. And when it comes to industrial parts cleaning, it is in some way the same—movement also helps to do a good and cost-efective job. Tis became obvious when I remembered what I have learned when I have started to get involved in industrial parts cleaning many years ago. Tere are four factors that infuence the efectiveness of wet chemical cleaning processes: chemistry, temperature, time and mechanical energy. Tey are interdependent factors. In most cases, increasing the temperature will enhance the solvent power of chemistry. Also adding some mechanical energy will help to break bonding forces between contamina- tion and surface more easily, which will lead to shorter cycle times and thus to more efcient cleaning processes. Depending on whether the process is carried out as immer- sion cleaning or as a spray cleaning application, there are several ways to intro- duce mechanical force. A simple method of applying mechanical energy to immersion cleaning procedures is to move the parts through the cleaning liquid by vertical agitation. Te repeated up and down motion is efective in cleaning simple parts, such as workpieces without blind holes, undercuts and/or drill holes. Another type of part agitation, which is used in aqueous and solvent cleaning processes in closed machines, is to slew or to rotate the parts. In this case, the workpieces are usually cleaned stacked or bulked in baskets. In order to avoid damage of the workpieces through part-on-part or part-on- basket contact special washing meshes can be placed in the basket as intermediate layers. More efective is the pressurized fow cleaning procedure, also called injection food washing process. Te cleaning basket is also fooded with the cleaning liquid and usually turned as well. At the same time, pumps draw fuid out of the cleaning bath and subsequently inject it back into the bath at high pressure levels through nozzles located underneath the fll level. Tis results in strong currents that wash over By Doris Schulz and around the workpieces and remove contaminants from surfaces, blind holes, cavities and recesses. An advantage of this method of adding mechanical energy is its versatility. Te jet system in pressurized fow cleaning does not have to be adjusted to target each specifc part, so it ofers a good level of cleanliness for parts of various shapes and sizes. Tis is also the case with ultrasonic cleaning, which is often used for cleaning machined parts. Here, the mechanical energy is based on the physical principle of cavitation: An ultrasonic generator emits electrical signals at a certain frequency, which are then transferred to the liquid as ultra- sound waves via a transducer. Te sonic pressure is character- ized by interaction of underpressure and overpressure. As a result of the high intensity, microscopic bubbles form in the underpressure phases, which then implode in the subsequent overpressure phase, releasing shock waves with considerable energy densities. Tis also triggers microfows in the liquid, which remove flm-like and particulate contaminants from the components to be cleaned, even for workpieces with complex geometry. In spray cleaning processes, contamination is partially dissolved or emulsifed by the cleaning media—usually an aqueous agent—and partially washed away by the kinetic energy of the spray jet. So mechanical energy here results from the pressure at which the medium is sprayed onto the surface to be cleaned. Depending on the application, working pressure can be as high as 25 bar (approx. 360 psi). High-pressure applications, which range from 150 bar (2,175 psi) up to more than 2,000 bar (29,000 psi) allow for cleaning and deburring in a single step. Shape and arrangement of the nozzles have decisive infuence on the cleaning result. It might be necessary to move the part being cleaned and/or the nozzles, to ensure even cleaning of all workpieces. In real life, one might take a walk to free his mind or do a hard workout to improve his shape, all depending on consti- tution and aim. Te same applies for cleaning processes: contamination, cleanliness requirements, part geometry and other factors will defne the right process choice.

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