Oven Maintenance

Oven maintenance is essential to guarantee its ideal conditions of operation and conservation. A properly maintained oven:

• Offers a longer service life to the baker
• Guarantees maximum equipment availability
• Works efficiently in terms of fuel consumption to directly bake the products
• Generates minimum heat losses (e.g., through the humid air extraction system and wall insulation)
• Ensures steady state conditions during baking, hence producing consistent quality
• Prevents breakdowns, idling, and rework
• Minimizes explosion risks (e.g., in the case of direct gas-fired ovens)
• Reduces downtime and prevents total plant shutdowns that directly affect production, order deliveries, and sales

Relevance

Oven maintenance is a key component of the whole plant maintenance program. Members of staff (e.g., in purchasing, maintenance, quality, and operations departments) should pay special attention to the oven because it:

• Imparts final and definite characteristics to the products
• Is the equipment with the longest cycle time in the production line
• Is the processing unit that consumes the majority of the energy (fuel and electricity) used by the plant
• Is the machine with the highest acquisition costs (lease/rental prices, depreciation and amortisation costs, value of asset, commissioning, and setup charges)
• Greatly affects the total manufacturing costs of a bakery, according to its energy efficiency

Broken and/or malfunctioning ovens can bring bread-making plants to a standstill. Medium-sized and retail bakeries usually operate under the “we fix it” approach, in which the maintenance department performs all maintenance activities and interventions. These activities are “firefighting” maintenance that occurs when one of the ovens, mixers, or proofers in the processing line breaks down.

In the traditional bakery, the production department works under the “we operate the oven and run it until it breaks” mentality. Oven operators generally do not perform any maintenance activities. Instead, the operators contact the maintenance department when the oven breaks down. In addition, the operators are inactive during the maintenance activities.¹

When the production line is operating smoothly, a down or broken piece of equipment impacts all preceding steps (i.e., mixing of ingredients, dough make-up operations, and proofing), thus increasing the risk of product contamination and deterioration.

This is why bakeries should migrate to a proactive maintenance approach for ovens, which covers:

1. Preventive maintenance: Planned sequence of inspections, interventions, and repairs designed to avoid equipment failure.
2. Corrective maintenance: Scheduled interventions or works for malfunctioning or broken equipment in order to restore it to proper working condition.
3. Unscheduled maintenance: Reactive interventions or works immediately performed when a critical repair and/or replacement is needed, often during unpredicted breakdowns.
4. Temporary repairs: Quick repairs that use a variety of approved temporary materials (e.g., tape, wire, strings, cardboard, plastic) and that are replaced with permanent repairs as soon as possible.²

How it works³

In order to execute and sustain oven maintenance activities, bakeries require management guidelines, operating procedures, safety instructions, oven maintenance manuals from the manufacturer, trained and educated personnel, documentation, and recordkeeping.

The following equipment parts and conditions should be taken into account in the oven maintenance subprogram:

Oven maintenance checklist⁴

Different types of ovens require special attention. A preventive oven maintenance subprogram, including adherence to the manufacturers’ recommendations, should be established and followed. This program should set a minimum maintenance schedule that includes inspection and work interventions. An adequate supply of spare parts should be maintained, and inoperable equipment should be cleaned, repaired, or replaced, as required.

Visual operational checklist

1. Burners, for ignition and combustion characteristics
2. Air–fuel ratios
3. Baking temperatures
4. Operation of ventilating equipment/air extraction fans or blowers

Regular shift checklist (checks performed at the start of every shift)

1. Check the set point of control instrumentation (e.g., temperature, heat flux, humidity of baking chamber, and air flow for convective drying mechanisms).
2. Check positions of hand valves, manual dampers, secondary air openings, and adjustable bypasses.
3. Check blowers, fans, compressors, and pumps for unusual bearing noise and shaft vibration; check belt tension and belt fatigue of V-belt-driven equipment.
4. Perform lubrication in accordance with manufacturer’s requirements.

Periodic checklist (maintenance activities performed at intervals based on the recommendations of the manufacturer and the requirements of the process)

1. Inspect flame-sensing devices for condition, location, and cleanliness.
2. Inspect thermocouples and loose connections.
3. Check setting and operation of low and high temperature limit devices.
4. Check igniters and verify proper gap.
5. Check control valves, dampers, and actuators for free, smooth action and adjustment.
6. Test fuel manual valves for operation and tightness of closure as specified by the manufacturer.
7. Test instruments for proper response to sensors failure.
8. Clean or replace the air blower filters.
9. Clean the water, fuel, gas compressor, and pump strainers.
10. Inspect burners for proper operation, air–fuel ratio, plugging, or deterioration.
11. Check all orifice plates, air–gas mixers, flow indicators, meters, gauges, and pressure indicators; if necessary, clean or repair them.
12. Test pressure relief valves; if necessary, repair or replace.
13. Inspect air, water, fuel, and impulse piping for leaks.
14. Inspect radiant tubes and heat exchanger tubes for leakage, and repair if necessary.
15. Lubricate the instrumentation, valve motors, valves, blowers, compressors, pumps, and other components.
16. Test and recalibrate instrumentation in accordance with manufacturer’s recommendations.
17. Test flame safeguard units.

Special considerations

Ovens, especially large-scale baking units, present the greatest challenge for maintenance and servicing due to their construction materials, variety of equipment components and spare parts, tight spaces, mechanical systems, burning system assembly, and presence of instrumentation and control equipment.

Staff responsible for the plant maintenance program should have in mind the following considerations:

• ABC classification system for inventory management of spare parts (e.g., essential equipment parts (A) should always have sufficient replacement stock)⁵
• Guidelines for ranking of equipment parts based on criticality (e.g., very critical equipment, critical equipment, and less critical equipment)⁵
• Equipment disassembly/intervention procedures
• Establish inspection, replacement, lubrication, and repairs schedules based on criticality ranking of equipment.
• Disassemble, inspect, and repair tools.
• Perform maintenance according to the oven manufacturer’s instructions.
• Order a complete oven shutdown in accordance with the oven manufacturer’s instructions  during maintenance activities and interventions.

References

1. Agustiady, T.K. “Introduction.” Total Productive Maintenance: Strategies and Implementation Guide, CRC Press, Taylor & Francis Group, LLC, 2016, pp. 1–3.
2. AIB International. “Food Safety and Sanitation Distance Learning Course, Chapter 7, Maintenance.”
3. Davidson, I. “Appendix 2: Oven Maintenance.” Biscuit Baking Technology: Processing and Engineering Manual, 2nd ed., Elsevier Inc. , 2016, pp. 301–315.
4. National Fire Protection Association (NFPA). “Annex C: Example of Class A or Class B Furnace Operational and Maintenance Checklist.” NFPA 86 – Standard for Ovens and Furnaces, 2015 Edition, pp. 119–120.
5. Mobility Work. “Maintenance Key Factors to a Better Management.” 12 July 2016, https://www.mobility-work.com/blog/industrial-maintenance-key-factors-better-management#.Wpere8aGZfM.linkedin.