Grease compatibility continued from page 50
Purging new grease through a system to replace an existing old grease may result in a situation where for a period of time there is a mixed ratio of different greases protecting machinery.
Mixing two greases that are not compatible can result in hardening or softening of the grease and so lead to sharp reduction in lubricating performance, which may lead to expensive repairs and excessive downtime. Taking care to select a compatible grease is therefore vital in the maintenance of operational efficiency and will save organisations significant time and money.
Incompatibility of greases can result in a factory closing down for days on end, causing major disruption with significant cost implications.
The solution? Greases are formulated from three classes of component: base oil, thickener and additives. The compatibility of two greases will depend on the interaction between these components. Reactions between certain thickener and additive combinations may cause adverse effects hindering grease performance and compatibility.
Charts are available to help users determine whether greases are likely to be compatible. However with ever-changing formulations, with each new blend of base oil, thickener and new additives, charts can only be a guideline and it is wise for the user to confirm the extent to which the greases can be mixed without adverse effects by undertaking a compatibility testing programme.
Fortunately, there is a well-established procedure developed by ASTM for evaluating this compatibility: ASTM D6185, Standard Practice for Evaluating Compatibility of Binary Mixtures of Lubricating Greases.
This test method describes how the compatibility of two greases can be assessed in the first instance by evaluating the performance of the fresh and 50:50 ratio blends of both greases in three tests:
• Dropping Point • Working Stability • Storage Stability at High Temperature
This is the primary stage of compatibility testing and must always be completed. After this testing is completed and the results evaluated it is usual to extend this stage to the further testing of 10:90 and 90:10 ratios.
Once the primary stage of compatibility testing is complete and no evidence of incompatibility has been observed, then more specific testing of the above mixtures, considered appropriate for the grease application, may be completed such as anti-wear or corrosion prevention testing.
The compatibility of some grease mixtures is already well established, and product suppliers may be able to advise on the degree of compatibility of two known greases.
Where this information is not available it is essential operators confirm the compatibility of the two greases in order to avoid costly equipment failure and operational downtime. Testing to ASTM D6185 can be performed, as part of Intertek’s comprehensive grease testing capabilities, to ensure such issues with compatibility will not arise. Intertek has many years’ experience in performing the testing required by ASTM D6185 to assess compatibility of greases - offering dropping point, working stability and storage stability testing, along with a host of other test methods to assess the performance of mixtures in relation to other relevant properties of the grease.
Intertek Farnborough can offer a wide range of testing options; we operate a dedicated grease testing laboratory with a wide range of testing equipment. We specialise in grease compatibility, performance testing, failure analysis and oil condition monitoring (OCM) testing of grease.
For more information contact Robert Belcher on Tel: +44 1252 392 100 Email:
flc.enquiries@intertek.com
LINK
www.intertek.com/ocm/grease
52 LUBE MAGAZINE NO.138 APRIL 2017
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
