SE437947B - SET FOR THERMOCHEMICAL GAS GRINDING OF A METAL WORK PIECE - Google Patents

Description

7810927-8 2 and become a security risk.

An improvement of the premixed flame was described by Jones et al in U.S. Pat. No. 2,556,19, in which oxygen and fuel gas are combined just before discharge from the nozzle. While this was an improvement over the state of the art, the device was still exposed to backfire. If the outer nozzle came to be clogged, e.g. with metal spray, while the oxygen and fuel gas holes inside the unit remained open, the two gases could be mixed inside the unit, thereby creating an explosive mixture exposed to backlash.

Allmang's U.S. Pat. No. 5,251,451 discloses a premix preheating device in which oxygen and fuel gas combine outside the unit, thereby completely eliminating the possibility of backfire. However, the intensity of the flame generated by this post-mixer is limited. While common method can be used to preheat hot workpieces, the low intensity of the flame requires an unacceptably long time to preheat the cold workpieces.

Lytle's US-PS 5,752,460 discloses a post-mixing preheating device which uses a stream of "trapped" oxygen to reduce the preheating time. While Lytle's invention is an improvement over Allmang, Lytle's device is not capable of preheating relatively cold workpieces quickly enough for commercial operations.

Engel's U.S. Pat. No. 5,966,505 describes a method of flying start in oxygen planing, which reduces the time required for preheating the workpiece to be practically zero.

Engel's method is faster than the method of the present invention; however, Engel's method requires a wire feed mechanism and a high intensity jet of oxygen which are not required by the present invention. Accordingly, the present invention is advantageous when a flying start in oxygen planing is not required, but when a rapid start on cold steel is desired.

Until the present invention, it has not been possible to rapidly preheat a portion of the surface of a relatively cold metal workpiece to gas planer temperature, using a flame, without the risk of back flame or without the use of high intensity wires, blowpipes or other auxiliary materials.

Accordingly, it is an object of the present invention to provide a method of gas planing the surface of a workpiece which provides acceptably short preheating times for gas planing of relatively cold workpieces, without being subjected to back flame and without requiring auxiliary materials. .

Another object of the present invention is to provide a method for producing a premixed gas planing preheating flame which is more intense than that produced by prior art.

The above and other objects, which will be readily apparent to those skilled in the art, are achieved by the present invention, which relates to: methods of thermochemical gas planing of a workpiece comprising: (1) preheating a spot on the surface of the workpiece where the gas planing reaction is to be starting by directing a premixed preheating flame towards said spot, the preheating flame being formed by: (a) discharging at least one stream of preheated oxidizing gas and at least one stream of preheated fuel gas from separate openings in such a way that the currents collide outside their discharge openings, over the working surface and in such a way that the axes of said currents form an acute angle between them, and (b) stabilize said preheating flame by discharging a low-intensity stream of oxidizing gas, the direction of the stabilizing stream being in the same general direction as the direction for said low and close to the impact of said preheated oxidizing gas and preheated fuel gas streams, and (c) proceeding steps (a) and (b) to said spot when its ignition temperature for oxidizing gas, and thereafter (2) directing a stream of planing oxidizing gas at an acute angle to the working surface of said preheated gas. stain, while simultaneously (3) causing relative movement between the gas planer oxidizing gas stream and the work surface, thereby producing a gas planer cut.

The method according to the invention can be carried out by means of a gas planing device consisting of: (a) means for forming a post-mixed preheating flame, (b) means for discharging a stream of oxidizing planing gas through a gas planing nozzle, and (c) means to provide relative movement between the planing oxidizing gas and a workpiece, the means for forming the preheating flame comprising: (1) orifice means for discharging a stream of preheating fuel gas, the shaft of the orifice means being directed towards the workpiece to be gas planed, (2) orifice means for discharging a stream of preheating oxidizing gas, the shaft of the orifice means being directed to intersect the axis of the orifice means of the preheating fuel gas at an acute angle outside the orifices and above the surface of the workpiece and (3) means for discharging a stream of stabilizing oxidizing gas of low intensity, the means consisting of a mouth, the axis of which is directed close to the core between the shafts of the preheating fuel gas orifice and the preheating oxidizing gas orifice and directed in the same general direction as the resultant of said shafts.

The preferred oxidizing gas is oxygen and the preferred acute angle of collision between the preheating streams is from 5 to 500. The preferred embodiment uses the same orifice to deplete the stream of preheating stabilizing oxygen and the planing oxygen stream. In the term "oxidizing gas" as used throughout the present specification and in the claims it is used to refer to a gas containing an oxidizing agent.

