CN202860219U - Filtering machine for processing grinding fluid - Google Patents

Filtering machine for processing grinding fluid Download PDF

Info

Publication number
CN202860219U
CN202860219U CN 201220582924 CN201220582924U CN202860219U CN 202860219 U CN202860219 U CN 202860219U CN 201220582924 CN201220582924 CN 201220582924 CN 201220582924 U CN201220582924 U CN 201220582924U CN 202860219 U CN202860219 U CN 202860219U
Authority
CN
China
Prior art keywords
screen cloth
water inlet
links
casing
filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
CN 201220582924
Other languages
Chinese (zh)
Inventor
俞竞
饶恒武
胡梁朝
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ningbo Jiang Chen Automation Equipment Co ltd
Original Assignee
NINGBO JIANGCHEN AUTOMATION EQPT CO Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by NINGBO JIANGCHEN AUTOMATION EQPT CO Ltd filed Critical NINGBO JIANGCHEN AUTOMATION EQPT CO Ltd
Priority to CN 201220582924 priority Critical patent/CN202860219U/en
Application granted granted Critical
Publication of CN202860219U publication Critical patent/CN202860219U/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Landscapes

  • Filtration Of Liquid (AREA)

Abstract

The utility model discloses a filtering machine for processing grinding fluid. The filtering machine comprises a rack and a tank body mounted on the rack; the tank body is provided with a water inlet connected with a water inlet tube and a water outlet connected with a water outlet pipe, a control valve is arranged on the water inlet tube, a screen cloth penetrates through the tank body and two ends of the screen cloth are in a circle after stretching out the tank body and are driven to rotate through a rotating mechanism; the water inlet and the water outlet are located at two sides of the screen cloth respectively, at least one rolling rod brush is arranged outside the tank body and one side of a screen cloth forward direction on a rack body, the rolling rod brush is driven to rotate through a rolling brush driving mechanism, and a slag hopper is arranged below the rolling rod brush on the rack body. With the adoption of the structure, grinding mud in the grinding fluid can be filtrated well, and pipes are not blocked, so that the grinding fluid is convenient to recycle; and meanwhile, a tank does not need to be cleaned, so that the labor force is saved and the regular production is not influenced.

