FI120458B - Blade in a web forming machine - Google Patents

Description

Blade forming machine blad i en banformningsmaskin

5 TECHNICAL FIELD

The invention relates to a method according to the preamble of claim 1. The invention further relates to a blade according to the preamble of claim 7.

10

The blade of the web forming machine comprises at least a first material layer and a second material layer connected to the first material layer, whereby the second material layer has a higher bending stiffness than the first material layer.

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BACKGROUND OF THE INVENTION

In web forming machines comprising at least paper, board, tissue and pulp machines, blades are used in many applications such as, for example, doctor blades, overlapping blades and creping blades, the blades acting against the roll, WO 2005/049919 discloses a method for stiffening a beam or support structure post-processing unit. The stiffening is accomplished by attaching at least one stiffening member made of a composite material to the outer surface of the beam or support structure. The idea of the stiffening member is, as its name implies, to stiffen the structure to which it is attached. The stiffening member may also increase the specific oscillation frequency of the structure to be stiffened so that it exceeds the main excitation frequency of the structure to be stiffened. The beam may be steel and the stiffening layer may be formed of a strip of carbon fiber composite ole-30 having a carbon fiber reinforcement in an epoxy resin matrix. Increasing the rigidity of the blade will not increase the blade damping but may even reduce it.

2 U.S. Patent 4,549,933 discloses a doctor blade having non-homogeneous stiffness properties and having a plurality of overlapping fibrous layers encapsulated in an epoxy resin. The composite scraper blade has a fibrous inner layer, 5 intermediate layers with parallel graphite fibers and outer fibrous layers. Intermediate layers containing parallel graphite fibers are oriented in the machine direction. The idea is to get enough rigidity in the machine direction so that the blade is well patterned and on the other hand to have flexibility in the cross machine direction so that the scraper blade follows the surface irregularities of the roll. Thus, an attempt has been made to optimize the blade so that the stiffnesses of the 10 blades are different in different directions. There is no mention in the publication of improving the blade damping properties.

FI patent 101636 discloses a scraper blade for a paper or board machine. The doctor blade comprises fiber reinforced plastic layers between which a metal layer 15, preferably a thin metal plate, is inserted. The doctor blade thus forms a sandwich-type structure. The directions of movement of the plastic sheets are selected according to the required properties. There is no mention in the publication of improving the blade damping properties.

20 A doctor blade is used in web forming machines to clean the roll surfaces, whereby the doctor blade is used to scrape off the outer surface of the roll. The friction between the blade and the outside of the roll may cause a so-called "stick-slip" oscillation phenomenon where the vibration of the scraper blade can damage the outside of the roll. The scraper blade may cause so-called sparse marking or dense marking on the outside of the roll. 25 The sparsely labeled doctor blade has a specific vibration frequency in the range of 300 to 500 Hz and the frequency labeled doctor blade has a specific vibration frequency in the range of more than 2000 Hz. At the lowest frequencies, larger structures, typically the entire pattern bar, participate in the oscillation. At higher frequencies, however, the oscillation is more local and at 2000 Hz the oscillation is limited to the doctor blade 30 itself or the combination of the blade and the blade holder. Therefore, the scraper blade must be optimally oscillated for a higher frequency of 2000 Hz.

3

Behind the enhancement of the sparse marking is the so-called synchronous resonance oscillation, which occurs as follows: 5 There is always Mata-wave interference in the sliding contact between the doctor blade and the outside of the roll. Disturbances cause the doctor blade to vibrate against the outer surface of the roll at its specific oscillation frequency.

Some interference between the scraper blade and the contact on the outside of the roll results in a pie-.10 ni notch on the outside of the roll. The mark formed on the outer surface of the roll forms a pattern whose wavelength is determined by the natural vibration frequency of the doctor blade and the rotational speed of the outer surface of the roll.

As the roll rotates on the outer surface of the roll, the pattern already formed on the outer surface of the roll re-comes into contact with the doctor blade. The pattern created on the outer surface of the roll serves as a reference for the vibration of the doctor blade, i.e. the pattern causes an impact on the doctor blade.

