GB2059941A - Tempering apparatus for glass sheets - Google Patents

Abstract

A tempering assembly for glass sheets comprises a load station conveyor, a furnace conveyor, a quench unit conveyor and an unload station conveyor in succession as well as a drive unit operatively connected to each conveyor and adapted during transport cycles to operate the conveyors synchronously at the same speed to transport glass sheets from each conveyor to the succeeding conveyor and during oscillating cycles between the transport cycles to drive the furnace and quench unit conveyors, as well as the glass sheets thereon, in an oscillating manner, with the furnace and quench unit conveyors being driven at optionally different stroke lengths. To achieve this, the drive motor (5) is coupled to one of the furnace and quench unit conveyors (12,47) via fixed transmission means (25) and to the other conveyor via alternately actuated fixed transmission means (33,34) (during the transport cycle) and variable gear means (37) (during the oscillating cycle). <IMAGE>

Description

SPECIFICATION Tempering assembly for glass sheets Background of the invention The present invention relates to a tempering assembly for glass sheets.

More particularly, the present invention relates to a tempering assembly for glass sheets comprising successively a load station, furnace, quench unit and unload station, each being provided with a horizontal conveyor formed by a horizontal roller table for supporting and conveying glass sheets in a horizontal plane. The furnace defines a passageway extending in the conveying direction, the opposite ends of the passageway comprising horizontal slits for the glass sheets to pass through, and the furnace is provided with heating elements for heating the glass sheets substantially to their softening temperature.

The tempering assembly further includes drive means operationally connected to each conveyor.

During transfer cycles the drive means operate the conveyors to move the glass sheets from load station to furnace, from furnace to quench unit and from quench unit to unload station. During the oscillating cycles between these transfer cycles, the drive means operate the furnace and quench unit conveyors, as well as the glass sheets thereon in an oscillating manner.

This type of apparatus has been disclosed in the United Kingdom Patent Publication 1 527 782. This type of apparatus has the characteristic of being suitable for small numbers of glass sheets of varying sizes and thicknesses as the time that the glass sheets spend in the furnace can be selected as desired by selecting the duration of the oscillating cycle, the duration being a constant experimentally predetermined for each type of glass. In this respect the continuously operated furnaces are different in that they are only suitable for large series of glass sheets of similar type since the minimum length of a continuously operated furnace is determined according to the heating period and minimum velocity of travel and, in addition, changing these conditions (feeding velocity and temperature) for a new type of glass requires a long time.In a tempering furnace whose temperature is approximately 700"C, glass sheets (thickness 5 mm) must remain approximately 200 seconds for them to reach their softening temperature of about 360"C, the minimum travel speed being approximately 10 -15 cm/s. This clearly proves that continuously operated furnaces are necessarily of considerable lengths.

For these reasons it is often more advantageous to have tempering plants in which the conveyors of the furnace and quench unit are driven in an oscillating or reciprocating manner during the heating and quenching cycles of the tempering process. Such a plant or assembly can be adjusted rapidly so as to comply with the conditions required by a new and different type of glass, whereby the plant can be used for tempering small amounts of varying types of glass sheets. Moreover the shortness of furnace and quench unit saves space and expenses.

The purpose of the oscillating motion is to eliminate the sagging of glass sheets between the rollers of the roller table. This sagging phenomenon is particularly critical during the last oscillating movement in the furnace when the glass sheet is at its softest.

United Kingdom Patent Publication 1 527 782 discloses suitable data for oscillation speeds, acceleration and travel distances by which the sagging between the rollers and resultant noticeable warpings in the glass sheet can be eliminated. A problem encountered here is the transfer of the glass sheet from furnace to quench unit since the velocities of the furnace and quench unit must be accurateiy synchronized to each other for this transfer cycle.

This problem could be resolved by making equal the lengths of the furnace and quench unit and by driving them both always synchronously and at common speeds. However this solution is not economically acceptable since the quench unit with its conveyor and a plurality of tubes for blowing cooling air is very expensive and thus must be dimensioned to be as short as possible in view of the conditions of quench technology. In the quench unit, the glass sheets only need be moved sufficiently for even distribution of cooling air on the glass sheet surface.

