US3416237A - Method and apparatus for drying flexible material such as paper and board formed from cellulosic fibrous material - Google Patents

Description

Dec. 17, 1968 c. A. o. SUTHERLAND ET Al.

Filed Dec. 21, 1966 5 Sheets-Sheet 1 FIGJ.

G FLEXIBLE MATERIAL SUCH AS PAPER AND BOARD FORMED FROM CELLULOSIG FIBROUS MATERIAL Filed D80. 21, 1966 5 Sheets-Sheet 3 Dec. 1-7. 1 6 c. A; o. SUTHERLAND ET AL METHOD AND APPARATUS FOR DRYIN ND ET AL 3,416,237

1386- 7, 6 c. A. o. SUTHERLA METHOD AND APPARATUS FOR D NG FLEXIBLE MATERIAL SUCH AS PAPER AND BOARD FORMED FR CELLULOSIC FIBROUS MATERIAL Filed Dec. 21, 1966 5 Sheets-Sheet 3 United States Patent O 3,416,237 METHOD AND APPARATUS FOR DRYING FLEXIBLE MATERIAL SUCH AS PAPER AND BOARD FORMED FROM CELLU- LOSIC FIBROUS MATERIAL Charles Arthur Orr Sutherland, and John Luckins, Surrey,

England, assignors, by mesne assignments, to The Research Association for the Paper and Board Printing and Packaging Industries, Leatherhead, Surrey, England, a British company Filed Dec. 21, 1966, Ser. No. 603,665 Claims priority, application Great Britain, Dec. 23, 1965, 54,748/ 65 19 Claims. (CI. 34-23) ABSTRACT OF THE DISCLOSURE A method of drying a continuously moving damp web of paper or board material, wherein heated gases are directed against side-by-side regions of the web, the gases after contact with each such region being withdrawn and operating a temperature sensing device for controlling the drying effect, for example, velocity or temperature, of the heated gases to be applied to that region. An apparatus for drying the web includes a drying hood with several compartments for blowing heated gases onto the different regions of the web, each compartment having an inlet for the drying gases, control means for controlling the drying effect of such gases, suction means for withdrawing the gases after contact with the web and a temperature sensing device for operating the associated control means to control the drying effect of the heated gases directed onto each region of the web in response to the temperature of gases withdrawn from that region.

Background of the invention This invention relates to a method and apparatus for the drying of flexible material such as paper and board formed from cellulosic fibrous materials.

Processes are already known in which a damp continuous web is formed on, for example, a Fourdrinier machine, the web being pressed and dried whilst still in the form of a continuous sheet, to obtain the finished paper or board. The drying of continuous webs or sheets of paper and board is carried out by leading the web or sheet around a large number of steam heated drying cylinders.

It is known that, to increase the drying effect and hence to allow the web or sheet to be formed and dried more quickly, one or more of the drying cylinders may be fitted with a forced convection drying hood, also known as an accelerator hood, or a high velocity air cap. These devices comprise a box-like casing containing blowing and heating means, the underside of which casing is concave and forms part of the surface of a horizontal cylinder of slightly greater radius than the drying cylinder in conjunction with which the hood is to be used. The hood is so positioned above the cylinder that the part cylindrical underside of the hood is co-axial with the drying cylinder, such that a small gap is left between the drying cylinder and the concave face of the drying hood.

There is provided over the concavely curved surface of the hood an array of jets, slots, perforations or other outlets for streams of heated gases. These impinge on the web of damp paper or board which is led around the drying cylinder and cause the web to be dried more quickly than by the effect of the drying cylinder alone. The gases may be for example, air, superheated steam, combustion gases or a mixture of these.

It is often found however that, whether the web is dried by contact with heated drying cylinders alone, or more 3,416,237 Patented Dec. 17, 1968 rapidly by contact with cylinders some of which are provided with forced convection drying hoods, the drying effect is uneven across the width of the sheet. Commonly, the edges of the sheet are dried more than the central part, or one edge is dried more than the other. In some cases the drying effect may be found to have varied in an irregular manner across the whole width of the web. These variations in moisture content commonly found across the width of the Sheet may cause difficulties in the subsequent processing, for example printing, according to the final use to which the paper or board will be put.

