GB2040195A - Changing the width of continuously cast strand - Google Patents

Abstract

The method comprises using an adjustable width casting mould comprising a pair of spaced apart longitudinal walls 3 and a pair of spaced apart transverse walls 2 movable along said longitudinal walls, stopping the pouring of metal into the mould, inserting a frame into the mould from the upper end at a speed equal to the descent, if any, of the molten metal, the frame including a pair of side plates 8, so that the lower ends of the plates are dipped into the molten metal in the mould, the plates 8 having vertically extending upper portions 9, which are spaced apart from each other at a distance equal to the new desired width define a cavity together with said longitudinal walls 3, pouring the molten metal into the cavity, beginning the withdrawal of the cast piece 1 together with the frame and moving said movable walls 2 of said mould to contact the outer surfaces of the upper portions 9 of the opposite side plates 8. <IMAGE>

Description

SPECIFICATION Method and apparatus for changing the width of a cast piece The present invention relates to a continuous casting technology, particularly to a method and apparatus for changing the width of a cast piece or strand in a continuous casting operation.

Various kinds of variable width casting molds have been recently developed for producing cast pieces having different widths from one charge of a molten metal. Such molds are usually formed of a pair of spaced apart parallel long copper side members and a pair of spaced apart, parallel short copper side members which are movable along the long side members. The long and movable short side members of the mold which are water-cooled define a cavity having a certain size. The width of the cavity corresponding to the spacing between movable side members may vary depending upon the width of the finished product required.

In the continuous casting operation, a molten metal is gravity poured into the cavity of the mold and partly solidified in the form of shell by being in contact with the water-cooled mold. A cast piece or strand is continuously withdrawn from the bottom of the mold.

When it is desired to change the size or width of the cast piece, the pouring of the molten metal into the mold is stopped; the molten metal as poured into the mold is withdrawn as a cast piece; thereafter one or both of the short side members are moved; a dummy bar corresponding to the changed width is positioned at the bottom of the mold; the molten steel is poured into the mold; and a cast piece with a new and changed width is withdrawn This arrangement it has the disadvantage that the casting operation must be stopped completely each time the width of casting is changed; that it takes a considerable time before the casting operation is resumed; and that the productivity of the continuous casting operation is thus largely lowered.

Many efforts have been made for developing a method and apparatus for changing the width of the cast piece and withdrawing the cast piece without involving discontinuation of cast piece due to the "break-out".

Japanese Patent Publications Nos. 46-39225, 47-25572 and 53-45781 disclose such methods and apparatuses for effectively overcoming the abovementioned disadvantages which have been encountered in the prior art. According to Japanese Patent Publication No. 46-39225, there are provided a pair of interconnecting upper and lower solid blocks having different widths depending upon the desired width of the cast piece. In order to change the width of the cast piece, the pouring of a molten metal into a mold is stopped. The upper and lower interconnecting blocks which have been combined each other are inserted into the mold for interconnecting the lower and upper cast piece having different widths. The blocks disclosed herein have disadvantages of high cost of fabrication and being cumbersome to handle due to their weight.

Japanese Patent Publication No. 47-25572 discloses an improved adjustable width continuous casting mold including upper and lower slidable plate members. According to this arrangement, the existing adjustable width casting mold and the oscillation mechanism for the same must be replaced, resulting in high cost of installation.

Japanese Patent Publication No. 53-45781 discloses a method of enlarging the width of a cast piece comprising stopping the pouring of a molten metal into a molt; positioning a supporting plate at the bottom of the mold; and then moving a side wall of the mold. This method can be performed for decreasing the width of a cast piece. There is a danger that the solidified shell will break since it is self-erecting and that the "break-out" of the cast piece will occur.

It is therefore an object of the invention to provide a method and apparatus for effectively overcoming the above-mentioned disadvantages which have been encountered in the prior art.

It is another object of the invention to provide a method and apparatus for enlarging and decreasing the width of a cast piece during the continuous casting operation with a minimal labor and time.

It is a further object of the invention to provide a method and apparatus for charging the width of a cast piece without involving leaks of molten metal or breaking out of the cast piece.

It is a further object of the invention to provide an method and apparatus for changing the width of a cast piece with a minimal length of the cast piece to be discorded where different width cast piece are connected each other.

