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Disadvantages:
1. Can swell during a sustained run but return to normal size when cool.
2. Will soften during a long run but will regain their normal hardness when cool.
3. They may tear if left in contact with a dry steel surface for any length of time.
4. They are costly.
(Clean with White Spirit or Kerosene only)
Davis Process Rollers
(Rubber core, Composition outer)
Advantages:
1. Higher speeds than normal Composition.
2. Advantages of Composition rollers.
3. Remade at low cost.
Disadvantages:
1. Outer shell susceptible to wear.
2. Greater care needed in setting them.
Natural Rubber Rollers
(used extensively in the newspaper trade)
Rubber rollers have a soft inner core and a hard outer core ranging from 1/8'' (3mm) to 1/4'' (6mm) in thickness. These rollers subtract the mineral oil out of quicksetting inks. Susceptible to metalic inks especially silver.
(Hint:- Saturate rubber rollers in boiled oil before use).
Advantages:
1. They are tough, therefore they have a long life.
2. Will not melt at high speeds.
3. No seasoning required.
4. Suitable for all climates.
5. Suitable for moisture set inks.
6. Do not require constant setting.
Disadvantages:
1. Cost (approximate 5 times Composition)
2. Some are affected by quicksetting inks.
3. Some are difficult to clean. (Carbon is put in to stop abrasiveness and wear)
4. No tack. Will not pick up dust or doolies/ickies on forme.
(All rubber is affected by direct light)
Vulcanized Oil Rollers
Advantages:
1. Not affected by humidity or temperature.
2. Resists moisture.
3. Safe on moisture set or water colour ink.
4. Will not absorb dyes or colour from ink.
5. Can be re-ground.
Disadvantages:
1. Do not have as high a resistance to abrasion as vulcanised rubber.
2. Can break and tear due to rough handling.
3. Extreme care needed in setting them.
4. Will tear and rip if ink dries on them.
5. Cannot wash up with solvents. (Only kerosine or turpentine)
Poly Vinyl Chloride Rollers
(These rollers are cast in a mould and heat treated. Difficult to bond to stock)
Advantages:
1. Easily cleaned.
2. Will not shrink or swell.
3. Can be used for any ink.
4. Unaffected by humidity, steam and suitable for moisture set inks.
5. Ideal for quickset inks.
6. Resist all oils and diluted acids.
7. Will not melt at high speeds.
8. Offer the greatest resistance to abrasion, scuffing, cutting by rules etc.
9. Tack everlasting.
Disadvantages:
1. Some solvents & vehicles in ink have a tendency to leach the plasticum out.
2. They can be ground but will be unsuitable for halftone work.
The Shore Durometer
This is an instrument for measuring the hardness of rollers. It is spring loaded with a ball bearing point which penetrates into the roller. The hardness reading is measured on a scale ranging from zero to 100. Zero reading corresponds to the hardness of air while the 100 reading corresponds to the hardness of glass. Shore reading of the various kinds of rollers is as indicated:
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