FI83968B - FOER TEMPERATURFOERAENDRINGAR UTSATT ANORDNING. - Google Patents

Description

Device exposed to temperature fluctuations 1 83968

The invention relates to the further development of a special device proposed in the preamble of claim 1, which comprises surface gluing of a fracture-sensitive body to a relatively non-fracture-sensitive body. At certain temperatures, very high tensile or compressive stresses are generated in fracture-sensitive parts, so that the body threatens to break or actually breaks if the temperature fluctuates too much. One skilled in the art is familiar with such devices, vert. e.g., EP-A-48 938. Furthermore, it is well known to a person skilled in the art that often, regardless of the risk of breakage of either fragile part, the gluing between the two parts ruptures due to temperature stresses and the device is therefore ruined, vert. e.g. EP-A 111 252.

The object of the invention is to reduce the temperature-induced -ex. use and / or storage - the internal risk of rupture within the normal temperature range of the device or increase the limit difference without increasing the risk of rupture.

This problem has so far been solved by a person skilled in the art, namely by selecting a second raw material for at least one of the pieces, so that the coefficients of thermal expansion of each piece are less different and / or the fracture is replaced by less fracture, and / or the gluing area is reduced by temperature. to reduce the internal stress caused by the fracture-sensitive body and / or by deforming at least one other body, e.g. by applying stretch seams and / or by using another, e.g. highly flexible, adhesive which is very flexible at least in the upper temperature range.

However, the invention solves this problem by the measures of claim 1. The invention thus shows a new, fifth method for solving this problem, in which this fifth method can be chosen alone or in addition to one or all of the four ways hitherto.

The additional measures in the subclaims allow additional benefits to be achieved. Thus, the measures according to claim 2 allow e.g. measures according to the invention according to claim 3, also by gluing to a thin fracture-sensitive ceramic plate together with a stable metal body, which is particularly difficult because the substances differ considerably in their breaking strength and thermal expansion, and the measures according to the invention in electrical engineering, in particular re-use of a device that has been used many times in dial-up transmission systems.

The invention and its further development will be explained in more detail in connection with the structural examples shown in the figures. In this case, Fig. 1 shows a section of a device according to claim 4 made according to EP-A 48 938, and Fig. 2 a diagram to illustrate the internal stresses present in a fractured body when using the measures according to the invention and without using them.

The invention was developed mainly for the device shown in Fig. 1, manufactured according to EP-A 48 938, and therefore has a thin fracture-sensitive ceramic support, the ceramic support 1 carrying an electrical structural element, namely e.g. resistance layers 4 connected to a conductor. -on-printed lines 5 one-in-line to the contact pins 6, and wherein the support 1 is glued to the aluminum heat sink 2 by means of a hardened adhesive 3, the coefficient of thermal expansion of which is very different.

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The device can still be covered with protective varnish 7. This known device is used regularly due to heat losses of its structural elements - on the one hand not more than +130 C hot, o in rare cases of overload maybe +150 C - on the other hand o cools down to at least -40 C, e.g. its use when sending by mail to many areas during a harsh winter.

However, the invention is not limited to this particular device. Namely, it can be defined directly as a device made of two pieces glued together with an expected or continuous maximum allowable temperature (eg + 150 ° C); the expected, or also the continuous or permissible lowest temperature (e.g. -40 ° C), so that a considerable limit difference arises between the highest and the lowest temperature, (in this case e.g.

190 C). The two hard adjacent pieces 1, 2 have clearly different coefficients of thermal expansion, whereby the second piece 1 (here the thin ceramic plate 1) also has a clearly lower breaking strength than the other piece 2 (here the cooling damper 2).

It further has an adhesive bond 3 between the two pieces 1, 2, which is by heating the cured adhesive 3, e.g. two components 1 i absorb 3, so that the fracture-sensitive piece 1 (here the ceramic plate 1) tends to break due to this very considerable boundary difference. In order to reduce this risk of breakage, an adhesive 3 is then used, which is cured (at least close to) the average temperature of the region between the highest and lowest temperature. oo o (e.g. close to +150 ° C to -40 ° C, e.g. +90 ° C) - wherein the curing temperature 1a is at least 18% lower than the limit difference (i.e. e.g. at least about 35 ° C) than the highest temperature.

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The most advantageous curing temperature 1a can in principle be determined in various ways, e.g. in such a way that the probability of fracture at it is equal at the highest and lowest temperatures, but still - or with certainty - still permissible low.