In a situation where the rotation speed of the roll is such that the pattern formed on the outer surface of the roll hits the doctor blade at the same stage as the already vibrating doctor blade, the vibration begins to increase. Over time, the vibration frequency of the doctor blade increases exponentially.

The same phenomenon can also occur between two nip-touch rollers, which is called barring.

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The mechanism for creating a dense label is different.

The geometry of the blade holder is such that the friction having a direction parallel to the tangent to the outer surface of the roll acts in a self-loading manner or by increasing the load on the doctor blade 30 due to the friction between the blade and the outer shell of the roll.

4

As the friction between the scraper blade and the outer surface of the roll increases, the scraper blade grips the rotating outer surface of the roll, which greatly increases the load on the scraper blade. Also, the contact angle of the doctor blade to the outer surface of the roll increases as the doctor blade and its holder bend.

5

When the loading of the scraper blade exceeds the strength of the outer surface of the roll, the scraper removes material from the outer surface of the roll, whereupon the loading of the scraper blade is released. The scraper blade then bounces back to its original position, 10 When the stick-slip oscillation marks on the outer surface of the roll, they act as sources of oscillation, thereby amplifying the oscillation.

The outer surfaces of the rolls are highly contaminated, which increases the friction between the scraper blades and the outer surfaces of the rolls, thus also increasing the risk that the scraper blades 15 start to vibrate.

It has also been found that as the calender thermocouple temperatures have been increased, the vibration levels of the scraper blades have increased. This is probably because the adhesion of the scraper blades to the outer surface of the roll increases at higher temperatures. Using the Mata-20 l thermal roller temperatures, the doctor blade can be used without problems for much longer compared to high thermal roller temperatures.

SUMMARY OF THE INVENTION

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With the solution of the invention, the vibration of the blade of the forming machine can be eliminated or at least significantly reduced.

The main features of the method according to the invention are set forth in the characterizing part of claim 1 of claim 30.

5

The main features of the blade according to the invention are set forth in the characterizing part of claim 7.

Other features of the invention are set forth in the dependent claims.

The blade according to the invention is characterized in that the second material layer is selected so that its loss coefficient achieves maximum value at the blade operating temperature and the problem blade vibration frequency, thereby maximizing the damping property of the second layer at the blade operating temperature and blade vibration frequency.

In a preferred embodiment, the blade further comprises a third material layer formed on the second material layer. The shear forces resulting from the vibration of the surface layers are thus effectively dampened in the middle layer.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic view of a scraping apparatus.

Figure 2 is an enlarged view of the doctor blade shown in Figure 1.

Figure 3 shows the bending stiffness and loss coefficient as a function of temperature.

25

Figure 4 shows the loss coefficient as a function of frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 is a schematic view of a scraping apparatus comprising a doctor blade 20 against the outer surface 11 of the roll 10, supported by a blade holder 6 30, which in turn is supported by a pivot point N on a support beam 40. Both sides of a pivot point N between the blade holder 30 and the support beam there are loading hoses 51, 52 for adjusting the position of the doctor blade 20 attached to the blade holder 30 with respect to the outer surface 11 of the sheath of the roll 10. The rotation center 5 of the roll 10 in cross section is denoted by C.

Fig. 2 is an enlarged view of the doctor blade 20 shown in Fig. 1. The doctor blade 20 consists of surface layers 21, 23 and an intermediate layer 22 therebetween.

Intermediate layer 22 is preferably doped epoxy. It is characteristic of all epoxies that the stiffness of the material decreases as the temperature increases. The stiffness of the epoxy does not decrease steadily, but it drops collapsing at a certain temperature called the glass transition temperature. In addition, the stiffness of the epoxy increases as a function of the load frequency, and this too occurs sharply at a certain frequency, the so-called transition frequency.

Under dynamic loading, part of the load exerted on the material is stored as elastic energy in the material and part of it is converted into heat by loss. The ratio of these energies is called the loss coefficient, i.e. the loss coefficient ~ one cycle loss energy / elastic energy.

At the transition frequency, the stiffness of the epoxy increases by about a decade depending on the epoxy and at the same time the material loss coefficient reaches its maximum.

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Both of the above properties depend on the amount and quality of the additives added to the epoxy. The epoxy doping must therefore be optimized so that the doping coefficient of the doped epoxy reaches its maximum at the problematic frequency and operating temperature.

