Maintenance of Biscuit Baking Ovens
Oven performance
Output
- Check product specification and baking time to calculate oven output capacity in kg/hour
- Check actual output of packed, saleable product over 8 hour shift
- Check downtime / causes / trends in oven output
- A log should be maintained of problems causing downtime. Any repetitive problems or trends in output can be identified and appropriate action taken.
Product specification / compliance
Check 10 biscuits from each lane every hour for compliance to the product specification.
Check variation across the width of the oven and variation with time:
- Biscuit weight
- Biscuit size (length, width, diameter)
- Colour (compare to standard samples)
- Moisture content
Identify any quality problems with Quality Control staff, such as “checking”, shelf life, packaging issues.
Energy usage
Check fuel consumption over the 8 hour shift (gas / oil usage)
Calculate energy in kW/kg of baked biscuits and compare with target consumption
Energy usage guide
| Biscuit type | Example | Energy required to bake product kW/kg |
Total energy required incl. heat loss from the oven | Typical range of energy required for baking kW/kg |
| Rotary moulded |  |
0.18 | 0.36 | 0.36-0.40 |
| Semi sweet |  |
0.25 | 0.50 | 0.50-0.55 |
| Crackers |  |
0.35 | 0.70 | 0.70-0.77 |
Oven band
Check the following:
- Band condition (edge damage, cleanliness)
- Band support skids / rollers (all rollers free and rotating, skids and rollers clean)
- Band tracking (band wander limit switch settings to detect +/- 10mm band deviation)
- Check alarms and shut down at the set point (over 25mm deviation)
- Band tension: check pneumatic system, air pressures, check actual tension applied compared to calculated requirement for the band type and oven length.
- Check oven drum support bearings and slides. Check lubrication of slides.
- Oven drive: check belts and chains for wear and tension
- Check gearbox and drive transmission lubrication
- Check bearings
- Alarms: Check all alarm and safety circuits for band rotation, tracking and tension
- Emergency drive / UPS (shut down power and check UPS system operates to empty the oven of biscuits)
- Band cleaner (condition of brushes)
Baking chamber
- Insulation / temperatures of outer covers
- Check temperatures and heat loss at the oven ends (temperatures of outer covers should not exceed ambient + 10oC
- Clean out doors / condition inside the baking chamber
- Check for broken biscuits which could cause a fire
- Check for distortion and leaks in the baking chamber structure
- Extraction system / fans / pressure switches
- Check fan rotation, clean filters, bearings and impellers
- Check pressure switches setting and operation
- Oven end hood and extraction
- Check extraction fan / heat loss around delivery end
Gas / oil trains
Check the following:
- Gas train installation / connections / gas filters
- Main gas supply pressure
- Main gas valve operation / pressure gauges / zero governor
- Gas proving system to detect any gas leaks
- Check the gas and air header pipes and flexible pipe connections
Burners for Direct Gas Fired ovens
- Check burner strips for dirt / blockages
- Check ignition / Flame monitor units
- Adjust electrode gaps
- Check flames: short blue flames (nor long, yellow, lazy flames)
- Adjust gas/air mix as required
Burners: Indirect Fired Ovens
- Check fuel supply / filters
- Check combustion air fan / filter / pressure switches
- Check operation of manual and solenoid valves
- Check gas governor / gas pressure gauges
- Check pressure in burner tube with a manometer, (should be negative pressure / positive pressure may indicate a leakage in the heat exchanger)
- Check burner ignition
- Check flame shape and stability
Temperature control systems
A data logger may be used to check the temperature profile of the oven and identify problems of variation across the width of the oven and variation from set temperatures in each zone
Measuring baking profiles
In order to monitor actual baking temperatures, a thermal data logger is used. These units are slim and will pass through the oven carried on the oven band.
Data loggers are available with multi channels, usually 6-8 for biscuit oven applications.
Each channel has a thermocouple sensor which is attached to a bar spanning the width of the oven band. In this way the baking temperature is monitored and recorded at multiple positions across the width of the oven.
Controls and electrical panels
- Check all temperature controllers are operational, including over-temperature controllers
- Check variation in set temperatures and actual temperatures on the controllers
- Check PID settings and adjust as required
- Check thermocouple positions and wiring
- Check all damper controls
- Check all wiring secure in panels and trunking
- Operate safety systems and alarms
- Check all E-stops function correctly
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