The present invention comtemplates to provide a method of changing the width of cast piece formed in a continuous metal casting operation using an adjustable width casting mold comprising a pair of spaced apart longitudinal walls and a pair of spaced apart transverse walls in contact therewith which are movable along said longitudinal walls, the improvement comprising stopping the pouring of a molten metal into said mold; stopping the withdrawal of the cast piece from said mold; inserting into said mold from the upper end thereof a frame means including a pair of opposite side plate members so that the lower ends of said plate members are dipped into the molten metal in the mold, said plate members having vertically extending upper portions which are spaced apart each other at a distance substantially equal to a desired width to thereby define a cavity together with said longitudinal walls; pouring the molten metal into said spacing; beginning the withdrawal of the cast piece having a changed width together with said frame means; and moving said movable walls of said mold to contact with the outer surfaces of said upper portions of said opposite side plate members.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designated corresponding parts in the several views.

and in which: Figures 1 through 6 are schematic sectional views showing a way of changing the width of a cast piece to smaller size, according to the present invention; Figures 7through 10 are schematic sectional views showing a way of changing the width of a cast piece to an enlarged size, according to the present invention; Figure 11 is a perspective view showing side plate members used for reducing the width of a cast piece; Figure 12 is a fragmental view of a modified side plate member for use for reducing the width of a cast piece, with the right half portion omitted; Figure 13 is a longitudinal cross sectional view taken along the line XIII-XIII in Figure 12; Figure 14 is a transverse cross sectional view taken along the line XIV-XIV in Figure 12; Figure 15 is a perspective view of frame used for producing a cast piece having an increased width; and Figure 16 is a front view of a modified side plate member for use in increasing the width of a cast piece with the right half portion omitted.

A method of reducing the width of a casting or cast piece in the continuous casting operation will be first referred to in conjunction with Figures 1 to 6.

Figure 1 shows a casting mold by which a casting 1 having a width L1 is produced in the continuous casting operation, wherein shown at 2 are movable walls of the mold, at 3 fixed walls of the mold, at 4 a nozzleforpouring molten steel into the mold, which is partly dippd in molten steel, at 5 molten steel; at 6 a solidified shell and at 7 powdered flux on the surface of molten steel for thermal insulation.

In order to produce cast piece 1 of a reduced width 11, the pouring of molten steel into the mold 2 and 3 is stopped, and the nozzle 4 is lifted above the surface of molten steel in the mold. The withdrawing of the cast piece from the mold 2 and 3 by means of pinch rollers (not shown) is continued. When the molten steel surface is lowered to a level of 100 to 200mm above the bottom of the mold 2 and 3, the withdrawing of casting from the mold 2 and 3 is stopped.

Figure 3 shows such condition of the casting in the mold. In this stage, the solidified shell 6 of the cast piece has grown to a greater extent and the top surface of the cast piece 1 is maintained in a molten state by virtue of the thermally insulating effect of powdered flux 7.

Under such condition, a frame as shown in Figure 3 is inserted into the mold 2 and 3, the frame comprising a pair of side plate members 8 inserted into a cavity defined by opposing movable walls 2 and fixed walls 3 and side plate members placed parallel to the movable walls of the mold, until the lower ends of the side plates in the molten steel 5 of the cast piece 1. The side plate members 8 have vertical portions 9 on the upper outer surface thereof, respectively, which portions are parallel to respective movable walls 2, so that the inner surfaces of the movable walls are in contact with the upper outer surfaces of respective side plate members when the movable walls are shifted to the side plate members, respectively, in a manner described below. Vertical portions 9 are spaced apart each other a distance substantially equal to the desired new width 12 of the cast piece 1.The lower ends of side plate members are located at a level of 100 to 200mm below the molten steel surface of the existing cast piece 1.

The side plate members 8 shown in the drawings are respectively made of a flat plate of 6 to 1 Omm in thickness and have anchor elements 10 at the lower ends thereof, respectively, so as to ensure the coupling of the cast piece being produced to the existing cast piece and locking projections 11 on the opposite inner surfaces thereof. The reason why the frame including opposite side plate member is inserted when the molten steel surface in the mold is at a level of 100 to 200mm above the bottom of the mold is firstly to prevent leak of molten steel, and secondly to ensure the rapid solidification of molten steel even in the event that leak of molten steel arises between side plate members 8 and fixed walls 3 of the mold.In the actual operation, it is preferable that a cooling agent, such as steel chips or nail scraps, be scattered on the surface of molten steel between the side plate members of the fame and the movable walls 2 of the mold.

