CN203556802U - Metal casting die with core pulling and locking structure - Google Patents

Metal casting die with core pulling and locking structure Download PDF

Info

Publication number
CN203556802U
CN203556802U CN201320702043.5U CN201320702043U CN203556802U CN 203556802 U CN203556802 U CN 203556802U CN 201320702043 U CN201320702043 U CN 201320702043U CN 203556802 U CN203556802 U CN 203556802U
Authority
CN
China
Prior art keywords
core
smooth
assembly
level
lock
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
CN201320702043.5U
Other languages
Chinese (zh)
Inventor
张正来
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.)
Zhejiang Huashuo Technology Co ltd
Original Assignee
Ningbo Huashuo Molding & Machine 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 Huashuo Molding & Machine Co Ltd filed Critical Ningbo Huashuo Molding & Machine Co Ltd
Priority to CN201320702043.5U priority Critical patent/CN203556802U/en
Application granted granted Critical
Publication of CN203556802U publication Critical patent/CN203556802U/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Abstract

The utility model discloses a metal casting die with a core pulling and locking structure. The die comprises a moving die and a fixed die which are vertically closed, an inclined core pulling assembly is arranged at the bottom side of the moving die, and an inclined core pulling body capable of flexibly running is arranged on the inner end of the inclined core pulling assembly; an inclined core locking assembly is arranged on one side of the moving die, a core locking pin is arranged on the inner end of the inclined core locking assembly and can be matched with the inclined core pulling body by a plug-in button; a first horizontal core pulling assembly and a second horizontal core pulling assembly are respectively arranged on two sides of the moving die. The core pulling assemblies are separately arranged, so that the metal casting die is reasonable in design, and flexible to operate, and the manufacture of different models can be conveniently and fast realized; all the core pulling assemblies adopt a hydraulic oil driving mode, the metal casting die is high in running automation level, direct to control, the working efficiency is improved and the labor cost can be lowered; core locking objects are separately arranged; when the two dies are assembled, by adopting the close fit action of a locking body and a smooth core, the model casting stability of the smooth core can be achieved, the metal casting die is firm in structure design and excellent in overall stability, and the quality of a cast die core can be greatly enhanced.

