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Interlocks balance throughput and safety

A Rockwell Automation - Allen-Bradley Guardmaster product story

Edited by the Engineeringtalk editorial team Mar 20, 2002

Achieving a balance between production schedules and operator safety is never easy, but Dailycer has achieved it by using Guardmaster Prosafe trapped key chain interlocks.

Achieving a balance between the requirements of ever more demanding production schedules and the need for high levels of operator safety is never easy, but Dailycer has achieved it on two mixing/stirring vessels with a simple but extremely effective system based upon Guardmaster Prosafe trapped key chain interlocks.

The mechanical safety system overcomes costly interruptions to production by allowing dosing/additives to be added whilst the mixing operation is in progress.

At the same time it prevents accidental contact with the moving agitators and shaft, providing high levels of safeguarding to operating personnel.

Dailycer makes cereals and cereal bars.

The scope of the company's operations means that most people in the UK have, at one time or another, breakfasted upon their products.

The company is one of the largest suppliers of cereals to major UK supermarkets and consequently has to meet demanding production schedules.

Central to Dailycer's operations are two large vessels, which are used for mixing syrups.

Entry points are provided on top of each vessel allowing access to Dailycer personnel in order to add extra ingredients, such as sugar, to the mixture.

These extra ingredients really need to be added whilst the mixer is in operation, otherwise sugars (for example) sink to the bottom of the vessel.

When this happens they sometimes do not dissolve properly, resulting in quality problems with the finished product.

Until recently, adding ingredients during machine operation was not an option due to safety concerns.

These centred around the fact that it was wholly possible for the rotating agitators and shaft within the mixing vessel to come into contact with the limbs of any personnel adding ingredients.

Dailycer is a very proactive company in terms of safety and actively pursued a solution to this problem.

The job of providing a solution was entrusted to Engineering Manager Gwilym Jones.

He takes up the story.

"We were fully aware from the outset with this project that by finding an answer to the safety problem we could also improve our production.

The problem was finding a balance between the two.

Any solution had to be simple because, in our experience, factory personnel bypass complicated guarding systems very quickly".

"A second major consideration was the environment.

The atmosphere around the mixing vessels is extremely steamy due to the boiling of syrups, so we really wanted to avoid using any safety system that was electrically based or susceptible to corrosion".

"The solution we came up with takes into account all the above considerations.

To overcome the problem of stopping the machine we have designed a basket that allows material to be added with no possibility of catching or trapping hands or arms.

The basket is square in section with sides of 3mm stainless steel.

A hole is drilled through one side, which also extends through the body of the mixing vessel itself.

Welded to the basket is a chain, complete with its attached actuator bolt, from one of Guardmaster's single key chain lock systems.

When the basket is in place the actuator bolt is pushed through the hole in its side and through the side of the mixing vessel, eventually being inserted into the main body of the Guardmaster Prosafe chain key interlock system, which is mounted on the outside of the mixing vessel.

With the bolt in place, the trapped key that resides in the key interlock can be released and subsequently inserted into the isolator that allows the mixing vessels to start.

If the key is removed from the isolator at any time the mixing operation stops.

The key can then be inserted into the key interlock to allow removal of the bolt and, subsequently, the basket itself".

"We installed the system ourselves and since installation it is working really well.

The Guardmaster Prosafe key interlock has proved to be the ideal choice for the application, providing robust mechanical operation which allows us to avoid electrics, and also a stainless steel construction that is untroubled by the steamy environment.

We can also get replacement coded keys in the event that we lose one, which is very important.

Overall, I think the success of combining our simple design with the Guardmaster safety interlock can be summed up simply as offering the best of both worlds: enhanced levels of safety and uninterrupted levels of production".