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    • 洛氏硬度计的常规检测流程
    • 本站编辑:莱州市试验机金刚石工具厂发布日期:2019-08-09 18:16 浏览次数:

      洛氏硬度计虽然结构简单,操作方便,但如果长期操作不当,检验硬度失准,将使产品质量受到很大影响,硬度计带来不佳后果。现将我们在检定中常见的几种误差及处理方法介绍如下:

        一、人为误差:

        1、操作人员技术熟练程度不够,实践经验较差,应由熟悉操作硬度计的人员使用;

        2、加荷过快,持荷时间短,低硬度的零件硬度偏高,而加荷过慢,持荷时间长,硬度偏低,操作时加荷应平整,保持一定加荷时间。

        二、被测零件影响的因素:

        1、不同的表面光洁度在洛氏硬度测试时,表现出不同的影响。表面光洁度愈低,高硬度测试时其硬度愈高,反之硬度越低,有刀痕的粗糙表面,淬火时首先*快冷却,或很坚硬的表层,硬度值就高。反之,调质件高温回火时,有刀痕的表层组织先转变,抗回火的能力小,硬度值就低。在测试表面光洁度Δ7以下的零件时,必须使用废砂轮精磨,再用锉刀锉磨光滑,或用细的手砂轮磨光,然后揩擦干净;

        2、热处理零件表面有盐渍、沙子等物,当加负荷时,零件会产生滑移,若有油腻存在,金刚头压入时起润滑作用,减小磨擦,增加压深。这两项原因使所测硬度值偏低。零件测试的部位氧化皮蔬松层薄的硬度值降低,氧化皮致密层厚的硬度值增高。对欲测硬度的零件必须去除氧化皮,揩擦干净,不得有脏物;

        3、斜面(或锥度)、球面及圆柱体零件对硬度测试的误差较平面大。当压头压入这种零件表面时,压入处四周的抗力比平面小,甚至有偏离、滑移的现象,压深增大,硬度降低。曲率半径愈小,斜度愈大,硬度数值的降低愈显著。金刚石压头也容易损坏。对这类零件要设计专用工作台,使工作台和压头同心。

        三、压头的影响:

        1、金刚石压头不符合技术要求或是使用一段时间后有磨损,简单判断金刚石压头是否损坏方法:用金刚石压头在光滑玻璃表面来回刮几下看玻璃表面如没有刮痕说明压头是好的,否则压头已经损坏。操作者如不能判断金刚石的好坏,可由计量测试机构进行检定;

        2、钢球压头强度和硬度不够,容易产生变形。钢球扳压扁产生长久变形后呈椭圆,短轴垂直于零件表面时,压痕浅,示值高;长轴垂直于零件表面时,压痕加深,示值降低,钢球允差小0.002mm。

        四、载荷方面:

        1、初负荷:弹簧和主轴、杠杆和百分表之间有摩擦,造成100N的增大或减小。调整螺丝松旷、调整移动,顶杆位置不当。起始线有差异,引起初负荷不对。如果初负荷不对,应调整弹簧、主轴、杠杆、百分表等处的配合。调整块的位置移动合适以后,紧固调整螺丝,同时要紧固顶杆位置,初负荷的允差应小于±2%;

        2、主负荷:杠杆比例不对,吊杆和砝码的配重有误差;主轴、杠杆和砝码有偏斜,均会使主负荷产生误差。杠杆比不对,应进行调整。刀口有磨损应修复或更换,主轴变形要进行校直。主轴、杠杆和砝码偏斜应拨正。各种标尺主负荷的允差小于±0.5%。

        五、硬度计(洛氏硬度计)安置不正。硬度计不处于水平位置,测试硬度时,其值偏低。用水平仪测量水平度,然后垫平硬度计。

        六、零件某一测试部位的表面与工作台接触不佳,或支承点不稳固,将会产生滑移、滚动、翘起等现象。这不仅使所得结果不准,还会损坏仪器。

    Although rockwell hardness tester is simple in structure and easy to operate, if it is improperly operated for a long time, the quality of products will be greatly affected, and the hardness tester will bring bad consequences. Now we will introduce some common errors and processing methods in the verification as follows:

    1. Human error

    1. Operators are not skilled enough and have poor practical experience, so they should be used by those who are familiar with the operation of durometer;

    2, too fast loading, short load holding time, low hardness parts hardness on the high side, and too slow loading, long load holding time, low hardness, the operation of loading should be flat, maintain a certain loading time.

