DRUM DRYER

Background of the invention

This invention relates to a drum dryer and to be precise the internal structure of a drum dryer to be used in drying fibres, such as e.g. chips.

Drying of chips is required in manufacturing chipboards, OSB boards or similar in order to evaporate excess moisture from the raw material e.g. wood (chips) and in order to obtain a desired, low enough moisture level for the chips. Drying time depends on the initial moisture content of the material to be dried but also on the wood species used and the thickness of the chip etc.

Especially when pressing above-mentioned boards, outer-layer particles and middle-layer particles must have a correct and even level of moisture. In the press stage, it is almost impossible to correct errors caused by excess moisture. The drying of chips is thus a substantial and very important stage in manufacturing chipboards or similar.

For drying chips are commonly used drum dryers including a rotating drum part in which the chips to be dried are rotated, mixed and conveyed forward. Inside the drum, there are members which mix the chips and which also function as drying profiles because of the contact between the chip and the hot mixing member.

Inside the drum there is quite a high temperature (obtained e.g. by sucking hot drying gas to the drum by means of a blower or some other way) for evaporating water in the chips. There can exist temperatures of several hundreds of degrees

Celsius inside the drum.

Drum dryers are known for drying fibres, such as chips, in which dryers an often grid-like or radial structure which carries mixing members i.e. drying profiles is fastened either by welding or with screw couplings to the shell of the drum dryer. Inside the drum dryer, different structures or components are in different temperatures. When starting up and running down the drying process, the temperature differences are especially high. E.g. the shell part of the drum heats up considerably more slowly than the internal structures of the drum. The thin parts of the internal structures heat up and cool down more quickly in the gas flow than parts manufactured of a thicker material. High stresses/stress peaks tend to be created to the structure because of thermal movement which stresses weaken the fatigue durability of the structure. Furthermore, stress is created from the mass of the parts of the dryer drum itself and from the mass of the chips to be dried.

The stresses of the structure of the rotating drum dryer should remain low mainly because of an alternating load caused by temperature differences and rotation. Stress is especially caused to the drum shell and the parts which carry drying profiles and to the dryer profiles themselves. Because of stresses created, quite large breaks and cracks occur commonly in the structures and their seams/welded seams, and the structures of the drum can also totally "fail" because of this. This frequently causes an interruption in the drying process. Repairing welded seams or similar is difficult and also then a time-consuming measure because of high temperatures in the drum and the narrowness of the drum which is caused by the structures inside the drum.

The object of this invention is thus to provide a drum dryer in which the thermal movement caused by temperature differences or the deformation of the drum shell or also the deflection caused by the weight of the structures themselves or the material to be dried does not cause too high stresses in the internal structures of the drum nor their fastening points.

Brief description of the invention

The apparatus according to the invention is characterised by the support parts of the dryer profiles having been fastened pivotedly or flexibly in respect of the shell part of the drum dryer.

In addition, the drum dryer according to the invention is characterised by what is stated in the accompanying claims 2-6.

The now presented device according to the invention has some considerable advantages compared to known solutions. The drum structure according to the invention eliminates practically totally the increase of stresses caused by thermal movements seen in the direction of both the radius of the drum and the longitudinal axle of the drum. Because of this, the structures in the drum and the seam/connection points of the structures endure essentially better and longer in the drum dryer according to the invention compared to conventional drum dryers used today. For this reason, also the operating reliability and the durability of the drum dryer are improved, the need for maintenance decreases and the operating life increases considerably.

Brief description of the figures

The invention will now be described in more detail by means of examples with reference to the accompanying drawings, in which

Figs. 1a and 1 b show a cross section as a side view of a drum dryer according to a known solution with its internal structures.

Figs. 2a and 2b show the structure and operating principle of a drum dryer according to the invention.

Fig. 3a shows a situation in which there is no temperature difference between the shell and the support parts of the drum dryer according to the invention.

Fig. 3b shows a situation in which the temperature of the support parts of the drum dryer according to the invention is higher than the temperature of the shell parts of the drum.

Fig. 4 shows a cross section of a drum dryer according to the invention.

Detailed description of the invention

Figs. 1a and 1b show a cross section as a side view of a drum dryer according to a known solution with its internal structures. Drying profiles 7 are installed to several zones 9. Grid-like support structures 10 carrying the drying profiles from their ends are fastened by welding to the shell of the drum dryer.

Figs. 2a and 2b show the structure and operating principle of a drum dryer according to the invention.

According to Fig. 2a, on the inner surface of the shell part of the rotating drum are fastened support parts which endure thermal expansions caused by temperature changes by means of pivotings 5 and 5' in them. Fig. 2a shows support parts 3 and 4 of the rotating drum, and Fig. 2b shows the same parts when the drum has rotated 180 degrees. Thermal expansion causes the support parts 3 and 4 to extend and an angular change in points A, B and C caused by it. Additionally, in the case of the figure, the angular change in points B and C is caused by a deflection in the support part 4 caused by the mass of the support parts themselves.

The support parts 3, 4 are pivoted in points A, B and C, whereby no moment caused by the angular change occurs in the support parts and on the shell. Then, the only factor causing stresses is the load caused by the mass of the structure itself. Thermal movement is free irrespective of temperature, whereby stresses are minimised, and whereby the life of the structure is considerably longer than that of a rigidly fastened structure in which the support parts were e.g. welded on the shell part.

Fig. 3 shows a situation in which the temperature of the support parts 3, 4 is higher than the temperature of the shell part 2 of the drum, whereby rotation takes place from pivot points 5, 5 ^' . The structure is also flexible in a situation in which the shell part 2 of the drum would for some reason be deformed.

Fig. 3 shows a cross section of the drum dryer. The drum has the shell part 2, the support parts 3, 4 fastened to the shell part and the drying profiles 7, 8 fastened to the support part.

The support parts of the drying profiles are fastened directly or indirectly in respect of the shell part of the drum pivotedly 5 or flexibly.

At least two or more support parts are fastened pivotedly with each other, with the pivot 5 ^' .

The pivoting 5 of the support parts is on the internal surface of the shell part 2, or the pivoting 5 of the support part is in a protrusion, projection or similar (not shown in the figure) in the shell part.

Several support parts are fastened to the shell part of the drum, and the support parts are pivoted from their one end to other support parts. The drying profiles 7, 8 are fastened to the support parts so that they are able to move in the direction of the drum axle, whereby they do not cause stresses to the support parts e.g. because of thermal extension.

Fig. 4 shows according to the invention the grid-like support structures 10 of Fig. 1 b fastened rigidly to the drum shell e.g. by welding having been replaced by the support parts 3, 4 according to Fig. 3 fastened by means of the pivots 5, 5'.

It is well known by those skilled in the art that the different embodiments of the invention are not solely limited to the examples described above, and thus they may vary within the scope of the appended claims.