BRIEF DESCRIPTION OF THE DRAWING
The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1 is a schematic cross section through the ideal sealing tools during a sealing process;
FIG. 2 is a schematic cross section through the sealing tools manufactured according to the invention, at the manufacturing temperature;
FIG. 3 is a view like FIG. 2 but showing the tools at the respective sealing temperatures; and
FIG. 4 is a view like FIG. 1 of the tools shifted into a staggered position.
SPECIFIC DESCRIPTION
As seen in FIG. 1 a pair of generally identical sealing tools 1 and 2 for use in a sealing machine, in particular in a thermoforming machine, in which a stack of foils 3 is guided between the sealing tools 1 and 2. The one sealing tool 1 has a sealing or operating temperature Ts1 during the sealing process, and the other sealing tool 2 has a sealing or operating temperature Ts2. In practice for carrying out the sealing process it is routine for the temperature of one sealing tool to be markedly increased by actively heating it, and the temperature of the other sealing tool to be decreased by actively cooling it. Ridges 4 are provided on the two sealing tools, on the sides facing the stack 3 of foils, that is the lower side of the upper tool 2 and the upper side of the lower tool 1. As shown in particular in FIG. 2, the ridges of the one sealing tool 1 are spaced at a distance ATf1 at the manufacturing temperature, and the ridges of the other sealing tool 2 are spaced at a distance ATf2. For the sake of simplicity, the sealing tools 1 and 2 are represented as being manufactured at the same temperature Tf1 and Tf2, typically ambient temperature. For manufacture at significantly different temperatures, the distance between the ridges would have to be taken into account. Ridge-to-ridge spacings ATf1 and ATf2 of the tools 1 and 2 at the manufacturing spacer are therefore different according to the invention, the latter being smaller than the former because it is heated more when used.
As shown in FIG. 1, the ridges 4 are at least partially pressed into the foils 3 during the sealing process. The sum of the submerged depths of the one sealing tool 1 and of the other sealing tool 2 corresponds to the tolerance compensation. The more deeply the ridges 4 press into the foils 3, the greater the possible variation of the evenness of the sealing tools 1 and 2 and the thickness of the foils 3. Based on the spacing ATs1 between the ridges of the one sealing tool 1 at the sealing temperature thereof, the distance ATf2 between the ridges of the other sealing tool 2 at the manufacturing temperature thereof are set such that the distance ATs2 at the sealing temperature thereof corresponds to the distance ATs1 between the ridges 4 of the one sealing tool 1.
According to the invention, for the manufacture of the other sealing tool 2 the distance ATf2 between the ridges 4 is set by use of the linear coefficients of thermal expansion α2 for the sealing tool 2 and a temperature gradient ΔT2 that is the difference between the sealing temperature Ts2 of the tool 2 and its manufacturing temperature Tf2, according to the relationship
A
Tf2
=A
Ts2/(α2*ΔT2+1).
FIGS. 2 and 3 show that, due to thermal expansion, the distance between the ridges of the sealing tool 2 increases during the transition from the cold state to the higher sealing temperature for the illustrated embodiment, so that during the sealing process the distance between the ridges 4 of the sealing tool 2 manufactured according to the invention is identical to the distance between the ridges 4 of the corresponding sealing tool 1, or ATs1=ATs2.
In this method, it is not absolutely necessary to physically measure the distance between the ridges 4 of the one sealing tool 1 at the sealing temperatures; instead, according to the invention the distance ATs1 between the ridges 4 of the one sealing tool 1 may be set a priori, and based upon this distance, the distance ATf2 between the ridges 4 at the manufacturing temperature may be set by reusing the linear coefficients of thermal expansion α1 for the sealing tool 1 and the temperature gradient ΔT1 that results from the difference of the sealing temperature Ts1 and the manufacturing temperature TF, according to the relationship
A
Tf1
=A
Ts1/(α1*ΔT1+1).
In this manner it is particularly simple to manufacture sealing tools 1 and 2 for the respective sealing temperatures Ts1 and Ts2 while making the distances between ridges equal when the tools 1 and 2 are in use.
With regard to heat expansion, in order to obtain a uniform distance between the ridges 4 it is necessary to fasten the sealing tools 1 and 2 to the associated tool holder (not illustrated in greater detail in the drawing) in the sealing machine such that unhindered, uniform expansion is allowed in all directions with respect to shrinkage of the material. This requirement is met by a one-point attachment such as indicated schematically at 5 in FIG. 3 and/or guiding to multiple points according to the invention.
Furthermore, for a homogeneous sealing profile it is essential that the ridges 4 of the two sealing tools 1 and 2 have a mirror-image configuration with respect to a plane P of the foil. Thus, the ridges 4 of the two sealing tools 1 and 2 are situated in the same position with respect to one another at each location on the foil stack 3, resulting in a spatially defined introduction of force and heat at comparable locations on the foils 3. This is indispensable for optimal seal quality, which is necessary in particular for the sealing of blister packaging and other packaging for pharmaceutical products. The geometry of the ridges may have a design that is pyramidal, conical with truncated end faces, spherical, or the like.
As shown in FIG. 4, the manufacture of sealing tools 1 and 2 according to the invention, which during the sealing process have a rippled surface pattern with identical distances between the ridges 4, is not sufficient for the mirror-image configuration of the ridges 4 with respect to the plane of the foil. According to the invention, an actuator 6 is provided that allows at least the position of one sealing tool 1 and 2 to be finely adjusted in the plane of the associated tool holder. This adjustment may be made by use of set screws, by piezoelectric or hydraulic means, or by use of a comparable apparatus.
Patent Application
20070251075
