METHOD FOR APPLYING SAND TO DRUM BRAKE LININGS

Abstract

The invention relates to a method for applying sand to the inner radius of drum brake linings comprising the following steps: a) rolling a UV-curing adhesive onto the inner radius of a drum brake lining, b) applying a frictional grain, such as zircon sand, to the adhesive layer, c) removing the frictional grain not retained by the adhesive from the lining surface, and d) curing the coating by means of UV radiation.

Claims

1. A method for applying, sand to the inner radius of drum brake linings, said method comprising the following steps: a) applying an adhesive onto the inner radius of a friction lining for a drum brake, b) applying abrasive particles onto the inner radius of the drum brake lining coated with the adhesive, c) removing the abrasive particles that have not been held by the adhesive from the surface of the drum brake lining, and d) curing the coating consisting essentially of the adhesive and the abrasive particles.

2. The method according to claim 1, wherein the adhesive is applied onto the inner radius of the drum brake lining using a roller.

3. The method according to claim 1, wherein the adhesive is a photo-initiated curing adhesive.

4. The method according to claim 1, wherein the adhesive is a UV-curing adhesive on the basis of acrylate.

5. The method according to claim 1, wherein the adhesive is applied onto the inner radius in an amount ranging from 0.008 g/cm.sup.2 to 0.024 g/cm.sup.2 .

6. The method according to one of claim 1, wherein the abrasive particles are selected from the group consisting of zirconium sand, zirconium silicates, metal oxides, quartz or corundum and mixtures thereof.

7. The method according to claim 6, wherein the abrasive particles are zirconium

8. The method according to claim 1, wherein the abrasive particles have a grain size within the range from about 0.03 mm to about 0.25 mm.

9. The method according to claim 1, wherein curing is by applying UV radiation in the wavelength range from about 180 nm to about 500 nm.

10. (canceled)

11. (canceled)

12. The method according to claim 1, wherein curing is by applying UV radiation in the wavelength range from about 250 nm to about 400 nm.

13. The method according to claim 1, wherein the applying step is carried out without overspraying adhesive onto surfaces beyond the inner radius of the drum brake lining.

14. A method for applying sand to the inner radius of drum brake linings, said method comprising the following steps: a) rolling an adhesive onto the inner radius of a friction lining for a drum brake, b) distributing abrasive particles onto the inner radius of the drum brake lining coated with the adhesive, and c) curing the coating consisting essentially of the adhesive and the abrasive particles.

15. The method according to claim 14, further comprising removing excess abrasive particles not entrained by the adhesive before curing.

16. The method according to claim 14, wherein the adhesive is applied onto the inner radius in an amount ranging from 0.008 g/cm.sup.2 to 0.024 g/cm.sup.2.

17. The method according to claim 14, wherein the abrasive particles are selected from the group consisting of zirconium sand, zirconium silicates, metal oxides, quartz or corundum and mixtures thereof.

18. The method according to claim 14, wherein the abrasive particles have a grain size within the range from about 0.03 mm to about 0.25 mm.

19. The method according to claim 14, wherein curing is by applying UV radiation in the wavelength range from about 180 nm to about 500 nm.

Description

DETAILED DESCRIPTION

[0021] The adhesive is applied by means of a process in which adhesive is only applied to the surface to be treated so that there is no material loss of the type encountered with overspray. According to the invention, preference is given to applying the adhesive using a roller, especially a foam roller, whose length (width of the roller) matches the width of the friction lining.

[0022] Since the lining of a drum brake is curved and therefore has an inner radius, it is also preferred according to the invention if the roller is guided automatically, for instance, by means of a robot, or else semi-automatically using a suitable mechanical means.

[0023] The applied amount of adhesive preferably ranges from 0.008 g/cm.sup.2 to 0.024 g/cm.sup.2 of coated surface.

[0024] Preferably, photo-initiated curing adhesives such as UV-curing and light-curing adhesives are employed as the adhesives. In this context, especially benzophenone and its derivatives serve as photo-initiators. Special preference is given to UV-curing adhesives on the basis of acrylate.

[0025] Adhesives that are suitable according to the invention are also employed to paint and/or to coat the friction side of disc brake linings used in trucks. Here, the coating or paint serves to ensure a sufficient braking action when the brake system has not been broken in yet; such adhesives are described, for example, in European patent specification EP 1 022 481 B1.