It is also preferable that the opposite side plate members 8 of the frame be coupled together by such as tie rods 12 shown in Figure 11, or that said plates form a framework, for ease of insertion.

After the insertion of the fame into the mold, the nozzle 4 is moved downward to be located within a cavity defined by opposite side members 8 and fixed walls 3 and the molten steel is gravity poured through the nozzle 4 into the cavity as seen in Figure 3. As the side members 8 are anchored at the lower ends thereof by the solidified shell 6 of the cast piece 1, the existing cast piece is pulled downward at a rate of 0.2 to 0.3mm/minute, as shown in Figure 4, until the top shoulder portion of the cast piece emerges from the lower edges of movable walls 2 of the mold.

Movable walls 2 are then moved horizontally in a direction to reduce the width 11 of the mold to the width 12, namely toward the frame to contact with the vertical upper portions 9 of frame 8, whereby the width 11, of the mold is reduced to width 12.

The movable walls are in general moved by remote control using hydraulic pressure or by a motor. In this embodiment, it is preferable that, for example, a synchronous mechanism be provided, so that an operator may recognize the movement by a given length, of the movable walls, or the movement or stopping of the movable walls may be automatically accomplished by presetting the length of movement.

The speed of movement of the movable walls 2 is determined so that the movable walls 2 complete their movement while one half or one third of each side plate member 8 of the frame as viewed from the top thereof is lodged in the mold.

After reduction of the width of the mold is completed, side plate members 8 are withdrawn downward, together with the cast piece 1, from the lower edge of the mold as shown in Figure 6 on the continuous casting basis as usual. A portion of cast piece to which the side plate members are secured is cut off by a cutter on the exit side of the pinch rollers (not shown). According to the method of the present invention, the portion of cast piece to be discarded is limited to only that portion to which the side plate members are secured. The length of the cast piece 1 to be cut off is remarkably reduced, as compared with that in the prior art.

The method of increasing the width of a cast piece 1 in the continuous casting operation will be ex plained with reference to Figures 7 to 10.

The procedures for increasing the width of cast piece 1 from a width L1 to a width L3 are the same as those for reducing the width of the mold as described with reference to Figures 1 to 6.

The pouring of the molten steel into the mold is stopped, then the nozzle 4 is lifted, and the withdrawal of the cast piece 1 from the mold is continued until the molten metal surface in the mold is lowered to a level of 100 to 200mm as measured from the lower edge of the mold.

With this situation maintained intact, a frame is set in the mold as seen in Figure 7. Also, in this case, the side plate members 8 forming the frame comprises the upper vertical portions 9', which are spaced apart from each other at a distance substantially equal to the width 13 of a cast piece 1 to be produced and lower vertical portions 9" which are in an opposed relation to the inner surfaces of movable walls 2. Lower vertical portions 9" of the side plate members 8 are convergent toward the lower end thereof, providing a funnel-shaped cross section.

The convergent portion is dipped in the molten metal 5 of cast piece 1 in the mold, with the lower end thereof located at a level of 100 to 200mm below the molten metal surface.

The procedures for increasing the width of the mold are identical with those for reducing the width thereof only except that the side plate members having a bent or curved shape are used, but they both produce a spacing between the upper portions of the opposite side members substantially equal to the new desired width of a cast piece, and the lower ends of the side members 8 are dipped in the molten metal 5 of existing cast piece 1.

Figure 15 shows an example of side plate members 8' which are coupled together by side spacer plates 13 for ease of insertion into the mold. Such side plate members may be made separately from each other. In the latter case, the side plate members are inserted individually into the mold in an opposed relation to the fixed walls of the mold and then fixed therein to form a temporary mold.

After the side plate members forming a frame have been set in the mold, the nozzle 4 is moved downward to a position within the mold, as seen in Figure 8 and a molten steel is then poured into the cavity defined by the opposite side members 8'.

When the side plate members 8' are anchored as at 10 at the lower ends thereof to the solidified shell 6 of cast piece 1, the withdrawal of cast piece 1 is recommenced.

