Method and device for the thermal treatment of friction linings

Abstract

The invention relates to a device and a method for the thermal treatment of friction linings by means of IR-radiation, characterized in that IR radiators or IR heating fields are used as a source of infrared radiation, said radiators or heating fields generating IR-radiation in the wavelength range of 2260 nm to 3000 nm.

Claims

1. A method for thermally treating friction linings, comprising: emitting IR radiation with wavelength(s) in the range of 2260 nm to 3000 nm from one or more IR radiation sources comprising one or more ceramic IR radiators or ceramic IR heating fields that generate IR radiation with a maximum radiation power in the wavelength range from 2260 nm to 3000 nm; directing the IR radiation onto a friction lining body for a duration of 300 seconds to 2400 seconds to heat the friction lining body, wherein the friction lining body has a top surface and a surface opposite the top surface and defines a thickness between the top surface and the opposite surface, and wherein the heating directs IR radiation from the one or more IR radiation sources onto the top surface of the friction lining body; and detecting a surface temperature of the friction lining body for controlling the one or more IR radiation sources to maintain a desired temperature of the friction lining body top surface and opposite surface, wherein following the heating for the duration of 300 to 2400 seconds the desired temperature of the top surface of the friction lining body is in the range from 300 C. to 500 C. (572 F. to 932 F.), and the desired temperature of the opposite surface of the friction lining body is at least 300 C. (572 F.).

2. The method according to claim 1, wherein the one or more IR radiation sources have a surface power of 10 kW/m.sup.2 to 80 kW/m.sup.2.

3. The method according to claim 1, wherein the one or more IR radiation sources have a surface power of 20 kW/m.sup.2 to 40 kW/m.sup.2.

4. The method according to claim 1, wherein the one or more IR radiation sources is an IR radiator comprising an electric resistance heat conductor that is mounted onto a ceramic substrate.

5. The method according to claim 1, wherein the one or more IR radiation sources is a IR radiation source that comprises IR heating fields that are gas-heated ceramic pore radiators.

6. The method according to claim 1, wherein after the heating, the friction lining body has a uniform hardness profile throughout its thickness.

Description

DETAILED DESCRIPTION

(1) The infrared radiator according to one embodiment of the invention is an electric resistance heat conductor that is preferably placed onto a suitable ceramic material or that is mounted onto this material. This protects the heat conductor from overheating and translates into a longer service life, especially also when the device is used continuously. This is preferred according to the invention and avoids a repeated switching on and off of the source of infrared radiation. As a result, an optimally uniform treatment temperature for the friction linings is made available inside the device according to the invention (the IR furnace or the IR tunnel according to the invention).

(2) The material that is used to attach the heat conductor is electrically non-conductive and should have good emission properties in the desired IR wavelength range. Taking these criteria into account, IR radiators with many different geometries are available. Thus, according to the invention, the furnace chamber or treatment chamber can be optimally lined, thereby ensuring an optimal temperature management and temperature constancy in the furnace chamber. Ceramic materials in combination with the electric heat conductor have proven their worth for purposes of the invention. Here, it is preferable to use ceramic substrates or ceramic tiles in combination with metal strips or metal wires.

(3) Such IR furnaces or IR tunnels that are equipped with ceramic radiators or heating fields or else corresponding furnace concepts including exhaust units for gases that are formed during the treatment and including a suitable conveying means to transport the material to be treated through the furnace chamber are all commercially available.

(4) As a rule, the IR radiators or heating fields according to one embodiment of the invention emit IR radiation in the wavelength range preferably from 2260 nm to 3000 nm, with a surface power of preferably 10 kW/m.sup.2 to 80 kW/m.sup.2, whereby the especially preferred value here is 20 kW/m.sup.2 to 40 kW/m.sup.2. According to this embodiment of the invention, these values result in treatment times for the thermal treatment or for the hardening of the friction linings of 300 to 2400 seconds, preferably from 600 to 1200 seconds, in the case of the friction lining mixtures commonly used for motor vehicle brake linings, especially disc brake linings. Here, a surface temperature of 300 C. to 500 C. [572 F. to 932 F.], preferably 350 C. to 450 C. [662 F. to 842 F.], is generated on the friction lining.

