At Zhongxing Industrial Machinery, every casting must undergo rigorous PMI testing to meet the customer's customized needs.

In the casting industry, those of us who've been around for a while know that controlling the composition of metal materials is the cornerstone of product quality and safety. Positive Material Identification (PMI) testing is a crucial means for us to maintain quality control, ensuring that cast components meet design standards. Among the myriad testing technologies available, Optical Emission Spectroscopy (OES) has emerged as an indispensable core detection method for casting enterprises due to its high precision and efficiency. Today, let's delve into the four major types of PMI testing technologies for casting components, with a special focus on the advantages, applicable scenarios, and detection contents of OES technology.

I. Four Major Types of PMI Testing Technologies for Casting Components

Handheld X-Ray Fluorescence Spectrometer (XRF)

This device is like a "scout" on the field, capable of rapidly screening the surface composition of raw materials. However, its ability to identify deep-seated defects in metals is limited. Therefore, it is generally used for preliminary inspection of raw materials, giving us a general idea of their quality.

Portable Laser-Induced Breakdown Spectroscopy (LIBS)

It analyzes elements by generating plasma through laser ablation, making it suitable for outdoor or complex working conditions. But compared to OES, its precision is slightly lower. It's a good option for emergency use in special environments.

Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)

This equipment boasts high sensitivity and can analyze multiple elements simultaneously. It is the go-to choice for trace element detection in laboratories. However, it comes with a high equipment cost and requires destructive sampling, so it is typically used for precise laboratory testing.

Optical Emission Spectrometer (OES)

Based on spark discharge to excite metal atoms to emit characteristic spectra, OES offers both high precision and non-destructive testing capabilities. It has become the mainstream detection technology in the casting industry, akin to a "sharp sword" on our production lines.

II. The Importance of Raw Material Inspection

We all understand that raw materials are the "foundation" of casting products. If the composition of raw materials is subpar, no matter how hard we try afterward, the quality of the cast components will never be up to par. Therefore, it is imperative to conduct sampling and re-inspection before raw materials enter the production process. This is akin to building a house; if the foundation is unstable, the house is bound to collapse. Only by ensuring that the composition of raw materials meets the requirements can we proceed smoothly with subsequent casting work and guarantee product quality.

III. Core Advantages of OES Technology

High Precision and Efficiency

OES technology excites metal atoms through spark discharge and, combined with a high-resolution diffraction grating spectrograph, can achieve ppm-level element content detection. Take the Thermo Fisher Scientific ICP-OES as an example; it can support the simultaneous analysis of over 70 metal elements, with each detection taking just a few seconds. This efficiency significantly speeds up our production progress, enabling us to deliver products faster and meet customer demands.

Non-Destructive Testing Capability

Spark discharge only erodes a micron-level thickness of the metal surface, typically around 5 - 50μm, without damaging the overall structure of the cast component. For precious components like automotive engine blocks and aerospace precision castings, using OES for testing eliminates the concern of structural damage caused by sampling, thus avoiding associated losses. This is a tangible benefit.

Wide Linear Range and Low Detection Limit

The calibration curve of OES has a linear range of 4 - 6 orders of magnitude. It can detect both high-content major elements, such as Fe and Al with contents exceeding 90%, and ppm-level impurity elements, like P and S with contents below 0.01%. In the composition control of high-end alloy materials, such as superalloys and titanium alloys, OES is an irreplaceable "hero."

Easy Operation and Cost Control

Compared to ICP-OES, OES equipment has lower maintenance costs and simpler sample pre-treatment requirements, only needing surface cleaning. For instance, spark direct-reading spectrometers with automated feeding systems can operate continuously for 24 hours, and the cost per detection is about one-third of that of ICP-OES. This saves our enterprises a significant amount of money.

IV. Applicable Product Types for OES Technology

High-End Alloy Castings

For nickel-based superalloys like Inconel 718 used in aviation engine blades and cobalt-based alloys like Stellite 6 used in gas turbine turbine disks, which have stringent requirements for the fluctuation of trace elements such as Cr, Mo, and Nb, OES testing is the perfect choice.

Precision Mold Castings

Automotive mold steels, such as H13 and P20, require the detection of the uniformity of elements like C, Si, and Mn to prevent mold cracking. OES can accurately detect these elements, helping us avoid mold problems and reduce losses.

Pressure Vessel Castings

Stainless steels like 316L used in nuclear power main pipes must comply with ASME standards. OES can quickly verify whether the contents of Cr, Ni, and Mo meet the requirements, ensuring the safety of pressure vessels.

Medical Device Castings

Titanium alloys like Ti - 6Al - 4V used in orthopedic implants require the detection of elements such as Al, V, and interstitial elements like O and N to ensure biocompatibility. This is a matter of great importance for patient health, and OES testing helps us strictly control the quality.

V. Detection Contents of OES Technology

Verification of Major Element Content

Detect whether the content of major elements like Fe, Al, and Cu meets the grade standards. For example, according to ASTM A351, the Cr content in CF8M stainless steel should be between 18.0 - 21.0%. Only when the content of major elements meets the standards can the performance of cast components be guaranteed.

Control of Trace Elements

Identify harmful elements like P and S. For instance, a P content exceeding 0.04% can reduce the toughness of cast components. We also need to control the addition amounts of grain refiners like B and Zr. Although these trace elements are present in small quantities, they have a significant impact on the quality of cast components.

Screening of Impurity Elements

Detect low-melting-point impurities like Pb and Sn. A content exceeding 0.01% may lead to hot cracks. We also need to screen the segregation degree of elements like Si and Mn. Impurity elements are like "pests" in cast components and must be eliminated in a timely manner.

Grade Identification and Adulteration Detection

By comparing multi-element fingerprint patterns, we can quickly distinguish between 304 and 316 stainless steels and detect impurity elements like Cu and Zn in scrap steel return materials. This helps prevent the use of inferior materials and ensures the quality of our raw materials.

VI. Case Study: Application of OES in Aviation Castings

A certain aviation engine manufacturing enterprise used OES technology to control the composition of Inconel 718 blades. The detection items included major elements like Ni, Cr, Fe, Mo, Nb, Ti, and Al, as well as interstitial elements like C, O, and N. The detection standards had to comply with the AMS 5662 specification, which required a Cr content between 17.0 - 21.0% and an Nb content between 4.75 - 5.50%. Through rapid OES screening, it was found that the Nb content in a certain batch of blades was low, at only 4.62%. The unqualified products were promptly intercepted, avoiding the scrapping of an engine worth millions of dollars. This would have been a huge loss.

VII. Conclusion

With its high precision, non-destructive testing capability, and cost advantages, OES technology has become the core tool for PMI testing in the casting industry. In the field of high-end equipment manufacturing, it safeguards product quality and, through data-driven process optimization, helps enterprises achieve intelligent manufacturing upgrades. At Sinostar Industrial Machinery, we have stringent QC controls. Every step is equipped with professional and advanced equipment, and from raw material inspection to cast component detection, we use OES technology to strictly monitor quality, ensuring that our products are of the highest quality. In the future, with the continuous development of spectroscopic analysis technology, OES is sure to play an even greater role in emerging fields such as materials genomics and additive manufacturing. Let's wait and see!