EP1550353A2

EP1550353A2 - Composite body and method for production thereof

Info

Publication number: EP1550353A2
Application number: EP03788951A
Authority: EP
Inventors: Herbert Günther; Christel Kretschmar; Uwe Partsch; Peter Otschik
Original assignee: Guenther and Co GmbH
Current assignee: Guenther and Co GmbH
Priority date: 2002-10-11
Filing date: 2003-10-13
Publication date: 2005-07-06
Anticipated expiration: 2023-10-13
Also published as: AU2003293613A1; DE50306133D1; CN1703935A; US7569799B2; AU2003293613A8; KR20050071566A; PT1550353E; ATE349877T1; CN1703935B; DK1550353T3; ES2279211T3; JP2006502882A; US20060165901A1; DE10247618A1; WO2004036956A3; CA2501868A1; WO2004036956A2; EP1550353B1

Abstract

The compound body has base body that is made of a precipitation-hardened steel and an applied heating coating. The steel is a high-alloyed steel and the base body has a round or curved surface for accommodating a heating coating. The base body can be tubular and can be a distribution or material pipe in a heating channel system. The heating coating can have several layers and/or elements. AN Independent claim is also included for the following: (a) a method of manufacturing an inventive compound body.

Description

Composite body and method for its production

description

The invention relates to a composite body with a steel base body and a heating coating applied thereon according to the preamble of claim 1 and a method for its production according to the preamble of claim 17.

Heaters using thick-film technology have been developed for various applications and are firmly attached as a coating to the surface of a metal substrate or a steel body. The heating elements, which usually consist of an arrangement of electrical resistance tracks, are electrically insulated from the metal substrate or the steel body by an insulation layer made of dielectric material or a glass ceramic. After application, all layers are solidified by baking into a layer composite, which together with the steel body forms a composite body. Examples of this are described in DE-A1-35 36 268 or DE-A1-3545445.

Problems always arise when the steel body has a round or curved surface and has to be hardened, as is often the case, for example, with hot runner systems in injection molding tools. The latter usually have a branched network of distribution channels and hot runner nozzles with material pipes made of steel, which, depending on the application, can be exposed to extremely high internal pressures. So that the hot mass in the distribution system does not cool down prematurely, the material pipes are provided on the circumference with a heating device. WO-A1-00 23 245 proposes for this purpose to apply the heating device in the so-called fine film printing process, the individual layers being applied by means of a dispenser. Such a method is relatively complex because the cannula of the dispenser for the application of the insulation and cover layers has to travel exactly over the entire surface of the ceramic sleeve or the material tube in order to produce self-contained layers. The latter consequently do not always have a uniform thickness or density, so that cracking can hardly be avoided.

A further disadvantage arises in the operation of the hot runner system, namely when the material tube is exposed at operating temperature to the pulsating internal pressure load which is technologically caused by the injection molding process. This load and the heating of the flow channel wall to temperatures between 300 and 450 ° C., which is necessary to reach the operating temperatures, lead to elastic expansion processes which are transferred directly to the heating. Their layers can reach tensile stresses very quickly, which can lead to cracks in the insulating layer, short circuits or even spalling of the entire heating system.

To counter this, the heating coating was applied to an unhardened steel (auxiliary) body, which is then placed on the material pipe. However, such a separate heater has no direct solid-state contact with the material pipe, which leads to a high heat transfer resistance and thus to a less efficient heat transfer from the heating element to the tubular flow channel. This in turn affects the overall temperature setting and the associated control effort.

From DE-A1-199 41 038 it is known to apply the heating layer system directly to the material pipe and to design it in such a way that it is under a defined pressure prestress against the material pipe wall after baking (forming). This is generated by specifying a specific mismatch of the linear expansion coefficient of the glass-ceramic insulation layer to the corresponding value of the metallic hot runner pipe as a function of the expansion-relevant parameters of the hot runner pipe. Such a stress-tolerant connection can withstand the elastic expansion processes in the material tube within limits. At high loads, however, cracks or other damage can still occur in the insulation layer. The aim of the invention is to overcome these and other disadvantages of the prior art and to provide a steel body with a heating coating which can withstand even extreme loads in the long term. The aim is in particular a method for crack-free application of the individual layers which are exposed to temperature changes to a tubular or curved steel body which is as economical as it is easy to implement. In particular, a heating coating should be permanently functional on a material pipe of a hot runner nozzle.

