EP0055350A2 - Device for fluidifying a fusible glue - Google Patents

Abstract

A hot glue gun works with a heating resistor (23, 24) with positive temperature coefficient. A resistance cartridge (43) made of a preferably elastically flexible, heat-resistant sleeve and a PTC mass resistor (44, 45) can be provided, which lies between at least two pressure bodies and to which a spring strip arrangement is additionally assigned. This results in a press fit that is independent of dimensional changes and has constant thermal and electrical contact properties.

Description

The invention relates to a device for liquefying an adhesive which is rod-shaped in the solid state and which can be melted by the action of heat. so that an inserted into the guide channel glue stick during the insertion movement _ is liquefied and UEN on an _M binding site of the guide channel in the liquid state emerges.

Known devices of this type are mostly constructed as hand-held devices and enable the production of bonds with a so-called hot glue. This hot glue is inserted into the guide channel in the form of an adhesive rod, and since the body containing the guide channel is heated by the electrical heating device to a temperature which corresponds at least to the melting temperature of the adhesive of, for example, 200 to 250 ° C., the adhesive becomes in the course of it Insertion movement in the guide channel is first liquefied with its front end in the direction of insertion, so that it can emerge in the liquid state by pushing in the adhesive rod at the mouth of the guide channel and is available for producing an adhesive bond.

In the previously known devices, an electrical resistance device is provided as the electrical heating device, to which a thermostat is assigned, by means of which a predetermined maximum temperature is prevented from being exceeded. The resistance heater can be attached to the heatable body on the outside or in a recess and is designed so that the heatable body is as uniform as possible, i.e. at all points to the specified operating temperature. The thermostat, for example a bimetallic switch, is directly assigned to the resistance heater and interrupts or closes the feed circuit for the resistance heater within a range of predetermined upper or lower temperature, as is known to the person skilled in the art.

In the practical application of the known devices, it is necessary to heat the heatable body for a relatively long time before inserting an adhesive rod, in order to ensure that it has reached its predetermined operating temperature at all points, so that an then inserted adhesive rod is liquefied with the shortest possible delay . This leads to an undesirable energy requirement before the device is actually used. In addition, it has also been shown that when inserting an adhesive rod into the heated guide channel, such a large drop in temperature occurs that, even when the heated body is preheated, an additional delay is caused until the liquefied adhesive emerges at the mouth of the guide channel. This also leads to an uneven liquefaction of the adhesive, i.e. the adhesive emerging from the guide channel at the beginning of an operating cycle can possibly be thicker than the subsequent emerging adhesive, which gives rise to uneven bonds.

It is an object of the invention to provide a device for liquefying an adhesive which is ready for use more quickly, so that the energy supplied to it is better used and avoids irregularities in the degree of viscosity of the emerging adhesive.

This object is achieved for a device of the initially mentioned type according to the invention in that the electric heater is a PTC _- heating resistor is arranged to the guide channel with an axial direction component and extending in this direction over a length which is a multiple of the center guide channel diameter.

A PTC heating resistor, i.e. a resistor with a positive temperature coefficient, initially carries a relatively high current when connected to a supply voltage, but this drops very quickly to a low value as the temperature rises. This meets the requirement for the lowest possible power consumption during heating and in the standby state of the device. The invention now provides for the use of such a PTC heating resistor in a very specific arrangement, namely — with a directional component that is axial to the guide channel. This means that the PTC heating resistor is not used for heating the heated body at any point, but also extends over a relatively large length in the direction of the longitudinal axis of the guide channel. This measure is based on the knowledge that a PTC heating resistor draws a higher current after reaching its predetermined operating temperature and cooling again, so that its electrical power consumption increases and the temperature again up to specified operating temperature increases. The arrangement of the PTC heating resistor in the manner explained above relative to the guide channel now results from the consideration that when an adhesive rod is inserted into the guide channel, cooling initially occurs in the area of the entry point, which cools over the heatable body to the section immediately adjacent to this point of the PTC heating resistor is transmitted. This section now reduces its resistance due to the temperature drop, so that the associated increase in current and increase in the total electrical power consumed by the PTC heating resistor occurs. However, this electrical power is now essentially absorbed by the section of the PTC heating resistor that is not in the immediate area of influence of the comparatively cool adhesive rod, so that the guide channel in front of the inserted adhesive rod is temporarily heated more than normal as a result. The result of this "shift" of the electrical power and thus that of the PTC resistor. created heating zone in the area in front of the inserted glue stick is that the glue stick melts faster at its front end and can thus be inserted faster into the guide channel. At the same time, however, it is also possible to insert the adhesive rod earlier, since the "power shift" at the PTC heating resistor produces a temporary increase in temperature or acceleration of the heating of the heatable body in its front region in the direction of insertion.