Description

A kind of band is loosed core, the casting of metals mould of lock core structure
Technical field
The utility model relates to the technical field of mould, particularly a kind of band loose core, the casting of metals mould of lock core structure.
Background technology
Its casting type cavity shape of existing casting mold is comparatively complicated, so such mould generally all has pulled core structure, but majority adopts mechanical systems and hydraulic driving modes when loosing core operation.
Mechanical system is mainly that the mechanical movement while utilizing folding mould is realized die cavity inner core-body and extracted operation, as the loose core structure of cast die > > (notification number is CN102554182A) of combination of the patent No. many taper pins of Chinese utility model patent < < tube connector that are CN201210058984.X; The low mold frame that this design includes and be fitted on die casting machine, can involutory pairing and upper framed, upper framed, low mold frame is furnished with respectively lower mold core and the upper mold core of closing rear composition foundry goods shaping mould; Tailstock unit is built-in with the slide block of sliding and running, is shaped with pin hole on slide block; Tailstock driver element is fitted with the taper pin of outwardly convex, and this taper pin can coordinate with corresponding pin hole eye-splice; After slide block slides, the intercalation simultaneously of its front end body is in the outer edge that joins of upper mold core and lower mold core; The structure that machinery is loosed core, because of its design principle foundation, has following defect: 1, mechanical system is easily in when design, complicated integral structure, bulky; 2, Mechanical Driven pattern, each quality of fit that leads is had relatively high expectations, and easily causes the larger difficulty of actual fabrication; 3, mechanical mode, when mould is often used, each auxiliary equipment abrasiveness is larger, and whole use shortened; 4, the machinery pattern of loosing core, its stroke, Core-pulling distance are from being scale structure, and stroke distances is unadjustable, just in case the requirement of loosing core is while slightly doing to change, this mould need redesign structure separately, so the scope of application of this mould is narrower.
Hydraulic driving mode mainly utilizes hydraulic principle, hydraulic power is changed into mechanical movement power, as the casting of metals mould > > (notification number is CN103273047A) of the patent No. Chinese patent application profit < < hydraulic pressure pulled core structure that is CN201310218495.0; This design includes up and down the upper framed and low mold frame fastening, and is embedded in the upper mold core of framed bottom surface and is embedded in the lower mold core of low mold frame end face, and lower mold core and upper mold core form the forming cavity of mould while matching up and down; Low mold frame left and right sides is furnished with respectively side one the loose core assembly, front and back side of assembly and side two of loosing core and is furnished with respectively side three assembly and side four assembly of loosing core of loosing core; According to the moulding complexity of metal casting mould, the separate configurations assembly of loosing core respectively in mould four sides, it is reasonable in design, and flexible operation is applicable to the convenient making of different models; The assembly hydraulic oil type of drive though respectively loose core, but the location of respectively loosing core is still fixed against hydraulic pressure self-lock force, the self-locking performance of hydraulic pressure still has the deficiency comparatively speaking, and sealed property is poor, and then can cause the high-quality of mould inner mould core moulding.
In sum, the loose core casting mold of pattern of existing machinery, still has larger deficiency, and overall technology is not perfect.
Summary of the invention
Technical problem to be solved in the utility model is the present situation for prior art, the casting of metals mould of the locking pulled core structure that provide a kind of reasonable in design, flexible operation, automaticity is high, control is direct, work efficiency improves, labor cost is low and core rod quality is high.
The utility model solves the problems of the technologies described above adopted technical scheme: a kind of band is loosed core, the casting of metals mould of lock core structure, this mould includes upper and lower involutory dynamic model and cover half, dynamic model bottom side is equipped with the assembly of tiltedly loosing core, and the assembly the inner of tiltedly loosing core is furnished with the body of tiltedly loosing core of flexible operation; Dynamic model one avris is furnished with oblique lock core assembly, and tiltedly lock core assembly the inner is furnished with lock core pin, and lock core pin can coordinate with the body eye-splice of tiltedly loosing core; Another two avris of above-mentioned dynamic model are furnished with respectively the first flat assembly and the second flat assembly of loosing core of loosing core.
The measure of taking also comprises:
The above-mentioned assembly outer end of tiltedly loosing core is furnished with oblique oil pumping cylinder, and this tailpiece of the piston rod of cylinder of tiltedly pumping is connected with the body of tiltedly loosing core.
Above-mentioned oblique lock core assembly outer end is furnished with oblique lock core oil cylinder, and the tailpiece of the piston rod of this oblique lock core oil cylinder is connected with lock core pin.