30 7

The epoxy is selected by measuring the operating temperature TO and the specific oscillation frequency F0 of the doctor blade 20 at the application. With a specific oscillation frequency of 2000 Hz and an operating temperature of 80 degrees Celsius, the alloyed epoxy is selected so that its glass transition temperature at a loading frequency of 2000 Hz is 80 degrees Celsius. 5 The alloyed epoxy has a low glass transition temperature, but as the alloy increases, the epoxy has a higher glass transition temperature.

The elastic modulus of viscoelastic material can be calculated using the equation (1) below, which is a material model of first order viscoelastic material 10. This model is able to describe with reasonable accuracy the transient behavior of the material in the temperature and frequency environment.

£ (ω) = £ „+ £, * —...... (1) 0 £, + η (Γ) · / ω 15 where: E0 and Ej are the elastic modulus of the material outside the glass transition range of the material, η is the viscoelasticity of the material parameter (re-activation time).

Equation (2), which is the absolute value of equation (1), gives the dynamic modulus of the material 20 and equation (3), which is the tangent to the phase angle of the complex number of equation (1), gives the material loss coefficient.

ih_ 1 (ΕβΕ, γ V Ε? + ω * χ \ 2 25 tan δ = -; —- (3) Ε0Ε; + ω η (£ 0 + £,) 8 The temperature dependence of the parameter η is given by the so-called WFL equation (Wilson -Landel-Ferry) (4).

i ° gn a;) - iogn) = - β -! '1}}. (4) 5

Selecting Λ \ for the glass transition temperature Tg) for most epoxies holds C] —17.4 and € 2 = 51.6, giving: f 17.4 (TT)) η (7) = βχρ (η (7)) «exp ---— (5) s 51.6 + (7-7) w 10

By varying the material parameters E0, Ei, η (Τ§) and T „in the above equations, curves can be drawn which can be used to select an alloyed epoxy with the highest loss coefficient at the desired temperature and frequency.

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The curves 1 * 6 in Fig. 3 illustrate the loss coefficients LF as a function of temperature T for the six differently doped epoxies E1, E2, E3, E4, E5 and E6, and the curves 01-06 in Fig. 3 illustrate the corresponding epoxies E1, E2, E3, E4, E5 and E6. logarithm of the modulus of elasticity as a function of temperature T T. The curves shown in Fig. 3 illustrate a state-20 network with a vibration frequency of 10 Hz.

Figure 4 shows the loss coefficient LF of one doped epoxy E3 in Figure 3 as a function of frequency F. Curves 1-6 shown in Figure 4 correspond to temperatures of -20, 20, 25, 30, 40 and 80 degrees Celsius for E3 doped epoxy. The horizontal axis of Figure 25 has an exponential scale.

The graph shown in Figure 3 shows that the alloyed epoxy E3 (curve 3) has a loss coefficient LF over a maximum range of about 38 degrees Celsius. The curve shown in Fig. 4, in turn, shows that the loss coefficient LF of doped epoxy E3 (curve 3) 9 is at a maximum oscillation frequency F of about 10 Hz at a temperature of 40 degrees Celsius.

Coating the doctor blade 20 with doped epoxy E3 provides the best attenuation at 5 oscillations at 10 Hz and at a temperature of about 40 degrees Celsius.

3-4, it can be concluded that the vibrations of the blade can be effectively suppressed by coating a preferably steel scraper blade 20 with an alloyed epoxy with a maximum loss coefficient at the operating temperature of the blade. The damping effect can be enhanced by making the blade 20 such that the surface layers 21, 23 are made of steel and the intermediate layer 22 is of doped epoxy. The shear forces resulting from the vibration of the surface layers 21, 23 are thus effectively dampened in the middle layer of the alloyed epoxy. What is essential is the difference in stiffness between the different layers and the high loss coefficient of the middle layer. Also, the top and bottom layers need not be of the same material. Since the best damping is achieved by appropriately selecting the damping and surface layer, an advantage is obtained if, for example, a stiffer material is used as the surface layer. The surface layer can then be left very thin. The blade can be manufactured e.g. with a base layer of steel, an intermediate layer of doped epoxy and a top layer of carbon fiber composite. The high tensile stiffness of carbon-20 fibers allows for a very thin surface layer. The thickness of the bottom layer of the blade could be 2 mm, the intermediate layer 3 mm and the top layer 1 mm. Preferably, the steel base layer forms the tip portion susceptible to wear of the blade.

