US3345441A - Hardboard pressing methods and apparatus - Google Patents

Hardboard pressing methods and apparatus Download PDF

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Publication number
US3345441A
US3345441A US324111A US32411163A US3345441A US 3345441 A US3345441 A US 3345441A US 324111 A US324111 A US 324111A US 32411163 A US32411163 A US 32411163A US 3345441 A US3345441 A US 3345441A
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United States
Prior art keywords
press
time
relay
rate
hardboard
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Expired - Lifetime
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US324111A
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English (en)
Inventor
Dibdin Robert William
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Colonial Sugar Refining Co Ltd
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Colonial Sugar Refining Co Ltd
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Priority claimed from AU24431/62A external-priority patent/AU275809B2/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
    • B27N3/08—Moulding or pressing
    • B27N3/20—Moulding or pressing characterised by using platen-presses
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21J—FIBREBOARD; MANUFACTURE OF ARTICLES FROM CELLULOSIC FIBROUS SUSPENSIONS OR FROM PAPIER-MACHE
    • D21J1/00—Fibreboard

Definitions

  • a method of manufacturing hardboard sheets of predetermined moisture content based on the discovery that the drying of hardboard under pressure is accompanied by a reduction in thickness and that the rate of reduction in thickness is proportional to the rate of drying and thus the moisture content of the board-
  • the method includes the steps of measuring the thickness reduction within -a predetermined time during pressing in which the rate of thickness reduction is markedly decelerated, and controlling the pressing operation dependently thereon. For example, the measurements of thickness reduction are converted into electric pulses of a duration proportional to the rate of thickness reduction, and these pulses control the pressing operation.
  • the corresponding apparatus produces electric pulses of varying duration propor-,
  • This invention relates to hardboard pressing methods and apparatus and more specifically to the control of the moisture content of such pressing cycle. 7 1
  • the drawing time is further dependent, amongst other factors, upon the kind of timber used as a starting material in the hardboard manufacture, the type of fibers prepared during processing, the density ofthe board mate"- rial and the thickness of the final board.
  • the invention is based on the discovery that the drying of hardboard under pressure is accompanied by a reduction in the thickness and that the rate of reduction in 3,345,441 Patented Oct. 3, 1967 ice . pending on a predetermined rate of thickness reduction.
  • This value determines a specific moisture content oi the pressed hardboard.
  • This latter range includes the moisture contents normally required in hardboard manufacture. Owing to the sudden changes in the rate of thickness reduction over a predetermined time a very precise gauging of the correct pressing or drying time to obtain the required moisture content is made possible.
  • the above described method operates independently of the actual thickness of the hardboard normally within the range of to thick.
  • the new method reduces the average time of pressing by 10 percent to 25 percent and at the. same time reduces significantly variations in board quality.
  • 'FIGURE 1 is a diagram showing the relation between pressing time and thickness reduction in the manufacture of hardboard sheets
  • FIGURE 2 is a block diagram of the apparatus to, carry out the method according to the invention.
  • FIG. 3 shows details of a microswitch arrangement to convert thickness reductions of the hardboard sheet during pressing into electric pulses
  • FIGURE 4 is a circuit diagram of a known electronic time-delay relay responsive to pulses exceeding a predetermined duration
  • FIGURE 5 shows a circuit diagram of a known press control unit including a timing device.
  • the curve 1 shows the relation betweenthe rate 'of reduction in thickness of a hardboard sheet during pressing and the pressing time. As can be seen the rate of thickness reduction remains fairly constant until a point 2 is reached at which the residual moisture content is approximately 10 percent. On further pressing the rate .of thickness reduction falls sharply in accordance.
  • the beforementioned change in the rate of thickness reduction is used to control the moisture content of a hardboard sheet during pressing by an arrangement as,
  • This linear movement of the press table 8 is converted to rotary movement of a rnultilobe cam or ratchet bed 9 by means of the moving table 8 actuating a lever l) which is connected to the input shaft of an amplifyi-g gear train or gearbox 11.
  • the rnultilobe cam 9 opertesthe microswitch 7 giving on-off electric impulses the uration of which depends upon the rate of movement f the press table 8 which is governed by the moisture ontent.
  • the microswitch 7 is the initiating switch of a standard lectronic time-delay relay 12. Each time the initiating witch 7 opens in less than the time preset on the timelelay relay 12 the latter resets to approximately zero. Fhus until the press movement reaches a certain rate herelay cannot operate. When the initiating switch 7 remains closed for a period in excess of the preset time he time-delay rel-ay operates and either opens the press ia the normal automatic controls 13 and the press conrol valve14- or provides a signal to indicate the press :ycle is complete and the press should be opened.
  • timing device is incorporated n the normal press control 13 and operated either auton-atically or manually.
  • This. period of overdrying can be accurately controlled ;ince it commences at a predetermined constant moisture :ontent and proceeds for a predetermined constant time.
  • FIGURE 3 The arrangement converting the thickness changes into electric pulses is shown in more detail in FIGURE 3.
  • the press table 8 when moving upwards during the pressing operation to press the sheet 19, moves via an extension 15 the lever in counterclockwise direction as the latter is pivoted within a gear box 11 by means of a shaft 16.
  • This shaft carries a gear wheel 20 which meshes with the gear wheel 21 on a shaft 22, the ratio being such that the movement of lever 10 is amplified.
  • Further gear trains are provided according to the required amplification and the last shaft 17 carries the camor ratchetwheel 9, which rotates in the direction of the arrow.
  • a microswitch 7 has its operating arm 18 in contact with the teeth of ratchet wheel 9 so that each time the arm 18 rides over one of the teeth the contact of switch 7 is closed, but open again as soon as the arm 18 falls into a valley between two teeth.
  • the duration of each pulse. produced by closing the contacts of switch 7 is dependent on the amount of movement produced by press table 8 within a predetermined time, i.e. the rate of thicknes reduction of the pressed sheet, which in'turn is an indication of the residual moisture content of the board.
