US3895138A

US3895138A - Impregnation of wood and the like

Info

Publication number: US3895138A
Application number: US369544A
Authority: US
Inventors: Charles Patrick Blackwo Sewell; William Morris Sherriff
Original assignee: Boliden AB
Current assignee: Boliden AB
Priority date: 1971-04-28
Filing date: 1973-06-13
Publication date: 1975-07-15
Anticipated expiration: 1992-07-15

Abstract

A method of impregnating wood with preservatives in a treatment solution in which the wood and treating solution are subjected to a schedule including cycles of alternate phases of high pressures and low pressure wherein the pressures in the high pressure and/or low pressure phase are changed in succeeding cycles whereby the differential of pressure between the low limit of the low pressure phase or the differential of pressure between the mean of the low pressure phase and the mean of the high pressure phase is progressively increased or decreased in succeeding cycles, or the limit of the pressure in the high pressure phase is progressively increased or decreased in succeeding cycles while the differential of pressure between the high limit of the low pressure phase and the low limit of the low pressure phase remains constant, with the variation of the pressure limits and/or the variations of the differential of pressures being controlled for ensuring that aspiration or absorption of a critical amount of air from within the wood cells is not exceeded before the wood is as deeply penetrated and as heavily loaded with the preservative as is desired.

Description

United States Patent Sewell et a1.

IMPREGNATION OF WOOD AND THE LIKE Boliden Aktiebolag, Helsingborg, Sweden Filed: June 13, 1973 Appl. No.: 369,544

Related US. Application Data Continuation of Ser. No. 138,266, April 28. 1971. abandoned, which is a continuation-in-part of Ser No. 104,150. Jan 5. 1971, abandoned, which is a continuation of Ser. No. 684,729, Nov. 21, 1967, abandoned.

[73] Assignee:

References Cited UNITED STATES PATENTS 1,008.864 11/1911 Ruping .t 117/116 2,786,784 3/1957 Henrikssom .d 117/116 FOREIGN PATENTS OR APPLICATIONS 385.327 12/1932 United Kingdom [451 July 15,1975

Primary Examiner-William R. Trenor Attorney, Agent, or Firm-H0lman & Stern [57] ABSTRACT A method of impregnating wood with preservatives in a treatment solution in which the wood and treating solution are subjected to a schedule including cycles of alternate phases of high pressures and low pressure wherein the pressures in the high pressure and/or low pressure phase are changed in succeeding cycles whereby the differential of pressure between the low limit of the low pressure phase or the differential of pressure between the mean of the low pressure phase and the mean of the high pressure phase is progressively increased or decreased in succeeding cycles. or the limit of the pressure in the high pressure phase is progressively increased or decreased in succeeding cycles while the differential of pressure between the high limit of the low pressure phase and the low limit of the low pressure phase remains constant, with the variation of the pressure limits and/or the variations of the differential of pressures being controlled for ensuring that aspiration or absorption of a critical amount of air from within the wood cells is not exceeded before the wood is as deeply penetrated and as heavily loaded with the preservative as is desired.

1 Claim, 17 Drawing Figures SYNCHRO FLOAT SEQUENCE AUTO vacuum TIMING SWITCH CONTROL vacuum PUMP CONTROL UNIT UNIT RELAY UNIT 1 J 1 230v 9 m it. 2 L i\ l b l 13 I 5 l a I 1, 1 14 l I SWITCH B FLOAT d SWITCH swncw'A" 78-49 17 TREATING CYLNDER 'sNAP-oN'NR couuecnou SUCTION PUMP 2 1 25a i A 0 5 \J u INTERLOCK F767 KEY TREATlNG SOLUTION LlNES VACUUM LINE ELECTRICAL CIRCUIT i iml'dd SHEET VACUUM PUMP CONTROL UNIT V 2 B "B E M 2 A i H m L W RN I I R EOU h 8L u m UV SC M OE H C Es New (L a n A0 WE H I\ a W N R LWE III... S FSR O WGT IT RA MW 7 R 1 NMU E Q? 1 Q. m 2* IIIIJIU H J W a m Ex U III. H TC 6 w 5 m m m T 0 hm Hww A w M n J 1 5 R 5 3 a T R P INTERLOCK 7 TREATING SOLUTION LINES VACUUM LINE ELECTRICAL CIRCUIT a" :r: un gl Q5 PRESS SWlTCH"A" 2 2 mDomm2 m0 mwI02 FLOAT SWITCH SWITCH 7 8 9 INVENTOR ATTORNEY OPSIG JHL 2 ms SEALED EN zooPsle END 34 150PSIG SOPSIG K 20 j 5 ZOPSIG w LIJ (I D.

,19 Q w g SPSlG 3: 3

TREATING CYLINDER MERCURY TREATING CYLINDER E/MERCURY 1P1'FS""."'"!'H "P"? SHEET 5 AIR CHARGING /TO TREAHNG INLET AND VALVE cY mnER k 1 o o 34 AUTOMATIC ISOLATING VALVE i /MERCURY a P V FIG. 77.

FIG. 7.

0 I000 O 0 O O O O O O 0 0 0 0 0 O O O SHEET CONNECTO JUMPER LE CONf SCTION TREATING CYLINDER COMMON ELECTRODE MERCURY o IIIIIIII ESE: 6 $10; $205; 56w F FIG. 17.

TIMTNG SCHEDULE PHASE VACUUM PRESSURE STAOE SRO.

ZNO.

SRO.

SEOUENCE CONTROL TTMER FLOAT SWITCH VACUUM RESET STARTS PRESSURE RESETS PRESSURE SWITCH "A" PRESSURE SWITCH 'B" OPERATES RETURNS RETUR.