The preferred oxidizing gas is commercially pure oxygen, and for simplicity the term "oxygen" is used hereinafter throughout the specification. However, the invention can be applied using oxidizing gases other than pure oxygen. For example, the oxidizing gas for planing and stabilizing may be oxygen having a purity as low as 99%, or lower. However, the results will be worse with especially with oxygen of less than 99% purity. Preheating oxidizing gas may contain as low as 21% oxygen, ie it may be air, but the preheating times will increase with decreasing oxygen percentage in the preheating oxidizing gas stream. 7810027-8 The term "preheating" is used herein to mean that a portion of the surface of a workpiece is brought to its ignition temperature for oxidizing gas; that is, the temperature at which the workpiece will ignite when it is in an atmosphere of oxidizing gas.

Fig. 1 is a side view of a gas planer unit showing a preferred embodiment of the present invention.

Fig. 2 is a sectional view of Fig. 1 taken along line 2-2.

Fig. 3 is an enlarged side view of Fig. 1 showing the key elements according to the invention.

Fig. 4 shows the preferred position of the molten bath with respect to the planing oxygen flow for planing starts on the flat part of a work surface.

Fig. 5 shows a start at the end of a work surface.

Fig. 6 graphically compares the preheating time obtained by applying the present invention with prior art methods for preheating the work surface.

Fig. 7 shows an embodiment according to the invention in which the preheating streams are discharged from the lower preheating block of the gas planing device.

Fig. 8 is a side view of the device with separate ports for stabilizing oxygen and planing oxygen.

Fig. 9 is a front view of the device of Fig. 8 taken along lines 9-9.

Fig. 10 is a front view of an alternative method for designing the device according to Fig. 8.

Figs. 1, 2 and 3 show a preferred embodiment of the invention.

A typical planing unit consists of an upper preheating block 1, a lower preheating block 2, a head 3, and a shoe 4.

Blocks 2 and 3 are called preheating blocks when preheating flames are discharged from these blocks in a conventional device. 7810027-8 However, in the device shown in Figs. 1, 2 and 3, only the flames discharged from the upper preheating block are used for preheating.

A slit-like planing nozzle 16, from which a sheet-like stream of planing oxygen is discharged, is formed by the lower surface 20 of the upper preheating block 1 and the upper surface 21 of the lower preheating block 2.

The lower preheating block 2 is provided with a row of fuel gas openings 19, communicating with usual suitable gas ducts (not shown).

Oxygen and fuel gas are supplied through the head 3 through pipelines (not shown) and then to the respective gas ducts by means well known in the art.

The shoe 4 rides on the surface of the workpiece W during planing to keep the planing nozzle in position with a constant distance Z (Fig. 3) from the work surface.

The gas planing reaction is carried out by striking on a molten bath according to a sheet-like stream of planing oxygen discharged from the nozzle 16 at an acute angle to the working surface, while relative movement is caused to take place between the workpiece and the planing unit.

The upper preheating block is provided with a series of openings 17 for preheating fuel gas and a series of openings 18 for preheating oxygen, each of the openings communicating with supply channels (not shown) for fuel and oxygen, respectively.

While the drawing shows the openings 18 for preheating oxygen located above the openings 17 for preheating fuel gas, a reverse arrangement, although not preferred, will also work.

More generally, it is preferred that the openings for preheating fuel gas be located between the openings for preheating oxygen and the opening for stabilizing oxygen described below, but different arrangements are operable. i '7810027-8 The device works as follows. Preheating oxygen streams 9 from the openings 18 and preheating fuel gas streams 10 from the openings 17 collide to form a combustible mixture. The collision appears as a point 50 in Fig. 5. Upon ignition, the combustible mixture forms a flame 14, which has a low intensity zone 15 and a high intensity zone 12. It has been found that the high intensity zone 12 can be extended so that its tip 27 is just above the surface of the workpiece W, thereby providing a longer, more intense flame, by stabilizing the preheating flame by providing a stream of low oxygen oxygen. intensity immediately adjacent to the point of collision 30 and in the same general direction as flame 14. Bringing the low-intensity current 15 "immediately adjacent to" the point of collision means that the current should approach the point of collision 30, but not through it. While the term "point of collision" has been used here, it should be understood that the term "place or place of collision" would be more correct, since there are many intersecting currents, consequently many points of collision; and further, since the currents are thick, the intersections or intersections are areas rather than just points. Accordingly, for simplification, the term "collision" is used throughout this specification and subsequent claims to refer to the location of the areas of collision between the streams of preheating fuel gas and preheating oxidizing gas. The preferred source of the stabilizing oxygen stream 15 is the planing nozzle 16. Conventional valve means (not shown) are provided to provide the flow of low intensity oxygen 15 (lower in intensity than a planing oxygen stream) through the planing nozzle 16.

