AU7481694A - Radiator tube and method and apparatus for forming same - Google Patents

Description

RADIATOR TUBE AND METHOD AND APPARATUS FOR FORMING SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to water tubes for copper/brass or aluminum radiators. More specifically, the invention relates to radiator tubes having welded seams and mating turbulator dimples forming pillars between the interior surfaces of the tubes, and a method

and apparatus for forming the tubes.

2. Related Art

Traditionally, water tubes for copper/brass radiators have been manufactured using a roll form process referred to in the heat exchanger industry as a "lockseam" process, to form a "lockseam" joint between the free edges of the metal strip used to form the tube. An example of a "lockseam" joint is disclosed in U.S. patent No. 2,252,211 to Seemiller. . To prevent the tubes from leaking after the radiator core is subjected to a baking process, a soft solder tin/lead alloy can be used in the lockseam joint during manufacture of the tube. The resulting joint is referred to in the heat exchanger industry as a "lockseam soldered" joint. An example of a "lockseam soldered" joint is disclosed in U.S. patent No. 4,470,452 to Rhodes.

As an alternative to the lockseam soldered joint, the prior art has employed a welded joint which does not rely on tin/lead solder. Roll forming techniques using forming rolls and side forming or helix guides are employed to take the strip from its original flat shape to a tubular shape of circular cross-section and precise diameter. During roll forming, the lengthwise edges of the strip are aligned precisely, and while the tube still has a circular cross-section, the edges are compressed at the apex under high temperature (the melting point of the parent metal) achieved through high frequency induction current or energy. This compression at high temperature yields a leak-free joint. However, a normal material or wall thickness increase is developed due to the compression and welding of the edges.

After welding, the tube is passed through reduction rolls or tooling and breakdown rolls to transform the cross-section of the tube from circular to flattened oval.

Thicker or higher density radiator cores, and consequently smaller face area or frontal surface in heat exchangers, are becoming more prevalent to meet the needs of automotive body styling, vehicle weight reduction, engine cooling, and air conditioning. As a result, one-row radiator cores, which traditionally were made in geometries with a height dimension (i.e. , the dimension along the major axis of the flattened oval shape, measured from exterior surface to exterior surface) from 15 mm. up to 38 mm., will now have to be made in geometries with a height dimension greater than 38 mm. Therefore, the height dimension of the flattened oval aluminum welded water tube will have to be increased to greater than 38 mm.

As the height dimension of the tube increases beyond 38 mm. , the parallel walls lose their column strength at high temperatures, causing them to sag or collapse. The resulting tube has a concave or "hour glass" cross-section, which decreases tube-to-fin surface contact.

In addition, because of the trend towards higher pressure operation in automobile radiators and the inherent stress limitations of thin-walled copper tube constructions, aluminum is increasingly being substituted for copper in view of its low cost, high thermal conductivity, and availability in tubes and thin sheets. The substitution of aluminum for copper in automotive heat exchangers, and the fabrication difficulties associated therewith, are discussed in U.S. patent No. 3,810,509 to Kun.

We have found that the high frequency induction welding-compression process previously used in the prior art to form solderless seams in copper/brass tubes, can be used with thin- walled materials, and can be used to form flattened oval tubes using aluminum strip in both clad and non-clad aluminum alloys. Here also, the parent material is used in conjunction with compression and high frequency welding to achieve a solderless leak-free joint. These flattened oval tubes made from aluminum can be used in the manufacture of aluminum brazed radiators and heaters, using either fluxless brazing (referred to in the heat

exchanger industry as "vacuum brazing") or flux brazing (referred to in the heat exchanger industry as NOCOLOX and/or "controlled atmosphere brazing"), as disclosed in U.S. patent No. 3,971,501 to Cooke and in U.S. patent No. 4,955,525 to Kudo et al. and the patents discussed therein.