In addition to these effects associated with better energy utilization and more uniform viscosity of the adhesive, the use of the PTC heating resistor leads to the advantages inherent in these elements, ie a thermostat switch is superfluous, the device can be used without switching different operating voltages work and the current consumption in standby mode is comparatively low.

Depending on the arrangement of the PTC heating resistor. Different possibilities conceivable. For example, a PTC resistance conductor can be arranged in or on the heatable body approximately parallel to the guide channel. Such an arrangement would be provided, for example, by a PTC resistance wire which is guided in the longitudinal direction of the guide channel and can also have a U-shaped course in order to act on a larger area of the heatable body. It is also possible to use so-called mass resistors, in which case a resistance rod or a resistance track runs in the longitudinal direction of the guide channel. Such resistance elements can be arranged in a recess in the heatable body, for example in an electrically insulating, but heat-conductive embedding.

Another type of arrangement of a PTC heating resistor with a directional component that is axial to the guide channel is provided if a PTC resistance conductor is arranged in or on the heatable body in a helical manner surrounding the guide channel. In the simplest case, this arrangement can consist of a PTC resistance wire with which the heatable body is wrapped. This also ensures that, due to the extension of the PTC heating resistor in the longitudinal direction of the guide channel, when inserting an adhesive rod, the "power shift" explained above occurs in the area of the PTC heating resistor.

With regard to the simplest possible construction of the device, a construction has proven to be very advantageous in which the heatable body has a second channel which is approximately parallel to the guide channel and in which an elongated resistance cartridge containing the PTC resistance conductor is arranged. The assembly of the device is then essentially limited to the insertion of the prefabricated resistance cartridge into the second channel and the installation of the heatable body thus supplemented in a housing with an electrical connecting line.

The above-explained effect of the temporarily stronger heating of the guide channel section in front of the inserted adhesive rod can be further improved in this embodiment of the device in that the second channel and the resistance cartridge are conically tapered in the direction of insertion of the rod-shaped adhesive. This intensifies the heat transfer from the PTC heating resistor to the heatable body in the front section of the device and at the same time ensures that the resistance cartridge is firmly seated after being pressed into the second channel.

If a PTC resistor is used in an elongated resistance cartridge, which is inserted into a special channel of the heatable body, the resistor should be arranged in contact with as large a surface as possible and remain firmly in place, even if the dimensions change due to aging after prolonged operation enter. Another requirement relates to the possibility of gradually switching parts of the PTC heating resistor on or off, e.g. to be able to set different operating temperatures.

To meet these requirements, a simple construction of the heating device should also be specified, which is easy to assemble, but also ensures consistently good contacting of the PTC heating resistor in mass production and also enables different types of wiring of the PTC heating resistor.

A corresponding development of the invention is characterized in that the resistance cartridge has an electrically insulating, preferably elastically flexible, heat-resistant sleeve, in the interior of which an elongated PTC mass resistor for electrical and / or thermal contacting between at least two optionally electrically conductive pressure bodies with an intermediate layer at least one spring strip arrangement provided with a curvature in the unloaded state is arranged in a press fit.