L ME

SUCTION PUMP STOPPEO RUNS STOPS VALVE 1 VALVE 2 VALVE 3 VALVE L VALVE 5 VALVE B OPENS CLOSED CLOSES OPENS CLOSEO CLOSED CLOSES OPENS CLOSES OPENS CLOSES OPENS OPEN INTERMITTANTLY OPENS CLOSES CLOSES CLOSES VALVE 7 CLOSED OPEN CLOSES VALVE O CLOSED oms VALVE S CLOSEO OPENS CLOSES INITIATING ACTIONS FOR EACH STAGE ARE UNDERLINED IMPREGNATION OF WOOD AND THE LIKE This application is a continuation of application Ser. No. l38,266 filed Apr. 28, 1971 (now abandoned), which application was a continuation-in-part of application Ser. No. lO4,l5O filed Jan. 5, l97l (now abandoned), which application, in turn, was a continuation of application Ser. No. 684,729 filed Nov. 21, I967 (now abandoned).

This invention relates to methods and apparatus for impregnating timber with preservatives.

In previous methods such as disclosed in US. Pat. No. 2,786,784 to Henriksson, there is described a method in which timber is impregnated with preservatives wherein the wood and treating solution are subjected to alternate phases of high and low pressure, with both the high and low pressure phase being kept at substantially constant levels and the period of each cycle being increased as the treatment progresses.

However, while such a method has been satisfactory for some timbers, due to the variable and complex nature of wool, the method has been found to be lacking in other timbers, especially in freshly felled timbers possessing a high moisture content from which the air within the cells can readily be removed, and in some unseasoned timbers in which the torus may be readily and permanently displaced.

The problems which have caused this treatment to be unsatisfactory have now been attributed to the inability of the method to control satisfactorily the rate of removal of the air from wood cells in timbers of high moisture content from which the air is readily removed, and the inability to control the pressure differential across the walls between the cells in which the connecting ports are known as bordered pits, in each of which bordered pit is located a membrane of which the thickened central portion forms a valve known as the torus, with the torus tightly closing the bordered pit whereby the fiow of liquids between cells is prevented if the torus ia adpressed to the pit border. The adpressing or permanent displacement of the torus is caused by too great a pressure differential or pressure drop across the wall of the cell.

In the case of the former problem, air must be present within the cells of green or freshly felled wood be fore a treating solution can be caused to replace the sap in the cells of the wood at a satisfactory rate. Once all of the air is removed from within the cells, the rate of impregnating the wood with the treating solution is found to be too slow for commercial purposes.

A simple and approximate explanation of this phenomenon can be advanced if a wood cell is viewed as a hollow tube containing wood sap leading into a sac which is three quarters or more full of sap and one quarter or less of air, with the other end of the tube being open into a treating solution inside a cylinder which is first subjected to a high presure phase. Under high pressure, the treating solution will force the sap upwardly into the tube and the sap and some treating solution will flow into the sac thus compressing the air in the sac. Upon release of this pressure when changing to a low pressure phase, the air in the sac expands and forces some of the mixture of sap and treating solution down the tube so that some of the liquid will overflow into the treating solution at the end of the tube. ln the next cycle in the high pressure phase, the mixture of sap and treating solution which was removed will be replaced by some of the treating solution, with the air in the sac again being compressed. The air will then expand in the next low pressure phase. Consequently, so long as there is air in the sac, the above cycles of high and low pressure will result in an exchange of the sap and the treating solution in the sac until the liquid within the tube and sac is substantially the same as the liquid within the treating cylinder.

[n the low pressure phase of the treating cycle, some of the air is removed either as dissolved air or as free air, and if the low pressure limit is too low, too much air will be removed and it will not be possible to provide a satisfactory equilibration of the strength of the sap solution with the treating solution before the movement of liquid associated with the air compression and decompression ceases.

In practice, it has been determined that a certain amount of fiber decompression occurs and this functions in the same way as air decompression but to a very much smaller degree, so that once air is removed from within the wood cells, the above cycle of compression and decompression will only work through the process of fiber compression and decompression and such a process has been determined to be far too slow to be of commercial value.

In the case of the latter problem, a reduction of the differential of pressures used in the treating cylinder will reduce the pressure drop across the cell walls and enable a flow of liquid to take place in both directions through the pits in the walls of the outer layers of wood cells by avoiding the permanent displacement or adpressing of the tori to the pit borders which occurs with previous methods due either to the aspiration of too much liquid and air from the inner cells of the outer layers and which aspiration displaces the tori of the aspirated cells inwardly toward the aspirated cells, or through a pressure build up in the outer cells which displaces the tori of those cells outwardly, or through a combination of pressure build up in the outer cells of the outer layers and the aspiration of the adjacent inner cells of the outer layers which acts to seal permanently the pits against liquid flow in either direction.

Depending on the variables of timber as covered in such broad groups as species, seasonal variations of the wood substances, growth, soil type and climate factors, a satisfactory impregnation of unseasoned or green wood can be achieved by maintaining a fixed pressure differential which is below the level at which permanent displacement of the tori will occur while progressively increasing or decreasing the upper and therefore also the lower pressure limit, or by commencing treatment with a low pressure differential, and as the outer layers of cells become saturated and consequently passive transmitters of the liquid flow to and from the inner cells, progressively increasing or decreasing the pressure differential by altering the upper and/or lower limits of the pressures used in succeeding cycles.

Thus, an important object of the present invention is to provide a method and apparatus for controlling the rate of removal of air from within wood cells to ensure that aspiration of the critical amount of air from within the wood cells is not exceeded, and permanent displacement of the tori or adpressing of the tori to the pit borders is not caused before the wood is as deeply penetrated with the preservatives as is desired.

At the present time, the knowledge of the properties of wood is insufficient to predict ad hoc a suitable rate of removal of air from within a new charge of timber. This is particularly the case as the properties of wood such as the percentage of air within the wood varies due to many factors such as seasonal variations, time elapsed from felling to treating, different species of wood, ano different densities and cell wall thicknesses. Thus, an adequate and commercially useful rate of removal of air can only be gauged by experience, and when treating wood, it is necessary to be in a position to vary the rate of air removal from within the wood after either manual observations or mechanical means demonstrate that air is removed at a too rapid or too slow a rate.

