FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a water jet cutter, also known as a water jet, capable of cutting materials using a jet of water or a mixture of water and an abrasive substance at high velocity.

Water jet cutting is often used for manufacturing of parts when the materials being cut are delicate or sensitive to high temperatures. Water cutting typically involves the use of high power pumps driven by electric or diesel motors of 25-250 HP. Such systems are less suitable for small scale applications, such as on-site cutting of outer stones and tiles of a pattern to dimensions, as measured on-site, during construction.

SUMMARY OF THE INVENTION It is an object of the invention, to provide a low-cost, lightweight water jet cutter for on-site use in for instance construction sites, road paving and for small workshops.

According to the invention, this object is achieved by providing a water jet cutter according to claim 1. Because the pump housing contains both the pump and the high pressure water conduit and the restriction and the high speed nozzle are fixedly mounted to the pump housing, a compact and lightweight design is obtained and energy losses due to friction and the damping effect of elasticity of the encasing of the high pressure water conduit between the pump and the restriction, where high pressure is converted into the high velocity allowing material to be cut, are substantially reduced. The fixed location of the pump close to the nozzle provides a particularly compact and lightweight construction which allows easy displacement of the water jet cutter, for instance at a construction site and even in and along a scaffolding. According to another aspect of the invention, this object is achieved by providing a water jet cutter according to claim 7. Because the motor is coupled to at least one plunger of the pump via at least one cam member rotationally drivable by the motor, the profile of the cam can be adjusted such that the pump generates a relatively constant flow rate and accordingly a relatively constant cutting power and a relatively constant motor load. Thus, a relatively high effective cutting capacity can be achieved, with a relatively low power motor and without using energy absorbing pressure buffers for producing a constant operating pressure.

Particular elaborations and embodiments of the invention are set forth in the dependent claims.

Further features, effects and details of the invention appear from the detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a frontal cross-sectional view along plane I-I in Fig. 2 of an example of a water jet cutter according to the invention;

Fig. 2 is a cross-sectional side view along the plane II-II in Fig. 1;

Fig. 3 is a perspective view of the cutter according to Figs. 1 and 2, partially cut-away along plane I-I in Fig. 2 and plane II-II in Fig. 1, and

Fig. 4 is a cross-sectional side view along the plane II-II in Fig. 1 of a water jet cutter according to the invention with an alternative design of a cam member.

DETAILED DESCRIPTION

The invention in general and particular features thereof are discussed below and illustrated by an example of a water jet cutter 1 according to the invention shown in Figs. 1-3. The water jet cutter 1 shown in Figs. 1-3 is for cutting materials using a jet of water or a mixture of water and an abrasive substance at high velocity. To that end, the water jet cutter 1 has two low pressure water inlet conduits 2. Two pumps 3 are each located downstream of one of the water inlet conduits 2. A motor 4 is coupled to the pumps 3 for driving the pumps 3. High pressure water conduits 5 extend downstream of the pumps 3 and unite upstream of a restriction 6 (also known as an orifice) forming a downstream end of the high pressure water conduits 5. The restriction 6 allows water to exit the high pressure water conduits 5 only at a small flow rate but, due to the large pressure drop maintained over the restriction 6, while being accelerated to a high speed. A high speed nozzle 7 with a focus tube extends downstream of the restriction 6. A pump housing 8 contains the high pressure water conduits 5. The restriction 6 and the high speed nozzle 7 are fixedly mounted to the pump housing 8. The restriction preferably has a diameter of less than 0.3 mm, more preferably less than 0.2 with further preference for a diameter of 0.1 mm or less, the latter for generating a water jet of 0.1 mm diameter or less.

The motor 4, the pumps 3 and the restriction 6 are preferably arranged for generating a pressure of at least 200 Mpa and more preferably 300 or 400 Mpa, in the high pressure water conduits 5.

