GB1600754A

GB1600754A - Method of and a heat sensitive arrangement for protecting machine parts

Info

Publication number: GB1600754A
Application number: GB2400878A
Authority: GB
Original assignee: Aerzener Maschinenfabrik GmbH
Current assignee: Aerzener Maschinenfabrik GmbH
Priority date: 1977-10-11
Filing date: 1978-05-30
Publication date: 1981-10-21

Description

(54) A METHOD OF AND A HEAT SENSITIVE ARRANGEMENT FOR PROTECTING MACHINE PARTS (71) We, AERZENER MASCHINENFA BRIK GmbH, of Postfach 7-9, 3251 Aerzen 1, Germany, a German Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method of and an arrangement for protecting machine parts, particularly during start-up conditions, which have mutually facing surfaces and which are movable relatively to each other.

Such protecting methods and arrangements serve e.g. for protecting fans, ventilators, turbines, compressors or pumps with rotors or rotary pistons wherein, in consequence of excessive heating and/or impermissible pressure fluctuations heat expansions occur in the rotary parts and/or the casings due to overloading, whereby the clearance space between the rotary parts or a rotary part and an associated casing is reduced, such spacing being necessary for satisfactory operation and to avoid the risk of damage to the machine.

Protection devices are known in which the clearance between the rotating part and the casing or between adjacently disposed rotating parts is monitored during start-up conditions by closing an electrical current circuit by means of electrical contacts arranged in the region of the clearance between the rotating part and the casing.

For the purpose of actuating the device an electrical current must flow in this case from the rotary part of the machine to the switch contact. However, in some cases lubricants or conveyed medium in the space between the rotary part and the casing can disadvantageously affect the contact making. In other cases an electrically conductive bridge is formed between the contacts and the casing, e.g. a bridge of iron-containing dust, whereby the contacts are rendered inoperative by short-circuiting dependently of the degree of soiling of the machine or installation. Furthermore, during the switching process sparks may be generated, whereby the use of the known starting-up protection is impossible in plants with a prescribed explosion protection, e.g. in the petroleum industry. Injected liquids or condensates likewise prevent the employment of the contact system.

According to the present invention, there is provided a method of protecting machine parts which have two mutually facing surfaces provided with a clearance space therebetween and which are movable relative to each other, wherein a heat sensor is supported by one the mutually facing surfaces and is movable relative thereto so as to protect adjustably into the clearance space between the mutually facing surfaces and wherein the heat sensor is arranged to produce a signal when frictionally engaged by the other surface during relative movement of the two surfaces to provide an indication that the clearance space has decreased to a certain value.

Preferably, the heat sensor comprises a heat sensitive element and a mounting member in which the heat sensitive element is encased.

Thus, the heat sensitive element is protected by the mounting member and cannot be influenced in its behaviour by external influences, such as dirt, corrosion, moisture, changes of spacing and frequency.

The mounting member may be of the same material as, or a different material from the machine part. Thus, by selecting the material of the mounting member, the heat conductivity of the mounting member can be provided which corresponds to the operating condi- tions.

The invention will now be more particularly described with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a rotary piston blower including one embodiment of a protection arrangement according to the invention Figure 2 is a sectional view of the embodiment shown in Figure 1; and Figure 3 is a schematic view of the protection arrangement shown in Figure 2 and incorporating a circuit diagram therefor.

Referring to Figure 1, there is shown therein a cylinder casing 10 of a rotary piston blower having rotary pistons 12 arranged therein. The rotary pistons are rotatably mounted in bearings 14 of the casing and are driven in opposite directions by means of a driving shaft 16 and gear wheels 18.

As shown in Figures 2 and 3 the rotary pistons 12 are so disposed within the cylinder casing 10 that a clearance space for satisfactory operation of the blower is provided between the mutually facing surfaces 20, 22 moving relatively to each other, of the casing and the pistons, respectively. The clearance space varies depending upon the size of the machine, but in general it amounts to only a few tenths of a millimeter. Between the end faces of the rotary pistons 12 and the corresponding casing surfaces the clearance space likewise amounts to only a few tenths of a millimeter, the clearance space being selected during the design of the machine and taking into account heat expansions occurring in normal operation.However, owing to operative disturbances or operating errors, greater heat expansions than provided for particularly during start-up conditions, may occur which result in damage to or even destruction of the machine.