In this case, the most preferred curing temperature is often not exactly halfway between the highest and lowest temperatures. There are several reasons for this:

The exact coefficient of thermal expansion of each of the bodies 1, 2 is in most cases more or less dependent on the respective absolute temperature. For example, for the pieces 1 and / or 2 in question, this coefficient may be much lower at the lowest temperature than at the highest temperature of the same pieces. Therefore, the tensile and compressive stresses of fracture-sensitive parts are often not linearly temperature-dependent; also the adhesive 3 as such is often rigid or flexible depending on the temperature, which also affects the optimum curing temperature. When, in order to optimize the curing temperature, the probability of breakage (e.g. 10) of a fracture-sensitive body (here a thin ceramic plate 1) must be equal at the highest temperature (150 ° C) to the lowest temperature (-40 ° C), therefore the flexibility of the adhesive 3 often differs. due to the temperature dependence, the most preferred curing temperature1a above or below the exact average heat (+55 C); in addition, there are many fracture-sensitive bodies 1, e.g. ceramics, very sensitive to tensile stress 1e, but slightly sensitive to compressive stress. Also for this reason, the most preferred curing temperature, in which the probability s of rupture is approximately the same at the highest and lowest temperatures, is not exactly halfway between the highest and lowest temperatures.

Assuming that the optimum has been reached, the most favorable curing temperature, as soon as the probability of rupture at the highest temperature is approximately the same as at the lowest temperature, is therefore often not theoretically determinable, but often most easily and accurately experimented.

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However, it is sufficient in many cases, although the curing temperature has not been chosen exactly as optimal in this sense, because the probability of rupture s at the highest and / or lowest temperature in many of these cases is extremely low, i.e. incomparably lower than the allowable curing temperature. relationship is unnecessary. It is sufficient for the curing temperature to roughly correspond to some optimal curing temperature, because the probability of rupture, despite the inaccurate optimization of the curing temperature, then remains below the permissible value at both the highest and lowest temperatures.

In many cases, the probability of rupture at the highest temperature is not even required to be equal to that at the lowest temperature. The device according to the invention has e.g. operating situations in which - for some reason - very large consequential damage occurs only when the fracture of the body 1, and thus the malfunction of the electrical component 4, i.e. e.g. the tearing of the resistance layer 4, occurs suddenly and is not economically represented. costs) could only be detected in another border temperature range - ie during the most thermally loaded operation of such a device in a large call transfer device with e.g. more than 100,000 such devices, which are always, including the plant). operate absolutely reliably during peak loads. In such an exceptional case, the allowable probability of rupture can often be much lower - than, for example, only when sending from the manufacturer to a downstream user - to the lowest temperature hardly ever occurring, which is why the optimal curing temperature may deviate - more or less - between the upper and lowest temperatures.

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Therefore, in the invention, the optimum temperature, even if determined, is rarely exactly halfway between the highest and lowest temperatures, but most often by a certain value above or below this average - and even often within a relatively wide temperature tolerance range, especially if the fracture probability is highest and / or at a temperature very much lower than allowed, and there is therefore no need to closely monitor the optimization of the curing temperature.

This will be explained in more detail in connection with a specific example of the device shown in Fig. 1: A device with - often very high heat loss - thin resistance layers 4 on the surface of a fracture-resistant ceramic support 1 is manufactured, for example, by first pressing a cooling fin 2 with the flowable adhesive 3, and then it is placed in the installation auxiliary device with the adhesive side facing upwards. The support provided with the resistance layer 1a can now be precisely positioned on the cooling fin 1 e 2 by means of the stops.

Crimping tools take care of the necessary compression, so that the two half bodies 1 and 2 are wetted adhesive, and keep the two pieces of prescribed positions 1 and 2, the adhesive 3 during curing.

In order to obtain high strength, the adhesive 3 was cured this time, contrary to the usual method according to the invention, at the maximum permissible operating temperature of the device, namely + 125 C, + 130 C or + 150 C. The proportion of wrecks due to rupture of the support 1 was usually very small. However, for some reason that could not be reliably elucidated after several studies, there were later a considerable number of fractures of the thin ceramic support 2, which then affected well over 10% of all the devices. Late occurrences were particularly unpleasant, as such fractures did not occur until after mailing and installation in a telephone exchange, and then caused severe, unexpected disruptions to the transmission system. Strong temperature fluctuations and the fractures it caused were just one of many reasons to consider. Also, such late occurrences could not be completely avoided by the thermal shock treatment of all the devices prior to mailing, so in the end it was dared to stop the production of these devices completely in order to redevelop them according to the above four methods.

However, detailed scientific studies gave the following result:

Figure 2 is a diagram of the temperature dependence of the longitudinal expansion (in abscissa) for a 50 mm long ceramic support 1e 1 and an aluminum cooling rib 2 of the same length, assuming that both pieces 1, 2 are not yet glued and that the thermal expansion would depend on .

In the right ordinate, absolute temperatures T are reported, and in the left ordinate, relative temperatures D are increased with a minimum temperature of -40 C.

Then curve 10 corresponds approximately to the device which was cured at +150 ° C, curve 9 corresponds to the same device at +125 ° C, and curve 8 corresponds to the same device which was cured at +90 ° C.