This further development ensures that the heating device can be installed extremely simply. For this purpose, only the sleeve has to be inserted into the second channel of the heatable body parallel to the guide channel, and then the pressure bodies are pressed into the sleeve together with the PTC mass resistor arranged between them and the spring strip arrangement. The spring strip or stripes on the one hand cause a firm press fit within the sleeve, on the other hand a constant contact pressure between the PTC mass resistance and the pressure bodies even with large temperature fluctuations, because the spring strip arrangement automatically compensates for dimensional changes in the individual elements, so that the electrical pressure remains constant Contact with low contact resistance is guaranteed.

If, in the simplest version of this design principle, a PTC mass resistance lies between two pressure bodies and a spring strip is arranged between the PTC mass resistance and a pressure body, the press fit in the sleeve causes a flat configuration of the spring strip, so that the PTC mass resistance is above the Spring strip is contacted electrically and / or thermally perfectly. Is for the sleeve e.g. Slightly elastic material is provided, which is nevertheless good heat conductivity, so the individual parts of the resistance cartridge do not have to have very tight dimensional tolerances, since a firm press fit can always be achieved when they are pressed into the sleeve due to their flexibility.

Even aging of the material of the individual elements of the resistance cartridge does not have a negative effect on the contacting of the PTC ground resistance, because if e.g. the material of the sleeve becomes harder and inelastic, so that there may be a slight expansion of its interior, this is compensated for by the spring strip, which can then curve slightly. It has been shown that this leads to thermal contacting. of the PTC mass resistance is practically not impaired because the contact pressure is maintained and the direct and unchanged flat contact with the second pressure body on the side of the PTC mass resistance facing away from the spring strip is apparently sufficient for heat transfer to the heatable body, if a good for the pressure body thermally conductive material such as Aluminum is used. In order to favor this and nevertheless to ensure an elasticity of the sleeve, even if it is only slight, it advantageously consists of a mixture of one or more metal oxides with a small proportion of silicone.

In such a device, different designs are conceivable for the heating resistor arrangement within the sleeve. It has proven particularly expedient if the interior of the sleeve has a circular cross section and the pressure bodies have an approximately semicircular cross section. The circular cross-section ensures that the arrangement consisting of PTC ground resistance, pressure elements and spring strips is pressed together uniformly from all sides and thus at the same time a uniformly distributed contact resistance between the PTC ground resistance and its contacting elements.

The immovable position of the spring strip arrangement is important, for example between one side of the PTC mass resistor and the pressure element (s) there. In order to be able to simply determine this position prior to assembly and to maintain it during assembly, the pressure element (s) on one side of the _P TC mass resistance are on its side facing the PTC mass resistance with a shallow recess with the Provide dimensions of the flattened spring strip arrangement. The respective spring strip is inserted into this recess before assembly, and the pressure bodies are then pressed into the sleeve with the PTC mass resistor arranged between them. Characterized in that the respective spring strip lies in the shallow recess, the dimensions of which are adapted to the dimensions of the flattened spring strip, however, there is the required tolerance which is required when the spring strip is flattened by the pressing forces acting on it during the assembly of the heating cartridge becomes.

If the spring strip arrangement extends over the entire length of the pressure element (s) and is slightly narrower than the PTC mass resistance, one of the pressure elements acts directly on the surface of the pressure element, while the other pressure element only acts on it with two longitudinal webs, which are affected by the result in a narrower dimension of the spring strip arrangement compared to the PTC mass resistance. When the overall arrangement is seated in the sleeve, however, the respective spring strip is flattened, so that this side of the PTC mass resistance is then also acted upon flatly.

Different possibilities are also conceivable for the formation of the PTC mass resistance. It can have, for example, a square or rectangular or semicircular cross section, which is then connected in each case to an adapted design of the pressing surfaces of the pressing bodies acting on it and a corresponding position of the spring strip arrangement. The PTC mass resistor expediently has a rectangular cross section, the broad sides lying between the pressure bodies. In addition, the PTC mass resistance can be divided into several individual elements over a longitudinal extent. This may be desirable in view of the commercially available sizes of the individual elements. However, a subdivision into individual elements is also conceivable if, with several pressure bodies or spring strips, a row of one another, e.g. step-by-step parallel resistors must be formed.

