A method for manufacturing a pressure roller

Abstract

 A method for manufacturing a pressure roller especially for a pellet mill, whereby a cylindrical body (1) on the outer side is provided locally with a surface profile preferably in the form of studs (2), which surface profile is obtained by locally welding of welding material on the outer surface of the cylindrical body.

Description

[0001] The invention relates to a method for manufacturing a pressure roller especially for a pellet mill, whereby a cylindrical body on the outer side is provided locally with a surface profile preferably in the form of studs.

[0002] Such a method is known from French Patent Specification 1,311,900.

[0003] A pressure roller of a pellet mill has only a restricted life as a result of abrasion during the rolling of the pressure roller against the inner surface of the annular die. Obviously this abrasion is strongly dependent on the nature of the material to be pressed.

[0004] The life is also dependent on the pressing pressure, which is required to prepare a solid pellet from the powdery material to be pressed and on the speed with which the pressing takes place.

[0005] By a user of the press, such as a mill owner for forage the costs of the pressure rollers are expressed in the cost per ton pressed product.

[0006] Thus, for the owner of the press it is desired to maintain these costs as low as possible, thus to reach a life of the pressure rollers which is as long as possible, in relation to the lowest possible costs.

[0007] At the method according to the French Patent Specification 1,311,900 the cylindrical surface of the cylindrical body is provided with grooves extending circumferentially and in axial direction, in which grooves the feet of studs are glued. These studs are formed as separate bodies and are very wear-proof.

[0008] This known method has different disadvantages. Said grooves must be arranged in the cylindrical body with narrow tolerances. The studs must be manufactured with very narrow tolerances and must be subjected to a heat treatment. The studs are easily loosened from the cylindrical body during pressing.

[0009] The invention aims to improve the known method and this is reached, in that the surface profile is obtained by locally welding of welding material on the outer surface of the cylindrical body.

[0010] The material of the cylindrical body can be cheap of composition as is the case at the method according to the French Patent Specification. The only requirement which must be fulfilled is that the material must be well weldable, thus must have a low carbon contents.

[0011] The quality or hardness of the wearing layer obtained by welding can easily be varied, whereby the costs are determining.

[0012] The profile of the outer side of the pressure roller is formed during the welding. The welding method is carried out in such a way, that during arranging a wear-proof layer, this layer is arranged in such a pattern on the basis material, that a further machining is superfluous and whereby the profile is maintained sufficiently during the whole life of the pressure roller.

[0013] It is observed that welding pressure rollers is known per se, see for instance Dutch published application 7710098. Hereby no profile is formed. The whole surface is covered with a layer of welding material.

[0014] From the practice it is known to harden the pressure roller by means of a heat treatment, either completely or only over a layer at the outer side in order to obtain a long life for the surface of the pressure roller, which is exposed to wearing.

[0015] The choice of material for the pressure roller is then very important. More wear-proof materials are of course more expensive than less wear-prcof materials.

[0016] Making thinner the pressure roller is neither unlimited, owing to the very high pressing pressures which can occur. In order to give the pressure roller sufficient grip so that the material to be pressed can be taken along and the offered quantity can be worked up the pressure roller is mostly provided with a surface profile.

[0017] This surface profile is then obtained by taking away material from the not yet hardened cylindrical body by means of machining, until the required surface profile is obtained, after which the pressure roller is hardened.

[0018] The surface profile consists then of the same material as the pressure roller itself and moreover the pressure roller must still be hardened. When the material of the pressure roller is a cheap material, the profile will not be very wear-proof. For a morep-proof profile the whole pressure roller must consist of an expensive material.

[0019] The invention will now be explained with reference to the drawing, in which:

Figure 1 is a side view of the pressure roller according to the invention, and

Figure 2 is a top view of said pressure roller.

[0020] The rim-shaped body of the pressure roller is indicated with 1 and may consist of cheap material, just as steel with a low carbon contents, but the material must be well weldable.

[0021] With a conventional welding process the cylindrical outer surface is provided with studs 2 of a desired height and diameter during supply of welding material. The height of the studs 2 is dependent on the diameter of the body 1 and may be between 1 and 8 mm. The diameter of the studs is also dependent on the diameter of the body and the material to be pressed. The diameter of the studs is preferably between 10 and 30 mm. The ratio between diameter and height of the studs must be as favourable as possible. A favourable ratio is 4 : 1.

[0022] A greater height of the studs gives the pressure roller a longer life.

[0023] It is favourable when about 75% of the cylindrical surface of the pressure roller is provided with welded material.

[0024] The welding takes preferably place by arc-welding, whereby inert gases or active gases and a filled or solid welding wire may be used. The used welding process is further conventional, but must be adapted to the aimed purpose.

[0025] Of course, also other profiles are possible, just as a fishbone profile and so on. However, a stud profile is preferred.

Claims

1. A method for manufacturing a pressure roller especially for a pellet mill, whereby a cylindrical body on the outer side is provided locally with a surface profile preferably in the form of studs, charac- terized in that the surface profile is obtained by locally welding of welding material on the outer surface of the cylindrical body.

2. A method according to claim 1, charac- terized in that the arranged surface profile has a thickness of 1-8 mm.

3. A method according to claim 1 or 2, whereby the profile exists of round studs arranged in longitudinal and cross rows, characterized in that the diameter of the studs is between 10 and 30 mm.

4. A method according to claim 2 or 3, charac- terized in that the ratio between diameter and height of the studs is about 1 : 4.

5. Pressure roller provided with a surface profile manuafactured with the method according to one or more of the preceding claims.

Drawing