The fulcrums of a cast iron platform are set differently according to its specifications. Generally, small-sized flat plates are equipped with three support points: two at one longitudinal end and one at the transverse center of the other end. This fulcrum arrangement ensures the stability of the flat plate while facilitating adjustment for users. For cast iron flat plates with a size exceeding 2000mm, additional support points are required; large-sized flat plates are typically designed with one support point every 1000mm. During the production, verification, and use of the flat plate, the position of its main support points may change due to bracket deformation or other factors. When adjusting the support points of a cast iron flat plate, a common practice is to first support three points along a line—even for large flat plates, three main support points should be properly positioned first, while the remaining points serve as auxiliary supports and can be fine-tuned after the flat plate is basically stabilized.

When verifying a cast iron platform used for inspection, the platform’s stability must be maintained; even slight vibrations can affect measurement results. The cast iron platform itself serves as the measurement reference surface and should be placed stably. When verifying with an autocollimator, the instrument and the flat plate should not be on the same rigid body, and the stability of the instrument bracket is particularly important. Therefore, verification regulations require that the verification site be solid and stable, and vibration should be avoided at the verification location.

The reason for this is as follows: Factories often place small flat plates on fitter benches or tables, which lack sufficient stability. The movement of verification personnel near the flat plate and the shifting of verification tools on the plate will generate varying gravitational forces, altering the flat plate’s spatial position and leading to inaccurate measurement results. Thus, when verifying such flat plates, they should be moved to a solid and stable site to avoid the impact of gravitational changes on measurement accuracy.

For small flat plates (especially rock flat plates) with dimensions below 400mm × 400mm, their own weight is relatively light, while verification tools (such as levels, reflectors, and bridge plates) are heavier. When these tools are placed at different positions, the load on the three fulcrums of the flat plate becomes unbalanced, causing contact deformation between the flat plate and its supports.

When verification personnel move on the cast iron platform during verification, the stability of the verification site should be considered, and attention should be paid to the impact of gravitational changes. In addition to ensuring the stability of the verification location, the weight of the verification tools should also be taken into account, and auxiliary supports should be added to enhance the stability of the flat plate’s placement.

How to Select a High-Quality Cast Iron Platform

Nowadays, cast iron platforms have become a crucial type of measuring tool in the measuring instrument industry and play an irreplaceable role in machine tool processing applications. So, how should we select a high-quality cast iron platform?

1. Check the Material

To choose a good cast iron platform, the first step is to examine its material. The market is flooded with cast iron platforms of varying quality, many of which do not meet standards and use substandard materials. Therefore, consumers must verify the material of the product when purchasing. The specified material grade for this type of measuring tool is HT200-HT300, so buyers should confirm that the product meets this requirement. Additionally, new cast iron platforms will have obvious polished marks, which are left by the scraping process during production—this can be used to judge the quality of the product’s manufacturing process.

2. Evaluate the Manufacturer

Due to the wide application range of cast iron platforms, there are many manufacturers on the market. However, a large number of manufacturers is not necessarily a good thing, as it may lead to vicious market competition. When purchasing, it is essential to choose a reputable manufacturer: first, check whether the manufacturer has complete production procedures, and do not pursue low prices at the cost of buying unqualified products (without manufacturer, production date, or quality certification). For safety, it is advisable to visit the manufacturer in advance to inspect the physical products before purchasing a cast iron flat plate—this helps reduce the risk of buying substandard products.

Machining Allowance of Cast Iron Platforms

During the casting process of cast iron platforms, a machining allowance must be reserved. The thickness of the metal layer removed from the blank during machining is called the machining allowance of the cast iron platform. Machining allowances can be further divided into process allowances and total allowances:

• A process allowance refers to the thickness of the metal layer that needs to be removed in a specific machining process.

• A total allowance is the total amount of metal to be removed from the blank to the finished product, which equals the sum of the process allowances for the corresponding surface.

The purpose of reserving a machining allowance for cast iron platforms is to eliminate machining errors and surface defects left by the previous process—such as the cold-hardened layer, blowholes, sand inclusions, decarburized layer, surface cracks on castings, the oxide scale on forgings, and the internal stress layer and surface roughness after cutting. This process ultimately improves the precision of the cast iron platform.

The size of the machining allowance has a significant impact on both machining quality and production efficiency:

• An excessively large machining allowance not only increases the workload of mechanical processing, reduces productivity, but also raises consumption of materials, tools, and electricity, thereby increasing machining costs.

• An excessively small machining allowance, on the other hand, cannot eliminate various defects and errors from the previous process, nor can it compensate for the clamping errors during the current machining process, which may result in waste products.

The principle for selecting the machining allowance is to keep it as small as possible while ensuring quality. Generally, the more precise the machining process (e.g., finishing), the smaller the process allowance.

Casting Process and Material Properties of Cast Iron Platforms

1. Resin Sand Molding for Cast Iron Platforms

Cast iron platforms use resin sand molding, which has high rigidity. This rigidity helps with the graphitization expansion of cast iron during the solidification process (especially in the early stage of pouring), effectively preventing defects such as shrinkage holes and porosity in the blank. As a result, castings can be produced with minimal risers or even no risers.

2. Chemical Composition of Cast Iron

The main chemical elements in ordinary cast iron are carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and sulfur (S). Among these, carbon and silicon are the most fundamental components, with typical contents of 3.2–3.6% for carbon and 1.9–2.2% for silicon. Manganese is usually present in low content and has little impact on performance. Phosphorus and sulfur are generally regarded as impurities and thus their contents are restricted: phosphorus content should be <0.15%, and sulfur content <0.12%. However, in anti-friction cast iron, a small amount of phosphorus is occasionally added.

3. Casting of Cast Iron Flat Plates

Most measuring tools in the cast iron flat plate series are cast using gray cast iron or ductile iron. To produce qualified castings from gray cast iron, multiple processes are required, including sand rolling, molding, smelting, pouring, cleaning, and inspection. The quality of measuring tool castings depends on strict control of each link in the casting process—among these, molding process control is critical for producing measuring tool castings, as it directly affects the casting quality.

Aging Treatment and Ductile Iron Platforms

1. Aging Treatment for Dimensional Stability

In mechanical production, to stabilize the dimensions of castings, inspection flat plate castings are often placed at room temperature for an extended period before being subjected to machine cutting. This processing method is also called aging treatment, though it does not belong to the metal heat treatment process. Aging treatment improves production efficiency, reduces casting costs, and facilitates the use and management of castings.

2. Ductile Iron Platforms

Ductile iron is increasingly widely used due to its excellent casting performance. Internal stress can cause cast iron platforms to deform, warp, and change in dimensions—even after machining, these defects cannot be eliminated. Therefore, cast iron platforms generally require aging treatment to relieve internal stress. Ductile iron flat plates are a new type of flat plate developed in recent decades, and their mechanical properties are close to those of medium-carbon steel.