Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Patent
1997-12-15
1999-07-06
Walberg, Teresa
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
219388, 432243, 392416, F27B 906, F27B 900
Patent
active
059190396
DESCRIPTION:
BRIEF SUMMARY
This invention relates to ovens of the kind that are suitable for use in continuous processes in which material to be heated (which may be in the form of discrete articles) is transported through the oven and is heated progressively during its passage through the oven. Such ovens are known as tunnel ovens because they are elongate and have at one end an entrance through which the material is introduced into the oven and, at the other end, an exit through which the material is withdrawn. Tunnel ovens are used for a variety of purposes, for example, to dry material or to effect the baking of food products.
For many applications, it is important to control accurately the thermal conditions to which material is subject during its passage through a tunnel oven. Accurate control is especially important when the oven is used to bake food products. Accordingly, although the invention is not limited either to the use of tunnel ovens for the baking of food products, for example, biscuits, or to tunnel ovens that are suitable for that purpose, it is convenient to discuss the matter in terms of the operation of a tunnel oven in a continuous process for the production of discrete baked food products.
When a tunnel oven is used to effect the baking of food products, baking proceeds progressively as the articles move through the oven. The length of time for which the articles are baked depends both on the path length of the articles within the oven and on the speed at which they are conveyed through it. The extent of the baking will, of course, also depend on the rate at which heat is transferred to the articles while they are in the oven.
It will be appreciated that, if a commercial baking process is to be successful, the baking conditions must be very carefully controlled. Not only must the baking conditions for a given article be kept within strict limits, but there must be a high degree of uniformity in the baking of all the articles of a given run.
The correct baking conditions for a particular kind of article having been established within a tunnel oven, it might be supposed that it would suffice simply to leave the settings of all the oven controls unchanged, but that is not so. A variety of things can necessitate changes in settings. For example, ovens are commonly provided with inspection windows at intervals along their length and, when an inspection window is opened, it will affect the conditions prevailing within the oven. A more serious problem arises when a run is interrupted.
If for any reason it proves impossible to maintain the supply of unbaked articles to the oven, or if the supply of unbaked articles has to be stopped because of a problem with the handling of the baked articles leaving the oven, for example, a failure of packaging equipment, then the run is interrupted. If, while the run is interrupted, the settings of the oven controls are left unchanged, the temperature within the oven will rise and, when the run is started again, the articles will be overbaked until the conditions settle down. The overbaked articles will not be acceptable, and there may be considerable wastage. The reason why stopping the supply of articles causes the temperature within the oven to rise is that the articles enter the oven at a relatively low temperature and leave it at a relatively high temperature, so that they act as heat sinks.
The problems that arise when a run is interrupted manifest themselves even more severely, but usually much less frequently, when an oven is started up after having been shut down, for example, for cleaning and maintenance, and also when a run with one type of article comes to an end and a run with a different type of article is started. It will be appreciated that articles of different types will generally require different baking conditions and they may also have different cooling effects.
With a view to avoiding problems of the kind referred to, many tunnel ovens used for baking food products are provided with an automatic control system, which is arranged to control the relevant settin
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Rolston Robert Mitchell
Shaw Simon Henry
Pasrija Krishan
United Biscuits (UK) Limited
Walberg Teresa
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