DVD-1650 High-Temperature Vertical Dilatometer

The DVD-1650 is a fully computerized dilatometer system designed to measure dimensional changes of a specimen brought about by changes in its thermal environment. This instrument measures linear thermal expansion coefficient (CTE), shrinkage attendant to sintering, phase transformations, annealing characteristics, and other physical or chemical changes manifesting in a change of a linear dimension. Processing parameters can be studied in great detail through duplication of thermal cycles and rates used in the actual process. Due to the extensive programming available to produce thermal cycles, complex processes can easily be simulated.

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DVD 1650 Design Features

• The high-temperature furnace is constructed of low thermal mass fibrous alumina insulation surrounding molybdenum disilicide (MoSi2) heating elements. Four hairpin-shaped elements act as eight linear heat sources equally spaced around the muffle tube (parallel to its axis). Length-to-diameter ratios are chosen to ensure excellent hot zone uniformity.
• The digital displacement transducer used in the system is an absolute device with no periodic calibration requirements. It is free of short term drift and long term changes, as its accuracy is based on a very stable internal glass grating whose movement is optically monitored.
• The vertical configuration of this instrument makes it especially suitable for testing ceramic materials where shrinkage often outweighs expansion. In a horizontal specimen holder, shrinkage of a specimen can cause it to pull away from the end plug (unless extensive push-rod force is applied), resulting in erroneous data. Vertical configurations are not subject to this problem. Pushrod tracking forces are governed by variable dead weight counter-balancing, and can be reduced to very low values. Optionally, specific pushrod loading can also be applied to operate the dilatometer as a Thermomechanical Analyzer (TMA). Optional program modules allow softening point determination and controlled-rate sintering cycles.
• The counter-balanced dilatometer head slides vertically on guide rods to extract the specimen holder (dilatometer tube) from the furnace cavity. When inserted, sliding hermetic seals engage the muffle tube collar to provide a protective environment for the specimen. Critical components, such as the ends of the muffle tube and the seals engaging it, along with the base of the dilatometer head, are water cooled.
• The standard alumina dilatometer tube and pushrod are readily interchangeable with a fused silica assembly for special applications. System correction for the tube is automatically made in software. The device automatically limits maximum furnace temperature (to 1000°C) when the fused silica tube is in place.

Temperature Programming and Control

The system offers a user programmable mix of ramps, dwells, soaks, and printing rates, delayed start, repeat-cycle capability with a program capacity of 16 thermal cycles (64 segments), and the ability to store and recall frequently used methods. The temperature program is fully displayed and is editable during a run. All vital test parameters are continuously displayed and updated. Digital temperature control with optimized adaptive routines is used to achieve accurate specimen, rather than furnace temperatures. Controlled heating rates up to 30°C/ min and ballistic rates up to 100°C/ min are available.

Data Recording

Measured data is displayed in real time and is continuously stored for further analysis. All test and program parameters along with system correction and standards data are also stored in each test data set for easy comparison tests at a later date.

System Correction and Calibration

Built-in system correction and calibration tables are included. System correction can be altered, based on calibration runs with NIST standards or other references.

Data Reduction, Analysis, and Reporting

Stored data is automatically processed by statistical methods, for all points (such as with ramp heating, where applicable). The analysis includes polynomial curve fitting, and tabulation of results (such as percent expansion, average coefficient, and instantaneous coefficient, etc.) as a function of temperature. A variety of single or multiple curves for a group of tests can be generated, displayed, and printed. Optionally, data files may be transfered to other computers for remote processing.

Safety and Diagnostic Features

Built-in safety provisions guard against operational malfunctions and protect against failure of the system or destruction of the specimen. For example, loss of water flow, furnace and specimen over-temperature, and dead computer detection are among the functions that are continuously monitored. Some will automatically shut down the equipment while others alert the operator via audio-visual indicators. Diagnostic routines are available for system interrogation.