Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2000-09-08
2001-06-26
Paik, Sang (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S535000, C285S021200
Reexamination Certificate
active
06252210
ABSTRACT:
SPECIFICATION
FIELD OF THE INVENTION
The present invention relates to an electrical sleeve heater. More particularly this invention concerns a tubular heater that is slipped, for example, over an injection-molding nozzle to maintain it at a predetermined temperature.
BACKGROUND OF THE INVENTION
A standard electrical sleeve heater has an inner tube centered on an axis, an electrical heater coil wound around the inner tube, and an outer tube engaged around the heater coil and inner tube. The inner tube is typically formed of a good heat conductor such as copper or brass and the outer tube of a poor heat conductor such as stainless steel. The heater coil is a resistance wire extending in a ceramic powder (MgO) inside a metallic sleeve and has ends extending out one end of the heater.
In order that such a heater can be used for accurate temperature control, it is necessary to provide it or the part being heated with a thermal sensor probe. A typical such sensor probe comprises a pair of constantan wires whose inner ends are connected to leads leading to the control circuitry and whose outer ends are fused together. These wires extend through a thin-walled sleeve of heat conductive material and can produce a millivolt output that is directly proportional to the temperature at the fused ends. The control circuit energizes the heater coil in accordance with the temperature detected by the sensor probe.
Accommodating the thin sensor probe in the sleeve heater is very difficult. There is little room between the coil and the inner tube and often no space at all between the inner tube and the object it is fitted over. If the sensor probe is mounted in place in such a heater it is invariably permanently fixed in position. Thus the critical temperature-sensing end of the sensor probe is often positioned in a disadvantageous location that is not critical to the operation of the system.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an improved electrical sleeve heater with a temperature sensor probe.
Another object is the provision of such an improved electrical sleeve heater with a temperature sensor probe which overcomes the above-given disadvantages, that is which neatly incorporates the sensor probe and that, if necessary, allows the position of the sensor probe to be changed or even allows the sensor probe to be replaced if necessary.
SUMMARY OF THE INVENTION
An electrical sleeve heater has according to the invention an inner tube centered on an axis and formed with an axially extending and radially inwardly open cutout open at an axial end of the tube, an electrical heater coil wound around the tube, an outer tube engaged around the heater coil and tube, and an axially elongated thermal sensor probe having a sleeve and a pair of wires extending axially in the sleeve fitted in the cutout.
Thus with this system the sensor probe is incorporated in the sensor probe within the coil so it will detect the temperature right where it is applied. At the same time the sensor probe does not complicate construction of the device and the heater coil can completely fill the space between the outer surface of the inner tube and the inner surface of the outer tube.
The inner tube according to the invention has substantially cylindrical inner and outer surfaces and the thermal sensor probe has a radial thickness smaller than a radial distance between the inner and outer surfaces. Thus the sensor probe lies wholly within the outlines of the inner tube, neither projecting inward into the space to be occupied by the object being heated nor outward into the space used by the heater coil.
The cutout has an angularly directed edge and according to the invention the sensor probe to the edge. This can be done adhesively or by fusion of the sensor-probe sleeve.
The sensor probe sleeve has a predetermined diameter and the cutout has a pair of angularly confronting edges spaced angularly apart by a distance greater than the diameter. Thus some thermal expansion of the inner tube can be tolerated without problems. In accordance with the invention the sensor probe sleeve has a diameter or at most about 1 mm and a wall thickness of about 0.15 mm and the outer tube fits tightly around the heater coil.
The cutout according to the invention is an axially full-length and radially through going slot. It can also be a radially inwardly open groove formed in the inner tube. In any case the sensor probe is a loose fit in the cutout and is axially slidable therein.
REFERENCES:
patent: 3849630 (1974-11-01), Halliday
patent: 3943334 (1976-03-01), Sturn
patent: 4176274 (1979-11-01), Lippera
patent: 4493985 (1985-01-01), Keller
patent: 5360333 (1994-11-01), Schmidt
patent: 5558888 (1996-09-01), Beck
patent: 5632919 (1997-05-01), MacCracken et al.
patent: 6025577 (2000-02-01), Schwarzkopt
patent: 6043466 (2000-03-01), Jenko et al.
Dubno Herbert
Hotset Heizpatronen u.Zubehor GmbH
Paik Sang
Wilford Andrew
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