Middleby Marshall PS224 PS310 Front-to-back uneven bake, PS300/350 Air Finger Shutter Adjustment

SECTION 2 - AIR FLOW AND HEAT TRANSFER

To perform the test bake:

1.Select identical pans for the test. Choose the pans based on the width of the conveyor; you should space the pans in line completely across the conveyor with- out having them touch each other. For instance, for a 32” /813mm-wide conveyor, you could use three 10”/ 254mm pans or two 15”/381mm pans.

You will need enough pans to have three complete rows. This eliminates the possibility of a single row distorting the results. If necessary, the test can be run with only 1 row of pans, but the results are not as reliable.

2.For a pancake batter test, mix the pancake batter as instructed by the manufacturer. Pour the batter EVENLY into the test pans to a depth of 1/4” (6mm). You may use any type of pancake mix that is available,

AS LONG AS YOU USE THE SAME TYPE THROUGH- OUT THE TEST.

For a dough test, have the customer make up a thin crust dough in each pan. The dough should be of a consistent thickness in each pan and should be no thicker than 1/4” (6mm). Thicker doughs will provide too great a “cushion” and will distort the test results.

3.Place the pans side-by-side on the conveyor. The front and rear edges of the pans should be aligned so that it is easier to see if there is a front-to-back bake prob- lem. DO NOT stagger the rows of pans diagonally. Also, check that the pans do not touch each other; this can transfer heat to the test product and distort the results.

4.Run the products through the conveyor at the customer’s normal bake time and temperature settings.

5.“Read” the results of the test. Each pan of product should have the same coloration.

If you used pancake batter, the sugar in the mix will brown very rapidly if over-baked. This highlights an out- of-balance oven.

If the product lightens or darkens slightly from front-to- back in only one row, there is probably not a significant front-to-back bake problem. If the product is notice- ably lighter or darker at the front or back in ALL of the rows of pans, there is a front-to-back bake problem. See Figure 7.

Also, remember that consistently uneven baking on the top of the product may indicate a problem with the upper air fingers. Likewise, consistently uneven bak- ing on the bottom of the product may indicate a prob- lem with the lower air fingers.

• If the oven has the current standard air finger type, you should contact Middleby Technical Services for assistance.

• If the oven has the PS300/350-style air fingers with a shutter plate, it is possible to adjust the posi- tions of the air shutters to correct a front-to-back bake problem. Proceed to Step D, “PS300/350 Air

Figure 7

Front-to-back uneven bake

NOTE: In this example, the front of the product is darker than the rear. The opposite condition is also possible.

Finger Shutter Adjustment.”

D.PS300/350 Air Finger Shutter Adjustment

Before attempting to properly balance a Middleby Marshall oven equipped with shutter fingers, you should understand the principles of operation of this type of finger.

The oven moves approximately 2000 ft.³ of air per minute. When this large amount of air is moved through the plenum and fingers it rushes through the plenum and to the end of the air finger. This creates a back pressure of air inside the finger and tends to deliver more air onto the product at the front of the air finger.

The inner plate has a separate shutter plate riveted to it at a slight angle. Since there is more pressure at the end of the fingers (front of the oven) than at the plenum (rear of the oven), the shutter plate is angled to restrict the air flow near the front of the oven. This creates a proper balance permitting an even amount of air to exit out of the holes across the width of the conveyor. See Figure 8.

Before adjusting the shutters, it is necessary to deter- mine if the finger is providing a balanced air delivery across the width of the conveyor. This is the purpose

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