Another two avris of above-mentioned cover half are shaped with respectively the first smooth type cavity and the second smooth type cavity, and the first smooth type cavity and the first flat assembly pairing of loosing core, the second smooth type cavity and the second flat assembly pairing of loosing core.
First above-mentioned flat assembly the inner of loosing core is furnished with the first level and smooth core, middle part is furnished with the first tailstock body, and the first tailstock body is fixedly connected with dynamic model corresponding side surface.
The first above-mentioned tailstock body outside is fitted with the first level and smooth cylinder bracket, and the outer end of the first level and smooth cylinder bracket is equipped with the first level and smooth oil cylinder, and the tailpiece of the piston rod of the first level and smooth oil cylinder is connected with the first level and smooth core.
Outside the first above-mentioned smooth type cavity, inner face is fixed with the first lock dog body, and the first lock dog inner body surface can be conflicted and coordinate with the first level and smooth core outer face.
Second above-mentioned flat assembly the inner of loosing core is furnished with the second level and smooth core, middle part is furnished with the second tailstock body, and the second tailstock body is fixedly connected with dynamic model corresponding side surface.
The second above-mentioned tailstock body outside is fitted with the second level and smooth cylinder bracket, and the outer end of the second level and smooth cylinder bracket is equipped with the second level and smooth oil cylinder, and the tailpiece of the piston rod of the second level and smooth oil cylinder is connected with the second level and smooth core.
Outside the second above-mentioned smooth type cavity, inner face is fixed with the second lock dog body, and the second lock dog inner body surface can be conflicted and coordinate with the second level and smooth core outer face.
Compared with prior art, the utility model includes upper and lower involutory dynamic model and cover half, and dynamic model bottom side is equipped with the assembly of tiltedly loosing core, and the assembly the inner of tiltedly loosing core is furnished with the body of tiltedly loosing core of flexible operation; Dynamic model one avris is furnished with oblique lock core assembly, and tiltedly lock core assembly the inner is furnished with lock core pin, and lock core pin can coordinate with the body eye-splice of tiltedly loosing core.The utility model has the advantage of: the separate configurations assembly of loosing core, it is reasonable in design, and flexible operation is applicable to the convenient making of different models; For further strengthening the positional stability of body when working of loosing core, set up especially oblique lock core assembly, utilize hydraulic power, realize comparatively easily the pinning of the body of loosing core and unclamp, and reached the location positioning of body in working order time of loosing core, be beneficial to the high-quality that improves core rod moulding; The assembly of respectively loosing core all adopts hydraulic oil type of drive, and its operation automaticity is high, controls directly, and work efficiency improves, and labor cost reduces; Separate configurations lock core object, when two moulds mate, utilizes lock dog body and the smoothly close-fitting effect of core, and to reach the stability of level and smooth core when model is poured into a mould, its structural design is firm, and resistance to overturning is good, and has greatly improved the quality of the injection-molded core of watering.
Accompanying drawing explanation
Fig. 1 is longitudinal cross-sectional schematic of the utility model embodiment;
Fig. 2 is that schematic diagram is looked on a left side of Fig. 1;
Fig. 3 is the horizontal layout schematic diagram of cover half in Fig. 1;
Fig. 4 is the horizontal layout schematic diagram of dynamic model in Fig. 1;
Fig. 5 is the partial schematic sectional view of assembly of tiltedly loosing core in the utility model embodiment;
Fig. 6 is the partial schematic sectional view of the second flat assembly of loosing core in the utility model embodiment.
The specific embodiment
Below in conjunction with accompanying drawing, embodiment is described in further detail the utility model.
As shown in Figures 1 to 6, figure grade is described as follows: cover half 1, the first smooth type cavity 11, the second smooth type cavity 12, the first lock dog body 13, the second lock dog bodies 14, dynamic model 2, the assembly 3 of tiltedly loosing core, the body 31 of tiltedly loosing core, oblique oil pumping cylinder 32, oblique lock core assembly 4, lock core pin 41, tiltedly lock core oil cylinder 42, the first flat assembly 5 of loosing core, the level and smooth cylinder bracket 53 of the first level and smooth core 51, the first tailstock body 52, the first, the first level and smooth oil cylinder 54, level and smooth core 61, the second tailstock bodies 62 of the second flat assembly 6, the second of loosing core, the level and smooth oil cylinder 64 of the second level and smooth cylinder bracket 63, the second.
