US 3199740 A
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Description (OCR text may contain errors)
Aug. 10, 1965 R. JUFFA EITAL 3,199,740
EJECTION DEVICE Filed Aug. 7, 1963 IN VENTORS I RICHARD JUFFA, HELMUT KRUGER, RUDOLF MICHAEL/5, HANS -JOACH/M REHBERG, JOSEF SU-/MAHL? HANS-HERMANN SCHULZ. t M
M ATTORNEYS United States Patent 3,19%,740 EJECTION DEVIQE Richard Julia and Helmut Kriiger, Levcrkusen, and Eli!- dolf Michaelis, Cologne-Berlitz, and Hans-Joachim Rehherg, Josef Schmahl, and Hans-Hermann Schulz, Leverkusen, Germany, assignars to Farhenfahrilren Bayer Alrtiengesellschaft, Leverkusen, Germany, a corporation of Germany Filed Aug. 7, 1963, Ser. No. 309,428 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 cool ing 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 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 ll, 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 engagement 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 it), 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 etfected 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 13 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 13 is connected by conductors l9 and 2.8 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 l, is coated with a fluorolefine lining 21 or 22 which is made suitable for gripping (e.g. by sand-blasting), the tube It? 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 lit 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 temperaturecontrolled 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 to 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.
it. An ejection device for extruding thermoplastic ma terial, which comprises:
(a) A support housing;
(b) A tubular ejection cylinder for receiving material to be extruded therefrom, said cylinder being made of an electrically conductive material having a selected resistivity for heating said material in response to an electrical current passed through said cylinder, thereby converting said material from a solid to a plastic state;
(c) Means connected to said housing for supporting said ejection cylinder;
(d) A piston slidably disposed within said ejection cylinder for extruding said material therefrom;
(e) Electrically conductive means for passing an electrical current through said ejection cylinder; and,
(f) Pneumatic actuating means for driving said piston whereby said material is extruded from the ejection cylinder in a plastic state.
2. The ejection device of claim It wherein the eiectri current for heating the iaterial flows in an axial direction through the wall of said ejection cylinder, said wall having a thickness which varies axially so as to provide a predetermined axial distribution of resistance throughout said cylinder for controlling the heating of the material therein.
3. The ejection device of claim 1 wherein the pneumatic actuating means for driving the piston includes a pneumatic actuating cylinder having a piston connected to the piston within the ejection cylinder and an external-- ly disposed air bleed orifice in the air supply line to said pneumatic cylinder whereby the ejection of material can be controllably varied by blocking said orifice.
4. The ejection device of claim 1 wherein the pneumatic actuating means for driving the piston includes a pneumatic actuating cylinder having a piston connected to the piston within the ejection cylinder, an air supply line connected to said actutaing cylinder, and a spring tube air discharge line, also connected to said actuating cylinder, said spring tube having an open end for the dis charge of air therefrom, said discharge end being disposed adjacent to a resilient closure disc ailixcd to the housing, whereby the ejection of material can be controllably varied by pressing said spring tube discharge end into abutting contact with said closure disc.
5. The ejection device of claim 1 wherein the ejection cylinder is disposed within an electrically conductive sleeve which is secured to the support housing, said cylinder being supported in spaced relation to said sleeve by means of an electrically conductive spacer and an electrically insulating spacer whereby said sleeve and conductive spacer form part of an electrically conductive path for passing an electric current through said ejection cylinder.
References Cited by the Examiner UNITED STATES PATENTS 1,575,152 3/26 Di Battista 222146 2,086,462 7/37 Bost 222146 X 2,272,780 2/42 Schweyer 2Z2-l46 X 2,567,960 9/51 Myers 222146 X EVERETT W. KIRBY, Primary Examiner.
HADD S. LANE, Examiner.