Then, movable walls 2 of the mold are moved horizontally outwards, so as to increase width 11 to width 13. In this instance, the movable walls 2 must complete their movement before the upper enlarged portion 9' of the side plate members 8' moving downward, together with cast piece 1, reaches the top edges of movable walls 2.

Thus, the width of the mold is increased. The side plate members 8' are pulled downward together with cast piece 1. The portion of the cast piece 1 to which the side plate members 849 are secured is cut off in such a manner described in the preceding example.

In changing the width of a cast piece to a desired size during the continuous casting operation, the pair of the opposite side wall members 8' are used for protecting the cast piece until it has sufficiently solidified thus making possible reliable and easy production of a cast piece of an increased or reduced width.

The period during which the withdrawal of a cast piece is stopped for increasing or decreasing the width of the mold is greatly shortened to of the order of 30 seconds. According to our experiments, during the continuous casting operation for pruducing a casting of 11 50mm wide x 270mm thick by continuously pouring a steel consisting of 0.09% of carbon, 0.15% of silicon and 0.61% of manganese into S-type continuous casting equipment at a rate of O.9m/minute, the width of the mold was increased to 1350mm, and a time of stopping of the withdrawal of the casting way 25 seconds. During the continuous casting operation for producing a castng of 1250mm wide x 270mm thick, the width of the mold was reduced to 1200mm, and a time of stopping of the withdrawal of the casting for that purpose was 35 seconds.In either case, the changing in a width of the mold to a desired size could be accomplished rapidly without involving the break out of the cast piece and leak of the molten steel.

As described above the frame including the opposite side plate members is inserted into the mold after the pouring of the molten metal is stopped.

However the frame may be inserted into the mold at a speed equal to the descent speed of the surface level of the molten metal with lower ends of the side plate members being dipped in the molten steel.

Then the withdrawal of the cast piece is stopped when the surface level of the molten steel is slightly above the lower end of the mold.

For realizing the method of the present invention easily, rapidly, safely and accurately, respective pairs of side plate members 8 and 8' should preferably meet the below-described requirements, particularly ease of insertion and the utility thereof: 1. The side plate members should be able to accommodate a large amount of molten steel therein for at least 5 minutes from the charging of molten steel until the movement of movable walls 2 for changing the width of the mold is completed.

2. Leak of molten steel must not be involved between the fixed walls 3 and the side plate members 8 while the molten steel is retained between side plate members.

3. The side plate members should be smoothly withdrawn together with the cast piece from the mold to pass through guide rollers in a secondary cooling zone and to be cut off from the cast piece, without causing any trouble with the casting equipment or the cast piece.

4. For ease of insertion of side plate members into the mold as well as reduction in time required for changing the width, side plate member should preferably be preassembled by means of a known tundish car or the like and placed above a mold, in such a manner that the side plate member assembly may be moved downward to position in place within the mold accurately and easily.

Figures 12 to 14 show a modification of the frame for producing a cast piece having a reduced width as shown in Figure 11 and Figure 16 shown a modification of the frame for producing a cast piece having an increased width, as shown in Figure 15. These two modifications also satisfy the above-described requirements.

Referring to Figures 12 to 14, a side plate member 8A for use in producing a cast piece having a reduced width is made of a steel plate of 9mm in thickness and has a dimension of 650mm in height and 273mm in width. The dimensions are dependent upon the configuration of the mold, which are determined by the configuration of a casting to be required and specifications of the continuous casting equipment. The side plate member 8A has a lower anchor portion 14covering a range of 100mm from the lower end thereof, the anchor portion being dipped in the molten steel 5 of cast piece 1 in the mold, width of which remains unchanged, as seen in Figure 12. The side plate member 8A further has opposite vertical edges 15 curved in conformity with curvatures of front and rear fixed walls 3 of the mold.

A strip of a deformable and refractory material, for example an asbestos plate of 25mm in thickness, is rigidly secured to the upper outer surface of each side plate member 8A. The asbestos plate has parallel vertical opposite edges curved in comformity with a counter of the side plate member 8A and is larger in width to some extent then that of the side plate member 8a, so that when front and rear fixed walls 3 are unfastened, the asbestos plate may be positioned between the curved fixed walls along the curved surfaces thereof at a right angle therewith, thereby providing a sealing function against leak of molten steel from an interstic between the opposite vertical edges 15 of the side plate member 8A and front and rear fixed walls 3.Furthermore, the relationship in width of asbestos plate 16 with the side plate member 8A is such that when movable walls 2 of the mold are moved to given positions for positions for reduction in the width and fixed walls 3 are again fastened together, a gap is left between the fixed walls 3 and the opposite vertical edges of the side plate member 8A as seen in Figure 14.