Thus the quench unit will be considerably shorter than the furnace and also the distance of oscillation required in the quench unit will be shorter. Thus the problem resolves to one of driving the conveyor of the furnace on one hand and that of the quench unit on the other in such a manner that during the oscillating cycle the stroke length of the quench unit oscillation is shorter than that of the furnace but during the transfer cycle from one section to the other the conveyor speeds are accurately synchronized to each other. United Kingdom Patent Publication 1 527782 does not disclose any particular design solution to this problem but only indicates that the drives of the quench unit and furnace conveyors can be separate and independent of each other or synchronized to each other.

In the glass sheet tempering apparatus disclosed in U.S. Patent No. 3,994,711, 1,the problem has been resolved by two separate, independently operated drive motors which drive the furnace and quench unit conveyors. However, the problem has only been resolved as far as the oscillation cycle is concerned, since there will be problems in providing a long conveying stroke in the transfer cycle for moving the glass sheets from the furnace conveyor to the quench unit conveyor. Since there is no solid or mechanical connection between the furnace and quench unit conveyors, their speeds must be synchronized during the transfer cycles by electronic control of separate drive motors.

It is an object of the present invention to provide a tempering assembly in which movements of the furnace and quench unit conveyors can be optimally controlled with respect to each other during both the oscillating cycles and the transfer cycles.

Summary of the invention It has now been found that the above and related objects of the present invention may be achieved by providing the furnace and quench unit conveyors with a common drive motor coupled to one of the furnace and quench unit conveyors by means of a fixed transmission and to the other of the furnace and quench unit conveyors by both a fixed transmission and a variable gear. Control means are provided for determining the optimum setting of the variable gear and optimizing the overall operation of the apparatus, as described in more detail below.

More particularly the present invention resides in a tempering assembly for glass sheets comprising in succession a load station, a furnace, a quench unit and an unload station, each being provided with a horizontal conveyor for supporting and conveying glass sheets in a horizontal plane. The furnace defines a passageway extending in the conveying direction, with opposite ends of the passageway comprising horizontally extending slits for the glass sheets to pass through, and includes means for heating the glass sheets substantially to their softening temperature in the furnace.The tempering assembly further includes drive means operationally connected to each of the conveyors and adapted during transfer cycles to operate the conveyors to move the glass sheets from the load station to the furnace, from the furnace to the quench unit, and from the quench unit to the unload station and during oscillating cycles between the transfer cycles to drive the furnace and the quench unit conveyors as well as the glass sheets thereon in an oscillating manner. The drive means includes a common drive motor for the furnace and quench unit conveyors, first fixed transmission means for coupling the drive motor to one of the furnace and quench unit conveyors (usually the former) and both second fixed transmission means and variable gear means for alternately coupling the drive motor to the other of the furnace and quench unit conveyors (usually the latter).

In a preferred embodiment, the tempering assembly additionally includes a first clutch connecting the drive motor to the variable gear means and a second clutch connecting the drive motor to the second fixed transmission means, whereby, with the first clutch open and the second clutch closed, the furnace and quench unit conveyors are adapted to be driven synchronously at the same speed. The tempering assembly additionally includes a third clutch connecting the drive motor to the load station conveyor and a fourth clutch connecting the drive motor to the unload station conveyor, whereby with the second, third and fourth clutches closed, all of the conveyors are adapted to be driven synchronously at the same speed for moving glass sheets from one of the conveyors to another thereof over a certain predetermined transfer distance.

To maximize automation,thetempering assembly should additionally include means for controlling the drive means, the control means including means for entering and storing said predetermined transfer distance. The control means additionally includes a timing element, means for entering and storing a heating period duration factor, means for selecting a stroke length for reciprocating the drive motor during said oscillating cycles and means for selecting a transmission ratio for the variable gear means.

The control means further includes means, operative after the conveyors have been synchronously driven over the predetermined transfer distance, for stopping the drive motor, controllably closing the first clutch and opening the second, third and fourth clutches, and thereafter controllably reciprocating the drive motor, whereby the furnace and quench unit conveyors are driven synchronously by the drive motor with optionally different stroke lengths, and means, operative after the expiration of the heating period duration factor, for opening the first clutch and closing the second, third and fourth clutches, thereby to initiate a transport cycle.The control means additionally includes means for entry and storage of the lengths of the glass sheets moving into the furnace and first means for calculating the length of the distance to be traveled by the glass sheet in the furnace back and forth. Sensing means are effectively disposed at the terminal end of the load station and associated with the control means, and sensing means being adapted during the conveying cycle to feed into the control means information on the length of the glass sheet moving into the furnace.