In addition to aluminum, other materials are conceivable for the design of the pressure bodies; preferably those that change their thermal conductivity relatively smoothly when a certain temperature is reached, and thus one Allow the characteristic of the PTC heating element to be influenced. The change in thermal conductivity results in a faster thermal shutdown of the PTC element, ie the thermal resistance is reached more quickly.

The spring strip arrangement can consist of a single spring strip or of several spring strips, which may depend on the number of pressure elements. The respective spring strip can cross in the unloaded state. be curved to its longitudinal extent. Likewise, it is also possible to bend the respective spring strip in the unloaded state in its longitudinal extent once or several times, so that a wavy spring is provided. These embodiments depend on the respective design of the PTC mass resistor in connection with its pressure bodies.

• Fig. 1 den Schnitt eines pistolenförmigen Handgerätes gemäß einem ersten Ausführungsbeispiel der Erfindung,
• Fig. 2 einen Vertikalschnitt 1-1 nach Fig. 1,
• Fig. 3 ein Ersatzschaltbild eines PTC-Heizwiderstands zur Erläuterung der Arbeitsweise einer Vorrichtung gemäß Fig. 1,
• Fig. 4 den Schnitt eines pistolenförmigen Handgeräts gemäß einem zweiten Ausführungsbeispiel der Erfindung,
• Fig. 5 eine Widerstandspatrone als Teil eines Vertikalschnitts 2-2 nach Fig. 4,
• Fig. 6 einen Federstreifen im unbelasteten Zustand für die Widerstandspatrone nach Fig. 5 und
• Fig. 7 den Längsschnitt einer weiteren prinzipiellen Anordnung innerhalb einer Widerstandspätrone.

The invention is explained in more detail below with reference to the drawing. In detail show:

• 1 shows the section of a pistol-shaped hand-held device according to a first exemplary embodiment of the invention,
• 2 is a vertical section 1-1 of FIG. 1,
• 3 is an equivalent circuit diagram of a PTC heating resistor to explain the operation of a device according to FIG. 1,
• 4 shows the section of a pistol-shaped hand-held device according to a second exemplary embodiment of the invention,
• 5 shows a resistance cartridge as part of a vertical section 2-2 according to FIG. 4,
• Fig. 6 shows a spring strip in the unloaded state for the resistance cartridge according to Fig. 5 and
• Fig. 7 shows the longitudinal section of a further basic arrangement within a resistance late.

1 shows a pistol-shaped hand-held device, which is also referred to as a hot-melt glue gun and contains a heatable body 11 in a temperature-resistant plastic housing 10. This body 11 is, for example, an aluminum die-cast part and has projections 12 with which it can be held in the housing 10 between appropriately molded ribs 13, which can also serve to anchor other elements.

The heatable body 11 has an elongated guide channel 14, the end on the right in FIG. 1 of which is extended by an insert 15 made of a plastic material, for example of silicone. The plug-in nozzle 15 is plugged onto the end of the heatable body 11 which is on the right in FIG. 1 and is guided up to the outside of the housing 10. It enables the easy and shock-free insertion of an adhesive rod 16 into the device and also ensures that no inappropriate heat loss occurs by dissipating heat from the right end of the heatable body 11 to the outside.

The guide channel 14 is tapered from right to left as shown in Fig. 1 and opens at the left end in a valve insert 17 which is provided with a mouthpiece 18 which the entli che outlet opening 19 for the liquefied in a manner yet to be described. The valve core ₁ 7 includes a one-way valve in the form of a ball valve 20, the valve spring 21 allows a valve opening under the action of a predetermined pressure from the guide channel 14 forth.

The valve insert 17 can likewise be made of an aluminum die-cast part or of another material, for example of brass.

