Ensure highest quality when using PRO-SET® products
Quality control measures can be employed by fabricators, large and small, to assure consistent high performance of PRO-SET epoxies.
This page covers:
Common PRO-SET problems solved
Getting the right mix ratio
Using a Durometer to achieve optimum epoxy ratio and hardness
Thorough mixing with a mechanical mixer
Compensating for temperature effects on epoxy curing
The vast majority of problems encountered when working with an epoxy system can be traced to either improper mix ratio or insufficiently mixed resin and hardener. Metering the two components at the proper mix ratio and thoroughly blending them helps ensure consistent, high-quality results.
To a lesser extent, problems may also arise from not properly compensating for changes in temperature. It is important to understand how changes in temperature can affect the cure characteristics of epoxy and how to counteract those effects.
PRO-SET pumps are designed to meter the correct ratio of resin and hardener for standard PRO-SET combinations. With any metering system, we recommend that you check the pump ratio frequently. You can use graduated containers to check the metered volume or a scale to check the ratio by weight. If the ratio is not within the acceptable range for the products you are using, fix the problem before carrying on.
Re-check the ratio anytime you experience problems with curing. We recommend that production facilities check their pump ratios on a regular basis.
Each resin/hardener combination will achieve optimum working, cure and mechanical properties at a specific mix ratio. If the actual mix ratio deviates from this ratio range, the physical properties of the resin system will decline as the ratio deviates from the acceptable range.
To check the cure of the epoxy we use the ASTM D-2240 method for Rubber Property—Durometer Hardness. This method is recommended for quality control purposes and not for establishing specifications. This test is performed using a durometer measuring the D scale. The indenter needle is pressed into the cured epoxy sample and the resistance is recorded on an indicator. Durometers are available from industrial supply companies.
Any instrument meeting the ASTM D-2240 requirements can be used. Some resin manufacturers specify Barcol hardness readings. However, we feel the D scale durometer is more sensitive than the Barcol tester and is more appropriate for epoxy testing. Unfortunately, there is no direct conversion from the D scale to Barcol scales.
It is often a good idea to prepare a special quality control sample for testing and to keep quality control samples of cured epoxy for future reference. It can be as easy as pouring a portion of the mixed epoxy you are using into a mould or suitable container.
Label this sample and cure it under the same conditions as your project. It may be sufficient to check the hardness right on the part you are building, as long as there is a flat area large enough to use the durometer.
A fully cured sample of epoxy will usually show a durometer D scale hardness of 81-90. A sample that has not had sufficient time to cure will have a lower hardness. However, if the hardness does not increase after a reasonable amount of time, there are several possible causes which should be investigated. The temperature may be too low to allow the epoxy to cure properly, the epoxy may have been mixed at the wrong ratio, or it may have not been mixed thoroughly, resulting in localised areas of off-ratio material.
When using a mechanical mixer to blend large batches of epoxy, it is crucial to scrape the sides and bottom of the container to ensure thorough mixing.
Low temperatures can increase working time, time to full cure and resin viscosity. Higher resin viscosity due to low temperatures can cause pumps to meter off ratio. It may be more difficult to thoroughly mix a very thick resin and hardener batch. It may also be more difficult to wet-out the fabric with very thick epoxy. The extended cure time can leave the epoxy vulnerable to damage if clamping pressure is removed too early.
Higher temperatures will reduce working time, cure time and resin viscosity. The builder should carefully evaluate the working conditions, size of job and number of workers in choosing the correct resin/hardener combination.