The thumb rule for grease application largely based on a nmumber of factors:
1. Operating Temp.
2. Operating speed
3. Water ingress
4. Pumpability ( NLGI number)
5. Type of base
6. Type of load - light/Medium/Heavy
First insist, the supplier furnish you with product brochure detailing the physio chemical properties of the grease.
To give a logical response based on the two parameters provided:
1. Operating temp:
At 550 F (or 288 C) - Choose a grease which has a drop point 30 to 40 C above operating temp. Thus the grease you choose should have a Drop point of 320 to 340 C. Alternatively, you may wish to choose a synthetic "base" grease, many of which have "No drop point."
2. Operating speed:
Most greases are suitable for slow speed operations like in spherical/ball bearings. For high speed bearings, heavy base oil viscosities, are desirable.
3. Water ingress:
If the grease has Marine applications or in areas where water ingress needs to be tackled, grease with low water wash-out tendencies may be used. In some Marine applications products may also have to meet Harmonised Offshore Chemical Notification Format (HOCNF) requirements, as these products do not harm underwater Marine life.
4. Pumpability:
For automatic lubricating systems NLGI 000,00,0, 1 would assist in conserving energy. For cartridge application NLGI 1 or 2 finds wide application.
5. Base of grease:
Lithium is probably, the most widely used base. Calcium or Soda Greases have good water washout properties. Li and Ca Complex greases are now getting popular. Most high temperature greases have a synthetic base. Poly Urea grease are also being used, however they have compatibility problems when mixed with other type of grease.
6. Load capacity:
Most greases (except probably, Chassis grease) are in the 30 - 45 Lbs range in Timken OK load and may be classified as EP type.
Trust the info above will assist you in choosing the best grease, from an array of suppliers.
Hussam
