The processing of printed circuit boards (PCBs) is today one of the most complex challenges in recycling engineering. Unlike other types of WEEE, electronic boards are a particularly difficult composite material: a fiberglass-reinforced resin matrix (FR-4) that encapsulates precious and industrial metals such as copper, tin, gold, and palladium.
The primary objective is not simple destruction, but liberation: physically separating the metal from the inert fraction to enable efficient recovery. In this context, the choice of milling technology determines the economic success or failure of the entire recycling plant.
In this technical analysis, we explain why traditional technologies (blade mills, hammer mills, vertical shredders) prove ineffective, and why the Stokkermill IM100 Impact Mill represents the definitive solution.
Many operators attempt to adapt standard machines for printed circuit board processing, but they quickly encounter structural and operational limitations. Below is a comparative analysis of the main issues.
A. Blade Mills: The Abrasion and Dust Problem
The first option that must be ruled out is the blade granulator. While highly effective for plastics, it is technically unsustainable when applied to PCBs for two main reasons:
Immediate Wear: The fiberglass base acts like an abrasive grinding wheel against the blades. Because the machine works by cutting, blade edges are destroyed within a few operating hours, leading to frequent downtime and unacceptable sharpening costs.
Loss of Precious Metals: Forcing a cutting action on such a hard material generates large amounts of fine dust. The most valuable metals (gold and palladium) end up in these fines, which are captured by the filtration system and permanently lost—dramatically reducing overall recovery yield.
B. Hammer Mills (HM Series): The Particle Size Limitation
Traditional hammer mills are robust machines for primary size reduction, but they are unsuitable for PCB refinement.
Lack of Liberation: Hammer mills typically produce an output size of 40–50 mm. At this size, metal and plastic remain firmly bonded and cannot be effectively separated using density tables.
The “Turbine” Issue: To compensate, a secondary turbine is often installed downstream. However, turbines operate through intense friction, which risks pulverizing thin gold coatings (gold flash) and dispersing them into the dust extraction system.
C. Vertical Mills (VM Series): Friction-Induced Wear
Vertical mills perform extremely well with electric motors, where copper is densified into compact nodules through friction and rolling. When applied to PCBs, however, they fail due to the “glass factor.”
The presence of fiberglass turns the grinding chamber into a highly destructive environment, rapidly eroding wear liners and internal components, making maintenance costs economically unsustainable.
Many PCB components have contacts coated with gold or precious metals a few microns thick.
- The abrasive action of the Turbo tends to remove these coatings by friction, transforming the precious metal into micronized powder (fines).
- This dust, which is too light to be separated by gravity, is captured by the suction systems and ends up lost in the filters.
Once cutting, hammering, and friction-based technologies are ruled out, the optimal engineering solution is the IM100 Impact Mill. This machine has been specifically calibrated to “solve the PCB recycling equation.”
How Does Impact Technology Work?
Unlike drag, cutting, or friction-based systems, the IM100 operates through ballistic impact. By leveraging rotor inertia and centrifugal acceleration, the material is violently impacted against internal surfaces.
This process fractures the brittle fiberglass matrix while plastically deforming the ductile metals, achieving effective liberation without relying on abrasive rubbing. As a result, wear is significantly reduced while metal integrity—and value—is preserved.
1. Perfect Delamination (2–4 mm)
The IM100 reduces material to a fine particle size of 2–4 mm in a single pass. At this size, metals are completely liberated from the plastic matrix, allowing density separation tables to sort materials with surgical precision.
2. Maximum Yield (Gold and Palladium)
Because size reduction occurs through impact rather than abrasion, precious metals retain their physical integrity and are not pulverized. This enables the recovery of gold and palladium that other systems typically lose in dust and fines.
3. Energy Efficiency
Impact technology requires significantly less power than cutting or densification systems. For example, with only 150 kW, it is possible to process 800–1,000 kg/h of PCBs, optimizing the overall energy balance (kW per ton processed).
4. Thermal Control
Kinetic energy is dissipated through fracture rather than friction-generated heat. This eliminates the risk of resin melting and the resulting machine clogging or shutdowns.
3. Modular Strategy: Beyond 300 kg/h
As throughput requirements increase, Stokkermill adopts a modular approach. Instead of building a single oversized mill—which would generate excessive and destructive kinetic energy on wear components—multiple IM100 modules are installed in series.
This configuration delivers critical operational advantages:
Production Continuity: Downtime on a single unit for maintenance does not stop the entire plant.
Fast, Cost-Effective Maintenance: Servicing compact machines is faster and more economical than maintaining large, monolithic systems.
In PCB recycling, technology choice defines profit margins. While blade mills and vertical mills generate high operating costs and significant losses of precious materials, the Stokkermill IM100 Impact Mill delivers optimal metal liberation, low operating expenses (OPEX), and maximum recovery of gold and palladium.