Under the guide channel 14, a second longitudinal channel 22 is provided in the heatable body 11, which is also tapered from right to left and is approximately parallel to the guide channel 14. It extends over most of the length of the Guide e ^g s-channel 14, in the illustrated embodiment, more than 3/5 of the length of the guide channel 14. In the second channel 22 is a PTC resistor cartridge 23 is arranged. It can be pressed into the channel 22 or else glued or screwed into it, for example. The PTC resistance cartridge 23 contains a PTC resistance conductor 24 which, in the exemplary embodiment shown, has a U-shaped course with a loop formation in an approximately horizontal plane and is supplied with electrical energy via two connecting lines 25 and 26. For this purpose, a connecting cable 27 is connected to the two via a connecting terminal 28. Connection lines 25 and 26 connected.

Instead of a PTC resistance conductor 24 with a U-shaped course, a ground resistance can also be provided within the resistance cartridge 23, for example a resistance rod with a length of that shown Resistor conductor 24 corresponding length. It is also possible, deviating from the exemplary embodiment shown in FIG. 1, in a manner already explained above to guide a PTC resistance wire in a helical manner around the heatable body, in such a way that this helical arrangement also extends over a large part of the length of the guide channel.

2 shows the section 1-1 according to FIG. 1. It can be seen that the housing 10 has two half-shells which together-glued, welded or bolted _'(29 ig in _F. 1) may be. The guide channel 14 lies over the second channel 22, in which the PTC resistance cartridge 23 is arranged. It can be seen that the PTC resistance conductor 24 is embedded in the resistance cartridge 23 and forms two branches due to the U-shaped course. Aluminum oxide, ceramic or silicone, for example, can be used as the electrically insulating, but thermally conductive material for embedding the PTC resistance conductor 24. These substances may also form a mixture.

The sectional view according to FIG. 2 reveals that the heat-transferring mass of the heatable body 11 between the guide channel 14 and the second channel 22 is small, since the heatable body 11 is made relatively narrow, so that its width is only slightly larger than the diameter of the two channels 14 and 22.

Fig. 3 shows schematically an electrical circuit with partial resistors R ₁ , R ' ₁ to R _n , R' _n . These series resistors are connected to a supply voltage V, so that by their resistance values certain current J causes a corresponding conversion of electrical power into heat at the partial resistors.

The arrangement of the partial resistors according to FIG. 3 should be understood such that the two resistors R ₁ , R ^l ₁ within the resistance cartridge 23 as shown in FIG. 1 furthest to the right and the partial resistors R _n , R ' _n within the resistance cartridge 23 furthest to the left.

If an adhesive rod 16 is now inserted in the direction of the arrow shown in FIG. 1 into the plug-in socket 15 and then into the guide channel 14, its front end first reaches the area of the section of the resistance cartridge 23 in which the partial resistors R ₁ , R ' ₁ may lie. The comparatively cool adhesive rod 16 causes a temperature reduction in the guide channel 14, which is first communicated to the section of the resistance cartridge 23 in which these partial resistors R ₁ , R ' ₁ are arranged. The resistance value of these partial resistors is thereby reduced significantly, which causes an increase in the current J absorbed by the resistor chain. The electrical power thereby increased must now largely be taken over by the remaining partial resistors, that is to say in the example according to FIG. 3 by the partial resistors R _n-1 , R ' _n-1 and R _n , R'. However, these partial resistors are located in a section of the PTC resistance cartridge 23 in front of the adhesive rod 16 inserted into the guide channel 14. As a result, cooling takes place at least during the time in which the right-hand section of the PTC resistance cartridge 23 considered first, in the remaining section in front of the adhesive rod 16 caused more intensive heating, since fewer partial resistances in this area have a higher electrical must convert cal power into heat. This means that the guide channel 14 is temporarily relatively strongly overheated in front of the adhesive rod 16 inserted into it, so that the adhesive rod 16 is liquefied more quickly, overcooling of the guide channel 14 is prevented and a constant viscosity of the fluid emerging at the mouth opening 19 is liquefied Glue is guaranteed. In addition, it is not necessary to preheat to the specified operating temperature before inserting an adhesive rod 16 because the temporary overheating of the guide channel 14 described before an inserted adhesive rod 16 shortens the waiting time required.

