Patent Application
20050000376
The invention relates to a printing machine with a machine frame and at least two cylinders that cooperate during printing and that are mounted in a framing formed by the machine frame.
In printing machines, the cylinders which cooperate during printing usually are mounted at each of both ends of each cylinder in a side member of the machine frame. In a flexographic printing machine, for example, several printing units with printing cylinders are arranged around an impression cylinder. To achieve high quality printing results it is necessary that an optimal distance between the impression cylinder and the individual printing cylinders of the printing units is precisely adjusted. An expansion or a contraction of the impression cylinder caused by temperature variations would notably impair the printed image due to the large diameter of the impression cylinder, which can be in the range from 2 m to 3.5 m, for example. For this reason, the impression cylinder usually is temperature-regulated by a liquid coolant system, so that the overall size is kept with the required precision.
From the European patent specification EP 0 150 047 of the applicant the problem is known that, within a short period of time after starting the printing machine, intermittent printing occurs due to temperature variations of the machine frame in spite of a temperature stabilized impression cylinder. Given a linear thermal expansion coefficient of cast iron of approx. 9×10−6 K−1, a variation of the temperature of the machine frame by 10° C. results in a change of the distance between the printing cylinder and the impression cylinder by an amount of approximately 90 μm to 160 μm, depending on the diameter of the impression cylinder.
As a solution to this problem, the EP 0 150 047 suggests a temperature stabilized machine frame. For these purposes, the printing machine frame may, for instance, be provided with water channels for a temperature-regulating system. With a temperature-regulating device with a liquid coolant system, for example, the temperature variation of the machine frame can be limited to an amount of ±1° C. or ±0.5° C., given a variation of the ambient temperature in the print shop between 15° C. and 35° C., so that the required dimensional stability of the distance between the cylinders is ensured.
It is an object of the invention to provide a printing machine of the type described above, wherein the dimensional stability of the machine frame required for optimum printing quality is achieved in a simpler manner.
According to the invention, this problem is solved with a printing machine of the type described above in which the framing consists of a material which has at least in a direction transverse to the axes of rotation of the cylinders a linear thermal expansion coefficient that is less than 2×10−6 K−1. When the side members of the machine frame are mainly made of such material, the thermal expansion coefficients of the material in directions transverse to the axes of rotation of the cylinders determine the thermal expansion of the machine frame. Thereby, notedly larger temperature variations, for instance by 4° C., are permissible as compared to the utilization of a conventional cast iron machine frame, for example. As a result, the temperature-regulation of the machine frame is simplified.
An internal temperature-regulating system of the machine frame can be completely dispensed with, if the ambient temperature in the print shop is kept sufficiently constant. Depending on the application, a larger deviation of the distance may be acceptable at higher temperature variations. In these cases, a temperature-regulating system employing a liquid circulating through the machine frame may be dispensed with.
However, preferably a material is used the linear thermal expansion coefficient of which in said respective direction is even less than 1×10−6 K−1, more preferably less than 0.5×10−6 K−1. The smaller the thermal expansion coefficient is, the smaller is-the need for temperature-regulating measures and the higher are the temperature variations in the print shop that may be tolerated while still ensuring a high print quality. By eliminating the liquid coolant device, the construction of the printing machine is simplified and, in addition, energy savings are achieved during operation.
When, in the following, a preferred range of less than 9×10−6 K−1 occasionally is specified for the linear thermal expansion coefficients, it also applies that a value less than 1×10−6 K−1 is more preferable and a value of less than 0.5×10−6 K−1 is especially preferred. In general, an expansion coefficient is the more advantageous, the closer it is to zero.
Preferred embodiments of the invention are indicated in the dependent claims.
In a particularly preferred embodiment, the framing has side members which comprise struts that form windows, said struts being of a material the linear thermal expansion coefficient of which is, for each strut, at least in the direction of the respective strut, less than 2×10−6 K−1. Therefore, it may be particularly advantageous to apply a material having a thermal expansion coefficient that is dependent on direction; for instance, the struts may be made of carbon fiber reinforced plastic the fibers of which are oriented in the lengthwise direction of each strut, respectively, and are surrounded by a plastic matrix. The linear thermal expansion coefficient in the direction of each strut may then be almost equal to zero.
In a strut that is constructed in the described manner, a thermal expansion coefficient in a direction transverse to the strut does contribute little to the thermal expansion of the machine frame. Therefore, the thermal expansion coefficient of the material in the respective directions of the struts determines the resulting thermal expansion of the machine frame along a imaginary line that connects two cylinders.
Preferably, the material of the frame is a composite material, in particular a fiber composite material. It is preferable that its strength is as high as possible. The composite material preferably is a material containing carbon fibers, more preferably carbon fiber reinforced plastic. Here, the carbon fibers may be oriented as described above. Composite materials of this type are disclosed, for example, in U.S. Pat. Nos. 6,523,470 and 6,701,838, the entire disclosures of which are incorporated herein by reference.
Preferably, the framing is made of a carbon fiber composite material containing carbon fiber mats.
In addition to the aforementioned materials, also concrete polymer or mineral casting may be used to produce the framing. This material may have the necessary mechanical properties if produced with a suitable process. Particularly, the material may have a thermal expansion coefficient, possibly dependent on the direction, that is less than that of steel. Utilizing this material has the same advantages as utilizing the materials described above. It shall be understood that other suitable, different composite materials, especially fiber composite materials, may be used to produce the framing.
In the following, an embodiment of the invention will be further explained in conjunction with the drawing, in which:
The side members 12 and 14 of frame 10 each are made as a formed component of carbon fiber reinforced plastic (CFRP) by placing carbon fiber mats in layers into a mold and casting with plastic.
Advantages of using carbon fiber reinforced plastics are their low specific weight, their high strength and rigidity, their small thermal expansion coefficient, which is significantly smaller than 1×10−6 K−1 and is, depending on the direction, even approximately equal to zero, and, in addition, low manufacturing costs.
Due to the construction of the side member 12 having windows 26 and struts 24, along the indicated connection line an expansion coefficient results that substantially corresponds to the expansion coefficients in the directions indicated by drawn through arrows. Thereby, within the plane of side member 12, for each direction connecting two cylinders a resulting thermal expansion coefficient is achievable that is less than or equal to 0.45×10−6 K−1.
Thereby, given an assumed temperature variation of the ambient temperature in the print shop in the range from 15° C. to 35° C., a dimensional stability of the machine frame results which at least corresponds to that of a cast iron machine frame being temperature-regulated to ±0.5° C. and having a thermal expansion coefficient of 9×10−6 K−1. Therefore, a liquid temperature-regulating system can be dispensed with.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03 015 092.4 | Jul 2003 | EP | regional |