Such a three-layer structure provides so-called "constrained layer damping". A softer material with a higher loss coefficient is added to the base material and an additional retaining layer is applied to it. In bending vibration, the damping factor transfers the shear force to the retaining layer as the structure bends. Due to the different elasticities of the materials, high shear forces are applied to the tensile layer and the material loss coefficient can be utilized. It is advantageous to optimize the layer thicknesses 10 so that the shear layer undergoes the greatest possible shear stress (deformation) and the overall thickness remains within the allowable limits. In addition, the structure must have sufficiently high bending stiffness.

The foregoing examples are based on the use of an alloyed epoxy optimized for the loss coefficient of a web forming machine blade, but other elastomer such as polyurethane or rubber, which behave similarly to the alloyed epoxy, could be used instead of the alloyed epoxy.

10

The invention has been described above in connection with a doctor blade, but the invention can also be used with a coating blade and a creping blade. The coating blade and the Krep blade are exposed to vibration similar to that of a doctor blade.

The blade holder 30, shown in the figure, is fixed by a pivot point N to the support beam 40, whereby the attachment between the blade holder 30 and the support beam 40 is flexible. In such a situation, it is generally sufficient that the blade 20 alone is dampened by an alloyed epoxy layer, the loss coefficient of which is optimally selected based on the blade operating temperature and the problematic vibration frequency. In a situation where the blade 20 and the blade 20 din 30 are rigidly supported on the support beam 40, it may be that mere epoxy damping of the blade 20 is not sufficient. Then the blade holder 30 and possibly also the support beam 40 must be dampened with epoxy.

Only some preferred embodiments of the invention have been described above, and it will be apparent to one skilled in the art that they may be subject to numerous modifications within the scope of the appended claims.

Claims (12)

A method of manufacturing a blade in a web forming machine, which blade (20) is formed by inserting a first material layer (21) and a second material layer (22) connected to the first material layer, the bending stiffness of the second material. - the layer (22) is larger than that of the first material layer (21), characterized in that: - the working temperature of the blade (20) is determined, - the problematic vibrational frequency of the blade (20) is determined, - 10 - the second material layer (22) is chosen so that its loss factor (LF) achieves a greatest possible value at the operating temperature of the blade (20) and the problematic vibration frequency (F) of the blade (20). Method according to claim 1, characterized in that a third material layer (23) is formed on the second material layer (22), 3. A method according to claim 2, characterized in that the first material layer (21) is selected as the base, the second material layer (22) is mixed with epoxy or polyurethane or rubber and the third material layer is made of carbon fiber composite. 20 Method according to any one of claims 1-3, characterized in that the blade (20) is used as a blade. 5. A method according to any one of claims 1-3, characterized in that the blade 25 (20) is used as a coating blade. Method according to any one of claims 1-3, characterized in that the blade (20) is used as a crepe blade. 7. A blade in a web forming machine, which blade comprises a first layer of material (21) and a second layer of material (22) connected to the first layer of material, the bending stiffness. of the second material layer (22) is larger than that of the first material layer (21), characterized in that the second material layer (22) is of such a nature that its loss factor (LF) reaches a maximum possible value at the operating temperature of the blade (20) and that of the blade. (20) problematic vibration frequency (F). 5 Blade according to claim 7, characterized in that the blade (20) further comprises a third material layer (23) formed on the second material layer (22). 9. A sheet according to claim 8, characterized in that the first material layer 10 (21) is of steel, the second material layer (22) of mixed epoxy or polyurctane or rubber. and the third layer of solid or carbon fiber composite. A blade according to any one of claims 7-9, characterized in that the blade (20) is a blade. 15 A blade according to any of claims 7-9, characterized in that the blade (20) is a coating sheet. Blade according to any of claims 7-9, characterized in that the blade (20) is a crepe blade.