It is known that the concavely curved surface of a forced convection drying hood can be divided across its width into several substantially separate compartments each having one or more outlets for the heated gases and inlets for the exhaust gases. The heated gases are supplied from a common duct or heater chamber to the several compartments at substantially the same temperature. Dampers or other valve means may be provided to regulate the flow of heated gases into each compartment and hence to vary the drying effect of the hood across the width of the sheet.

Drying hoods modified in this way are known as cross corrector hoods or cross-corrector air caps and provide a known means by which the moisture content of the sheet of paper or board may be made more even across its width. Some cross-corrector hoods have valve means adapted to be actuated manually while the hood is in use. An operator can for example determine the variation in moisture content across the width of the dried or partially dried sheet by means of a known moisture meter instrument, the operator then adjusting the dampers or valve to provide an increased drying effect where the sheet is found to be too wet or a reduced drying effect where the sheet is too dry. However, such an arrangement involves laborious and time-consuming operations and is unsatisfactory in view of the speed of travel of the web or sheet to be dried, on the paper or board making machine.

Summary of the invention An object of this invention is to devise a method and apparatus by which an improved evenness in the drying of flexible material such 'as paper and board material can be achieved.

Accordingly, the invention provides a method of drying flexible material such as paper and board formed from cellulosic fibrous materials, the method comprising the steps of directing heated gases onto a web or sheet of the material for drying different regions of the Web or sheet disposed in side-by-side relationship across the width thereof, and controlling the drying effect of the heated gases directed onto such regions in response to the temperature of gases withdrawn from corresponding regions of the web or sheet after contact therewith, thereby to produce a substantial even drying of the web or sheet across the width thereof.

In general it is desirable that the paper or board after drying should still have some moisture in it. It may for example be desired that this moisture should form 8 percent of the total weight of the paper or board. Hence, the reference herein to drying is to be understood as meaning the reducing of the moisture content of a damp web or sheet of the paper or board material, to the desired amount.

The invention further provides drying apparatus for drying flexible material such as paper and board formed from cellulosic fibrous materials, comprising a drying hood having a plurality of side-by-side compartments through which heated gases can be directed onto a like plurality of different regions disposed in side-by-side relationship across the width of a web or sheet of the material to be dried, means for controlling the drying effect of the heated gases to be directed through each compartment, means for sensing the temperature of gases after contact with the Web or sheet, said sensing means being operatively connected to the control means so as to vary the drying effect of the heated gases applied in each region in response to the temperature of gases withdrawn from the web or sheet after contact therewith, thereby to produce a substantial even drying of the web or sheet across the width thereof.

Brief description of the drawings FIGURE 1 is a side elevational view illustrating drying apparatus according to one embodiment of the invention,

FIGURE 2 is a cross-sectional view taken along the line IIII of FIGURE 3, and illustrating on an enlarged scale, part of the apparatus shown in FIGURE 1,

FIGURE 3 is a fragmentary axial sectional view taken along the line III-III of FIGURE 2,

FIGURE 4 is an enlarged detail of FIGURE 2,

FIGURE 5 is a further enlarged detail view illustrating a modification,

FIGURE 6 is a cross-sectional view taken along the line VI-VI of FIGURE 5, and

FIGURE 7 is a longitudinal sectional view illustrating a further embodiment.

Description of the preferred embodiments Referring to FIGURES 1 to 4 of the drawings, the drying apparatus illustrated is intended for the drying of a wet web or sheet of paper or board formed from cellulosic fibrous material. The apparatus comprises a series of hollow drying cylinders 1 adapted to be heated by steam and arranged in staggered relationship at the drying end of a paper or board making machine. Two of the drying cylinders 1 are each equipped with a drying hood 2 to provide an increased drying effect, each drying hood comprising a casing structure 7 having a concave wall 3 spaced from the peripheral surface of the associated drying cylinder. One of the drying hoods is shown disposed above an upper drying cylinder, and the other disposed below a lower drying cylinder. The drying hoods are otherwise identical each of such hoods being provided with means for directing heated air or other drying gases onto the web or sheet, such means including an impeller fan 40 for forcing the gases through a heater 41 operated by steam or, alternatively by oil or gas burners. Each drying hood is provided also with means for withdrawing the gases after being cooled by contact with the wet web or sheet, such withdrawing means including a suction fan 42. The web or sheet to be dried travels along a serpentine path by passing over and under the successive drying cylinders as shown at 4.