Main features of the invention are specified in the characterizing part of claims 1 and 17. Refinements are the subject of claims 2 to 15 and 18 to 28. A preferred use is specified in claim 16.

As a solution, the invention provides according to claim 1 that in a composite body with a base made of steel and a heating coating applied thereon, the base is made of a precipitation-hardening steel.

Precipitation-hardening steels have the property that intermetallic precipitates form during cooling, which, in addition to the purely temperature-related volume reduction, lead to a further reduction in the steel body volume. A precipitation hardening steel therefore shrinks during the aging process, so that the prestressing of a heating coating previously applied to the surface of a base body is increased after hardening. The coating is always permanently attached to the steel body surface, even if the composite body is exposed to extremely high temperature or pressure loads.

By using high-alloy steels according to claim 2, the size and distribution of the compressive stress within the insulation layer can be adjusted particularly precisely, which is particularly important if the steel body according to claim 3 has a round or curved surface for receiving the insulation layer, or if the steel body in the embodiment of claim 4 has a tubular shape and the heating coating is to be applied to the outer wall.

There are also particular advantages if the base body is a distributor or material pipe of a hot runner system. In the area of hot runner technology in particular, it is important that the injection molding compound to be supplied to a mold cavity is precisely and uniformly tempered right into the nozzle or gate area. Cracks in the heating coating would immediately cause the nozzle to fail and to Interruptions in the manufacturing process lead, but this is effectively avoided by the inventive design of the composite body.

The heating coating according to claim 6 is preferably a layer composite composed of a plurality of layers and / or layer elements, which according to claim 7 has an insulation layer applied to the base body. The latter is, in accordance with claim 8, a ceramic or glass-ceramic insulation layer which, depending on the application method and the desired layer thickness, can consist of one or - as provided in claim 9 - two or more individual layers. On the insulation layer, an arrangement of resistance elements is applied according to claim 10. The latter form a heater which is covered at least in sections by an insulating cover layer to protect the resistance tracks (claim 11).

In terms of production technology, it is favorable if the insulation layer, the resistance elements and / or the cover layer are baked-in dispersions, for example thick-film pastes. These can be applied evenly and precisely, which is important for the subsequent adhesive strength and functionality of the heater. Alternatively, the individual layers or partial layers of the heating coating can also be designed as baked films.

In order to be able to determine both the temperature distribution and its development within the heater or within the base body, the embodiment of claim 14 provides that at least one temperature sensor is arranged in the plane of the heater coating. This is therefore housed in the layer composite, which does not lead to any noticeable increase in volume. At the same time, temperature changes can be recorded extremely promptly and precisely.

According to claim 15, connection contacts for the resistance elements and / or the temperature sensors are integrated in the heating coating. The entire heater can thus be integrated directly into a control circuit.

Further important advantages result when using a composite body according to the invention, namely when it is used as an externally heated material tube in a hot runner manifold and / or a hot runner nozzle. The cohesive application of the heater in layers ensures a permanent, firm connection to the wall of the base body and thus a firm hold on the hot runner manifold or the hot runner nozzle. In addition, the inventions a very effective chipping or loosening of the heater, namely by specifically increasing the pressure preload in the heater coating through precipitation hardening of the base body.

Due to the small thickness dimensions achieved by the direct coating, the heating coating takes up little space overall, so that extremely compact designs can be realized in comparison with conventional heating devices with almost the same performance characteristics. In addition, the power density can be increased significantly because the heat is generated and removed directly on the surface of the hot runner element to be heated. Overheating of the usually sensitive heating elements is reliably avoided.

In a method for producing a composite body with a base body made of steel and a heating coating applied thereon, for which independent protection is claimed, the invention provides according to claim 17 that a compressive prestress previously generated in the heating coating is reinforced by precipitation hardening of the base body.

