Dual-belt press for a continuously advancing web of material

The invention relates to a dual-belt press for a continuously advancing web of material comprising a rigid press frame, deflection drums mounted for rotation on bearing bridges of the press frame, upper and lower endless press belts guided over the deflection drums and pressure plates disposed at the rear sides of the press belts for exerting pressure on the web of material. So that the web of material may be simultaneously calendered in such a press, at least those deflection drums provided on the entry side of the press are mounted for movement relative to the pressure plates and are adapted to be tensioned against one another by adjusting means such that the pressure exerted in the gap between these drums (calendering) is preferably greater than and independent of the pressure exerted by the pressure plates.

The invention relates to a dual-belt press for a continuously advancing web 
of material comprising a rigid press frame, deflection drums mounted for 
rotation on bearing bridges of the press frame, upper and lower endless 
press belts guided over the deflection drums and pressure plates disposed 
at the rear sides of the press belts for exerting pressure on the web of 
material. 
With dual-belt presses of this type, webs of material, for example in the 
form of decorative, multi-layered laminates, chipboards, fibreboards, 
plywood sheets and electrolaminates, may be continuously pressed to form 
finished products under the effect of heat. 
It is known to arrange special calibrating rollers in front of the entry 
side to the dual-belt press in order to apply nip effects to the web of 
material before it enters the reaction zone of the press, i.e. to calender 
the material to be pressed. A calender arranged in front of the dual-belt 
press entails additional costs and resources with respect to apparatus and 
considerably increases the total length of such apparatus. The object of 
the invention is to design a dual-belt press in which the web of material 
may be calendered as well without any appreciable increase in costs or 
apparatus. 
The object of the invention is accomplished in that at least those 
deflection drums provided on the entry side of the press are mounted for 
movement relative to the pressure plates and are adapted to be tensioned 
against one another by adjusting means such that the pressure exerted in 
the gap or nip of these drums (calendering) is preferably greater than and 
independent of the pressure exerted by the pressure plates.