Referring to the previously explained method by which preservatives are introduced into wood, after the first cycle of high pressure and low pressure, some of the air will have been removed from the wood in the low pressure phase and in order to obtain a similar degree of exchange between the treating solution and the sap solution in subsequent cycles, a similar degree of movement due to the compression and decompression of the air within the wood should be accomplished. Hence, the high limit of the high pressure phase may be increased or the low limit of the low pressure phase may be decreased in the succeeding cycles or both the high limit and the low limit may be increased and decreased respectively. In other words, the differential of pressure between the low limit of the low pressure phase and the high limit of the high pressure phase is increased in succeeding cycles. This may also be achieved by holding the above-mentioned limits constant and increasing the differential of pressure between the mean pressure of the low pressure phase and the mean pressure of the high pressure phase.

Similarly, the pressure differential may be decreased if the variable properties of the wood as mentioned above necessitate the same.

SUMMARY OF THE INVENTION According to this invention, there is provided a method for impregnating timber with preservatives in a treating solution in which the wood and treating solution are subjected to alternate phases of high pressure and lower pressure, characterized in that the pressures in the high pressure and low pressure phases are altered in succeeding cycles such that the differential of pressure between the low limit of the low pressure phase and the high limit of the high pressure phase or the differential of pressure between the mean of the low pressure phase and the mean of the high pressure phase is increased or decreased in succeeding cycles, or the limit of the pressure in the high pressure phase is progressively increased or decreased in succeeding cycles while the differential of pressure between the high limit of the high pressure phase and the low limit of the low pressure phase remains constant, with the pressure limits and the increase of the differential of pressures being controlled to ensure that aspiration of the critical amount of air from within the wood cells is not exceeded before the wood is as deeply penetrated with the preservatives as desired.

The amount of preservatives which penetrates into the wood is termed the loading and the desired loading is that required by the authorities, or in the absence of an authority, by the preservative manufacturer or their agents. This depends on the type of wood, the type of timber and their proposed uses, and also varies in various countries depending on the regulations of the country involved.

According to this invention, there is also provided an apparatus by which the above-mentioned method may be effected automatically with provision for manual operation of the apparatus for varying the method when observations indicate that air is being removed at a rate too rapid or too slow for satisfactory results.

The invention will now be more fully described with reference to the drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic layout of the plant showing the parts thereof and electrical circuits thereof,

FIG. 2 is a schematic view of a control panel and the circuits thereof,

FIG. 3 illustrates the electrical connection within the automatic vacuum control panel,

FIG. 4 shows a pressure tube used to control low pressures below atmospheric pressure,

FIG. 5 shows a pressure tube used to control pressures above atmospheric pressure.

FIG. 6 shows a pressure tube used to control pressures above and below atmospheric pressure,

FIG. 7 shown a pressure tube used with an induced air pressure,

FIG. 8 is a front elevational view of a general construction of a pressure tube and its mounting,

FIG. 9 is a side view of FIG. 8,

FIG. 10 is a rear view of FIG. 8,

FIG. 11 is a rear view of the cover according to FIG.

FIG. 12 is a side elevation of the pressure tube shown in FIG. 8,

FIG. 13 is a cross-section of the pressure tube taken along line A-A of FIG. 9,

FIG. 14 is a graph showing a typical progression of the suction pump running time,

FIG. 15 is a graph showing a typical progression of a cycle duration,

FIG. 16 is a graph showing a typical progression of low pressure intensity, of below atmospheric pressure, and

FIG. 17 shows a typical operation of the apparatus in one cycle using a low pressure phase below atmospheric designated vacuum" and a high pressure phase designated pressure."

DETAILED DESCRIPTION OF THE INVENTION The pressure reservoir is charged to 28 p.s.i. with compressed air through a snap-on air connection. The pressure and vacuum pumps are started and run throughout the schedule.

The preservation solution held in a storage tank 15 is pumped into a treating cylinder by means of a suction pump (through valves not shown in FIG. 1) until the treating cylinder is full thereby causing the contacts in a float switch to close thus energizes the float switch relay.

A sequence control unit contains a changeover switch 13 which is placed in position b (pressure) and the circuit is through the float switch relay to a pressure valve 3 which opens. Solution is pumped from the storage tank 15 into the treating cylinder by a pressure pump through the valve 3 until a relief valve (1 1) opens at a preset pressure of I25 p.s.i. and allows the solution to return to storage. The process is now in stage 3 of the high pressure phase (FIG. 17).

The sequence control unit initiates the first stage of the low pressure phase (FIG. 17) by moving the switch 13 to position a which causes the valve 3 to close and the circuit is through a pressure switch A to a main line valve 1 which opens and allows the pressure in the treating cylinder to kick-back to the storage tank. When the pressure in the treating cylinder is reduced to 65 psi, the contacts in a pressure switch B close causing a pressure reservoir valve 4 to open allowing the pressure pump to pump solution from the storage tank through the valve 4 to the pressure reservoir. When the pressure in the pressure reservoir reaches I40 p.s.i., a bypass valve opens preventing the pressure from rising any higher. When the pressure in the treating cylinder is reduced to p.s.i., the contacts in the pressure switch A changeover thus causing the valve 1 to close and the circuit is now through a synchronous timing unit which causes the suction pump to run and

valves

2 and 10 to open. Solution is pumped from the treating cylinder to the storage tank and air is vented into the cylinder through a cylinder venting valve 9. The suction pump thus creates a void volume in the treating cylinder for purposes to be later described and this is the second stage of the low pressure phase (FIG. 17).

After a preset time (FIG. 14), contacts in the synchronous timing unit changeover thereby causing the suction pump to stop and

valves

2 and 9 to close and the circuit is now through the float switch relay, which has returned to its normal position with the above mentioned fall in the level of the solution in the treating cylinder, to A.V.C. isolating valve 7 which opens, and through an automatic vacuum control unit to auxiliary vacuum valve 6 which opens and allows a vacuum to be drawn on the treating cylinder from a vacuum reservoir 14. The process is now in the third stage of the low pressure phase (FIG. 17) and valve 6 opens and closes being intermittently controlled by the A.V.C. unit and the float switch, the operation of which will be later discussed.

The operation of this phase as above described is for a low pressure phase of below atmospheric pressure and the variations using a low pressure phase of about or above atmospheric pressure will be hereinafter further discussed.