This procedure, which is as simple as it is inexpensive to implement, leads to a permanent, firm connection between the base body and the heating coating, because the latter is contracted again within definable limits by the contraction movement of the base body that occurs during cooling in the hardening process, whereby a particularly effective stress-tolerant connection is created. All layers or partial layers of the heater have an extraordinarily good adhesive strength. In particular, the insulation layer withstands even extreme mechanical and thermal loads permanently, so that optimal production results are always guaranteed.

According to claim 18, each layer or layer element of the heating coating is applied to the base body, dried and baked or formed, the composite body being cooled to room temperature after each baking process. In this way, all process parameters can be individually adapted to the respective heating layer, which - depending on the performance requirement - can always be optimally applied.

The invention further provides in claim 19 that the steel alloy of the base body is homogenized or solution annealed during the stoving process, which has a particularly favorable effect on the processing economy. Claim 20 also contributes to this, namely when the stoving temperature is equal to the temperature for the homogenization or solution annealing of the base body. While the individual layers or layer elements of the heating coating are being formed, the solution annealing creates stable, homogeneous mixed crystals (α-crystals). Separately controlled manufacturing steps are no longer necessary.

Of particular advantage is the embodiment of claim 21, according to which the individual layers can be applied by means of screen printing, by means of dispensing, by dipping or by spraying. You can therefore select the optimal method for each shift. All layer parameters such as layer thickness, density, shape and the like. can be adjusted evenly and precisely, so that the heating coating always works.

In the embodiment of claim 22, each layer or layer element is baked or formed under an air atmosphere, the baking temperature being between 750 ° C and 900 ° C according to claim 23.

Claim 24 provides that the surface of the base body is roughened before the heating coating is applied, for example by means of sandblasting. This improves the mechanical adhesion of the insulation layer. The chemical adhesion can be optimized by cleaning and oxidizing the base body according to claim 25 before applying the coating.

After the heating coating has been applied, the steel alloy of the base body is outsourced or aged in accordance with claim 26 by renewed annealing. This forms fine intermetallic precipitates, which lead to a targeted reduction in the volume of the basic body. Thus, a compressive stress is created within the heating coating applied to the base body, which is able to permanently compensate mechanical loads on the base body, for example the internal pressure loads of a material pipe of a hot runner nozzle.

It is important here that the aging temperature is lower than the baking temperature for the individual layers of the heating coating. As a result, neither the formation of the individual layers or layer elements of the heating coating nor their cohesion is disturbed. Furthermore, the pressure preload in the heating coating is optimally increased without its performance Parameter or functionality is impaired. The entire process can be precisely controlled with simple means, whereby the process costs remain low.

Expediently, the outsourcing process is carried out in an air or nitrogen atmosphere.

Further features, details and advantages of the invention emerge from the wording of the claims and from the following description of exemplary embodiments.

In a preferred embodiment of the invention, a precipitation-hardening steel, for example X 3 Cr Ni Al Mo 12 9 2 1, which is high-alloyed with Ni, Co Mo, Ti and / or Al, is used as the starting material for the production of the base body. The base body forms, for example, a material tube with a round surface for an externally heated hot runner nozzle, which is used in an injection mold.

A heating coating is applied to the base body. This consists of a glass-ceramic insulating layer lying directly on the base body, an arrangement of resistance tracks as a heating element and an overlying top layer to protect the heating against external influences. The heating coating and base body are inextricably linked and therefore form a composite body.

The precipitation hardening of the material tube usually takes place in two steps, namely the solution annealing of the alloy and the subsequent aging or aging.

Before this, however, the individual layers or layer elements of the heating coating are applied in the form of thick-film pastes and baked or formed, the solution annealing of the metal alloy being carried out simultaneously with the baking of the thick-film pastes.

At the beginning of the process, the still unhardened steel body is first sandblasted after completion of the mechanical processing in order to improve the mechanical adhesion properties for the heating coating, with a certain surface roughness having to be maintained. The material tube is then cleaned with ethanol and warm nitric acid (HN03) and oxidized at around 850 ° C. hereby a thin oxide film is formed on the surface of the base body, which improves the adhesion of the insulation layer.

