Question 7 of 7: Material Handling Equipment Characteristics, and Facility Design for a Fertilizer Bagging Operation

Question 7: Material Handling Equipment Characteristics, and Facility Design for a Fertilizer Bagging Operation (20 marks: i–8, ii–12)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i)(a) Belt Conveyor

A belt conveyor is a continuous, flexible belt (fabric-, rubber- or steel-reinforced) running over head and tail pulleys and supported along its length by idler rollers, driven at one end to move unit or bulk loads in a fixed horizontal, inclined, or combined path. Its characteristic features are: continuous, high-throughput transport well suited to a steady, repetitive flow of unit loads or bulk material; a fixed, unchangeable path once installed, so it commits the facility to that specific flow route; relatively low cost per unit of distance covered compared to point-to-point vehicle handling; the ability to handle inclines within the belt's friction/slip limits, unlike rigid roller conveyors; and a requirement for ongoing maintenance of belt tracking, tension and splice integrity, plus guarding along its full exposed length for personnel safety.

(i)(b) Bridge Crane

A bridge crane (overhead travelling crane) runs on rails mounted on two parallel runway beams along the length of a bay, with a bridge girder spanning between the rails and a trolley/hoist that travels along the bridge — together giving coverage of the full rectangular floor area beneath the runways in two independent directions (bridge travel and trolley travel) plus vertical hoist motion. Its characteristic features are: it consumes essentially no floor space itself, since the load path is entirely overhead, leaving the floor free for other equipment and traffic; high load-carrying capacity, well suited to heavy, bulky or intermittent lifts that would be impractical for a conveyor or lift truck; coverage limited strictly to the rectangular envelope of its runway (it cannot serve any area outside that footprint); a requirement for structural runway support that must be designed into the building's structural design (Question 1(i)) from the outset, since retrofitting runway beam capacity into an existing structure is costly; and, because it typically serves one bay at a time, its use must be scheduled/coordinated when multiple lifts or floor activities compete for the same covered area.

(i)(c) Industrial Robot

An industrial robot is a programmable, multi-axis manipulator fitted with an interchangeable end-effector (gripper, weld head, spray gun) capable of performing a defined sequence of positioning and manipulation tasks automatically and repeatably. Its characteristic features are: reprogrammability — unlike fixed (hard) automation, the same robot can be retasked for a new product or operation by reprogramming rather than rebuilding, giving it far greater flexibility for product changeover; high positional accuracy and repeatability, valuable for precision tasks (welding, precise placement) and for tasks requiring exact, fatigue-free repetition; suitability for hazardous, monotonous, or physically demanding tasks that would otherwise expose an operator to injury or repetitive-strain risk; a relatively high capital cost and the need for safety fencing/interlocks and skilled programming and maintenance support; and, because it operates from a fixed base, a working envelope limited to its reach, so facility layout must place the robot where every task it performs falls within that envelope.

(ii)(a) Problems Anticipated With the Heat Sealer, Sewing Machine, Steel Wheel Conveyor and Palletizer

Ammonium nitrate is a fine, granular, mildly hygroscopic (moisture-absorbing), corrosive-when-wet, and strongly oxidizing material, and each downstream piece of equipment interacts with those properties differently:

Heat sealer (plastic bags). Dust and residual product fines at the bag mouth can contaminate the seal area, preventing a clean, continuous heat seal and producing weak or leaking seams; the sealer must hold a consistent temperature and dwell time at production line speed without scorching or perforating the thin plastic film; and because ammonium nitrate is a strong oxidizer, a heat source operating in close proximity to residual product/dust is a genuine fire-and-reactivity hazard requiring dust extraction, temperature control, and separation distance as explicit design safeguards, not an afterthought.

Sewing machine (paper bags). Airborne dust from the granular product readily fouls the stitching mechanism and needle, causing thread breakage, skipped stitches, or a weakened valve seam; consistent bag-mouth alignment and fill level are needed for the sewn seam to close properly every cycle; and the humid, mildly corrosive micro-atmosphere around a fertilizer bagging line accelerates wear and corrosion of the machine's moving parts, increasing maintenance frequency versus a dry-goods application.

Steel wheel conveyor. Bare or poorly coated steel wheels and frame members are vulnerable to accelerated corrosion from residual product dust and ambient humidity picked up by the hygroscopic fertilizer, so protective coating or corrosion-resistant material selection is required; the harder, less compliant contact surface of steel wheels (versus a belt or roller conveyor) increases the risk of bag abrasion or puncture in transit, particularly for the heavier 30 kg bags; and wheel-bearing maintenance under continuous dusty conditions is more demanding than in a clean-material application.

