EP0522512B1 - Process and installation for the thermic treatment of workpieces - Google Patents

Abstract

In a process for the thermic treatment of workpieces, the workpieces are moved on grates (24) through at least one furnace chamber (26) of a furnace (10). For advance, the grates (24) are raised from the furnace floor during a lifting phase, then in the raised state moved translationally in the direction of transport, preferably via a pusher (28), and finally set down again on the furnace floor in a lowering phase. As a result of the translational movement in the raised state of the grates, frictional forces are avoided and operational safety is increased. A furnace for implementing the process has at least two slides arranged one above the other under the grates (24), the upper slide being raisable in relation to the lower slide, in order to lift the grates (24) from the furnace floor, and both slides being displaceable together in the raised position for transport of the grates (24). Both slides preferably have inclined planes lying on one another in order to make possible raising or lowering of the upper slide. <IMAGE>

Description

• zunächst der obere Schieber in der Hubphase angehoben wird, bis die Roste vom Ofenboden abgehoben sind,
• in der anschließenden Vorschubphase beide Schieber vorgeschoben werden, um die Roste translatorisch in Transportrichtung zu bewegen,
• in der anschließenden Absenkphase der obere Schieber auf den unteren Schieber abgesenkt wird, und
• beide Schieber in einer anschließenden Rückschubphase in ihre Ausgangsposition zurückbewegt werden.

The invention relates to a method for the heat treatment of workpieces, in which the workpieces are moved on grates in a transport direction through at least one furnace chamber of a furnace and the grids are lifted off the furnace floor during a lifting phase or set down again on the furnace floor during a lowering phase two slides arranged below the grids, of which an upper slider is supported on a lower slider, whereby the grids are advanced

• first the upper slide is raised in the lifting phase until the grids are lifted off the furnace floor,
• in the subsequent feed phase, both slides are pushed forward in order to move the gratings translationally in the transport direction,
• in the subsequent lowering phase, the upper slide is lowered onto the lower slide, and
• both slides are moved back to their starting position in a subsequent push-back phase.

• mindestens zwei unterhalb der Roste übereinander angeordnete Schieber, wobei der obere Schieber gegenüber dem unteren Schieber anhebbar ist, um die Roste vom Ofenboden abzuheben und die beiden Schieber in der angehobenen Position gemeinsam zum Transport der Roste verschiebbar sind, und
• einen Durchstoßer, der in Transportrichtung am unteren Schieber angreift, und
• einen Rückschieber, der entgegen der Transportrichtung am unteren Schieber angreift.

The invention further relates to a furnace for the heat treatment of workpieces, with at least one furnace chamber, with grates for receiving the workpieces and with a transport device for transporting the grids through the furnace chamber along a transport direction, the transport device comprising:

• at least two sliders arranged one above the other below the gratings, the upper slider being able to be raised relative to the lower slider in order to lift the gratings off the furnace floor and the two slides can be moved together in the raised position for transporting the gratings, and
• a piercer, which acts on the lower slide in the direction of transport, and
• a back pusher, which acts against the transport direction on the lower pusher.

To increase the throughput, industrial furnaces are usually designed as continuously or intermittently operating furnaces. The individual workpieces or batches are transported in cycles on grates within an oven chamber. The term "grates" is to be understood broadly below, so that this term also baskets or the like. includes. Various transport systems are known for transporting the grids within an oven space.

In particular in industrial furnace systems with carburizing gas atmospheres and high throughput, push-through transport systems are preferred because of the high operational reliability. The individual grids are arranged one behind the other in the transport direction and are pushed through the furnace in cycles through a piercer at the end of the furnace. This structure has proven itself particularly because of the simple mechanics.

However, the puncture principle also has a number of specific disadvantages. For example, the oven must always be operated with the full number of grates, which means, for example, when empty at the weekend that empty grates must be moved between the occupied grates. The heating of this "dead weight" increases the energy requirement of the furnace. In addition, the supply of empty gratings in automatic operation means additional effort and additional malfunctions. Furthermore, the number of grids that slide against one another is limited, since the grates that follow must absorb the pushing torque of the leading grids. Since the grate grows considerably during continuous operation at high temperatures, it is also not possible to guide the grids sideways, which means that there is a transport fault considerable damage in the oven, for example on the heating, can result. Finally, due to the frictional contact between the grates and the furnace floor, there is considerable wear on the floor and the grates.