  • FIGURE 4 The circuit of the electronic time-delay relay 12 is shown in FIGURE 4.
  • a thermionic valve V has its filament connected to an AC power supply via a transformer TR1.
  • the anode is connected over a relay CR1 with the power supply, while the cathode. is connected with the power supply over the external microswitch 7.
  • the grid of valve V is connected over resistor R1 with parallel condenser C1 to a potentiometer P which is connected in. series with a resistor R3 across the power supply.
  • the condenser C1 When the microswitch 7 is open, the condenser C1 is charged with the polarity as indicated, the current flowing from terminal N over potentiometer P and its slider to condenser C1 and from there through valve V and resistor R2 to terminal A.
  • the grid and cothode of the valve act in this case as a rectifier.
  • valve V When the microswitch 7 is closed by the operation of the press as mentioned above, the cathode of valve V is. directly connected to terminal N, and thus a circuit is prepared. for relay CR1 from terminal A over'relay CR1, Valve V to terminal N.
  • the valve does not yet pass any current, as the grid. is blocked. by the DC voltage across condenser C1, which is greater than the AC voltage from terminal N to the slider of the potentiometer P.
  • the condenser C1 starts to discharge over the resistor R1 and as soon as the voltage across the condenser C1 is sufficiently low the valve V will pass current and relay CR1 will operate closing its contact crl.
  • the time delay for the operation of CR1 can be adjusted by shifting the slider of potentiometer P.
  • a condenser C2 is connected in parallel thereto, which discharges through the relay winding during the half-cycles at which the valve V does not pass any current.
  • microswitch 7 When microswitch 7 opens again, the circuit for relay CR1 is interrupted and condenser C1 is charged again. Thus, if microswitch 7 is opened, before condenser C1 is sufiiciently discharged to allow valve V to pass current, relay CR1 remains unoperated. The relay operates only if the microswitch 7 remains closed longer than the time set on potentiometer P for the discharge of condenser C1.
  • the hydraulic pressure rises when the press is closed, and, after a predetermined pressure, closes pressure switch PSW and thus energises relay PSWR.
  • This relay opens contact pswrl, releasing press relay CPR, and closes contact pswr2 which energises the cycle clock solenoid CCS, starts the cycle clock motor CCM and the time cycle control motor TCCM via the normally closed contact tccrl.
  • the time cycle control motor TCCM commences operations and drives a cam shaft operating in accordance. with pre-set times the switches TCC3, TCC-7 and TCC-8. It closes firstly switch TCC-8, which then remains closed until the end of the cycle, by-passing contact pswr2.
  • the press moving table 8 (FIGURE 3) is actuating the microswitch 7 by means of the arm 15 projecting from the moving press table 8 and engaging the arm 10 on the amplifying gearbox 11.
  • This gearbox amplifies the gradually decreasing linear movement of the press into rotary movement of the cam 9 as mentioned above to open and close the microswitch 7 at a gradually decreasing rate thus providing timed electrical impulses to the, electronic time-delay relay TME (FIGURE 5).
  • TME electronic time-delay relay
  • the initiating switch 7 remains on for a period of-time in excess of the preset timer delay, the time-delay, relay completes its cycle, operates and closes contact cr1 which closes a circuit for relay TMER via the previously closed contact tccr2.
  • the relay TMER provides its own holding circuit over con ract tmez-Z; and r starts he cyc e lo k. motor CCM.
  • the press cycle is now complete and control again rests with the time cycle control motor TCCM which closes switch TCC-7 to energise the open-press relay OPR.
  • This relay opens contact oprl to break the circuit for close-press solenoid CS, and closes contact opr2 to energise press-open solenoid OS via normally closed contact cpr3.
  • the solenoid moves the hydraulic valve from the press-close to press-open position and allows the press to open.
  • the time cycle control motor TCCM continues to operate via switch TCC-S, opens switches TCC-7 and TCC-3 releasing relay TCC2 ready for the next press cycle and stops itself by opening switch TCC-8.
  • Overdrying if desired may be achieved by repositioning switch TCC-7 on the time cycle cam shaft to give any preset desired time of overdrying.
  • the overdrying period can thus be controlled accurately, as it always starts from a point at which the board has reached a pre-determined moisture content.
  • the press cycle is controlled solely by operation of the time-delay relay TME dependent on the rate of reduction in moisture content of the fibrous mats which is directly related to the rate of press closing movement.
  • FIGURE 5 shows one form in which the invention can be superimposed on a known press control arrangement but the invention can be applied to other press control arrangements without in any way materially altering the normal control methods and/or apparatus.
  • a method of manufacturing hardboard sheets under heat and pressure including the steps of determining the required moisture content of the sheet by measuring the thickness reduction within a predetermined time during pressing and by controlling the pressing operation depending on a predetermined rate of thickness reduction.
  • Apparatus for determining the required moisture contents of hardboard sheets manufactured in a press including a press table, said apparatus comprising converting means operated by said press to convert the movement of the press table into electric pulses of a duration proportional to the rate of thickness reduction of said sheet produced by said press table, pulse responsive means connected with said converting means and operable by said pulses when the duration of each pulse exceeds a predetermined value and connections from said pulse responsive means to press control means, to control the movement of said press table when a predetermined rate of thickness reduction is reached independent of the actual thickness of the pressed sheet.
  • said converting means consist of a microswitch in working relationship with a ratchet wheel and intermittently operated thereby, said ratchet wheel being coupled by a gear train to an operating lever, said operating lever being in engagement with a press arm fixed to said press table, to translate linear movement of said press table into rotating movement of said ratchet wheel.
  • the pulse responsive means consists of an electronic time-delay relay, said relay being operable by electric pulses of a duration exceeding a predetermined value, and having means to pre-set said relay to said predetermined value.
  • the press control means include a timing device to terminate the pressing operation with a predetermined time delay.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Wood Science & Technology (AREA)
  • Forests & Forestry (AREA)
  • Control Of Presses (AREA)
US324111A 1962-11-19 1963-11-15 Hardboard pressing methods and apparatus Expired - Lifetime US3345441A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AU24431/62A AU275809B2 (en) 1962-11-19 Improvements in hardboard pressing methods and apparatus

