BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a cutting edge for a plow, wherein the cutting edge comprises a wear area which comprises a contact surface with a ground surface during operation of the plow.

Most snow plows comprise cutting edges which constitute the contact surface of the plow with the ground surface to be plowed. The ground surface is generally a paved road surface. The cutting edges have the task to protect the plow blade from wear. They have also the task to provide a good plow result. Larger snow plows which are attached to heavy vehicles generally include a plurality of segments of releasably mountable cutting edges at a lower end. Thus, a cutting edge may be replaced one by one when they are worn down. There are different kinds of cutting edges. The most common cutting edges are manufactured of steel. They are inexpensive but they are worn relatively quickly and they wear relatively hard on the road surface. Cutting edges of hard metals wear less but they are expensive and they wear also hard on the road surface. Plastic cutting edges are gentle to the road surface but they are sensible for wear and they are more expensive than steel cutting edges. Rubber cutting edges have a good contact with the road surface and thus away slush in a good manner but they also are sensible for wear. Plastic cutting edges and rubber cutting edges are gener- ally thicker than metal cutting edges.

Airports have lighting devices projecting up a short distance above the road surface for start, landing and taxiing of airplanes. Plows used in airports have only cutting edges of plastic or rubber in order to avoid damage of the lighting devices. In order to further reduce the risk that the lighting devices will be damaged, the cutting edges may have a resilient attachment to the plow blade.

Consequently, plastic cutting edges and rubber cutting edges are sensible for wear. Thus, they need to be replaced relatively frequently. A large part of the material body of a cutting edge is used to attach the cutting edge to the plow blade. This is necessary in order to retain the cutting edge in a safe manner in an intended mounting position on the plow blade. A smaller part of the material body is used as wear area. After the wear area has been worn down, the cutting edge has to be replaced such that the plow blade or the fastening device connecting the cutting edge with the plow will not come in contact with the road surface. Plastic and rubber cutting edges consist of molded homo- geneous material bodies containing a relatively large amount of plastic or rubber material. Since the cost for plastic and rubber cutting edges is relatively high, at the same time as the cutting edges must be replaced relatively frequently, the total cost for the cutting edges during a snowy winter in an airport is relatively high.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a cutting edge of a polymeric material which has a construction such that the cost for each individual cutting edge becomes considerably lower than the cost for conventional cutting edge of a corresponding material and size. This object is achieved with the cutting edge of the initially mentioned kind which is characterised in that the cutting edge comprises a wear part which comprises a material body which mainly consists of a polymeric material, wherein the wear part comprises the whole wear area of the cutting edges and a hol- low-shaped space with at least an opening, and a core part which constitutes a separate unit in relation to the wear part, wherein the core part is insertable in the hollow-shaped space of the wear part via said opening and it has a shape such that it completely fills out the hollow-shaped space when it is in an intended fastening position in the space. Consequently, the cut- ting edge consists of two separate parts, namely a wear part which contains the wear area and a core part which does not contains any part of the wear area. The core part, which does not contains any part of the wear area, provides thus substantially no wear. The core part can thus be used many times to- gether with a new wear part. As a result of that, the material cost for the cutting edge may be reduced. Advantageously, the core part is made as large as possible in relation to the wear part. The core part may constitute about 40-60 % of the total volume of the cutting edge. The material cost for a new cutting edge may thus be reduced in a corresponding degree. Since the core part fills out the whole hollow-shaped space of the wear part, the parts may in a connected state have substantially the same properties as a conventional homogeneous cutting edge of a corresponding material and size. With a polymeric material means a plastic material which may be a thermosetting plastic or a thermoplastic. A polymeric material may also mean a rubber material in the form of synthetic rubber or natural rubber.

According to an embodiment of the invention, the core part is manufactured of the same polymeric material as the wear part. Thus, the cutting edge obtains substantially the same properties as a conventional cutting edge which is manufactured of a corresponding polymeric material in one piece. Advantageously, the wear part is manufactured of a polyurethane material. Polyure- thane material is available in many forms and they have many properties that make it suitable to use in cutting edges for plows. Polyurethane has, for example, good resistance against mechanical wear, high load bearing capacity, can handle operating temperatures between about -40°C and +80 °C, has good resistance against water and has god resistance against oil, petrol etc. at the same time as they have a good sound-absorbing properties. Polyurethane materials are available in various forms such as, for example, thermoplastic, hard plastic, solid rubber, etc.. According to an embodiment of the invention, the wear part has an elongated shape and the hollow-shaped space extends substantially along the whole length of the wear part. Advantageously, the elongated wear part has a constant cross-section profile along its entire extension. Thus, the wear part may be given a relatively simple design which facilitates the manufacturing process of the wear part. Thus, the core part has also here a corresponding elongated shape as the hollow-shaped space and can thus also have a constant cross-section profile along its entire extension.

