|2.||A magnetic holding device to secure a steel backed polymer plate to a foil stamping heating element, said device having: a body having a body surface to engage the plate; a plurality of magnets embedded in the body so as to each have a magnetic surface substantially coplanar with respect to said body surface, the magnets being provided to urge the plate into contact with the body and magnetic surface; and a layer of nickel covering said body surface and the magnetic surface.|
|3.||The magnetic holding device of claim 1, wherein said body is generally planar and said body surface is also generally planar.|
|4.||The magnetic holding device of claim 1, wherein said body is generally circular in transverse crosssection so that said body surface is generally cylindrical.|
|5.||The device of claim 1,2 or 3, wherein the layer of nickel is between 0.1 mm and 0.025 mm.|
|6.||A method to produce the device of any one of claims 1 to 4, said method including the steps of : providing said body with apertures to receive said magnets; placing an adhesive in the apertures; placing the magnets in the apertures so as to be secured to the body with the aid of an adhesive; machining the body of the magnets so as to provide said body surface and magnetic surface; nickel plating the body and magnets so that the layer of nickel covers said body and magnetic surfaces.|
|7.||The method of claim 5, wherein the machining step is a grinding or milling process.|
|8.||The method of claim 5, wherein the body provided is heat annealed to relieve surface tension prior to machining.|
Background of the Invention The above-mentioned Australian patent application discloses a holding device which secures a steel back polymer plate to a heating element, for the purposes of transferring thin metal foil or leaf to paper, card, plastics material or similar media.
Use of the above-mentioned holding device demonstrated a number of shortcomings including the magnets employed progressively loosing their magnetic strength. A further problem was securing the magnets to the body of the device.
Various methods employed were found to be unsuitable when subjected to continuous heat and pressure. A more significant problem was oxidation of the surface of the device after machining. This oxidation led to the surface of the magnets being gradually eroded until they were below the surface of the device. This resulted in uneven surface dimensions which gave poor stamping results.
Object of the Invention It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages.
Summary of the Invention There is disclosed herein a magnetic holding device to secure a steel backed polymer plate to a foil stamping heating element, said device having: a body having a body surface to engage the plate; a plurality of magnets embedded in the body so as to each have a magnetic surface substantially co-planar with respect to said body surface, the magnets being provided to urge the plate into contact with the body and magnetic surface; and a layer of nickel covering said body surface and the magnetic surface.
Preferably, said body is generally planar and said body surface is generally planar.
In an alternative arrangement said body is generally arcuate and said body surface is generally arcuate. In a specific form the body is circular in transverse cross- section and said body surface is circular.
Preferably the layer of nickel is between 0.1 millimetres and 0.025 millimetres.
Preferably the magnets are secured within the body by Loctite 620 (registered trade mark).
Preferably the magnets are Samarium Cobalt Disc Magnets.
There is further disclosed herein a method to produce the above-described attachment device, said method including the steps of : providing said body with apertures to receive said magnets; placing an adhesive in the apertures; placing the magnets in the apertures so as to be secured to the body with the aid of the adhesive; machining the body and magnets so as to provide said body surface and magnet surfaces; nickel plating the body and magnets so that the layer of nickel covers said body and magnetic surfaces.
Preferably the machining step is a grinding or milling process.
Preferably the body provided is heat annealed to relieve surface tension prior to machining.
Preferably the body is engraver's brass.
Preferably the body is milled so as to provide a flat surface to be drilled to form said apertures.
Preferably the nickel layer is 0.05 millimetres in thickness prior to machining.
Preferably the nickel layer is 0.1 to 0.025 mm in thickness after machining.
Preferably a sealant is applied to the magnetic surface after machining, which sealant is removed before the nickel plating.
Detailed Description of the Preferred Embodiment In the accompanying drawing there is schematically depicted in sectioned side elevation a portion of a magnetic holding device securing a steel backed photo polymer plate to a foil stamping heating element.
More particularly, there is shown in the attached drawing a portion of a holding device 10, securing a steel back photo polymer plate 11 to a foil stamping heating element 12. In that regard it must be appreciated that the device 10 has at spaced locations a plurality of magnets 13 embedded in the body 14.
The body 14 is formed of engraver's brass that when initially provided has been heat annealed to relieve surface tension. The body 14 provided has its surface 15 milled to remove approximately. 2 millimetres from both major surfaces. This leaves the body 12 with a depth of approximately 5.3 millimetres. The body 14 is drilled to provide a pilot hole to facilitate the drilling of a blind hole to a depth of approximately 2.85 millimetres. The blind holes receive the magnets 13. The magnets 13 initially are approximately 3 millimetres thick and about 10 millimetres in diameter. As mentioned previously, the magnets 13 are preferably Samarium Cobalt Disc magnets. However, to ensure securing of the magnets 13 within the body 14, there is provided in each blind hole a layer of adhesive (Loctite 620 (registered trade mark)) 15. The layer 15 generally surrounds the magnets 15 so as to compensate for imperfections in the magnets 15 and formation of the blind holes within which they are located. The body 14 and magnets 13 are then machined (preferably by grinding or milling) so as to provide the body 14 with a body surface 17 and each of the magnets 13 with a magnetic surface 18. The surfaces 17 and 18 are therefore substantially coplanar and provide an attachment surface 16. After machining, a sealant such as Rocol Moistureguard Spray Sealant is placed over the surfaces 18. The body 14 and magnets 13 are also nickel plated so that a layer of nickel 20 overlays the surfaces 17 and 18, only after the sealant has been removed.
Preferably the Loctite is allowed to cure for approximately 12 hours prior to grinding or milling to provide the surfaces 17 and 18. Preferably the milling or grinding is performed in two stages, one stage removing 0.15 millimetres to provide the surfaces 17 and 18 and the second stages removing. 15 millimetres to provide the surface 21. The thickness of the body 14 after grinding is approximately 5 millimetres, the thickness of the layer 20 (prior to machining) is approximately 0.075 millimetres.
The layer 20 is preferably applied after the surfaces 17 and 18 have been lightly sanded.
Finally, the external surface 22 of the layer 20 may also be lightly grounded in order to
improve its smoothness. The device 10, after final grinding will be about 5.05 millimetres thick.
Preferably the layer 20 has a thickness (after machining) of 0.1 millimetres to 0.025 millimetres, most preferably about 0.025 millimetres.
The above-described preferred embodiment of the present invention exhibits a number of advantages including greater cycle life. Still further, the Samarium Cobalt Disc Magnets have a greater operating temperature (250°C to 350°C) which provides the magnets with a prolonged life. The use of the above-mentioned Loctite also enables the device to stand up to continuous heat and pressure typical of the environment of the present invention. Still further, the engraver's brass has been found to be easier to machine while providing superior toughness and heat conductivity while also resisting corrosion.
Engraver's brass is 70/30 Arsenical Brass Alloy 259. As an alternative brass alloy 377 can be used.
The Samarium Cobalt magnets are sintered, with their composition being about 35% Samarium, 60% Cobalt, the balance being Fe and Cu.
It should further be appreciated that the above preferred embodiment is also useable with copper and brass steel backed plates and steel plates.
The above described embodiment may be modified by forming a"through hole" rather than drilling a blind hole within which the magnet 13 is located. Where a through hole is formed the aperture remote from the surface 17 could be closed by a plug (bath).
In respect of the above referred embodiment, the body 14 is generally planar (flat). Accordingly, the surfaces 17 and 18 are also flat. In an alternative arrangement the body 14 could be generally cylindrical so as to have a generally circular transverse cross- section. In such an instance, the surfaces 17 and 18 would be cylindrical.
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