The liquefied adhesive emerges at the mouth opening 19 in that a pressure is exerted on already liquefied adhesive by inserting an adhesive rod 16 into the guide channel 14. As soon as this pressure exceeds the force of the valve spring 21, the ball valve 20 opens. The conical tapering of the guide channel 14 up to approximately the diameter of the ball valve 20 favors this process.

4 to 7 a further embodiment of the invention is shown. In these figures, the same reference numerals are used for parts which are correspondingly also present in the exemplary embodiment illustrated in FIGS. 1 to 3 in order to identify the correspondences. These parts are therefore not explained again below.

Under the guide channel 14 shown in FIG. 4, a second longitudinal channel 42 is provided in the heatable body 11, which is approximately parallel to the guide channel 4. It extends over the largest part of the length of the guide channel 14, in the exemplary embodiment shown, over more than 3/5 of the length of the guide channel 14. In the second channel 42, a PTC resistance cartridge 43 is arranged. It is pressed or screwed into the channel 42. The PTC resistor cartridge 43 contains a PTC ground resistor, which in the exemplary embodiment shown consists of two individual elements 44 and 45 and is supplied with electrical energy via two connecting lines 25 and 26. For this purpose, a connecting cable 27 is connected to the two connecting lines 25 and 26 via a connecting terminal 28.

The housing of the PTC resistance cartridge 43 is a slightly elastic sleeve 46, which is electrically non-conductive, but good heat conductor and compensates for dimensional tolerances of the channel 42 and the elements to be pressed into it during assembly. The sleeve 46 is closed at its left end in FIG. 1 and open at the right end. In this sleeve 46, an arrangement is pressed, which consists of the two PTC mass resistance elements 44 and 45, a feather bed 47 and two pressure bodies 48 and 49. The PTC mass resistance elements 44 and 45 consist of a sintered material known per se. They are between e.g. existing pressure bodies made of aluminum 48 and 49 and are acted upon between them with an electric current which is supplied via the connecting lines 25 and 26. The ends 25 'and' 26 'of these connecting lines 25 and 26 are connected to the two pressure bodies 48 and 49. The electrical and thermal contact between the PTC mass resistance elements 44 and 45 and the pressing bodies 48 and 49 is not deteriorated by the spring leaf 47, since this is flattened due to the press fit of the arrangement in the sleeve 46 and thus a flat contact on the PTC mass resistance elements 44 and 45 guaranteed.

_F ig. 5 shows a cross section of the resistance cartridge 43 in accordance with the section 1-1 shown in FIG. 1. It can be seen that the pressure bodies 48 and 49 have an approximately semicircular cross section and together with the respective PTC mass resistance elements 44 (FIG. 4) and 45 form an almost circular cross section, which is only falsified by the amount which is due to the narrower design of the respective PTC mass resistance element 44 or 45. The upper pressure body 49 has a flat depression 50 on its underside, into which the spring leaf 47 is inserted. The depression 50 is somewhat narrower than the width of the rectangular PTC mass resistance element 45, so that it is in contact on its upper broad side with the two longitudinal webs, which are due to the narrower design of the depression 50 on the pressure body 49.

FIG. 6 shows an end view of the spring leaf 47, as viewed from the right with respect to the illustration according to FIG. 4, for the unloaded state. In this state, the spring leaf 47 has a curvature transversely to its longitudinal extent, so that it can initially only tangentially touch the PTC mass resistor 44, 45 during assembly and before the resistance arrangement is pressed into the sleeve 46. After being pressed into the sleeve 46, however, it has assumed the flat shape shown in FIG. 5, in which it then ensures a uniform pressure between the PTC mass resistor 44, 45 and its pressure bodies 48 and 49.

