JPH029925B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a sheet thickness control method when manufacturing a sheet by calendering a thermoplastic material such as rubber or plastic. [Prior art and its problems] In calender molding, controlling the thickness of the product is important. Conventionally, as a method for controlling the thickness of a sheet as a product, a method of adjusting the gap between forming rolls or a method of adjusting the take-up speed by a take-off roll has generally been adopted. The former method involves measuring the gap size between the forming rolls and operating the rolling device of one roll to adjust the gap to a proper gap.
However, this method requires a roll gap measuring device, and when performing control that requires high responsiveness, such as roll eccentricity correction, which is the subject of the present invention, a normal electric motor type rolling down device is insufficient. Therefore, there is a problem in that it is necessary to change to a hydraulic cylinder type lowering device with high responsiveness and high output. In addition, in the latter method, the rotation speed of a take-off roll (take-off roll) installed immediately after a pair of final forming rolls is changed to adjust the take-up speed of the sheet. The sheet thickness is adjusted by stretching and pulling the wrapped sheet. However, this method has the disadvantage that the speed of each roll after the take-off roll must be made equal to the speed of the take-off roll, making control difficult. [Object of the Invention] The present invention has been made in view of the above circumstances, and it is possible to correct sheet thickness fluctuations caused by roll gap fluctuations due to roll eccentricity without using conventional gap adjustment methods or sheet take-up speed adjustment methods. It is an object of the present invention to provide a sheet thickness control method in calender molding that can be easily and reliably corrected. [Structure of the Invention] The sheet thickness control method in calender forming of the present invention is such that when a sheet to be calender formed by a pair of rolls passes through the rolls, the rotational speed of the roll on the side where the sheet is taken up while being wound is adjusted to In this method, the thickness of the sheet is controlled by periodically adjusting the gap between the two rolls caused by the eccentricity of the two rolls. [Principle underlying the invention] The present invention is based on the principle that sheet thickness can be adjusted by changing the relative speed of the final stage forming rolls. , which attempts to offset the change in sheet thickness caused by the change in relative speed of the forming rolls. First, to briefly explain the above principle with reference to FIG. 1, a pair of rolls Ra and Rb are rotating in the direction of the arrow at speeds Va and Vb, respectively.
The thermoplastic material of the raw material bank 1 is formed into a sheet 2, which sheet 2 is taken off by a take-off roll Rt rotating at a speed Vt. At this time, the sheet 2 is taken up while being wound around the roll Rb on the taking-up side. In such calender forming, the speeds Va and Vt of the roll Ra and take-off roll Rt mentioned above are
The above roll wraps the sheet while keeping the
When speed Vb of Rb is increased (or decelerated), a tensile force (or compressive force) is applied to sheet 2 at point A, and conversely, B
A compressive force (or tensile force) is generated in the sheet 2 at the point. The tension or compression force on the sheet 2 generated at these points A and B causes the gap Go between both rolls Ra and Rb and the rotational speed of the take-off roll Rt.
The thickness of the sheet 2 can be made thinner or thicker without changing the take-up speed determined by Vt. In this case, the change in the product thickness of the final sheet taken off from the take-off roll Rt appears as the result of vectorial addition of the effects of sheet thickness changes at points A and B. Therefore, below, when the roll gap is G ₀ , the amount of change in sheet thickness at points A and B when the speed Vb of roll Rb is changed, and this sheet thickness change will be used to correct it in the present invention. Let us consider the change in sheet thickness caused by the change in roll gap. Change in Sheet Thickness at Point A First, the following relationship is derived from the continuity equation at point A and any intermediate point between points A and B. Go・Va+Vb/2・K=HA・Vb (1) Here, HA: sheet thickness K: swell ratio Note that the details of the swell ratio K will be described later. The above equation (1) is derived from the fact that the amount of volumetric movement of the sheet 2 per unit time of the sheet 2 that is continuously formed is constant at any position on the forming line. The left side of the equation corresponds to the amount of volume movement at the roll gap Go at point A, and the right side of the equation corresponds to the amount of volume movement from point A to B.
It corresponds to the amount of volume movement at an arbitrary point located between the points. Next, when formula (1) above is expanded for HA, HA = (1+Va/Vb)・Go・K/2 = (1+1/fr)・Go・K/2 ...(2) Therefore, fr becomes Δfr The thickness change ΔHA when the change occurs is ΔHA=-1/fr ²・Go・K/2・Δfr, and if this is divided by the above formula (2), the thickness change rate ΔHA/HA is ΔHA/ HA=-1/1+fr・Δfr/fr...(3) Here, fr=Vb/Va: Speed ratio (variable) Δfr/fr: Rate of change in speed ratio. Description of Swell K Next, the above swell ratio K will be explained in detail. First, the passing speed of the resin in the gap Go can be expressed as shown in FIG. As shown in the figure, the flow velocities at points A1 and A2 in contact with the rolls Ra and Rb are the surface velocity Va of the rolls Ra and Rb,
It becomes Vb. The flow velocity between A1 and A2 points is the velocity
Trapezoid A1, A formed by Va, Vb
2, A3, and A4.
Figure 5a shows the actual parabolic flow velocity distribution.
The flow velocity distribution of trapezoids A1, A2, A3, and A4 is extracted and shown in Figure b. This difference in flow velocity distribution is due to the fact that the central portion of the flow when passing through the gap Go receives processing pressure generated by the rotation of the rolls Ra and Rb. Considering the amount of resin Q that passes through the gap Go at point A within a unit time, Q = ΣυΔg = ∫ ^A2 _A1 υdg, and the average speed of the two rolls Ra and Rb is (Va + Vb) / 2, so Q It is expressed as =Go・Va+Vb/2・K. Here, K is the above-mentioned swell ratio and has the following meaning. In the above equation, Go・Va+Vb/2 means the resin flow rate of the flow velocity distribution of trapezoids A1, A2, A3, and A4 in Figure 5b, so this resin flow rate and the actual parabolic flow velocity distribution of Figure 5a are The ratio of the resin flow rate (Q) is the swell ratio. That is, the ratio of the actual resin flow rate of the latter to the former resin flow rate is the swell ratio, and its value is greater than "1.00". Resin gap Go
When the processing pressure due to the rotation of rolls Ra and Rb is released, the resin appears to have the same shape as if it swelled, which is why it is generally referred to as the swell ratio. It has been theoretically and experimentally confirmed that the swell ratio K is normally between 1.25 and 1.40 for various resin materials (rubber, PVC (vinyl chloride resin), etc.) and molding conditions. There is.
Therefore, when the molding material is determined and the operating conditions are constant, the gap Go will fluctuate (for example,
Even if Go=200 μm and ΔGo=2 to 5 μm), the swell K can be regarded as a constant value. Change in sheet thickness at point B At point B, the rate of change in the thickness of sheet 2 is equal to the rate of change in speed, so