[0026] The preferred UV-curing adhesives, especially acrylate systems, have only one single component, are free of solvents and are cold-curing. Generally speaking, the system functions in that the liquid adhesive is filled, among other things, with photo-initiators that are activated by UV light and that form radicals which, in turn, initiate the curing process. Acrylates and epoxies constitute the basis of most UV adhesives. These adhesives are characterized by their very short curing times and volume constancy during the curing process.

[0027] Moreover, no harmful reaction products, especially no harmful gases, are generated during the curing process. The linings coated with adhesive onto which abrasive particles (sand) have been scattered are transported on a conveyor belt at a uniform speed and preferably at ambient temperature through a so-called UV tunnel under a UV lamp, The length of the tunnel, the conveying speed and the distance of the treated linings, which altogether correspond to the duration of the irradiation, are selected in such a way that a complete curing of the adhesive is achieved. The typical range for the energy absorption of such coatings is from 0.2 J/cm.sup.2 to 4 J/cm.sup.2, preferably within the range from 0.5 J/cm.sup.2 to 1 J/cm.sup.2. The typical exposure time with appropriate UV light is from 3 to 40 seconds. The time is dependent on the applied amount or on the layer thickness of the UV paint.

[0028] The preferred wavelength range for the UV radiation, depending on the adhesive used, is from 180 nm to 500 nm, especially 250 nm to 400 nm. Especially preferably, the wavelength is approximately 395 nm; this holds true particularly for UV acrylate adhesive. Consequently, this wavelength is in the range of the boundary between UVA and visible light. On the one hand, this means that transparent and yet UV light-absorbing adhesives can be effectively transluminated or cured. On the other hand, the storage stability of such adhesives does not pose any special problems.

[0029] The abrasive particles are applied onto the inner surface or inner radius of the friction lining coated with adhesive by scattering abrasive particles onto the surface. An important aspect is to distribute the particles as uniformly as possible onto the lining surface. This is preferably accomplished using an automatic or semi-automatic device with a container that is filled with abrasive particles and that has a linear outlet, whereby the lining is passed under the outlet at a speed that is as uniform as possible. Subsequently, the excess abrasive particles, which can also be referred to as sand, are removed. This is preferably done by simply tilting the friction lining, as a result of which the abrasive particles that have not been bonded by the adhesive fall off of the lining surface.

[0030] As an alternative, the excess sand can also be removed by being vacuumed up or blown off. This results in the desired coating thickness of sand, which is generally within the range from 0.02 g/cm.sup.2 to 0.15 g/cm.sup.2, preferably within the range from 0.04 g/cm.sup.2 to 0.09 g/cm.sup.2. The abrasive particles that have fallen off of the lining surface are collected in a container, which is a simple way to avoid material losses.

[0031] According to the invention, zirconium sand, which consists primarily of the mineral zirconium silicate (ZrSiO.sub.4), is employed as the abrasive particle or sand to be applied onto the surface. In general, preference is also given to synthetic zirconium silicates (ceramic pigments), metal oxides (for instance, zinc oxide and titanium dioxide), silicon dioxide (quartz) or aluminum oxide such, as, for example, corundum. The abrasive particles or sand can consist of one or more of the cited substances which, as a rule, can be combined as desired. The grain size of the abrasive particles is preferably within the range from 0.03 mm to 0.25 mm.

[0032] The features described in the individual method steps can be combined as desired.

[0033] Drum brake linings onto which sand has been applied to the inner radius or inner surface by means of the method according to the invention stand out for an environmentally friendly mode of production that saves on material. Drum brakes that have the drum brake linings or friction linings according to the invention are characterized by high mechanical stability. Even at high braking torques, the inventive application of sand to the inner surface of the friction lining reliably prevents the brake lining from shearing off of the brake shoe. For this reason, such drum brake linings are also particularly well-suited for the initial installation of drum brakes in trucks.

[0034] Additional objectives, advantages, features and application possibilities of the present invention can be gleaned from the description herein. In this context, all of the described and/or depicted features, either on their own or in any meaningful combination, constitute the subject matter of the present invention, also irrespective of their compilation in the claims or in the claims to which they refer back.