US3865343A

US3865343A - Mold assembly for making a magnetic base

Info

Publication number: US3865343A
Application number: US422400A
Authority: US
Inventors: William A Jenkins
Original assignee: Monarch Marking Systems Inc
Current assignee: Avery Dennison Retail Information Services LLC
Priority date: 1970-11-09
Filing date: 1973-12-06
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11

Abstract

There is disclosed a magnetic printing base for one or more printing plates, a method of making the magnetic base, and a mold in which moldable,non-magnetic adhesive material is molded about various parts of the magnetic base. The base is structured to permit magnetic circuit devices and end plates to be interconnected by the non-magnetic material into a unitary arrangement. Each magnetic circuit device includes a flat magnet disposed between and in ccontact with a pair of flat magnetizable plates. The permanent magnetsextend short of the finaldesired dimension of the base. The plates and the molded material initially extend beyond the final desired dimension of the base, but are trimmed off by a cutter to the final desired dimension after assembly of the base. To obviate the tendency of the printing plate to creep or drift, the spacing between the magnetic circuits is such that the strength, at surface of the base, of the magnetic flux field between next adjacent pole plates of adjacent magnetic circuit devices is equal to the strength, at the surface of the base, of the magnetic flux field between the pole plates of a magnetic circuit device itself.

Description

United States Patent [191 Jenkins Feb. 11, 1975 Related US. Application Data [62] Division of Ser. No. 87,673, Nov. 9, 1970.

[52] [1.8. CI 249/95, 164/108, 249/96 [51] Int. Cl. 322d 19/00 [58] Field of Search 249/83, 84, 705, 171, 173, 249/175, 176, 177, 180, 184, I60, 163, 164. 122,123,124,129,143,144,151,108,165, 95, 96; 425/D1G. 33, DIG. 10; 164/109, 139,

[56] References Cited UNITED STATES PATENTS 1,407,569 2/1922 Pedersen 249/164 X 1,915,488 6/1933 Gere 249/164 X 2,083,395 6/1937 Pfalzgraff 249/95 X 3,058,156 10/1962 O'Connor 249/108 X 12/1967 Kolberg 249/151 X Primary Examiner-Francis S. Husar Assistant Examiner-John S. Brown Attorney, Agent, or Firm--Joseph J. Grass [571 ABSTRACT There is disclosed a magnetic printing base for one or more printing plates, a method of making the magnetic base, and a mold in which moldable,nonmagnetic adhesive material is molded about various parts of the magnetic base. The base is structured to permit magnetic circuit devices and end plates to be interconnected by the non-magnetic material into a unitary arrangement. Each magnetic circuit device includes a flat magnet disposed between and in ccontact with a pair of flat magnetizable plates. The permanent magnetsextend short of the finaldesired dimension of the base. The plates and the molded material initially extend beyond the final desired dimension of the base, but are trimmed off by a cutter to the final desired dimension after assembly of the base. To obviate the tendency of the printing plate to creep or drift, the spacing between the magnetic circuits is such that the strength, at surface of the base, of the magnetic flux field between next adjacent pole-plates of adjacent magnetic circuit devices is equal to the strength, at the surface of the base, of the magnetic flux field between the pole plates of a magnetic circuit device itself.

11 Claims, 8 Drawing Figures MOLD ASSEMBLY FOR MAKING A MAGNETIC BASE CROSS-REFERENCE TO RELATED APPLICATIONS This is a division of application Ser. No. 87,673 filed Nov. 9, 1970, which is assigned to the same assignee as the present application.

BACKGROUND OF THE INVENTION This invention relates to the art of magnetic printing bases, and methods of and molds for making same. There are numerous prior art patents relating to magnetic bases and the like; examples are US. Pat. Nos. l,657,287, 2,178,774, 2,481,191, 2,952,205, 2,992,733, 3,024,392, 3,027,835, 3,039,390, 3,086,461, 3,097,598, 3,180,259 and 3,509,819.