The utility model embodiment, a kind of band is loosed core, the casting of metals mould of lock core structure, and this mould includes upper and lower involutory dynamic model 2 and cover half 1, and dynamic model 2 bottom sides are equipped with the assembly 3 of tiltedly loosing core, and assembly 3 the inners of tiltedly loosing core are furnished with the body 31 of tiltedly loosing core of flexible operation; Dynamic model 2 one avris are furnished with oblique lock core assembly 4, and tiltedly lock core assembly 4 the inners are furnished with lock core pin 41, and lock core pin 41 can coordinate with body 31 eye-splices of tiltedly loosing core.Assembly 3 outer ends of tiltedly loosing core are furnished with oblique oil pumping cylinder 32, and this tailpiece of the piston rod of cylinder 32 of tiltedly pumping is connected with the body 31 of tiltedly loosing core.The separate configurations assembly of loosing core, it is reasonable in design, and flexible operation is applicable to the convenient making of different models; The assembly of respectively loosing core all adopts hydraulic oil type of drive, and its operation automaticity is high, controls directly, and work efficiency improves, and labor cost reduces.
Tiltedly lock core assembly 4 outer ends are furnished with oblique lock core oil cylinder 42, and the tailpiece of the piston rod of this oblique lock core oil cylinder 42 is connected with described lock core pin 41.For further strengthening the positional stability of body when working of loosing core, set up especially oblique lock core assembly, utilize hydraulic power, realize comparatively easily the pinning of the body of loosing core and unclamp, and reached the location positioning of body in working order time of loosing core, be beneficial to the high-quality that improves core rod moulding.
Another two avris of dynamic model 2 are furnished with respectively the first flat assembly 5 and the second flat assembly 6 of loosing core of loosing core; Another two avris of cover half 1 are shaped with respectively the first smooth type cavity 11 and the second smooth type cavity 12, and the first smooth type cavity 11 and the first flat assembly 5 pairings of loosing core, the second smooth type cavity 12 and the second flat assembly 6 pairings of loosing core.
First flat assembly 5 the inners of loosing core are furnished with the first level and smooth core 51, middle part is furnished with the first tailstock body 52, and the first tailstock body 52 is fixedly connected with dynamic model 2 corresponding side surface.The outer end that the first tailstock body 52 outsides are fitted with the first level and smooth cylinder bracket 53, the first level and smooth cylinder brackets 53 is equipped with the first level and smooth oil cylinder 54, and the tailpiece of the piston rod of the first level and smooth oil cylinder 54 is connected with the first described level and smooth core 51.
The first smooth type cavity 11 outside inner faces are fixed with the first lock dog body 13, and the first lock dog body 13 inner faces can be conflicted and coordinate with the first level and smooth core 51 outer faces.Separate configurations lock core object, when two moulds mate, utilizes the close-fitting effect of the first lock dog body and the first level and smooth core, to reach the stability of the first level and smooth core when model is poured into a mould, its structural design is firm, and resistance to overturning is good, and has greatly improved the quality of the injection-molded core of watering.
Second flat assembly 6 the inners of loosing core are furnished with the second level and smooth core 61, middle part is furnished with the second tailstock body 62, and the second tailstock body 62 is fixedly connected with described dynamic model 2 corresponding side surface.The outer end that the second tailstock body 62 outsides are fitted with the second level and smooth cylinder bracket 63, the second level and smooth cylinder brackets 63 is equipped with the second level and smooth oil cylinder 64, and the tailpiece of the piston rod of the second level and smooth oil cylinder 64 is connected with the second described level and smooth core 61.
The second smooth type cavity 12 outside inner faces are fixed with the second lock dog body 14, and the second lock dog body 14 inner faces can be conflicted and coordinate with the second described level and smooth core 61 outer faces.Separate configurations lock core object, when two moulds mate, utilizes the close-fitting effect of the second lock dog body and the second level and smooth core, to reach the stability of the second level and smooth core when model is poured into a mould, its structural design is firm, and resistance to overturning is good, and has greatly improved the quality of the injection-molded core of watering.
The advantage of the utility model embodiment is: the separate configurations assembly of loosing core, and it is reasonable in design, and flexible operation is applicable to the convenient making of different models; For further strengthening the positional stability of body when working of loosing core, set up especially oblique lock core assembly, utilize hydraulic power, realize comparatively easily the pinning of the body of loosing core and unclamp, and reached the location positioning of body in working order time of loosing core, be beneficial to the high-quality that improves core rod moulding; The assembly of respectively loosing core all adopts hydraulic oil type of drive, and its operation automaticity is high, controls directly, and work efficiency improves, and labor cost reduces; Separate configurations lock core object, when two moulds mate, utilizes lock dog body and the smoothly close-fitting effect of core, and to reach the stability of level and smooth core when model is poured into a mould, its structural design is firm, and resistance to overturning is good, and has greatly improved the quality of the injection-molded core of watering.
Most preferred embodiment of the present utility model is illustrated, and the various variations of being made by those of ordinary skills or remodeling can not depart from scope of the present utility model.

