Oven Maintenance

What is Oven Maintenance?

Oven maintenance refers to all the procedures and activities (covered by a program for plant maintenance) carried out to preserve the initial operating conditions (mechanical, thermal, and electrical) of an oven and and its parts.

Oven maintenance activities should focus on the following aspects:

Scheduled inspection of the oven’s overall status

Replacement of loose/flaking, worn, rusty, damaged, or broken components (e.g., nuts, screws, bolts, screw threads, taper pins/fasteners)

Regular lubrication of moving parts and/or metal-to metal contacts (drives, motors, bearings, chains)

Repair and welding of equipment subject to stress and load

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:

Preventive maintenance: Planned sequence of inspections, interventions, and repairs designed to avoid equipment failure.

Corrective maintenance: Scheduled interventions or works for malfunctioning or broken equipment in order to restore it to proper working condition.

Unscheduled maintenance: Reactive interventions or works immediately performed when a critical repair and/or replacement is needed, often during unpredicted breakdowns.

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:

Welded metal components

Driving chains and belts

Motors and drives

Steam lines and fittings

Air lines and fittings

Seals and gaskets

Fans/blowers

Fan filters

Explosion door arrangement

Oven flues

Bearings

Conveyor belts/bands

Oven band tension

Automatic tracking rollers

Temperature controllers

Sensors

Motors and electrical control equipment

Dampers

Burners and gas equipment

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

Burners, for ignition and combustion characteristics

Air–fuel ratios

Baking temperatures

Operation of ventilating equipment/air extraction fans or blowers

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

Check the set point of control instrumentation (e.g., temperature, heat flux, humidity of baking chamber, and air flow for convective drying mechanisms).

Check positions of hand valves, manual dampers, secondary air openings, and adjustable bypasses.

Check blowers, fans, compressors, and pumps for unusual bearing noise and shaft vibration; check belt tension and belt fatigue of V-belt-driven equipment.

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)

Inspect flame-sensing devices for condition, location, and cleanliness.

Inspect thermocouples and loose connections.

Check setting and operation of low and high temperature limit devices.

Check igniters and verify proper gap.

Check control valves, dampers, and actuators for free, smooth action and adjustment.

Test fuel manual valves for operation and tightness of closure as specified by the manufacturer.

Test instruments for proper response to sensors failure.

Clean or replace the air blower filters.

Clean the water, fuel, gas compressor, and pump strainers.

Inspect burners for proper operation, air–fuel ratio, plugging, or deterioration.

Check all orifice plates, air–gas mixers, flow indicators, meters, gauges, and pressure indicators; if necessary, clean or repair them.

Test pressure relief valves; if necessary, repair or replace.

Inspect air, water, fuel, and impulse piping for leaks.

Inspect radiant tubes and heat exchanger tubes for leakage, and repair if necessary.

Lubricate the instrumentation, valve motors, valves, blowers, compressors, pumps, and other components.

Test and recalibrate instrumentation in accordance with manufacturer’s recommendations.

Test flame safeguard units.