Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-12-20
2001-11-27
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S424000, C219S426000, C425S549000
Reexamination Certificate
active
06323465
ABSTRACT:
The present invention relates to an externally heated hot-runner nozzle and, in particular, to the resistance wire (heating cable) thereof.
Plastic moldings are produced by injection molding using such a hot-runner nozzle. It is the function of the nozzle to guide the melt from the hot-runner manifold through the melt passage to the gate. Heat losses which are detrimental to the viscosity required for the melt in the melt passage of the nozzle are compensated by the resistance wire which is wound around the nozzle body in the form of a heating coil. Thus the resistance wire guarantees constant isothermal conditions along the melt passage.
Such a hot-runner nozzle is known and marketed by the company Mold-Masters Ltd.
The connection between the resistance wire and the voltage source is established via relatively large connector plugs, so-called terminals. Said terminals require a lot of space, which limits the use of several hot-runner nozzles in one module. Moreover, said terminals are prone to power disconnection, one reason being e.g. that the resistance wire burns out during heating or during control of the set temperature at a voltage within the low-voltage range. Finally, the high temperatures of the resistance wire effect undesired changes in the material in the area of the connections because the resistance wire is exposed to air at said place. This results in embrittlements, which may cause the resistance wires to break.
It is therefore the object of the present invention to provide a hot-runner nozzle which can be heated without any trouble for a long time, which is connected with the aid of simple electrical connections to the voltage source and which shows a reduced heat development in the area of the connections.
Said object is achieved by the subject matter of claim
1
.
The advantage of the present invention is that the resistance wire only starts to heat at the nozzle body while a permanently lower temperature is set in the end portions of the resistance wire as compared with the heating portion. As a result, the terminal which requires a lot of space because of its heat-resistant construction can be replaced by a normal connection provided between resistance wire and voltage source, which need not have any special heat-resistant characteristics. Such a simple connection is more space-saving than the terminal which has so far been used, whereby the flexible use of the hot-runner nozzle, in particular in modular manifolds, is extended. In addition, a simple connection is less expensive than a complicated terminal.
Furthermore, since the terminal can be dispensed with thanks to the invention, this has the advantage that the nozzle heating unit can be supplied with power in a trouble-free manner not only from a source of standard voltage, but also from a source of low voltage. This is of great importance as compact nozzles of a small constructional size can only be operated with a low voltage because the application of a standard voltage would cause the resistance wire in such nozzles to burn out.
Finally, the temperatures achieved with the present invention at the end portions of the resistance wire are sufficiently low to prevent any oxidation of the resistance wire on the air-exposed portions. This enhances the service life of the resistance wires of the invention considerably.
Preferred embodiments and improvements of the invention are indicated in the subclaims.
Advantageously, the intermediate section of the resistance wire can be heated to temperatures of up to 600° C., so that the necessary flowability of the melt in the melt passage is ensured. To achieve such a condition, the voltage applied to the end portions may be in the low-voltage range, in particular of up to 50 V. A preferred d.c. voltage of 24 V makes it possible to give the heating element a more compact design and thus to make the insulating intermediate layer thinner without provoking the development of leakage current. As for the structure of the resistance wire, it has been found to be an advantage that a heating conductor of a chromium-nickel alloy exhibits excellent heating characteristics. An efficient insulation of the current-carrying heating conductor which prevents or at least reduces leakage current is efficiently achieved by a ceramic insulating intermediate layer which consists essentially of MgO. Said insulating intermediate layer, in turn, is surrounded by a metal sheath which consists of oxidation-resistant steel, in particular of stainless steel. This ensures sufficient strength and stability of the resistance wire. Advantageously, the end portions of the resistance wire are arranged in the area of the entry end of the nozzle, and a 180° bend of the resistance wire is arranged in the area of the exit end. Such an arrangement of the resistance wire is preferred for a uniform and efficient heating of the melt passage from the circumference of the nozzle.
REFERENCES:
patent: 3607475 (1971-09-01), Schrewelius
patent: 4403405 (1983-09-01), Gellert
patent: 4446360 (1984-05-01), Gellert
patent: 4557685 (1985-12-01), Gellert
patent: 5051086 (1991-09-01), Gellert
patent: 5266023 (1993-11-01), Renwick
patent: 5282735 (1994-02-01), Gellert
patent: 5421716 (1995-06-01), Gellert
patent: 5507636 (1996-04-01), Gellert
patent: 1 615 121 (1967-10-01), None
patent: 0 069 997 A1 (1982-07-01), None
patent: 996666 (1951-12-01), None
patent: 2193530 (1974-02-01), None
Gellert Jobst U.
Scheffler Andreas
McDonnell & Boehnen Hulbert & Berghoff
Mold-Masters Limited
Pelham Joseph
LandOfFree
Externally heated hot-runner nozzle with resistance wire does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Externally heated hot-runner nozzle with resistance wire, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Externally heated hot-runner nozzle with resistance wire will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2617314