US3610734A

US3610734A - Temperature-controlled orifice or slit for optical, ion-optical and electron-optical instruments

Info

Publication number: US3610734A
Application number: US849310A
Authority: US
Inventors: Hermann Wollnik; Gottfried Munzenberg
Original assignee: GOTTERIED MUNZENBERG
Current assignee: GOTTERIED MUNZENBERG
Priority date: 1968-08-14
Filing date: 1969-08-12
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05
Also published as: GB1248825A; FR2022123A1; DE1797091B2; DE1797091A1

Abstract

A temperature-controlled orifice or slit for optical, ionoptical and electron-optical instruments, comprising one or more pairs of slit-defining platelet-shaped jaws which in conjunction with support means common to said jaws serve to vary the width of an orifice or slit formed by the inner edges of the jaws. In the simplest embodiment the ends of said jaws remote from their slitdefining edges are firmly secured to said support means which consist of a material having a coefficient of thermal expansion that substantially differs from that of the material of which said jaws are made, the temperature of said jaws and of said support means being controllable by heating means common to both.

Description

Ulllleu Dial-Ba 3,610,734

[ 1 lnvenwn Hermann Wollnlk 56]" References c1166 129, Eichendorflrlng, GQSSGII; UNITED STATES PATENTS gafif "mjgfi 1,951,018 3/1934 Herdman 350/269 [21] AWL 849,310 2,059,504 11/1936 Whitman... 350/269 [22] Filed Au 12 1969 2,852,684 9/1958 Payne 250/419 0 3 242 796 3/1966 Strickler 350/271 X [45] Patented 0&51971 [32] Priority 14 1968 3,447,875 6/1969 Goldberg 350/253 A X [33] Germany Primary Examiner-Ronald L. Wibert [3 l] P 17 97 091 Assistant Examiner0rville B. Chew, ll

Attorney-Markva, Smith & Kruger ABSTRACT: A temperature-controlled orifice or slit for optical, ion-optical and electron-optical instruments, comprising [54] TEMPERATURBCONTROLLED ORIFICE on suT one or more paihrs of slitjefimng platelet-shapettll aws which in FOR OPTICAL, loNomCAL AND ELECTRON con unction wit suppo means common 0 sm aws serve o OPTICAL INSTRUMENTS vary the width of an orifice or slit formed by the inner edges of 12 claims 12 Drawing at the jaws. ln the simplest embodiment the ends of said jaws remote from their slit-definin edges are firmly secured to said 8 [52] [1.8. II 350/269, u on means which consi t of a material having a coefficient I 350/271 of thermal expansion that substantially differs from that of the [51] Int. Cl. G02! 1/30 material of which said jaws are made, the temperature of said [50] FleldolSear-ch 250/419 jaws and of said support means being controllable by heating means common to both.

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F169 FIG/0 FIG. I!

IN VE N TORS HE RMANN WQL L/WK GOT T FRIED MUNZENBERG v M If firoR/ws YS J! TEMPERATURE-CONTROLLED ORIFICE OR SLIT FOR OPTICAL, ION-OPTICAL AND ELECTRON-OPTICAL INSTRUMENTS BACKGROUND OF THE INVENTION This invention relates to temperature-controlled apparatus, and more specifically to an orifice or slit defined by the edges of platelet-shaped jaws and the width of which is variably by control means that change in length with varying temperature, for use in optical instruments and more particularly in ion-optical or electron-optical instruments.

Such orifices or slits of which one is described in US. Pat. No. 3,242,796 must be capable of being opened and closed with great precision both for the purposes of adjustment and for operating instruments of variable resolving power. Particularly when incorporated in ion-optical instruments the slit is required to be capable of continuous narrowing to a width of only a few microns. Moreover, the slit must remain symmetrical with respect to the center plane and its width adjustable without jerks while the edges of the jaws remain perfectly parallel.

it was hitherto the practice to adjust such orifices and slits with the aid of precision mechanical drive means. Particularly in inaccessible locations in apparatus or diaphragm systems in high-vacuum apparatus this involved considerable mechanical complexities. Moreover, such precision mechanical drive means are sensitive to undue stress, such as that imposed upon 'them when say high-vacuum apparatus is being baked out.

