Simple Solutions That Work! Issue 12

Continued on next page 61 BACK TO BASICS PUSHKRAJ JANWADKAR CEO & Executive Director VERSATILE EQUIPMENT PVT LTD ARTICLE TAKEAWAYS: • Understanding sieve grades and analysis • Establishing relationship between Master and Working Sieve Set and Sieves INTRODUCTION: It is widely recognized that sieve analysis of molding sand is a critical test and helps governing quality of casting in many ways. It is tough to judge if a test sieve is no longer useful for measurement of grain size distribution and AFS number calculation. Though a certificate accompanying the sieve or sieve set might have an expiry date, we know that a sieve, as opposed to other testing equipment, cannot be corrected once it has gone out of tolerance. I would like to shed some light on maintaining good practices to make sure that every measurement taken with sieve analysis is an actual representation of the state of the sample being tested. Let’s begin with understanding what “Grade” means in terms of sieve. Sieve Grades and What they Mean Sieves can be categorized in many ways, see the non- would confuse many users. The standards divide the sieves into three main categories, each costing much more than the previous sequentially. Compliance grade sieve: Issuing a compliance certificate is mandatory for a manufacturer who claims conformance to ASTM E11 or ISO3310-1 standard. The certificate may not give any statistical data that is generated during inspection of the sieve because the measurements are supposed to be taken on the sieve cloth (mesh) before it is mounted on a frame. The certificate only states that the sieve complies with XYZ standard and must have predicted value of confidence level of standard deviation at 66% for the process of compliance grade certification. Inspection grade sieve: Upon request, the manufacturer should provide an inspection grade certificate. An inspection grade sieve certificate mentions the statistical data. Statistical data includes average aperture size, separately in both the warp and weft direction of the wire cloth. The manufacturer may charge you extra for this data. There must be predicted value of confidence level of standard deviation at 99% for the process of inspection grade certification. Calibration grade sieve: Calibration grade sieve gets checked for more than double the number of apertures than their less fortunate counterparts. There must be predicted value of confidence level of standard deviation at 99.73% for the process of calibration grade certification. Important: The manufacturer must give you results SIEVE MESH: MAINTAINING THE PRECISION Figure 1 comprehensive classification in Fig. 1. Let’s focus on the last column, grade. Why focus on grades when we are talking about maintaining precision? That will be discussed later in this article. Worldwide, analytical sieves for foundry use are governed largely by two standards: ASTM E11-17 and ISO3310-1: 2016. The recent edition shows that the ASTM standard is following it’s ISO counterpart to be more strict, so a sieve mesh which qualifies for ISO standard invariably qualifies with ASTM. Previously, when ASTM standard was more relaxed, mismatch in grain size distribution