After the pretreatment has been completed, the heating coating is produced.

The starting material for the insulation layer is preferably a dispersion, in particular an electrically insulating thick-layer paste, which is printed onto the base body surface with a uniform thickness using the screen printing method. Four individual layers are preferably applied in succession, each layer being dried separately. Once the desired layer thickness has been reached, the material tube with the insulation layer is formed in a suitable kiln under an air atmosphere at approximately 850 ° C., so that a glass ceramic structure is formed that is homogeneous in itself.

The baking temperature corresponds to the temperature required for the homogenization or solution annealing of the base body. Both processes - baking and solution annealing - therefore take place simultaneously.

Furthermore, due to a specific mismatch between the linear thermal expansion coefficient of the insulation layer and the linear thermal expansion coefficient of the material tube, when the insulation layer is burned in, a mechanical compressive prestress is generated within it. The resulting stress-tolerant connection in the composite body already enables the insulation layer as the support layer of the heater to withstand the pulsating internal pressure loads in the material pipe, which are technologically caused by the injection molding process, within certain limits without cracks or damage to the heater.

When the base body with the burned-in insulation layer has cooled to room temperature, the connection contacts for the current-conducting resistance elements and, if appropriate, for a temperature sensor are first applied and dried. Starting from the connection contacts, the mostly meandering or spiral resistance tracks for the heating and for the temperature sensor are applied, using electrically conductive pastes for this - as well as for the connection contacts - which are applied either by screen printing or with a dispenser on the insulating layer. Drying takes place after the individual layers have been applied. All conductive layer elements are then fired together and cooled to room temperature. Here too the base body is solution annealed again, but this has no final effect on its structure.

The cover layer is also an electrically insulating glass ceramic, which is screen-printed onto the resistance elements, the connection contacts and the insulation layer still exposed in some areas, dried and then formed at about 750 to 900 ° C.

After the last baking process, the base body together with the heating coating already applied is heated again to about 525 ° C. under a nitrogen atmosphere and kept at this temperature for a defined time. After the holding time has elapsed, the composite body is cooled, preferably at a cooling rate of 10 K / min.

The precipitation-hardening steel shrinks by around 0.07% on all sides during hardening at 525 ° C and again by around 11 ppm / K during cooling, as a result of which the previously applied and formed layers of the heater are further pressurized. Precipitation hardening therefore leads to an additional pressure preload so that the entire heating coating can withstand even extreme temperature and internal pressure loads in the material pipe. The hot runner nozzle is always optimally temperature-controlled at every stage of the process due to the integral heating.

The hardness of the base body achieved after the hardening process is approximately HRC 52.

The temperature sensor is preferably in the same plane as the resistance tracks of the heater. It is therefore integrated in the heating coating just like the connection contacts. The latter forms a layer composite composed of several layers or layer elements, which forms a heatable composite body in non-detachable connection with the base body.

Due to the high TKR, the heating resistor itself can also serve as a temperature sensor. For this purpose, voltage taps are led to the outside from the desired regions of the meandering or spiral-shaped resistance tracks. If the current is known, the temperature in the area in question can be determined via the determined partial voltage. The invention is not limited to one of the above-described embodiments, but can be modified in many ways. Individual or all layers or layer elements of the heating coating can also be applied by spraying or dipping. Alternatively, foils can be used that are baked in the same way as the thick-film pastes.

The steel alloy of the base body can also be a nickel-cobalt hot-work steel. It is important that the steel is suitable for a peak temperature of up to 850 to 900 ° C with regard to the heating coating being burned in or sintered. It must also withstand temperatures of up to 450 ° C and internal pressure loads of up to 2000 bar under operating conditions.

It can be seen that precipitation-hardening steels are used as the starting material for the steel body. In contrast to the usual hardening using carbon martensite, these undergo intermetallic precipitations, which can be precisely controlled via the choice of alloy. The contraction that occurs during curing increases the compressive stress in the insulation layer or in the entire heating coating, which significantly improves the durability and functional reliability of the heating.