In Fig. 5 it is also shown that the ends 25 'and 26' of the connecting lines 25 and 26 in recesses on the. The bottom and top of the pressure body 48 and 49 are. They can be crimped or welded here, so that there is an electrical connection to the metal pressure bodies 48 and 49.

Deviating from the device described above, changes in the structural design of the resistance cartridge 43 are possible. For example, a spring leaf can be provided that does not have a transverse curvature, but is curved in the direction of its longitudinal extent. To this end, then, if necessary, the so that the PTC-resistor is mass 44, 45 directly acted upon by a _'r larger area of the pressing body 49 be slightly narrower design in Fig. 5 shallow recess 50 shown. The narrower design of the recess 50 is possible because there is no widening of the spring leaf during assembly and when the individual parts are pressed into the sleeve 46, but rather an extension. Furthermore, a spring leaf can be provided which does not have a simple curvature but, for example, a wavy curvature. Such a curvature is expediently provided in the longitudinal direction of the spring leaf.

In particular when the division of the PTC resistor composition into a plurality of individual elements, such as strength for the arrangement of _F. 4, it can be expedient to provide a separate spring leaf for each individual element. This is also conceivable, for example, if a separate electrical connection of such individual resistors is carried out via separate pressure elements. A suitable arrangement of partial resistors and pressure bodies and spring strips is shown in FIG. 7 in a longitudinal section.

Three PTC ground resistors 55, 56 and 57 are between a pressure body 58 and three further pressure bodies 59, 60 _. and 61 with the interposition of three spring strips 62, 63 and 64. The PTC ground resistors 55, 56 and 57 and the pressure bodies 59, 60 and 61 are insulated from one another by electrically non-conductive intermediate layers or coatings 65 and 66. The lower pressure body 58 is connected to an electrical connection line 67, the upper pressure body 59, 60 and 61 are connected to electrical connection lines 68, 69 and 70.

One or more of the PTC measuring resistors 55, 56 and 57 can thus optionally be energized between the lower pressure body 58 and the upper pressure bodies, so that e.g. a gradual activation and increase in heating is possible.

In the arrangement shown in FIG. 7, only a single spring strip can also be provided, which then has to lie between the lower pressure body 58 and the PTC ground resistors 55, 56 and 57.

If, in the arrangement shown in FIG. 7, the lower pressure body consists of an electrically insulating, but highly heat-conductive material and instead of three partial resistors 55, 56 and 57 insulated from one another, only a single continuous PTC ground resistance is provided, then with a suitable dimensioning of the first one and "of the last pressure element, a circuit can also be implemented in which a current flows in the longitudinal direction through the PTC mass resistor. However, this must then have an electrically insulating, but thermally conductive coating on the side that is acted upon by the spring leaves.

Claims (28)