The current15 is directed in the same general direction as the flame. Ie. that if current 15 were dissolved in two vector components, one parallel to and one perpendicular to the direction of the flame, the vector component parallel to the flame would point in the same direction as the flame. When applying the embodiment according to the invention shown in Fig. 5 with the preferred values according to Tables I and II, the bearing will be close to the resultant of (or more correctly the bisectisia of the angle formed by) the axes of the preheating oxygen and preheating gas openings. Preferably, the axes of current 15 and flame 14 form an acute angle as shown in Figs. 1 and 5. It is also preferred that the axis of the stabilizing current 15 be parallel to that of the current of preheating fuel gas, which also shown in Figures 1 and 3.

The streams of preheating fuel gas and oxygen must strike each other or collide with an acute angle, ie an angle greater than 0 ° but less than 90 °. The preferred range is 50 to 50 °, and the most preferred collision angle is 15 °.

The stabilizing oxygen stream 15 from the nozzle 16 must be of low intensity, i.e. with a lower nozzle speed than that of preheating oxygen and the fuel gas from nozzles 18 and 17. Preferably, the nozzle speed of the stabilizing oxygen is about 10% of that of the preheating streams.

If the preheating layer is not stabilized as described above, the length of the high intensity zone (from the collision 50 to the tip 27) would be so short that the preheating step could not be performed in acceptably short times unless the holding distance Z was reduced. Reducing the hole spacing Z to bring the tip of the high-intensity zone of an unstabilized flame close to the workpiece would cause the planer unit excessive damage from spray metal and slag than occurs at normal hole spacings.

Flames created by means of fuel gas from lower ports 19 mixed with oxygen from nozzle 16 were used to maintain the gas planing reaction. These flames are not necessary during preheating, but fuel gas should flow from the openings 19 during preheating to prevent its plugging.

After the molten bath is formed at spot 1B, the valve means regulating the oxygen flow from slot 16 is adjusted to increase the intensity of the oxygen flow from low intensity to gas planing intensity, and a relative movement between the workpiece and the planing unit is started, thereby creating a planing cut on the surface at the workpiece. During the planing operation, the preheating layers formed by the currents 9 and 10 are allowed to continue at a lower intensity than during preheating to help maintain the gas planing reaction. A flange 28 arranged over the preheating openings 1? and 18 was used to prevent low intensity flame blowout during gas planing.

There are many design variables to consider in the manufacture of an apparatus for carrying out the method of the present invention, many of which are not independent of each other. For a standard gas planing device, the following are usually fixed: (1) G, the angle between the planing oxygen and the surface of the workpiece, (2) X, the height of the nozzle 16, (3) Z, the hole spacing, (4) U, the width of the planing unit (see Fig. 2), (5) the type of available fuel gas, (6) the type of oxidizing gas available.

For each set of values for the above-mentioned parameters, there will be an operable range and a preferred value for the variables used to design the preheating device in accordance with the invention.

Tables I and II give examples of values which have proved satisfactory for the practice of the invention. Table I lists a set of typical values for parameters for ordinary gas planing equipment, known for achieving good gas planing.

Table IG, angle for planing oxygen 350 X, height of nozzle 16 5.6 mm Z, hole spacing 25 mm U, width of planing unit 270 mm fuel gas natural gas oxidizing gas oxygen Table II indicates operable range and preferred value of variables that proved useful for application of the invention, when the fixed parameters are those shown in Table I. 7810027-8 Table II - Preferred Operable value approximate range Diameter of openings 17 for preheating fuel gas 1.0 mm 0,? - 1.7 mm Flow rate of preheating fuel gas per opening: Distance between the openings for preheating fuel gas (dimension Y, in fig. 2) 6.0 mm 5 - 16 mm 1.7 Nmšh 1 - šöNmšh Diameter of openings 18 for preheating oxygen 1 .6 mm 1 - 2.5 mm Flow rate of preheating 5 5 SVT6 PSI '0PPHl118 = 5.7 Nm h 1.5 ~ 6 Nm h Distance between the openings for preheated oxygen (dimension I, in fig. 2) 6.0 mm Collision angle between the axes of the preheating fuel openings and the axes of the preheated oxygen openings (angle D, in rig. 5) 15 ° Distance 26 between surface 20 and the preheating fuel gas openings 16 mm 5 16mm \ NI 5 ° - so ° 15mm Angle between the shaft of opening for preheating oxygen and workpiece oo (angle H, in rig. 5) 50 40 - 75 Distance 51 and 52 from collision 50 O i to preheating openings 15 mm 5 - 22 mm Distance 29 (see fig 2) between the central lines of opening 17 and opening 18 4 mm 1.5 - 6 mm Flow rate of stabilizing oxygen from slot 16 below sleeve per cm zh 6 Nm of slot width 5 - 10 Nmšh The variables shown in Table II are interdependent.