Namely, during the curing of the adhesive 3, both the support 1 and the aluminum cooling rib 2 are virtually free of internal mechanical stresses, with the exception of the internal stresses in the support β 83968 m 1 due to the inhomogeneity of the raw material of the support 1, cf. the difference in length expansion of curves 8, 9, and 10 0 yum. However, as soon as the cooling starts after the adhesive 3 has hardened, different length differences arise between the ceramic support 1 and the aluminum cooling rib 2, cf. again curves 8, 9, and 10. In the experiments, the devices were placed at a minimum temperature of -40 ° C, with all these devices being exposed to a maximum temperature difference of 190 ° C D, cf. curve 10. The 50 mm long support 1 was affected by this 190 ° C temperature D as such, i.e. without hardened gluing, a thermal elongation of 67 [mu] m, but for a 50 mm long aluminum cooling fin 2 as such a 3.3 times greater length difference, namely 223 [mu] m. The difference between these length changes is 156 μm, cf. again Fig. 2. Thus, the cured glued device acts like a bimetal and bends so that tensile stresses and compressive stresses are applied to the support 1 as long as the device is hotter than the curing temperature, but compressive stresses are applied to the support 1 and the aluminum cooling fin 2 colder than the cup, cf. curves 8, 9 and 10. Above all, the tensile stresses in the support 1 can cause fractures immediately or even after months, which can cause a malfunction in the resistance layer 4 supported by it.

The problem according to the invention is solved by changing the high maximum value of the compressive stress caused by the expansion of the support 1 of the curve 10 corresponding to the cooling of the support 1 from + 150 ° C to -40 ° C to zero-varying tensile / compressive stress, which indicates the permissible, i.e. a sufficiently small maximum value of the tensile stress at the lowest temperature, e.g. -40 ° C, and permissible, i.e. a sufficiently small maximum value of the tensile stress for the support 1 at the highest temperature, e.g. + 150 ° C.

This solution can be implemented by lowering the curing temperature, e.g. in this case by curing according to the curve 8 9 83968 o +90 C, after which the thermal expansions of both bodies 1, 2 differ as such theoretically only by a maximum of 107 μm, i.e. 30% less than before. Although the required curing time of the adhesive 3 was longer than at much higher curing temperatures, the duration of the lower curing temperature was still tolerable.

Thus, the curing of the adhesive 3 1a near the average temperature thus reduces the internal stresses of the device below the critical values, and no fractures of the ceramic support 1 were observed in the laboratory tests, nor after the introduction of the reduced curing temperature.

In contrast, in the cured devices according to curve 9, fractures were observed in the support 1 from time to time, although rarely. For this device, on the other hand, in order to control the problem, after the introduction of curve 8 according to the invention, it was completely unnecessary to use in addition any of the four other known methods mentioned above.

The curing temperature 1a after curing can also be subsequently determined from the finished device in general with sufficient accuracy by artificially breaking the fracture-sensitive body 1, e.g. with strong cold shock11a, and determining the temperature at which the fracture closes under continuous heating or cooling under a microscope.

The temperature at which the fracture closes corresponds quite closely to the curing temperature.

Claims (4)

10,83968 Patent Requirements 1. A device exposed to temperature fluctuations, having o the expected or permissible maximum temperature - eg 150 C - as one of the limit temperatures; o the expected or permissible minimum temperature - e.g. -40 C - as the second limit temperature, so that there is a limit difference between the highest and lowest temperature o, then e.g. 190 C; operating temperatures which are continuously or repeatedly close to at least one of the second limit temperatures, i.e. close to the highest and / or lowest temperature, i.e. e.g. + 150 ° C; two hard, side-by-side pieces (1, 2), - with a clear, different coefficient of thermal expansion, and - of which pieces (1, 2) one (1) has a clearly lower breaking strength than the other (2), and a heat-curable adhesive (3), e.g. a two-component surface adhesive (3) made by surface gluing (3) between the pieces (1, 2), characterized in that 1i ima, - is hardened at least close to the average temperature, aa e.g. ooo + 85 C + ^ 10 C, i.e. e.g. at +90 C - to achieve a very large limit difference for the body (1) without the risk of breakage, - and at a temperature of at least 18% of the limit difference - i.e. at least about 35 C - lower than the highest temperature. Device according to Claim 1, characterized in that the body (1) having a lower tensile strength of, for example, at ultimate thermal temperatures of, for example, +150 ° C and -40 ° C, always has the same breaking value del 1e. Device according to Claim 1 or 2, characterized in that it has, in one piece (1), a thin ceramic plate (1) with a relatively low tensile strength and in another piece (2) a piece of metal (2) of relatively high tensile strength. li n 83968 Device according to Claim 3, characterized in that it has at least one electrical resistance layer (4) generating high waste temperatures in use on the opposite side of the adhesive layer (3) of the ceramic plate (1) and a rigid cooling plate (2) as a metal body (2).