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【拉力試驗機 】教你選購拉力試驗機的辦法

日期:2020-06-11  瀏覽次數:

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

1. Tensile properties of high molecular polymers...

當用作材料時,高分子聚合物需要具有必要的機械性能。

可以說,對于高分子聚合物的大多數應用而言,機械性能比其他物理性能更為重要。

高分子聚合物在所有已知材料中均具有廣泛的機械性能*。 這是因為聚合物由長鏈分子組成,并且分子運動具有明顯的弛豫特性。

如果聚合物材料具有相對較高的伸長率,則PE的斷裂伸長率通常為90%至950%(包括低密度聚乙烯LLDPE的線性伸長率較高),通過特殊的制造工藝,某些材料的伸長率可以達到 1000%,而普通聚合物材料的斷裂伸長率通常在50%至100%之間。

通常,為了材料的拉伸性能,需要熱收縮膜和拉伸膜。

2.拉伸試驗。

拉伸測試(應力-應變測試)通常將材料樣品的兩端以一定距離夾在兩個固定裝置上。 這兩個夾具分開并以一定速度拉伸樣品,以測量樣品上的應力變化。 直到樣品被破壞。

拉伸試驗是研究材料的機械強度*的廣泛使用的方法之一,它需要使用恒速拉伸試驗機。

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.

對于塑料薄膜,標記線之間的距離通常在25-50mm之間。

因為拉伸試驗中樣品的變形和伸長率不僅在標記線之內,所以兩個固定裝置之間的所有樣品都會得到不同程度的拉伸變形。

在標準中,與標記線之間的距離相對應的夾具之間的初始距離在80至115 mm之內。 如果兩個夾具之間的樣品可以保持相同的伸長率并假定為500%,則拉伸機的有效行程需要為480690mm,如果樣品的伸長率為1000%,則拉伸機的有效行程為 至少應確保880mm以確保正常測試。

3.2

樣品夾具。

GB13022-91“塑料薄膜拉伸性能測試方法”中對夾具的描述為:“測試機應配備合適的夾具。夾具不得使樣品在夾具上斷裂。 在試驗機上安裝夾具后,應立即將其對準一條直線,以使樣品的長軸與通過夾具中心線的拉伸方向重合。

......將樣品放置在測試機的兩個固定裝置中,以使樣品的縱軸與上下固定裝置的中心線重合,并應緊緊并適合防止樣品滑落 并破壞固定裝置。

"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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