According to an embodiment of the invention, the opening to the hollow-shaped space has an extension along the whole length of the hollow-shaped space. It is thus easy to insert an elongated core part in the hollow-shaped space of the wear part. In this case, the core part is inserted into the hollow-shaped space of the wear part in a transverse direction. Alternatively or in combination, the opening to the hollow-shaped space may be arranged at a short side of the wear part. Advantageously, the opening has a shape corresponding to the cross-sectional pro- file of the core part. In this case, the core part is inserted into the hollow-shaped space of the wear part in a longitudinal direction. Alternatively, the hollow-shaped space may be provided with the both openings according to the above. Thus, the core part may be inserted into the wear part both in a transverse di- rection and a longitudinal direction. If the core part tends to get stuck inside the wear part, it can be suitable to have the possibility to move the core part out from the wear part in several different directions. Advantageously, the core part and the hollow- shaped space of the wear part have relatively slippery surfaces such that the insertion and removal of the core part from the hoi- low-shaped space of the wear part can be performed in a simple manner.

According to a preferred embodiment of the invention, the cut- ting edge comprises connection means which is adapted to fix the wear part and the core part in relation to each other in said fastening position. If the wear part and the core part will be able to work as a unit, the parts ought to have a good fixation in relation to each other in the fastening position. Said connection means may comprise at least a hole in the wear part and a hole in the core part which together form a common hole for an elongated fastening member such as a bolt or the like which connect the wear part and the core part in the fastening position. With a suitable number of such holes at suitable distances from each other, substantially the entire outer surface of the core part may be fixed in relation to the internal surface of the wear part in a simple and effective manner. Advantageously, said connection means may also be used for fastening the cutting edge in a mounting position at the lower end of the plow blade. Thus, no separate fastening members need to be used for fastening the cutting edge to the plow blade or to a component attached to the plow blade. Such a component may be a resilient element such that the cutting edge will obtain a resilient movement in relation to the plow blade when the cutting edge hits an obstruction. By means of such a resilient attachment of the cutting edge, the risk is further reduced that the cutting edge damages any sensible component in the road surface such as a lighting device.

According to a preferred embodiment of the invention, the wear part comprises two different wear areas with a respective contact surface. Advantageously, the contact surfaces are, in this case, arranged in opposite ends of the wear part. A symmetrically shaped wear part may here be loosened and turned such that the second wear area comes in contact with the ground sur- face when the first the wear area has worn down. A turnable cut- ting edge with two wear areas obtains twice as a long lifetime as a cutting edge with one wear area.

According to a preferred embodiment of the invention, at least the wear part comprises ceramic particles which are arranged in the polymeric material. Preferably, small ceramic particles in powder form are added in the polymeric material. Ceramics are very hard materials, they are heat resistant, they have a high melting point, they do not corrode and they are generally chemi- cally stable. By mixing a suitable amount of a ceramic powder in a polymeric material, the wear of the polymeric material in the wear part may be considerably reduced. Thus, the cutting edge obtains a longer lifetime. The ceramic particles constitute with advantage 0-20% of the material body of the wear part. Advan- tageously, the ceramic particles constitute of aluminium oxide. Aluminium oxide is a ceramic which is practically insoluble in water and relatively inexpensive to procure. Although the core part is not subjected to any direct wear, it may be appropriate to also mix ceramic particles in the core part if it is manufactured of a polymeric material.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the invention are described with reference to the attached drawings, on which: shows a plow with a plurality of cutting edge sections, shows a cutting edge according to a first embodiment of the invention in an unmounted state,

shows a cutting edge according to a second embodiment of the invention in a mounted state on a plow blade and

shows a cutting edge according to a third embodiment of the invention in a mounted state on a plow blade. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

Fig. 1 shows a plow 1 for plowing of snow. The plow is, in a suitable manner, attached to a vehicle driving the plow 1 . In this case, the plow 1 is a diagonal plow comprising a plow blade 2 with a snow outlet part 2a on one side and a plurality of sections of cutting edges 3 which are fasten in a row at a lower end of the plow blade 2. The cutting edges 3 constitute the part of the plow 2 which abuts against the ground surface 4 to be plowed. In this case, the cutting edges 3 are manufactured of a polymeric material making the cutting edges especially suitable to be used for plowing of snow on landing strips, runways and conveyor lines on airports where there is lighting devices projecting up from the ground surface 4. Cutting edges 3 of polymeric materials may also, of course, be used in other plowing contexts.