In fact, the control means includes means for entry and storage of information on two succeeding lengths of glass sheets, the first length being the length of the trailing sheet in the furnace and the second length being the length of the leading sheet in the quench unit as well as second means for calculating the length of the distance to be traveled by the glass sheet in the quench unit back and forth, and third means for calculating the transmission ratio to be set on the variable gear means. More particularly, the control means is adapted to calculate the transmission ratio as the ratio of the length of distance traveled by the glass sheet in the quench unit back and forth, relative to the length of the distance traveled by the glass sheet in the furnace back and forth.

One form of the invention will now be described with reference to the accompanying drawings.

Brief description of the drawings Figure 1 is a schematic side elevation view of a tempering assembly according to the present invention; Figure 2 is a diagram of the drive assembly of the tempering assembly of Figure 1; and Figure 3 is a block diagram of the drive assembly control system.

The glass sheet tempering assembly comprises in successive order a load station 1, furnace 2, quench unit3 and unload station 4. In a known and conventional manner, each of these is filled with horizontal roller tables provided by rollers 10, 20, 30 and 40, said tables supporting and conveying the glass sheets through the assembly. The conveyors provided by each roller table are in Figure 2 generally indicated by reference numerals 11,12,47 and 48.

Each roller is coupled to a common drive by means of a web or chain connecting the drive wheels at the ends ofthe rollers. Since the detailed design, bearings and drive of the rollers is well known, they need not be further described in this context, but reference is made for example to U.S. Patent Nos.

3,994,711; 1,856,668; 1,879,998; 3,447,788 and 3,594,149.

Furnace 2 defines a through-passage 21 whose opposite ends are shaped like horizontal slits and define an entrance opening 23 adjacent load station 1 and exit opening 24 adjacent quench unit 3. The furnace includes heating resistors 22 for maintaining its temperature at approximately 700"C.

The quench unit 3 comprises, on opposite side of the roller table 30, cooling air blowing means 31 and 32. Each means 31,32 comprises a large number of parallel tubes disposed at small distances from each other, the cooling air being blown through the tubes onto the opposite surfaces of one or more glass sheets located upon the rollers 30.

The conveyor drive assembly, as presented in Figure 2, comprises a common drive motor 5 which through a fixed transmission 25 drives the drive wheel 26 of the furnace conveyor 12 (comprising the roller table formed by rollers 20). Through a web, chain, belt or like transmission band 6, the drive motor 5 is arranged to drive the quench unit conveyor 47 in a two-way manner. On the one hand, transmission band 6 drives, via a magnetic clutch 33, a band 34 which in turn drives the drive wheel 35 of quench unit conveyor 47. The fixed transmission ratio of the drive effected via band 34 is selected to be such that furnace and quench unit conveyors 12 and 47 have exactly the same speed.On the other hand, with the magnetic clutch 33 coupled off, band 6 drives, via a magnetic clutch 36 and variable gear 37, a transmission means 38 (comprising a band, chain, gearwheel transmission or the like) which in turn drives the drive wheel 35. The variable gear 37 can comprise either a mechanical, e.g., 5-step gear wheel, or a stepless hydraulic gear. When the variable gear 37 is driven, the speed of quench unit conveyor 47 is always lower than that of furnace conveyor 12, the ratio depending on the gear selected. Magnetic clutches 33 and 36 are operated so that when one of them is closed the other is always open. From the drive wheel 35 power is transmitted by means of a band, chain or gear wheel transmission 41, via a magnetic clutch 43, to drive wheel 42 of the unload conveyor 48.Magnetic clutch 43 is always on together with magnetic clutch 33 and always off when magnetic clutch 36 is on.

