Indeed, the belt cleaning question can often be of greater importance for a bakery than price, belt tracking, maintenance, installation etc. There are bakeries with tunnel ovens, who say “we have to change our oven belts every ~2 ½ years not because they are worn, but they get so dirty, we cannot clean them anymore”
As a matter of fact dirt on an oven belt:
- reduces the operational lifetime of the belt
- reduces the heat circulation in the tunnel oven (bad for convection baking)
- increases the energy consumption bill for the oven
- extends the baking time needed
- downgrades the quality of the baked product
- worsens the aesthetic appeal of the product (dirt spots)
But there is no such thing as a “one and only” solution……..
Over the last decades, several possibilities of belt cleaning have been thought of, tested and used. None of them, however, is with the 100%-satisfaction for the tunnel oven operator.
The cleaning system(s) would depend on:
- the type of tunnel oven belt installed
- the baked product
- the general care and skill of the maintenance people
- technical availabilities
- economic situation
1. Doing nothing
OK, this is not really a cleaning method, but you find this more often than expected. The end users either have a “nice” bake product, which is not causing any dirt “headaches” or just live with the dirt problem and change their belt every ~1 ½ years.
To keep the costs down, they buy low price and low-quality belts and “live” during the time of use with more often considerable operational and maintenance disadvantages.
This is indeed the most frequently used method of belt cleaning. You find brush systems in nearly all tunnel oven lines. Depending on the oven-OEM their design of the brush cleaning system can vary, since everyone has his / her own “philosophy” behind. However, there are things that are more unfavourable and can be done better:
- The brush wire hairs have to be of a material harder than the belt to show at least some effect on sticky and thick dirt layers. Therefore synthetic brushes are not recommended.
- Most brush systems work only from the bottom side of the belt, but this means that some of the dirt is pushed back into the mesh holes.
- Consequently there should be also a brush from the top side, so that the cleaning treatment is avoiding this
- The brush(es) from below should be motor-driven in counter direction for a better cleaning effect.
- The brush from above must be positioned before the bottom brush and self-driven only without motor. Otherwise dirt loosened by this brush cannot fall through the belt mesh holes and with time something like a “dirt sausage” might appear.
- With regards to the pressure, the brushes should only swipe over the belt surface. A too high pressure towards the belt lead to breaks of the hair wires and is counterproductive for the cleaning
- Finally, the principal disadvantage of brush system remains: with hard dirt crusts, sticking to the mesh structure and slowly clogging the holes, brushes are “helpless”
3. Flip-Flop needle felt cylinders
Like a carpet beater this motorized cylinder with needle felt strips should push against the belt from below, sometimes in combination with a brush (see below picture). The results are questionable (some dirt is pushed back into the mesh holes).
As an alternative, some end users experimented with a system, in which little metal hammer pushed against the belt from below so that the caused vibration let dirt fall down. But these systems were not really successfully either.
4. Hot air
If dirt resulting from the product is not too greasy or fat and not sticking too firmly to the belt’s mesh structure, cleaning by hot air produces some results. Some end users blow it manually in certain intervals, other designed their own firmly installed hot air nozzle stations, which they can switch on and off as needed.
At first sight, to clean a belt with a steam nozzle is not a bad cleaning method with less impact to the oven and its environment. However, it tends to only work for relatively loose non-carbonized dirt particles. Since the time needed for steam cleaning is the nearly same as water jet cleaning, most end users prefer the latter method.
6. Water jet cleaning
This is another quite popular way of belt cleaning, often used in combination with brushes. Again, for some ovens it is done manually in certain intervals, whereas some users build their own permanent equipment, which is installed as part of the oven.
Recently a European OEM introduced a water jet cleaning equipment to be firmly installed at the oven exit. All this certainly helps to get the belt cleaner, but there are obvious disadvantages:
- What to do with the considerable amount of waste water?
- The manual water jet cleaning could be a “hell of a mess” for the ovens surrounding and some protection for this is needed
- The belt has to be warmed up or dried immediately after the water jet cleaning to avoid rust stains on the belt surface (most of the tunnel oven belt are not in stainless steel).
7. Dry ice
The principal handling is the same as water jet cleaning. It’s only that dry ice replaces the water. Clients report no big differences in cleaning results than with water jet, so it does not justify the considerable additional costs. Additionally, the contact of dry ice to the belt wires results in considerable negative stress to the ionic lattice of the metal mesh, which might lead to wire breaks and definitely reduces the operational lifetime.