Therefore, if one is made to deviate significantly from the preferred value, the preferred value and operable range for other variables may change. If any of the fixed parameters according to Table I change, the preferred value and operable range for some of the variables in Table II may change.

Those skilled in the art will appreciate that an almost unlimited number of combinations of values for Tables I and II will give satisfactory results.

The preferred shape of the openings 1? and 18 are circular, but different shapes can work. For example, the openings could be square or rectangular. A single elongate nozzle for preheating oxygen could be used with a single elongate nozzle for preheating fuel gas, although such an arrangement is not preferred. However, the present invention works best if a plurality of openings for oxygen and fuel gas are arranged, arranged in rows opposite each other as shown in Figs. 2 and 10. If a plurality of preheating openings are used, the opening distance, dimension Y in Fig. 2 should be be uniform. Each oxygen port 18 should be directly opposite a fuel gas port 1 ”. This preferred arrangement provides the most uniform and fastest preheating, but a non-uniform opening distance or zigzagged openings for fuel gas and oxygen or both will also work.

Angle F, ie. the angle formed by the axis of the flame 14 with respect to the surface of the workpiece W should be between 40 ° and 550 °, for a holding distance Z of 25 mm. If the angle F exceeds 550, the flame tends to gas chisel the workpiece. If the angle F is less than 400, the tip 27 of the high intensity zone 42 will be too far from the workpiece T to give desired short preheating times. The angle F of the flame is determined by the values of the parameters in Tables I and II. The preferred values for the variables listed above will provide a satisfactory angle for the flame, but those skilled in the art will appreciate that many other successful compositions are possible.

The invention works best if the openings for the preheating gas and oxygen are as close to each other as possible without the gases converging inside the unit, which would create the possibility of premixing and reverse flame.

Fig. 4 shows the preferred position of the starting melting bath B with respect to the extension of the axis 15 of the planing oxygen nozzle 16 in the center line, when starting on the top surface T of a workpiece W. As shown in rig. 4, the oxygen flow from slot 16 should strike the rear end C of the starting melt bath B with respect to the direction of the planar insert or section indicated by arrow J. This position of the starting melt bath allows all molten material from the bath to be blown forward, thereby leaving no to form axes or fins at the posterior end of the incision. If a start is to be made on the end of the workpiece W, as shown in Fig. 5, the results will be satisfactory if the planing oxygen flow from slot 16 strikes any part of the starting melt bath, since there is no working surface T on the rear part of the molten bath, on which ridges can be formed and it does not matter if fins are formed on the end surface E.

Fig. 7 t.o.m. 10 shows alternative embodiments of a gas planer, which, although not preferred, are nevertheless capable of providing a stabilized post-mixed preheating flame.

Fig. 7 is a side view of a planing unit similar to that shown in Figs. 1, 2 and 3, except that the openings for preheating oxygen and fuel gas 18 and 17, respectively, are located in the lower preheating block 2.

The device functions in the same way as the device according to Figs. 1, 2 and 3.

Figs. 8 and 9 show an arrangement in which the stabilizing oxygen is supplied from opening 16 'separately from the slot 16 for planing oxygen. Here, a stream of preheating oxygen 9 from orifice 18 collides with a stream of preheating fuel gas 10 from orifice 17 to form a post-mixed flame 14. The flame is stabilized by a low intensity oxygen stream 15 'from orifice 16', directed immediately adjacent to the collision 30 and in the general direction of the flame.

The preheating and stabilizing openings 17, 18 and 16 'are shown located in the upper preheating block 1.

They could also have been located in lower preheating block 2.

After preheating has been performed, a stream of planing oxygen is connected from slot 16 to plan the workpiece. As previously described, the fuel gas discharged from orifice 19 assists in supporting the gas planer reaction.

