The preceding post defined two dimensions of concern when considering cleaning orifices. Before moving on, let's now consider how the various types of contamination that might be found in an orifice and how each affects the cleaning task. Liquids - Liquids are common contaminants in orifices. Liquid contamination can result from manufacturing operations but also may be the result of use as in the orifice of a nozzle, for example. Liquids are usually the simplest contaminants to remove from orifices. This is because even if the orifice is completely obstructed by the contaminating liquid, the gross amount of the contamination can be removed by simply applying pressure to one end of the orifice thereby pushing it out the other end. This applies for virtually any width or length orifice. Once the contaminant has been sufficiently removed to allow cleaning liquid to penetrate the length of the orifice, cleaning of any residual liquid contaminant is dependent on mechanisms that will be discussed in more detail in ongoing blogs. Solids - As you might imagine, solid contaminants present a significantly different challenge than liquids when it comes to removing them from an orifice. Solids may either partially or completely block an orifice. Solid material in an orifice might be either soluble or insoluble. Solids may be held in place by a number of different mechanisms ranging from adhesion (a hardened glue, for example) or something as weak as cohesive forces (fine particles from a grinding or broaching process, for example). Let's look at these things and some of the interactions between them one at a time. If an orifice is partially blocked by a solid there is a chance that a cleaning chemistry can be used to penetrate the length of the orifice and either dissolve or, in some cases, deliver sufficient mechanical energy to break the solid contaminant free so that it can be flushed out. If the orifice is completely blocked, the effectiveness of either of the above mechanisms will depend on being able to introduce liquid into the length of the orifice leading to the blockage and provide physical contact with it. Soluble solid contaminants are best removed using a chemistry that will dissolve them. Dissolution may be achieved using a simple flush. The use of other mechanisms depends on the geometry of the orifice. Non-soluble solid contaminants require some means of delivering sufficient mechanical energy to the attachment site to physically displace them. In cases where insoluble solids are adhered along the length of an orifice the removal mechanism nearly always involves the delivery of mechanical energy. Sometimes a simple flushing with liquid is adequate to do the job but in many cases more energy than can be delivered by moving liquid is required. Note - An especially difficult (almost nearly impossible) to remove contaminant is a solid particle that is wedged into an orifice along its length. Curled chips which are made "springy" by the cutting process, for example, often defy removal by normal batch cleaning processes. It is in such cases that probes, ultrasonics and other mechanisms are required. The effectiveness of these mechanical means depends on the geometry of the orifice and, to some degree, the placement of the orifice within its surrounding mass. Subsequent blogs will discuss means of delivering mechanical energy within an orifice and how geometry may affect the ability to do this.
- FJF -