Drive motor 5, also drives, via a transmission band 7 and a magnetic clutch 18, a band 19 which in turn drives the drive wheel 17 of the load conveyor 11. On the other hand, drive wheel 17 is also coupled via a band 16 to drive wheel 15 which in turn is driven by a setting motor 13 over a magnetic clutch 14. Setting motor 13 and magnetic clutch 14 are controlled by means of a press button 49 which is pressed after glass sheet loading upon the load conveyor 11 is completed. The terminal end of load conveyor 11 is provided with an optical or electric eye 45 which detects the leading and trailing edges of the glass sheets.When the glass sheets are being fed in the furnace, this sensing means 45 provides information on the length of a glass sheet or a batch of glass sheets fed in at any given time, such information being fed into control means such as the microprocessor 8. On the basis of this information and the prefed constant data based on constructional dimensions of the tempering assembly, the microprocessor 8 performs calculations to be discussed in more detail below and, on the basis thereof, controls the operation of drive motor 5 and the magnetic clutches. In addition, this control means includes an adjustable switch clock 9 on which the heating time required by each type of glass sheet is set prior to feeding the glass sheet into the furnace 2. By means of an impulse giver 44, microprocessor 8 continuously monitors the travel distances of drive motor 5.

The following describes the operation of the tempering assembly.

With the preceding glass sheet being heated in the furnace 2, the succeeding glass sheet (whose length is indicated by letter 1) is placed on the load area L and the receipt button 49 is pressed. This closes magnetic clutch 14 and actuates setting motor 13 to move the glass through distance A until the glass leading edge reaching the sensing means 45. Then the sensing means 45 provides an impulse, thus stopping the setting motor 13 and opening the magnetic clutch 14. The glass remains on load conveyor 11 and waits in this initial position until the glass sheet in the furnace reaches the quench temperature determined by the period pre-set on the switch clock 9.Upon completion of this period, clock 9 provides a control impulse, thus closing magnetic clutches 18, 33 and 43 and subjecting drive motor 5 to the long transport stroke of the transfer cycle which transfers glass sheets from conveyors 11, 12 and 47 onto the following conveyors 12, 47 and 48, respectively. Transmission ratios are selected such that during the transport stroke each conveyor advances at the same speed.

The operation of magnetic clutches is effected with the furnace conveyor 12 stopped.

The length of transport stroke B can be adjusted by the operator and set in the microprocessor 8, this distance determining the point at which the leading edge of the glass stops in the furnace 2. Without as yet dealing with the operation of the quench unit and unload station conveyors, the following examines the operation of the furnace conveyor 12. Upon the completion of the transverse by the glass sheet of set transfer distance B, the magnetic clutch 18 opens and the reversible drive motor 5 reverses its direction, thereby beginning oscillation of the glass in the furnace 2 with the stroke length x1. The maximum speed of oscillating motion can in the beginning be the same as the set transfer speed of the long transport stroke, e.g., 0.5 - 1 misec. If a heating period set on the clock 9 is said to be T, after period 0.05 - 0.15 x Tthis maximum speed can be reduced to some desired set oscillation speed, e.g., 0.1 - 0.3 m/sec.

The effective inner length C of the furnace limits the distance between the leading and trailing edges of the glass sheet in the terminal positions of the oscillating motion. Length C can be specified by the operator and set in microprocessor 8 as a setting value. Microprocessor 8 receives the glass sheet length 1 from sensing means 45 when the glass sheet is being fed in the furnace. Thus, microproces sor 8 is able to calculate the length of oscillation stroke x1 required according to the length 1 of a given glass sheet to be fed in, the calculation being based on the formula xl = C1. Thereafter microprocessor 8 controls the reversible electric motor 5 at the abovementioned speeds and with stroke length x1.

Since, for moving the glass sheet from furnace 2 to quench unit 3, the leading edge of the glass sheet must always commence from a certain point, the microprocessor 8 will change the set instruction speed of oscillation to just such a degree that, after the period T, the leading edge of the glass sheet will be positioned at the desired last point of reversal (as shown by the glass sheet in phantom). This is the commencing point of the long stroke of the transfer cycle and at a distance Z from the point which the leading edge of the glass reaches during the oscillating cycles. The distance Z is defined by the formula Z = 2B - E wherein E is the distance between the sensing means 45 and the extreme position of the leading edge of the glass sheet in quench unit 3. The distance E is a function of the tempering apparatus and is pre-set into the microprocessor 8 by the operator.

