Conveyor & Sortation Systems

Conveyor and sortation systems are throughput multipliers — they add capacity by moving product faster and more accurately than manual methods, but only if sized correctly for actual volume. The most common failure modes are over-specification (buying capacity that will never be used) and under-specification (system runs at 95% utilization from day one and creates bottlenecks).

---

Conveyor Technology Overview

Belt Conveyors

The workhorse of warehouse material handling.

• Speed: 50-300 FPM; standard induction conveyors: 100-180 FPM
• Width: 12”-48”; 18”-24” standard for parcel/carton
• Capacity: 50-300 cartons/hour per lane depending on product size
• Limitation: Cannot divert product; all sorting requires a separate sortation mechanism downstream

Applications: Induction lines, merge points, shipping takeaway, case conveyor in pick zones

Roller Conveyors (MDR)

Motor-Driven Roller: each zone individually powered; zero-pressure accumulation.

• Speed: 50-200 FPM
• Minimum product length: must span at least 3 rollers
• Zero-pressure accumulation: products stop without contact — prevents damage

Applications: Accumulation lines, order consolidation, pick-to-conveyor, shipping staging

Spiral Conveyors

Vertical helix for moving product between floor levels continuously.

• Throughput: 500-1,200 cartons/hour typical
• Height: typically 6-40 feet vertical rise
• Footprint: 6-12 ft diameter — minimal floor space for vertical transport

Applications: Multi-level pick modules, mezzanine-to-ground-level product flow

---

Sortation Technology Comparison

Technology	Throughput	Product Handling	Cost	Best Application
Pop-up diverter/pusher	1,000-3,000 items/hr	Gentle-moderate	Low	Low-volume; simple induction
Sliding shoe sorter	8,000-18,000 items/hr	Gentle	Medium	Parcel; flat cartons; general fulfillment
Crossbelt sorter (flat)	5,000-15,000 items/hr	Very gentle	Medium-high	Soft goods; irregular; poly bags
Crossbelt sorter (loop)	10,000-25,000 items/hr	Very gentle	High	High-speed parcel; postal; fashion
Tilt tray sorter	10,000-20,000 items/hr	Gentle	High	Small items; mixed irregular; postal
Bomb-bay sorter	15,000-35,000 items/hr	Moderate	Very high	Parcel carriers; high-speed postal

---

Sliding Shoe Sorter: The Standard for Parcel/Carton

The most common sortation technology for general merchandise and parcel fulfillment. Plastic “shoes” slide diagonally across the conveyor surface to divert items.

Design parameters:

• Minimum product: 8” × 4” × 0.5”
• Maximum product: 40” × 30” × 24”
• Weight range: 0.2-150 lbs
• Divert accuracy: >99.9% with proper induction
• Read rate requirement: >99.5% barcode read at induction

Throughput calculation:

Max throughput = 3,600 sec/hr ÷ Minimum gap (seconds)
Minimum gap = (Product length + Minimum spacing) ÷ Belt speed (in/sec)

Example:
Product: 14" long | Spacing: 6" | Speed: 180 FPM = 36 in/sec
Minimum gap = (14 + 6) ÷ 36 = 0.556 sec
Max throughput = 3,600 ÷ 0.556 = 6,475 items/hr
Design throughput (80%): 5,180 items/hr

Design to 80% of maximum. Induction spacing is the primary throughput constraint.

---

Crossbelt Sorter: Required for Poly Bags and Soft Goods

Each carrier contains a small belt that runs perpendicular to travel direction. Product is deposited by the carrier belt — no sliding or tilting.

• Fashion/apparel operations have standardized on crossbelt because poly bags fold when slid
• Loop configuration allows items to recirculate if no chute is available
• Cost premium: 30-60% more than sliding shoe for equivalent throughput

Use crossbelt when: poly bags, irregular shapes, significant size variance, or fragile/high-value goods

---

System Sizing Methodology

Step 1: Required Throughput

Peak throughput (items/hr) = Design day cartons ÷ Sort window (hours)

Example: 45,000 cartons ÷ 8 hours = 5,625 cartons/hr

Step 2: Design Buffer

System capacity = Required throughput ÷ Target utilization (80%)
5,625 ÷ 0.80 = 7,031 cartons/hr required

Step 3: Select Technology

7,031 cartons/hr with standard carton mix → sliding shoe sorter (8,000-18,000 range). Crossbelt or tilt tray would work but cost significantly more for this throughput.

Step 4: Lane Requirements

Lanes = Outbound routes + 10-15% buffer lanes (no-reads, exceptions)
Example: 40 routes + 6 buffer = 46 lanes

Lane depth: size to absorb minimum 30 minutes of throughput without staff intervention.

Step 5: Induction Feed

If one induction conveyor delivers 2,000 items/hr and sorter needs 7,000 items/hr
→ need at least 4 induction lines (merge with automatic gapping)

---

Integration Details That Get Missed

No-Read Handling — No-read rate should be <0.5% but is never zero. Requires dedicated no-read lane(s), scan tunnel reading all orientations, and staffed manual exception station.

Accumulation Zones — Required wherever throughput rates change. Without accumulation, sorter backs up when downstream staffing lags. Rule: Size accumulation at 2-5 minutes of throughput at every major transition point.

Merge Conflicts — Multiple induction feeds merging into one sorter require automatic gapping equipment. Manual merging is not reliable above 1,000 items/hour.

Conveyor Crossings — Wherever conveyor crosses a pedestrian aisle or forklift path: must be elevated (bridge) or sunken (trench), never at-grade. At-grade crossings are OSHA violations. Cost: $15,000-50,000 per crossing.

---

Economics: Minimum Volume for ROI

Operation Type	Minimum Daily Volume
Parcel/carton sort (manual alternative: scan-to-cart)	1,000-3,000 cartons/day
Multi-carrier outbound sort	2,000-5,000 cartons/day
Full sliding shoe or crossbelt	5,000-10,000+ cartons/day

Below these thresholds, capital and maintenance costs typically don’t pencil out against labor savings.

ROI structure:

Annual Labor Savings = (Manual FTE - Automated FTE) × Burdened Labor Rate
Simple Payback = Capital Cost ÷ (Annual Labor Savings + Accuracy Savings)

Conveyor/sortation: 3-5 year payback typical. System life 15-25 years makes NPV very attractive if volume holds. High peak-to-average ratios hurt the economics.