Fig. 10 is similar to Fig. 9, except that the stabilizing oxygen comes from an elongate, slit-like nozzle 16 ". The preheating oxygen and fuel could also be supplied from elongated, sludge-like nozzles, although such an arrangement is not preferred. 7810027-8 13 Without wishing to be bound by any particular theory, the following explanation is given of how the invention achieves shorter preheating times. It has been observed that an unstabilized post-mixed flame formed by the collision between a preheating fuel gas and a preheating oxygen alone, tends to have a relatively large low intensity zone and a very small high intensity zone.In some cases no high intensity zone can be observed.An unstabilized post-mixed flame also tends to flutter.If an attempt is made to increase the intensity in an unstabilized flame by increasing the flow of preheating oxygen and preheating fuel gas, fluttering becomes more pronounced.

Finally, the unstabilized flame is blown away from the outflow openings of the preheater through the increased gas flow and extinguished. It has been observed that flanges help to keep the flame in position and allow slightly higher flow rates for preheating gas before the flame is extinguished.

When a post-mixed flame is stabilized by means of a low intensity oxygen stream, in accordance with the invention, the stabilized flame very quickly develops a long, distinct high-intensity zone and fluttering ceases. The flame remains stable even if the flows of preheating fuel gas and preheating oxygen are increased to amounts higher than those that extinguish the unstabilized flame.

The beneficial effect of the stabilizing current, especially when directed as shown in Fig. 5, is believed to be achieved due to the following: (1) Since the stabilizing oxygen is added with a low intensity current, it does not interfere with it. outside the mixture of the preheating oxygen and preheating fuel gas streams. But it adds oxygen which helps to support combustion and creates an oxygen atmosphere surrounding the zone of the flame that has high intensity. This oxygen atmosphere provides an excellent medium for the flame to spread backwards in the direction of the discharge openings for the preheating, igniting non-combusted fuel gas closer to said openings. (2) The stabilizing oxygen flow also forms a shield to protect the flame from air, which does not produce as good a low-spreading medium as oxygen and causes the flame to become unstable and blow away from the preheating discharge openings. 781OÛ27-8 14 Examples based on Tables I and II Gas planing starts on the top surface of a workpiece shown in Fig. 4 were made in the laboratory using a device with values given in Table I and the preferred values according to Table II. The test results are represented graphically by curve X in Fig. 6, in which the initial temperature (TOC) of the workpiece is plotted along one axis, while the required preheating time (t) is plotted in seconds along the other axis. From a comparative point of view, curve Y shows the results obtained under comparable conditions using the gas planer described by Lytle in U.S. Pat. No. 5,752,460, while curve Z shows the results obtainable by means of a conventional post-mixing preheating layer formed from oxygen depleted from gas planer nozzle and fuel jets, as described by Allmang in U.S. Pat. No. 5,254,451.

As shown in Fig. 6, for cold workpieces, the present invention represents a significant improvement over prior art preheating methods, resulting in preheating times less than half of that required by the Lytle method for workpieces over 20,000. The present invention considerably less than half the preheating time according to Lwtle's method. Note that the diagram shows that the "trapped" oxygen method of Iwtle is not capable of achieving preheating times below 20 seconds for workpieces below 25,000, while the present invention requires less than 20 seconds to preheat a workpiece at 0 ° C.

Claims (4)

Ü 7810027-s Patentkrav 1. l. In the case of thermochemical gas planing of a metal workpiece, characterized in that it comprises: (1) preheating a spot on the surface of the workpiece where the gas planing reaction is to begin by directing a postmixed preheating flame towards the spot, thereby heating the preheating flame. by: (a) discharging at least one stream of preheating oxidizing gas and at least one stream of preheating fuel gas from separate openings in such a way that the streams collide outside their discharge openings, over the working surface and in such a way that the axes of the streams form an acute angle between them, and (b) stabilizes the preheating flame by discharging a stream of low intensity oxidizing gas, the direction of the stabilizing stream being in the same general direction as the direction of the flame and the near collision between the preheating oxidizing gas the gas flow and the preheating fuel gas flow, and (c) the steps (a) and (b) until the spot reaches its ignition temperature for oxidizing gas, and then (2) directs a stream of planing oxidizing gas at an acute angle to the working surface at the preheated spot, while simultaneously (3) causing relative movement between the planing oxidizing gas stream and the work surface, thereby creating a gas planing cut. 2. A method according to claim 1, characterized in that the acute angle between the axes of the streams with preheating oxidizing gas and with preheating fuel gas, respectively, is between s ° and so °. k ä n n e t e c k n a t of that it A method according to claim 2, the oxidizing gas is oxygen. 4. A method according to claim 3, characterized in that the stabilizing oxidizing gas and the planing oxidizing gas are discharged from the same opening.