0 0 73 28 Powder and Bulk Engineering, September 1989 ra2. 5 d history 0 cn 0 77 t its Michigan Division in Mid- The pharmaceutical enters the 12-by-15- land, Mich., The Dow Chemical foot packaging room as a granular mate- A Company manufactures a phar- rial, which is fed into a grinder. The maceutical powder that it sells in 3O-gallon grinder reduces the pharmaceutical to an Electronic fiber drums. Accurate shipping weight is 80-mesh powder and dischargesit directly essential for the high-value product -un- into a liner in a fiber . -0 0 derweight drums result in dissatisfiedcus- Each drum is filled with 110 pounds (50 d tomers, while overweight drums reduce kilograms) of powder. Depending on the Q scale profits. production schedule, drum fingis per- % formed 30 to 40 hours per week. P, 3 improves Q m r_ accuracy of 7i powder weighinga ma

Scale platform and digital indicator allow Dow Chemical to accurately and reliably weigh 30-gallon fiber drums as they’re filled with a pharmaceutical powder.

Dow Chemical uses this cart-mounted scale platform to weigh a pharma- ceutical powder as it’s loaded into fiber drums. The scale is accurate to within 0. I pounds per drum. Powder and Bulk Engineering, September 1989 29

Initially, an electronic scale system con- New scale must meet special sisting of componentsfrom Merent man- requirements ufacturers weighed the drums as they were Dow began searching for an electronic filled. The scale wasn’t accurate enough scale that would be accurate to 0.1 pound Dow tried using two other fypes of for Dow’s needs and couldn’t be over- per drum and meet the special require- scales to weigh drums of loaded if powder was poured into the - ments of the packagmg room. drums too quickly, the scale would stop pharmaceutical powder, but neither working and go into a “sleep” mode. The Because fine dust from the powder pre- was accurate enough. The new scale was also cumbersome to use because sented an explosion hazard, the scale had electronic scale is accurate to within it couldn’t be reset to zero after the drum’s to be rated explosion-proof for that envi- 0.1 pounds per drum. tare weight was recorded. ronment. To reduce the dust hazard and the possibility of contamination, the scale This scale was replaced with an analog had to withstand daily washings with soap scale, but it was also inaccurate and diffi- and water. The scale also had to fit into the cult to use. available space and be easy to operate. Dow purchases electronic scale Dow purchased an electronic scale system consisting of a scale platform and digital weight indicator. The scale platform is 24 inches square and has a capacity of 200 pounds. The scale uses a “floating” isola- ted strain gage to provide good sensitivity, repeatability, and linearity. Weighmg res- olution is as high as 1 part in 50,000. The digital indicator includes a time delay to ensure a stable numeric display. As weight is added to the scale, the readout numbers advance slowly so they’re easy to read. Push-button zeroing allows the op erator to quickly determine the product weight. The indicator includes a large LED display, a decimal point positioning switch, pounds/lalograms selection, auto- matic tare, and net/gross weight display. The indicator is enclosed in a stainless- steel NEMA 4 housing; both the scale plat- form and indicator can be washed.

Scale simplifies powder weighing operation The scale platform is mounted on a cart that’s positioned directly under the dis- charge chute of the grinder. The digital weight indicator is mounted at a conve- nient heat on a steel beam.

The operator pushesa button to return the digital indicator to zero, then places an empty fiber drum, drum liner, , and clamp on the scale platform. The indicator then displays the tare weight, which is re- corded on a shipping .

The scale’s digital indicator is mounted on a beam near the drum-loading station. The indicator is mounted in a NEMA 4 housing and can be washed down. 0 0 30 Powder and Bulk Engineering September 1989 73 ra2. 5 Removing all items except the drum and d drum liner, the operator again zeros the in- 0 dicator to prepare for filling.The neck of cn the drum liner is secured to the chute to 0 control dust. Activating the grinder dis- 77 charges the powder into the drum liner.

-0 “The scale and indicator have 0 operated accurately and reliably d Q since they were put into use.” - Dow % operating technician. P, 3 Q

The operator watches the digital indicator and stops the grinder as the net weight of the drum nears 110 pounds. The operator then removes the drum liner from the dis- charge chute, adjusts the net weight by adding or subtracting powder, closes and secures the drum liner, installs a drum lid with a tamper-proof seal, and enters the net weight on the drum’s shipping label. Sealed drums are then moved to a holding area to await approval by the quality con- trol department.

Scale system improves accuracy The new scale system is unaffected by the loading speed. It provides the precision weighing that Dow requires and ensures efficient, cost-effective processing.

“The system has operated accurately and reliably since it was put into use, “ says Larry Sprague, a Dow operating techni-, cian. “It was tailored to meet our require- ments, built of matched components, and integrated into the existing production equipment.”

The only problem Dow has had with the new scale system was caused by interfer- ence from static electricity in the atmo- sphere. This was easily solved by humidi- fying the air in the packagmg room. PBE

GSE Inc., Farmington Hills, MI. #35 1