Claims (10)

  1. A band loose core, the casting of metals mould of lock core structure, this mould includes upper and lower involutory dynamic model (2) and cover half (1), it is characterized in that: described dynamic model (2) bottom side is equipped with the assembly of tiltedly loosing core (3), the described assembly of tiltedly loosing core (3) the inner is furnished with the body of tiltedly loosing core (31) of flexible operation; Described dynamic model (2) one avris are furnished with oblique lock core assembly (4), and described oblique lock core assembly (4) the inner is furnished with lock core pin (41), and lock core pin (41) can coordinate with the described body of tiltedly loosing core (31) eye-splice; Another two avris of described dynamic model (2) are furnished with respectively the first flat assembly of loosing core (5) and the second flat assembly of loosing core (6).
  2. A kind of band according to claim 1 loose core, the casting of metals mould of lock core structure, it is characterized in that: the described assembly of tiltedly loosing core (3) outer end is furnished with oblique oil pumping cylinder (32), the tailpiece of the piston rod of this cylinder (32) of tiltedly pumping is connected with the described body of tiltedly loosing core (31).
  3. A kind of band according to claim 1 loose core, the casting of metals mould of lock core structure, it is characterized in that: described oblique lock core assembly (4) outer end is furnished with oblique lock core oil cylinder (42), the tailpiece of the piston rod of this oblique lock core oil cylinder (42) is connected with described lock core pin (41).
  4. A kind of band according to claim 1 loose core, the casting of metals mould of lock core structure, it is characterized in that: another two avris of described cover half (1) are shaped with respectively the first smooth type cavity (11) and the second smooth type cavity (12), and the first smooth type cavity (11) and the first flat assembly of loosing core (5) pairing, the second smooth type cavity (12) and the second flat assembly of loosing core (6) pairing.
  5. A kind of band according to claim 4 loose core, the casting of metals mould of lock core structure, it is characterized in that: the first described flat assembly of loosing core (5) the inner is furnished with the first level and smooth core (51), middle part is furnished with the first tailstock body (52), and the first tailstock body (52) is fixedly connected with described dynamic model (2) corresponding side surface.
  6. A kind of band according to claim 5 loose core, the casting of metals mould of lock core structure, it is characterized in that: described the first tailstock body (52) outside is fitted with the first level and smooth cylinder bracket (53), the outer end of the first level and smooth cylinder bracket (53) is equipped with the first level and smooth oil cylinder (54), and the tailpiece of the piston rod of the first level and smooth oil cylinder (54) is connected with the first described level and smooth core (51).
  7. A kind of band according to claim 6 loose core, the casting of metals mould of lock core structure, it is characterized in that: the first described smooth type cavity (11) outside inner face is fixed with the first lock dog body (13), and the first lock dog body (13) inner face can be conflicted and coordinate with the first described level and smooth core (51) outer face.
  8. A kind of band according to claim 4 loose core, the casting of metals mould of lock core structure, it is characterized in that: the second described flat assembly of loosing core (6) the inner is furnished with the second level and smooth core (61), middle part is furnished with the second tailstock body (62), and the second tailstock body (62) is fixedly connected with described dynamic model (2) corresponding side surface.
  9. A kind of band according to claim 8 loose core, the casting of metals mould of lock core structure, it is characterized in that: described the second tailstock body (62) outside is fitted with the second level and smooth cylinder bracket (63), the outer end of the second level and smooth cylinder bracket (63) is equipped with the second level and smooth oil cylinder (64), and the tailpiece of the piston rod of the second level and smooth oil cylinder (64) is connected with the second described level and smooth core (61).
  10. A kind of band according to claim 9 loose core, the casting of metals mould of lock core structure, it is characterized in that: the second described smooth type cavity (12) outside inner face is fixed with the second lock dog body (14), and the second lock dog body (14) inner face can be conflicted and coordinate with the second described level and smooth core (61) outer face.
CN201320702043.5U 2013-11-08 2013-11-08 Metal casting die with core pulling and locking structure Expired - Lifetime CN203556802U (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201320702043.5U CN203556802U (en) 2013-11-08 2013-11-08 Metal casting die with core pulling and locking structure

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201320702043.5U CN203556802U (en) 2013-11-08 2013-11-08 Metal casting die with core pulling and locking structure

Publications (1)

