Ejection device

Aug. 10, 1965

3,199,740

R. JUFFA ETAL

EJECTION DEVICE

Filed Aug. 7, 1963

FIG. 1

<img file="US3199740A_D0001.tif" />

<img file="US3199740A_D0002.tif" />

FIG. 2 inventors:

RICHARD JUFFA, HELMUT KRUGER, RUDOLF MICHAELIS

HANS-JOACHIM REH BERG, JOSEF SCHMAHL™

HANS-HERMANN SCHULZ n

ATTORNEYS

United States Patent Office

3,199,740

Patented Aug. 10, 1965

3,199,740

EJECTION DEVICE

Richard feffia and Helmut Kruger, Leverkusen, and Rudolf Michaelis, Cologne-Deutz, and Hans-Joachim Rehberg, Josef Schmahl, and Hans-Hermann Schulz, Leverkusen, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a corporation of Germany

Filed Aug. 7, 1963, Ser. No. 300,428

Claims. (Cl. 222—146)

The invention relates to an ejection device for ejecting and applying extremely small quantities of compositions which are liquefied or softened by heat action, e.g. thermoplastic plastics, comprising an ejection cylinder which can be heated electrically and in which is displaceably arranged a piston fixed to the end of a push rod.

The heating of ejection cylinders has hitherto been effected by encircling them with electric heater strips or by induction. The expense of equipment combined therewith is uneconomical for extremely small ejection devices. Furthermore, the use of such heating methods is not desirable for such instruments for reasons of dimensions and weight. The high heat capacity necessary with strip heating necessitates long heating up and cooling times and consequently the use of separate cooling means.

It has now been found that these disadvantages are obviated if the ejection cylinder or a part thereof is heated according to the invention by direct passage of electric current. Depending on the requirements of the local heating intensity and the heat conduction, the ejection cylinder according to the invention has a wall thickness which increases or decreases steadily or suddenly in the direction of ejection.

The result hereby obtained is that the heating and cooling times of the cylinder are very short and thus the material being processed is protected. When using the instrument as a dental ejector, the inconvenience to the patient is slight, due to the fact that it is possible to dispense with an additional cooling. The direct heatting of the cylinder admits the use of the lowest possible voltages, e.g. 2 volts, so that any danger to the patient or dentist is excluded. Moreover, the instrument can be made with extremely small dimensions such as have not so far been possible, e.g. with cylinder and nozzle diameter below 10 mm. and even down to 1-2 mm., since heating coils, induction coils and cooling systems are omitted. The composition to be sprayed is supplied as a granulated material or in the form of a small rod to the cylinder.

The advancing movement of the piston can be effected manually or also pneumatically.

For the pneumatic advancing movement and for the subsequent firm pressing of the ejected compositions on to the application surface, the ejection cylinder is enclosed by a pneumatic pressure cylinder, which is provided on the inlet side of the pressure medium with a closable opening or a resilient branch tube.

In the accompanying drawings:

FIGURE 1 is a diagrammatic longitudinal section through one embodiment of the complete device, and

FIGURE 2 is a diagrammatic longitudinal section showing the head of a second embodiment of the device.

Referring to FIGURE 1, in a pressure cylinder 1, under the influence of compressed air supplied at 9, a piston 2 slides towards the left against the force of the spring 3 and carries with it a small ejection piston 5 connected to the piston 2 by the piston rod 4. When the pressure is relaxed, the spring 3, which is supported on an insulating guide member 6 and the circlip 7, forces the piston back to its starting position, which is determined by en30 .

gagement of the insulating cap 8 with the cylinder end. In the arrangement illustrated, an increase in pressure is produced from the compressed air entering the nozzle 9 by blocking the end of a spring tube 10, which forms the air outlet, by pressing the tube opening onto an elastic disc 11.

As shown in FIGURE 2, the blocking of the outlet can be effected by closing a suitably arranged opening 12 in a branch pipe 13 of the compressed air supply by means of a finger.

The compressed air contributes to the cooling of the device when the piston is not actuated. By using an inert gas instead of the compressed air, a protective gas atmosphere can be formed in addition to the dissipation of heat. For injecting into deep cavities and also for better cleaning, the small ejection piston can be advanced to beyond the opening of the ejection cylinder 18 surrounding it.

A sleeve 15 is inserted in the pressure cylinder 1 so that it can be easily released by a bayonet connection 14, which sleeve co-axially retains the ejection cylinder 18 (made of corrosion-resistant metal of high specific electrical resistivity) by means of a heat-insulating intermediate member 16 and brazed webs 17 which are of low heat conductivity because of their small cross-section.

The ejection cylinder 18 is connected by conductors 19 and 20 to a low voltage source and is thus heated. By local reduction of the external diameter, the current density is increased at those places where higher heating capacity is required. The external diameter of the ejection cylinder decreases for example towards the ejection aperture (FIGURE 1); on the other hand, for improving the heat conduction, the external diameter can be generally increased outside the electrically heated region (e.g. at the projecting tip). If desired, the orifice of the heated ejection cylinder can be constricted by screwing on a nozzle.

The sleeve 15, and also the pneumatic cylinder 1, is coated with a fluorolefine lining 21 or 22 which is made suitable for gripping (e.g. by sand-blasting), the tube 10 being embedded in said lining. The lining 21 has an opening which is connected through bores to the atmosphere and is also cooled by the air stream discharging from the tube 10 in the rest position. One or both electrical conductors can be placed inside the compressed air tube adjoining the nozzle 9 for purposes of better handling.

The device operates as follows:

A small rod of suitable dimensions of thermoplastic material or a few granules thereof are placed in the opening of the cylinder 18. The opening is then optionally constricted by screwing on a nozzle. The heating is switched on and off or increased and reduced by a temperature-controlled switch or a time switch adjusted to values obtained by experience. The device is gripped like a pencil and is positioned on the cavity which is to be filled, which is possibly preheated or is pretreated with a solvent or even with a release agent. Finger pressure on the small tube 10 discharging cooling air in the rest position figure or closing of the opening 12 (FIGURE 2) leads to the hot composition being ejected by means of the mechanism described; pressure can be maintained as long as desired by means of the piston, whereby a union with the foundation material and good filling of the cavity is guaranteed and any possible occurring shrinkage compensated for.