With a view to eliminating the required transmission means, cams, servomotors and like mechanical devices and the consequent unavoidable'friction and wear, and also for simplifying the overall construction to provide relatively rapid adjustability of the orifice or slit, the arrangement described in the above-mentioned US. Patent specification comprises a control means for adjusting the slit width, in the fonn of a rod which varies in length in functional dependence upon the temperature to which it is exposed. The changes in length of the rod are transmitted by a lever system which includes numerous retaining springs and a special restoring spring to the jaws to produce a relative shift of said jaws. However, the general construction of such a slit comprises a multitude of parts and it is still rather complicated.

SUMMARY OF THE INVENTION It is an object of the present invention further to simplify the means for varying the slit width and of thereby reducing the structural size of the entire arrangement.

More particularly it is the object of the present invention to eliminate the numerous levers and springs which the abovedescribed prior art slit control apparatus still requires.

Another object of the invention is to ensure that the slitdefining jaws can be relatively moved quickly, precisely and symmetrically, while their edges are maintained exactly in parallel.

To attain these objects the present invention provides a temperature-controlled orifice or slit defined by the edges of platelet-shaped jaws whereof the width is variable by control means that change in length with varying temperature, for use in optical instruments and particularly in ion-optical and electron-optical instruments, wherein said jaws themselves in conjunction with support means common to said jaws are arranged to function as said control means, and the ends of said jaws remote from their slit-defining edges are firmly secured to said support means which consist of a material having a coefficient of thermal expansion that substantially differs from that of the material of which said jaws are made, the temperature of said jaws and of said support means being controllable by heating means common to both.

In this arrangement the choice of the materials of which the jaws and the support means are made will determine whether the width of the orifice or slit will increase or decrease when the temperature rises.

According to another feature of the present invention the slit may be defined by a pair of jaws which rert flush on a baseplate fonning said supportmeans. or by two or more pairs of jaws disposed in stacks for further enlarging the controllable variability range of the orifice or slit. in an alternative arrangement more than two jaws disposed in pairs that are superimposed in several planes and radially project inwards from a ring forming the support means may together define an orifice in a manner similar to an iris diaphragm.

The baseplate supporting the jaws need not be flat. In another embodiment of the invention the side of the baseplate facing the jaws may be formed with a central sill and the jaws may be provided with a perpendicularly off-angled portion that may be of bimetal construction. in a modification of this embodiment the sill may be widened to form lateral'abutments for the bimetal parts of the jaws.

The jaws may be flat and rest in coplanar disposition on a flat baseplate or they may be disposed in different planes and rest on a correspondingly stepped baseplate. In the latter case the inner edges of the jaws may be arranged to overlap so that V notches in the edges of the jaws will define specially shaped orifices for the passage therethrough of the rays or beams.

For achieving the widest possible variability range for the width of the orifice or slit, the baseplate may consist of a material having a low coefiicient of thermal expansion, such as molybdenum, and the jaws of a material having a large coefficient of thermal expansion, such as nickel, copper, aluminum and the like, provided it is desired to narrow the slit at rising temperatures. Alternatively, if it is desired that the orifice or slit should widen at rising temperatures, then materials will be so chosen for the baseplate and the jaws that the relative magnitudes of the coefficients of thermal expansion are reversed. Moreover, the variability range of the orifice or slit width can be further enlarged by constructing the jaws or parts thereof of a bimetal.

The width of the orifice or slit defined by the jaws be controlled by the heating means that are provided.

The temperature may be raised by heating the support means in any way known in the art, for instance by the direct passage of a current through the baseplate, by electron or ion bombardment, by indirect heating with special heating elecan then ments, by radiant or inductive heating or by heating the entire vessel or room in which the orifice or slit is being used. in the interests of rapidity of slit width adjustment heating should preferably be so performed that substantially greater heating power is employed at temperatures that are still remote from the required temperature level than at temperatures close to the required temperature level.

Control loops of a kind conventional in'systems control readily permit a constant slit width to be maintained. However, sometimes it may be quite sufficient to operate a heating means from a constant voltage supply.