Because the pump housing contains the pumps and the high pressure water conduits and the restriction and the high speed nozzle are fixedly mounted to the pump housing, a compact and lightweight design is obtained and very little energy is lost in the damping effect of elasticity of the encasing of the high pressure water conduits between the pumps and the restriction where high pressure is converted into the high velocity allowing material to be cut. The fixed location of the pumps close to the nozzle provides a particularly compact and lightweight construction which allows easy displacement of the water jet cutter, for instance at a construction site and even in and along a scaffolding. Efficiency and compactness is particularly enhanced, because no external piping is present between the pump chamber(s) and the restriction. To this end, the nozzle is preferably mounted directly to the pump housing.

The pump housing 8 has a pump housing block 9 and the pumps 3 each have a pump chamber 10 formed by a cavity in the pump housing block 9. The high pressure water conduits 5 are formed by bores in the same pump housing block 9. The bores are sealed by end stops 11. The common pump housing block 9 in which the pump chambers 10 and the high pressure conduits 5 are formed by cavities forms a particularly rigid encasing of the chambers and conduits subjected to high pressure when the water jet cutter 1 is in operation, so the motor power transferred to the pumps 3 is efficiently converted into water pressure and subsequently speed of the water jetting out of the restriction 6. Furthermore, no external high pressure tubing and connections of such tubing are required, which further contributes to compactness, simplicity and reducing manufacturing costs.

Rigidity of the encasing of the high pressure cavities is further enhanced, because the pump housing block 9 is a single piece pump housing block in which the cavities forming the pump chambers 10 and the high pressure water conduits 5 are located.

Efficiency and compactness are further enhanced, because the motor 4 is fixedly mounted to the pump housing 8.

The pumps 3 each have inlet and outlet valves 12, 13 for opening and closing inlet and outlet ports 14, 15 formed in inlet and outlet port valve seat members 16, 17 of the pump chambers 10. The valve seat members 16, 17 directly and sealingly contact bores 18, 19 in the pump housing 8. Since the valve seat members directly and sealingly contact the bores in the pump housing, pump efficiency is further enhanced, because elastic deformation of sealing members such as O-rings with each pump stroke is avoided, so energy losses associated with such deformations are avoided.

For pressurizing water in the pump chambers 10, plungers 22 are provided. One end of each plunger 22 can be moved into one of the pressing chambers 10 and back to displace and pressurize water in the pump chamber 10 and press the water into the high pressure conduits 5 during each pressing stroke and to draw water into the pump chamber 10 during each return stroke. The plungers 22 are each sealed against a plunger guide 41 by a dynamic high pressure seal 42. The plunger 22 is preferably of a ceramic material, so that a dynamic high pressure seal of a relatively hard material can be used.

Like the valve seat members 16, 17, also the plunger guide 41 and pump chamber plugs 43 directly and sealingly contact bores 44, 45 in the pump housing 8 to reduce flexibility in the boundaries of the pump chambers 10. To ensure that these static high pressure seals do not leak, the valve seat members 16, 17, the plunger guide 41 and the pump chamber plugs 43 each have a threaded portion engaging a threaded portion of the respective bore 18, 19, 44, 45 and a conical sealing surface contacting a conical sealing surface of the respective bore 18, 19, 44, 45. The conical sealing surfaces have a

relatively small taper, preferably 10-20° relative to the central axis and more preferably 13-16° relative to the central axis, the tapering angle of the male part preferably being 0.25 - 1 smaller than the tapering angle of the female part, so that a very tight fit and an accordingly reliable sealing is achieved.

The valve seat members 16, 17, the plunger guide 41 and the pump chamber plugs 43 are all provided in the form of plugs that can be screwed into and out of position from the outside, so maintenance and replacement can be carried out in a simple manner. Also the plungers 22 and the dynamic high pressure seals 42 can easily be reached from the outside after the pump chamber plugs 43 have been removed, so also these parts can be repaired or replaced easily.

The inlet and outlet valves 12, 13 are one-way valves, so the valves are light and no valve control mechanism is required. For closing off the inlet and outlet ports 14, 15, valve members 20, 21 in the form of balls are provided. The balls 20, 21 are preferably of a ceramic material, such as S13N4 Because such material is very hard, the valve members have a high wear resistance and because of the low specific weight of ceramic material, a fast opening and closing action of the valve members is achieved.