The sequence control unit initiates the first stage of the pressure phase (FIG. 17) by moving switch 13 to position b which causes the

valves

6 and 7 to close and the circuit is now through the float switch relay to the main vacuum valve 5 and to the main line valve 1 causing such valves to open. The solution is forced into the cylinder by atmospheric pressure on the storage tank through the valve 1 until it lifts the float switch causing the float switch relay to operate which in turn causes the

valves

1 and 5 to close. The circuit is now through the float switch relay to

valves

3 and 8 which open, and this is the second stage of the high pressure phase (FIG. 17). Air enters the A.V.C. unit through valve 8 to reset this unit for the next phase. The pressure reservoir dishcarges rapidly through

valves

3 and 4 into the treating cylinder until the pressure therein rises to 70 p.s.i. when the contacts in pressure switch B open to cause valve 4 to close. The pressure pump then continues to pump solution from the storage tank into the treating cylinder through the valve 3 and when the pressure reaches I25 p.s.i., the relief valve 11 opens as previously stated. The purpose of the pressure reservoir is to provide a rapid buildup in the second stage of the high pressure phase and thus make the changeover from low pressure to high pressure as quickly as possible. The process is now on the final stage of the high pressure phase.

The opening and closing of the valves and the starting and stopping of the suction pump is controlled by timing means, i.e. the sequence control until and synchronous timer, by pressure means, namely pressure switches A and B and the A.V.C. unit, and level detecting means, i.e. the float switch. The sequence of operation of these means and the valves and pump discussed above is shown for one complete cycle of a high pressure phase and a low pressure phase of below atmospheric pressure in FIG. 17.

The operation of the float switch as described above is for an ideal operation in which the float is raised and closes the contacts thus energizing the float switch relay when the cylinder is initially filled, is lowered in the second stage of the low pressure phase when the suction pump creates a void volume in the treating cylinder, and is again raised when the cylinder fills under vacuum at the end of the first stage of the high pressure phase and so on in succeeding cycles. However, it is normal in the first few cycles of a schedule for a new charge of wood, for the float to be raised during the third stage of the low pressure phase due to the too rapid aspiration of the air compresed in the wood and the expansion of the dissolved air in the liquid displacing the liquids before the bubbles formed can rise to the void space at the top of the treating cylinder. The float switch relay then causes the

valves

6 and 7 to close before liquid can escape from the cylinder. The air bubbles will rise to the surface and gradually lower both the liquid level and the intensity of the vacuum, the latter, of course, serving to prevent further aspiration of the air from the wood, causing the float to again fall and vacuum to again be applied. This cycle may be repeated several times during this stage of the low pressure phase until the air in the outer layers of the wood is completely aspirated and the float switch ceases to be raised by fluctuating levels. Further discussions of the float switch operation will later follow.

During the high pressure phase, there will be a substantial amount of solution forced into the wood and when this high pressure is released, the liquid is forced out of the wood (liquid kick-back" from the wood) and this liquid kick-back" can be of quite substantial proportions, namely about 200 gallons in a normal charge and sometimes even up to 300 gallons, depending upon the size of the treating cylinder and the quantity of wood.

A proportion of this kick-back" is returned to the storage tank through the valve I during the first stage of the low pressure phase and a further proportion is removed during the second stage of the low pressure phase by the suction pump which creates a void in the cylinder to accommodate the remainder.

If, however, the float switch continues to be tripped after the first two complete cycles, then the degree of vacuum being applied is too severe and upon such observation, the low limit of the vacuum phase is adjusted to a lower level of vacuum i.e. a higher absolute pressure.

If, on the other hand, the float switch, after the first two or three cycles, rises before the end of the low pressure phase and does not again fall, this indicates that the cylinder is too full of liquid and the liquid does not contain any great amount of air bubbles so that the surface level of the liquid cannot fall when vacuum is arrested. This condition may be attributed to the timer per se either being very permeable or containing more air than would be reasonably predicted, and thus there is a greater liquid knick-back when the pressure is reduced and as a consequence the suction pump running time would have to be increased to create sufficient void volume within the cylinder per se.

Thus, in accordance with the present method, it is possible to vary the pressure limits of the high pressure and low pressure phases, to vary the suction pump running time to create sufficient void volume and to vary the time of each phase such as described and claimed in U.S. Pat. No. 2,786,784 and such variation is controlled so as to produce a satisfactory penetration of the wood. As the properties of wood vary from charge to charge and especially from species to species, it is not possible to place an ad hoc hypothesis on the variables but from the variation in the float switch and from experience, one can alter a method during the treatment to produce a satisfactory result. Hence, it has been found that Pinus Radiata and Corsican Pine are satisfactorily treated using a low pressure phase below atmospheric, but with Douglas Fir, it is necessary to start with a low pressure phase above atmospheric pressure.

Referring to FIGS. 1 and 17, the switches A and B are operated by the pressure in the treating cylinder, with the switch A being operable over a range of plus or minus psi and switch B over a range minus 75 psi. In FIG. 17, the term "operates" means the switch A or B of FIG. 1 is in the upper position.

In FIG. 17, the indicated action for each stage is underlined.

Referring to FIG. 1, the A.V.C. unit controls the intensity of the pressure applied to the treating cylinder, and the synchro-timing unit controls the operation time of the suction pump. The float switch relay as described above is actuated by the float switch to override the opening of the vacuum line to the treating cylinder, and the treating cylinder also has a combined vacuum pres sure gauge 18 for manual observation thereof.

As shown in FIG. 2, the sequence of operations in a treating schedule are controlled by a punched tape (not shown) having three tracks of holes therein. The tape is driven by a constant speed synchronous motor (not shown) is fed between sensing switches of a miniature micro-gap type provided with normally closed contacts or otherwise photoelectric cells. The tape holds the contacts open until the sensing probe or light beam falls into a punched hole giving an impulse of about 1-2 seconds duration. The impulses from the sensing switches located on the top and bottom tracks referred to as T, and T feed to the sequence control relays h and i which operate the low and high pressure signals. The sequence control relays h and i are mechanically interlocked to hold one or the other in the operative position and thus provide a continuous high pressure or low pressure output signal. The impulse from the sensing switch located on the center track referred to as T feeds directly to a vacuum control relay j which, in turn, energizes the coil of unisector relay v having multi-position stops causing the uniselector relay to advance one step. Each punched type is punched with eleven holes in the center track thus bringing the uniselector relay v to its twelfth step at the finish of the schedule. In FIG. 2, the uniselector relay v is shown on step 1, i.e. the beginning of the treating schedule.

