Figure 1: SRV (Wide Range Inline Viscometer)

in turn affecting the quality of the investment castings.

2. Reducing costs by reducing waste: Over-mixing can not only affect the quality of end product but waste ingredients, raw materials, time and energy. Viscosity management in the mixing process can identify the endpoint reliably and accurately.

3. Efficiency: Hassle free, real time monitoring of mix viscosity eliminates the costly and time- consuming laboratory analysis, which often results in delayed response to changes in the slurry properties. Ensuring consistency throughout the coating process significantly reduces reject rates saving cost and time and assists in continuous casting processes.

4. Automation: Automatically monitoring and controlling slurry preparation and coating process eliminates a manual task that is prone to errors and enables operators to focus on the quality of the final product.

Advantages Of Inline Viscosity Monitoring – Reducing Key Shell Defects Viscosity control can help alleviate the frequency of defects in the coating process – sticking and picking, twinning, peeling, splitting, cracking, roughness, blistering, bridging, surface erosion and reduce poor flow characteristic which lead to poor shell build resulting in casting defects. With continuous online viscosity monitoring, shell formation can be controlled more effectively, therefore significantly improving the metallurgical properties of the final product.

Figure 2: SRD (Inline process density meter and viscosity meter)

Process Monitoring and Control Challenges Engineers and operators in the investment casting industry recognize the need to monitor viscosity for top-quality shell manufacturing, but making that measurement has challenged process engineers and quality departments over the years.

Challenges with traditional viscosity measurements Traditionally, operators in investment casting

industry have measured the

viscosity of slurry using the Zahn flow cup. The measurement is reported as the time elapsed for the cup volume to flow through a hole in the bottom of the cup. The end point of the test must be chosen so that it is consistent from test to test. The procedure is messy and time-consuming. It

is inaccurate,

inconsistent and non-repeatable even with an experienced operator. In the continuous casting process, the interval sampling causes excessive delays. The viscosity of slurry can’t be adjusted in real time. Besides, the drum containing the slurry are open; due to changes in ambient temperature, humidity and other factors, such as temperature, dry climate, solvents are likely to be volatile, so cup-based viscosity measurement technique becomes ineffective. Viscosity and other characteristics relatable to it (e.g. shear rate and weight percent of solids) vary with depth in a tank containing substantial amounts of ceramic slurry, conditions of movement of slurry (generally induced to maintain homogeneity), capture by cast parts and replenishment or adjustments. There are several approaches to measuring viscosity online through instrument probes inserted into the casting bath at


various depths, but they have been prone to drift and error over the course of casting operations and some may need frequent removal, cleaning or replacement, down time and recalibration of the probes and instruments. There are some probes which can be cleaned in situ, but they are subject to malfunction due to exposure to undesirable and variable coating of transducer elements. Slurry coating systems need the ability to accurately measure the actual viscosity of the ceramic slurry or other material. In particular, it would be desirable to provide the systems with an in-line viscometer to be used with a closed-loop control system for monitoring and controlling the coating processes in shell building.

Smart Foundries – Drivers for Casters’ Embrace of Industry 4.0 and Digitalization Temperature and humidity fluctuations, mixing equipment condition, substrates, solvents, formulations, line-integration, machine interactions and time of mixing are few of the many parameters which can alter the ceramic slurry quality in investment casting across batches. In foundries,

the downtimes and delay

in deliveries involved due to rejects can hurt the profitability seriously. But what if there was a system which can continuously monitor the product quality and consistency, and could take corrective actions automatically and adaptively without disrupting the whole operation? Technologies required to deliver

such transformational changes in the foundry now exist. Once the manufacturer invests in process monitoring equipment, the current

Continued on pg 30 January 2021 ❘ 29

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