4.1 A Rockwell hardness number is a number derived from the net increase in depth impression as the load on an indenter is increased from a fixed minor load to a major load and then returned to a minor load (Procedure A). A Rockwell alpha (α) hardness number represents the maximum possible remaining travel of a short-stroke machine from the net depth of impression, as the load on the indenter is increased from a fixed minor load to a major load (Procedure B). Indenters are round steel balls of specific diameters. Rockwell hardness numbers are always quoted with a scale symbol representing the indenter size, load, and dial scale used. This test method is based on Test Methods E18. Procedure A (Section 11) yields the indentation of the specimen remaining 15 s after a given major load is released to a standard 10-kg minor load. Procedure B (Section 12) yields the indentation of the indenter into the specimen after a 15-s application of the major load while the load is still applied. Each Rockwell scale division represents 0.002-mm (0.00008-in.) vertical movement of the indenter. In practice, the Rockwell hardness number is derived from the following relationship:
where: | ||
HR | = | the Rockwell hardness number, and |
e | = | the depth of impression after removal of the major load, in units of 0.002 mm. This relation only holds for the E, M, L, R, and K scales. |
4.2 A Rockwell hardness number is directly related to the indentation hardness of a plastic material, with the higher the reading the harder the material. An α hardness number is equal to 150 minus the instrument reading. Due to a short overlap of Rockwell hardness scales by Procedure A, two different dial readings on different scales may be obtained on the same material, both of which may be technically correct.
4.3 For certain types of materials having creep and recovery, the time factors involved in applications of major and minor loads have a considerable effect on the results of the measurements.
4.4 The results obtained by this test method are not generally considered a measure of the abrasion or wear resistance of the plastic materials in question.
4.5 Indentation hardness is used as an indication of cure of some thermosetting materials at room temperature. Generally, an uncured specimen has a hardness reading below normal.
4.6 Each Rockwell hardness scale in Table 1 is an extension of the proceeding less severe scale, and while there is some overlap between adjacent scales, a correlation table is not desirable. Readings on one material may be satisfactory for such a table, but there is no guarantee that other plastic materials will give corresponding readings because ......
努氏硬度 努氏硬度是作为绝对数值而测得的硬度,主要在加工方面使用该数值。一般来说,金刚石的努氏硬度为7000~8000千克/平方毫米韦氏硬度 一定形状的硬钢压针,在标准弹簧试验力作用下压入试样表面,用压针的压入深度确定材料硬度,定义0.01mm的压入深度为一个韦氏硬度单位。韦氏硬度单位表示为HW。...
根据试验机的用途分类可分为两类试验机:有试验机的机械测量仪、试验机等都属于这一类的机械性能的测定:一个静载试验机、拉力试验机、压力试验机,扭转试验机、复合应力试验机、试验机、蠕变破裂强度试验机、试验机、布氏硬度、罗克韦尔硬度计和维氏。动态负载测试机:冲击试验机、布氏硬度计、在冲击疲劳试验机、硬度计。高温度温室,高温炉,低温箱。高温炉拉伸试验:配套使用液压试验机和电子试验机为样品提供高温环境。...
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