1. A device for liquefying an adhesive rod-shaped in the solid state and meltable by the action of heat, with a heatable body containing a guide channel for the adhesive rod, to which an electrical heating device is assigned, which generates in the guide channel a temperature corresponding at least to the melting temperature of the adhesive, so that Adhesive rod pushed into the guide channel is liquefied during the insertion movement and emerges in a liquid state at an opening point of the guide channel, characterized in that the electrical heating device is a PTC heating resistor (23, 24) which is arranged with an axial directional component relative to the guide channel (14) and extends in this direction over a length that is a multiple of the average guide channel diameter. 2. Device according to claim 1, characterized in that the PTC heating resistor (23, 24) extends over at least 3/5 of the length of the guide channel (14). 3. Apparatus according to claim 1 or 2, characterized in that a PTC resistance conductor (24) in or on the heatable body (11) is arranged approximately parallel to the guide channel (14). 4. Apparatus according to claim 1 or 2, characterized in that a PTC resistance conductor is arranged in or on the heatable body surrounding the guide channel helically. 5. The device according to claim 3, characterized in that the heatable body (11) has a to the guide channel (14) approximately parallel second channel (22) in which the PTC resistance conductor (24) containing elongated resistance cartridge (23) is arranged is. 6. The device according to claim 5, characterized in that the second channel (22) and the resistance cartridge (23) in the direction of insertion-the rod-shaped adhesive (16) are tapered. 7. The device according to claim 3, characterized in that the resistance cartridge (23) is pressed into the second channel (22). 8. Device according to one of the preceding claims, characterized in that the heatable body (11) is an aluminum die-cast part. 9. The device according to claim 8, characterized in that the insertion opening of the guide channel (14) is surrounded by an elastic insert (15). 10. Device according to one of the preceding claims, characterized in that the guide channel (14) in the insertion direction of the rod-shaped adhesive (16) .. is tapered. 11. Device according to one of the preceding claims, characterized in that a one-way valve (20) is provided at the outlet opening of the guide channel (14), which is exerted by a liquid adhesive located in the guide channel (14) by inserting an adhesive rod (16) Minimum pressure is opened. 12. The apparatus according to claim 11, characterized in that the one-way valve (20) is a spring-loaded ball valve. 13. The apparatus according to claim 11 or 12, characterized in that the one-way valve (20) has a housing (17, 18) in the form of a mouthpiece dimensioning the adhesive. 14. Device according to one of the preceding claims, characterized by a heatable body (11) and an electrical feed line (25, 26, 27) receiving pistol-shaped housing (11). 15. Device according to one of claims 1 to 14, characterized in that the resistance cartridge (43) has an electrically insulating, preferably elastically flexible, heat-resistant sleeve (46), in the interior of which an elongated PTC mass resistor (44, 45) for electrical and / or thermal contacting between at least two pressure bodies (48, 49) with the interposition of a spring strip arrangement (47) provided with a curvature in the unloaded state in a press fit. 16. The apparatus according to claim 15, characterized in that the interior of the sleeve (46) has a circular cross section and that the pressure body (48, 49) have an approximately semicircular cross section. 17. The apparatus of claim 15 or 16, characterized in that the spring strip arrangement (47) between one side of the PTC mass resistor (44, 45) and one or more pressure elements (48, 49). 18. The apparatus according to claim 17, characterized in that the or the pressure body (48, 49) on one side of the PTC mass resistance (44, 45) on his or her the PTC mass resistance (44, 45) facing Side have a shallow recess (50) with the dimensions of each flattened Federstreifenanordnun ^g (47). 19. The apparatus according to claim 18, characterized in that the spring strip arrangement extends over the entire length of the pressure body (s) (49) and is slightly narrower than the PTC mass resistance (44, 45). 20. Device according to one of claims 15 to 19, characterized in that the PTC mass resistor (44, 45) has a rectangular cross-section, the broad sides lying between the pressure bodies (48, 49). 21. Device according to one of claims 15 to 20, characterized in that the PTC mass resistance (44, 45) is divided over its longitudinal extent into several individual elements. 22. The apparatus according to claim 20, characterized in that a spring strip is assigned to each individual element (44, 45) of the PTC mass resistance. 23. The apparatus of claim 21 or 22, characterized in that a pressure body is assigned to each individual element of the PTC mass resistor. 24. The device according to claim 23, characterized in that the individual elements of the PTC mass resistance are electrically insulated from one another. 25. Device according to one of claims 15 to 24, characterized in that the spring strip arrangement (47) is curved transversely to its longitudinal extent in the unloaded state. 26. The device according to one of claims 15 to 24, characterized in that the spring strip arrangement is curved or corrugated in its longitudinal extent in the unloaded state. 27. The device according to one of claims 15 to 26, characterized in that a single PTC mass resistor is provided, on one side of which a pressure body made of electrically insulating, but highly thermally conductive material is arranged, while on the other side several pressure bodies insulated from one another are provided, of which at least those at the beginning and at the end of the PTC ground resistance are electrically conductive. 28. Device according to one of claims 15 to 27, characterized in that the respective pressure body (48, 49) consists of a material which changes its thermal conductivity largely without transition when a certain temperature is reached.

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