Specific Gravity is the ratio of the density of a substance to the density of a standard. Plastics are compared to the density of gas-free distilled water at 23°C. The test method used to measure this physical property is either ASTM D792 or ISO 1183 with a unit of measurement of g/cm3 and can be found on the material’s Technical Data Sheet.
Different resins have different specific gravities, therefore will weigh more or less than the others. Material costs and product weight are two important factors we consider when investigating best materials for an application. When choosing resins either for a new project or for lower cost alternatives this key measurable can often be overlooked.
Calculating Volumetric Cost is the solution for an equivalent comparison between materials of different densities. Volumetric Cost is the cost per unit volume ($/cm3 or $/in3), as compared to the cost per unit weight ($/kg or $/lb.). To calculate volumetric cost, multiply the Specific Gravity of the material by the Cost/lb. by the conversion factor of 0.03614.
In the example below we compare two different grades of ABS; Grade 1 is a higher cost/lb. but lower density material while Grade 2 is the lower cost/lb. material with a higher density. The Volumetric Cost of ABS Grade 1 is the best cost and weight option, resulting in a $3,000 annual save and 4,500 lb. annual weight savings.
As you can see in the example above understanding this calculation can have a huge impact on heavy parts or high- volume programs. Munger Tech has created an easy to use spreadsheet that auto calculates these cost comparisons for you. Feel free to download the excel spreadsheet to help you in your material analysis and cost comparison projects. I hope you find this information is useful!
Munger Tech is committed to share our wealth of knowledge and provide tools to help you make informed business decisions. Please visit us at www.munger-tech.com to learn more.
Comments