EP0184766B1 - Method and device for the heating of heatable machine parts at a double-belt press - Google Patents

Description

The invention relates to a method for heating the heatable machine parts in a double belt press by means of a heated heat transfer medium flowing through the machine parts. Furthermore, the invention relates to a device for carrying out such a method with a heating device that heats the heat transfer medium and is connected to a first and a second side of the machine part that can be heated via supply and return lines for the heat medium.

It is known (DE-OS-2 421 296), double belt presses for the production of endless, web-shaped materials, in particular for the production of, for. B. decorative laminates (laminates), particle board, fiberboard, electrical laminates and the like. These presses have two press belts, each stretched over two deflecting drums, between which the material to be pressed is treated, in particular cured, under the action of pressure and heat. The heat required for this is absorbed by the press belt runs on the deflection drums, which are heated by a flowing heat transfer medium, and are released to the material to be pressed. In addition to the deflection drums, other machine parts are also heated by a flowing heat transfer medium in order to keep the entire press frame at a constant temperature. It has been shown that even local temperature differences in the press frame can lead to thermal expansions, which have an adverse effect on the dimensional accuracy of the finished pressed product. In addition, of course, no places with temperature gradients may occur in the heated deflection drums, because this would also transfer temperature differences to the material to be pressed via the press belts.

The invention has for its object to develop a generic method so that no local temperature differences occur in the heatable machine parts of a double belt press that could affect the quality of the material to be pressed.

In connection with a solution to this problem, it was first found that the heat transfer medium cools itself as it passes through the machine parts to be heated, thereby releasing a gradually decreasing amount of heat in the direction of flow to the machine parts to be heated. In order to take this fact into account, the solution according to the invention consists in periodically reversing the direction of flow of the heat transfer medium at certain time intervals.

A device for performing the method according to the invention has a reversing valve through which both sides of the machine part can be connected alternately to the supply and return lines of the heating device.

• Fig. 1 schematisch eine Seitenansicht einer Doppelbandpresse;
• Fig. 2 eine Schnittansicht entlang der Linie 2-2 in Fig. 1;
• Fig. 3 ein Prinzipschaubild zur Erläuterung der Richtungsumkehr eines strömenden Wärmeträgermittels und
• Fig. 4 schematisch den Temperaturverlauf in einem zu erwärmenden Maschinenteil.

The following description of a preferred embodiment of the invention serves in conjunction with the accompanying drawings for further explanation. Show it:

• Fig. 1 shows schematically a side view of a double belt press;
• Fig. 2 is a sectional view taken along line 2-2 in Fig. 1;
• Fig. 3 is a schematic diagram for explaining the reversal of direction of a flowing heat transfer medium and
• Fig. 4 shows schematically the temperature profile in a machine part to be heated.

In the press frame of the double belt press 1 shown in FIG. 1, four deflection drums 4, 5, 6, 7 are rotatably mounted in bearing bridges 2, 3. Around the two upper drums 4, 6 and the two lower drums 5, 7, a press belt 8 or 9 is guided, usually a high-tensile steel belt. One of the upper and lower deflection drums is driven in a manner not shown. The direction of rotation is indicated by arrows in the deflection drums 4. Between the two press belts 8, 9 lies the so-called reaction zone 10 in the interior of the double belt press, in which a material web 11 which runs from right to left in FIG. 1 and which can consist, for example, of laminates impregnated with synthetic resin, fiber-binder mixtures or the like, using Heat and pressure is compressed.

The deflection drums 4 arranged on the inlet side of the machine have, in their cylinder wall, axially parallel channels 12 through which a heated heat transfer medium, for example a thermal oil, circulates, which is supplied and removed in a known manner. The jacket of the deflection drum in question is heated by heat exchange with this heat transfer medium preheated to a certain high temperature. The heat is transferred from the drum by heat conduction to the press belts 8, 9, which they then give off to the material web 11, for example for the purpose of curing the resin.

The pressure to be exerted on the material web 11 in the reaction zone 10 is applied hydraulically or mechanically to the inner sides of the press belts 8, 9 by pressure plates 13, 14. The reaction forces that occur are passed on from the pressure plates 13, 14 into the machine frame of the double belt press 1. For this purpose, a plurality of support beams 16, 17 with a double-T profile are attached to one another on the pressure plates 13, 14 and extend over the entire width of the press 1. Head plates 18, 19 are welded onto the front and rear end faces of the support beams 16, 17, which in turn are screwed to the bearing bridges 2, 3.