Description

A kind of filter of processing grinding fluid
(1) technical field
The utility model relates to a kind of filter of processing grinding fluid.
(2) background technology
After grinding fluid uses a period of time, will accumulate the grinding mud of lower some in the grinding fluid pond, will blocking pipe if grinding mud is not filtered out, the time-consuming again effort in traditional hand sweeping pond, also impact is normal produces.
(3) summary of the invention
Have above-mentioned deficiency in the prior art in order to overcome, the utility model provide a kind of simple in structure, easy to use, and be used for the filter of processing grinding fluid that grinding fluid grinding mud is filtered.
The technical scheme in the invention for solving the technical problem is: a kind of filter of processing grinding fluid, comprise frame, described frame is provided with casing, this casing is provided with water inlet and delivery port, described water inlet links to each other with water inlet pipe, described water inlet pipe is provided with control valve, described delivery port links to each other with outlet pipe, be equipped with a screen cloth in the described casing, thereby the two ends of this screen cloth are stretched out to form a circle behind the described casing and driven by rotating mechanism and are rotated, described water inlet and delivery port lay respectively at the both sides of described screen cloth, a side that is positioned at the outside of described casing on the described support body and is positioned at described screen cloth direction of advance is provided with at least one roller brush, thereby this roller brush is driven by the round brush driving mechanism and rotates, and the below that is positioned at described roller brush on the described support body is provided with the receiving hopper of slagging tap.
Further, described casing is provided with the pressure sensor of the pressure that bears because of the accumulation of grinding mud for detection of described screen cloth, also comprise a control system, this control system comprises switch feedback unit and comparing unit, the output of described pressure sensor links to each other with the input of described switch feedback unit, the output of described switch feedback unit links to each other with the input of described comparing unit, prestore desired pressure value on the described comparing unit, described comparing unit compares the detected force value of described pressure sensor and described desired pressure value, the output of described comparing unit and described control valve, rotating mechanism links to each other with the round brush driving mechanism.Thereby detect the accumulation situation of grinding mud on the force value real time monitoring screen cloth that screen cloth bears by pressure sensor, the detected force value of pressure sensor is transported to comparing unit by the switch feedback unit, comparing unit compares force value and desired pressure value, when force value during greater than desired pressure value, thereby comparing unit drive control valve, rotating mechanism and round brush driving mechanism are made corresponding action.
Further, also be provided with gas hole on the described water inlet pipe, this gas hole links to each other with tracheae, and this tracheae is provided with the air blowing magnetic valve, and this air blowing magnetic valve links to each other with the output of described comparing unit.In use, when collection is expired grinding mud on the screen cloth, be that the detected force value of pressure sensor is during greater than desired pressure value, the comparing unit drive control valve is closed water inlet pipe and is opened the air blowing magnetic valve, thereby the tracheae conducting dries up grinding mud by gas hole, is convenient to grinding mud is for further processing.
Further, described casing comprises warehouse and the lid of sealable lid on this warehouse, one end and the described support body of this lid are hinged, and the other end of this lid drives and can lift by relatively described warehouse by the hoisting mechanism of being located on the described support body, and is simple in structure.
Further, described water inlet is located on the described lid, described delivery port is located on the described warehouse, described screen cloth has part to place between the junction of described lid and warehouse, be provided with Turbogrid plates on the described warehouse between described delivery port and screen cloth, described pressure sensor is located on the described warehouse, and described hoisting mechanism is at least one lifting cylinder, this lifting cylinder is installed on the frame by fixed claw, and the output of this lifting cylinder links to each other with described lid.In use, when pressure sensor detected force value that screen cloth bears and is higher than desired pressure value, lifting cylinder lifted an end of lid, thereby the screen cloth of being convenient to collect full grinding mud produces outside the casing.
Further, described screen cloth outside described casing part and described casing between be provided with nozzle system, this nozzle system links to each other with cleaning hose, this cleaning hose is provided with solenoid purge valve, this solenoid purge valve links to each other with the output of comparing unit, the below of described screen cloth is provided with water-collecting tray, and the bottom of this water-collecting tray is provided with the outlet of catchmenting.In use, after grinding mud on the screen cloth is brushed off by roller, still having a small amount of grinding mud remains on the screen cloth, when the part screen cloth that then has residual grinding mud turned to the below of nozzle system, comparing unit was opened solenoid purge valve, thereby the cleaning hose conducting is washed screen cloth by nozzle system, thereby wash out grinding mud residual on the screen cloth, water with grinding mud flows out from the outlet of catchmenting of water-collecting tray, and is back in the pending sewage, can improve like this filter effect of screen cloth.