From [formula],

[Specific configuration of the invention]

Based on the above principle, a sheet thickness control method for correcting periodic sheet thickness fluctuations due to roll eccentricity will be specifically described below. In the continuity equation mentioned above, that is, H=(1+1/fr)・Go・K/2...(2), fr→fr+Δfr and G ₀ →G ₀ +ΔG at the same time
Considering the thickness change ΔH when _{the thickness} changes to
V ₃ )・ΔV ₄ , Therefore, ΔH=∂H/∂V ₄ ΔV ₄ +∂H/∂GΔG……(2)′ In equation (2)′, the first term on the right side means that the above fr is fr
It represents the thickness change ΔHm when the thickness changes to +Δfr. At this time, as mentioned above, the sheet thickness changes at points A and B due to changes in fr, so H in the same term includes HA and HB, and therefore the thickness at point A If the change is ΔHmA and the thickness change at point B is ΔHmB, then ΔHm=ΔHmA+ΔHmB. On the other hand, the second term represents the thickness change ΔHg when the roll gap G ₀ changes to G ₀ +ΔG. Therefore,
Equation (2)′ is expressed as ΔH=ΔHm+ΔHg, and ΔH=0, that is, ΔHm+ΔHg=
If the rotational speed of the final stage roll is adjusted so that the sheet thickness is changed by ΔHm, the sheet thickness can be kept constant by canceling out the change in sheet thickness ΔHg caused by the change in roll gap G ₀ . It is possible to maintain the First, consider the change in sheet thickness ΔHg caused by a change in roll gap _G0 . FIGS. 2 and 3 show an example of calender forming using calender rolls arranged in a so-called inverted L shape. In FIG. 2, the thermoplastic material of bank 1 is successively formed into sheet 2 by rolls R ₁ , R ₂ , R ₃ and R ₄ , which sheet 2 is taken off from the final roll R ₄ by take-off roll Rt. Here, as shown in FIG. 3, roll R ₃ and roll R ₄ forming the pair of rolls in the final stage are eccentric by amounts indicated by e ₃ and e ₄ , respectively. Therefore, as mentioned above, the gap G between roll R ₃ and roll R ₄ varies due to these eccentricities e ₃ and e ₄ , and the variation ΔG is ΔG=e ₃ cos(ω ₃ t+α ₃ ). +e ₄ cos (ω ₄ t + α ₄ )...(4) It is expressed as: Here, ω ₃ : angular velocity of roll R ₃ ω ₄ : angular velocity of roll R ₄ . Therefore, by substituting equation (4) into the second term on the right-hand side of equation (2) and (2)' above, the amount of variation ΔHg in the thickness H of sheet 2 due to the amount of variation ΔG in roll gap G ₀ can be calculated. , ΔHg=∂H/∂GΔG=K・1+fr/2fr・ΔG=K・1+f
r/2fr・{e ₃ cos (ω ₃ t + α ₃ ) + e ₄ cos (ω ₄ t + α ₄ )}
...It is expressed as (5). Next, considering the above ΔHm (=ΔHmA + ΔHmB), roll R ₃ and takeoff roll
While keeping the rotational speed of Rt constant, only the rotational speed _v4 of roll _R4 is changed. Then, a tensile force or a compressive force is applied to the sheet 2 at each point indicated by A and B in FIG. The above point A is the point where the sheet 2 is sandwiched between rolls R ₃ and R ₄ , and the above point B is the point where the sheet 2 is pulled by the take-off roll Rt and peeled off from the roll R ₄ . are shown respectively. Here, when the speed v ₄ of the roll R ₄ is changed by Δv ₄ , the thickness changes at points A and B of the sheet 2 are as follows from equation (2) considering only the first-order component. (b) The thickness change ΔHmA of sheet 2 at point A is It is expressed as Here, Hm: average thickness of sheet 2 = ₄ /v ₃ : average speed ratio. (b) The thickness change ΔHmB of sheet 2 at point B is It is expressed as In (a) and (b) above, ΔHmA and ΔHmB shown in equations (6) and (7), respectively, are both vector quantities. Therefore, hereinafter, these ΔHmA and ΔHmB will be expressed as ΔHmA-→ and ΔHmB-→, respectively. Then, ΔHm-→ obtained by combining these ΔHmA-→ and ΔHmB-→ is the speed v ₄ of the roll R ₄ above.