The bearing bridges 2, 3 contain hydraulic cylinders 20, 21 with which the press belts 8, 9 can be tensioned. The pair of upper bearing brackets 2 is supported on the lower pair of bearing brackets 3 via screw spindles 22. The screw spindles 22 are used to adjust the height of the reaction zone 10 between the belts 8, 9. As FIG. 2 shows, the lower bearing bridge 3 on the rear of the double belt press 1 is supported cantilevered between legs 23 of two L-shaped stands 24. The stands 24 are in turn fastened in a stationary, heavy base plate 25. Arms 26 protrude from the part of the upper bearing bridge 2 on the right in FIG. 2, which are braced via a coupling 27 with the stand 24, so that overall there is a stable, self-supporting arrangement, which requires the replacement of the press belts from the front of the Press 1 allowed here.

In order to avoid temperature differences and thus locally different thermal expansions in the press frame with regard to the dimensional accuracy of the pressed material web 11, in addition to the deflection drums 4, 5, 6 and 7, further machine parts of the double belt press 1 are heated. These machine parts include in particular the pressure plates 13, 14. Longitudinal bores 28 (see also FIG. 3) are provided in these plates, through which a heated heat transfer medium can flow. The inflow and outflow of the heat transfer medium takes place via transverse collecting lines 52, 53 which are formed on opposite sides of the pressure plates 13, 14.

As FIG. 2 shows, the webs in the double-T profiles of the support beams 16, 17 are also provided with bores 49, through which a heat transfer medium also flows for the purpose of heating.

Heatable compensating flanges 30, 31 are welded onto those flanges of the support beams 16, 17 which face away from the reaction zone 10. Bores 32 are also machined into these flanges 30, 31, through which a heat transfer medium can also flow.

The heat transfer medium passes through a continuous cycle in the heatable machine parts mentioned, it being in a heating device, for. B. an oil burner, is itself heated, then flows through the lines or channels of the parts to be heated, to then return cooled to the heater. During this cycle, the heat transfer medium circulating in the bores 12 of the deflecting drum 4, or in the bores 32 of the compensating flanges 30, 31, for example, continuously emits heat to the relevant machine parts, as a result of which it continuously becomes colder. Since the amount of heat given off is proportional to the temperature difference between the part to be heated and the heat transfer medium, those areas of the machine parts to be heated which are flowed through in the cycle of the heat transfer medium at respective later periods can no longer be heated to the same temperature as those areas which during earlier periods the heat transfer medium flowed through. Up to now, this has resulted in an undesirable, local temperature gradient in the press frame, which has caused machine parts to bend and, as a result, ultimately leads to poorly dimensioned pressed material.

In order to avoid such local temperature differences with their disadvantageous consequences within the double belt press 1, the principle of a reversal of the flow direction of the heat transfer medium is proposed according to the invention. This principle is explained with reference to FIG. 3, which schematically shows the pressure plate 13 in plan view. However, this principle applies analogously to all other machine parts of the double belt press 1 that can be heated.

In Figure 3, the pressure plate 13 is divided into two symmetrical parts A and B in the middle by an (imaginary) dashed line 33. In part A, the collecting line 51 is located on the left edge, in part B on the right edge thereof, the collecting line 52. As shown schematically in FIG. 3, the lines 28, which are designed as longitudinal bores, lead away from these collecting lines 51, 52, which lines the collecting lines 51, 52. 52 connect with each other.

To heat the pressure plate 13, the manifolds 51, 52 are connected to the circuit of the heat transfer medium. This is heated in a burner 34, which has a flow line 35 and a return line 36. These lines 35, 36 are connected to a commercially available reversing valve 37, which is remotely controlled via a schematically indicated electromagnet 38. In the position of the reversing valve 37 shown in FIG. 3, the feed line 35 of the burner 34 is connected to the collecting line 51 and the return line 36 is connected to the collecting line 52. Thus, the manifold 51 is connected as an inflow and the manifold 52 as an outlet for the heat transfer medium in the pressure plate 13. The heated heat transfer medium runs via the manifold 51 and the lines 28 first into part A of the plate 13 and then into part B to the manifold 52, from which it returns to the burner 34 via the return line 36. This direction of flow of the heat transfer medium is shown in FIG. 3 with the black arrows 39. Since the heat transfer medium cools itself while flowing through the pressure plate 13, but the amount of heat given off is proportional to the temperature difference between the pressure plate and heat transfer medium, part A of the pressure plate 13 receives a higher temperature than part B. This temperature curve is shown in FIG. 4 for that in Figure 3 shown position of the reversing valve 37 is shown schematically. Accordingly, the temperature T 2 is set on the left edge of part A and the temperature T 1 on the right edge of part B, where T 2 is greater than T 1.