The following again deals with a step when all conveyors are driven synchronously and at the same speed in the long transport stroke of the transport cycles. With the long transport stroke produced to such an extent that the length 1 of the glass coming in the furnace has been measured, the microprocessor 8 must calculate a new setting value for the variable gear 37 and adjust the working means of gear or variator 37 to their new value prior to the end of the long stroke. The minimum time for calculation and necessary adjustment is 3 seconds and a typical time is 4-5 seconds. Accuracy of the adjustment can be approximately +20%, i.e., adjustment can be effected also stepwise.For adjustment of setting gear 37, the microprocessor 8 must first calculate the length of reciprocating movement x2 of the quench unit conveyor 47, such length being determined according to the glass sheet length 12 in the quench unit and the available quench unit length D as follows: x2 = D - 12. Forthis calculation process, the microprocessor must hold in its memory not only the length 1 of the glass sheet in the furnace 2 but also the length 12 of the glass sheet transferred into the quench unit 3, which lengths can be different.

This, amongst other factors, enables the apparatus effectively to temper glass sheets of various sizes in small series.

After this the microprocessor 8 will calculate transmission ratio kofvariable gea r o r va riato r 37 from the formula k = x21x1. If the variable gear is stepped, the nearest available transmission ratio to k will be used. Afterthe long transport stroke, magnetic clutches 18, 33 and 43 open and magnetic clutch 36 closes, whereafter microprocessor 8 controllably reciprocates the electric motor 5 so as to oscillate furnace and quench unit conveyors 12 and 47 with stroke lengths x1 and x2, which stroke lengths depend on lengths 1 and 12 of the glass sheets in the furnace as well as the effective lengths of the furnace and quench unit, the latter lengths having been selected as desired in view of their optimum functions.

Although the invention has been described, for the sake of simplicity, in terms of a single glass sheet being placed on the load station at a time, it is natural that, when tempering smaller glass sheets, an arbitrary number of glass sheets may be placed on load area L, all these sheets thereafter moving simultaneously as one batch in the same manner as one glass sheet. In this case, for a determination of the length 1 of the entire batch of glass sheets, the microprocessor 8 selects the first and last pulse of the sensing means 45 as indicating the leading and trailing edges of the entire batch of glass sheets, whereby the entire length of the batch can be determined as in the case of one glass sheet.

It will be appreciated that the effective inner lengths C of the furnace and D of the quench unit are physical parameters entered into the system control means by the operator in accordance with the configuration of the particular tempering apparatus.

The set transfer distance B (representing the distance from the sensing 45 means to the extreme leading edge of the glass sheet in the furnace 2 during an oscillating cycle) and the distance E (representing the distance for the sensing means 45 to the extreme leading edge of the glass sheet in the quench unit 3 during an oscillating cycle) are similarly physical parameters related to the configuration of the tempering apparatus and entered by the operator into the system control means. The heating period duration T is determined by the type or quality of glass to be tempered (and in particular by its thickness), and is entered by the operator into the clock 9 of the system control means. The lengths of the glass sheets in the furnace 1 and in the quench unit 12 are provided to the control means by the sensing means 45.The remaining variable factors such as the furnace stroke length x1 and quench unit stroke length x2 are calculated from the aforementioned data available in the control means, and the transmission ratio k for the variable gear 37 is similarly calculated by the control means for the stroke lengths x2 and x1. Thus the quality of succeeding glass sheets may vary in nearly an arbitrary manner, with the control assembly automatically regulating the conveyors so as to operate in an optimum manner. When the quality of glass sheet changes, the operator only needs to know the new glass sheet thickness and set in the clock 9 a heating period predetermined for the new sheet thickness.

It will be appreciated further that by coupling the drive motor to one of the furnace and quench unit conveyors by a fixed transmission means and to the other of the furnace and quench unit conveyors alternately by fixed transmission means and variable gear means, the present invention enables said conveyors to be driven by a common electric motor over the entire effective lengths thereof, regardless of the mutual differences in the effective lengths thereof and the differences in the lengths of succeeding batches of glass sheets thereon. As the variable gear means enables the furnace and quench unit conveyors to be driven at different speeds during the oscillating cycles, so the fixed transmission means enables both conveyors to be driven synchronously at the same speed during the transport cycles.

Now that the preferred embodiments of the present invention have been shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be limited only by the appended claims, and not by the foregoing disclosure.