Further, described rotating mechanism comprises two cylinders, wherein a described cylinder is provided with Rolling motor, the two ends of another described cylinder are provided with sprocket wheel, the both sides of described screen cloth are provided with chain, the two ends that are positioned at described screen cloth on the described casing are provided with groove, the chain of both sides that is positioned at the described screen cloth of described casing places described groove and can move along described groove, described screen cloth outside described casing passes between two described cylinders, and the described chain at described screen cloth two ends is sleeved on the described sprocket wheel.In use, comparing unit is opened Rolling motor, and the cylinder that Rolling motor drives on it rotates, and cylinder drives another adjacent cylinder rotation, and moves by the drive of the sprocket wheel on cylinder chain, moves thereby drive screen cloth.
Further, described round brush driving mechanism is the round brush motor, and is simple in structure.
Further, described control valve is butterfly valve, precise control.
The utility model in use, the water inlet pipe entrance places in the cesspool with grinding mud and is provided with solution feed pump, the outlet of outlet pipe places in the water purifying tank, then open control valve and solution feed pump, then solution feed pump sucking-off in the cesspool has the sewage of grinding mud, and is sprayed onto on the screen cloth from water inlet by water inlet pipe, grinding mud rests on the screen cloth, and the grinding fluid after being filtered passes screen cloth, and in inflow water purifying tank behind the outlet pipe, thereby so that grinding fluid can be recycling.When grinding mud is accumulated to a certain degree on the screen cloth, closed control valve and solution feed pump, then open the air blowing magnetic valve, thereby the tracheae conducting dries up the grinding mud on the screen cloth by gas hole, then lifting cylinder lifts lid, then Rolling motor action, thereby driving screen cloth rotates, thereby the grinding mud that screen cloth drives on it moves to roller brush direction, make simultaneously the round brush motor action, rotate thereby drive the roller brush, the grinding mud that the roller brush will remain on the screen cloth brushes off, when the part that has residual grinding mud when screen cloth turns to the below of nozzle system, open simultaneously solenoid purge valve, thus the cleaning hose conducting by nozzle system screen cloth is washed, thereby wash out grinding mud residual on the screen cloth, water with grinding mud flows out from the outlet of catchmenting of water-collecting tray, and is back in the pending sewage.After screen cloth is walked about half-turn, Rolling motor, round brush motor, solenoid purge valve and air blowing magnetic valve are all closed, thereby lifting cylinder puts down lid and is sealed on the warehouse, then control valve is opened, solution feed pump is opened, can carry out the filtration link of next round, so go round and begin again, the grinding mud in the grinding fluid will filter out.
The beneficial effects of the utility model are: adopt said structure, can the grinding mud in the grinding fluid well be filtered, and can blocking pipe, thereby be convenient to the recycling of grinding fluid, and need not to clean the pond, save the labour, also can not affect normal production.
(4) description of drawings
Fig. 1 is exploded perspective view of the present utility model.
Fig. 2 is installation diagram of the present utility model.
Fig. 3 is cutaway view of the present utility model.
(5) specific embodiment
Below in conjunction with the drawings and specific embodiments the utility model is described in further detail.
With reference to Fig. 1; Fig. 2; Fig. 3; a kind of filter of processing grinding fluid; comprise frame 1; described frame 1 is provided with casing; this casing is provided with water inlet and delivery port; described water inlet links to each other with water inlet pipe 2; described water inlet pipe 2 is provided with control valve; control valve can be butterfly valve; described delivery port links to each other with outlet pipe 3; be equipped with a screen cloth (not shown) in the described casing; thereby the two ends of this screen cloth are stretched out to form a circle behind the described casing and driven by rotating mechanism and are rotated; described water inlet and delivery port lay respectively at the both sides of described screen cloth; a side that is positioned at the outside of described casing on the described support body 1 and is positioned at described screen cloth direction of advance is provided with at least one roller brush 4; thereby this roller brush 4 is driven by the round brush driving mechanism and rotates; described round brush driving mechanism is round brush motor 5; in the present embodiment; described roller brush 4 has two; and by round brush motor 5 drive; and the parallel outside that is positioned at described screen cloth; the below that is positioned at described roller brush 4 on the described support body 1 is provided with the receiving hopper 6 of slagging tap, and also is provided with cover of upholstery 7 outside the receiving hopper 6 of slagging tap, and can protect the receiving hopper 6 of slagging tap.
Described casing is provided with the pressure sensor of the pressure that bears because of the accumulation of grinding mud for detection of described screen cloth, also comprise a control system, this control system comprises switch feedback unit and comparing unit, the output of described pressure sensor links to each other with the input of described switch feedback unit, the output of described switch feedback unit links to each other with the input of described comparing unit, prestore desired pressure value on the described comparing unit, described comparing unit compares the detected force value of described pressure sensor and described desired pressure value, the output of described comparing unit and described control valve, rotating mechanism links to each other with the round brush driving mechanism.Thereby detect the accumulation situation of grinding mud on the force value real time monitoring screen cloth that screen cloth bears by pressure sensor.The detected force value of pressure sensor is transported to comparing unit by the switch feedback unit, comparing unit compares force value and desired pressure value, when force value during greater than desired pressure value, thereby comparing unit drive control valve, rotating mechanism and round brush driving mechanism are made corresponding action.
