The clamshell bucket for excavators is the reference equipment for handling scrap metal, bulky waste, wood, and large bulk materials. Its name derives from its characteristic shape: multiple arms that open in a radial pattern like the tentacles of a spider, capable of securely grasping bulky and irregular materials that traditional buckets cannot handle.
In scrap collection centers, waste treatment platforms, and industrial demolition sites, the spider for excavators is the tool that allows for the rapid, precise, and safe movement of large volumes of material — all with a single operator from the machine’s cabin. In this guide, we will see how it works, the differences with the clamshell bucket, the main applications, and the criteria for choosing the most suitable model.
How the Clamshell Bucket for Excavators Works
The clamshell bucket connects to the excavator’s arm attachment and is powered by the auxiliary hydraulic circuit. The arms — from 3 to 6 depending on the model — are articulated to the central structure and are opened and closed by one or more hydraulic cylinders. When the cylinders contract, the arms close converging towards the center, grasping and compressing the material between them; when they extend, the arms open radially to position themselves around the next material.
The feature that distinguishes the spider from other grapples is the closing geometry: the arms converge from multiple directions simultaneously, wrapping the material instead of squeezing it between just two sides as a two-arm grapple would. This principle allows for stable grasping even of very irregularly shaped material — a pile of scrap of different shapes, a bundle of pipes of different lengths, a block of metal mesh — ensuring that the piece does not slip during handling.
The most advanced models integrate a continuous 360° rotating joint, which allows for rotating the grasped material around the vertical axis of the arm. This function is essential for loading onto trucks, where the material must be correctly oriented in the vehicle’s bed to optimize space and comply with axle weight limits.
Clamshell Bucket vs Clamshell Bucket: Different Applications, Not Interchangeable
The two terms are often confused even by experienced operators, but the clamshell bucket and the clamshell bucket are equipment designed for completely different purposes. Understanding the difference is crucial for making the right choice.
The clamshell bucket consists of two symmetrical shells that open and close like a shell. It is designed for digging and loading fine-grained materials: sand, gravel, earth, clay. The shells open above the pile of material, sink by gravity or hydraulic pressure, close to collect the loose material, and hold it during handling. It is not suitable for large or irregular materials because it does not exert gripping force.
The clamshell bucket, on the other hand, does not dig: its arms grasp from the outside material already present on the pile or on the ground. It is designed for handling single pieces or aggregates of significant size — from a metal plate to a bundle of pipes, from a block of scrap to a stack of wood. The gripping force is exerted radially by the arms, ensuring a secure grip even on heavy and irregularly shaped materials.
The choice between the two depends exclusively on the type of material to be handled: fine-grained and excavatable → clamshell bucket; irregular, bulky, or large material → spider.
Main Applications of the Clamshell Bucket for Excavators
The versatility of the spider makes it one of the most used attachments in industrial and recycling contexts. The main applications focus on three sectors.
Handling Scrap Metal
In scrap collection and processing centers, the spider for excavators is the main equipment for moving incoming material, distributing it in processing areas, and loading onto containers for transport to steel mills. The dimensional and shape variety typical of scrap — plates, profiles, beams, pipes, mechanical parts of all kinds — makes the spider ideal: the arms adapt to the shape of the material and always ensure a secure grip. Paired with a hydraulic shear on the same excavator (changing the attachment), the spider is part of the complete cycle of sorting and reducing scrap.
Handling Bulky Waste and Selective Collection
In ecological platforms and selective collection centers, the spider is used to move bulky waste (appliances, furniture, mixed construction materials) that cannot be handled with standard equipment. The ability to grasp and move pieces of very different sizes and weights without manual intervention from operators is a significant advantage in terms of productivity and workplace safety.
Industrial Demolition Sites
After the demolition of industrial warehouses, metal structures, and plants, the spider is used for the handling and pre-selection of demolished material. In combination with the demolition grapple (for concrete structures) and the hydraulic shear (for metal structures), the spider completes the demolition cycle by handling and loading material already reduced to the correct size.