The uniselector relay v is a three level (or 3 pole) 12 position stepping relay which advances one step with each impulse from the center track of the sequence controller. If for some reason it gets out of step (e.g. tape breakage), it can be manually advanced by manual control switch w in position a. The switch w is also used to reset the relay to step 1 with the switch w in position b through push button F0 for the next charge of timber. Level I of the uniselector relay v is connected to conducting probes of a pressure tube as discussed hereinbelow via vacuum intensity manual control switch U, and connections r and thus controls the pressure intensity in the low pressure phase and/or the high pressure phase. Level II of the uniselector relay v is connected to suction pump synchronous timer q via pump timing manual control switch U, and thus controls the running time of the suction pump during each low pressure phase.

During normal operation, the uniselector relay advances solely on receipt of impulses from the center track T of the sequence control tape but both the alteration of the pressure intensity and the alteration of the suction pump running time can be and is varied either independently or together by adjustment of the manual switches U, and U The manual switches U, and U, have five positions which can be selected manually. In FIG. 2, both switches U, and U, are shown in the manually selected position 3. The manual selection of the position depends on the species of timber and/or its use and the switches may also be adjusted independently or together during treatment if circumstances so demand.

The sequence control relays h and i can be overridden by manual control switches y and t with the switch y being in position b for automatic operation and in position a for manual operation. When switch y is in position a, then the switch 1 is manually operated; position a is for low pressure phase control and position b for high pressure phase control. Two indicator lights Pr and Va indicate which phase is in operation.

Terminals A to K connect to the similar terminals on the AVC panel shown in FIG. 3. The float switch directly operating the float switch relay R is energized whenever the treating cylinder (in FIG. 1) is full of solution. Thus, when a low pressure phase is in operation, the signal from the sequence control relay i comes through the pressure switch A (FIG. 2) and then through terminal H to central terminals bb of timer relay R, which will be in the up position by virtue of the actuation of the timer relay R, from suction pump timer q. The signal then passes to terminals ff of the float switch relay and then back to the terminals of the vacuum valve relay R, which will be in the down position when the low pressure phase of the schedule is in operation. This operates through its appropriate switch s the auxiliary vacuum valve 6 (FIG. 1) through terminal V6.

The float switch has two functions:

1. When the cylinder has filled with solution while under vacuum during the first stage of the high pressure phase, the float switch operates and closes vacuum valve (FIG. 1), closes the main line valve and opens the pressure valve 3, allowing the pressure reservoir to discharge into the cylinder.

2. If insufficient solution was removed from the treating cylinder by the suction pump during the second stage of the low pressure phase, the expansion of the air under vacuum, both within the timber and dissolved in the solution, will cause the solution level to rise sufficiently to fill the cylinder. When this occurs, the float switch operates and closes the AVC valve 6 (FIG. 1) preventing overflow into the vacuum reservoir and also the isolating valve 7 preventing solution entering a pressure tube as discussed herein below.

In FIG. 2, d represents four Phillips OAZIO Diodes, c a 25 VA transformer, the relays R and R the alarm relay and suction pump relay respectively, 3 fuses, r the main line switch, n neon light indicators, and S three position switches; the position as shown being the closed position while position b represents the automatic position and position a open position. The terminals designated V to V represent the terminals for the valves 1 to 6 (FIG. 1) respectively, the terminal designated S.P. represents the suction pump terminal; I the pressure pump interlock, Al the alarm terminal and T T and T the impulses from the punched tape. In FIG. 3, the symbols V-,, V;, and V designate valves corresponding to

valves

7, 8 and 9 respectively in FIG. 1.

Referring to FIGS. 8-13, a pressure tube 19 of any non-conducting substance is provided with probes 20 of electricity conducting material inserted through the tube wall, with the probes 20 being at suitable intervals and adequately sealed in place in the tube 19. The probes 20 are connected to the terminals r shown in FIG. 2 and a common electrode (FIG. 9) connects to the terminal com of FIG. 2. The pressure tube I9 is supported on a frame 30, and upper end 27 of the tube 19 leads to the treating cylinder (not shown) while the lower end 35 leads into a mercury container 36 which is open to the atmosphere. The common electrode also dips into the mercury in the mercury container 36. As shown in FIG. 8, the pressure tube 19 can be arranged against a pressure scale indicating inches of mercury. The connections from the probes 20 to the terminals r (FIG. 2) are shown in section in FIG. 13 and the probe 20 leads to a connector, thence to a jumper lead and then to a terminal strip which leads to the manual control switch U, of FIG. 2.

When it is desired to operate and vary the limits of the low pressure in the low pressure phase of the pressure cycle when the low pressure is below atmospheric pressure, then the pressure tube illustrated in FIG. 4 is used. Lower end of the pressure tube 19 leads into a mercury reservoir 26 which is itself open to the atmosphere. In this arrangement, the common electrode corn is placed towards the lower end 25 of the pressure tube 19 and the probes 20 are situated at intervals above the lower end 25 of the pressure tube 19. Upper end 27 of the pressure tube connects through a moisture trap 28 and damping device or needle valve (not shown), and through the A.V.C. isolating valve 7 to the treating cylinder. An A.V.C. relief valve 8 is suitably placed to allow atmospheric pressure to be into the line of the pressure tube 19 through vent 17 and through the A.V.C. relief valve 8, between the A.V.C. isolating valve 7 and the pressure tube 19 and also to allow a filter II to be inserted in the line between A.V.C. isolating valve 7 and the treating cylinder, if desired. Alternatively, a pneumatic, hydraulic or electrical pressure transducer may be incorporated in the line of pressure tube 19 to transmit any desired ration of the pressure in the treating cylinder to the upper end 27 of the pressure tube. 19.