Also be provided with gas hole on the described water inlet pipe 2, this gas hole links to each other with tracheae, and this tracheae is provided with the air blowing magnetic valve, and this air blowing magnetic valve links to each other with the output of described comparing unit.In use, when collection is expired grinding mud on the screen cloth, be that the detected force value of pressure sensor is during greater than desired pressure value, the comparing unit drive control valve is closed water inlet pipe 2 and is opened the air blowing magnetic valve, thereby the tracheae conducting dries up grinding mud by gas hole, is convenient to grinding mud is for further processing.
Described casing comprises warehouse 8 and the lid 9 of sealable lid on this warehouse 8, one end and the described support body 1 of this lid 9 are hinged, the other end of this lid 9 drives and can lift by relatively described warehouse 8 by the hoisting mechanism of being located on the described support body, and is simple in structure.
Described water inlet is located on the described lid 9, described delivery port is located on the described warehouse 8, described screen cloth has part to place between the junction of described lid 9 and warehouse 8, between described delivery port and screen cloth, be provided with Turbogrid plates 10 on the described warehouse 8, described pressure sensor is located on the described warehouse 8, described hoisting mechanism is at least one lifting cylinder 11, in the present embodiment, lifting cylinder 11 is two, lay respectively at the both sides of lid 9, thereby make lid 9 more steady when lifting, this lifting cylinder 11 is installed on the frame 1 by fixed claw 12, and the output of this lifting cylinder 11 links to each other with described lid 9.In use, when pressure sensor detected force value that screen cloth bears and is higher than desired pressure value, lifting cylinder 11 lifted an end of lid 9, thereby the screen cloth of being convenient to collect full grinding mud produces outside the casing.
Described screen cloth outside described casing part and described casing between be provided with nozzle system 13, this nozzle system 13 links to each other with cleaning hose, this cleaning hose is provided with solenoid purge valve, this solenoid purge valve links to each other with the output of comparing unit, the below of described screen cloth is provided with water-collecting tray 14, and the bottom of this water-collecting tray 14 is provided with the outlet 15 of catchmenting.In use, after grinding mud on the screen cloth is brushed off by roller brush 4, still having a small amount of grinding mud remains on the screen cloth, when the part screen cloth that then has residual grinding mud turns to the below of nozzle system 13, comparing unit is opened solenoid purge valve, thereby the cleaning hose conducting is washed by 13 pairs of screen cloths of nozzle system, thereby wash out grinding mud residual on the screen cloth, water with grinding mud flows out from the outlet 15 of catchmenting of water-collecting tray 14, and be back in the pending sewage, can improve like this filter effect of screen cloth.
Described rotating mechanism comprises two cylinders 16, wherein a described cylinder is provided with Rolling motor 17, the two ends of another described cylinder are provided with sprocket wheel, the both sides of described screen cloth are provided with chain, the two ends that are positioned at described screen cloth on the described casing are provided with groove, the chain of both sides that is positioned at the described screen cloth of described casing places described groove and can move along described groove, described screen cloth outside described casing passes between two described cylinders, and the described chain at described screen cloth two ends is sleeved on the described sprocket wheel.In use, the cylinder 16 that comparing unit unlatching Rolling motor 17, Rolling motor 17 drive on it rotates, and cylinder 16 drives another adjacent cylinder 16 rotations, and moves by the drive of the sprocket wheel on the cylinder 16 chain, moves thereby drive screen cloth.
The utility model in use, water inlet pipe 2 entrances place in the cesspool with grinding mud and are provided with solution feed pump, the outlet of outlet pipe 3 places in the water purifying tank, then open control valve and solution feed pump, then solution feed pump sucking-off in the cesspool has the sewage of grinding mud, and is sprayed onto on the screen cloth from water inlet by water inlet pipe 2, grinding mud rests on the screen cloth, and the grinding fluid after being filtered passes screen cloth, and in inflow water purifying tank behind the outlet pipe 3, thereby so that grinding fluid can be recycling.When grinding mud is accumulated to a certain degree on the screen cloth, closed control valve and solution feed pump, then open the air blowing magnetic valve, thereby the tracheae conducting dries up the grinding mud on the screen cloth by gas hole, then lifting cylinder 11 lifts lid 9, then make Rolling motor 17 actions, thereby driving screen cloth rotates, thereby the grinding mud that screen cloth drives on it moves to roller brush direction, make simultaneously 5 actions of round brush motor, thereby driving roller brush 4 rotates, the roller brush 4 grinding mud that will remain on the screen cloth brush off, when the part that has residual grinding mud when screen cloth turns to the below of nozzle system 13, open simultaneously solenoid purge valve, thus the cleaning hose conducting wash by 13 pairs of screen cloths of nozzle system, thereby wash out grinding mud residual on the screen cloth, water with grinding mud flows out from the outlet 15 of catchmenting of water-collecting tray 14, and is back in the pending sewage.After screen cloth is walked about half-turn, Rolling motor 17, round brush motor 5, solenoid purge valve and air blowing magnetic valve are all closed, thereby lifting cylinder 11 puts down lid 9 and is sealed on the warehouse 8, then control valve is opened, solution feed pump is opened, can carry out the filtration link of next round, so go round and begin again, the grinding mud in the grinding fluid will filter out.