SUMMARY OF THE INVENTION The invention resides in a mold assembly for making a low-cost, unitized magnetic base especially adapted for holding a printing plate. Although the mold assembly is illustrated with a circular cylindrical roll, it is also applicable to a flat base of the type disclosed in above mentioned US. Pat. Nos. 2,481,191 and 3,027,835. The mold for making the base of the invention is economical to construct having basically a pair of mold sections and end caps or plates. The mold sections have positioning means specifically in the form of grooves, formed at its inner surface. The end plates are clamped against the ends of the mold sections by means of tie rods which extend through the end plates externally of the mold sections. A nozzle disposed at the bottom of the mold distributes moldable material lengthwise of the mold cavity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a magnetic base for printing plates;

FIG. 2 is a side elevational view, partly in section, of the magnetic base shown in FIG. 1;

FIG. 3 is a sectional view taken generally along line 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary sectional view showing a portion of the magnetic base as it appears during one of the manufacturing steps;

FIG. 5 is an exploded perspective view of a mold in which the magnetic base can be molded;

FIG. 6 is a vertical sectional view of the mold, showing the magnetic base in the mold after the moldable material has filled the mold;

FIG. 7 is a sectional view taken generally along line 77 of FIG. 6; and

FIG. 8 is a sectional view taken generally along line 88 of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference to FIGS. 1, 2, and 3, there is shown a magnetic base in the form of a printing cylin der or drum generally indicated at 10 mounted on shaft 11. The base 10 can be secured to and driven by the shaft 11 or the base 10 can be rotatable with respect to the shaft 1 and driven by other means, as desired. The magnetic base 10 is illustrated as including a plurality of spaced apart permanent magnetic circuit devices generally indicated at 12. Each magnetic circuit device 12 includes a flat, annular, permanent magnet 13 and a pair of magnetizable pole plates 14. Each magnet has a central hole 13 and each plate 14 has a central hole 14. A cylindrical mounting member 15 in the form of a sleeve is shown to pass through the holes 13' and 14' and forms a flux path for each of the magnetic circuits. The plates 14 and the member 15 are composed of magnetizable, easily machinable material such as low carbon steel. End plates 16 are received about reduced portions 17 of the mounting member 15 at locations spaced apart from the endmost magnetic circuit devices 12. The magnetic circuit devices 12 are all constructed with equal strength; the magnets 13 are of the same size and composition and the pole plates 14 are of the same size and composition. The magnets 13 are so arranged that alternate pole plates 14 are poled north-south-north-south, and so on, in a direction longitudinally of the base 10 as indicated by N and S in FIG. 2. Accordingly, the next adjacent pole plates 14 of adjacent magnetic circuit devices 12 are of opposite polarity. In accordance with the invention, the distance between adjacent magnetic circuit devices 12 is not arbitrary, but rather it is established by spacing the magnetic circuit devices 12 apart by a distance at which the magnetic flux field strength between next adjacent pole plates 14 of adjacent magnetic circuit devices 12 are equal, or substantially so, to the magnetic flux field strength of the magnetic circuit devices 12 themselves. Once the spacing has been established for a magnetic base having circuit devices of a particular size, strength, material and configuration, any number of such bases can be constructed using the same spacing.

The external diameters of the magnets 13 are less than the external diameter of the base 10 whereas the plates 14 extend all the way to the final surface of the magnetic base 10. Each of the plates 14 has four equally spaced apart holes 18 near its periphery. The holes 18 extend at least partly beyond the associated magnets 13. The end plates 16 have four spaced apart apertures or holes 19 which are larger in diameter than the holes 18 in the plates 14. Moldable, non-magnetic, adhesive material 20, such as epoxy fills: the space between the magnets 13 and the surface of the base 10 between associated plates 14, the spaces between the outer surface of the cylinder member 15 and the outer surface of the base between plates 14 of adjacent magnetic circuit devices 12, the spaces between the plates 14 of the endmost magnetic circuit devices and the associated end plates 16 between the cylindrical member 15 and the surface of the base 10, and the

holes

18 and 19 in

respective plates

18 and 19. The magnetic base 10 is accordingly formed into a unitary support structure in which a magnetizable printing plate or a printing plate having a magnetizable holding portion is held to the base 10 by magnetic attraction, and in addition, the plates 14 and the non-magnetic material 20 serve to provide a solid support for the printing plate or plates. To assure adequate keying of the material 20 to the member 15, the outer surface of the member 15 between the next adjacent plates 14 of adjacent magnetic circuit devices 12, and between the plates of endmost circuits l2 and associated end plates 16 is roughened at annular zones 15. A fragmentary portion of one of these zones 15' is shown in FIG. 6. Roughening can be accomplished by knurling or any other suitable means.

With reference to FIGS. 1 and 3, printing plates P constructed at least in part of magnetizable material are shown held onto the base by magnetic attraction. The base 10 is shown to be provided with four longitudinally extending slots or grooves 21 in its periphery. The slots 21 cut through the end plates 16, the non-magnetizable material 20, and the plates 14. Leading edges of four of the printing plates are shown to be received in the grooves 21 which prevents the printing plates P from creeping around the base 10 as its rotates during the printing operation. The grooves 21 are preferably milled into the base 10 by a milling cutter (not shown).