Claims (13)

1. Tempering assembly for glass sheets comprising (A) in succession a load station, a furnace, a quench unit and an unload station, each being provided with a substantially horizontal roller table forming a horizontal conveyor for supporting and conveying glass sheets in a substantially horizontal plane, said furnace defining a passageway extending in the conveying direction with opposite ends of said passageway comprising substantially horizontally extending slits for the glass sheets to pass through, said furnace including means for heating the glass sheets substantially to their softening temperature in said furnace; and (B) drive means operationally connected to each of said conveyors and adapted during transfer cycles to operate said conveyors to move the glass sheets from said load station to said furnace, from said furnace to said quench unit, and from said quench unit to said unload station and during oscillating cycles between said transfer cycles to drive said furnace and said quench unit conveyors as well as the glass sheets thereon in an oscillating manner, said drive means including a common drive motor for said furnace and quench unit conveyors, first fixed transmission means for coupling said drive motorto one of said furnace and quench unit conveyors, and both second fixed transmission means and variable gear means for alternately coupling said drive motor to the other of said furnace and quench unit conveyors.

2. Tempering assembly according to Claim 1, additionally including a first clutch connecting said drive motor to said variable gear means and a second clutch connecting said drive motor to said second fixed transmission means, whereby, with said first clutch open said second clutch closed, said furnace and quench unit conveyors are adapted to be driven synchronously at the same speed.

3. Tempering assembly according to Claim 2, additionally including a third clutch connecting said drive motor to said load conveyor and a fourth clutch connecting said drive motor to said unload station conveyor, whereby with said second, third and fourth clutches closed, all of said conveyors are adapted to be driven synchronously at the same speed for moving glass sheets from one of said conveyors to another thereof over a certain predetermined transfer distance.

4. Tempering assembly according to Claim 3, additionally including means for controlling said drive means, said control means including means for entering and storing said predetermined transfer distance.

5. Tempering assembly according ta Claim 4, wherein said control means additionally includes a timing element, means for entering and storing a heating period duration factor, means for selecting a stroke length for reciprocating said drive motor during said oscillation cycles and means for selecting a transmission ratio for said variable gear means.

6. Tempering assembly according to Claim 5, wherein said control means further includes means, operative after said conveyors have been synchronously driven over said predetermined transfer distance, for stopping said drive motor, controllably closing said first clutch and opening said second, third and fourth clutches, and thereafter controllably reciprocating said drive motor, whereby said furnace and quench unit conveyors are driven synchronously by said drive motor with different stroke lengths, and means, operative after the expiration of said heating period duration factor for opening said first clutch and closing said second, third and fourth clutches, thereby to initiate a transport cycle.

7. Tempering assembly according to Claim 4, 5 or 6, wherein said control means additionally includes means for entry and storage of the lengths of the glass sheets moving into said furnace and first means for calculating the length of the distance to be traveled by the glass sheet in said furnace back and forth.

8. Tempering assembly according to Claim 7, wherein said control means is adapted to calculate the length of the distance to be traveled by the glass sheet in said furnace back and forth according to the formula x, = C - L wherein x, is the length of the distance to be traveled by the glass sheet in said furnace back and forth, C is the distance between the leading and trailing edges of the glass sheet in said furnace at extreme positions during said oscillating cycles, and L is the length of the glass sheet moving into said furnace.

9. Tempering assembly according to Claim 8, additionally including sensing means effectively disposed at the terminal end of said load station and associated with said control means, said sensing means being adapted during the conveying cycle to feed into said control means information on the length of the glass sheet moving into said furnace.

10. Tempering assembly according to Claim 9, wherein said control means includes means for entry and storage of information on two succeeding lengths of glass sheets, the first length being the length of the trailing sheet in said furnace and the second length being the length of the leading sheet in said quench unit, means for calculating the length of the distance to be traveled by the glass sheet in said quench unit back and forth, and means for calculating the transmission ratio to be set on said variable gear means.

11. Tempering assembly according to Claim 10, wherein said control means is adapted to calculate the length of the distance traveled by the glass sheet in said quench unit back and forth according to the formula x2 = D -- 12 wherein x2 is the length of the distance traveled by the glass sheet in said quench unit back and forth, D is the length available in the quench unit and 12 is the length of the glass sheet in the quench unit whereafter the control means is programmed to calculate the transmission ratio to be set on the variable gear means from formula k = x2/x,.

12. Tempering assembly according to Claim 11, wherein the variable gear means is stepped and transmission ratio (h) will be the transmission ratio of the nearest step.

13. Tempering assembly substantially as shown in the accompanying drawings and described herein with reference thereto.