    Ii. Factors affecting the tested parts:

    1. Different surface finishes show different effects in rockwell hardness test. The lower the surface finish, the higher the hardness in the high hardness test, and vice versa, the lower the hardness, the rough surface with knife marks, when quenching * fast cooling first, or very hard surface, the hardness value is high. On the contrary, when tempering at high temperature, the surface structure with knife marks changes first, the resistance to tempering is small, and the hardness value is low. Δ surface finish of the test the following seven parts, must use the grinding wheel finishing grinding, reoccupy file file grinding smooth, or with a hand wheel polishing, then wipe and clean;

    2, heat treatment parts surface salt, sand and other things, when the load, the parts will produce slippage, if there is greasy, diamond head into the lubrication, reduce friction, increase the depth of pressure. These two reasons make the hardness measured low. The hardness value of the thin oxide peel pinewood layer decreased and the hardness value of the thick oxide peel dense layer increased. To measure the hardness of the parts must be removed from the oxide skin, wipe clean, no dirt;

    3, bevel (or taper), spherical and cylindrical parts of the hardness test error than plane. When pressing a head into the surface of this kind of part, the resistance all round pressing place is smaller than plane, have deviation, the phenomenon of slip even, press deepness increase, hardness decreases. The smaller the radius of curvature, the larger the slope, the more significant the decrease of hardness value. Diamond head is also easily damaged. To this kind of spare parts must design the special work table, causes the work table and the pressure head to be homocentric.

    Iii. Impact of head:

    1. The diamond indenter does not meet the technical requirements or is worn after being used for a period of time. A simple method to determine whether the diamond indenter is damaged: scrape the glass surface with the diamond indenter for several times to see that the glass surface is good if there is no scratch, otherwise the indenter has been damaged. If the operator cannot judge whether the diamond is good or bad, it can be verified by a measuring and testing institution.

    2, steel ball head strength and hardness is not enough, easy to produce deformation. When the short shaft is perpendicular to the surface of the part, the indentation is shallow and the indication value is high. When the long shaft is perpendicular to the surface of the part, the indentation deepens, indicating value decreases, and the tolerance of steel ball is 0.002mm smaller.

    Iv. Load:

    1. Initial load: there is friction between spring and spindle, lever and dial indicator, resulting in the increase or decrease of 100N. Adjust the screw loose, adjust the movement, the ejector position is improper. The difference of starting line causes wrong initial load. If the initial load is not correct, adjust the spring, spindle, lever, dial indicator, etc. When the position of the adjusting block is moved properly, tighten the adjusting screw and tighten the position of the ejector. The tolerance of initial load should be less than ±2%.

    2. Main load: the proportion of lever is wrong, and the balance weight of derrick and weight is wrong; The deviation of spindle, lever and weight will make the main load error. Lever ratio is wrong, should undertake adjusting. Blade wear should be repaired or replaced, spindle deformation to be straightened. The deviation of spindle, lever and weight should be corrected. The tolerance of main load of various scales is less than ±0.5%.

    5. Improper placement of hardness tester (rockwell hardness tester). The durometer is not in a horizontal position and its value is low when the hardness is tested. Measure levelness with a leveler and flatten the hardness tester.

    Six, the surface of a certain test part and the table contact is not good, or the support point is not stable, will produce sliding, rolling, warping phenomenon. This not only makes the results inaccurate, but also damages the instrument.