The dual-belt press illustrated schematically in FIG. 1 has four deflection 
drums 2, 3, 4 and 5 mounted for rotation on a press frame 1. An upper 
endless press belt 6 extends around drums 2, 3 and a lower endless press 
belt 7 around drums 4, 5. The press belts 6, 7 may consist of metal, 
preferably stainless steel, and comprise one or more layers. The direction 
of travel of the belts 6, 7 is indicated by the arrows in the deflection 
drums 3, 5. The drums 3, 5 mounted at the entry side to the apparatus are 
heated in the manner known per se, for example by a heated thermo-oil. The 
amount of pressure to be exerted on a web of material (not illustrated) 
fed between the drums 3, 5 at the entry side of the press is transferred 
from pressure plates 8, 9 to the rear sides of the facing strands of the 
press belts 6 or 7 and thereby to the web of material continuously 
advancing therebetween. The pressure plates 8, 9 are heated, for example 
by thermo-oil circulating in them. Those sections of the pressure plates 
8, 9 located towards the delivery side of the press may also be cooled, 
along with the deflection drums 2, 4 mounted at this side. 
As is apparent from the schematic illustration in FIG. 2, the press frame 1 
comprises a stationary bottom plate 12 to which two uprights 13 are 
rigidly connected. A bearing arrangement for the deflection drums 2, 3, 4, 
5 is cantilevered to the uprights 13. This bearing arrangement consists 
essentially of bearing bridges 14, 15 arranged in pairs. Each pair of 
bearing bridges is connected by height-adjustable spindles 16 which serve 
to adjust the height of the reaction zone between the press belts 6, 7 in 
the region of the pressure plates 8, 9. The two bearing bridges 15 are 
mounted on the upright 13 (FIG. 2) in a cantilever manner. The bearing 
bridges 14 are supported on the bearing bridges 15 via the spindles 16. 
The arrangement formed by these bearing bridges is connected under tension 
to the upright 13 via arms 17 (FIG. 2) which protrude from the upper 
bearing bridges 14 and via tensile coupling members 18. This results in an 
altogether stable, cantilever arrangement. As shown in FIG. 1, bearing 
blocks 19, 21 and 22, 23 are articulatedly attached to the bearing bridges 
14, 15 so as to be movable towards and away from one another with a 
motional component directed perpendicularly to the main plane of the press 
belts 6, 7. The shafts of the deflection drums 2, 3, 4 and 5 are mounted 
in these bearing blocks 19, 21, 22, 23. This means that the deflection 
drums are also displaceable relative to one another and to the pressure 
plates 8, 9 stationarily mounted on the frame. The bearing blocks 19, 22 
and 21, 23 are engaged by adjusting members in the form of piston-cylinder 
units 24 and 25 actuated by pressure medium. When a pressure medium, e.g. 
hydraulic fluid, impinges on the chamber 27 of the cylinder 28 located 
above the piston 26, the deflection drums 3, 5 are tensioned against one 
another and exert considerable pressure between the press belts 6, 7 in 
the region of the nip and this pressure may be utilized to calender the 
web of material fed to the press. The pressure thus exerted is greater 
than that between the pressure plates 8, 9 and may be utilized to produce 
certain effects in the web of material which is, for example, impregnated 
with resin. This eliminates the necessity of a special pair of calendering 
rollers placed in front of the dual-belt press. 
The piston-cylinder units engaging on the left-hand and right-hand end 
faces of the deflection drums 2, 3, 4 and 5 may have pressure medium 
acting on them independently of one another so that the pressure exerted 
in the nip increases or decreases along the drum axes. This may be 
utilized, for example, to adjust the distribution of resin in a web of 
material fed to the press. 
The pressure to be exerted in the gap between two superposed deflection 
drums may be made dependent on a continuous spacing measurement. A desired 
spacing value is specified and the pressure then regulated as a function 
of measured spacing values. It is also possible to regulate the pressure 
to be exerted as a function of the pressure in the piston-cylinder units 
24, 25. In this way, the material to be pressed in the gap between the 
drums may be influenced to a high degree of accuracy. 
Means, for example pressure cylinders, are provided on the bearing bridges 
14, 15 in a manner known per se and therefore not illustrated for the 
purpose of altering the spacing between the deflection drums associated 
with the respective bearing bridges to produce tension in the press belt 
extending around these drums. Since this tensional force acts practically 
at right angles to the pressure force exerted by the piston-cylinder units 
24, 25, these forces cannot interfere with one another. 
At the delivery side of a nip serving to calender material, the web of 
material thus treated sometimes exhibits undesired spring-back effects. In 
order to counteract such effects, slide wedges 31, 32 may be disposed, as 
shown schematically in FIG. 3, between the pressure plates 8, 9 and the 
gap between the drums 3, 5 serving to calender the web of material. The 
wedges extend across the entire width of the drums and the web of material 
which is designated as 10 in FIG. 3. These slide wedges 31, 32 each have a 
flat side engaging on the rear sides of the press belts 6, 7 and a flank 
which is correspondingly curved to engage on the outer surface of the 
drums 3, 5. The wedges are pressed by the pressure plates into the gap 
between the drums 3, 5 and held firmly. It is also possible to have 
pressure members (not illustrated), for example in the form of hydraulic 
piston-cylinder units, disposed between the pressure plates 8, 9 and slide 
wedges 31 and 32. These pressure members press the slide wedges 31, 32 
firmly into the gap between the drums and against the web of material. In 
this way, a considerable amount of pressure may be maintained between the 
gap of the drums 3, 5 and the pressure plates 8, 9 and this prevents any 
"springing back" of the web of material 10 calendered between the drums 3, 
5. The slide wedges 31, 32 consist of metal and may also be designed to be 
heatable. 
During practical operation of the invention, it will often be sufficient 
for calendering to be carried out merely at the entry side of the press 
between the deflection drums 3, 5. In this case, the deflections drums 2, 
4 disposed at the delivery side of the press may be rigidly mounted, as 
previously, on the bearing bridges 14, 15 and the piston-cylinder units 24 
provided for these drums in the embodiment illustrated are not required.