In addition, walking beam transports are known in which the gratings are lifted and moved forward by walking beams. The walking beams are each articulated to at least two rotary drives, so that an approximately elliptical movement curve results for the walking beam. During the lifting phase, the walking beam is raised and moved forward in the transport direction. As soon as the walking beam lifts the grids off the furnace floor, they are moved in the transport direction. After reaching the culmination point, the lowering phase of the walking beam begins, in which the grids are moved forward until they are put back on the furnace floor and the walking beam is finally moved back to its starting position by further rotation of the rotary drives. Walking beam transports are only used sporadically in gas atmospheres, since complex and therefore fault-prone mechanics have to be installed in the hot furnace chamber. In addition, the constantly moving up and down walking beam creates a pumping effect that undesirably affects the gas atmosphere.

A device of the type mentioned at the outset which overcomes the disadvantages discussed above is known from GB-A-1 417 373.

In such a furnace, the workpieces to be treated are lifted off the furnace floor during a lifting phase, transported during a feed phase and placed on the furnace floor in a lowering phase. In order to carry out the individual movement phases mentioned above, there is a transport device in the furnace provided, which consists of one or more pairs of slides, which are arranged below the workpieces. Each pair consists of an upper and a lower slide. The upper and the lower slide have guide surfaces designed as inclined planes, on which the upper slide is supported on the lower slide. In a starting position, the lower and upper slides are positively on top of each other. By moving the lower slide relative to the upper slide by means of a return slide against the transport direction, the upper slide is raised by sliding onto the lower slide. The upper slide is held in place by a stop opposite the return slide. After the workpieces have been lifted off the furnace floor in this way, a piercer pushes the lower slide in the transport direction. The upper slide follows the lower slide due to a frictional contact that exists between the guide surfaces of the lower and upper slide. Subsequently, by pushing the lower slide further in the transport direction, the upper slide is lowered again onto the lower slide by holding the upper slide spatially fixed by a second fixed stop at the end of the furnace lying in the transport direction. Finally, both slides lying on top of each other in a form-fitting manner are pushed back into the starting position by means of a back slider, and the cycle begins again.

While in the embodiment variant explained above two drives are required for the movement of the slide, an alternative is also known from GB-A-1 417 373, in which all movements of the two slide are conveyed by a single rotary drive which is connected to a connecting rod attacks the lower slide.

The invention has for its object to develop a method and an apparatus of the type mentioned in such a way that the operational safety of such a system is further improved.

According to the invention, the object is achieved according to the method mentioned at the outset in that in the feed phase both slides are moved forward together by means of a pusher acting on both slides, and in the lowering phase the upper slider is moved back against the transport direction by means of a pusher.

According to the invention, the object is achieved according to the oven mentioned at the outset by the fact that the pusher also acts on the upper slide in the feed phase and that a pusher is arranged at the end of the transport device lying in the transport direction, which acts on the upper slide in the lowering phase against the transport direction.

This completely solves the task.

Because both slides are moved forward together in the feed phase by means of a pusher acting on both slides, the operational safety is increased in such a way that in the event of increased frictional resistance when the slides pass through the guides due to increased abrasion or soot formation or falling clamping workpieces a premature lowering of the upper slide on the lower slide and thus an undesired premature depositing of the workpieces on the furnace floor is prevented.

A particular advantage of the combination of a push-through with a push-off and a push-back is to be seen in the fact that the entire movement sequence of the transport system can be controlled via pushing parts, which results in an extremely simple, less prone to failure mechanism.

In a preferred embodiment of the furnace, the slides have guide surfaces lying one on top of the other for lifting and lowering the upper slide.

The guide surfaces can be coordinated so that the desired displacement in the vertical direction results.

The conversion of a movement in the horizontal direction into a movement in the vertical direction can be achieved in a particularly simple manner in that the guide surfaces are in relation to one another parallel inclined planes of the upper slide or lower slide are formed.

When using guide surfaces in the form of inclined planes or also differently shaped guide surfaces, frictional contact of the guide surfaces occurs with a relative movement of the slide, but the frictional forces are limited to the guide surfaces, which can be designed accordingly. In contrast, the grates are moved against the furnace floor without wear.

In a further embodiment of the invention, eccentric elements can be provided between the two slides to raise and lower the upper slider.

In this way, frictional contact between the two sliders and thus wear due to friction is completely avoided. The use of eccentric elements means a somewhat more complicated structure of the mechanics, without, however, reducing operational reliability. The adjustment movement of the eccentric can be done via a separate drive, in addition the eccentric can also be coupled to a common linkage that triggers a rotation of the eccentric and thus a lifting or lowering movement by moving the slide in the longitudinal direction.