It shows the change in thickness given to sheet 2 and its direction when changing by Δv ₄ . Therefore, from the above equations (6) and (7), the above ΔHm−→ is It is expressed as Here, since the amount of change in fr during one rotation is small, there is no practical problem even if ² = fr ² in the above equation. Therefore, the above ΔHm−→ is, , and its phase φ ₄ is It is expressed as As mentioned above, the thickness variation ΔHg of the sheet 2 caused by the eccentricity of the rolls R ₃ and R ₄ is
In order to correct the thickness variation amount ΔHm of the sheet 2 caused by changing the speed v ₄ of R ₄ , it is sufficient that ΔHg−|ΔHm|=0. Therefore, from the above equations (5), (8) and (9), Expressing this in terms of Δv ₄ , we get It is expressed as Here, φ ₃ =1/fr·φ ₄ . In other words, the eccentricity e ₃ of roll R ₃ and roll R ₄ ,
Correction of the thickness variation of sheet 2 by e ₄ is performed using the roll
This can be done by adding a periodic fluctuation represented by Δv ₄ in the above equation (10) to the rotational speed v ₄ of R ₄ . The various coefficients for obtaining the above Δv ₄ are determined based on the values of eccentricity e ₃ , e ₄ and phases α ₃ , α _{4 ,} etc. measured individually for each roll in advance, the commonly used value of fr, etc. Therefore, it can be easily determined. Further, by numerically analyzing the sheet thickness variation obtained by rotating roll R ₃ and roll R ₄ at a constant speed in advance, various coefficients for obtaining a more accurate Δv ₄ can be determined. Then, the various coefficients obtained from these are applied to an analog or digital beat generator synchronized with the rotation of the two rolls, and the above (10) is applied.
Generate the same waveform as the formula and add and input this to the speed control circuit of the rotation speed v ₄ of the roll R ₄ . This makes it possible to correct variations in the thickness of roll _R4 . [Effects of the Invention] As explained above, the sheet thickness control method in calender forming of the present invention involves passing a sheet to be formed between a pair of rolls, and then taking the sheet while wrapping it around one of the rolls. During calender forming using a calender device, by periodically adjusting the rotational speed of the rolls around which the sheet is wound, in response to gap fluctuations between the rolls caused by eccentricity of each of the rolls, Since this method controls the thickness of the sheet, it is possible to extremely easily and reliably correct the sheet thickness caused by roll eccentricity, which requires high responsiveness and minute correction. In addition, even when the sheet thickness is corrected, the take-off speed does not change, so the take-off roll (take-off roll) and subsequent line speeds can be kept constant. There is no need for troublesome control to synchronize the rotation speed of the take-off roll and the subsequent line speed, which was necessary in the case of the take-off speed adjustment method.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, and FIGS. 2 and 3 are diagrams for explaining one embodiment of the present invention. FIG. 4 is an explanatory diagram of the flow velocity distribution of resin passing through the gap of the roll, FIG. 5 a is an explanatory diagram of the actual parabolic flow velocity distribution, and FIG. 5 b is an explanatory diagram of the trapezoidal flow velocity distribution. R ₃ , R ₄ ... Roll, 2 ... Sheet, e ₃ , e ₄ ...
...Eccentricity, H...Sheet thickness, G...Gap.

Claims (1)

[Claims] 1. When calender forming is performed using a calendar device that passes a sheet to be formed between a pair of rolls and then takes the sheet while winding it around one of the rolls, the rotational speed of the roll around which the sheet is wound is controlled. . A sheet thickness control method in calender forming, characterized in that the thickness of the sheet is controlled by periodically adjusting it in response to gap fluctuations between both rolls caused by the eccentricity of each of the rolls.