A pair of trough-shaped resilient stiffening plates 17 made of curved spring steel of 3mm in thickness are placed internally of and along the opposite vertical edges of each the plate member 8a, with the convex trough portions thereof maintained resilient ly in engagement with the inner surfaces of front and rear fixed walls 3 of the mold over the full length thereof, as seen in Figures 13 and 14.

Where a vertical type mold is used in the continuous casting machine, the opposite vertical edges of each the side plate member 8A should be made parallel and linear, rather than curved, and hence the trough-shaped resilient stiffening plates therealong should be made parallel and linear, rather than curved, unlike that shown in Figure 13.

A frame functioning as a mold is formed by coupling a pair of side plate member 8A in an opposed relation to each other and by attaching asbestos strips 16 to the upper outer surfaces of respective side plate members in such a manner that a distance between the outer surfaces of these asbestos defines the width 12 of a cast piece to be molded. In this connection, as tie rods 12, four steel bars of 12mm in diameter are used. In the aforementioned frame, the opposite asbestos strips 16 are convergent toward the lower ends thereof, this presenting a funnel-shaped cross section. Since the outer surfaces of respective strips 16 define positions to which movable walls 2 are moved to reduce or increase the width of a cast piece, then, an angle of inclination of these strips is determined with reference to the contraction due to the solidification of a cast piece.

When the molds for producing a casting having a width in the range of 975 to 1350 mm are used, several kinds of tie rods different in length or variable-length spacer bolts are prepared so that the spacing between the outer surfaces of the opposite side members may be varied over a range of 5 or 10mm depending upon the customer's requirements.

A horizontal tongue piece 18 projects from the top outer surface of each anchor portion 14 of the side plate member 8A in such a manner that it is on the surface of molten steel of the existing cast piece 1 unchanged in width when the frame is inserted into the mold, so asto prevent the molten steel surface from rising. Each tongue piece 18 prevents the adverse rising of the surface of molten steel in the space defined by the movable walls 2 and the side plate members 8Awhich would be caused by increase in static pressure as a result of the pouring of molten steel into the temporary mold, thereby ensuring the smooth movement of the movable walls 2. Shown at 19 is a guide piece for inserting the frame into the mold in parallel with movable walls 2 with its center aligned with the center of the mold.

This guide piece is provided if desired. As locking projections 11, Y-shaped studs may be attached at a pitch of 500mm to the side plate members.

Referring to Figure 16, a side plate member 8'A for increasing the width of a cast piece has a lower anchor portion 14', similarly to the side plate member 8A for production of a cast piece of a reduced width. The side plate members in this embodiment are identical with those in the preceding embodiment except that each strip 16' is attached to the upper outer surface of each side plate member; trough-shaped resilient stiffening plates 17 are disposed internally of and along the upper opposite side edges of each side plate members 8'A; and these members coupled by tie rods 12 into a casting mold frame.

When the frame including the side plate members 8A or 8'A is used, a gap between the side plate members and the fixed walls of the mold is closed by resilient strips 16 and trough-shaped resilient stiffening plates 17, respectively. Thus, respective strips 16 function to effectively prevent the molten steel from leaking through the aforesaid gap, which would occur upon the pouring of the molten steel into the gap between the side plate members. Furthermore, the trough-shaped resilient stiffening plates also prevent the molten steel from leaking through the aforesaid gap, which would occur when the frame contracts by being cooled by the fixed walls of the moid.The trough-shaped resilient stiffening plates are slidingly moved at the convex trough portions thereof, thereby to protect the join between the existing cast piece and the cast piece having a changed width, which join is likely to be broken when the mold undergoes oscillation and/or a casting (or cast piece) is withdrawn from the mold.

