O Ring Weight Calculator
Estimate molded or cut-and-spliced O-ring mass from inside diameter, cross-section, compound density, cord volume, flash allowance, splice allowance, and production quantity.
Weight Results
| Preset | Inside Diameter | Cross-Section | Typical Use |
|---|---|---|---|
| AS568-010 | 0.239 in | 0.070 in | Small fittings, stems, and compact face seals |
| AS568-112 | 0.487 in | 0.103 in | Hydraulic adapters and small radial glands |
| AS568-214 | 0.984 in | 0.139 in | Common static and dynamic radial seal size |
| AS568-325 | 1.475 in | 0.210 in | Larger static housing and flange seals |
| Metric 50 x 3.5 | 50 mm | 3.5 mm | Metric hydraulic and pneumatic glands |
| Elastomer | Typical Density | Common Hardness | Specification Notes |
|---|---|---|---|
| NBR nitrile | 1.15 to 1.25 g/cc | 60A to 90A | Oil service, general industrial seals |
| FKM fluoroelastomer | 1.75 to 1.90 g/cc | 70A to 90A | High temperature and chemical resistance |
| EPDM | 1.05 to 1.20 g/cc | 50A to 80A | Water, steam, brake fluid, outdoor exposure |
| Silicone VMQ | 1.10 to 1.25 g/cc | 40A to 80A | Wide temperature range, low tear strength |
| HNBR | 1.18 to 1.30 g/cc | 70A to 90A | Fuel, oil, and improved heat resistance |
| Manufacturing Case | Allowance Input | Flash Input | Practical Note |
|---|---|---|---|
| Compression molded ring | 0 in to 0.02 in | 1% to 4% | Use actual trim history for each mold |
| Transfer molded ring | 0 in to 0.01 in | 2% to 6% | Gate and runner waste may be tracked separately |
| Extruded cord splice | 0.05 in to 0.50 in | 0% to 2% | Allowance covers overlap and trimmed ends |
| Large custom ring | 2 mm to 20 mm | 1% to 5% | Measure a trial ring before production release |
| Conversion | Formula | Use In Calculator | Check Value |
|---|---|---|---|
| in to mm | in x 25.4 | Unit toggle and metric presets | 1 in = 25.4 mm |
| in3 to cm3 | in3 x 16.3871 | Volume conversion before density | 1 in3 = 16.3871 cm3 |
| g to oz | g / 28.3495 | Imperial result display | 1 oz = 28.3495 g |
| g to lb | g / 453.592 | Large batch display | 1 lb = 453.592 g |
When engineer and the procurement departments wants to price a new batch of O-rings, the first question they will ask is: how much does each O-ring weigh? The weight of an O-ring will determine how much material will have to be ordered for the batch, how much the freight will weigh, and what size mixing equipment will be required. Calculating the weight of an O-ring can be a dificult task due to several factor that affect the weight of the O-ring.
These factor include the inside diameter of the O-ring, the thickness of the cord that make up the O-ring, the specific gravity of the compound of the O-ring, and how much material is lost during the molding process of the O-ring. The geometry of the O-ring will be the first factor that must be consider in determining the weight of the O-ring. The volume of the O-ring can be calculated using the circumference of the O-ring and the cross-sectional area of the cord that make up the O-ring.
How to Find the Weight of an O-Ring
If the inside diameter of the O-ring and the diameter of the cord are known, the theoretical volume of the O-ring can be calculate in cubic centimeters. Multiplying this value by the density of the rubber compound will provide the weight of the O-ring. The size of the O-ring will impact the weight of the O-ring.
For instance, if the size of the O-ring are changed, then the weight of the O-rings will change. Another factor that may change the weight of the O-ring is the density of the rubber compound. For instance, EPDM compounds may have a density of around 1.12 g/cc, while FKM compounds may have a density of around 1.85 g/cc.
Thus, the FKM O-rings may weigh more then the EPDM O-rings despite using the same sizes for the O-rings. The density of rubber compounds can change based off the fillers that is added to the compound or the age of the polymer in the compound. Thus, the supplier should use the specific gravity of the compound measured by the supplier to determine the weight of the O-ring.