However, we have also found in accordance with the present invention that a hollow flattened oval tubular shape of aluminum collapses toward the middle (i.e., into an "hour glass" shape) during high temperature brazing, preventing satisfactory contact at the tube-to- fin joints, both during and following brazing. We have further found that, by providing pairs of opposed turbulator dimples which extend inwardly from each of the principle heat transfer surfaces of the tube and make contact in the tube interior to define a pillar, the flattened oval shape is prevented from collapsing during the brazing process. In addition, the pillars increase the heat transfer surface on the water side of the tube, in comparison with turbulator indentations which do not make contact in the tube interior, as disclosed in U.S. patent No. 4,470,452 to Rhodes. It is known in the prior art to provide islands, projections, or depressions extending inwardly from their walls in order to maintain a constant spacing between the principle heat transfer surfaces, to increase the strength of the tube, to establish a plurality of flow paths for the fluid flowing through the tube, and to reduce the pressure drop of the fluid as it flows through the tube. Examples of such islands, projections, or depressions are disclosed in U.S. patent No. 790,884 to Coffin; U.S. patent No. 3,056,189 to Campbell; U.S. patent No. 4,180,129 to Sumitomo; U.S. patent No. 4,600,053 to Patel et al.; U.S. patent No. 4,688,631 to Peze et al.; and U.S. patent No. 4,932,469 to Beatenbough. However, such islands, projections, and depressions have only previously been used in tubes having lockseam formed joints, lockseam welded joints, or straight welded joints; and have not previously been used in the context of the high frequency induction welding-compression process; nor have their optimum dimensions and placement been sufficiently investigated.

Conventionally, islands, projections, or depressions are formed by stamping or embossing, as set forth in U.S. patent No. 4,932,469 to Beatenbough. Although these methods provide a satisfactory product, they are relatively slow, and ill-suited to be performed in line with roll forming of the metal strip to form a tube and the high frequency induction welding-compression process. Further, the methods employed by the prior art do not readily provide for adjustments to the alignment and height of the islands, projections, or depressions. It is to the solution of these and other problems to which the present invention is directed. SUMMARY OF THE INVENTION

The solution to these and other problems is achieved by the provision of a radiator tube having a flattened oval shape, and which comprises opposed first and second generally planar, principal heat transfer surfaces, a first generally continuous curved surface interconnecting and integrally formed with the first and second principal heat transfer surfaces, and a second generally continuous curved surface interconnecting and integrally formed with the first and second principal heat transfer surfaces. The first and second principal heat transfer surfaces have a plurality of pairs of opposed turbulator dimples formed

therein, which dimples extend inwardly and meet in the tube interior to define a plurality of pillars.

In one aspect of the invention, the second curved surface has a longitudinal, leak-free seam formed therein. In another aspect of the invention, the tube surfaces have a thickness of less than 0.23 mm.

In accordance with the invention, there is also provided a method of forming a radiator tube having a flattened oval shape. In this method, a generally planar strip or blank of a metal material is provided, the metal material comprising a parent metal and a second metal, and the strip or blank having opposed side edges and a longitudinal center line intermediate the side edges. Turbulator dimples are formed in the blank on either side of the longitudinal center line to define a pattern of dimples which is symmetric about the longitudinal center line. The blank is then subjected to roll forming techniques in order to form it into a tube of circular cross-section with the opposed side edges precisely aligned. Following roll forming, the side edges are simultaneously compressed at the apex and welded together by heating at the melting point of the parent metal using a high frequency induction current, to form a leak free joint. Reduction and breakdown rolls are then used to transform the cross-section of the tube from circular to a flattened oval, to define opposed first and second generally planar, principal heat transfer surfaces, a first generally continuous curved surface having the longitudinal center line approximately at its apex and interconnecting and

the first and second principal heat transfer surfaces, and a second generally continuous curved surface opposite the first generally continuous curved surface, the second generally continuous curved surface having the leak-free joint approximately at its apex and interconnecting the first and second heat transfer surfaces. In one aspect of the method, the step of forming the turbulator dimples comprises passing the blank between a pair of rotatable cylindrical rolls a predetermined distance apart, one of the rolls having male punches formed thereon and the other of the rolls having female sections formed therein in alignment with the male punches.

In another aspect of the method, phasing gears are used to maintain alignment of the male punches with the female sections.

