Deadman Switch Air-Only Control to Prevent Blast Media Slugs
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Solution Overview
Problem
Abrasive blasting apparatuses experience the formation of slugs of blast media due to inadequate airflow and residual media in the hose, leading to loss of control and potential damage.
Innovation Solution
A control system with a deadman's switch featuring an intermediate position that allows compressed air to flow without blast media, ensuring proper airflow establishment before media introduction and continued airflow after media cessation to flush the hose.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If compressed air and blast media are supplied together to the blast hose, then the abrasive blasting apparatus can operate efficiently, but blast media accumulates and forms slugs that cause loss of control and potential damage
Solution Approach 1:
The control system performs preliminary action by establishing compressed air flow through the blast hose before introducing blast media. The deadman's switch is designed with an intermediate position that activates only the air supply, allowing the hose to be pressurized and ready for media transport, thereby preventing slug formation that would occur if media were introduced into stagnant air flow
Solution Approach 2:
The control system segments the supply process into distinct phases: an initial phase where only compressed air is supplied to establish flow, and a subsequent phase where blast media is introduced. This segmentation is achieved through the deadman's switch mechanism that can selectively activate air supply independently of media supply, preventing the harmful interaction that causes slug formation
2Productivity
If compressed air and blast media are stopped together, then the operation can be terminated efficiently, but residual blast media remains in the hose and forms or enlarges slugs upon reactivation
Solution Approach 1:
The control system performs preliminary flushing action by continuing compressed air flow after blast media supply is stopped. This preliminary action clears residual media from the hose before the apparatus is fully deactivated, preventing residual media from forming or enlarging slugs when the system is reactivated
Solution Approach 2:
The control system maintains continuity of the useful flushing action by keeping compressed air flowing after media supply ceases. This continuous air flow serves the dual purpose of completing the blasting function and performing the additional function of flushing residual media from the hose, thereby preventing slug formation upon reactivation
3Device complexity
If a traditional deadman's switch with only two positions is used, then the control system is simple, but it cannot establish proper airflow before media introduction or flush the hose after media cessation
Solution Approach 1:
The deadman's switch is segmented into three distinct positions: off, air-only (intermediate), and air-plus-media (full operation). This segmentation allows independent control of air supply and media supply, enabling the system to establish proper airflow before media introduction and continue air flow for flushing after media cessation, thereby preventing slug formation while maintaining mechanical simplicity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The control system significantly reduces the frequency and severity of blast media slugs, enhancing user control and safety by ensuring consistent airflow and effective hose flushing.
Implementation Method 1
a flow of compressed air is used to entrain blast media such as sand, grit or glass beads. The high-pressure air/media mixture is then fed down a blast hose
Data Source
AI summary
A control system for controlling abrasive blasting apparatus and an abrasive blasting apparatus including such a control system. The control system controls delivery of air and blast media to a blast nozzle of the abrasive blasting apparatus. The control system includes a deadman's switch, the deadman's switch features a user operable control. The user operable control is moveable from a first position, where the control system causes the abrasive blasting apparatus to not deliver air or blast media, to a second position where the control system causes the abrasive blasting apparatus to deliver both air and blast media. When the user operable control is in an intermediate position between the first and second positions, the control system causes the abrasive blasting apparatus to deliver air but not blast media. The control system may have control elements whose state may be sequentially changed by the user operable control as it moves.