(5) In addition to the above-mentioned electric resistance infrared radiators, it is also possible to use, for example, gas-heated ceramic heating fields (such as ceramic pore radiators) as the IR radiators. According to an embodiment of the invention, the essential and preferable aspect is the adherence to the above-mentioned process parameters, rather than the type of IR radiator used to attain these parameters.

(6) Consequently, the use according to an embodiment of the invention of IR furnaces/devices with sources of infrared radiation (gas-heated ceramic heating fields or electric IR radiators) especially yields the following advantages: there is no need for additional cooling of the IR radiators/heating fields, the furnace chamber can be have a simple design, the temperature management, coupled with appropriately reproducible product quality, is optimal, and the energy savings due to lower treatment temperatures are considerable. Moreover, by varying the treatment time and the IR intensity/temperature (radiator distance), it is possible to set any desired hardness profile (ranging from surface hardening all the way to a hardening of the entire friction lining compound) for the friction lining and thus also their mechanical properties simply by performing routine experiments.

(7) The further configuration of the device according to an embodiment of the invention for the thermal treatment of friction linings can be very easily adapted to the individual requirements of the operation in question and can comprise equipment of the type found in commercially available products and in the state of the art, for example, according to European patent EP 1 085 231 B1 or German patent DE 100 63 256 C2. These include, for example: an exhaust unit, preferably in the furnace chamber or treatment chamber, to remove the gaseous substances formed by the thermal treatment, a cooling device to cool the friction linings after the thermal treatment, a transport means such as, for example, a conveyor belt to transport the friction linings/friction lining surfaces through the furnace chamber/treatment chamber, process monitoring sensors, especially temperature sensors for the friction lining surfaces. Thus, for example, adjoining the furnace chamber/treatment chamber, there can be a temperature sensor that is connected to the control unit for the source of infrared radiation and that can monitor and control the adherence to the desired product surface temperature of the friction linings. By means of this temperature detection, it is also possible to directly segregate defective friction linings from the production process. Sensors for detecting objects before and after they enter the treatment chamber can be used for the further control of the method/device according to the invention.

(8) The device according to embodiments of the invention and the corresponding method thus correspond largely to the devices and methods according to European patent EP 1 085 231 B1 [US 2002/046789 A1] and/or German patent DE 100 63 256 C2 [WO 0250448], and they differ from them especially through the use of an IR furnace/IR tunnel that is equipped with the described sources of infrared radiation, as well as through the use of the process parameters that prevail there. The disclosure of these two documents is thus hereby explicitly incorporated as an integral part of the present description.

(9) Below, properties and advantages of the method according to an embodiment of the invention are described by way of example. This serves to illustrate the present invention, without thereby limiting it in any way whatsoever. Any technically meaningful combination of parameters and/or of equipment found by the person skilled in the art is encompassed by the present invention.

(10) In view of the markedly longer treatment times and the lower surface power of the IR radiators in comparison to the state of the art, the method according to an embodiment of the invention for the thermal treatment of friction linings causes the entire friction lining to be heated up, rather than just its surface. This gives rise to a relatively flat temperature gradient throughout the thickness of the friction lining, whereby the highest temperature is on the friction lining surface while the lowest temperature is on the opposite side (facing away from the IR radiators), although the temperature there is preferably still at least 300 C. [572 F.]. In other words, the entire friction lining compound is heated to a relatively constant temperature, resulting in a uniform hardness profile throughout the thickness of the friction lining. Inhomogeneities of the products due to different temperatures during the thermal treatment on (parts of) the surface and in the interior of the friction lining are thus largely avoided. The reproducibility of a uniform product quality is markedly improved.

(11) Additional advantages of the thermal treatment according to an embodiment of the invention are, for example, the following:

(12) due to the lower surface power of the IR radiators, they can be positioned much closer to the friction linings that are to be treated, the energy (heat) is efficiently transmitted to the friction lining compound, thereby saving energy, and the quantity of undesired exhaust gases during the treatment is markedly reduced.

(13) The present invention also comprises a method for the thermal treatment of friction linings in which the described thermal treatment over a prolonged treatment time at moderate temperatures is followed by a second, short treatment time as is described, for example, in the cited state of the art, in which the heating power of the IR radiators is briefly increased and, due to this intense heating, only the surface of the friction lining is heated to a high temperature. In this context, the first step constitutes a continuous hardening of the entire friction lining compound, while the second step constitutes a scorching of only the friction lining surface.