Further in accordance with the invention, there is also provided apparatus for forming a radiator tube having a flattened oval shape and interior pillars. The apparatus includes first and second parallel, rotatable shafts, a first cylindrical roll mounted on the first shaft, and a second cylindrical roll mounted on the second shaft. The first roll has male punches formed thereon, while the second roll has female sections formed therein in alignment with the male punches. First and second phasing gears are mounted to the first and second shafts, respectively, in meshing engagement with each other to maintain alignment of the male punches with the female sections. BRIEF DESCRIPTION OF THE DRAWINGS The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which: Figure 1 is a partial perspective view of a tube blank with turbulator dimples formed thereon.

Figure 2 is a partial perspective view of a tube blank which has been formed into a tube of circular cross-section, with its side edges in precise alignment, prior to compression

and welding. Figure 3 is a partial perspective view of a radiator tube in accordance with the present invention.

Figure 4 is a cross-sectional view taken along line 4-4 of Figure 3. Figure 5 is a cross-sectional view taken along line 5-5 of Figure 3. Figure 6 is a cross-sectional view taken along line 6-6 of Figure 3. Figure 7 is a perspective view of apparatus in accordance with the present invention for maldng the radiator tube of Figure 3.

Figure 8 is a perspective exploded view of a dimple-forming roll of the apparatus of Figure 7.

Figure 9 is an enlarged, exploded view of a male dimple-forming disk and an spacer

disk of the roll of Figure 8.

Figure 10 is an enlarged, exploded view of a female dimple-forming disk and an spacer disk of the roll of Figure 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention

is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Referring now to Figures 3-5, there is shown a radiator tube 10 in accordance with the present invention. Radiator tube 10 comprises first and second opposed, generally planar principal heat transfer surfaces 12 and 14 and first and second opposed, continuous curved surfaces 16 and 18 interconnecting first and second principal heat transfer surfaces 12 and 14. Curved surfaces 16 and 18 are substantially semi-circular; the diameters of the circles of which curved surface 16 and 18 form a part are referred to as the end diameters of tube 10. A plurality of pairs of turbulator dimples 20 are formed in principal heat transfer surfaces 12 and 14 in opposed relation to each other and meet in the interior of tube 10 to define a plurality of pillars.

Tube 10 can be formed from strips or blanks of copper and brass, clad aluminum alloy, non-clad aluminum alloy, or any other metal material suitable for use in a heat exchanger which comprises a parent metal which can be welded by melting at a high temperature, and a secondary material. The presence of the pillars permits the use of blanks having a thickness of less than 0.23 mm.

As shown in Figure 1, radiator tube 10 is made from a generally planar strip or blank 30 having opposed side edges 32 and a longitudinal line 36 intermediate side edges 32. Turbulator dimples 20 are formed in rows 40 on either side of longitudinal line 36 in a pattern which is symmetric about longitudinal line 36. Longitudinal line 36 can be centered between side edges 32, or it can be off-center, but in either case, turbulator dimples 20 must be formed in a pattern which is symmetric about the line.

Dimples 20 are formed with flattened upper faces 42 which are generally square or rectangular in configuration, with rounded corners. In the completed tube 10, faces 42 of

5 each pair of dimples 20 are aligned with and contact each other, in order for the pillars so defined to support principal heat transfer surfaces 12 and 14 and prevent them from collapsing during high temperature brazing.

The use of rounded corners in dimples 20 lessens cavitation, in comparison with right-

angle corners; and also allows the parent material to flow during formation of the dimples

10 20, in comparison with right-angle corners, thereby lessening the chances of fracturing the parent material at the internal and external surfaces of dimples 20. It is noted that fracturing of the parent material lessens the strength of the flattened oval cross-section; it also accelerates silicon-aluminum diffusion or migration of the clad alloy from the aluminum brazing materials into the parent material at the fracture point of each pillar during high

15 temperature brazing.

