GB2216370A

GB2216370A - Heater for elongate test samples

Info

Publication number: GB2216370A
Application number: GB8904679A
Authority: GB
Inventors: Stephen Michael Mcmahon; David Willard Scanlon
Original assignee: Instron Corp
Current assignee: Instron Corp
Priority date: 1988-03-01
Filing date: 1989-03-01
Publication date: 1989-10-04
Anticipated expiration: 2009-03-01
Also published as: FR2628209A1; DE3906490A1; JPH01269038A; GB2216370B; FR2628209B1; GB8904679D0

Description

2 16370 -HEATER FOR ELONGATE TEST SAMPLES The invention relates to heating

elongate test samples, e.g., ceramic samples being tested on a load frame.

Stress/strain and other material strength characteristics of an elongate sample of material are measured in a load frante by engaging a sample at its two ends by grips which apply compressive or tensile loads or both along the longitudinal axis of the sample (axial loading). The samples can be heated to a desired elevated test temperature using a heater that surrounds the sample. The heater typically includes insulating material that defines a chamber receiving the sample and electrical resistance heating elements that have heating portions in the chambers.

A design by another for an elongate- sample heater prior to the invention herein employed hinged clamshell" insulating material members that defined a chamber and opened up to permit placing a sample in or removing it from the chamber. U-shaped electrical resistance heating elements providing a single heating zone had legs that passed through horizontal passages in the insulating material and curved heating portions between legs at the outer region of the chamber surrounding the sample.

2 In one aspect our invention features, in general, heating an elongate material sample in a furnace that includes insulating material defining a chamber for receiving the-sample and a plurality of electrical resistance heating elements having legs passing through horizontal passages in the insulating material and heating portions in the outer region of the chamber, the heating elements being grouped into plural horizontal zones. The horizontal arrangement permits achieving a very-- high temiDerature, -requiring a large amount of-power, in a small furnace chamber around a relatively short sample (e.-g., a distance between upper and lower grips of about 4 inches). The ability to use short specimens reduces the cost of testing at least some materials (e.g., ceramics), and the low furnace height permits use of low-temperature grips outside of the furnace. The use of plural horizontal zones provides temperature uniformity across the central testing region of interest of the material sample.

In preferred embodiments the heating elements are U-shaped and are arranged one ontop of the other and in two groups on opposite sides of the sample region; the heating.elements are made of a cermet., material; and the heating elements of each zone are separately electrically controlled.

In another aspect our invention features, in general, heating an-elongate test sample in a furnace that includes insulating material defining a chamber or receiving the sample and a plurality of electrical resistance heating elements having legs passing through horizontal passages in the insulaLing material and heating elements in an outer region of the chamber. The insulating material has a vertical slot through which a vertically oriented sample can pass into the chamber. The slot provides a one-piece construction without moving parts and allows a hot furnace to be removed from the test'sample as soon as the test is over without subjecting the heating elements to a drastic thermal shock, thereby prolonging the lives of the heating elements.

In preferred embodiments a plug made of insulating material is used to close up the slot in use; there are plates made of insulating material for sliding into receiving slots in order to partially define the chamber; and the plates have arcuate portions for mating with similarly shaped surfaces of sample engaging components.

other advantages and features of the invention will be apparent from the following description of a preferred embodiment thereof,

The preferred embodiment will now be described.

Fig. 1 is a perspective view of a material testing load frame including a sample furnace according to the invention.

Fig. 2 is a diagrammatic, exploded perspective view of the Fig. 1 furnace.

Fig. 3 is an elevation of a heating element of the Fig. 2 furnace.

Fig. 4 is a diagrammatic plan view showing the orientation of the Fig. 3 heating elements in the Fig. 2 furnace.

4 -Fig. 5 is a diagrammatic elevation showing the two-zone orientation of the Fig. 3 elements in the Fig. 2 furnace.

- Referring to Fig. 1, there is shown material testing load frame 10 including feet 12, table 14, vertical columns 16, 17 extending upwardly from table 14, and crosshead 18 between columns 16, 17.

Connected to crosshead 18 are load cell 20 and upper grip 22, for gripping the upper end of sample under test 30. Directly therebelow and supported by table 14 are hydrostatic bearing 24, actuator rod 26, and lower grip 28, for gripping the lower end of sample 30. Actuator 31 is supported below table 14 and drives rod 26, which passes through a hole through table 14.