With particular reference to FIG. 4, there is shown in exaggerated form, the manner in which plates 14 initially extend beyond the final desired surface S of the base 10. In the particular embodiment of a base 10 of cylindrical form illustrated in the drawings, the plates 14 initially extend beyond the final desired surface S and in particular have a larger diameter than the final diameter of the base 10. It has been found to be most economical to eliminate close tolerances by sizing the plates 14 larger than necessary and allowing wide positive tolerances, and by sizing the magnets 13 smaller than necessary and allowing wide tolerances. As one of the final steps in the manufacturing operation, the base 10 is turned on a lathe by rotating the base 10 in conventional manner relative to a cutter which moves at a predetermined rate of feed in a direction longitudinally with respect to the base 10, thereby removing material 20 and the portions of the plates 14 radially beyond the final desired surface S of the base 10.

With reference to FIGS. 5-8, there is shown a mold generally indicated at 30 which is useful in performing the molding step of the invention. The mold 30 is shown to include a pair of

mold sections

31 and 32 and a pair of

end plates

33 and 34. The

mold sections

31 and 32 are curved and extend through arcs of about 170 each. The mold section 31 has side edges 31 and 31", and the mold section 32 has side edges 32' and 32". When the mold is assembled side edges 31" and 32" of the

respective mold sections

30 and 31 are in liquid-tight abutment with an elongated nozzle 35, and there is a gap between the side edges 31' and 32 as best shown in FIGS. 7 and 8. A plurality of tie rods 36 cause the

end plates

33 and 34 to exert clamping pressure on the ends of the

mold sections

31 and 32 when nuts 37 are tightened.

Each of the

mold sections

31 and 32 has a plurality of positioning and holding grooves 38 formed at its inside surface. These grooves 38 extend in an arcuate direction between the respective side edges 31' and 31" and 32 and 32". Assuming that a circular cylindrical printing base is to be fabricated, a circular cylindrical member shown to take the form of a sleeve is provided. Then plates 14 and magnets 13 can be assembled onto the member 15 either individually or as sets or groups of magnet circuits. In the illustrated embodiment, one magnetic circuit comprises a permanent magnet 13 disposed between and in contact with a pair of plates 14. If the magnetic circuits are to be assembled as sets the attractive force of the magnet 13 will hold the associated magnetizable plates 14 to it and hence each magnetic circuit is easily moved into position by sliding the magnetic circuit onto the member 15. In the illustrated embodiment the magnetic circuits 12 are shown to be spaced apart. As the magnets 13 have a diameter which is intentionally less than the final diameter of the base 10 and the plates 14 having a diameter greater than the final diameter of the base 10, the accuracy of the outer surface of the base 10 is not dependent upon accurate sizing or location of the holes 13 and 14'. Accordingly, holes 13 and 14' are acceptable even though larger than necessary by a considerable tolerance.

Endmost grooves 39 in the

mold sections

31 and 32 are shown to receive end plates 16. The grooves 38 have a width which is slightly greater than the combined thicknesses of two plates 14 and the magnet 13 so that during the molding operation the magnetic circuits 12 are not apt to be displaced by the moldable material. Here again accuracy of positioning the magnetic circuits 12 is not necessary. With the components which are to comprise the base 10 disposed within the mold and the mold in the clamped condition as shown in FIG. 6, the moldable, non-magnetic adhesive material is forced into the mold through orifices 35' in the nozzle 35. As the material enters the mold, air escapes through the gap between side edges 31' and 32' of the

mold sections

31 and 32. As the magnets 13 and the associated plates 14 have flat sides, the moldable material does not flow between the contacting surfaces. However, material is able to flow into the spaces between plates 14 of adjacent magnetic circuits 12, into the space around the magnets 13 and between the associated plates 14, between the plates 14 of the endmost magnetic circuits 12 and the end plates 16, into and through holes 18 in the plates 14, and into holes 19 in the end plates 16, thereby providing a unitized base. As the moldable material, preferably in the form of epoxy gradually fills the spaces described above until excess non-magnetic material flows into the gap between side edges 31 and 32' at the time flow of additional material into the mold through the nozzle 35 is interrupted and the moldable material is allowed to set and harden. After the material 20 sets and hardens, the mold 30 is removed with respect to the base 10 and the base 10 is ready to be turned on a lathe.

lf desired, many of the benefits of this invention can be achieved by applying the invention to a flat bed type of magnetic base. ln that event the final desired surface of the base 10 can be achieved by using a milling cutter (not shown). The milling cutter would make passes relative to the base 10 in the same direction as the direction in which the plate and magnets extend.

It is preferred to use one-piece magnets 13 although segmented magnets can be employed, if desired, within the spirit of the invention.