Referring now to Figure 2, strip 30 is subjected to roll forming in order to form it into continuous tubing 50 of circular cross-section with opposed side edges 32 precisely aligned to abut each other. In the case where dimples 20 are formed in a pattern which is symmetric about a longitudinal line 36 which is centered between side edges 32, side edges

20 32 are aligned diametrically opposite longitudinal line 36, as shown in Figure 2. Side edges 32 are then simultaneously compressed at the apex and welded together by heating at a high temperature (i.e., the melting point of the parent metal) using a high frequency induction current, to form a leak free joint 52, such that second curved surface 18 is effectively integrally formed with first and second principal heat transfer surfaces 12 and 14. Following formation of the leak free joint 52, reduction and breakdown rolls are used to transform the cross-section of tubing 50 from circular to a flattened oval, to define opposed first and second principal heat transfer surfaces 12 and 14, first curved surface 16 which incorporates longitudinal center line 36, and second curved surface 18 which incorporates

leak free joint 52. Leak free joint 52 is located approximately at the apex of second curved

surface 18, i.e. within 45n of the apex.

Once leak free joint 52 has been formed and tubing 50 has been roll formed to achieve the desired flattened oval cross-section, lengths can be cut from tubing 50 to form a plurality of tubes 10. Tubes 10 can then be assembled to inlet and outlet header and tank assemblies (not shown) and brazed in a high temperature brazing furnace in accordance with conventional practice to achieve a leak-free joint between tubes 10 and the tank and header assembly.

We have discovered that, for a tube 10 having a flattened oval geometry in accordance with the present invention and having end diameters between 0.075 inch (1.905 mm) and 0.080 inch (2.032 mm) and having an outside center dimension (i.e. , the dimension along the minor axis of the flattened oval shape, measured from exterior surface to exterior surface) between 0.076 inch (1.95 mm) and 0.085 inch (2.03 mm), the height of each dimple 20 when formed (i.e., the distance dimple 20 extends above the plane of strip 30) must be between 0.009 inch (0.250 mm) and 0.029 inch (0.760 mm). Further, we have discovered that each face 42 must have a length dimension (as measured in the direction of the longitudinal axis of tube 10) of between 0.30 mm and 1.90 mm and a width dimension (as measured in the direction perpendicular to the longitudinal axis of tube 10) of between 0.012 inch (0.30 mm) to 0.081 inch (2.05 mm) in order to provide sufficient contact between facing dimples 20, and in order to obtain the maximum scrubbing of the fluid to break or distort the laminar flow of the fluid on the inner surfaces of tube 10, and to prevent cavitation of the fluid at given fluid flows. We have further discovered that maximum performance per flattened oval tubular dimension is achieved when the distance between the centerline of dimples 20 is between 0.2085 inch (5.296 mm) and 0.482 inch (12.24 mm). Referring now to Figure 6, there is shown apparatus 100 for forming the turbulator dimples 20 in a strip 30. Apparatus 100 comprises a station 102 having an inboard (or front) stand 104, an outboard (or rear) stand 106, and a top or cover plate 108 attached to the upper edges of inboard and outboard stands 104 and 106. Inboard and outboard stands 104 and 106

are provided with lower and upper cylindrical shafts 110 and 112 respectively mounted in lower bearing blocks 114 and upper bearing blocks 116. An adjusting plate 118 is connected to upper bearing blocks 116 at their upper edges, for a purpose to be described hereinafter.

Rolls 120 and 122 are respectively supported on shafts 110 and 112 a fixed distance apart. One of rolls 120 and 122, preferably lower roll 120, is provided with male punches

140, while the other of rolls 120 and 122, preferably upper roll 122 is provided with female dies or sections 142 positioned to align with male punches 140 as rolls 120 and 122 rotate. The alignment and shape of the pillars can be varied by varying the alignment and shape of male punches 140 and female dies 142.

Referring now to Figures 8, 9, and 10, rolls 120 and 122 preferably are modular in construction, so that the number of rows and columns of dimples and the surface area of the dimples can readily be varied. In order to achieve this modular construction, each of rolls 120 and 122 comprises a central hub 150 keyed to shaft 110 or 112, a plurality of pillar disks 152 axially aligned on either side of hub 150, and one or more spacer disks 154 separating each of pillar disks 152. Pillar disks 152 on roll 120 are provided with male punches 140, as shown in Figure 10, while pillar disks 152 on roll 122 are provided with female dies 142, as shown in Figure 9.

