Classification of Shield Tunneling Methods

There are many types of tunnel boring machines, and they can be classified in various ways. Based on the excavation method—whether manual or mechanical—they are divided into hand-excavated shields and mechanized shields. Additionally, depending on how the working face supports the soil, shields can be categorized as open-type or closed-type. Finally, shields can also be classified according to their design and excavation techniques, falling into either hand-excavated or mechanically operated categories.

2013-08-28

Wear Characteristics of Wear-Resistant Hammer Heads Used in Cement Plant Limestone Crushing

The silicon content in the chemical composition of limestone directly affects the service life of hammer heads—higher silicon levels lead to shorter lifespans. Ideally, the silicon content in limestone should remain below 2%. On the other hand, the compressive strength of limestone is closely linked to hammer head durability: the higher the compressive strength, the less brittle the material becomes, but paradoxically, this also reduces the hammer head's lifespan. Hammer head selection and manufacturing quality play a critical role in determining how long a hammer head will last. Historically, the materials used for crusher hammers in the cement industry were primarily high-manganese steels, with ZGMn13Cr2 being the preferred choice due to its excellent wear resistance. However, even this material struggles under conditions involving high-silicon content and extremely hard limestone—and when combined with unfavorable operating conditions, its lifespan can drop dramatically. For instance, a single set of hammers might fail after processing just 100,000 tons of material. With advancements in hammer technology, newer materials have emerged, such as ultra-high-manganese steel and dual-alloy composite wear-resistant hammers. Ultra-high-manganese steel, specifically ZGMn18Cr2MoRe, features an increased manganese content compared to the traditional ZGMn13Cr2. This enhancement aims to boost the material’s hardness during heat treatment, thereby improving wear resistance and extending the hammer’s service life. Yet, there’s a practical limit to how much manganese and alloy elements can be added, as increasing these components often compromises the material’s toughness. As a result, ultra-high-manganese hammers are not recommended for applications involving significant impact forces. Dual-alloy composite wear-resistant hammers come in three main designs: First, a layer of hard alloy is welded onto the working surface of the hammer, significantly enhancing its abrasion resistance. Second, during casting, the alloy content (particularly chromium) in the hammer’s working area is carefully controlled to maximize wear performance. Finally, hard alloy rods or blocks may be embedded directly into the hammer’s working zone for added durability. Ultimately, the quality of hammer head manufacturing depends heavily on factors like precise geometric dimensions, carefully calibrated alloy compositions and contents, as well as the depth and uniformity of the heat treatment process. Additionally, operational conditions during crushing activities have a profound impact on hammer life: for example, the particle size of the limestone greatly influences hammer durability; moisture content in the limestone directly affects wear rates; frequent blockages in the crusher’s discharge grate, coupled with continued operation despite these obstructions, can severely shorten hammer life; and finally, the presence of impurities in the raw limestone material can also significantly degrade hammer performance. Each of these factors plays a crucial role in determining the overall longevity of wear-resistant hammers.

2013-08-27

Analyzing 4 Factors That Influence Hammer Head Lifespan

Crusher hammer heads include: hammer crusher hammers, compound crusher hammers, sand-making machine hammers, fine-crushing machine hammers, and stone-crushing machine hammers, among others. Their lifespan depends on the following four key factors: 1. The physical properties of the mineral and the characteristics of its accompanying materials (such as abrasiveness to metal, soil content, moisture levels,黏塑性 [viscoplasticity], compressive strength, etc.). 2. The rationality of the machine’s internal structural design. 3. The appropriateness of the material selection for the hammer head and the quality of its manufacturing process. 4. The proper operational techniques employed during use. The first factor is an inherent, objective condition—something that exists naturally and must be understood accurately from the outset. As for the second factor, it involves making necessary adjustments within the machine to ensure optimal performance tailored to both the properties of the material being processed and the specific requirements of the production process.

2013-08-27

Non-Destructive Construction Techniques for Large-Diameter Pipelines

In recent years, Tianjin has seen rapid advancements in its urban infrastructure development, with the city steadily expanding in size. As a result, sewage discharge volumes have been on the rise. At the same time, efforts to protect rainwater resources, implement stormwater-sewage separation systems, and enhance the city's flood-control capabilities have driven significant year-on-year growth in the scale of Tianjin’s newly constructed underground drainage networks. Meanwhile, with the city’s traffic volume steadily increasing—leading to longer and wider roads—the length and diameter of rainwater and sewage pipes beneath road surfaces have also grown substantially, ensuring that the city’s infrastructure can effectively meet its evolving needs.

2013-08-27