If in a further operating phase the flow direction is reversed by shifting the reversing valve 37 (to the left in FIG. 3), the heat transfer medium heated in the burner is fed from the supply line 35 to the collecting line 52. After flowing through the pressure plate 13, the heat transfer medium finally flows back via the manifold 51 and the valve 37 to the return line 36 of the burner 34. In this phase, the heat transfer medium flows through the pressure plate 13 in the opposite direction, indicated by the white arrows 40, than in the case determined by the position of the reversing valve 37 in FIG. 3. In this way, part B and then part A of the pressure plate 13 are flowed through first. In this flow direction, a heat gradient forms from part B to part A, which is also shown in FIG. 4. In this second operating phase, the right edge of part B has the higher temperature T 2 and the left edge of part A has the lower temperature T 1.

Since a heat gradient from part A to part B occurs in the first operating phase, but a heat gradient from part B to part A occurs in the second phase and the two phases follow one another in time, both heat differences equalize and an average temperature T (in FIG 4 shown in dash-dotted lines) over the two parts A and B. The second phase described is now followed in turn by operating phase 1, which is shown in FIG. 3, etc.

If this phase change takes place periodically at suitably selected time intervals, then after a certain running-in period a constant temperature T is established across the entire pressure plate 13 so that it no longer has any local temperature differences and consequently no change in its geometry due to different thermal expansions.

In a first embodiment of the invention, the time intervals from the beginning of one phase to the beginning of the next phase are chosen to be the same. The operation is therefore carried out with a constant period. In another advantageous embodiment of the invention, however, the reversal of the direction of flow of the heat transfer medium can be controlled by a control circuit forming a control loop in such a way that a target temperature which is constant for the machine part to be heated is specified and the actual temperature is recorded at various points on this machine part , then depending on the size of the deviations between the target and actual temperature, the time intervals are changed by the control loop until the target temperature is reached again.

FIG. 3 schematically shows a control circuit 41 which on the one hand actuates the reversing valve 37 via the electromagnet 38 and on the other hand is connected via lines 42, 43 to temperature sensors 44, 45, which in turn are arranged in part B or part A of the pressure plate 13.

The method of reversing the direction of the heat transfer medium explained with reference to the pressure plate 13 and the associated device can, according to the invention, also be transferred to the other heatable machine parts of the double belt press, in particular to the deflection drums 4, 5, the support beams 16, 17 and the compensating flanges 30, 31 In each case, the uniform and constant temperature of the machine parts is avoided, changes in the geometry of the press frame due to heat differences are avoided, and there is a very dimensionally stable, evenly treated material web 11 on the outlet side of the double belt press 1

A particular advantage of the invention is that it can be implemented without any significant additional manufacturing outlay and, in particular, can also be used on existing double belt presses.

Claims (4)

1. Method for the heating of the heatable machine parts in a double-belt press by means of a heated heat carrier medium flowing through the machine parts, characterised thereby, that one reverses the direction of flow of the heat carrier medium periodically at certain time intervals.

2. Method according to claim 1, characterised thereby, that one so regulates the time intervals in dependence on temperature values ascertained locally at the machine part that the machine part everywhere assumes a uniform temperature.

3. Device for the performance of the method according to claim 1 or 2, with a heating device which heats the heat carrier medium and is connected by way of forward (35) and return (36) ducts for the heat carrier medium with a first (A) and a second (B) side of the heatable machine part, characterised by a reversing valve (37), through which both sides (A, B) of the machine part (4, 5; 13,14; 16, 17; 30, 31) are connectable alternately with the forward and return ducts (35, 26) of the heating device (34).

4. Device according to claim 3, characterised by a regulating circuit (41), which actuates the reversing valve (37) and is connected with temperature sensors (44,45) arranged at the machine part (13).

Images