Hub 150 comprises a cylindrical main body portion 160 having an outer side wall 162 and opposite end walls 164, cylindrical necked-in portions 166 extending outwardly from end walls 164, and a central annular flange 166 extending outwardly from side wall 162. Pillar disks 152 and spacer disks 154 are assembled to central annular flange 168, for example by screws (not shown) inserted through aligned holes 158 through pillar disks 152, spacer disks 154, and flange 168. The inner diameters of pillar disks 152 and spacer disks 154 are substantially equal to the outer diameter of side wall 162, and the outer diameters of pillar disks 152 and spacer disks 154 are substantially equal to the outer diameter of flange 168 to provide an integral structure when assembled.

Pillar disks 152 and spacer disks 154 are further held in place on hub 150 by front and back end caps 170 inserted over necked-in portions 166 and abutting against end walls 164. End caps 170 are affixed to hub 150 by screws 172 inserted through aligned holes 174 through end walls 164 and end caps 170. Front and back end caps 170 have inner diameters substantially equal to the outer diameters of necking-in portions 166 and outer diameters substantially equal to the outer diameters of pillar disks 152, spacer disks 154, and flange 168, further to provide an integral structure when assembled.

Apparatus 100 is positioned immediately upstream of a roll forming station (not shown), and rolls 120 and 122 are driven as strip 30 is pulled through the roll forming station by the vertical forming rolls. Pulling strip 30 through rolls 120 and 122 permits strip 30 to be in precise line speed with the roll forming and welding stations. Were rolls 120 and 122 driven, they would create a loop that has to be in synchronization with the mill strip speed to prevent drag which would cause high frequency welding problems. In order to ensure proper alignment of punches 140 and dies 142 as rolls 120 and 122 rotate, phasing gears 180 are journaled on the front ends of shafts 110 and 112 and are in meshing engagement with each other. Phasing gears 180 are provided with phase adjusting screws 182, for adjusting their pitch diameter and enabling male punches 140 to align with female dies 142, in a manner which will be appreciated by those of skill in the art. As a result, the finish radius within each dimple 20 is uniform, and fracturing of the parent material as previously described is prevented.

Further, male and female alignment gears 184 and 186 are journaled respectively on

the back ends of shafts 110 and 112. Male and female alignment gears 184 and 186 horizontally align pillar disks 152 on roll 120 with their mating pillar disks 152 on roll 122.

The height of dimples 20 can be adjusted through a pillar height adjusting nut 190 rotatably mounted to top plate 108, a threaded rod 192 inserted through adjusting nut 190 and attached to adjusting plate 118, and a pair of positive stop pins 194 inserted into a pair of holes 196 extending horizontally into inboard and outboard stands 104 and 106 between lower and upper bearing blocks 114 and 116.

Counterclockwise rotation of adjusting nut 190 raises adjusting plate 118 and upper bearing blocks 116 attached thereto, to permit removal and insertion of stop pins 194; while clockwise rotation of adjusting nut 190 lowers adjusting plate 118 to cause upper bearing blocks 116 to rest on the inner portion 194a of stop pins 194. The diameter of the inner portion 194a of positive stop pins 194 determines the height of dimples 20, in that the diameter of inner portion 194a is proportional to the distance between rolls 120 and 122. Decreasing the diameter of the inner portion 194a of positive stop pins 194 decreases the distance between bottom and top rolls 122, and thus increases the height of dimples 20. Thus, stop pins 194 of one diameter can be exchanged for stop pins 194 of a different diameter to change the height of dimples 20.

It is noted that both stop pins 194 which are in use together must have inner portions

194a of the same diameter. Unlike diameters will cause uneven spacing between lower and upper rolls 120 and 122, effecting the shape and height of dimples 20 and creating uneven flow distribution of the fluid in the resulting formed tube 10.

As will be appreciated by those of skill in the art from the foregoing disclosure, variations in the size, shape, number, and alignment of dimples 20 within a tube 10 can be easily achieved using the apparatus 100 in accordance with the present invention. As will further be appreciated by those of skill in the art, varying the size, shape, number, and alignment of dimples 20 in a tube 10 will have an effect on the performance of the tube 10 with respect to fluid flow resistance. For example, decreasing the number of aligned pairs of dimples 20 in a tube 10 having a flattened oval shape generally results in a decrease in resistance and performance, while increasing the number of aligned pairs of dimples 20 increases fluid resistance and therefore tube performance.

Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described.