When it is intended to operate with a low pressure range at or above atmospheric pressure, or when it is intended to vary the limit of the high pressure in the high pressure phase of the pressure cycle, then use is made of the pressure tube shown in FIG. 5. The pressure tube 19 has a sealed end 34 and a lower end 36 leading through a mercury chamber to a treating cylinder. The connections to the treating cylinder are as shown in FIG. 4. with the preferred use of a pressure reducing valve (not shown) in the connection to the treating cylinder to reduce the high pressures transmitted from the treating cylinder to a ratio that suits the operation of the pressure tube or alternatively a pneumatic, hydraulic or electrical pressure transducer may be used to transmit any desired ratio of the high pressure from the treating cylinder to the lower end 36 of the pressure tube 19.

The alternative arrangement illustrated in FIGS. 6 and 7 can also be used when it is desired to use a low pressure phase at or above atmospheric pressure. This pressure tube can also be used when it is desired to vary the pressure limits in both low pressure and the high pressure phases. FIGS. 6 and 7 show a U pressure tube I9 with one end 34 being sealed (FIG. 6) or containing an air pressure charging valve 35 (FIG. 7) and the other end 36 being connected to the treating cylinder as mentioned in reference to FIG. 4 with the preferable addition of a pressure reducing valve as described in FIG. 5.

Referring further to FIG. 7, the air pressure charging valve 35 is installed in the closed end of the pressure tube when it may be desired to increase the air pressure in the closed end 34 in order that linear compression of the air cushion may be reduced for any given pressure applied through the open end 36 of the tube 19. When this is required, the vent in the open end 16 of the pressure tube must be associated with a reducing or balancing valve, or the line between the open end of the tube 19 and the vent (A.V.G. relief valve 8 FIG. 4) must be fitted with a further automatic valve to maintain an air pressure in the open end of the tube 19 and thus prevent the mercury from being blown out. This further automatic valve is shown in FIG. 7 as an automatic isolating valve, and in FIGS. 6 and 7, the probes 20 may be located in either arm of the tube 19 when it is desired to vary either the low limit of the low pressure phase or the high limit of the high pressure phase, or the probes 20 may be located in both arms to vary both of the limits and may operate by making an electric circuit or breaking the circuit, whichever is most suitable to the range of pressures and the electrical equipment and apparatus used in this invention.

The tube 19 as shown in FIGS. 6 and 7 may have arms of equal or unequal length and these arms may be fixed in relation to each other and/or may be made adjustable by their manufacture from a flexible material, or by the inclusion of a flexible portion at the base or upturn of the tube 19 to allow some pressure adjustment to be effected by manipulation of the length of the arms of the tube 19.

When operating on the low pressure phase of the pressure cycle, the apparatus operates as follows:

On or after commencing the low pressure phase, the desired valves (described in reference to FIG. 1) operate to subject the pressure tube 19 to the pressure in the treating cylinder or the desired ratio thereof. The level, or levels, of the mercury in the pressure tube 19 alter due to the change in pressure and continue to alter as the pressure in the treating cylinder drops and the mercury in the pressure tube 19 makes contact with one of the probes 20 to complete an electric circuit through the mercury to the fixed common electrode com.

Such energizing of the electric circuit controls the opening or part opening, closing or part closing, of the auxiliary vacuum valve 6 shown in FIG. 1 through which the low pressure phase in the treating cylinder is controlled, induced or through which the pressure intensity within the treating cylinder is permitted to alter. When a lower pressure of less than atmospheric pressure is being induced, the mercury column in tube 19 will operate the circuit to close the auxiliary vacuum valves as soon as the required low pressure has been reached at which stage the pressure in the treating cylinder will be such that the mercury will complete the circuit between the common electrode and the probes 20 and thus the auxiliary valve 6 will be closed. Air will be then expelled from the wood being treated due to the internal pressure within the wood exceeding the external pressures and to the expansion of the fibers within the wood due to initial fiber decompression.

Some of this air at the time of its exit from the wood will be in the form of free air, and some will be dissolved in the liquid which is expelled from the wood at the same time by the internal air movement and fiber decompression.

Due to this release of air and liquid and to a less extent to fiber and wood decompression, the pressure of the liquid in the treating cylinder (and of any void volume in the treating cylinder) which surrounds the charge gradually rises.

This rise in pressure causes the mercury column in the pressure tube 19 to again change its level, with the mercury movement being back towards its original non-operative level, and the electric circuit is now broken or open as the operative probe 20 is bared. The breaking or opening of the electric circuit initiates the opening of the auxiliary vacuum valve 6 and the cylinder pressure is again reduced until the mercury in the pressure tube initiates the closing of the auxiliary vacuum valve 6.

Such procedure repeats itself automatically until the low pressure phase is almost completed at which time, as explained above in FIG. 1, immediately prior to the high pressure phase, the treating cylinder is automatically filled through the main line valve 1 with liquid while still under vacuum through the main vacuum valve in order to enable a rapid change to be made to the required pressure of the high pressure phase. If a pressure tube as shown in FIGS. 5 or 6, and 7 is used, the operation of the auxiliary vacuum valve 6 may be initiated by the reverse of the circuits described above with the auxiliary vacuum valve 6 opening when the circuit is made or closed and closing when the circuit is broken or open.

When operating the low pressure phase at/or above atmospheric pressure, the line will not be into the vacuum reservoir but instead to a storage tank. The opera tion of the pressure tube 19 is substantially the same,

with the auxiliary vacuum valve 6 being closed at the low peak of the low pressure phase and opening as the pressure rises towards the high pressure phase to allow more liquid or liquid and air to flow from the treating cylinder In this case, little free air will emerge from the wood during the low pressure phase as most of the air is dissolved in the liquid.

When operating on the high pressure phase, the pressure tube acts in a manner similar to its operation dur ing the low pressure phase above atmospheric pressure with the pressure tube controlling the opening or partial opening, closing or partial closing, of the cylinder relief valve 9 through which the upper limit of the high pressure is controlled.

Many obvious variations can be made in the above described invention, including the use of a pressure tube equipped with inductance, capacitance, magnetic, sonic or light sensitive devices or other sensing equipment in lieu of the probes 20 inserted through the pressure tube wall.

