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【拉力试验机 】教你选购拉力试验机的办法

日期:2020-06-11  浏览次数:

【Tensile testing machine】Teach you how to choose tensile testing machine

1. Tensile properties of high molecular polymers...

当用作材料时,高分子聚合物需要具有必要的机械性能。

可以说,对于高分子聚合物的大多数应用而言,机械性能比其他物理性能更为重要。

高分子聚合物在所有已知材料中均具有广泛的机械性能*。 这是因为聚合物由长链分子组成,并且分子运动具有明显的弛豫特性。

如果聚合物材料具有相对较高的伸长率,则PE的断裂伸长率通常为90%至950%(包括低密度聚乙烯LLDPE的线性伸长率较高),通过特殊的制造工艺,某些材料的伸长率可以达到 1000%,而普通聚合物材料的断裂伸长率通常在50%至100%之间。

通常,为了材料的拉伸性能,需要热收缩膜和拉伸膜。

2.拉伸试验。

拉伸测试(应力-应变测试)通常将材料样品的两端以一定距离夹在两个固定装置上。 这两个夹具分开并以一定速度拉伸样品,以测量样品上的应力变化。 直到样品被破坏。

拉伸试验是研究材料的机械强度*的广泛使用的方法之一,它需要使用恒速拉伸试验机。

According to the different load measurement methods, the tensile testing machine can be roughly divided into two types of pendulum tensile testing machine and electronic tensile testing machine. At present, the electronic tensile testing machine is mostly used.

3. Electronic tensile testing machine

Select indicators.

Since the flexible packaging material is mainly a polymer or its related materials, as mentioned above, the elongation of the polymer material is much better than that of metals, fibers, wood, plates, etc., so the tensile machine for detecting polymer There is a certain difference from the conventional tensile testing machine for tensile properties of materials. In particular, it is necessary to pay attention to the effective stroke of the electronic tensile machine and the sample fixture.

3.1

Effective itinerary.

In the tensile test, although the size of the sample used is small, the elongation of the material is generally relatively high, so the tensile performance of the flexible packaging material needs to be equipped with a tensile machine with a large stroke, otherwise the fixture operation may exceed The service limit of the stroke causes damage to the equipment.

The calculation formula for the elongation at break or yield elongation (εt, unit is %) given in GB13022-91 "Test Methods for Tensile Properties of Plastic Films" is as follows: where: εt is the elongation at break or yield extension Elongation; L is the distance between the marking lines when the specimen breaks or yields; L0 is the distance between the marking lines.

It should be noted that in the calculation of elongation, we only collect the elongation between the two markings on the sample.

The marking lines are drawn on the finished sample by printing or manually (the addition of the marking line should have no effect on the sample), and what is the distance between the marking lines? Most of the distances given by different standards are different, and in the same standard, different sample sizes are often given for different materials, so the distance between the marking lines is also different, but this is conducive to the detection of extension Very long or very small material and get the best test results.

对于塑料薄膜,标记线之间的距离通常在25-50mm之间。

因为拉伸试验中样品的变形和伸长率不仅在标记线之内,所以两个固定装置之间的所有样品都会得到不同程度的拉伸变形。

在标准中,与标记线之间的距离相对应的夹具之间的初始距离在80至115 mm之内。 如果两个夹具之间的样品可以保持相同的伸长率并假定为500%,则拉伸机的有效行程需要为480690mm,如果样品的伸长率为1000%,则拉伸机的有效行程为 至少应确保880mm以确保正常测试。

3.2

样品夹具。

GB13022-91“塑料薄膜拉伸性能测试方法”中对夹具的描述为:“测试机应配备合适的夹具。夹具不得使样品在夹具上断裂。 在试验机上安装夹具后,应立即将其对准一条直线,以使样品的长轴与通过夹具中心线的拉伸方向重合。

......将样品放置在测试机的两个固定装置中,以使样品的纵轴与上下固定装置的中心线重合,并应紧紧并适合防止样品滑落 并破坏固定装置。

"Due to the particularity of the mechanical properties of polymer materials and the special use of flexible packaging materials, the thickness of the samples tested by the flexible packaging materials is very thin, and the general fixtures cannot meet the requirements. Improper use will cause the specimens to break at the fixture and cause the test to fail. .

3.3

TF-213 intelligent electronic tensile testing machine.

Shanghai Instrument is an enterprise specializing in the production of flexible packaging materials testing equipment. Especially for the characteristics of large elongation of flexible packaging materials, the TF-213 intelligent electronic tensile testing machine has been made with a stroke of up to 1000mm, which can be stretched, peeled, torn, and heated. Sealing and other seven kinds of tests, and professionally designed various types of test fixtures dedicated to flexible packaging materials. It is a mechanical property tensile testing machine tailored for flexible packaging materials.

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