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US3345441A true US3345441A (en) 1967-10-03

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US (1) US3345441A (en:Method)
DE (1) DE1436923A1 (en:Method)
FI (1) FI40579B (en:Method)
SE (1) SE303669B (en:Method)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3940465A (en) * 1973-01-03 1976-02-24 Bucher-Guyer Ag, Maschinenfabrik Method for regulating the hardening time of a plastic mass in the mold of an injection molding machine
US20140354716A1 (en) * 2013-06-04 2014-12-04 Canon Kabushiki Kaisha Ink jet printing apparatus and method for estimating moisture content of print sheet

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2618813A (en) * 1950-09-14 1952-11-25 Curtis Companies Inc Method for making cellulosic board
US2822028A (en) * 1956-01-16 1958-02-04 Allwood Inc Method of manufacturing wood particle boards
US2956307A (en) * 1956-03-26 1960-10-18 Fahrni Fred Method for pressing boards composed of particles
US3026800A (en) * 1959-08-21 1962-03-27 Olin Mathieson Pressure release devices

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2618813A (en) * 1950-09-14 1952-11-25 Curtis Companies Inc Method for making cellulosic board
US2822028A (en) * 1956-01-16 1958-02-04 Allwood Inc Method of manufacturing wood particle boards
US2956307A (en) * 1956-03-26 1960-10-18 Fahrni Fred Method for pressing boards composed of particles
US3026800A (en) * 1959-08-21 1962-03-27 Olin Mathieson Pressure release devices

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3940465A (en) * 1973-01-03 1976-02-24 Bucher-Guyer Ag, Maschinenfabrik Method for regulating the hardening time of a plastic mass in the mold of an injection molding machine
US20140354716A1 (en) * 2013-06-04 2014-12-04 Canon Kabushiki Kaisha Ink jet printing apparatus and method for estimating moisture content of print sheet
US9038444B2 (en) * 2013-06-04 2015-05-26 Canon Kabushiki Kaisha Ink jet printing apparatus and method for estimating moisture content of print sheet
US9452621B2 (en) 2013-06-04 2016-09-27 Canon Kabushiki Kaisha Ink jet printing apparatus and method for estimating moisture content of print sheet

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Publication number Publication date
SE303669B (en:Method) 1968-09-02
FI40579B (en:Method) 1968-11-30
DE1436923A1 (en:Method) 1970-03-26

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