HEATED GAS BLOWER DEVICE

Abstract: A heated gas blower device for use in welding or forming plastics has a blower (38) directing air through a nozzle (12) containing resistance heating elements (70). A thermocouple (88) or other sensing element in the nozzle opening allows the temperature of the outflowing air to be controlled to a selected temperature preset with a manual control (32, 34).

Description: HEATED GAS BLOWER DEVICE This invention relates to heated gas blower devices and in one example to hand-held devices for use in such tasks as welding or forming thermoplastic materials. For this use, the blower device should he capable of producing a flow of heated gas - usually air - at a temperature which can be varied. It would be desirable if the user could select the temperature needed for the particular welding or forming operation to be performed and then be assured that the temperature of the heated air leaving the device would not deviate to any substantial extent from the selected temperature, either with time or with changes in the flow rate caused for example by the use of different nozzle attachments. It is an object of this invention to provide an improved heated gas blower device having these desirable characteristics. Accordingly, the present invention consists in a heated gas blower device comprising a nozzle defining a nozzle opening; blower means for establishing a flow of gas outwardly through the nozzle opening; electrical heating means for heating the flow of gas; preselecter means enabling selection of a required gas temperature; a temperature sensing element located at the nozzle opening to provide an electrical indication of the temperature of the gas flowing out of the nozzle opening and electrical control means adapted, in response to said indication of temperature , so to control the electrical heating means as to achieve said selected gas temperature at the nozzle opening. OMPI Advantageously, the preselecter means comprises a manually operable control calibrated in degrees of temperature. Preferably, the electrical heating means comprises resistance heating elements * supported within the nozzle. It will thus be seen that with a blower device according to this invention, the actual temperature of the gas leaving the nozzle opening is measured and this information used to control the heating means. Direct and accurate control of temperature can therefore be achieved notwithstanding possible changes in gas flow rate. This invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 is a longitudinal section through a heated air blower device according to this invention; Figures 2 and 3 are respective end views of the device of Figure 1; Figure 4 is a section on line 4-4 of Figure 1; Figure 5 is a section on line 5-5 of Figure 1; and Figure 6 is a diagram showing the control circuit of the device of Figure 1. The device or gun shown in the drawings is formed from a plastics body 10 to which is secured a stainless steel nozzle 12. The body comprises a cylindrical motor housing 14 serving also as a handle, and an integral turbine housing 16 of somewhat greater diameter. The body is in fact made up from two separately moulded halves which join in a longitudinal plane and which are held together by self-tapping screws. Within the motor housing 14, there is supported a universal motor 18 having a drive shaft 20. Electrical supply for the motor is taken from a control board 22 details of which will be given later. The control board is in turn connected through an on/off switch 24 with a mains cable (not shown) extending through cable aperture 26. The on/off switch 24 is mounted in a housing end plate 28 provided with a series of slots 30 serving as the air intake for the gun. Also provided in the end plate 28 is a temperature selecter knob 32 controlling a potentiometer 34 mounted on the control board. This knob is calibrated in degrees Centigrade. A centrifugal turbine 36 is mounted on the motor drive shaft 20, within the turbine housing 16. The turbine 36 comprises a boss 38 carrying an outer disc 40 disposed normally to the drive shaft axis. Six blades 42 curve radially outwardly from the boss, each blade having one lateral edge secured to the outer disc 40 and the other lateral edge secured to an inner disc 44 disposed coaxially with the outer disc. An annular opening 46 is provided in the inner disc 44 around the boss 38, to define the turbine air inlet. The nozzle 12 is provided with a mounting flange 50 enabling the nozzle to be secured to the body through bolts 52. A heat-insulating ring 54 is disposed between the mounting flange 50 and the turbine housing 16. The same bolts 52 serve also to support - inwardly of the turbine housing - a deflector 56 having a pair of deflector arms 58 carried on a mounting ring 60. Within the nozzle 12, there is positioned a ceramic element holder 62 comprising a series of cylindrical sections 64 supported on a common axial support tube 66, the ends of which are swaged over to hold the sections together. As shown best in Figure 5, the holder 62 is formed with eight bores 68 parallel to and equiangularly spaced about the support tube. Within each bore there is disposed a helically wound resistance element 70, these elements being electrically connected between a pair of terminals 72 mounted in the innermost holder section 64a. Each section 64 of the holder is provided with a square projection 73 at one end and a complementary recess (not shown) at the other. In this way relative rotation of the sections is prevented. OMPI The terminals 72 of the ceramic element holder are received within sockets 74 of a terminal block 76 mounted within the turbine housing. These sockets are electrically connected with the control board 22 by the use of leads 78 and it will be seen that these leads are passed through one of a pair of diammetrically opposed channels 80 formed in respective thickened wall sections 82 of the turbine housing. In this way, the leads are prevented from fouling the turbine. The free end of the nozzle 12 is closed by means of an end cap 84 having parallel slots 86 defining a nozzle opening. At this opening, there is mounted within the nozzle a thermocouple 88. Leads 90 pass from this thermocouple through the center of the ceramic holder support tube 66 -, through the second channel 80 in the turbine housing wall and thus to the control board 22. The mechanical operation of the described gun can now be understood. When the motor 18 is energised, rotation of the turbine draws air * in through the housing slots 30, over the motor and into the turbine through opening 46. The air is then forced radially outwards passing through the turbine housing to the nozzle 12. The deflector arms 58 serve to ensure that most of the air passes directly to the nozzle and thus minimise energy dissipation within the turbine housing itself. In the nozzle, the air passes at high pressure through the bores 68 and is heated by the resistance elements contained therein. The heated high pressure air then passes out of the nozzle through the nozzle opening defined by slots ' 86. The manner in which the temperature of the heated air is controlled will now be described with reference initially to Figure 6. The thermocouple 88, which is a Type K thermocouple, produces a low voltage signal indicative of air temperature. This voltage is amplified by a high gain dc operational amplifier Al (LF 13741 ) having negative feedback through resistor R2 and capacitor Cl and with its operating point set by resistors R6 and R3« Offset control is provided at variable resistor RV2. The output of the amplifier Al is divided by resistors R4 and R5 and a diode Dl is provided to ensure, in conjunction with R4, that the output cannot go significantly negative. The output taken from the junction of R4 and R5 is passed through resistor R9 to the input amplifier of a burst control integrated circuit (SGS L12l). The preset temperature potentiometer RVl (reference 34 in Figure 1 ) is connected to the burst control IC through resistors RIO and Rll. The control band of the IC is set by the feedback resistor R8 with the periodicity of the burst cycle being set by resistor R7 and capacitor C2. Positive and negative low voltage supplies are obtained from the mains terminals L and N through dropper resistor R12; rectifiers and stabilizers are contained within the IC and smoothing is provided by capacitors C4 and C5« The operational amplifier Al is selected to operate with a small dc supply consumption which enables it to be supplied from the small surplus power available from the IC. The output of the burst control IC consists of trigger pulses phase locked to the mains supply and these trigger a power control triac TR (BT 137 500k) at the zero crossing point of the main cycle. This triac is connected between the neutral mains supply terminal N and one of the element sockets 74, the other « element socket being connected to the live mains supply L. The OMPI length of each pulse applied to the triac, and thus the proportion of each main cycle for which the resistance element is energised, is proportional to the difference between the temperature set by temperature selector 32 and the temperature sensed by the thermocouple 88. It will be appreciated that since the thermocouple is provided at the nozzle opening, the voltage signal it provides will be indicative of the temperature of the air as it leaves the nozzle. The control circuit will then operate to ensure that this temperature is brought rapidly to the temperature preselected by selector 32 and then maintained, within acceptable limits, at that temperature. Since the control IC provides a pulse output the pulse length of which is proportional to the difference between actual and selected temperature, heating of the element will be very rapid when the device is first switched on, the rate of heating slowing down as the selected temperature is approached. Since the temperature selector is calibrated in degrees Centigrade, no independent temperature measurement is needed to ensure that the correct operating temperature is being used. It will be appreciated that this invention has been described by way of example and numerous modifications are possible without departing from the scope of the. invention. Different circuit elements could of course be used on the control board and the thermocouple replaced by another temperature responsive element such as a thermistor. OMPI <