Normal hardening steels cannot do all of this unless you cool the steel body at a critical cooling rate. However, the required high temperature and the high cooling rate destroy the heating coating, which the invention avoids in a simple and inexpensive manner.

All of the features and advantages arising from the claims and the description, including constructive details, spatial arrangements and method steps, can be essential to the invention both individually and in the most varied of combinations.

Claims

protection claims

1. Composite body with a base body made of steel and a heating coating applied thereto, characterized in that the base body is made of a precipitation-hardening steel.

2. Composite body according to claim 1, characterized in that the steel is a high-alloy steel.

3. Composite body according to claim 1 or 2, characterized in that the base body has a round or curved surface for receiving the heating coating.

4. Composite body according to one of claims 1 to 3, characterized in that the base body is tubular.

5. Composite body according to one of claims 1 to 4, characterized in that the base body is a distributor or material tube of a hot runner system.

6. Composite body according to one of claims 1 to 5, characterized in that the heating coating is a layered composite composed of a plurality of layers and / or layered elements.

7. Composite body according to claim 6, characterized in that the heating coating has an insulating layer applied to the base body.

8. Composite body according to claim 7, characterized in that the insulation layer is a ceramic or a glass ceramic.

9. Composite body according to claim 7 or 8, characterized in that the insulation layer consists of at least two individual layers.

10. Composite body according to one of claims 7 to 9, characterized in that an arrangement of resistance elements is applied to the insulation layer.

11. Composite body according to claim 10, characterized in that the resistance elements are covered at least in sections by an insulating cover layer.

12. Composite body according to one of claims 7 to 11, characterized in that the insulation layer, the resistance elements and / or the cover layer are baked-in dispersions, for example thick-film pastes.

13. Composite body according to one of claims 7 to 11, characterized in that the insulation layer, the resistance elements and / or the cover layer are baked films.

14. Composite body according to one of claims 6 to 13, characterized in that at least one temperature sensor is integrated in the level of the heating coating.

15. Composite body according to one of claims 6 to 14, characterized in that connection contacts for the resistance elements and / or the temperature sensors are integrated in the heating coating.

16. Use of a composite body according to one of claims 1 to 15 as an externally heated material tube in a hot runner manifold and / or a hot runner nozzle.

17. A method for producing a composite body with a base body made of steel and a heating coating applied thereon, in particular according to one of claims 1 to 15, characterized in that a pressure preload previously generated in the heating coating is reinforced by precipitation hardening of the base body.

18. The method according to claim 17, characterized in that each layer or each layer element of the heating coating is applied to the base body, dried and baked or formed, and that the composite body is cooled to room temperature after each baking process.

19. The method according to claim 17 or 18, characterized in that the steel alloy of the base body is homogenized or solution annealed during the stoving process.

20. The method according to any one of claims 17 to 19, characterized in that the baking temperature is equal to the temperature for the homogenization or solution annealing of the base body.

21. The method according to any one of claims 17 to 20, characterized in that the layers or layer elements of the heating coating are applied by means of screen printing, by means of dispensing, by dipping or by spraying.

22. The method according to any one of claims 17 to 21, characterized in that each layer or each layer element is baked or formed under an air atmosphere.

23. The method according to claim 22, characterized in that the

Baking temperature is between 750 ° C and 900 ° C.

24. The method according to any one of claims 17 to 23, characterized in that the surface of the base body is roughened before applying the heating coating, for example by means of sandblasting.

25. The method according to any one of claims 17 to 24, characterized in that the base body is cleaned and / or oxidized before the heating coating is applied.

26. The method according to any one of claims 17 to 25, characterized in that the steel alloy of the base body is removed or aged by annealing after the heating coating has been applied.

27. The method according to claim 26, characterized in that the aging temperature is lower than the baking temperature for the individual layers of the heating coating.

28. The method according to any one of claims 17 to 27, characterized in that the aging is carried out under an air or nitrogen atmosphere.