The motor 4 is coupled to the plungers 22 via a cam member 23 that is rotationally drivable by the motor 4. Using a cam member for transferring motor power to the pump plunger allows determining the time-displacement profile of the plungers at a given rate of rotation in accordance with pressure build-up and other requirements with a simple, robust construction. Driving the pump using a cam member is particularly advantageous in combination with high pressure conduits in the pump housing and the restriction and the nozzle fixed to the pump housing because it further contributes to a compact architecture and because a constant flow rate generated by the pump is of particular importance if there is relatively little flexibility in the conduit between the pump chamber and the restriction. Nevertheless, the advantage that coupling the motor to the pump via a cam member allows determining the time-displacement profile of the plungers at a given rate of rotation in accordance with pressure build-up and other requirements with a simple, robust construction can also be achieved without a pump housing containing the high pressure water conduit and without the restriction and the high speed nozzle being fixedly mounted to the pump housing.

In the present example, the cam member 23 is carried by bearings 24,

25 on opposite sides of the cam member 23. An outer one of the bearings 24 is mounted in the housing block 9 of the pump housing 8 so it is accurately and rigidly positioned and the inner one of the bearings 25 is mounted in a transmission housing 26 mounted between the motor 4 and the housing block 9 of the pump housing 8. The transmission housing 26 also carries a first gear wheel 27 coaxial with a drive shaft 28 of the motor 4 and mounted thereto so as to be fixed in rotational sense for co-rotation with the drive shaft 28. A common bearing 29 mounted in the transmission housing 26 carries both the first gear wheel 27 and the drive shaft 28 of the motor 4. Teeth of the first gear wheel 27 engage teeth of a second gear wheel 30 coaxial with the axis of rotation 31 of the cam member 23. In the present example, the first and second gear wheels 27, 30 are dimensioned to cause the second gear wheel 30 and the cam member 23 to rotate with a rotational velocity lower than the rotational velocity of the motor drive shaft 28 and the first gear wheel 27.

The cam member 23 has a contiguous profile (visible as the

circumferential contour of the cam member 23 in Fig. 1) composed of a plunger pressing section 32 and a plunger return section 35. The cam member profile is shaped such that the plunger pressing section 32 extends at a radial distance p to the rotational axis 31 of the cam member 23 which gradually increases over the pressing section 32 in a first sense of rotation 33 for pressing the plungers 22 to press water out of the pump chambers 10 as the cam member 23 is rotated in a second, opposite, operating sense of rotation 34. The plunger return section 35 of the cam member profile extends at a radial distance p to the rotational axis 31 of the cam member 23 which gradually decreases over the plunger return section 35 in the first sense of rotation 33 for allowing the plungers 22 to return as the cam member 23 is rotated further in the second, operating sense of rotation 34. A circle 36 coaxial with the axis of rotation 31 of the cam member 23 and marking with a radius equal to the smallest distance p from the cam member profile to the axis of rotation 31, to better visualize the plunger displacements Δρ into the pressing chambers 10 effected by the cam member 22 in relation to the circumferential position on the cam member profile.

The plunger return section 35 extends over a smaller angular arc than the plunger pressing section 32. Thus, the time during which the plungers 22 return after having pressed water out of the pressing chambers 10 is each time relatively short and periods during which the plungers are pressing water into the high pressure conduit show a considerable mutual overlap and periods during which none of the plungers 22 is pressing water into one of the high pressure conduits 5 do not occur. Preferably, the angular arc occupied by the plunger return section 35 is less than one third and more preferably less than one fourth of the angular arc occupied by the plunger pressing section 32.

For returning the plungers 22 quickly after each pressing stroke, plunger return springs 36 are provided which bias the plungers towards the cam profile. Because the plunger return section 35 of the cam profile is shorter than the plunger pressing section 32, it forms a relatively steep ramp so the return pressure exerted by the springs 36 onto the plunger return section 35 significantly contributes to driving the cam member 23 in the second, operating sense of rotation, so that a temporarily increased angular velocity of the cam member 23 is obtained, which in turn increases the velocity at which the other plunger 22 is pressed into the associated pressing chamber 10. This provides some compensation for the temporary absence of pressing action exerted by the returning plunger 22. This effect can also be achieved in a water jet cutter with more than two pressing plungers driven by cam followers circumferentially distributed around the cam member.

