There are many raw material tests for industrial yarn and thread and not all manufacturers follow the same test methods. One common property seen on industrial yarn specifications is the results for hot air shrinkage. The primary test method used for hot air shrinkage, ASTM D4974, tells the end user if the raw material meets their shrinkage requirements. When comparing shrinkage results, it is important to understand the test method and if there are any variables.
For example, if a supplier tests at a condition of 190C for 10 minutes with a 9g pretension, you will get a vastly different result with material from another supplier who tests at 177C for 2 mins at 0.05 g/dn. However, when both of these yarns are tested under the same conditions, they may be nearly identical. Wherever the method is not specified, we default to the ASTM D4974 testing method.
This is one of the many ASTM tests Service Thread uses to ensure our product quality meets or exceeds our customers expectations.
Hot air shrinkage is important, specifically in the manufacturing of rubber goods such as belts and hoses. If you use a high shrinkage yarn in a hose for example, it will constrict around the inside tube in the hose and draw the diameter down, rendering your product useless.
In this video, we demonstrate the ASTM D4974: Hot Air Shrinkage Test.
The shrinkage test is performed at a temperature of 177 degrees Celsius for two minutes. We use a pretension weight that is 0.05 grams per denier. For this example, we are going to use a thousand-denier low shrink material. That means I need a 50-gram weight to apply as pretension.
1. Secure the 50-gram weight to the yarn.
2. Put the yarn in the clamps, resetting the scale to zero.
3. Wait for two minutes and read the result. Wait for the timer to go off.
When the timer expires, you read the shrinkage value in percentage on the scale. This particular sample has a shrinkage of 1.2%.
For comparison, we’ll look at a thousand-denier high shrinkage yarn using the same method.
1. Again, secure the weight and fix the yarn in the clamps and start the test.
2. As you can see, even the initial shrinkage is much higher.
Would you like to learn more about conducting an ASTM D4974 Hot Air Shrinkage Test? View our post on Hot Air Shrinkage Tests For Yarn & Cord Explained.