Other embodiments and modifications of this invention will suggest themselves to those skilled in the art, and all such of these as come within the spirit of this invention are included within its scope as best defined by the appended claims.

1 claim:

1. A mold assembly for making a cylindrical magnetic base having a cylindrical member and spaced apart magnetic circuit means disposed on the cyclindrical member, said mold assembly comprising: mold sections positioned to provide a mold cavity, a pair of end plates disposed at opposite ends of the mold sections for closing off the ends of the cavity, means provided at the inner surface of at least one of the mold sections for locating the magnetic circuit means at predetermined positions lengthwise of the mold cavity, wherein the locating means comprises spaced apart grooves in at least the one mold section for receiving the magnetic circuit means and holding them in spaced apart relationship while the mold is being filled, means for holding the end plates and mold sections together, the cylindrical member and the magnetic circuit means being disposed in the cavity, and means including a nozzle extending lengthwise of the mold cavity for introducing moldable material into the mold cavity around the cylindrical member and the magnetic circuit means.

2. A mold assembly as defined in claim 1,wherein the end plates are positioned to exert clamping forces against the ends of the mold sections, and means for exerting clamping force against the end plates to hold the mold sections together.

3. A mold assembly as defined in clalim 1, wherein the holding means comprises a plurality of tie rods.

4. A mold as defined in claim 1, wherein the end plates receive the end portions of the mold sections.

5. A mold assembly as defined in claim 1, wherein the nozzle extends substantially throughout the length of the mold cavity, the nozzle having a plurality of orifices.

6. A mold assembly as defined in claim 1, wherein the nozzle is disposed in the lower region of the mold cavity between adjacent mold sections, and an air vent in the upper region of the mold cavity.

7. A mold assembly as defined in claim 1, wherein the nozzle is disposed in liquid-tight relationship between the two mold sections.

8. A mold assembly for making a cylindrical magnetic base having a cylindrical member and spaced apart magnetic circuit means disposed on the cylindrical member, said mold assembly comprising: a pair of generally semi-circular mold sections positioned to provide a generally circular mold cavity, a pair of end plates disposed at opposite ends of the mold sections for closing off the ends of the cavity, the cylindrical member and the magnetic circuit means being disposed in the cavity, means provided at the inner surface of at least one of the mold sections for locating and holding the magnetic circuit means at predetermined spaced apart positions lengthwise of the mold cavity, means for holding the end plates and mold sections together. and a nozzle having means for distributing moldable material along substantially the entire length of the mold cavity, said nozzle being in liquid-tight relationship with the mold sections along the lengths of mold sections.

9. A mold assembly as defined in claim 8, wherein the end plates receive the end portions of the mold sections.

10. A mold assembly as defined in claim 9, wherein the ends of the mold sections are received in the end plates, and means for releasably clamping the end plates against the ends of the mold sections.

11. A mold assembly as defined in claim 8, wherein the nozzle is disposed between the two mold sections. {F k UNITED STATES PATENT AND TRADEMARK FFICE CERTIFICATE CF (IQECTEN PATENT NO. 3,865,343

DATED February ll 1975 N Q) William A. Jenkins It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Assignee: "Monarch Marking System Company" should be -Monarch Marking Systems, Inc.. In the Abstract, line 9, "contact" is misspelled;

Column 1, line 64, "1" should be l0-. Column 3, line 5, "non-magnetizable" should be non-magnetic-. Column 6, line 22, "9" should be 8-.

Signed and Sealed this fourteenth Day of October 1975 [SEAL] Arrest.

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner oflarents and Trademarks

Claims

2. A mold assembly as defined in claim 1, wherein the end plates are posiTioned to exert clamping forces against the ends of the mold sections, and means for exerting clamping force against the end plates to hold the mold sections together.

8. A mold assembly for making a cylindrical magnetic base having a cylindrical member and spaced apart magnetic circuit means disposed on the cylindrical member, said mold assembly comprising: a pair of generally semi-circular mold sections positioned to provide a generally circular mold cavity, a pair of end plates disposed at opposite ends of the mold sections for closing off the ends of the cavity, the cylindrical member and the magnetic circuit means being disposed in the cavity, means provided at the inner surface of at least one of the mold sections for locating and holding the magnetic circuit means at predetermined spaced apart positions lengthwise of the mold cavity, means for holding the end plates and mold sections together, and a nozzle having means for distributing moldable material along substantially the entire length of the mold cavity, said nozzle being in liquid-tight relationship with the mold sections along the lengths of mold sections.

11. A mold assembly as defined in claim 8, wherein the nozzle is disposed between the two mold sections.