In the plunger pressing section 32, the radial distance of the cam member profile to the rotational axis 31 of the cam member 21 increases over the pressing section 32 in the first sense of rotation 33 opposite to the second, operating sense of rotation 34 at a constant rate per unit of angle of rotation for pressing the plungers 22 to press water out of the pump chambers 10 at a constant speed as the cam member 23 is rotated at a constant angular velocity. Thus, the rate at which water is pressed into the high pressure conduits 5 is essentially constant over the pressing stroke of each plunger 22 (except for variations in the angular velocity of the cam member, for instance during the return stroke of another one of the plungers as described above) and the torque required for driving the pump varies very little. Accordingly a relatively constant water supply and pressure is achieved and water supply pressure is efficiently used for generating a high speed jet with constant cutting capacity.

The plungers 22 are coupled to the cam member 23 via cam follower rollers 37, so that friction at the cam surface is substantially reduced. Friction is further reduced, because the cam follower rollers 37 are rotatably suspended via needle bearings 38. Instead of needle bearings, other bearings, such as plain (friction) bearings may also be used.

The cam follower rollers 37 are suspended from cam follower guides, which each have a face 40 contacting an end surface of a plunger 22 of the pumps 3. Because the plungers 22 are actuated via a cam follower guide lateral forces exerted by the cam followers due to friction and sloping of the cam surface in relation to the circle 36 coaxial with the axis of rotation 31 of the cam member 23 are not transferred via the plungers 22, so lateral loading of the plungers 22 and associated friction are avoided.

The cam follower guides 39 are provided in the form of pivotably suspended arms, so that movement of the cam follower guides 39 even when loaded by cam follower load components perpendicular to the plungers 22 entails very little friction.

In the present example, two plungers 22 are simultaneously coupled to the motor 4 via a common cam surface in positions uniformly distributed in rotational sense around the axis of rotation 31 of the common cam surface. Loads exerted by the cam followers 37 are oriented in opposite directions and therefore cancel each other out at least partially, so that loads exerted on the bearings 24, 25 via which the cam member 23 is suspended are reduced and also friction is reduced accordingly, which further contributes to an efficient conversion of motor power into cutting jet effectivity. The uniform distribution around the common cam surface of the positions where the cam surface is coupled to the plungers also contributes to a uniform pumping action and therefore relatively little variation in pumping pressure. It is noted that these advantages of actuating the plungers via positions on the cam surface that are uniformly distributed in circumferential sense can also be achieved if the plurality of plungers is larger than two, for instance three, four or more.

Since in the present example the two plungers 22 have center lines oriented in diametrically opposite directions perpendicular to the axis of rotation 31 of the common cam surface, a compact structure with short high pressure conduits 5 is obtained.

For easy handling of the water jet cutter 1, a handle 46 is provided, which is connected to the pump housing 8 via an arm 47 in a position such that, when the centre of gravity of the water jet cutter 1 is vertically below the handle 46, the nozzle 7 is oriented vertically downward for directing the water jet vertically downward. However, for safety reasons, the water jet cutter 1 is preferably operated while supported by a stand equipped with shielding for avoiding that body parts such as a hand or a foot of the user are cut by the water jet.

For increasing the cutting effectivity of the water jet, an abrasive can be admixed to the water jet in a mixing chamber 48. For supplying the abrasive, an abrasive supply conduit 49 is provided.

Such a pressure allows cutting many building materials, for instance containing quartz, such as roofing tiles for a sloping roof to be arranged along oblique edges, dormers and chimneys, which are often cut on the roof with angle grinders. When grinding such tiles a large amount of dust is formed.

In particular the emission of silica dust has a negative impact on the health of worker and on productivity. Vision is often temporarily impaired and dust masks are uncomfortable and do not allow free breathing. Also cleaning of dust from the construction and tools is time consuming.