In a further embodiment, a link guide can be provided between the two slides, in which a cam engages.

In this way, any movement curves can be achieved during the lifting and lowering phase.

In an additional development, the slides are guided in guides on the furnace floor.

Since lateral guidance is also possible, this results in a significant improvement in operational safety. Even asymmetrically loaded grids, which could possibly be rotated in a conventional push-through furnace due to the different frictional forces and could thus lead to considerable damage to the furnace system, can be easily transported with this version.

In a further embodiment, the transport device is modular, i.e. composed of individual modules, which are arranged one behind the other in the transport direction.

Individual slide elements are therefore provided, from which the upper or lower slide is assembled in a modular manner. This modular design means that the transport system can be easily adapted to a desired furnace length, which is determined by the number of grate locations, and the number of spare and wear parts can be reduced.

The modular structure also significantly increases the flexibility in building and operating the furnace. For example, with a two-lane furnace, it is possible to set different dwell times for the individual workpieces in the furnace by pushing grids across the previously calculated gap locations on the opposite path. In this way, almost any dwell times can be set within the limits of the throughput times of the different lanes.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

Fig. 1

eine Aufsicht eines erfindungsgemäßen Ofens in schematischer Darstellung;

Fig. 2a

einen Querschnitt des Ofens gemäß Fig. 1 mit auf dem Ofenboden abgesenkten Rosten;

Fig. 2b

einen Querschnitt gemäß Fig. 2a mit vom Ofenboden abgehobenen Rosten;

Fig. 3a

einen Längschnitt durch einen Teil der Ofenkammer gemäß Fig. 1 mit auf dem Ofenboden aufliegenden Rosten in schematischer Darstellung;

Fig. 3b

einen Längsschnitt gemäß Fig. 3a mit vom Ofenboden angehobenen Rosten;

Fig. 4a

einen Längsschnitt durch einen Teil der Ofenkammer mit auf dem Ofenboden aufliegenden Rosten in einer gegenüber Fig. 3 abgewandelten Ausführung in schematischer Darstellung;

Fig. 4b

einen Längsschnitt gemäß Fig. 4a in der Hubphase;

Fig. 4c

einen Längschnitt gemäß Fig. 4b in der Vorschubphase;

Fig. 4d

einen Längsschnitt gemäß Fig. 4c in der Absenkphase;

Fig. 4e

einen Längsschnitt gemäß Fig. 4d in der Rückschubphase;

Fig. 5

einen Längsschnitt durch den Teil einer Ofenkammer in einer weiteren, gegenüber Fig. 4 abgewandelten Ausführung und

Fig. 6

einen Längsschnitt durch den Teil einer Ofenkammer in einer weiteren, gegenüber Fig. 5 abgewandelten Ausführung.

Preferred embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it:

Fig. 1

a top view of an oven according to the invention in a schematic representation;

Fig. 2a

a cross section of the furnace of Figure 1 with the grate lowered on the furnace bottom.

Fig. 2b

a cross-section according to Figure 2a with grate lifted off the furnace floor;

Fig. 3a

a longitudinal section through part of the furnace chamber according to FIG 1 with grids resting on the furnace floor in a schematic representation.

Fig. 3b

a longitudinal section according to FIG 3a with grates raised from the furnace bottom.

Fig. 4a

a longitudinal section through a part of the furnace chamber with grates resting on the furnace floor in a modified embodiment compared to FIG. 3 in a schematic representation;

Fig. 4b

a longitudinal section of FIG 4a in the lifting phase.

Fig. 4c

a longitudinal section of FIG 4b in the feed phase.

Fig. 4d

a longitudinal section of FIG 4c in the lowering phase.

Fig. 4e

a longitudinal section of FIG 4d in the retraction phase.

Fig. 5

a longitudinal section through the part of a furnace chamber in a further, modified version compared to FIG. 4 and

Fig. 6

a longitudinal section through the part of a furnace chamber in a further, modified from FIG. 5 embodiment.

1 shows an oven designated overall by the number 10. A furnace chamber 26 is enclosed by a furnace housing 12, through which a plurality of gratings 24 can be moved by means of a transport device 14.

The gratings 24 can be pushed into the furnace chamber 26 via a pusher 18 and an inlet door 16 and can be extended from the furnace chamber 26 via an ejector 22 and an outlet door 20 at the other end. A pusher is used to advance the grids 24 28 is provided, for pushing back or pushing back a push-back 32 or a push-off 30 are provided at the outlet of the furnace chamber 26, the function of which will be explained in the following.