BRIEF DESCRlPTlON OF THE DRAWINGS Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which:

FIG. 1 is a perspective view of a slit defined by a pair of jaws made of a material having a different coefficient of thermal expansion from that of a baseplate which carries said pair of jaws and showing an induction heater for heating the baseplate and the jaws;

FIG. 2 is a schematic cross section of the slit according to FIG. 3 is a schematic cross section of a modification of thearrangement according to FIGS. 1 and 2, which pennits the variability range of the slit width to be substantially enlarged;

FIG. 4a is a top plan viewof a pair of jaws of particular shape for defining a square orifice;

FIG. 4b is a cross section thereof;

FIG. 5 is a top plan view of an orifice defined by a plurality of jaws mounted on a supporting ring so as to extend radially therein;

FIG. 6 is a perspective view of a slit of which the width can be varied by the deflections of a pair of jaws consisting partly or completely of bimetal;

FIG. 7 is a schematic cross section of a slit according to FIG. 6 at a given temperature; 7

FIG. 8 is a view similar to that shown in FIG. 7 but showing the slit afier the temperature has changed; FIG. 9 is a sche DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show an orifice or slit formed by a baseplate l and two platelet-

shaped jaws

2 and 3, baseplate and jaws having different coefficients of thermal expansion. The baseplate 1 has an opening 6 through which light or a particle stream can pass. A slit is defined above the opening 6 between facing edges 2' and 3 of the

jaws

2 and 3 which are secured to the baseplate 1 by means of screws 4 and 4'. The

jaws

2 and 3 may be thin platelets, say 5 X25 X0.l mm. in size. The thickness of the baseplate 1 may be substantially greater. The width of the slit 5 is adjustable to within a few 1.. An induction heater coil 2a disposed adjacent the slit assembly is energized from a suitable source to heat both the jaws and the baseplate to a desired temperature.

FIG. 2 illustrates the manner in which the slit functions. Let it be assumed that the width d of the slit 5 has been adjusted at a given temperature level to a given value. Two cases can then be distinguished:

I. Either the coefiicient of thermal expansion of the

jaws

2 and 3 exceeds that of the baseplate 1. When the temperature rises above the initial temperature level the baseplate 1 will expand but the expansion of each of the

jaws

2 and 3 due to this temperature change will be greater owing to their higher coefficient of thermal expansion. Consequently the width d of the slit 5 will become less.

II. Or the coefficient of thennal expansion of the

jaws

2 and 3 is less than that of the baseplate 1. The width of the slit 5 will then change in the opposite direction.

A particularly useful form of construction comprises a baseplate made for instance of molybdenum and jaws consisting for instance of nickel, copper or aluminum. If a slit constructed as shown in FIGS. 1 and 2 is adjusted at room temperature to about 0.1 mm. and assuming that the distance between the screws 4 and 4', Le. between the points of affixation of the jaws on each side of the slit 5, is 2 cm., then the width of the slit will change by about 0.2 ;r./' C. At a temperature of the slit of about 500 C. which is a favorable temperature for operating a mass spectrometer (at this temperature the slits remain free from adhering surface impurities) the slit width in case I will close to a few p.if the above-mentioned materials are used.

By a combination .of materials of different coefficients of thermal expansion slits which have varying temperature/slit width characteristics can be produced.

FIG. 3 shows an arrangement in which the slit width can be varied within a wider range than in the arrangement according to FIG. 2. Two jaws in the form of

platelets

36 and 37 having a coefficient of thermal expansion b are affixed to a baseplate 31 having a coefficient of thermal expansion a. These

platelets

36 and 37 carry a further pair of jaws or

platelets

38 and 39 having the coefficient of thermal expansion a and to these are affixed slit-defining jaws 32 and 33 which are more closely spaced than the platelets and which again have a coefficient of thermal expansion 1:. The platelets are securely connected to each other at points A and B (by soldering or welding) and at C they are secured to the baseplate 31. They are finnly pressed on the baseplate 31 by means of screws 34 and 34'.

. Assuming that the coefi'icient of thermal expansion a is less than b and that the distances (1,, d have been adjusted at a given temperature, then the distanced. between the

platelets

36 and 37 will change analogously to the slit width in FIG. 2 when the temperature rises. The

platelets

38 and 39 will change their length in the same direction as the baseplate 3], whereas the jaws 32 and 33 will expand codirectionally with the

platelets

36 and 37. Consequently the change in the width of the slit d will be twice that in the length of the distance d,. The same temperature change in this latter arrangement will therefore produce twice the change in the slit width obtained in the arrangement according to FIG. 2. By providing further analogously stacked and interconnected pairs of platelets, the change in slit width can be multiplied.