Claims (9)

1. filter of processing grinding fluid, comprise frame, it is characterized in that: described frame is provided with casing, this casing is provided with water inlet and delivery port, described water inlet links to each other with water inlet pipe, described water inlet pipe is provided with control valve, described delivery port links to each other with outlet pipe, be equipped with a screen cloth in the described casing, thereby the two ends of this screen cloth are stretched out to form a circle behind the described casing and driven by rotating mechanism and are rotated, described water inlet and delivery port lay respectively at the both sides of described screen cloth, a side that is positioned at the outside of described casing on the described support body and is positioned at described screen cloth direction of advance is provided with at least one roller brush, thereby this roller brush is driven by the round brush driving mechanism and rotates, and the below that is positioned at described roller brush on the described support body is provided with the receiving hopper of slagging tap.
2. according to the filter of processing grinding fluid claimed in claim 1, it is characterized in that: described casing is provided with the pressure sensor of the pressure that bears because of the accumulation of grinding mud for detection of described screen cloth, also comprise a control system, this control system comprises switch feedback unit and comparing unit, the output of described pressure sensor links to each other with the input of described switch feedback unit, the output of described switch feedback unit links to each other with the input of described comparing unit, prestore desired pressure value on the described comparing unit, described comparing unit compares the detected force value of described pressure sensor and described desired pressure value, the output of described comparing unit and described control valve, rotating mechanism links to each other with the round brush driving mechanism.
3. according to the filter of processing grinding fluid claimed in claim 2, it is characterized in that: also be provided with gas hole on the described water inlet pipe, this gas hole links to each other with tracheae, and this tracheae is provided with the air blowing magnetic valve, and this air blowing magnetic valve links to each other with the output of described comparing unit.
4. according to the filter of claim 1 or 2 or 3 described processing grinding fluids, it is characterized in that: described casing comprises warehouse and the lid of sealable lid on this warehouse, one end and the described support body of this lid are hinged, and the other end of this lid drives and can lift by relatively described warehouse by the hoisting mechanism of being located on the described support body.
5. according to the filter of processing grinding fluid claimed in claim 4, it is characterized in that: described water inlet is located on the described lid, described delivery port is located on the described warehouse, described screen cloth has part to place between the junction of described lid and warehouse, between described delivery port and screen cloth, be provided with Turbogrid plates on the described warehouse, described pressure sensor is located on the described warehouse, described hoisting mechanism is at least one lifting cylinder, this lifting cylinder is installed on the frame by fixed claw, and the output of this lifting cylinder links to each other with described lid.
6. according to the filter of processing grinding fluid claimed in claim 4, it is characterized in that: described screen cloth outside described casing part and described casing between be provided with nozzle system, this nozzle system links to each other with cleaning hose, this cleaning hose is provided with solenoid purge valve, this solenoid purge valve links to each other with the output of described comparing unit, the below of described screen cloth is provided with water-collecting tray, and the bottom of this water-collecting tray is provided with the outlet of catchmenting.
7. according to the filter of claim 1 or 2 or 3 described processing grinding fluids, it is characterized in that: described rotating mechanism comprises two cylinders, wherein a described cylinder is provided with Rolling motor, the two ends of another described cylinder are provided with sprocket wheel, the both sides of described screen cloth are provided with chain, the two ends that are positioned at described screen cloth on the described casing are provided with groove, the chain of both sides that is positioned at the described screen cloth of described casing places described groove and can move along described groove, described screen cloth outside described casing passes between two described cylinders, and the described chain at described screen cloth two ends is sleeved on the described sprocket wheel.
8. according to the filter of claim 1 or 2 or 3 described processing grinding fluids, it is characterized in that: described round brush driving mechanism is the round brush motor.
9. according to the filter of claim 1 or 2 or 3 described processing grinding fluids, it is characterized in that: described control valve is butterfly valve.
CN 201220582924 2012-10-30 2012-10-30 Filtering machine for processing grinding fluid Expired - Lifetime CN202860219U (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN 201220582924 CN202860219U (en) 2012-10-30 2012-10-30 Filtering machine for processing grinding fluid