The principle of operation of the transport system 14 can be seen from FIGS. 2a and b. While the grids 24 are placed on the furnace floor 34 in the basic position according to FIG. 2a, they are lifted off the furnace floor 34 for advancement according to FIG. 2b.

The transport system 14 has a lower slide 38 and an upper slide 36, which are arranged below the grids 24 and wherein the upper slide 36 is supported on the lower slide 38.

According to FIGS. 3a and b, parallel guide surfaces in the form of inclined planes 44 and 42 are provided on the lower slide 38 and on the upper slide 36. The inclined planes 42, 44 are connected by bearing surfaces 45 and 43 of the upper slide 36 and of the lower slide 38 parallel to the furnace floor 34, so that both slides 36, 38 have a sawtooth shape in longitudinal section. The upper slide 36 and the lower slide 38 are divided into individual modules 40 which are arranged one behind the other in the transport direction 46. 3a shows the basic position in which the two slides 36, 38 lie flat on one another and the grids 24 are on the furnace floor 34.

In FIG. 3b, the upper slide 36 has been displaced in the transport direction 46 relative to the lower slide 38, as a result of which the upper slide 36 has been displaced relative to the inclined plane 44 of the lower slide 38 by displacing its inclined plane 42 compared to the latter was raised until both support surfaces 43, 45 parallel to the furnace floor 34 rest on one another. Then, in the next phase (not shown in FIG. 3), both sliders 36, 38 are moved forward for transport in the manner described below.

The individual phases of the movement sequence are shown in FIGS. 4a-e.

FIG. 4a shows the upper slide 76 and lower slide 78 of the oven, designated overall by the number 50, in the basic position in which the grids 64 rest on the oven floor 74. The construction of the furnace 50 corresponds to the construction of the furnace 10, only the two slides 76, 78 differing from the slides 36, 38 described above in that none between the inclined planes 82, 84 of the upper slider 76 and lower slider 78 support surfaces parallel to the furnace floor 74 are provided.

Here, too, the upper slide 76 and the lower slide 78 consist of individual modules 80 arranged one behind the other (shown in simplified form). To push the slides 76, 78 in the transport direction, a piercer 68, which is driven and guided by a drive 69, is provided at the entrance to the furnace chamber. To counter hold the lower slide 78 and to return both slides 76, 78, a return slide 72 is provided at the opposite end of the furnace chamber, which is driven and guided by a drive 73.
In order to push the upper slide 76 against the transport direction from a raised position for lowering into the basic position, 72 is also above the return slide a pusher 70 is provided which is driven and guided by a drive 71. For reasons of clarity, the drives 69, 71, 73 are not shown in the following FIGS. 4b-e.

The piercer 68 has a nose 66 protruding in the transport direction and a vertical thrust surface 67 set back in the transport direction. To lift the upper slide 76 relative to the lower slide 78, the piercer 68 is moved in the transport direction by its drive 69, the lower slide 78 being held in its initial position by the return slide 72. The nose 66 of the piercer 68 protruding in the transport direction pushes the upper slide 76 obliquely upwards on the inclined planes 82, 84, so that the grids 64 are lifted off the furnace floor 74 according to FIG. 4b.

As soon as the thrust surface 67 of the piercer 68 strikes the lower slide 78, the return slide 72 is retracted as shown in FIG. 4c, so that both pushers 76, 78 can be moved together in the transport direction by means of the piercer 66 in order to move the grids 64.

According to FIG. 4d, the upper slide 76 is now moved back against the transport direction by advancing the pusher 70, so that the upper slide 76 moves downward.

As soon as the upper slide 76 has reached its lower end position, the pusher 70 is withdrawn, and both slides 76, 78 are moved back in their starting position according to FIG. 4e by pushing the return slide 72 against the transport direction.

Figures 5 and 6 show a slightly modified structure of the furnace.

5, an upper slide 126 and a lower slide 128 are also provided in order to lift the grids 114 from the furnace floor 124 and to move them forward. Instead of the inclined planes described above, eccentric elements 130 are arranged between the upper slide 126 and the lower slide 128, via which the upper slide 126 can be moved upwards in order to lift the grids 114 off the furnace floor 124. An additional mechanism can be provided for actuating the eccentrics 130, but the eccentrics 130 can also be rotated via a common push rod 132, which is shown in broken lines in FIG. 5 and is connected to the eccentrics via joints 134. The push rod can protrude in the direction of the push rod, so that the eccentrics are actuated when the push rod hits the push rod 132.

