|Title of Invention
"A METHOD FOR STABILIZING THE TWO SNAP TEMPERATURES OF SNAP ELEMENTS"
|A method for stabilizing the two snap temperatures of snap elements made of thermostatic bimetal, characterized in that the embossed snap elements are pressed flat at an aging temperature which is above the upper snap temperature.
|Method for producing snap disks
The present invention relates to a method for stabilizing the two snap temperatures of snap elements made of thermostatic bimetal, in which the mechanized work steps are not interrupted by the heat treatment.
Snap elements are stamped out of thermostatic bimetallic strip and preferably have a circular shape. However, other shapes are also possible and typical, such as squares, rectangles, rhomboids, and shapes having a tongue in the middle. When snap disks are referred to in the following patent specification, all of these shapes may be meant.
Snap elements made of thermostatic bimetal comprise a large area of application for regulating and limiting thermal procedures. The two temperatures at which the curvature of the disks suddenly changes with a jump are referred to as "lower snap temperature and upper snap temperature".
It is generally known that the varyingly strongly embossed curvature of the disks is decisive for the position of these two temperatures. This curvature is applied with different strengths of embossing from both sides. The curvature preferably has the shape of a very fiat spherical cap, but other shapes are also possible, however, such as a very flat truncated cone.
WO 97/39466 discloses a method of making snap-acting thermally sensitive bimetallic actuators in which a series of actuator blanks is formed in a strip of bimetallic material. Adjacent blanks are joined by one or more bridges of the strip material. The blanks are indexed through one or more deforming operations whilst they are joined together by the bridges, by indexing means associated with the bridges. The blanks are then separated to form individual actuators. After forming, the actuators may be heat-treated either after, or more preferably before, they have been separated from each other.
US 4 796 355 discloses an inherently mechanically bistable self-supporting blade element for actuating snap-action switches. The elements are formed from initially flat, unstressed spring material. There is no hint to a heat treatment of the elements."
However, there is no disclosure of a simultaneous forming and heating of the actuators in WO 97/39466 or the elements in US 4 796 355.
Figure 1 shows the relationship between temperature and curvature. The temperature is plotted on the abscissa and the curvature of the snap disks is plotted on the ordinate. Upon reaching the upper and lower snap temperatures, the curvature suddenly jumps to the other side. The aging temperature, which will be discussed later, is far above the upper snap temperature, but still below the temperature which results in softening of the bimetal.
After the embossing, the snap disks still have too little thermal stability, i.e., the snap temperature changes with the number of the snap movements. It is necessary and typical
to "thermally age" the snap disks after the embossing procedure; they are subjected, for a duration of several minutes up to an hour, to a high temperature which is above the upper snap temperature but still below the temperature range in which softening of the bimetal occurs.
The duration of this heat treatment requires a premature interruption of the automatic manufacturing procedure and it is hardly possible to perform the work steps which are still lacking automatically to the end again, i.e., testing, selection, and stamping free.. Therefore, there is a justified desire for a method of temperature stabilization which may be classified by an extremely short action duration in the machine cycle of one to two seconds.
The achievement of this object is the subject matter of the present invention.
The idea according to the present invention is that the embossed disks are pressed flat at a high aging temperature. This procedure may also be repeated multiple times, e.g., two to six times.
During the mechanical manufacturing of the snap disks, the disks must be guided step-by-step from one work position to the next position. There is an array of methods for this purpose, to cyclically transport further the finished, stamped disks or the disks which are still connected to the stamping strips by one or two webs.
In the manufacturing method described as an example in the following, the latter cited transport method having the stamping strips is selected, in which the disks still remain hanging by one or two narrow webs.
Figure 2 shows a method of this type.
The bottom of the U-shaped furnace, which extends over multiple work positions, is identified by 1. The required heating element has the number 2. The stamped and
embossed bimetallic strip 3 slides on the base of the U-groove. Because of the ability to heat the base of the U-groove, the thermostatic bimetallic strip 3 resting on the base is rapidly heated to the aging temperature, i.e., a temperature which is above the upper snap temperature, but below the softening temperature of the bimetallic strip 3. The pressure bar 4, which has the same dimensions as the base of the furnace bottom, moves vertically in the groove. The bar is pressed onto the embossed disks by a force element 5 (pneumatically, hydraulically, via cams, or magnetically), so strongly that all embossed disks which are located in the U-shaped furnace are pressed flat. The pressing procedure, using which the snap elements are pressed flat, is thus performed at a temperature of the snap elements which lies above the upper snap temperature, but below the softening temperature of the snap elements. Both procedures, i.e., heating and pressing, occur in the clamping furnace 1, the procedure of pressing lasting less than one to one half seconds depending on the cycle time of the embossing machine. A transport cycle, in which the stamping strips are pulled forward by precisely one position, subsequently follows. This cyclically executed procedure provides an aged disk after each cycle without it being necessary to remove the disks from the machine.
The disks thus remain in the machine and the thermal aging is performed in the machine, and in the work cycle of the machine.
It is a useful side effect that the most rapid possible heat transmission from the furnace to the disks is obtained in the clamping furnace 1 by the pressing of the disks. This contributes to the rapid execution of the work steps.
Figure 2 shows that the furnace U-bottom and the pressure bar 4 have prong-shaped teeth, which engage in one another. These teeth are used for the purpose of obtaining such an intimate heat transmission from the furnace to the pressure bar that separate heating of the pressure bar may be dispensed with.
The work positions which are required before and after the U-clamping furnace are not shown in above-mentioned Figure 2.
1. A method for stabilizing the two snap temperatures of snap elements made of thermostatic bimetal (3), characterized in that the embossed snap elements are pressed (4,5) flat at an aging temperature which is above the upper snap temperature.
2. The method as claimed in claim 1, wherein the procedure of pressing flat occurs once or multiple times.
3. The method as claimed in claim 1 or 2, wherein a clamping furnace (1) is used for the
purpose of heating to the aging temperature and for pressing (4,5) the disks flat, in which, in a heated, metallic U-form, one or more snap elements are pressed flat by a metal bar (4) which is also heated.
4. The method as claimed in claim 3, wherein the metal bar (4) has such an intimate
thermal contact with the U-shaped bottom of the clamping furnace (1) that no separate
heating of the bar (4) is required.
5. The method as claimed in claim 3, wherein the snap elements, which are still
connected to the stamping strips by a retention web, are pulled forward cyclically by
one work position each.
6. The method as claimed in claim 5, wherein the cyclic transport movement is performed in the work cycle of the machine.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|ELEKTRONIK WERKSTATTE ING WURMB GES M.B.H
|WIENERWALDSTRASSE 2, 3032 EICHGRABEN, AUSTRIA
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date