Method and device for washing and drying glass tubes for lamps

Details Method and device for washing and drying glass tubes for lamps Method and device for washing and drying glass tubes for lamps

1999-02-05

2001-02-13

Beck, Shrive (Department: 1762)

Coating processes

Electrical product produced

Hollow article

C427S157000, C427S231000, C427S346000, C427S372200, C118S055000, C118S312000, C118S416000, C118S681000

Reexamination Certificate

active

06187373

ABSTRACT:

The invention relates to a method and a device for producing bulbs for lamps, in particular discharge lamps and/or fluorescent lamps. It follows thus that it relates to a part of the method for producing fluorescent lamps, to be precise, in particular, that in which the glass tubes generally used as lamp tubes are coated from inside with a fluorescent layer which is as uniform as possible, and this layer is dried thereafter.
To date, methods have been used for this purpose in which, during coating, the lamp tubes stand or are suspended vertically and are coated with a pasty coating means starting from the top side.
Drying has also been performed in a vertical position by feeding warm air from above and partly also from below or by infrared radiation from outside with simultaneous air flushing of the interior of the lamp tube.
The following disadvantages have become plain in this case:
In order to ensure that the inflowing coating means is distributed on the inner wall of the lamp tubes as far as the upper end, appropriately shaped coating valves and relatively high inflow rates have been necessary. This holds, in particular, for lamp tubes with so-called “roll-ins”, that is to say tapers at the tube ends. It was particularly problematical in this case to pass the coating means into the upper shoulder region produced by the roll-in. The required high flow rates led, on the one hand, to contamination problems for the corresponding device or system and, moreover, caused eddies of the coating means in the lamp tube which become visible in the finished lamp in the form of streaks, cloudiness, stripes or run-off noses.
Furthermore, there were irregularities in the layers to be produced, specifically in the form of oblique coating edges on the upper tube ends in the case of inexactly centered lamp tubes or incomplete coverage in the case of lamp tubes not suspended or standing exactly vertical.
The following difficulties arose in connection with the drying:
Hot air drying systems require long drying times and require a considerable amount of space, in particular in the case of continuously traversing bulbs. Furthermore, irregular layer thicknesses occur over the length of the lamp tubes, in particular very thin layer thicknesses occur at the upper end and undesirably large thicknesses at the lower end. Moreover, the hot air leads to the formation of stains in the coating of those bulb regions which are touched by the bulb supporting elements.
In the case of infrared drying, it has been necessary to rotate the lamp tubes about the longitudinal axis of the tube in order to achieve uniformity of the layer thicknesses. The required rotation devices have not only been relatively expensive but also vulnerable—particularly in connection with contamination problems caused by the coating. Furthermore, glass breakage has led to a high rate of rejection.
Independently of the above discussions, the invention proceeds very generally from a method for producing bulbs for lamps, in which lamp tubes are coated with a coating means and dried thereafter, and from a device for carrying out this method.
The term “tube” comprises in this case all suitable shapes with two open ends which can be connected by an axis, here termed longitudinal axis; symmetry is not required.
The technical problem on which the invention is based here is to improve said method and said device with regard to their operating characteristics and their efficiency.
This problem is solved by means of a method in which, during coating and drying, the lamp tubes are arranged with their longitudinal axis at an oblique angle to the horizontal, and by a device having a holding device with one or more lamp tube positions situated at the oblique angle to the horizontal.
The invention renders high flow rates of the coating means superfluous, because owing to the oblique position the upper edge of a lamp tube can be reached much more easily by the coating means. This also holds, in particulr, for lamp tubes with roll-ins or comparable complicating geometrical shapes. The sensitivity with respect to eccentric or tilted positions is also of no importance.
In the case of a partial coating (coating not over the entire circumference but only as longitudinal strips such as, for example, with reflector lamps) the method according to the invention can be carried out successfully without rotation about the longitudinal axis. If, however, a uniform layer is to be produced around the tube circumference, the lamp tubes are rotated about their longitudinal axis in the oblique position. The invention exhibits particular advantages in this case, because it is precisely in the case of lamp tubes coated all round that uniformity is particularly important.
The efficiency of the invention with respect to the uniformity of the layers to be achieved can be further increased when coating and drying are performed not only in the same oblique angular position and with the same rotation about the longitudinal axis, but there is also no interruption of this state of position or movement in the meantime. If changes in the state of position or movement are unavoidable, they should be performed as slowly and uniformly as possible. Specifically, it has proved that any, in particular abrupt change in movement or position leads to impairment of this uniformity. The aim is thus to ensure in the lamp tubes a state of flow which is as continuous and uniform as possible both during coating and during drying.
Devices and methods according to the invention are further simplified by virtue of the fact that the continuity, already addressed, in the oblique position and the rotation about the longitudinal axis is enhanced by a continuous transport process, preferably essentially transverse to the direction of the longitudinal axis. The lamp tubes can thereby be transported simply and uniformly through different stations of a device according to the invention in which coating steps, drying steps and also other method steps are carried out.
With respect to the angle, defining the oblique position, of the longitudinal axis of the lamp tubes to the horizontal, it has proved that the inventive advantages are already achieved by each clear deviation from the vertical position, that is to say approximately from 85°. A lower limit for the angle results from the fact that no gravity flow occurs in the horizontal position. An lower limit can thus be situated at a few degrees, preferably approximately at 5°. It is true that a small angle slows down the flow through the lamp tubes, but it leads to particularly uniform results. Consequently, angles of between 5 and 15° are preferred. However, a suitable lower limit can also be 10°, while suitable upper limits can also be 75°, 60°, 45° or 30°. If a roll-in or taper is present on the lower end of the lamp tubes, this angle is to be increased by an angle typifying the roll-in or taper. Otherwise, there is a risk of coating means building up in front of the lower end, and thus of irregularities being formed in the layer. This characteristic angle is that for which the coating means does indeed run out slowly from the corner formed by the roll-in; it frequently amounts to approximately 45°.
The disadvantages of conventional rotation devices for lamp tubes which have been used in drying by means of infrared radiation have already been described in the above discussions on the prior art. Furthermore, it has already been explained that the invention is advantageously carried out with a rotation of the lamp tubes about the longitudinal axis both during coating and during drying. According to the invention, the device is further developed for this purpose by providing two transport devices instead of one, which act separately on the lamp tubes in such a way that a speed difference between them ensures rotation of the lamp tubes about the longitudinal axis. The disadvantages of the conventional rotation devices are thereby avoided. The solution according to the invention proves effective above all in the case of the said continuous transverse transport o

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