By giving the edges of the jaws 42 and 43 a particular shape shown in FIG. 4a square orifices, as are desirable for instance in electron microscopes, can be created'instead of elongated slits. It will be understood from FIG. 4b that the face of the baseplate 41 carrying the

jaws

42 and 43 is stepped, and that said jaws are therefore relatively oflset in different planes. The edges of the jaws defining the slit are each provided with a central notch 42 or 43' of triangular shape so that according to the shape of the notches the overlapping edges will define a rectangular, square or rhombic orifice for the passage therethrough of the rays.

By the provision of a plurality of jaws 52 to 59 afiixed to a baseplate modified to form a supporting ring 51, as shown in FIG. 5, and by location of the jaws in pairs in different offset parallel planes, an orifice resembling an iris diaphragm for very small openings can be created by appropriately selecting the length of the jaws. Although thermal expansion of the supporting ring 51 operates to withdraw the radially remote ends of the jaws from the center of the supporting ring 51, the jaw edges forming the orifice will nevertheless move closer towards the ring center if their coefficient of thermal expansion exceeds that of the ring 51. Otherwise the arrangement functions in the same way as that shown in FIG. 2.

In the embodiment illustrated in FIGS. 6, 7 and 8 a baseplate 61 formed with a central sill 68 traversed by an opening 69 for the passage therethrough of a particle beam carries two

jaws

62 and 63 and the edges of said jaws defining a slit 65 bear flush under flexural tension on the face of the sill 68. This tension is generated by a portion or 67 of each jaw remote from the slit 65 being bent perpendicularly downwards and this bent portion which is affixed to the baseplate 61 being of bimetal construction so that it will flex when the temperature changes. The width d of the slit 65 will therefore change according to the degree of flexing of these portions.

FIGS. 9 and 10 illustrate a modification of the slit according to FIG. 1 in the case of which the

entire jaws

92 and 93 themselves are bimetal elements and bend when the temperature changes. They thus cause the slit width to change, as indicated in FIG. 10, the change exceeding that attainable according to FIG. 1.

FIG. 11 shows a slit of which the width d is coarsely variable within a given temperature range and finely variable as a function of temperature in another directly adjoining temperature range. In a baseplate 111 which is formed with a central sill 114 resembling that of the baseplate in FIG. 6, so that the edges of the

jaws

112 and 113 fonning the slit 115 can bear flushagainst the face of the sill 114, the latter is widened and forms

lateral projections

118 and 119 which serve as abutment faces for perpendicularly off-angled

bimetal portions

116 and 117 of the jaws. When the temperature rises the

jaws

112 and 113 are first moved fairly rapidly across relatively large distances, such as l mm. However, above a given temperature, such as 200 C., the deflection of the bimetal portions I16 and H7 is intercepted by the lateral projections I18 and 119, and when the temperature continues to rise only the .contact pressure increases and the slit width d ceases to be af- The advantage of the proposed orifice or slit over hitherto conventional arrangements is that its overall construction is substantially simpler and more compact and that mechanical drive means are not required, notwithstanding that the jaws are very precisely and symmetrically adjustable in relative parallelism.

The invention may be embodied in other specific fonns without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive.

What is claimed is:

l. A temperature-controlled adjustable orifice or slit for various types of instruments comprising, in combination a support formed from a material having a first coefficient of thermal expansion, said support having an opening therein;

a first jaw mounted on said support, said first jaw having a slit-defining edge and an outer portion remote from said slit-defining edge, said first jaw being formed from a material having a coefficient of thermal expansion different from the coefficient of thennal expansion of the material of said support;

a second jaw mounted on said support, said second jaw having a slit-defining edge in opposed relation to the slitdefining edge of said first jaw, whereby a controllable slit or opening is defined between said slit-defining edges, said second jaw being formed from a material having a coefficient of thermal expansion different from the coefficient of thermal expansion of the material of said support;

means securing said outer portion of said first jaw to said support only at a location remote from said slit-defining edge, whereby a substantial length of the jaw is free to expand and contract;

means securing said second jaw to said support at a location spaced from said slit-defining edge of the second jaw; and

means to controllably heat said support and jaws to adjust the sizeof the slit or opening defined thereby as a result of 7 thermal expansion of both said support and said jaws.