The concave wall of each hood 2 is formed with a number of axially spaced and circumferentially extending flanges 5 which are arranged to divide the gap between the hood and the associated drying cylinder into substantially separate side-by-side compartments 6 (FIGURE 3). The casing structure 7 is formed with a circumferentially extending duct 8 for the heated gases, this duct 8 being disposed on the radially outer side of the concave wall 3 and being divided into separate chambers or compartments across the width of the hood by radial walls 9 extending radially outwardly from and corresponding to the radially inwardly directed flanges 5. Each chamber or compartment 10 has an inlet 11 through which the heated gases are blown into the chamber from the heater 41. Each chamber 10 also has a number of outlet orifices for the heated gases, these outlet orifices being formed by perforations in the concave wall 3 and being indicated by arrows 12 in FIGURES 2 t0 4 of the drawings.

Four exhaust ports 13 are formed in each compartment 6, the exhaust ports having pipes 14 extending radially through the associated radially outer chamber or compartment 10. The arrangement is such that heated gases issuing through the orifices 12, in the portion of the concave wall 3 extending around each compartment 6, will be directed against a corresponding region of the Web or sheet 4. Hence, as the latter travels through the gap between the drying cylinder 1 and the hood 2, dilferent side-by-side and longitudinal regions of the damp web or sheet will be exposed to the heated gases, the different regions being shown in FIGURE 3 and being designated X, Y and Z respectively. The heated gases are cooled on contact with the damp web or sheet, and the cooled gases are drawn from each compartment 6 through the associated exhaust pipes 14 by the suction fan 42. The cooled exhaust gases extracted from the several compartments 6 are mixed in a mixing chamber 43 and after being reheated, are returned to the separate chambers 10 for further drying of the web or sheet. This arrangement forms a recirculatory system for the gases, although there Will be a leakage of the gases between the drying hood and the web or sheet, and a desired proportion of the exhausted gases can be discharged to atmosphere through a outlet 44. However, the amount of gas circulating in the system may be kept at the desired level by introduction of a fresh supply through an inlet 45.

The apparatus further comprises control means for controlling the drying effect of heated gases blown against the web or sheet, in response to the temperature of the cooled gases leaving the web or sheet. Referring to FIG- URE 4, the control means comprises a temperature sensing element in the form of a metal bulb 16 mounted in one of the exhaust pipes 14 leading from each separate compartment 6 of the hood, the bulb containing a suitable liquid and being connected by small bore tubing 17 to a metal bellows 18. The bellows are operatively connected by a push-rod 19 and crank 20 to valve means for controlling the flow rate of heated gases through the inlet 11. The valve means comprises a damper 15 pivotally mounted in the inlet 11 of the associated chamber 10. The arrangement is such that each damper 15 can be displaced about its pivot axis in accordance with the thermal expansion and contraction of the liquid in the bulb 16, to vary the rate of flow of heated gases which are to be blown onto that region of the web or sheet passing through the associated compartment 6. The higher the temperature of exhaust gases surrounding the bulb 16 of liquid, the more the damper will be closed. The exhaust pipe 14 is surrounded by thermal insulation 21 to prevent the hot gases in each chamber 10 from seriously affecting the operation of the temperature sensing bulb 16.

