Quality control testing is essential for manufacturing industries to ensure that the products meet specifications. Viscosity and consistency are characteristics amongst other physical properties that are tested. The problem arises when dealing with semi-solid substances since measuring viscosity chiefly pertains to liquid substances. However, there are methods such as a rotational viscometer and a rheometer that resolves this issue. In this paper, we will be focusing on the penetrometer, a newly designed tool for measuring the viscosity of semi-solid substances that is inexpensive and easy to use. The penetrometer works by dropping a cone onto a test subject under the influence of gravity and measuring the depth of the resulting hole to calculate consistency. There are myriad applications of the penetrometer in different industries for measuring the consistency of products such as asphalt, Vaseline, greases, cosmetic creams, chocolate, cheese, yogurt, ketchup, mayonnaise, and more. The significance of this test and instrumentation to perform this very simple to run test cements the penetrometer as a crucial new instrument for years to come.
The operation of the penetrometer is straightforward. The penetration measurement is the depth in tenths of millimeters to which a standard penetrant such as a cone or a needle sinks into a semi-solid substance under defined conditions of sample size, penetrant weight, geometry, and time. A softer consistency sample prompts a deeper penetration of the cone which increases the penetration number. The automatic digital penetrometer shown in Figure 1 demonstrates how simple to use this technique is. Some features of this instrument include adjusting time intervals for the penetrant drop, calibrating the plunger, and setting penetration limits. The cone or needle can be easily fixed into the penetrometer and the test starts with the press of a button. Other than the unit itself, there are accessories that complement it, such as the penetrometer bath and the grease worker. The bath adjusts the temperature of the subject and the grease worker works the subject by applying force through repeated strokes. These accessories aid in evaluating consistency under different conditions.
Figure 1– Digital Penetrometer: A Simple Tool for Consistency Measurements
Penetrometers are used in various grease industries for measuring consistency. Greases are available in countless consistencies ranging from very viscous, fluid-like, greases to non-viscous, block-like, greases. The pumpability of a grease is a vital factor in feeding and distributing greases correctly onto areas for lubrication. Non-viscous greases can be too hard to adequately pump onto surfaces while very viscous greases may leak away from the areas that need to be lubricated. The environment and external factors also play a part in influencing the specifications for the product. The importance of consistency testing for quality control is undeniable so it is critical to examine and differentiate greases for proper application.
While penetrometers were primarily used in grease and oil industries for years, the range of applications is branching out into other fields such as food and cosmetics. The integration of penetrometers in these other industries helps evaluate different consistencies of products for desired consumer use. Food products such as peanut butter, jam, honey, and mayonnaise might require softer consistencies to spread while cheese, candy, and chocolate bars might lean toward harder consistencies to provide a chew. Also, cosmetic products such as lipsticks, face creams, and compact powders require a specific consistency specification to ensure proper amounts of the product is applied. Other than food and cosmetics, there are other daily essential products that require consistency testing such as soap, toothpaste, putty, and paint. All these products have a wide range of consistencies which requires specific accessories to help achieve a satisfactory result. There are unique penetrants for different test, where each penetrant has a different shape and weight based on the subject being tested. Table 1 lists the different penetrants, test standards, and products tested using the penetrometer. The versatility of the different penetrants for each subject is important. Non-viscous and hard substances like asphalt or cosmetic paste lean toward using sharp and strong penetrants such as needles while softer substances like Vaseline and greases suffice with a cone. If the distance traveled by the penetrant is too high or low, the time of penetration and weight of the penetrant can be modified to tailor the test.
The practice of penetrometers is branching out of labs and into consumer industries. The automated instrument poses as one of the few effective methods to easily measure the consistency of semi-solids. The expanding range of applications to come for this instrument establishes it as a leading frontier for consistency testing in years.
References
1. A Useful Tool for the Determination of Consistency in Semi-Solid Substances. (n.d.). Retrieved from https://docplayer.net/19197521-A-useful-tool-for-the-determination-of-consistency-in-semi-solid-substances.html.