Solutions for catching away the dust are difficult to implement without severely restricting freedom of movement of the worker on the roof. More in particular, solutions involving suction typically only remove dust on the upper side of the material being cut and a good seal on non-planar materials (such as a roof tile, with its curvature) is usually not possible, so that much of the dust escapes and the required extraction system has to be moved separately of the cutter, which hampers ease of use and flexibility drastically. Also disposal of dust and maintenance of filtering means entails additional costs and

complexity. Solutions involving water addition require the supply and disposal of large amounts of water, where in particular the disposal of a stream of water colored with particles is difficult and tends to smear facades and gardens.

Because, compared to other cutting techniques, the width of the cutting slit is very small, water consumption is very low and only a minimal amount of material is transformed into powder. Compared with a conventional diamond blade, which cuts a slit of about 3.2 mm wide, the material in this slit being transformed into dust, the width of a cut made by a water cutter according to the present invention is much narrower, preferably only 0.1 mm, i.e. about 32 times smaller. Thus, the amount of dust that is generated is much smaller and can be bound with the relatively small volumes of water of the cutting jet. In water jet cutting, the particles are instantly wet and, at least most of the particles, will not be become airborne and spread as a cloud of dust.

Since a water jet cutter can replace the angle grinder, it does not constitute an additional piece of equipment that has to be taken along onto the roof.

In Fig. 4, a water jet cutter 101 is shown which is equal to the water jet cutter according to Figs. 1-3 except for the shape of the cam member 123. As the cam member 23 shown in Figs. 1-3, the cam member 123 has a contiguous profile with a plunger return section 135 at a radial distance p to the

rotational axis 131 of the cam member 123 which gradually decrease over the plunger return section 135 in a first sense of rotation 133 for allowing the plungers 122 to return as the cam member 123 is rotated further in a second, operating sense of rotation 134 opposite to the first sense of rotation 133. Also in the cam member 123, a plunger pressing section 178, 179, 180 extends at a radial distance p to the rotational axis 131 of the cam member 123 which gradually increases over the plunger pressing section 178, 179, 180 in the first sense of rotation 133 for pressing the plungers 122 to press water out of the pump chambers 110 as the cam member 123 is rotated in the second, operating sense of rotation 134 opposite to the first sense of rotation 133. Over a subsection 179 of the plunger pressing section 178, 179, 180, the increase of the radial distance p to the rotational axis 131 of the cam member 123 in the first sense of rotation 133 has a higher rate per angle of rotation than over remaining sections 178, 180 of the plunger pressing section. The subsection 179 with the higher rising rate extends over a range angularly spaced from the plunger return section 135 over the angle between the positions where the cam followers 137 contact the circumference of the cam member 123. Thus, at a given angular velocity, one of the plungers 122 is actuated via the subsection 179 with the higher rising rate each time while the other plunger 122 is returning under control of the plunger return section 135. Thus, each time one of the plungers 122 returns, the other plunger is urged into the pumping chamber 110 at a higher velocity than the velocity at which the plungers 122 are moved into the pressing chambers while both plungers 122 are each being pressed into one of the pumping chambers 110. This does at least provide some compensation for the temporary absence of the pressurizing effect of one of the plungers 122 during its return.

The rate at which the distance p increases per unit of angular

displacement in the high rising rate subsection 179 may for instance be twice the rate at which the distance p increases over the other subsections 178, 180 of the plunger pressing section 178, 179, 180, so that in principle each time full compensation for the absence of the pressing action of one of the plungers would be achieved.

In addition to this variant, many other variants are conceivable within the framework of the invention as defined by the appending claims. For instance a single plunger pump or more than two plunger pumps can be provided instead of a two plunger pump as shown and described. Also, one or more cam followers of a different design or no cam followers can be provided. In the latter example, the plungers could directly contact the cam profile and/or could be guided using low friction lateral bearings, such as linear ball bearings. Furthermore, the pump drive train could also be provided in another form, for instance with a motor driving a crankshaft coupled to the plungers or in the form of a hydraulic or pneumatic motor in which the plungers are driven by suitably switching fluid pressure received from an external pressure source. The operating pressure of the fluid would then preferably be much lower than the pressure in the high pressure conduit between the pump chamber and the restriction.