In operation, the damp web or sheet 4 to be dried is led around the several drying cylinders 1, as shown in FIGURE 1, the drying cylinders being supplied internally with the steam, so as to heat the peripheral surfaces of the cylinders for the purpose of drying or reducing the moisture content of the web or sheet as it travels over the cylinders. In general, the drying effect of the cylinders is relatively slow and uneven across the Width of the web and, for the purposes of the present description, it will be assumed that, before passing through the hoods 2, each longitudinal marginal portion or region X of the web has a lower moisture content than the intermediate portions or regions Y, and the regions Y have a lower moisture content than the central region Z of the web. To provide an increased drying effect, heated drying gases at a temperature in the region of, for example 340 F., are supplied under pressure to each of the chambers 10 corresponding to the regions X, Y and Z respectively of the web or sheet, the hot gases being supplied through the associated inlets 11 controlled by the dampers 15. The hot gases issue from the orifices 12 and are directed onto the corresponding regions of the moving web or sheet, the gases being rapidly cooled on contact with the damp web or sheet due mainly to the evaporation of water therefrom. The cooled exhaust gases in each compartment 6 are withdrawn from the corresponding region of the web or sheet by being sucked through the exhaust ports 13 and pipes 14 associated with that particular compartment 6. The temperature of the exhaust gases will vary according to the misture content of the web or sheet. For the purpose of illustration, it will be assumed that, in the case of the first or lowermost drying hood shown in FIG- URE 1, the exhaust gases drawn from the marginal region X of the web or sheet will be at a temperature of say 275 F the gases drawn from the intermediate regions Y will be at say 272 F. and the exhaust gases drawn from the central region Z will be at a temperature of say 270 F. The temperature sensing bulbs 16 located in the exhaust pipes 14 of the different compartments 6 operate the associated bellows 18 in response to the temperature of the exhaust gases and thereby produce a corresponding adjustment of the associated dampers 15. Hence, in the present example, the dampers 15 associated with the endmost compartments 6 of the hood, corresponding to the region X of the web or sheet, will then tend to restrict the flow of the heated gases into the associated chamber to a greater extent than the dampers for controlling the heated gases to be directed onto the intermediate regions Y, Z of the web or sheet. Any changes in the moisture content of the different regions of the web or sheet as the latter travels through gaps between the drying hood and the adjacent drying cylinder will be detected by the temperature sensing bulbs 16 thereby to bring about automatically a corresponding variation in the associated dampers so as to control the flow of heated gases into the corresponding compartments 6 in response to changes in temperature of the exhaust gases. The second or upper drying hood 2 arranged as shown in FIGURE 1, will operate in a manner similar to that of the first or lower hood, the two hoods combining to effect an additional drying of the web or sheet and to ensure a substantial even drying of the web across the width thereof. It will be understood that the exact temperature to which the gases are cooled by contact with the web or sheet in the various regions thereof, will depend in part on the amount of moisture in the regions of the web with which the gases have been in contact.

In the modification of FIGURES 5 and 6, the temperature sensing bulb 16 arranged in each exhaust pipe 14, is replaced by a temperature sensing element comprising a spirally wound bimetallic strip 22. One end of the strip 22 is anchored to the exhaust pipe 14 and the other end thereof is connected to a rotatable rod 23. The rod is operatively connected through crank and push-rod mechanism (not shown) to the associated damper 15, the arrangement being such that changes in curvature of the bimetallic strip due to changes in temperature of the exhaust gases passing through the exhaust pipe 14, will impart a corresponding angular rotational movement to the rod 23 to cause the damper to take up a position depending upon the temperature of the exhaust gases.

In FIGURES 1 and 2, the duct 8 of each drying hood is divided across the width of the hood by the walls 9 into the separate chambers 10 each having a compartment 6 in which a corresponding region of the web or sheet 4 is dried, the control of the heated gases passing through each compartment 6 being in response to the temperature of the cooled exhaust gases withdrawn from that same compartment after contact with the corresponding region of the web or sheet. If desired, however, the temperature sensing device of each compartment 6 of one drying hood, for example, the first or lowermost hood in FIGURE 1, may be operatively connected to the damper for controlling the heated gases passing through the compartment 6 of another drying hood, for example, the second or uppermost drying hood, such compartment 6 corresponding to the same region of the web or sheet being dried. Hence, where the apparatus comprises two or more of the drying hoods spaced from one another in the direction of travel of the web or sheet, the dying effect imposed by one dying hood on any one region of the web or sheet can be varied in response to the temperature of gases cooled by contact with the same region but withdrawn through a corresponding compartment of another drying hood through which the web or sheet passes either before or after passing through the hood in which the drying effect is varied.

Moreover, each chamber 10 may be divided radially into two or more smaller parts, each of such parts having an associated inlet for heated gases and at least one exhaust pipe for the cooled gases. It may also be advantageous in this form of construction, to connect the temperature sensing element in the or an exhaust pipe of one part of the chamber 10 for operation of the damper associated with another part of the same chamber 10 in order to prevent instability or hunting of the control system.

In the foregoing arrangements, the exhaust gases removed from the several separate compartments 6, or parts of such compartments, are thoroughly mixed before being re-heated and re-circulated through the inlets 11. In this way, the separate compartments across the width of the web or sheet are supplied with variable flow rates of gases at substantially the same temperature.