8. Cleaning with detergent or chemical substances
Occasionally you hear from the market, that clients clean their belts by hand and rubbing the belt surface with cleaning detergents or some chemical substances with big balls of absorbent cotton. This is a labour intensive work and detergents might and chemical liquids will definitely react aggressively and damage the wires in making the surface rougher, so new dirt can stick easier to the belt. Furthermore, many such chemical “cleaners” are flammable. I recall a case, where a client used a chemical liquid for belt cleaning, but this substance was flammable and although he thought to have rinsed it off sufficiently an oven fire started when he began to heat up the oven. That was the end of the lifetime circle of the belt and the oven required some repairs.
This is what most tunnel oven users are doing whether unintentionally or on purpose. The idea behind: the less humidity the dirt contains the higher the chance that it can simply be broken off the belt wires and surface. The strategy is to let the oven run empty without product and increase the oven temperature to a higher level (usually +~50 o C) to let the dirt carbonize. Then a good brush system has an easier job to clean off the dirt. There have been some tests, even by OEMs to install special “dirt burners” as part of the oven line, which could be switched on and off. But the results were below expectation. To heat up the belt in this special “chamber” with a length of only 2-3 m was not enough to achieve carbonization.
I have seen it more than once, that clients were so “desperate” with their belt dirt problem that they developed some self-made scraper systems to scrape off thick mostly carbonized dirt layers. The cleaning results of such scrapers were and are not bad, but:
- Such scrapers do not leave the belt surface plain and smooth
- Often cause belt damages during use
- Definitely shorten the belt’s lifetime
Scrapers might do a good job for solid steel belts but for mesh belts.
11. CLEANBELT Belt cleaning & dirt breaking device
This is still a comparatively new device. It is an additional “independent” non-motorized equipment that improves the efficiency of (good) brush systems. It consists of an individually designed cylinder with an arrangement of independent special sprockets, where the teeth punch into the belt mesh’s holes to break the dirt, so that the brushes following afterwards have a much easier job swiping off the broken dirt.
The “disadvantages” of this new cleaning device are:
- It is a “team player” only, for supporting the efficiency of a good brush system
- It only works for Z-belts (rolled baking oven belts) which need to have a very regular and equal mesh structure, achieved only by a German belt producer
Many users are satisfied with the cleaning results and slowly starting to install it in all oven lines possible.
12. Using other belt types
Yes, changing to another type of belt can also be a way to solve dirt problems in tunnel oven lines. The principal idea behind it is: “The less wire surface there is in your belt, the less opportunities for the dirt to stick to the belt wires”.
The less wire surface there is in your belt, the less opportunities for the dirt to stick to the belt wires.
Change of steel belt to a Z-belt
A client using a solid steel belt changed to a Z-Belt F2510 (aka ~Z28) with a very fine open mesh structure. In this way there was less surface for the dirt to stick on and brushes could be used more efficiently. A side effect of this change was that the open mesh structure reduced the energy costs since convection in the oven was now possible.
Admittedly the consistency of the dough is an important criteria for allowing this change.
Change between two different type of Z-Belts
When it comes to biscuit and cookies with a very high contents of fat and sugar it is pretty certain, that there will be a dirt problem with the belt. This dirt is very sticky and the mesh structures usually gets clogged very quickly, even when brushes are used.
Traditionally in 8 out of 10 cases the standard “Z47”-belt is used (aka as F4012), often for dough with high fat and sugar contents. But there is also a belt type F6014 (aka~Z48), having the same weight and an identical mesh structure but with a more favourable and open ratio between wire thickness and mesh opening.
Bakeries who had the “courage” to change from F4012 to F6014 never regretted it. They changed as many lines as possible to this type of belt.
- Questioning the belt type used
- + Realising the basic rule “Clean permanently to avoid a belt to get dirty”
- Good metal wire brush systems (used permanently, if possible)
- + CLEANBELT brush support system (also used permanently, if possible)
- + Dirt carbonizing during regular cleaning/maintenance shifts
- + Occasional water jet cleaning (if needed)
But it is up to the end user to make decisions and actions. A good belt supplier is always willing and happy to help with his experience.