It will be noted that a conventional, variable width casting mold is utilized without modification; and a frame including a pair of the opposite side members parallel to the movable walls of the mold is inserted into the casting mold, so as to protect the coupled portion between upper and lower cast pieces from being broken out. By such arrangements, changing of width of a casting mold, for producing a casting of an increased or decreased width, is accomplished during the continuous casting operation. An existing cast piece having an unchanged width and a cast piece having a changed width are coupled together safely, easily and rapidly. The operation for changing the width of a casting mold may be conducted by remote control or may be automatically conducted if desired. A portion of a casting to be cut to discard is limited to only a portion of cast piece to which the side plate members are secured, thus providing an higher yield. Reduction of a time for changing the width of a cast piece results in reduction in a stopping interval time of the casting operation and an increase in productivity, and allows economical manufacture of many kinds of product from one charge of a molten steel.

Claims (18)

1. A method of changing the width of a cast piece formed in a continuous metal casting operation comprising using an adjustable width casting mold comprising a pair of spaced apart longitudinal walls and a pair of spaced apart transverse walls in contact therewith which are movable along said longitudinal walls, stopping the pouring of a molten metal into said mold; inserting a frame means into said mold from the upper end thereof at a speed substantially equal to the descent speed if any, of the molten metal, said frame means including a pair of opposite side plate members, so that the lower ends of said plate members are dipped into the molten metal in the mold, said plate members having vertically extending upper portions which are spaced apart from each other at a distance substantially equal to a desired width of casting thereby to define a cavity together with said longitudinal walls; pouring the molten metal into said spacing, said distance being shorter than the existing cast piece width; beginning the withdrawal of the cast piece having a changed width together with said frame means; and moving said movable walls of said mold to contact the outer surfaces of said upper portions of said opposite side plate members.

2. A method as claimed in claim 1 wherein said opposite side plate members are spaced apart from each other at the upper portions thereof at a distance shorter than the existing cast piece width.

3. A method as claimed in claim 1 wherein said opposite side plate members are spaced apart from each other at the upper portions thereof at a distance longer than the existing cast piece width.

4. A method claimed in any one of claims 1 to 3 further including rigidly securing and spacing said opposite side members by space means.

5. A method as claimed in claim 4 wherein said spacer means comprises a rod.

6. A method as claimed in claim 4 wherein said spacer means comprises a plate.

7. A method as claimed in any one of claims 1 to 6 further including securely engaging said side members with the lower existing cast piece by hook means at said side members.

8. A method as claimed in claim 7 wherein said hook means is an elongate plate secured at right angles to said plate member, said elongated plate having a width larger than the thickness of the side plate member.

9. A method as claimed in any one of claims 1 to 8 wherein the side members are secured to the cast pieces by a plurality of projections on the interior of the side members.

10. A method as claimed in any one of claims 1 to 9 wherein the withdrawal of the cast piece is temporarily stopped when the surface level of the molten metal is slightly above the lower end of the mold.

11. A method as claimed in any one of claims 1 to 10 wherein a cooling agent is placed upon the surface of the molten metal between said side plate member of said frame means and said movable walls of said mold.

12. A method as claimed in any one of claims 1 to 11 wherein the withdrawal of the cast piece from the mold is stopped while the frame is being inserted into said mold.

13. A method as claimed in any one of claims 1 to 12 wherein said movable walls are moved to contact the outer surfaces of said upper portions of said opposite side plate members before pouring the molten metal into said spacing; and beginning the withdrawal of the cast piece having a changed width together with said frame means.

14. Aframe for changing the width of a cast piece in continuous casting operation comprising a pair of opposite side plate members extending in a vertical direction having a width substantially equal to a spacing between longitudinal walls of a casting mold, said side plate members having lower portions which may be dipped into the molten metal in the mold and having upper vertical portions parallel to said movable walls, which are spaced apart each other at a distance equal to the width of the desired cast piece.

15. Aframe as claimed in claim 14 further including strips of a deformable and refractory material are applied upon the outer surfaces of said opposite side plate member, said strips having such a width that the gap between said longitudinal walls of said mold and the side plate member is sealed by said strips.

16. A frame as claimed in claim 15 wherein the strips are of asbestos.

17. Aframe as claimed in claim 14 wherein a spring means having a semicircular section which biases the inner surface of said longitudinal wall of said mold and is secured to the inner surface of the side plate member.

18. Aframe as claimed in claim 14 wherein a spring means which projects from the outer surface of the side plate member biases upon the inner surface of the movable wall.