6 shows a further modification of the furnace according to the invention, which is generally designated by the number 140. This embodiment differs from the embodiment according to FIGS. 3a and b in that instead of inclined planes on the lower slide 168, slide guides 174 are provided, which engage in the cams 172 of the upper slide 166. A predetermined movement curve when raising and lowering the upper slide 166 relative to the lower slide 168 can be set by the link guide. The remaining movement sequence corresponds entirely to the movement sequence in the embodiment according to FIGS. 3a and b.

Claims (8)

1. Process for the thermal treatment of workpieces, in which the workpieces are moved on grates (24; 64; 114; 154) in a direction of transport (46) through at least one furnace chamber (26) of a furnace (10; 50; 100; 140) and the grates (24; 64; 114; 154), for advancement purposes, are lifted during a lifting phase from the furnace bottom (34; 74; 124; 164), or are re-deposited during a lowering phase on the furnace bottom (34; 74; 124; 164), having two slides (36, 38; 76, 78; 126, 128; 166, 168) which are disposed beneath the grates (24; 64; 114; 154) and of which an upper slide (36; 76; 126; 166) is supported on a lower slide (38; 78; 128; 168), in which case, for the advancement of the grates (24; 64; 114; 154),

   - firstly the upper slide (36; 76; 126; 166) is raised in the lifting phase until the grates (24; 64; 114; 154) are lifted from the furnace bottom (34; 74; 124; 164),

   - in the following advancement phase, both slides (36, 38; 76, 78; 126, 128; 166, 168) are advanced so as to move the grates (24; 64; 114; 154) in a translatory motion in the direction of transport (46),

   - in the following lowering phase, the upper slide (36; 76; 126; 166) is lowered onto the lower slide (38; 78; 128; 168), and

   - both slides (36, 38; 76, 78; 126, 128; 166, 168), in a following reversal phase, are moved back into their original position,

   characterized in that

   - in the advancement phase, both slides (76, 78) are moved jointly forward by means of a pusher (66-68) acting upon both slides (76, 78), and

   - in the lowering phase, the upper slide (76) is moved back counter to the direction of transport (46) by means of a down-slide (70).
2. Furnace for the thermal treatment of workpieces, having at least one furnace chamber (26), having grates (24; 64; 114; 154) for the reception of the workpieces and having a transport device (14) for the transport of the grates (24; 64; 114; 154) through the furnace chamber (26) along a direction of transport (46), the transport device (14) comprising:

   - at least two slides (36, 38; 76, 78; 126, 128; 166, 168) disposed one above the other beneath the grates (24; 64; 114; 154), the upper slide (36; 76; 126; 166) being able to be raised relative to the lower slide (38; 78; 128; 168) so as to lift the grates (24; 64; 114; 154) from the furnace bottom (34; 74; 124; 164), and the two slides (36, 38; 76, 78; 126, 128; 166, 168), in the raised position, being jointly displaceable for the transport of the grates (24; 64; 114; 154), and

   - a pusher (28; 66-68), which acts in the direction of transport (46) upon the lower slide (38; 78; 128; 168), and

   - a return slide (32; 72), which acts counter to the direction of transport (46) upon the lower slide (38; 78; 128; 168),

   characterized in that the pusher (66-68), in the advancement phase, acts additionally upon the upper slide (76) and in that at that end of the transport device (14) situated in the direction of transport (46) there is disposed a down-slide (70), which acts in the lowering phase counter to the direction of transport (46) upon the upper slide (76).
3. Furnace according to Claim 2, characterized in that the slides (36, 38; 76, 78; 166, 168) have guide faces resting one upon the other for the raising and lowering of the upper slide (36; 76; 166).
4. Furnace according to Claim 3, characterized in that the guide faces are configured as mutually parallel, oblique planes (42, 44; 82, 84) of the upper slide (36; 76; 166) and lower slide (38; 78; 168) respectively.
5. Furnace according to one of Claims 2 to 4, characterized in that for the raising and lowering of the upper slide (126) eccentric elements (130) are provided between the two slides (126, 128).
6. Furnace according to one of Claims 2 to 4, characterized in that for the raising and lowering of the upper slide (166) there is provided between the two slides (166, 168) a connecting link guide (174), in which a cam (182) engages.
7. Furnace according to one of Claims 2 to 6, characterized in that the slides (36, 38; 76, 78; 126, 128; 166, 168) are guided in guides (39) on the furnace bottom (34; 74; 124; 164).
8. Furnace according to one of Claims 2 to 7, characterized in that the transport device (14) is made up of individual modules (40; 80) disposed one behind the other in the direction of transport (46).

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