Fig. 2 shows one of the cutting edges 3 in Fig. 1 in an unmounted state. It is here apparent that the cutting edge 3 con- sists of two separate units namely a wear part 5 and a core part 6. The wear part 5 and the core part 6 constitute homogeneous material bodies which, with advantage, are manufactured of a suitable polyurethane material. The wear part and the core part may be manufactured by casting. The wear part 5 comprises a front surface 5a, a rear surface 5b a contact surface 5c with the ground surface 4, an upper surface 5d and two side surfaces 5e. The surfaces are here named after their position when the cutting edge 3 is in a mounted state on a plow blade 2. The front surface 5a and rear surface 5b of the wear part are in parallel. Thus, the wear part 5 has a constant thickness which may be on the order of 3-5 cm.

The wear part 5 comprises a wear area 5f extending from the contact surface 5c up to a limit 5c ₀ defining a maximum permit- ted wear of the cutting edge 3. The limit 5c ₀ for maximum permitted wear is marked with a dashed line in Fig. 2. During operation of the plow, the wear area 5f will be worn down such that the contact surface 5c successively approaches the limit 5c ₀ for maximum permitted wear. The wear part 5 has an elongated hollow-shaped space 5g which extends substantially along the whole length of the wear part 5. In this case, the hollow-shaped space 5g is substantially U-shaped in a transverse plane. The hollow-shaped space 5g has an opening 5gi at the upper surface 5d of the wear part. The wear part 5 comprises a plurality of mounting holes 5h which extend between the front surface 5a and rear surface 5b of the wear part.

The core part 6 has a shape such that it can be inserted into the hollow-shaped space 5g of the wear part via the opening 5g-i . The core part 6 has a substantially U-shaped profile in a trans- verse plane. The core part 6 also comprises two plane side surfaces 6b and a plane upper surface 6c. The core part 6 has a corresponding shape and size as the hollow-shaped space of the wear part 5g. The core part 6 is here moved in a transverse direction into the hollow-shaped space 5g. Consequently, when the core part 6 reaches a fastening position inside the wear part 5 it fills out the hollow-shaped space 5g completely. In the fastening position, the upper surface 6c of the core part 6 is in the same plane as the upper surface 5d wear part. The core part 6 comprises mounting holes 6h at corresponding places as the mounting holes 5h of the wear part. The mounting holes 5h of the wear part and the mounting holes 6h of the core part create thus common mounting holes extending both through the wear part 5 and the core part 6. When the core part 6 has been arranged inside the hollow-shaped space 5f, the wear part 5 forms all external surfaces except the upper surface which is formed of both the upper surface 5d of the wear part and the upper surface 6c of the core part 6. The wear part 5 and the core part 6 create in said connected state a cutting edge 3 which has substantially the same properties as single conventional cutting edge of similar material and shape. Fig . 3 shows a side view of a cutting edge in a mounted state on a plow blade 2. The wear part 5 of the cutting edge and the core part 6 has here the same design as in Fig . 2 except that the side surfaces 5e of the wear part in this case also comprises open- ings 5g ₂ to the hollow-shaped space 5g. The core part 6 has here a length which completely corresponds to the length of the wear part 5. When the core part 6 is mounted in the wear part 5, the side surfaces 6b of the core part is in the same plane as the side surfaces 5e of the wear part. It is here apparent that the contact surface 5c of the wear part has an inclination of about 45°C against the front surface 5a of the wear part. Consequently, the wear part 5 is mounted on the plow blade 2 with a corresponding inclination in relation to the ground surface 4. The contact surface 5c has here a width of about 5 cm .