2. An adjustable orifice according to claim 1 wherein said support is an integrally formed fiat baseplate; and said opening in said support is a circular opening.

3. A temperature controlled adjustable slit or orifice according to claim 1 wherein said support comprises 7 a baseplate having an opening therein and a pair of end edges, each edge of said pair being remote from said opening,

a first pair of plates mounted on said baseplate and having outer edges thereof secured respectively to said baseplate adjacent said end edges thereof, said pair of plates each having inner edges,

a second pair of plates mounted on said first pair of plates and having inner edges thereof secured respectively to said inner edges of said first pair of plates, said second pair of plates having outer edges;

said baseplate, first pair of plates, and second pair of plates being parallel with each other;

said baseplate and said second pair of plates being formed from a material having the same coefficient of thermal expansion;

said first and second jaws having outer edges secured respectively to the outer edges of said second pair of plates; and

said jaws and said first pair of plates being formed from a material having the same coefficient of thermal expan- SlOn.

4. A temperature controlled adjustable orifice or slit according to claim 1 wherein said support is an integral ring;

said first and second jaws extend along the same diameter of said ring with said slit-defining-edges in opposed relation to each other at a location generally centrally of the ring;

said additional jaws having inner edge portions in overlapping relation to said slit-defining edges of said first and second jaws; and

said edge portions of said several jaws being of sufficient length to define a polygon-shaped opening generally at the center of said ring. 5. A temperature-controlled adjustable orifice according to claim 1 wherein said support is a baseplate having a first jaw support surface and a second jaw support surface in a plane spaced from the plane of the first jaw support surface; said first jaw extends along said first jaw support surface; said second jaw extends along said second jaw support surface in overlapping relation to said fust jaw; said slit-defining edges are each generally triangular notches and extend across each other; whereby, said edges define a polygon-shaped orifice. 6. A temperature-controlled adjustable orifice according to claim 1 wherein said first and second jaws are mounted on said flat baseplate in coplanar relation to each other. 7. A temperature controlled adjustable orifice according to claim 1 wherein said first and second slit-defining edges are straight; and said jaws are mounted with said edges in spaced-apart parallel relation to each other. 8. A temperature controlled adjustable orifice according to claim 7 wherein said slit-defining edges are chamfered to provide knife edges at the slit. 9. A temperature-controlled adjustable orifice according to claim 1 wherein the material of said jaws has a coefficient of thermal expansion substantially greater than the coefficient of thermal expansion of the material of said support. 10. A temperature controlled adjustable orifice or slot according to claim 1 wherein 1 said support has ajaw-supporting surface; said first and second jaws engage said jaw support surface. 11. A temperature-controlled adjustable orifice or slot according to claim 10 wherein said jaw-supporting surface is flat; and said first and second jaws are flat and move along said jaw-supporting surface to adjust said slit. [2. A temperature-controlled adjustable orifice according to claim 1 wherein said support includes a base having sides, and a centrally located projection extending from the base, said projection presenting a generally centrally located jaw-supporting surface having an opening therein; said first and second jaws are each generally L-shaped and include bimetal leg portions secured respectively to said sides of said base, and I end portions in engagement with and movable along said jaw-supporting surface, said end portions having said slit-defining edges fonned thereon and extending across said opening;

stop means on said support in opposed relation to said bimetal leg portions to'limit the movement of said end portions after attainment of an initial temperature; whereby, coarse adjustment of said slit or orifice is obtained from said bimetal leg portions by heating said support and jaws to said initial temperature, and thereafter. fine adjustment of said slit or orifice is obtained from unequal expansion of said end portions of said jaws and said support as a result of further heating.

as a

Claims

1. A temperature-controlled adjustable orifice or slit for various types of instruments comprising, in combination a support formed from a material having a first coefficient of thermal expansion, said support having an opening therein; a first jaw mounted on said support, said first jaw having a slit-defining edge and an outer portion remote from said slitdefining edge, said first jaw being formed from a material having a coefficient of thermal expansion different from the coefficient of thermal expansion of the material of said support; a second jaw mounted on said support, said second jaw having a slit-defining edge in opposed relation to the slit-defining edge of said first jaw, whereby a controllable slit or opening is defined between said slit-defining edges, said second jaw being formed from a material having a coefficient of thermal expansion different from the coefficient of thermal expansion of the material of said support; means securing said outer portion of said first jaw to said support only at a location remote from said slit-defining edge, whereby a substantial length of the jaw is free to expand and contract; means securing said second jaw to said support at a location spaced from said slit-defining edge of the second jaw; and means to controllably heat said support and jaws to adjuSt the size of the slit or opening defined thereby as a result of thermal expansion of both said support and said jaws.

