Oven Conveyor Application
A leading cookie manufacturer is adding a new product that requires a greater distance to the top heating element of their conveyor oven. The oven originally only had a static-top heating element and with this new order, it needs to be adjustable up to 14 inches. The top heating element weighs 5,000 lb. The manufacturer anticipates only making adjustments to the height once or twice a month with the use of linear motion systems.
Step 1: Determine Specifications
- Single motor and drive
- Food grade grease
- The load will be in compression
- Total travel 14 inches
- The actuators and power train must be located outside of the oven frame
- Travel Rate negligible as long as the total travel can be reached in less than 60 seconds
- 2 × safety factor
Step 2: Analysis
Due to infrequent cycles, the use of a worm gear machine screw jack system would be best suited for this application. Using upright rotating jacks will allow the jacks to be easily retrofitted to the existing oven with minimal modifications.
The jacks will be fully loaded in both the retracted and extended position. Because of the retrofit condition, it is not possible to have a support bearing on the lift shaft. Using mounting condition A on the Column Strength Chart located on page 68 of our Worm Gear Screw Jacks Catalog and the manufacturer's safety requirements, the 10 ton jack was selected.
Speed and Horsepower:
Using a standard 1750 AC Motor and the 24:1 gear ratio, full travel would be reached in 36 seconds. Using the horsepower formulas on page 15 a 5 HP AC motor running at 1750 rpm will be adequate for the requirements.
|HPper jack =||.0192 in-lb × 1.250 lb × 1,750 rpm||= .66 hp / jack|
|HParrangement =||.66 hp per jack × 4 jacks||= 3.83 total hp|
|.85 × (.9)2|
LinkJac Line Shafting:
The longest center to center distance between any two jacks is 79 inches, leaving a shaft length of 72 inches. Using the formula on page 189, based on Critical Speed, the proper Line Shafting to use would be the LJT-50.
|NSpeed =||.6192 × (||π||)2 × 1.907 × 106 = 2,248 rpm|
|NTwist =||153.6 in-lb × (||72 in||) = .44o|
Step 3: Product Selection
Create a Reference Number for the Assembly
From page 69, create reference numbers for the following: four 10 ton machine jacks, upright rotating configuration, 24:1 worm gear ratio, 21 inches "L" dimension. One jack to have a 56C motor mount and a 5 HP brake motor, and one jack to have a 2 circuit limit switch.
- (2) 10-MSJ-UR 24:1/SSE-1/SSE-2/FA/21/M
- (1) 10-MSJ-UR 24:1/SSE-1/50BT-2/FA/21/M
- (1) 10-MSJ-UR 24:1/SSE-1/2CA-8/FA/21/M
- M = Food grade grease
- (1) GB15 Type G
- (1) 1) GB15 Type F
- (2) LJT-50 72" OAL
- (1) LTJ-50 36" OAL
- (4) P-2200-XX (1" - 22mm)
- (2) P-2200-177 (1" - 1")
- 5 HP AC Motor 1750rpm