Before the cutting edge 3 is mounted on the plow blade 2 , the core part 6 is moved down into the hollow-shaped space of the wear part 5g. In this case, the core part can be both inserted into the hollow-shaped space 5g in a transverse direction via the opening 5Q† or in a longitudinal direction via the opening 5g ₂ . Combinations of said movements are also possible. The rear surface 5b of the wear part 5 is then applied to a mounting position on the plow blade 2 in which the mounting holes 5h of the wear part coincide with the mounting holes 2h in the plow blade 2. An elongated mounting plate 7 is applied on the front surface 5a of the wear part 5. The mounting plate 7 is provided with mounting holes 7h in corresponding positions as the mounting holes 5h of the wear part. Bolts 8 is then threaded through the holes 2h , 5h, 6h , 7h in the mounting plate 7, the wear part 5, the core part 6 and the plow blade 2 whereupon they are fasten by nuts 9 on the rear side of the plow blade 2. The bolts 8 and the nuts 9 are now securing the wear part 5 and the core part 6 in a fastening position in relation to each other at the same time as they hold the cutting edge 3 in a mounting position on the plow blade 2. During operation of the plow 1 , the wear area 5f is successively worn down. When the contact surface 5c reaches the limit 5c ₀ for maximum permitted wear, it is time to replace the cutting edge 3. The nuts 9 are loosen whereupon the bolts 8 are pulled out from the mounting holes 2h, 5h, 6h, 7h. The mounting plate 7 is removed from the cutting edge 3 and the cutting edge 3 is removed from the plow blade 2. The core part 6 is pulled out from the hollow-shaped space of the wear part 5g. The core part

4 is then pushed into a new wear part 5. This unit is mounted on the plow blade 2 in the above mentioned manner. In this case, the replacement of a worn out cutting edge is performed in the same manner as the replacement of a worn out conventional cutting except the step of loosening the core part 6 from the wear part 5 during demounting of the cutting edge and inserting the core part 6 in the wear part 5 during mounting of the cutting edge. By forming the hollow-shaped space of the wear part 5g and the core part 6 with a high accuracy, these additional steps may be carried out relatively quickly and in an uncomplicated manner.

Fig. 4 shows a further alternative embodiment of a cutting edge 3 according to the present invention. In this case, the wear part

5 has a wear area 5f with a contact surface 5c at an end and a wear area 5f with a contact surface 5c at an opposite end. The wear part 5 has a symmetrical design such that when one of the wear areas 5f has been used, the wear part 5 is turned and the other wear area 5f with the second contact surface 5c is turned downwardly into contact with the ground surface 4. In this case, the wear part 5 comprises a hollow-shape space 5g extending along the whole length of the wear part 5. The hollow-shaped space 5g has openings 5g ₂ in the side surfaces 5e of the wear part. The core part 6 has a corresponding shape and size as the hollow-shaped space of the wear part 5g. In this case, the core part 6 is thus inserted into the hollow-shaped space 5g by a lon- gitudinal movement via the opening 5g ₂ in the side surfaces 5e of the wear part. Since the cutting edge 3 is turned, the core part 6 does not need to be demounted from the wear part 5. Consequently, the core part 6 needs only to be demounted from the wear part 5 when the both wear areas 5f are worn down and the wear part 5 is to be replaced.

Cutting edges of polymeric material are thicker than cutting edge of metal material. Thus, a cutting edge of a polymeric material contains a relatively large amount of polyurethane which is a relatively expensive material. Cutting edges of polyurethane material are resistant to wear but they provide a considerably more wear than cutting edge of metal material. Therefore, they need to be replaced relatively frequently. The cutting edge, according to the above, may have a width of 5cm, a height of 20 cm and a length of 1 m. Thus, such a cutting edge contains a relatively large amount of polyurethane. The total cost for conventional cutting edges of polyurethane can therefore be relatively high. According to the present invention, a core part 6 is retained when the wear area of a cutting edge has been worn down. Thus, only the wear part 5 of the cutting edge needs to be replaced. Since the wear part 5 has a hollow-shape space, it contains significantly less polyurethane than a conventional massive cutting edge of polyurethane. The cost for only replacing the wear part 5 of the cutting edge will therefore be much lower than if the whole cutting edge is to be replaced. The core part 6 is of course made as large as possible in relation to the wear part 5. In order to keep the core part intact, it must not extend into the wear area 5f. It also ought to be a small external surface of the cutting edge 3 as possible since there is always a risk that external surfaces of the cutting edge are exposed to wear. The core part 6 ought to have a rounded shape since sharp edges can be worn down by the forces arising on the cutting edge 3 during operation of the plow.

In order to further reduce the cost for cutting edges of polymeric material, a ceramic material such as aluminium oxide may be mixed into the polymeric material. Relatively small particles of aluminium oxide are suitably applied to a polymeric material of polyurethane. Aluminium oxide in powder form is mixed into the polyurethane during a manufacturing process of the wear part 5. Also the core part 6 may be manufactured of polyurethane with aluminium oxide. The proportion of aluminium oxide in the polyurethane is in the order of 10-20% preferably about 15 %. The hard particles of aluminium oxide in the wear part 5 reduce significantly the material wear in the wear part 5. The wear part 5 therefore does not need to be replaced as frequently.

The present invention is not limited to the above described embodiments on the drawings but may be varied freely within the scoop of the claims.