When testing on a platform, vibration should be minimized and support points should be properly controlled. The layout of the platform's support points varies depending on the platform's specifications. Generally speaking, small platforms typically use three support points: two at each longitudinal end and one at the center. This design ensures stability and facilitates user adjustment. Cast iron platforms exceeding 2000mm require additional support points. Large platforms typically have support points spaced every 1000mm.
During the manufacturing, calibration, and use of the platform, the positions of the main support points may shift due to deformation or other issues with the bracket. When adjusting a cast iron platform, the main support points, which form a three-point line, are typically adjusted first. Even for large platforms, the three main support points should be stabilized first, with the remaining support points serving as auxiliary points. Fine-tuning can then be performed once the platform is generally stable. The testing platform must remain stable during calibration; even slight vibration can affect measurement results. Since the platform itself serves as the reference surface for measurement, its placement must be secure. When using an autocollimator for calibration, the instrument and platform are not mounted on the same rigid body, making the stability of the instrument bracket particularly critical. Therefore, calibration procedures clearly require that the testing environment must be sturdy and stable, and away from sources of vibration.
Many factories often place small flatbeds directly on benches or ordinary tabletops, which lack stability. Movement of the calibration personnel or the movement of tools on the platform can cause gravity fluctuations, leading to slight displacement of the platform and measurement errors. Therefore, these flatbeds should be moved to a sturdy testing area during calibration to minimize the impact of gravity fluctuations on the results. Small flatbeds under 400mm x 400mm, especially granite flatbeds, are lightweight, while the testing tools (such as levels, reflectors, or bridges) are relatively heavy. When the tools are repositioned, the three-point support forces can be uneven, causing slight deformation between the platform and the supports. When calibration personnel move around the platform, they should also be aware of the stability of the site and the effects of gravity fluctuations. If necessary, additional supports should be added to enhance stability.
Material is a key factor when selecting a platform. Currently, the quality of products on the market varies greatly, and many do not meet standards. Qualified cast iron platforms should be between HT200 and HT300, so carefully check before purchasing. Additionally, new products often show signs of polishing from the scraping process, which is a crucial indicator of the quality of the workmanship. Secondly, pay attention to the manufacturer. Due to its wide application, there are many manufacturers in the market, leading to fierce competition. However, a large number of manufacturers does not necessarily guarantee high quality. It is particularly important to choose a reputable and qualified manufacturer. Avoid buying products that are "three-no" just for the sake of cheapness. A safer approach is to visit the manufacturer and inspect samples before purchasing to avoid substandard products.
During the casting process, platforms must have a certain amount of machining allowance, which is the thickness of the metal layer to be removed from the blank. Machining allowance is divided into process allowance and total allowance. The former is the thickness of the metal layer to be removed in a specific process, while the latter is the total amount removed from the blank to the finished product. The purpose of machining allowance is to eliminate errors and defects left by previous processes, such as chill layers, pores, sand inclusions, decarburization layers, cracks, scale, and internal stress layers after cutting, thereby improving the accuracy of the platform. Excessive allowance not only increases machining workload and reduces efficiency, but also wastes materials, tools, and energy. Excessive allowance, on the other hand, makes it impossible to eliminate defects or errors and may even result in scrap. Therefore, machining allowance should be minimized while ensuring quality. Generally speaking, process allowances are smaller during finishing.
During the casting process, using resin sand molds can increase mold rigidity, facilitate graphitization and expansion during the initial pouring phase, thereby reducing defects such as shrinkage cavities and porosity in the blank and achieving low-riser or no-riser casting. Common chemical compositions of cast iron include carbon, silicon, manganese, phosphorus, and sulfur. Carbon and silicon are the primary components, with carbon generally ranging from 3.2 to 3.6, and silicon controlled between 1.9 and 2.2. Phosphorus and sulfur are generally considered impurities and must be strictly controlled to <0.15 for phosphorus and <0.12 for sulfur, respectively. However, phosphorus is added in appropriate amounts to some anti-friction cast irons.
Cast iron flat plate measuring tools are mostly made of gray cast iron or ductile iron. To obtain qualified castings, multiple steps must be taken, including sand making, molding, smelting, pouring, cleaning, and inspection, with strict quality control at every step. The molding process, in particular, directly impacts casting quality. In mechanical manufacturing, to ensure dimensional stability, flat castings are often left at room temperature for a period of time before machining. This method, known as natural aging, is not considered a heat treatment process, but it can effectively reduce production costs and improve reliability.