In the cylinder casing 10, heat sensors, each comprising a heat sensitive element 24, e.g. a thermistor, PTC or NTC resistor, or the like and a mounting member 26 for the element 24, are provided in the casing surface 20 and project adjustably into the clearance spaces between the casing surface 20 and the piston surface 22. The heat sensitive elements have a temperature dependent resistance. Thus, when the clearance space between the piston surface 22 and the casing surface 20 becomes smaller than permissible owing to displacement or excessive heat expansion, the member 26 mounting the heat sensitive element is touched and heated in consequence of resulting friction.

Owing to the increasing temperature the electrical resistance of the heat sensitive element changes whereby a signal for switching off the machine is produced. At the same time an audible or visible warning signal may be produced in known manner.

Advantageously each member 26 with associated heat sensitive element for the production of a signal is arranged in the axial and radial casing surfaces at critical locations which may vary depending upon the respective construction.

The member 26 is in the form of an adjustment screw having a fine thread and a cavity 30 formed in the shank thereof. A heat sensitive element 24 is arranged in the cavity 30 by means of a thermally conductive casting mass. The material of the screw may be selected in accordance with the respective heat conductivity required and may be the same as or different from the material of the machine part with which is engages. The tip of the screw shank projects inwardly from the casing surface 20, into the space between the piston and the casing surface in an adjustable manner.

As shown in Figure 3 a signal produced by one of the feeler elements is fed by electrical leads to station 32 which effects switch-off of the machine and/or the energisation of an acoustic and/or visible warning signal. The signal may likewise be used for controlling any quantity of the machine such as. rotary speed, pressure, temperature in order to avoid by way of certain auxiliary devices a critical operation of the machine in respect of the clearance adjustment.

It is obvious that such a protecting device may be provided likewise in the moving machine parts, in which case the signal produced is taken off by means of sliding contacts.

Thus, adjustable protection, particularly for start-up conditions, is provided for machine parts which move relatively to each other and have mutually facing surfaces, wherein a heat sensitive element is located and completely protected in an adjustment screw or the like and is not influenced in its operation by external influences, such as dirt, corrosion, moisture, spacing and frequency changes.

WHAT WE CLAIM IS: 1. A method of protecting machine parts which have two mutually facing surfaces provided with a clearance space therebetween and which are movable relative to each other, wherein a heat sensor is supported by one of the mutually facing surfaces and is movable relative thereto so as to project adjustably into the clearance space between the mutually facing surfaces and wherein the heat sensor is arranged to produce a signal when frictionally engaged by the other surface during relative movement of the two surfaces to provide an indication that the clearance space has decreased to a certain value.

2. A method as claimed in Claim 1, wherein the heat sensor comprises a heat sensitive element and a mounting member in which the heat sensitive element is encased.