2. An adjustable orifice according to claim 1 wherein said support is an integrally formed flat baseplate; and said opening in said support is a circular opening.

3. A temperature controlled adjustable slit or orifice according to claim 1 wherein said support comprises a baseplate having an opening therein and a pair of end edges, each edge of said pair being remote from said opening, a first pair of plates mounted on said baseplate and having outer edges thereof secured respectively to said baseplate adjacent said end edges thereof, said pair of plates each having inner edges, a second pair of plates mounted on said first pair of plates and having inner edges thereof secured respectively to said inner edges of said first pair of plates, said second pair of plates having outer edges; said baseplate, first pair of plates, and second pair of plates being parallel with each other; said baseplate and said second pair of plates being formed from a material having the same coefficient of thermal expansion; said first and second jaws having outer edges secured respectively to the outer edges of said second pair of plates; and said jaws and said first pair of plates being formed from a material having the same coefficient of thermal expansion.

4. A temperature controlled adjustable orifice or slit according to claim 1 wherein said support is an integral ring; said first and second jaws extend along the same diameter of said ring with said slit-defining edges in opposed relation to each other at a location generally centrally of the ring; and additional jaws like said first and second jaws are secured to said ring and extend along different diameters of said ring from said first and second jaws; said additional jaws having inner edge portions in overlapping relation to said slit-defining edges of said first and second jaws; and said edge portions of said several jaws being of sufficient length to define a polygon-shaped opening generally at the center of said ring.

5. A temperature-controlled adjustable orifice according to claim 1 wherein said support is a baseplate having a first jaw support surface and a second jaw support surface in a plane spaced from the plane of the first jaw support surface; said first jaw extends along said first jaw support surface; said second jaw extends along said second jaw support surface in overlapping relation to said first jaw; said slit-defining edges are each generally triangular notches and extend across each other; whereby, said edges define a polygon-shaped orifice.

6. A temperature-controlled adjustable orifice according to claim 1 wherein said first and second jaws are mounted on said flat baseplate in coplanar relation to each other.

7. A temperature controlled adjustable orifice according to claim 1 wherein said first and second slit-defining edges are straight; and said jaws are mounted with said edges in spaced-apart parallel relation to each other.

8. A temperature controlled adjustable orifice according to claim 7 wherein said slit-defining edges are chamfered to provide knife edges at the slit.

9. A temperature-controlled adjustable orifice according to claim 1 wherein the material of said jaws has a coefficient of thermal expansion substantially greater than the coefficient of thermal expansion of the material of said support.

10. A temperature controlled adjustable orifice or slot according to claim 1 wherein said support has a jaw-supporting surface; said first and second jaws engage said jaw support surface.

11. A temperature-controlled adjustable orifice or slot according to claim 10 wherein said jaw-supporting surface is flat; and said first and second jaws are flat and move along said jaw-supporting surface to adjust said slit.

12. A temperature-controlled adjustable orifice according to claim 1 wherein said support includes a base having sides, and a centrally located projection extending from the base, said projection presenting a generally centrally located jaw-supporting surface having an opening therein; said first and second jaws are each generally L-shaped and include bimetal leg portions secured respectively to said sides of said base, and end portions in engagement with and movable along said jaw-supporting surface, said end portions having said slit-defining edges formed thereon and extending across said opening; stop means on said support in opposed relation to said bimetal leg portions to limit the movement of said end portions after attainment of an initial temperature; whereby, coarse adjustment of said slit or orifice is obtained from said bimetal leg portions by heating said support and jaws to said initial temperature, and thereafter, fine adjustment of said slit or orifice is obtained from unequal expansion of said end portions of said jaws and said support as a result of further heating.