Sample 30 is shown connected between smaller diameter grip extensions 32, 34 of grips 22, 28, respectively. Extensometer assembly 36 is supported on column 17 via horizontal bar 38, vertical rod.40 and horizontal bar 42. Horizontal bars 38, 42 are arranged so that extensometer fingers 44, 46 of extensometer assembly 36 are in line with sample 30 and can move into and out of position along a path generally perpendicular to a plane through the centers of columns 16, 17.

Furnace.48- (shown somewhat diagrammatically in Fig. 1 and in more detail in Figs. 2-5) is slidably mounted on blocks 50, 52 on horizontal rods 54, 56. Furnace 48 has vertical slot 58 for receiving sample 30 as furnace 48 is moved into position after sample 30 has been mounted in grips 22, 28.

Referring to Fig. 2, furnace 48 is shown in partially assembled form. Furace 48 includes a central assembly 60 of insulating material that defines a furnace chamber 62 therein, The insulating material of assembly 60 is fibrous aluminum oxide available from Zircar Corp. under the Sali trade designation.

Assembly 60 includes central layers 64, providing the majority of the assembly, and three layers 66, 68, 70 that are positioned at the top and bottom of assembly and are shaped to receive top and bottom covers 72, 74.

Plug 76 is shaped to fill up the remainder of slot 58 after cover 72 and 74 have been inserted and includes two horizontal passages 78, 80 for receiving extensometer fingers 44, 46, respectively. Covers 72, 74 and plug 76 are made of the same material as the layers of assembly 60. Covers 72, 74 have curved surfaces 75 shaped to provide a tight clearance with grip extensions 32, 34. To the right and left of assembly 60 are further insulating blocks 82 made of aluminum oxide fire brick available under the Kaocrete trade designation from Babcock and Wilco.x and plates 84 made of ceramic reinforced structured alumina material available under the RSIOO trade designation from Zircar. The block 82 and plate 84 on the left side are not seen, as they are covered by side cover 86, top cover 87 and end cover 88; corresponding covers 86-88 for the right-hand side of furnace 48 are not shown on Fig. 2. Cover 88 includes fan 99 to direct cooling air to the-ends of U-shaped heating elements 92.

Referring to Fig. 3f it is seen that heating element 92 is U-shaped, including legs 94, 96 and curved heating portion 98. Heating element 92 is made of cermet material consisting principally of molybdenum disilicide (MoSi 2) and available from Kanthal Furnace Products, Hallstahammar, Sweden under the Kanthal Super 33 trade designation. Legs 94, 96 are 12 mm in diameter and include tapered portions 100, 102. Legs 94, 96 are 6.5 inches (16. 51cm.) lon from their ends to the ends of conical portions 100, 102 and are spaced from each other by 1 inch (2.54 cm.) at their centres. Conical portions 100, 102 are 20 an) long. Curved portion 98 is 6 mm in diameter and 1. 58 inches (4.0132 carn) from the junction with conical portions 100, 102 to the end. The 40 mm ends 104, 106 of legs 94, 96 are aluminized to provide good electrical contact with electrical connections (not shown) as described in Kanthal Super Handbook, 1984 (printed in Sweden by Ljungforetagen, Orebro, cat. no 2-A-1-3.5').

Referring to Figs. 4 and 5, there are two horizontal heating zones of heating elements 92, and there are six heating elements 92 in each zone. At the center of furnace chamber 62 is central sample region 108 for receiving sample 30 and outer heating element region 110 in which heating portions 98 of heating elements 92 are located. The volume of furnace chamber -62 is about 850 cm 3. The distance between the top of upper layer 66 and the bottom of lower layer 66 is four inches. The gage length, the distance between the ends of extensometer fingers 44, 46, is 25 mm. Legs 94, 96 of heating elements 92 pass through horizontal passages 112 of insulating layers 64, blocks 82 and plates:', 84. 25 Between legs 94, 96 of the same heating element 92 are ceramic plugs 114. The heating elements 92 of the upper heating zone are electrically connected in one series, and the heating elements 92 of the lower heating zone are separately electrically connected in another series (through connections not shown on Fig. 2).

1.

7 In operation, ceramic sample 30 is connected to grip extensions 32, 34 while furnace 48 is in the stand-by position shown in Fig. 1 and extensometer assembly 36 is pulled back away from sample 30. Furnace 48 is then moved toward sample 30 along horizontal guide bars 54 until sample 30 is within sample region 108. Covers 72, 74 are then slid into their respective positions with their arcuate front surfaces 75 moved close to similarly shaped grip extensions 32, 34.