Claims: CLAIMS 1. A heated gas blower device comprising a nozzle defining a nozzle opening; blower means for establishing a flow of gas outwardly through the nozzle opening; electrical heating means for heating the flow of gas; preselecter means enabling selection of a required gas temperature; a temperature sensing element located at the nozzle opening to provide an electrical indication of the temperature of the gas flowing out of the nozzle opening and electrical control means adapted in response to said indication of temperature so to control the electrical heating means as to achieve said selected gas temperature at the nozzle opening. 2. A device according to Claim 1 wherein said preselecter means comprises a manually operable control calibrated in degrees of temperatuTe. 3. A device according to Claim 1 or Claim 2 wherein said preselecter means provides an electrical indication of said selected gas temperature, the electrical control means including means for comparing said indication of selected gas temperature with said electrical indication of the temperature of the gas flowing out of the nozzle opening. 4« A device according to any one of the preceding claims, wherein the electrical heating means comprises resistance heating elements supported within the nozzle. 5. A device-according to Claim 4 wherein there is provided a ceramic support in the nozzle for said heating elements, the support having a through bore, spaced from said heating elements for accommodating an electrical lead extending between the temperature sensing element and the control means. 6. A device according to any one of the preceding claims wherein said ceramic support comprises a series of axially aligned cylindrical portions. 7. A device according to Claim 6 wherein there are formed complementary bosses and recesses respectively on each pair of adjacent portions, engagement between said bosses and recesses preventing relative rotation of the cylindrical portions. 8. A device according to Claim 6 or Claim 7 wherein a hollow rod extends in tension along a through aperture in the support securing together said portions.

Inventors: BOWSKILL ROBERT, BOWSKILL, ROBERT
Applicants: SKILTEN ELECTRONICS, SKILTEN ELECTRONICS LIMITED
Application year: 1984
Main classification: F24H3
IPC codes: F24H3, F24H9