3. An arrangement when used to perform the method of claim 1, the arrangement comprising a heat sensor for producing a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 1 is a perspective view of a rotary piston blower including one embodiment of a protection arrangement according to the invention Figure 2 is a sectional view of the embodiment shown in Figure 1; and Figure 3 is a schematic view of the protection arrangement shown in Figure 2 and incorporating a circuit diagram therefor. Referring to Figure 1, there is shown therein a cylinder casing 10 of a rotary piston blower having rotary pistons 12 arranged therein. The rotary pistons are rotatably mounted in bearings 14 of the casing and are driven in opposite directions by means of a driving shaft 16 and gear wheels 18. As shown in Figures 2 and 3 the rotary pistons 12 are so disposed within the cylinder casing 10 that a clearance space for satisfactory operation of the blower is provided between the mutually facing surfaces 20, 22 moving relatively to each other, of the casing and the pistons, respectively. The clearance space varies depending upon the size of the machine, but in general it amounts to only a few tenths of a millimeter. Between the end faces of the rotary pistons 12 and the corresponding casing surfaces the clearance space likewise amounts to only a few tenths of a millimeter, the clearance space being selected during the design of the machine and taking into account heat expansions occurring in normal operation.However, owing to operative disturbances or operating errors, greater heat expansions than provided for particularly during start-up conditions, may occur which result in damage to or even destruction of the machine. In the cylinder casing 10, heat sensors, each comprising a heat sensitive element 24, e.g. a thermistor, PTC or NTC resistor, or the like and a mounting member 26 for the element 24, are provided in the casing surface 20 and project adjustably into the clearance spaces between the casing surface 20 and the piston surface 22. The heat sensitive elements have a temperature dependent resistance. Thus, when the clearance space between the piston surface 22 and the casing surface 20 becomes smaller than permissible owing to displacement or excessive heat expansion, the member 26 mounting the heat sensitive element is touched and heated in consequence of resulting friction. Owing to the increasing temperature the electrical resistance of the heat sensitive element changes whereby a signal for switching off the machine is produced. At the same time an audible or visible warning signal may be produced in known manner. Advantageously each member 26 with associated heat sensitive element for the production of a signal is arranged in the axial and radial casing surfaces at critical locations which may vary depending upon the respective construction. The member 26 is in the form of an adjustment screw having a fine thread and a cavity 30 formed in the shank thereof. A heat sensitive element 24 is arranged in the cavity 30 by means of a thermally conductive casting mass. The material of the screw may be selected in accordance with the respective heat conductivity required and may be the same as or different from the material of the machine part with which is engages. The tip of the screw shank projects inwardly from the casing surface 20, into the space between the piston and the casing surface in an adjustable manner. As shown in Figure 3 a signal produced by one of the feeler elements is fed by electrical leads to station 32 which effects switch-off of the machine and/or the energisation of an acoustic and/or visible warning signal. The signal may likewise be used for controlling any quantity of the machine such as. rotary speed, pressure, temperature in order to avoid by way of certain auxiliary devices a critical operation of the machine in respect of the clearance adjustment. It is obvious that such a protecting device may be provided likewise in the moving machine parts, in which case the signal produced is taken off by means of sliding contacts. Thus, adjustable protection, particularly for start-up conditions, is provided for machine parts which move relatively to each other and have mutually facing surfaces, wherein a heat sensitive element is located and completely protected in an adjustment screw or the like and is not influenced in its operation by external influences, such as dirt, corrosion, moisture, spacing and frequency changes. WHAT WE CLAIM IS:

1. A method of protecting machine parts which have two mutually facing surfaces provided with a clearance space therebetween and which are movable relative to each other, wherein a heat sensor is supported by one of the mutually facing surfaces and is movable relative thereto so as to project adjustably into the clearance space between the mutually facing surfaces and wherein the heat sensor is arranged to produce a signal when frictionally engaged by the other surface during relative movement of the two surfaces to provide an indication that the clearance space has decreased to a certain value.

signal and supported by one of the mutually facing surfaces, the heat sensor being movable relative to said surfaces for adjustment purposes.

4. An arrangement as claimed in claim 3, wherein the heat sensor comprises a heat sensitive element and a mounting member in which the heat sensitive element is encased.

5. An arrangement as claimed in claim 4, wherein said member is of a material different from the machine part.

6. An arrangement as claimed in claim 4, wherein the member is of the same material as the machine part.

7. An arrangement as claimed in any one of claims 4-6, wherein the heat sensitive element is encased in a screw.

8. An arrangement as claimed in claim 7 wherein the screw has a fine screw thread and an indicating device.

9. An arrangement as claimed in any one of claims 3-8, wherein the heat sensitive element is connected to a protection circuit by means of electrical leads.

10. An arrangement when used to perform the method of claim 1, substantially as herein described with reference to and as shown in the accompanying drawings.