Plug 76 is then inserted to fill up the remaining portion of slot 58 between covers 72, 74, and extensometer assembly 36 is moved forward. Fingers 44, 46 pass through passages 78, 80 of plug 76 until they contact sample 30. Furnace 48 heats sample 30 to the design temperature, for example, 15000C. Fan 90 circulates air through the enclosure within end cover 88 to cool the ends of heating elements 92. Grip extensions 32, 34 are water cooled.

The horizontal arrangement of heating elements permits concentrating a large amount of power into the small furnace chamber in order to heat test sample 30.

The use of two heating zones and the separate control of them provide uniform temperature along the gage length of sample 30. E."g., a silicon carbide test specimen heated to 1500'C had only +5'C temperature nonuniformity along the gage length.

After testing, extensometer assembly 36 is moved out of position, and plug 76 and covers 72, 74 are removed. Furnace 48 is then moved along guide rods 54, 56 away from sample 30. The use of slot 58 permits the simple one-piece construction without moving parts and also permits the hot furnace to be removed from test sample 30 as soon as the test is over without subjecting 1 the heating elements 92 to drastic thermal shock. The ability to remove samples quickly acts to avoid oxidation of fracture surfaces and to increase throughput. In addition, t he use of cermet heating elements provides long life to the heating elements. If a heating element 92 does fail, it can simply be removed from its horizontal passage and replaced with another heating element without disassembling the furnace.

9 b

Claims

CLAIMS:

r 1. A heater for heating an elongate material sample comprising: insulating material defining a chamber includi-ng a central sample region for receiving said elongate sample and an outer heat element region, said material including horizontal passages therethrough for receiving heating elements, said passages being grouped in two horizontal zones; and a plurality of electrical resistance heating elements having legs passing through said horizontal passages and heating portions in said outer heat element region, said heating elements being grouped in two horizontal zones.
2. A heater according to Claim 1, wherein said electrical resistance heating elements are U-shaped and each have two legs.
3. A heater according to Claim 2, wherein said two legs for each heating element are arranged one on top of the other.
4. A heater according to any preceding claim, wherein said heating element is made of a cermet material.
5. A heater according to any preceding claim, wherein said heating elements of each zone are separately electrically controlled.
6. A heater according to any preceding claim, wherein the heating elements in each zone are arranged in two groups on opposite sides of said sample region.
7. A heater according to any preceding claim, wherein the insulating material has a vertical slot through which a vertically oriented sample can pass into said chamber.
8. A heater according to Claim 7, further comprising a plug made of insulating material for closing up said slot in use.
9. A heater according to any preceding claim, further comprising plates made of insulating material for sliding into receiving slots in order to partially define said chamber.
10. A heater according to Claim 9, wherein said plates have arcuate portions for mating with similarly shaped surfaces of sample engaging components.
11. A heater for heating an elongate material sample comprising: insulating material defining a chamber including a central sample region for receiving said elongate sample and an outer heat element region, said material including horizontal passages therethrough for receiving heating elements, and said material having a vertical slot through which a vertically oriented sample can pass into Said chamber; and a plurality of electrical resistance heating elements having legs passing through said horizontal passages and heating portions in said outer heat element region.
12. A heater according to Claim 11, further comprising a plug made of insulating material for closing up said slot in use.
13. A heater according to Claims 11 or 12. further comprising plates made of insulating material for sliding into receiving slots in order to partially define said chamber.
14. A heater according to Claim 13, wherein said plates have arcuate portions for mating with similarly shaped surfaces of sample engaging components.
15. A heater according to any of Claims 11 to 14, wherein said electrical resistance heating elements are U-shaped and each have two legs.
16. A heater according to Claim 15, wherein said two legs for each heating element are arranged one on top of the other.
17. A heater according to any of Claims 11 to 16, wherein said heating element is made of a cermet material.
18. A heater according to any of Claims 11 to 17 wherein the heating elements are arraDged in two groups on opposite sides of said sample region.
19. A heater, substantially as hereinbefore described with reference to and as shown in the accompanying drawings, for heating an elongate material sample.
20. A material testing load frame comprising: a frame; a pair of opposing grips supported by said frame and adapted to grip an elongate sample between them; and a heater according to any preceding claim for heating an elongate material sample held in said frame.

L Published 1989 atThe Patent Office, State House, 85.171 High Holborn. London WClB 4TP. Further copies maybe obtainedftm The Patent Oface. Was Branch, St Mary Cray, Orpington, Kent BR5 M. Printed by Multiplex techniques lul, St Mary Cray, Kent, Con. 1187