Publication Number Publication Date
CN203556802U true CN203556802U (en) 2014-04-23

Family

ID=50506553

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201320702043.5U Expired - Lifetime CN203556802U (en) 2013-11-08 2013-11-08 Metal casting die with core pulling and locking structure

Country Status (1)

Country Link
CN (1) CN203556802U (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105081270A (en) * 2015-08-25 2015-11-25 无锡贺邦金属制品有限公司 Die-casting die
CN103551518B (en) * 2013-11-08 2016-03-09 宁波华朔模具机械有限公司 A kind of casting of metals mould of locking pulled core structure
CN107042283A (en) * 2017-03-29 2017-08-15 旌德县玉屏电子电器厂(普通合伙) A kind of automobile lock core mould
CN107096896A (en) * 2017-03-29 2017-08-29 旌德县玉屏电子电器厂(普通合伙) A kind of automobile lock core lock housing mould

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103551518B (en) * 2013-11-08 2016-03-09 宁波华朔模具机械有限公司 A kind of casting of metals mould of locking pulled core structure
CN105081270A (en) * 2015-08-25 2015-11-25 无锡贺邦金属制品有限公司 Die-casting die
CN107042283A (en) * 2017-03-29 2017-08-15 旌德县玉屏电子电器厂(普通合伙) A kind of automobile lock core mould
CN107096896A (en) * 2017-03-29 2017-08-29 旌德县玉屏电子电器厂(普通合伙) A kind of automobile lock core lock housing mould

Similar Documents

Publication Publication Date Title
CN203556802U (en) Metal casting die with core pulling and locking structure
CN104325111A (en) Die structure for production of automobile filter
CN103551501B (en) The casting of metals mould of the oblique pulled core structure of a kind of machinery
CN102275264B (en) Oblique core-pulling compound slider device of injection mold for oblique Y-opening outer margin products
CN204052849U (en) The die casting mold structure of the outer demoulding of a kind of machine
CN103551518A (en) Metal casting mold with core locking and pulling structure
CN203830689U (en) Double-sliding-block secondary core-pulling mechanism of cylindrical lamp shell die-casting die
CN203556852U (en) Metal pouring mold adopting mechanical inclined core pulling and automatic core locking structure
CN203992322U (en) Location die casting in a kind of tiltedly odd test
CN104552816A (en) Inclined core-pulling sliding block structure of female mold
CN207578975U (en) The cavity oil cylinder of the large and medium-sized mold of automobile turns to oblique core drawing mechanism
CN204194723U (en) A kind of box mold of gear box casing
CN207709788U (en) A kind of metal die structure
CN106270450A (en) A kind of die casting with multiple pulled core structure
CN206083818U (en) Die casting die with multiple structure of loosing core
CN211191761U (en) Titanium metal semisolid thixoforming device
CN203779800U (en) Inclined core-pulling sliding block structure of female mold
CN102950726B (en) Injection mould for connecting rod
CN202318833U (en) Double-oil-cylinder built-in injection molding machine mold clamping mechanism
CN204747457U (en) A accurate die casting die for processing engine bumper shock absorber cavity
CN107351328B (en) Mould for lower decorative plate of automobile back door
CN104723512A (en) Double-opposite-direction inward-folded T-shaped groove core pulling mechanism of injection mold
CN203284350U (en) Mobile workbench of large-tonnage precise numerical-control explosive powder hydraulic press
CN203764945U (en) Anti-back locking structure of die-casting die
CN205075284U (en) Transparent dirt cup mould

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
CP01 Change in the name or title of a patent holder

Address after: 315806 Ningbo, Zhejiang Province, Beilun science and Technology Park in the west of the road, Yang Mao mountain road, 518

Patentee after: ZHEJIANG HUASHUO TECHNOLOGY Co.,Ltd.

Address before: 315806 Ningbo, Zhejiang Province, Beilun science and Technology Park in the west of the road, Yang Mao mountain road, 518

Patentee before: NINGBO HUASHUO MOULDING & MACHINE CO.,LTD.

CX01 Expiry of patent term

Granted publication date: 20140423

CX01 Expiry of patent term