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Maintenance of Biscuit Baking Ovens

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 Rotary-moulded-biscuit 0.18 0.36 0.36-0.40
Semi sweet Semi-sweet 0.25 0.50 0.50-0.55
Crackers 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

Related articles

The secret of a long bake oven belt life – the first part

Steel belts have been used as a conveying medium in continuously operating bake ovens for more than 90 years and their inherent strength, ruggedness and unparalleled thermal properties means that an operational life of 20 or 30 years is far from unusual.

The secret of a long bake oven belt life – the first part

The Secret of a Long Bake Oven Belt Life – Maintenance

Regular planned maintenance is key to maximizing the working life of a bake oven belt

The Secret of a Long Bake Oven Belt Life – Maintenance

The Best Way of Cleaning a Belt is to Avoid Getting Dirty

The belt cleaning question can often be of greater importance for a bakery than price, belt tracking, maintenance, installation, etc.

The Best Way of Cleaning a Belt is to Avoid Getting Dirty

Oven Efficiency

As energy costs increase in almost every country, the efficiency of the oven is of growing importance.

Oven Efficiency

Oven Efficiency - Comparison of Direct and Indirect Fired Ovens

The most important method of heat transfer for crackers and biscuits is radiation. Read more about the difference between Direct Gas Fired oven and Indirect Radiant ovens.

Oven Efficiency - Comparison of Direct and Indirect Fired Ovens

Oven Inspection and Audit

It is recommended that each oven is given a complete inspection and audit every 12 months. The annual inspection and audit will support the preventative maintenance program and help to ensure excellent oven performance, economy and long life.

Oven Inspection and Audit

Visit TechTalks Discussion

Oven maintenance checklists
Please share the oven maintenance checklist (Daily, Monthly, and yearly) for the convection ovens and direct-fired ovens.

Heat input required
Can any one tell me how to calculate the Heat energy required to bake one kg of biscuits or one square meter of oven area.  Pl consider the moisture loss as 18% when you have 100kgs dough.  with at least 2% moisture still there in biscuits.

Changing the type of belt in tunnel ovens
As a former product manager and now a consultant for tunnel oven belts, I would be interested to ask for your experience in changing the principal type of belt used in your tunnel oven and for what reason. Did you change from solid steel belt to mesh belt or (multiple spiral) CB5-belt to Z-belt (rolled baking oven belt)? Or was it vice versa?

Oven for water cracker
We are going to buy a new dedicated oven for water cracker, (like Carr's) what are the most suitable configurations of the oven should we looking for? (e.g. heating mode, oven band type, etc.)

Fouling on direct oven flue heat exchanger
I was wondering if anyone can me some insight into fouling issues on a potential combustion air preheater, for use on a direct oven. I am aware that combustion air preheaters have been installed successfully on indirect oven lines, but I am unsure if it is feasible on a direct oven. The flue stream will contain small solid particles and possibly fat alongside the obvious combustion products and water vapor.

Has anyone here successfully installed a heat exchanger on a direct oven flue line? Or heard of such a project?

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Recommended reading

Biscuit Baking Technology published by Elsevier

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