vibrating screen flow chart

Vibrating Screen Flow Chart: A Guide to Process Design and Optimization

A vibrating screen flow chart is a visual representation of the material handling process involving screening equipment. It outlines the sequence of operations, from feed input to product separation into various size fractions (e.g., oversize, midsize, and undersize). This schematic is crucial for designing efficient screening circuits, troubleshooting performance issues, and communicating process logic. The flow chart typically details key stages such as feed distribution, screening surface action, material transport, and discharge points. By mapping the entire process, engineers can identify bottlenecks, optimize screen selection, and ensure the system meets specific capacity and separation efficiency goals.

Core Components in a Screening Flow Chart

Every vibrating screen process flow chart incorporates several standard elements that define the material's journey.

1. Feed Source & Pre-Processing: This indicates the origin of the raw material (e.g., crusher discharge, raw ore stockpile). It may include pre-screening or scalping to remove excessively large material.
2. Feed Distribution: The method by which material is presented to the screen surface (e.g., feed box, conveyor), critical for ensuring even distribution across the full width of the deck.
3. Screening Action: The heart of the chart. It represents the vibrating screen itself, where stratification and separation occur. The flow chart often specifies the number of decks (single or multi-deck) and screen media (mesh size, panel type).
4. Product Streams: These are the output paths:
   • Oversize/Throughs: Material that does not pass through the top deck apertures. It is conveyed for further processing (e.g., recrushing) or as a final product.
   • Midsize(s): On multi-deck screens, intermediate products are separated according to different aperture sizes on each deck.
   • Undersize/Fines: Material that passes through all decks or the bottom deck apertures, collected as a final product.
5. Material Handling Post-Screening: Arrows show the destination of each product stream—conveyors to stockpiles, transfer to next-stage crushers, or storage bins.

Key Design Considerations Illustrated in a Flow Chart

The flow chart forces clarity on design choices that directly impact performance.

• Screen Type Selection: The choice of screen motion (linear, circular, elliptical) is dictated by material characteristics and application.
• Deck Configuration: Single-deck for simple splits vs. multi-deck for producing several graded products simultaneously.
• Circuit Layout: This includes decisions on open-circuit screening (single pass) versus closed-circuit screening, where oversize material is recirculated back to a crusher for further size reduction before returning to the screen.

The table below contrasts two common circuit layouts often depicted in flow charts:

Feature	Open-Circuit Screening	Closed-Circuit Screening
Flow Path	Simple, single-pass; products are final after one screening event.	Involves a feedback loop; oversize is returned to a crusher for re-processing.
Typical Application	Final product sizing (e.g., sand and gravel classification), scalping.	Grinding circuits in mineral processing where controlled particle size is critical.
Advantage	Simpler layout, lower capital cost.	Provides better control over final product size, improves overall system efficiency.
Disadvantage	Less control over top-size; may require larger downstream crushers if further reduction is needed later.	More complex layout with additional equipment (crusher, conveyors), higher capital and operating cost.

Real-World Application: Crushed Stone Aggregate Plant

A concrete aggregate plant in Texas required producing three specification products: 1) Base Material (-1.5"), 2) Coarse Aggregate (-3/4" +3/8"), and 3) Fine Aggregate (-3/8").

The initial single-screen setup struggled with low efficiency and poor product purity. A revised process was designed using a detailed flow chart:

1. Primary crusher discharge fed onto a scalping screen (heavy-duty linear vibrator) with a 1.5" top deck.
2. +1.5" oversize was routed back to a secondary crusher.
3. -1.5" material from the scalper fed a triple-deck horizontal vibrating screen.
   • Top Deck: 3/4" apertures separated +3/4" stone (recirculated).
   • Middle Deck: 3/8" apertures produced clean Coarse Aggregate (-3/4"+3/8").
   • Bottom Deck: Collected Fine Aggregate (-3/8").

The flow chart visualized this circuit clearly, allowing engineers to balance conveyor loads and correctly size all equipment before installation.Post-implementation data showed a 22% increase in overall plant throughput and significantly reduced product contamination, meeting strict ASTM C33 specifications for concrete aggregates.

Frequently Asked Questions (FAQ)

Q1: What is more important in screen selection: capacity or efficiency?
Both are interdependent; however,the primary goal is achieving required efficiency at the needed feed rate. Screen manufacturers use capacity-efficiency curves based on empirical data from organizations like the Vibrating Screen Manufacturers Association (VSMA). Oversizing for capacity alone can reduce efficiency due to poor bed depth stratification.

Q2: How does moisture content affect screening performance as shown in a flow chart?
High moisture content can cause blinding (plugging of apertures) and agglomeration of fines.In a flow chart, this might necessitate including additional process steps such as:

• A pre-screening "scalping" deck with heated decks or ball trays to dislodge sticky material.
• Switching from wire mesh to polyurethane panels with slotted apertures that resist blinding.
• In extreme cases,incorporating a dryer ahead of the screening stage, which would be clearly shown as an additional unit operation box.

Q3: When should we consider multiple smaller screens versus one large screen?
This is a key layout decision.Multiple smaller screens in parallel, shown side-by-side in a flow chart offer redundancy (if one fails), easier maintenance access,and greater flexibility if feed rates vary widely.A single large screen has lower capital cost per unit area but presents risks associated with single-point failure.Decision factors include plant footprint availability,variability in feed rate,and reliability requirements based on historical mean time between failures(MTBF).

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References & Basis

• Principles outlined are consistent with industry-standard references such as Mineral Processing Plant Design,Practice,and Control(Mular et al.)and VSMA guidelines.
• Circuit design examples reflect common industry practices documented by major equipment suppliers( Metso,Terex,Sandvik).
• Case study details are generalized from published aggregate plant optimization reports but anonymized regarding specific location.*