Palletizer. The palletizer must handle three distinct bag weights (10, 20, 30 kg) and two different bag materials (plastic, paper) with different surface friction and stacking behaviour, requiring a flexible, product-aware stacking-pattern program rather than a single fixed pattern; stack stability must withstand the vibration and handling loads of subsequent rail transport, so the pattern (interlocking courses, appropriate pallet overhang limits) needs deliberate design, not just maximum density; airborne dust can interfere with the palletizer's position sensors or vision system if it is not adequately sealed/protected; and, as with the conveyor, the mildly corrosive dust atmosphere affects the service life of exposed mechanical and electrical components over time.

(ii)(b) Factors in the Selection and Installation of the Material Handling Equipment

Selecting and installing the handling equipment for this line requires weighing: (1) the nature of the material handled — ammonium nitrate's granular form, hygroscopicity, mild corrosivity and, critically, its oxidizer/fire-reactivity classification, which drives material-of-construction, sealing and ignition-source decisions across every piece of equipment; (2) unit load characteristics — the three bag weights and two bag materials each equipment item must accommodate without reconfiguration between runs; (3) required throughput — every downstream piece of equipment (scale, hopper, sealer/sewing, conveyor, palletizer) must be rated to match the screw conveyor's delivered production rate, or it becomes the line's bottleneck; (4) flow path and elevation changes — the distances and any changes in level between the production plant, the bagging workstation, and the railcar siding, which the handling system must span reliably; (5) building and site constraints — floor loading capacity, headroom, and the rail-siding/dock configuration the equipment must interface with; (6) hazard classification and regulatory requirements — oxidizer storage/handling regulations, dust-explosion mitigation, and (in the Canadian context) WHMIS hazard communication and provincial OH&S requirements for the facility; (7) equipment interface compatibility — each item (screw conveyor → scale → hopper → sealer/sewing → conveyor → palletizer → railcar) must hand off the unit load to the next without manual intervention or mismatch in bag orientation/spacing; (8) maintenance requirements and reliability — given the corrosive/dusty duty, spare-parts availability and ease of access for cleaning and service; (9) capital versus operating cost — balancing equipment purchase cost against energy, labour and maintenance cost over the equipment's service life; and (10) flexibility for future change — the ability to accommodate a future bag-size, bag-material, or throughput change without a full re-equip.

(ii)(c) Proceeding to Design the Facility, Including Manpower Requirements and Work Method

The facility design should follow the systematic layout planning procedure of Question 5(iii), applied specifically to this bagging line: (1) define the objectives and gather the P-Q-R-S-T data — the three bag weights, two bag materials, required throughput, and the fixed process routing (screw conveyor → scale → turret hopper → sealer/sewing → steel wheel conveyor → palletizer → railcar); (2) build the flow-of-materials and activity-relationship data for this largely serial process, noting that most closeness ratings here are driven by the fixed process sequence itself rather than by shared-service considerations; (3) determine the space requirements for each piece of equipment (Question 3(i)/(ii)), including the extra clearance the oxidizer-handling and dust-control requirements impose (separation distances, dust-collection ductwork, spill containment); (4) develop and evaluate layout alternatives, then select and implement the layout, including the fire/reactivity and WHMIS-driven safeguards identified in part (a) — dust extraction at the sealer, spark-free electrical classification where required, and adequate egress/ventilation.

For manpower and work method, a methods and work-design study (the companion Analysis and Design of Work discipline) should be performed at each manual or semi-automated station — bag placement/removal at the hopper spouts, seal/seam quality checks, and palletizer tending — to establish standard times and allowances for each. Required manpower is then determined by balancing these station standard times against the line's required output rate, using the same logic as the assembly-line balancing of Question 3(iii): where a station is only partially loaded relative to the line's cycle time, a multiple-machine-assignment analysis (an operator tending more than one semi-automated station, e.g. the sealer and the adjacent conveyor transfer point) can reduce the operator count without slowing the line, provided the two duties do not conflict at the required cycle rate. Finally, given the oxidizer classification of ammonium nitrate, the work method must build in the safety provisions specific to this material — dust exposure control, spark-free equipment in dusty zones, operator PPE, and an emergency response/evacuation plan for the bagging area — before the line is commissioned, piloted at reduced rate to validate the balance and safety provisions, and then ramped to full rate with operator training and a continuous-improvement review built into the ongoing operation.