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN 201220582924 CN202860219U (en) 2012-10-30 2012-10-30 Filtering machine for processing grinding fluid

Publications (1)

Publication Number Publication Date
CN202860219U true CN202860219U (en) 2013-04-10

Family

ID=48026979

Family Applications (1)

Application Number Title Priority Date Filing Date
CN 201220582924 Expired - Lifetime CN202860219U (en) 2012-10-30 2012-10-30 Filtering machine for processing grinding fluid

Country Status (1)

Country Link
CN (1) CN202860219U (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102961909A (en) * 2012-10-30 2013-03-13 宁波江宸自动化装备有限公司 Filter for processing grinding fluid

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102961909A (en) * 2012-10-30 2013-03-13 宁波江宸自动化装备有限公司 Filter for processing grinding fluid

Similar Documents

Publication Publication Date Title
CN102961909A (en) Filter for processing grinding fluid
CN104343096B (en) Sanitation truck drags suction road surface cleaning device
CN205815234U (en) A kind of sludge dehydration device being applied to mud cleaning
CN104074023A (en) Washing machine and clothes washing control method
CN209735104U (en) Backwashing device of micro-filter
CN106994265A (en) A kind of precise filtering device and its application method
CN201905210U (en) Fruit and vegetable washing machine
CN202860219U (en) Filtering machine for processing grinding fluid
CN109224582B (en) Energy-saving automatic water treatment equipment with backwashing barrier
CN112501841A (en) Rope-shaped washing machine
CN205436427U (en) Salted duck egg's cleaning machine
CN205575843U (en) Chemical industry waste water cyclic utilization device
CN205575856U (en) Sewage treatment device
CN210131443U (en) Internal water inlet type rotary screen for sewage treatment
CN206008199U (en) Drum type accurate filter
CN213925455U (en) Fabric dyeing device with good wrinkle resistance and wear resistance based on environmental protection
CN207733553U (en) A kind of drum type washing oyster equipment
CN103316523A (en) Repair-free square filter cloth filter equipment
CN207805148U (en) A kind of intelligent filtering machine
CN208145558U (en) A kind of low concentration coal chemical industrial wastewater processing equipment
CN112544559A (en) Pond filtration equipment convenient to maintain and change filter screen
CN206762406U (en) A kind of precise filtering device
CN205590483U (en) Intelligent energy -conserving sewage treatment plant
CN206008143U (en) A kind of purifying water process automatic backwash system
CN212093486U (en) Fiber filter bag recycling and cleaning device

Legal Events

Date Code Title Description
C14 Grant of patent or utility model
GR01 Patent grant
C56 Change in the name or address of the patentee
CP03 Change of name, title or address

Address after: 315312, Zhejiang, Ningbo province Cixi emerging industrial clusters, Han Han street, Xinxing Road, No. 2

Patentee after: NINGBO JIANG CHEN AUTOMATION EQUIPMENT Co.,Ltd.

Address before: 315301 Jintang village, high street village, Han Han street, Zhejiang City, Cixi province (105 room, Chengbei water supply office building, Cixi water supply company)

Patentee before: NINGBO JIANGCHEN AUTOMATION EQPT Co.,Ltd.

CX01 Expiry of patent term

Granted publication date: 20130410

CX01 Expiry of patent term