In the modified embodiment of FIGURE 7, the web or sheet 4 to be dried is passed through a drying tunnel 30 instead of being passed around drying cylinders as in the foregoing embodiments. The drying tunnel 30 comprises an outer casing structure having an inlet 31 for the web or sheet at one end and an outlet 32 at the opposite end, there being at the inlet and outlet co-operating guide rolls 33 for the web or sheet. During its passage through the drying tunnel, the web or sheet is supported by conveyor means comprising an endless band 34 of chain-like or open mesh material, which passes around rotatable conveyor rolls 35, 36. Within the drying tunnel there are arranged two drying hoods disposed at opposite sides of the upper run of the endless conveyor, there being an upper drying hood 37 and a lower drying hood 38 dis posed in face-to-face relationship and spaced apart to provide a narrow gap through which the web 4 carried by the upper conveyor run, passes from the inlet 31 to the outlet 32. The two drying hoods are provided on the opposed faces with compartments 6 and 10 extending longitudinally of the hoods and equivalent to the corre sponding compartments 6 and 10 of the drying hood described with reference to FIGURES 1 to 4. The hoods 37, 38 are each provided also with means for the supply of heated gases and the removal of the cooled exhaust gases. Thus, each of the drying hoods 37, 38 constitutes in effect a development of the drying hoods 2 of the first described embodiment and, in cross-section, the hoods 37, 38 are substantially of the form shown in FIGURE 3. The arrangement is such that as the damp web or sheet 4 passes between the upper and lower drying hoods 37, 38, the drying of different regions across the width of the web will be controlled in a manner similar to that achieved in the first embodiment.

In the aforedescribed embodiments, the heated gases are controlled by varying the flow rate or velocity thereof. If desired, however, the drying effect of the heated gases may be controlled by varying the temperature and/or humidity of such gases. The means for varying the temperature may comprise a thermostat device arranged to control the heater 41 and adapted to be operated by the sensing element 16 for determining the temperature of the exhaust gases. Means for varying the humidity of the heated gases, may comprise a gas recirculatory system including a device operable by the temperature sensing elements 16 and adapted to control the mixing of exhaust gases carrying the water or moisture evaporated from the web or sheet, with a fresh supply of air or gases, the proportions in which such exhaust gases and fresh air or gas supply are mixed being controlled so as to provide a gas mixture of the necessary humidity and temperature to provide the required drying effect.

As previously described, the temperature sensing elements may comprise a bulb containing a liquid capable of thermal expansion. Alternatively, the bulb may contain a gas or volatile liquid capable of producing relative movement of the bellows, by changes in pressure of the gas, or changes in vapour pressure of the liquid, to actuate the damper or other valve means. Similarly, the change in volume of a solid, such as wax, upon fusion, may also be used to cause relative movement for controlling the heated drying gases.

The temperature sensing elements may be operatively connected to the associated damper or other control members, by a mechanical linkage and/or by a hydraulic or pneumatic system. In addition, servo-mechanisms may be included to increase the force produced by the sensing elements.

It is to be understood, moreover, that electrical forms of temperature sensing elements may be employed, for example, electrical resistance thermometers, thermocouples or thermistors. The signals derived from such sensing elements may be amplified electrically for operating the damper or other valve means to vary the drying effect of the heated gases.

What is claimed is:

1. A method of drying a web of flexible material such as cellulosic fibrous material, including the step of directing heated gases onto several different regions of the web for the drying of the different regions of the Web extending along the web and disposed in side-by-side relationship acros the Width thereof, withdrawing gases from the several different regions of the Web after the cooling of such gases by contact with said web, sensing the temperature of the gases withdrawn from each of said different regions of the web and controlling the drying effect of the heated gases directed onto each diiferent region of the web in response to the temperature of the gases after being cooled by contact with that region so as to produce substantially even drying in the several different regions across the width of the web.

2. A method as claimed in claim 1, wherein the web is subjected to the drying effect of the heated gases whilst being moved and supported on a heated drying cylinder.

3. A method as claimed in claim 1, wherein the web is subjected to the drying effect of the heated gases whilst being passed through a tunnel-drier, the web being supported during the drying operation by endless conveyor means located within said tunnel-drier.

4. A method as claimed in claim 1, wherein the drying effect of the heated gases is controlled by varying the flow rate of the heated gases as they are directed onto the web.

5. A method as claimed in claim 1, wherein the drying eifect of the heated gases is controlled by varying the temperature of the heated gases.

6. A method as claimed in claim 1, wherein the drying effect of the heated gases is controlled by varying the humidity of the heated gases.