An air, gas or liquid (including oil and other liquids) pressure regulating valve may be employed to maintain a pressure above atmospheric pressure on the open end of the U pressure tube 19 when it is desired to maintain a pressure in the open end of the tube and thus increase the operating pressure range and/or pressure differences between the operating probes 20; or a reducing valve in the liquid line to the treating cylinder so that reduced ratios of the pressure in the treating cylinder may be used as the operative pressure in the pressure tube. Furthermore, a needle valve or throttling device by which the rate of movement of the mercury in the pressure tube 19 may be directly or indirectly controlled or adjusted to provide a suitable time lag, or pressure differential between cylinder pressure and mercury column levels to allow for efficient operation of the unit can be utilized.

The trap 28 and the liquid drain is arranged to prevent liquid such as water from contaminating the mercury, and/or alternatively a diaphragm or an air reservoir to provide an air cushion may be used for the same purpose.

Referring to FIGS. 2 to 13 each of the terminals r shown in FIG. 2 are connected to one of the conducting probes. Thus, an impulse from the timing tape steps the multi-position stepped relay V around one step, and this will connect the stepping relay with a probe situated further upwardly on the pressure tube 19. Hence, as the stepping relay moves through its 10 positions it will step through 10 different operative probes. There fore, the initial limit of the low pressure phase on the first step of the stepping relay will be at a low pressure and the multi-position stepped relay will step progressively through operative probes at increasingly lower pressures. As a result, at the beginning of a schedule, the low pressure will be at a low absolute pressure while at the end of the schedule, the low pressure will be at a relatively lower absolute pressure. Similarly, when varying the high pressure phase limits, the schedule will begin with a low absolute pressure and will end with a relatively high pressure.

There are provided 15 terminals designated r in FIG. 2 and these will each be connected to 15 different probes on the pressure tube 19. With the manual control switch U it is possible to select an initial probe to begin each schedule.

Thus one can begin a schedule with a lower or high pressure as desired by selecting one or another of the manual positions. This will then leave probes connected to the terminals corresponding to each step on the t0 stepping relay. Similarly, when one is operating by varying the high pressure phase. there will be probes all told with generally 10 being operated in any schedule. It will be appreciated that the invention has provision for the increase of the differential of pressure between the limit of the low pressure phase and the limit of the high pressure phase, and/or the progressive increase of the mean pressure of the low pressure and high pressure phases.

FIG. 14 shows the progressive changes in the low limit of the low pressure phase when using a low pressure at or below atmospheric pressure. Five curves are shown, with each curve corresponding to a different position of the manual control switch U Thus, step 3 corresponds to the manual control switch U. being in its position shown in FIG. 2. While the curves are shown as smooth lines they are actually more of a step like progression as the multi-position stepped relay steps around one step. If as explained above, it is found that the level of the vacuum is too high, that is the float switch is being tripped on and off, then the operator will turn the manual control switch U, downwardly from say step 3 to say step 2 to decrease the level of vacuum. The selection of the position of the manual control switch is governed primarily by experience and for most normal timbers, one starts on step 3 and thus allows for provision either upwardly or downwardly from this position. The criteria of the schedule is in order to obtain satisfactory loading of the treating solution in the timber when the schedule has been completed. The curves shown in the drawings reach their maximum vacuum intensity before the uniselectory relay has reached its step ll. If it is found that a charge of wood has not been satisfactorily impregnated with the treating solution at the end of the schedule. then this means that the increase of the differential of pressure or the differential of pressure is not large enough and thus the manual control switch will be switched upwardly one step for the next similar charge of wood or else a pressure tube with large pressure differentials between the probes will be used.

The figures shown in FIG. 16 relate to a treatment of Pinus Radiata with Boliden K33 having a fixed high pressure limit of 125 p.s.i. and varying the low pressure shown using step 3. The time of the schedule is dependent upon the size of timber in use. If one is using 2 inch thick timber. then the schedule will be set to take two hours. If one is using 3 inch thick timber, then the schedule will be set to take 3 hours.

However, timber from Douglas Fir will not give a satisfactory result when using a low pressure phase which is initially below atmospheric pressure and it has been found preferable to vary both the low pressure phases and the high pressure phases starting with a low pressure limit of 40 lbs. p.s.i.g. and a high pressure limit of 60 lbs. p.s.i.g. taking the low pressure limit down at the end of the schedule to about 2.5 lbs p.s.i. absolute and taking the limit of the high pressure phase at the end of the schedule up to I89 p.s.i.g.

Generally, it has been found that the initial low pressure limit is selected from within the range between 55 p.s.i.a. and 8 p.s.i.a., preferably between 55 p.s.i.a. and 10 p.s.i.a. while the initial high pressure limit is selected from within the range of 50 p.s.i.a. and 265 p.s.i.a., preferably between p.s.i.a. and p.s.i.a. When the high pressure limit is varied during the schedule, at the end of the schedule, the high pressure limit will be at least 40% greater, more preferably 50% greater, than the limit at the beginning of the schedule while, when the low pressure limit is varied, during the schedule, at the end of the schedule, the low pressure limit will be at leaast 50% less, more preferably 70% less. than the low pressure limit at the beginning of the schedule.

Referring to FIG. 14, it shows curves depecting the progressive change in the suction pump running time as the schedule progresses. If, as previously described, it is found that there has been insufficient void volume created at the top of the treating cylinder, then the operator can turn the manual switch U up to a stop to increase the suction pump running time. Again for normal operation, one will begin a schedule on step 3 and ifA is found that such running time is insufficient, then the manual control switch U; will be advanced from step 3 to step 4.

It is also possible in accordance with this invention to vary the duration of each phase of the pressure cycles as previously described in U.S. Pat. No. 2,786,784 and thus illustrated in FIG. 15. The duration of each phase is determined by the placement of the punched holes on the timing tape.

Before the beginning of each schedule, it is generally preferred to subject the charge within the treating cylinder and the treating solution to an initial pressure for about 10 minutes as is generally used in the art.