The method in which the O-rings are manufacture can also impact the weight of each O-ring. If the molding process makes the O-rings, then some of the material will be lost due to the molding process. For instance, molded O-rings will have areas of excess material that the worker will have to trim off the O-rings after they are molded.
Thus, a percentage value can be added to the weight calculation to account for this lost material during molding. Cut-and-splice O-rings will have the cord cut longer then the circumference of the O-ring because some of the cord must overhang the O-ring to allow for the two ends of the O-ring to be bond together. Thus, an allowance for this extra length of cord must be account for in the calculation of the weight of the O-rings.
This allowance should be entered into the calculator as a length because the amount of extra length of cord required for each splice will depend upon the diameter of the cord. Another factor that can impact the weight of the O-rings on the production floor is the density of the compounds. For instance, nitrile compounds may have a density of 1.20 g/cc on the manufacturer’s catalog, but the actual density may be 1.18 g/cc or 1.23 g/cc depending upon the ingredients are added to the compound during the manufacturing process.
Fluoroelastomers have similar issue with density. For instance, heavy metal oxide fillers can be added to the fluoroelastomer compounds to improve some properties of the rubber. These metal oxides will increase the density of the fluoroelastomer compounds rapid.
Thus, the density of compounds will change when large amounts of O-rings is ordered. The actual density of the compound can be found on the lot sheet from the compounder and this variable should be used to calculate the weight of the O-rings. In addition to the variables related to the compound, allowances must also be made for the lost O-rings during the manufacturing process.
For instance, a percentage value can be made for flash. Flash is material that is molded onto the O-ring during the molding process and it must be trimmed off the O-ring before it is use. Flash allowances for compression molded O-rings are typically between 2 and 4 percent.
Transfer molded O-rings have higher allowances for flash because the mold has additional material that must be trimmed off the O-rings. In addition to the flash allowances, another percentage value can be made for the number of O-rings that is rejected during the manufacturing process. For instance, some O-rings will have quality control defect and will be cut or discarded.
Thus, O-rings will be lost to the manufacturing process. These percentages will be added to the calculated weight of the net amount of O-rings that will be manufactured. The engineer in the manufacturing process should determine these percentages because they are the ones that is familiar with the specific molding method and how much flash will be trimmed off of the O-rings.
Finally, the number of O-rings that will be manufacture will impact the calculations for the weight of the O-rings. For instance, at low volumes of O-rings, it may make sense to use a higher percentage value for the number of O-rings that are rejected during the manufacturing process. At high volume, the cost of the O-rings may be impacted by the total weight of the batch of O-rings that will be manufactured since the total weight may impact the costs of the freight for the order or the minimum order requirement for the O-rings from the supplier.
Thus, it may make sense to calculate the weight of the O-rings at both low and high volumes of O-rings to compare the cost of the O-rings manufactured in each instance. An additional step that can be taken to improve the accuracy of the calculations of the weight of the O-rings is to actually weigh the first few O-rings that are manufactured from each mold. If the weight of the O-rings that are measured is more higher than the calculated weight of the O-rings, then the diameter of the cord may be higher than the calculated diameter of the cord, or the density of the compound may be higher than the density of the compound that is calculated.
In these instance, the calculations will need to be adjusted and the calculation of the weight of the O-rings will need to be run again. The accuracy of the calculation of the weight of the O-rings is essential so that the procurement department doesnt discover after the O-rings are manufactured that the weight of the O-rings was calculate incorrectly. Lastly, if a customer should change the drawing for the O-rings, the weight of those O-rings will need to be recalculated.
If a customer request that the inside diameter of the O-rings be changed, then the volume of the O-rings will change, which will impact the weight of the O-rings. If a customer request a change in the cross-section of the O-rings, the volume of those O-rings will change, which will impact the weight of the O-rings. These change to the designs will impact the calculations of the weight of those O-rings; thus, a calculator can be utilized to model these changes.
Overall, the weight of an O-ring is a calculation that link the geometry of the O-rings to the density of the compounds of the O-rings and the cost of manufacturing those O-rings. When utilized with the various measured variable, the calculation of the weight of an O-ring will be a dependable tool for the procurement departments of companies that manufacture O-rings.