Claims (13)

WHAT IS CLAIMED IS:

1. A radiator tube having a flattened oval shape comprising: opposed first and second generally planar, principal heat transfer surfaces; a first generally continuous curved surface interconnecting and integrally formed with said first and second principal heat transfer surfaces; and a second generally continuous curved surface interconnecting and integrally formed with said first and second principal heat transfer surfaces, said first and second principal heat transfer surfaces and said first and second generally continuous surfaces

defining a tube interior; said first and second principal heat transfer surfaces having a plurality of pairs of opposed turbulator dimples formed therein and extending inwardly therefrom and meeting in said tube interior to define a plurality of pillars.

2. The radiator tube of claim 1, wherein said surfaces have a thickness of less than 0.23 mm.

3. The radiator tube of claim 1, wherein said second curved surface includes a longitudinal, welded leak-free seam.

4. A method of forming a radiator tube having a flattened oval shape, comprising the steps of: providing a generally planar strip of a metal material comprising a parent metal and a second metal, the strip having opposed side edges and a longitudinal line intermediate the side edges; forming turbulator dimples in the strip on either side of the longitudinal line to define a pattern of dimples which is symmetric about the longitudinal line; roll forming the strip to form it into a tube of circular cross-section with the

opposed side edges abutting and in alignment; compressing the opposed side edges together and simultaneously welding them together by heating at the melting point of the parent metal using a high frequency induction current, to form a solderless joint between the side edges; transforming the cross-section of the tube from circular to a flattened oval having opposed first and second generally planar, principal heat transfer surfaces, a first generally continuous curved surface having the longitudinal line approximately at its apex and interconnecting and the first and second principal heat transfer surfaces, and a second generally continuous curved surface opposite the first curved surface and interconnecting the first and second heat transfer surfaces, the second curved surface having the solderless joint therein.

5. The method of claim 4, wherein said step of forming the turbulator dimples comprises passing the strip between a pair of rotating cylindrical rolls a predetermined distance apart, one of the rolls having male punches formed thereon and the other of the rolls having female sections formed therein in alignment with the male punches.

6. The method of claim 5, wherein said step of forming the turbulator dimples further comprises using phasing gears to maintain alignment of the male punches with the female sections.

7. Apparatus for forming a radiator tube having a flattened oval shape and interior pillars, comprising: first and second parallel, rotating shafts; a first roll mounted on said first shaft, said first roll having a generally cylindrical outer surface having male punches formed thereon; a second roll mounted on said second shaft, said second roll having a generally cylindrical outer surface having female sections formed therein in alignment with said male

punches; and

phasing gears mounted on said first and second shafts, to maintain alignment of said male punches with said female sections.

8. The apparatus of claim 7, wherein said first and second rolls each comprises a hub and a plurality of annular pillar disks mounted on said hub, said male punches being

formed on said pillar disks of said first roll and said female sections being formed in said pillar disks of said second roll.

9. The apparatus of claim 8, wherein said first and second rolls further comprise a plurality of annular space disks, said spacer disks separating said pillar disks.

10. The apparatus of claim 7, further comprising adjusting means for adjusting the separation between said first and second rolls.

11. The apparatus of claim 7, further comprising: first and second spaced apart stands, said first and second shafts being mounted for rotation between said first and second stands and said second shaft also being mounted between said first and second stands for parallel movement relative to said first shaft; and adjusting means for moving said second shaft in a parallel direction relative to said first shaft.

12. The apparatus of claim 11, wherein said adjusting means comprises: a cover plate fixedly attached to and extending between said first and second stands; first and second bearing blocks movably mounted in said first and second stands, respectively, between said first roll and said cover plate, said second shaft being rotatably mounted in said first and second bearing blocks; an adjusting plate fixedly attached to said first and second bearing blocks and interposed between said first and second bearing blocks and said cover plate; an adjusting nut rotatably mounted to said cover plate; and a threaded rod fixedly attached to said adjusting plate and extending through said adjusting nut.

13. The apparatus of claim 12, wherein said first and second stands each have a hole extending therethrough intermediate said first and second shafts, said apparatus further comprising a pair of stop pins insertable in said holes under said first and second bearing plates for preventing inward movement of said second roll towards said first roll.