Solid and Perforated Steel Belts for Bake Ovens

The endless carbon steel belt was a breakthrough and rapidly became an important item when the modern bake oven was developed early 1920ties

The chemical composition, as well as the mechanical properties of the steel belts, has proven its stability and quality in thousands of bake ovens all over the world ever since these early days.

Below I will try and explain a few facts that is not so often talked about and frankly said not too well known about either. But, if one only can follow some basic guidelines regarding design, usage and maintenance I promise all oven owners that there is money to save. Lots of money.

To make things easy; You probably know better than I why your oven has a steel belt in it. You also know if it is a solid belt or a perforated one, if so, you have also chosen a hole pattern and an open area in your belt. This is your expertise. Mine is the belt itself and how to make this piece of cold rolled carbon steel to produce the products of your choice as efficient as ever possible.

 Solid bake oven band for biscuit baking, photo by IPCO

It’s needed to have a steel belt that is straight and flat. General standard belt specifications tell us that a camber or curve of maximum 20 mm (3/4”) on belts 100-200 meters (300-600 ft) long with maximum 5 mm (13/64”) camber per 30 meters (100 ft) lengths can be allowed. This is the basics for keeping the belt on the line. Remember that a steel belt is a stiff creature. The curvature or camber within the belt will remain in the belt as it was when it left its production site.

All belts are inspected at room temperature before delivery. So, when installed on the oven conveyor they should be as straight and flat as before. But this is a sheet metal product, don’t forget, one can say that each belt has three different “centre lines”. One at “room temperature”. One at “baking temperature” and finally one when products being baked. This is needed to understand when you start to run your belt. Even if you have run a previous belt on your line the new one will have new criteria built in, and can defiantly act different.

Before this bake oven belt was installed on the oven conveyor it went through a number of important production steps. Each and every one of them affected the belt performance you now can study in your oven. Good or bad.

It started as a steel melt. It became a “hot rolled band” and finally a “cooled rolled band” with the properties of a bake oven belt, well almost. In order for achieving the right hardening properties and the dark even colour a heat treatment procedure is needed. And here it is, the raw material for what will become a bake oven belt made of steel.

Anyone can buy a roll of carbon steel band from a steel mill. But to transform it into a functional machine element basically without deviations in straightness, flatness, width, etc to meet every expectation that bakeries is in need of to producing the finest biscuits, or other top of the line bakery products, is something that cannot be done by too many people. And this is the real secret. In order to achieve the straightness and flatness required an advanced procedure of rolling or levelling this hard steel material takes place. Without by any mean damaging any parts of the sometimes 600-meter-long steel band it takes special production machines that cannot be bought on eBay and furthermore a skill within the heads and hands of a few dedicated belt specialists.

Well, now it’s time for the most basic but also most underestimated field test of your new belt.

Let’s assume that your belt is professionally joined on your oven conveyor. Welded or riveted. The joint should of course be straight and flat according to the specifications already mentioned.

Does the belt run straight on the conveyor at room temperature?

If yes, slowly increase temperature until baking temperature is reached. Still runs, OK? If yes, try with product. Now if all looks all right you can relax, a while.

Perforated oven band for biscuit baking, photo by: IPCO

Your steel belt and especially its surface is a map of the conditions within the oven, and of the entire conveyor status. Shiny areas or lines is telling that something is touching and wearing on the surface. Initially after upstart the belt should be carefully monitored. Make sure that the belt is regularly inspected on both sides and on the edges also over time. This might be boring but is time is well spent. Look also for any signs of product build-up on drums or on rollers.  Talking about rollers; they should rotate. A frozen roller can mess up a belt very fast.

As the belt in this example was behaving from cold to hot and with product you know that the belt is OK. But if something all of a sudden happens? If the belt starts tracking towards one side and the emergency system is activated how to troubleshoot?

Even if the belt is moving without problems in a room temperature environment a difference of only a few degrees in an oven can change the tracking abilities completely. The product distribution on the steel belt can be essential. The more of the surface that is covered the better it is. If an inspection door is left open the temperature gradient can differ as well. Many small and bigger things one has to be aware of. For sure.

Maybe the most important inspection topic of a steel belt is the belt edge. The edge should be smoothly rounded and not have any cuts, shavings or be worn at all. A nicely maintained belt edge is an insurance for a long belt life.

Its time to sum up but before that we will talk a little about perforations. Hardened punches are used for hole making. When this process is finished and maybe 25 % of the steel material is removed it’s important to check that every hole punched is nice and smooth, burls, cracks or dents at this point can be catastrophic.

The punching was performed on a flat and straight belt. Now it’s far from straight and flat. Back to re-flattening and re-straightening it all up.

A perforated steel belt is basically very much the same as a solid one. Same properties. Basically, same life time. And the lifetime of a steel belt is most often in the hands of its user. I’ve seen 70-year-old bake oven bands still delivering.

All of this is about the Steel Belt.  In the next article we are going to dig even deeper!

Leading image Steel belt production mill by: IPCO