Quality control visual standards

Sensory analysis The odour of an essential oil can be evaluated by conducting investigations on the evaporation of an essential oil under standardized conditions and comparing this to a standard sample of the oil. This is sometimes referred to as odour purity but is a rather subjective method. It involves putting the essential oil and a standard sample onto separate smelling strips and allowing them to evaporate to a final dry-out under the same environmental conditions and time scale. This, along with a visual inspection of the oil, is the only immediate quality control measure available to the aromatherapist. 

In quality control of colored objects, production requires more consistency than absolute accuracy. After all, there will generally be a product standard having the correct color to which we may reference the color of parts from the current production run. Since the production part and the product standard will be free from the small errors in accuracy, because any small inaccuracies will be the same in measurements of the batch and the standard and thus will subtract out in the different components. What is needed is an instrument with higher day-to-day objectivity than our visual system, and for such an increase in consistency, one must be willing to give up some of the absolute accuracy. This requires an analog simulation of visual colorimetry. 

Machine vision, also referred to as computer or robot vision, is a term that describes the many techniques by which machines visually sense the physical world. These techniques, used primarily for monitoring industrial manufacturing, are becoming increasingly popular as today s manufacturing environments become more automated and quality control standards increase. Whether the task is to sort and assemble a group of machined parts, to determine if a label has been placed properly on a soda bottle, or to check for microscopic defects in an automotive door panel, machine vision plays an essential role. 

Control of dirt and other particles involves use of a membrane filtration method (ASTM D-2276, IP 216) in which the dirt retained by filtration of a sample through a cellulose membrane is expressed as weight per unit volume of the fuel. This test provides field quality control of dirt content and can be supplemented by a visual assessment of membrane appearance after test against color standards (ASTM D-3830). However, no direct relationship exists between particulate content weight and membrane color, and field experience is required to assess the results by either method. 

In the present writer s opinion, this summary of selected papers indicates that a detailed understanding of the raw feed mineralogy-particle size relationship and the effects of the temperature profile in a kiln is absolutely mandatory for continued quality control. These papers, and many others of similar subject matter, demonstrate the practicality of cement plant microscopy. The microscope, perhaps better than any other instrument of analysis, and certainly as a corroborative tool, provides the means for visual appreciation of the cement-making process. But what kind of training is necessary What are the essential microscopical observations and the "standard" microscopical procedures that one can use to help ensure a quality product Knowing the microscopical nature of the raw materials is the first step. 

In many instances, quality control consists of little more than visual inspection of a product to check for defects. This is a general and useful starting point for any quality-control function. Quality control is first and foremost a feedback process. When quality control is used to detect errors in the output stream, the information that it provides is used to adjust the manner in which the particular process treats the input stream. Determining the quality of the product (the output stream of the process) requires the creation of a product-specific system of quality-control testing and unequivocal methods of measuring designated features of the product, which can be compared with the ideal or standard features. 

Color labs are outfitted with laboratory size equipment that simulates the larger machines used for production internally and by their customers. Typical processing equipment found in the lab are small extruders, two-roll mills, ban-burry mills, and media mills. Small rotational, injection and blow molding machines are used to duplicate the customers process. Instruments and computers are required for testing physical properties and color. Most labs have a computer-controlled color measuring system and a light booth to evaluate color. The spectrophotometer with computer is initially used to assist in colorant formulation and later as a quality control (QC) tool to provide certification of the quahty of match to standard. The light booth provides a standardized set of conditions to visually observe color and appearance. 

One of the reasons for the tremendous success of plastic products in the consumer market is that products made from plastic materials are aesthetically more appealing in terms of color and feel than products made from other materials. The majority of quality control systems fail to recognize the importance of visual standards or guidelines. Quite often, too much emphasis is placed on measurement and testing of the product and not enough on the visual standards. 

The precision and accuracy of instrumental color measurements and the associated color tolerance can provide a system of control that equals that of an experienced color matcher. But to achieve this performance, the product standard and production test specimens must be of the highest quality. As was pointed out, more than two decades ago, the weak link in instrumental color control is the specimen. The human visual system can scan a specimen marred by many inconsistencies and the human mind will ignore those features that are not relevant to the job at hand. A analog or digital colorimeter cannot ignore those defects. A spectrocolorimeter is a tool for the color matcher but it is not a hammer. It needs to be treated like the precision instrument it is. A mold-maker would never use his or her tools in a dirty... 

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