7. A method as claimed in claim 1, wherein the drying effect of the heated gases directed onto one part of each region of the web, is controlled in response to the temperature of gases after being withdrawn from, and cooled by contact with, another part of the same region of the web.

8. Drying apparatus for drying a Web of flexible material usch as cellulosic fibrous material, including a drying hood comprising a chamber, partition means dividing said chamber across its width into a plurality of side-byside compartments through which heated gases can be directed onto a like plurality of regions disposed in sideby-side relationship across the width of the Web to be dried and means for withdrawing gases from the web after contact therewith, characterized by means for controlling the drying effect of the heated gases to be directed through each compartment, means for sensing the temperature of such gases withdrawn from each region of the Web, said sensing means being operatively connected to the control means so as to vary the drying ettect 'of the heated gases applied in each region in response to the temperature of gases Withdrawn from each region of the web, thereby to produce a substantially even drying of the web across the width thereof.

9. Apparatus as claimed in claim 8, wherein there is provided an inlet through which heated gases under pressure can be directed through each compartment onto a corresponding region of the web, and an exhaust outlet through which gases after being cooled by contact with the web can be withdrawn, said temperature sensing means for each compartment being located in an exhaust outlet of that compartment.

10. Apparatus as claimed in claim 8, wherein the means for varying the drying effect of the heated gases to be directed through each compartment, comprises for each individual compartment valve means for varying the flow rate of the heated gases.

11. Apparatus as claimed in claim 8, wherein the means for varying the drying effect of the heated gases to be directed through each compartment, comprises a heater device for varying the temperature of such gases.

12. Apparatus as claimed in claim 8, wherein the means for sensing the temperature of the gases withdrawn from the web, comprises a heat responsive device incorporating a fluid medium adapted, up'on thermal expansion, to produce relative movement for operating the associated means for controlling the drying eflect of the heated gases to be directed onto the web.

13. Apparatus as claimed in claim 8, wherein the temperature sensing means comprises a spirally wound bimetallic strip, a rod rotatable by said spirally wound strip in accordance with changes in temperature of gases Withdrawn from the web, and means operatively connecting said rod to the associated means for controlling the drying effect of heated gases to be directed onto the web.

14. Apparatus as claimed in claim 8, wherein the means for sensing the temperature of the gases withdrawn from the web, comprises a heat responsive device incorporating a material which is solid at normal temperatures and which upon fusion, changes its state and produces relative movement for operating the associated means for controlling the drying effect of the heated gases to be directed onto the web.

15. Apparatus as claimed in claim 8, wherein the means for sensing the temperature of the gses withdrawn from the web comprises a heat responsive device incorporating a volatile liquid, said device being operatively connected to said control means to control the drying eflect of the gases to be directed onto said Web, in accordance with changes in vapour pressure of such volatile liquid due to changes in temperature of the gases withdrawn from the web.

16. Apparatus as claimed in claim 8, wherein the temperature sensing means is operatively connected to said control means by a mechanism including a bellows device operated by a fluid under pressure derived from said temperature sensing means.

17. Apparatus as claimed in claim 8, including a tun nel-drier, the drying hood being located within the tunnel-drier, conveyor means mounted within said tunneldrier for moving the web whilst substantially flat, though said tunnel drier, and means supporting said drying hood adjacent said conveyor means, so that the several compartments of the drying hood are arranged to direct heated drying gases onto corresponding side-by-side regions of the substantially flat web during the drying operation.

18. Apparatus as claimed in claim 8, wherein the drying hood has for the said compartments, a concave wall formed with orifices through which heated gases can be directed from each compartment onto the web, and wherein there is provided a drying cylinder, for supporting said 10 direct heated gases, onto corresponding parts of said sideby-side regions of the web, the temperature sensing means of one compartment of one of said drying hoods being arranged to control the drying eifect of the heated gases to be directed onto the web through the corresponding compartment of the other of said drying hoods.

References Cited UNITED STATES PATENTS 2,837,830 6/1958 Fry et al. 34-1 14 XR 3,167,408 1/1965 Justus et al 3454 XR 3,259,995 7/1966 Powischill 3448 XR 3,284,920 11/ 1966 Hayrinen et a1. 34122 KENNETH W. SPRAGUE, Primary Examiner.

US. Cl. X.R. 3454, 114

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