In New Zealand as in many countries throughout the world, timber impregnation is subject to Government Regulations. One must satisfy the requirements in regard to the standard of treatment. In New Zealand. and with those species of timbers which can be treated satisfactorily by the method described in U.S. Specification No. 2,786,784. the regulations required for building timbers up to 2 inches thick, a minimum anahydrous solution concentration of Boliden K33 of 0.60% by weight while for a similar solution the regulations require a strength of 0.75% for building timbers up to three inches thick. With the method of the present invention, the New Zealand Regulations have now allowed a reduction in the solution strength and will allow a minimum strength for building timbers up to two inches thick of 0.45% by weight and for building timbers up to 4 inches thick a minimum strength of 0.50% by weight without any other requirements imposed on the method such as for example. the number and duration of the pressure/vacuum oscillations are the same for both the original method as described in U.S. Pat. No. 2,786,784 and for the method of the present invention. Similar reduction in solution strength have been approved for other types of timbers such as marine piles, poles and posts. sawn timber for ground contact and high decay hazard use and fence battens and palings. This reduction in solution strength possible by the present method is of considerable economic advantage to an operator.

The invention also includes equipment set up to perform a similar function to the equipment herein described or shown, or any methods substantially similar to that described, or substantially similar to that described but to which have been added sonic, sub-sonic. super sonic or any other energy pulsation. It is also possible to use in lieu of mechanical probes to detect the holes in the punched tape, a photo electric cell detecting the holes in the punched tape.

IN THE SPECIFICATION l All references to pressure are in terms of absolute pressure, unless otherwise indicated and low pressure may be taken to read vacuum or low pressures around and above atmospheric pressures, but significantly lower than the high pressure range around and below the maximum pressures used.

For ease of understanding, the low pressure range shall generally be considered to be the lower 50% of the total range of absolute pressure used in any schedule, and the high pressure range shall generally be considered to be the upper 50% of the total range of absolute pressures used in that schedule, subject to any charge of 50 lbs. p.s.i. or greater indicating a change from high to low or vice versa.

2. Schedule denotes the total time and the full process devoted to the impregnation of preservative treatment of a charge of wood.

3. Cycle denotes a complete application of low pressure followed by a complete application of high pressure or vice versa.

4. Phase denotes that portion of a cycle which is predominantly either the low pressure portion or the high pressure portion, with the commencement of a phase being that point in a cycle at which the change from low pressure to high pressure is initiated (or vice versa).

A low pressure phase therefore commences at high pressure at the instance that the reduction of pressure is initiated, and a high pressure phase commences at the low pressure at the instance when the increase of the pressure is initiated.

5. Mercury shall also cover any suitable liquid conductor of electricity.

6. Charge is a load of wood or other substance to be treated.

7. Liquid denotes the sap or the treating solution or more usually a mixture of the two, except where indicated.

8. Wood or timber includes all other substances suitable for treating in the manner outlined.

Hence, by this invention it is possible to control the rate of aspiration of the air from within the wood cells and by such control, it is possible to provide a more rapid method for impregnating wood with a treating solution.

We claim:

1. In a method for impregnating wood with preservatives in a treating solution in which the wood and treating solution are subjected to a treating schedule including cycles of alternate phases of high pressure and low pressure, the improvement comprising selecting the pressures at commencement as being within the limit imposed by the variables of the wood per se, with the high pressure at the start of treatment being between p.s.i. absolute and 265 p.s.i. absolute and the low pressure at the start of treatment being between p.s.i. absolute and 8 p.s.i. absolute, and then increasing progressively the differential of pressure so that at completion of treatment in terms of the initial absolute pressures, the high limit in the high pressure phase will be at least 40% greater than the initial high pressure and/or the low limit in the low pressure phase will be at least 50% less than the initial low pressure, including during said treatment, sensing the rate of aspiration or absorption of air from within the wood cells and when said rate exceeds a predetermined value, adjusting at least the intensity of pressure of the low pressure phase so that said rate is reduced and continuing said treat ment until the wood is so deeply penetrated and heavily loaded with preservative as is desired

Claims

1. IN A METHOD FOR IMPREGNATING WOOD WITH PRESERVATIVES IN A TREATING SOLUTION IN WHICH THE WOOD AND TREATING SOLUTION ARE SUBJECTED TO A TREATING SCHEDULE INCLUDING CYCLES OF ALTERNATE PHASES OF HIGH PRESSURE AND LOW PRESSURE, THE IMPROVEMENT COMPRISING SELECTING THE PRESSURES AT COMMENCEMENT AS BEING WITHIN THE LIMIT IMPOSED BY THE VARIABLES OF THE WOOD PER SE, WITH THE HIGH PRESSURE AT THE START OF TREATMENT BEING BETWEEN 50 P.S.I. ABSOLUTE AND 265 P.S.I. ABSOLUTE AND THE LOW PRESSURE AT THE START OF TREATMENT BEING BETWEEN 55 P.S.I. ABSOLUTE AND 8 P.S.I. ABSOLUTE, AND THEN INCREASING PROGRESSIVELY THE DIFFERENTIAL OF PRESSURE SO THAT AT COMPLETION OF TREATMENT IN TERMS OF THE INITIAL ABSOLUTE PRESSURES, THE HIGH LIMIT IN THE HIGH PRESSURE PHASE WILL BE AT LEAST 40% GREATER THAN THE INITIAL HIGH PRESSURE AND/OR THE LIMIT IN THE LOW PRESSURE PHASE WILL BE AT LEAST 50% LESS THAN THE INITIAL LOW PRESSURE, INCLUDING DURING SAID TREATMENT, SENSING THE RATE OF ASPIRATION OR ABSORPTION OF AIR FROM WITHIN THE WOOD CELLS AND WHEN SAID RATE EXCEEDS A PREDETERMINED VALUE, ADJUSTING AT LEAST THE INTENSITY OF PRESSURE OF THE LOW PRESSURE PHASE SO THAT SAID RATE IS REDUCED AND CONTINUING SAID TREATMENT UNTIL THE WOOD IS SO DEEPLY PENETRATED AND HEAVILY LOADED WITH PRESERVATIVE AS IS DESIRED.