Available Configurations: How to Choose the Right Number of Arms
The number of arms is the first configuration parameter of the spider. Each configuration has advantages and limitations that make it more or less suitable for specific applications.
The 3-arm spider offers the greatest relative opening compared to the overall size of the equipment and is ideal for grasping single large pieces (long beams, large plates). The grip on irregular material is less secure compared to configurations with more arms.
The 4-arm spider is the most common and versatile configuration: it offers a good balance between opening, gripping force, and cycle speed. It is suitable for the vast majority of scrap handling, bulky waste, and demolition material applications.
The 5 or 6-arm spider offers the most secure grip on irregular and bulk material but has a lower relative opening and slightly slower cycles. It is preferred in applications where grip safety is a priority, such as loading scrap onto trucks at high cycle speeds in industrial environments.
In addition to the number of arms, the choice between fixed spider and rotating spider depends on the application: for handling in a limited area, the fixed model is sufficient; for loading onto trucks or working in tight spaces, the 360° rotating model is practically indispensable.
Technical Parameters to Check Before Purchase
As with all hydraulic equipment for excavators, verifying compatibility between the spider and the machine is the fundamental step before purchase. The weight of the spider should not exceed 6-8% of the operating mass of the excavator. The available auxiliary hydraulic flow (l/min) and operating pressure (bar) must fall within the values required by the chosen model: always check in the excavator’s technical manual or request the data from the manufacturer.
The load capacity (in kg or t) indicates the maximum weight of the material that the spider can safely lift. This parameter should be compared with the average weight of the material to be handled: a spider with a capacity of 2 t is not suitable for lifting scrap bundles weighing 3-4 t even if the grip is geometrically possible. The capacity is determined both by the structural strength of the arms and by the stability of the excavator with the arm extended in the typical working position.
The CMB Spider for Handling Scrap and Materials
CMB Attachments produces clamshell buckets for excavators in multiple configurations (3, 4, and 5 arms, fixed and rotating) for machines from class 6 to over 50 tons. The construction with high-strength steels for the arms and wear-prone structures ensures long life in the most demanding industrial applications, with 100% testing before delivery.
The CMB range includes models specifically optimized for handling scrap metal, bulky waste, and industrial demolition applications. The technical team is available to help select the most suitable model based on the available excavator and the type of material to be handled.
Frequently Asked Questions about the Clamshell Bucket for Excavators
What is the difference between a clamshell bucket and a clamshell bucket?
The clamshell bucket consists of two symmetrical shells that open and close like a shell: it is designed for digging and loading earth, sand, and fine loose materials. The clamshell bucket has more arms that open in a radial pattern and is designed to grasp bulky, irregular, and large materials such as scrap metal, wood, and bulky waste. The two are not interchangeable: the clamshell bucket does not dig, and the clamshell bucket does not grasp irregular material.
Can the clamshell bucket be mounted on any excavator?
The clamshell bucket requires a functioning auxiliary hydraulic circuit on the excavator, with flow and pressure compatible with the requirements of the chosen model. Most excavators from 8 tons upwards have an adequate auxiliary circuit. For mini-excavators under 6 tons, compatibility must be verified on a case-by-case basis, as auxiliary flows may be insufficient for standard models.
How many arms should a clamshell bucket have for scrap metal?
For mixed scrap metal, the most common configuration is 4 or 5 arms, which offers the best balance between opening, closing force, and cycle speed. 3-arm models have a greater opening but a less secure grip on irregular pieces; 6-arm models have a more secure grip but slower cycles.
Is a rotating spider necessary for scrap handling?
The 360° rotating joint is highly recommended for scrap handling and loading onto trucks: it allows you to orient the grasped material in the desired direction without having to reposition the excavator, significantly increasing productivity. For simpler applications, the fixed model may be sufficient, but in a professional scrap collection center, the rotating spider is practically indispensable.
Are you looking for a clamshell bucket for your excavator? The CMB technical team is available to help you choose the most suitable model for your machine and specific application. Contact us for a consultation or discover the CMB spider for scrap handling.